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 in 2017 with funding from 
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 THE 
 
 BOYS’ PLAYBOOK OF SCIENCE 
 
‘BaHantjme pm# 
 
 BALLANTYNE, HANSON AND CO., EDINBURGH 
 CHANDOS STREET, LONDON 
 
Wheatstone’s telephonic concert at the Polytechnic, in which the sounds and vibra- 
 tions pass inaudible through an intermediate hall, and are reproduced in the lecture- 
 room unchanged in their qualities and intensities. Frontispiece. 
 
 WiT. 
 
THE 
 
 BOYS’ PLAYBOOK 
 OF SCIENCE 
 
 EY 
 
 JOHN HENRY PEPPER 
 
 AUTHOR OF “THE PLAYBOOK OF METALS” 
 
 ILLUSTRATED WITH 
 
 FOUR HUNDRED AND FIFTY-THREE ENGRAVINGS 
 
 CHIEFLY EXECUTED FROM THE AUTHOR’S SKETGHES 
 
 By H. G. HINE 
 
 REVISED WITH MANY ADDITIONS 
 
 BY 
 
 T. C. HEPWORTH 
 
 Lecturer on Science and late Assistant Superintendent of the Royal Polytechnic 
 Institution , London 
 
 LONDON 
 
 GEORGE ROUTLEDGE AND SONS 
 
 BROADWAY, LUDGATE HILL 
 
 NEW YORK: 9, LAFAYETTE PLACE 
 
 £ . 
 
BY TEE SAME AUTHOR. 
 
 THE PLAYBOOK OF METALS 
 
 INCLUDING 
 
 Jlmsonal Jparralifos of Visits to Coal, 3T*aO, 
 Copper, anb Cin lltttus ; 
 
 WITH 
 
 A Large Number of Interesting Experiments 
 
 RELATING TO ALCHEMY AND THE CHEMISTRY OF THE 
 FIFTY METALLIC ELEMENTS. 
 
 With Three Hundred Illustrations . 
 
TO 
 
 PROFESSOR LYON PLAYFAIR, C.B., F.R.S 
 
 PROFESSOR OF CHEMISTRY IN THE UNIVERSITY OF 
 EDINBURGH, 
 
 Dear Sir, 
 
 I dedicate these pages to your Children, whom I 
 often had the pleasure of seeing at the Polytechnic during 
 my direction of that Institution. I do so as a mark of 
 respect and appreciation of your talent and zeal, and of 
 your public-spirited advocacy of the Claims of Science in 
 this great and commercial country. 
 
 Without making you responsible in any way for the 
 shortcomings of this humble work on Elementary Science, 
 allow me to subscribe myself, 
 
 Dear Sir, 
 
 Yours most respectfully, 
 
 JOHN HENRY PEPPER. 
 
 b 
 
REVISER’S PREFACE. 
 
 A new edition of the 11 Boy’s Playbook of Science” having been called 
 for while the Author was at the antipodes, the publishers intrusted 
 me with the work of revision. My position as Lecturer on 
 Science, and Assistant Superintendent of the Institution with which 
 Professor Pepper’s name has so long been associated, has given 
 me the advantage of being able to follow his track more closely 
 perhaps than an outsider could have done. In carrying out my 
 task I have naturally refrained from altering any of the original 
 work, except so far as progress in Science has rendered absolutely 
 necessary. As a case in point, I may instance the Section devoted 
 to Chemistry, where modern notation has rendered many amend- 
 ments indispensable. The Chapters upon Photography and the 
 Magic Lantern have been wholly rewritten. I am also answerable 
 for many additions. Among these I may mention the descriptive 
 matter relating to the Telephone, Microphone, Phonograph, recent 
 advances in Telegraphy and Electric Illumination, the Heliograph, 
 and the article upon the Spectroscope. I have thus endeavoured to 
 carry out the instructions I received to bring the book up to date. 
 The new matter is copiously illustrated. 
 
 37 , St. Paul's Crescent y 
 
 Camden Square , 
 
 London , N, W, 
 
 T. C. HEPWOBTH. 
 

CONTENTS. 
 
 PAGE 
 
 INTRODUCTION 1 
 
 CHAPTER I. 
 
 THE PROPERTIES OE MATTER — IMPENETRABILITY 3 
 
 CHAPTER II. 
 
 CENTRIFUGAL FORCE ....... 17 
 
 CHAPTER III. 
 
 THE SCIENCE OF ASTRONOMY ............ 19 
 
 CHAPTER IV. 
 
 CENTRE OF GRAVITY 32 
 
 CHAPTER V. 
 
 SPECIFIC GRAVITY 48 
 
 CHAPTER VI. 
 
 ATTRACTION OF COHESION 59 
 
 CHAPTER VII. 
 
 ADHESIVE ATTRACTION . . 6 7 
 
 CHAPTER VIII. 
 
 CAPILLARY ATTRACTION 69 
 
CONTENTS. 
 
 CHAPTER IX. 
 
 PAGB 
 
 CRYSTALLIZATION * . • 73 
 
 CHAPTER X. 
 
 CHEMISTRY 81 
 
 CHAPTER XI. 
 
 CHLORINE, IODINE, BROMINE, FLUORINE 132 
 
 CHAPTER XII. 
 
 CARBON, BORON, SILICON, SELENIUM, SULPHUR, PHOSPHORUS . . 1G3 
 
 CHAPTER XIII. 
 
 FRICTIONAL ELECTRICITY 185 
 
 CHAPTER XIV. 
 
 VOLTAIC ELECTRICITY 205 
 
 CHAPTER XV. 
 
 MAGNETISM AND ELECTRO-MAGNETISM 218 
 
 CHAPTER XVI. 
 
 ELECTRO-MAGNETIC MACHINES 223 
 
 CHAPTER XVII. 
 
 THE ELECTRIC TELEGRAPH 230 
 
 CHAPTER XVIII. 
 
 ruhmkorff’s, hearder’s and bentley’s coil apparatus . . 261 
 CHAPTER XIX. 
 
 MAGNETO-ELECTRICITY 271 
 
 CHAPTER XX. 
 
 DIA-MAGNETISM ^86 
 
CONTENTS. 
 
 XI 
 
 CHAPTER XXL 
 
 PAGE 
 
 LIGHT, OPTICS, AND OPTICAL INSTRUMENTS 294 
 
 CHAPTER XXII. 
 
 THE REERACTION OF LIGHT . . . . 341 
 
 CHAPTER XXIII. 
 
 REFRACTING OPTICAL INSTRUMENTS 346 
 
 CHAPTER XXIY. 
 
 THE ABSORPTION OF LIGHT 387 
 
 CHAPTER XXV. 
 
 THE INFLECTION OR DIFFRACTION OF LIGHT 388 
 
 CHAPTER XXVI. 
 
 THE POLARIZATION OF LIGHT • . . 395 
 
 CHAPTER XXVII. 
 
 HEAT 412 
 
 CHAPTER XXVIII. 
 
 THE STEAM-ENGINE 466 
 
 CHAPTER XXIX. 
 
 the steam-engine — continued ... 478 
 
 INDEX • • • . 501 
 
INTEODUCTION 
 
 TO 
 
 THE ORIGINAL EDITION. 
 
 Although “The South Kensington Museum” now takes the lead, and 
 surpasses all former scientific institutions by its vastly superior collec- 
 tion of models and works of art, there will be doubtless many thousand 
 young people who may remember (it is hoped) with some pleasure t lie- 
 numerous popular lectures, illustrated with an abundance of interesting, 
 and brilliant experiments, which have been delivered within the walls of 
 the Royal Polytechnic Institution during the last twenty years. 
 
 On many occasions the author has received from his young friends* 
 letters, containing all sorts of inquiries respecting the mode of performing 
 experiments, and it has frequently occurred that even some years 
 after a lecture had been discontinued, the youth, now become the young 
 man, and anxious to impart knowledge to some “home circle” or 
 country scientific institution, would write a special letter referring to a 
 particular experiment, and wish to know how it was performed. 
 
 The following illustrated pages must be regarded as a series of philo- 
 sophical experiments detailed in such a manner that any young person 
 may perform them with the greatest facility. The author lias endea- 
 voured to arrange the manipulations in a methodical, simple, and popular 
 form, and will indeed be rewarded if these experiments should arouse 
 dormant talent in any of the rising generation, and lead them on 
 gradually from the easy reading of the present “ Boy’s Book,” to the 
 study of the complete and perfect philosophical works of Leopold 
 Gmelin, Faraday, Braude, Graham, Turner, and Fownes. 
 
 Every boy should ride “ a hobby-horse” of some kind ; and whilst 
 play, and plenty of it, must be his daily right in holiday time, he ought 
 not to forget that the cultivation of some branch of the useful Arts and 
 Sciences will afford him a delightful and profitable recreation when 
 
 B 
 
2 
 
 INTRODUCTION. 
 
 satiated with mere play, or imprisoned by bad weatner, or gloomy with 
 the unamused tediousness of a long "winter s evening. 
 
 The author recollects with pleasure the half-holidays he used to devote 
 to Chemistry, with some other King’s College lads, and in spite of 
 terrible pecuniary losses in retorts, bottles, and jars, the most delightful 
 amusement was enjoyed by all who attended and assisted at these 
 juvenile philosophical meetings. 
 
 It has been well remarked by a clever author, that bees are geome- 
 tricians. The cells are so constructed as, with the least quantity of 
 material, to have the largest sized spaces and the least possible interstices. 
 The mole is a meteorologist. The bird called the nine-killer :s an arith- 
 metician, also the crow, the wild turkey, and some other birds. The 
 torpedo, the ray, and the electric eel are electricians. The nautilus is 
 a naviaator. He raises and lowers his sails, casts and weighs anchor, 
 and performs nautical feats. Whole tribes of birds are musicians. The 
 beaver is an architect, builder, and wood-cutter. He cuts down trees 
 and erects houses and dams. The marmot is a civil engineer ■. He does 
 not only build houses, but constructs aqueducts, and drains to keep 
 them dry. The ant maintains a regular standing army. Wasps are 
 paper manufacturers. Caterpillars are silk-spinners. The squirrel is a 
 ferryman. With a chip or a piece of bark for a boat, and his tail for a 
 sail, he crosses a stream. Dogs, wolves, jackals, and many others, aie 
 hunters. The black bear and heron are fishermen. The ants are day- 
 labourers The monkev is a rope dancer. Shall it, then, be said that any 
 boy possessing the Godlike attributes of Mind and Thought with Tree- 
 will can only eat, drink, sleep, and play, and is therefore lowmr in the 
 scale of usefulness than these poor birds, beasts, fishes, and insects . 
 Xo ' no ! Let “ Young England” enjoy his manly sports and pastimes, 
 but let him not forget the mental race he has to run with the educated 
 of liis own and of other nations ; let him nourish the desire for the 
 acquisition of “ scientific knowledge,” not as a mere school lesson, but 
 as a treasure, a useful ally which may some day help him in a greater or 
 lesser degree to fight “ The Battle of Life. 
 
THE 
 
 BOY’S PLAYBOOK OF SCIENCE. 
 
 CHAPTER I. 
 
 THE PROPERTIES OP MATTER — IMPENETRABILITY. 
 
 In the present state of our knowledge it seems to be universally agreed, 
 that we cannot properly commence even popular discussions on astro- 
 nomy, mechanics, and chemistry, or on the imponderables, heat, light, 
 electricity, and magnetism, without a definition of the general term 
 “ matter which is an expression applied by philosophers to every 
 species of substance capable of occupying space, and, therefore, to 
 everything which can be seen and felt. 
 
 The sun, the moon, the earth, and other planets, rocks, earths, metals, 
 glass, wool, oils, water, alcohol, air, steam, and hosts of things, both 
 great and small, all solids, liquids and gases, are included under the 
 comprehensive term matter. Such a numerous and varied collection of 
 bodies must necessarily have certain qualities, peculiarities, or properties; 
 and hence we come in the first place to consider “ The general powers 
 or properties of matter.” Thus, if we place a block of wood or stone in 
 any position, we cannot take another substance and put it in the space 
 filled by the wood or stone, until the latter be removed. Now this is 
 one of the first and most simple of the properties of matter, and is called 
 impenetrability , being the property possessed by all solid, liquid, and 
 gaseous bodies, of filling a space to the exclusion oi others until they be 
 removed, and it admits of many amusing illustrations, both as regards 
 the proof and modification of the property. 
 
 Thus, a block of wood fills a certain space: how is it (if impenetrable) 
 that we can drive a nail into it ? A few experiments will enable us to 
 answer this question. 
 
 Into a glass (as depicted at fig. 1) filled with spirits of wine, a quantity 
 of cotton wool many times the bulk of the alcohol may (if the experiment 
 is carefully performed) be pushed without causing a drop to overflow 
 the sides of the vessel. 
 
 Here we seem to have a direct contradiction of the simple and indis- 
 
 b 2 
 
4 
 
 boy’s playbook of science. 
 
 putable truth, that * c two things cannot occupy the same space at once.” 
 But let as proceed with our experiments : — 
 
 We have now a flask full of water, 
 
 and taking some very flnely-powdered 
 J sugar, it is easy to introduce a not- 
 able quantity of that substance with- 
 out increasing the bulk of the water ; 
 the only precaution necessary, is not 
 to allow the sugar to fall into the 
 flask in a mass, but to drop it in 
 grain by grain, and very slowly, al- 
 lowing time for the air-bubbles (which 
 will cling to the particles of sugar) 
 to pass off, and for the sugar to dis- 
 solve. Matter, in the experiments 
 adduced, appears to be penetrable, 
 and the property of impenetrability 
 seems only to be a creation of fancy : 
 reason, however, enables us to say 
 that the latter is not the case. 
 
 A. nail may certainly be hammered into wood, but the particles are 
 thrust aside to allow it to enter. Cotton wool may bo placed m spirits 
 of wine because it is simply greatly extended and bulky matter, which, 
 if compressed, might only occupy the space of the kernel of a nut, and 
 
 Fig. 2. 
 
THE PROPERTIES OF MATTER IMPENETRABILITY. 
 
 5 
 
 if tliis were dropped into a half-pint measure full of alcohol, the increase 
 of bulk would not cause the spirit to overflow. The cotton-wool expe- 
 riment is therefore no contradiction of impenetrability . The experi 
 ment with the sugar is the most troublesome opponent to our term, and 
 obliges us to amend and qualify the original definition, and say, that the 
 ultimate or smallest particles or atoms of bodies only are impenetrable ; 
 and we may believe they are not in close contact with each other, because 
 certain bulks of sugar and water occupy more space separately than 
 when mixed. 
 
 Fig. 3. 
 
 If we compare the flask of water to a flask full of marbles, and the 
 sugar to some rape-seed, it will be evident that we may almost pour 
 another flask full of the latter amongst the marbles, because they are not 
 in close contact with each other, but have spaces between them ; and 
 after pouring in the rape-seed, we might still find room for some fine 
 sand. 
 
 The particles of one body may thus enter into the spaces left between 
 those of another without increasing its volume ; and hence, as has been 
 before stated, “ The atoms only of bodies are truly impenetrable.” 
 
 This spreading, as it were, of matter through matter assumes a very 
 important function when we come to examine the constitution of the 
 air we breathe, which is chiefly a mechanical mixture of gases : seventy- 
 nine parts by volume or measure of nitrogen gas, twenty-one parts of 
 oxygen gas, and four parts of carbonic acid vapour in every ten thousand 
 parts of air having the following relations as to weight : — 
 
 Specific gravity. 
 
 Nitrogen 972 
 
 Oxygen 1105 
 
 Carbonic acid 1521 
 
 It might be expected that these gases would arrange themselves in 
 our atmosphere in the above order, and if that were the case, we should 
 nave the carbonic-acid gas (a most poisonous one) at the bottom, and 
 touching the earth, then the oxygen, and, last of all, the nitrogen \ a 
 
6 
 
 boy’s playbook of science. 
 
 state of things in which orgcmizedYife could not exist. The gases do not, 
 noweyer, separate : indeed, they seem to act as it were like vacuums to 
 one another, and “ the diffusion of gases” has become a 
 recognised fact, governed by fixed laws. This fact is 
 curiously illustrated, as shown in our cut, by filling a 
 bottle with carbonic acid, and another with hydrogen ; 
 and having previously fitted corks to the bottles, perfo- 
 rated so as to admit a tube, place the bottle containing 
 the carbonic acid on the table, then take the other full 
 of hydrogen, keeping the mouth downwards, and fit in 
 the cork and tube : place this finally into the cork of 
 the carbonic-acid bottle, which may be a little larger than 
 the other, in order to make the arrangement stand firmer ; 
 and after leaving them for an hour or so, the carbonic 
 acid, which is twenty-two times heavier than the hydro- 
 gen, will ascend to the latter, whilst the hydrogen will 
 descend to the carbonic acid. The presence of the car- 
 bonic acid in the hydrogen 
 bottle is easily proved by 
 pouring in a wineglassful 
 of clear lime-water, which 
 speedily becomes milky, 
 owing to the production of 
 carbonate of lime; whilst 
 the proof of the hydrogen 
 being present in the car- 
 bonic acid is established 
 by absorbing the latter 
 with a little cream of lime 
 — i.e., slacked lime mixed 
 to the consistence of cream 
 with some water — and set- 
 ting fire to the hydrogen 
 that remains, which burns 
 quietly with a yellowish 
 || flame if unmixed with air ; 
 but if air be admitted to 
 the bottle, the mixture of 
 air and hydrogen inflames 
 rapidly, and with some 
 noise. One of the most 
 elegant modes of showing 
 the diffusion of gases is by taking a large 
 round dry porous cell, such as would be 
 employed in a voltaic battery, and having 
 cemented a brass cap with a glass tube 
 attached to its open extremity, it may then 
 be supported by a small tripod of iron 
 
 Fig. 5. 
 
 a. The porous cell. b. The jar 
 of hydrogen, c. The brass cap and 
 glass tube d, the end of which 
 dips into the tumbler containing 
 the solution of indigo e. e e. The 
 wire and stand supporting the 
 porous cell and tube in tumbler. 
 
THE PROPERTIES OF MATTER — IMPENETRABILITY. 7 
 
 wire, and the end of the glass tube placed in a tumbler containing a 
 small quantity of water coloured blue with sulphate of indigo. If a 
 tolerably large jar containing hydrogen is now placed over the porous 
 cell, bubbles of gas make their escape at the end of the tube, because 
 the hydrogen diffuses itself more rapidly into the porous cell than the 
 air which it already contains passes out. When the jar is removed, the 
 reverse occurs, hydrogen diffuses out of the porous cell, and the blue 
 liquid rises in the tube. 
 
 This diffusive force prevents the accumulation of the various noxious 
 gases on the earth, and spreads them rapidly through the great bulk of 
 the atmosphere surrounding the globe. 
 
 Although air and other gases are invisible, they possess the property 
 of impenetrability, as may be easily proved by various experiments. 
 Having opened a pair of common bellows, stop up the nozzle securely, 
 and it is then impossible to shut them ; or, fill a bladder with air by 
 blowing into it, and tie a string fast round the neck , you then find that 
 you cannot, without breaking the bladder, press the sides together. 
 
 It is customary to say that a vessel is empty when we have poured out 
 the water which it contained. Having provided two glass vessels full 
 of water, place each of them in an empty white pan, to receive the over- 
 
 Fig. 6 represents the water overflow- 
 ing, as the glass, with the orifice closed, 
 is pressed down, proving the impene- 
 trability of air. 
 
 Fig. 7. The orange has entered the 
 glass vessel, and the air having passed 
 from the orifice, no water overflows. 
 
 flow, then lay an orange upon the surface of the water of one of them, 
 and being provided with a cylindrical glass, open at one end, with a 
 hole in the centre of the closed end, place your finger firmly over the 
 orifice, and endeavour, by inverting the glass over the orange, and 
 pressing upon the surface of the water, to make it enter the interior 
 of the glass cylinder ; the resistance of the air will now cause the water 
 to overflow into the white pan, whilst the orange will not enter. The 
 
8 
 
 EOY S PLAYBOOK OF SCIENCE. 
 
 orange may now be transferred to the other vessel of water, and on 
 removing the finger from the orifice of the cylindrical glass, and in- 
 verting it as before over the orange, the air will rush out and the orange 
 and water will enter, whilst there will be no overflow as in the preceding 
 experiment. The comparison of the two is very striking, and at ouce 
 teaches the fact desired. 
 
 Whilst the vessels of water are still in use, another pretty experiment 
 may be made with the metal potassium. First throw a small piece of 
 the metal on the surface of the water, to show that it takes fire on con- 
 tact with that fluid; then, having provided a gas-jar, fitted with a cap 
 
 Fig. 8. Gas-jar with stop-stock closed. Fig. 9. Gas-jar; stop-cock open ; 
 
 and potassium in ladle ; air prevents the the air passes, the water enters, and 
 
 entrance of the water. the potassium is inflamed. 
 
 and stop-cock, and a. little spoon screwed into the bottom of the stop- 
 cock inside the gas-jar, place another piece of potassium in the little 
 snoon, and, after closing the stop-cock, push the jar into one of the 
 vessels of water : as before, the impenetrability of the air prevents the 
 water flowing up to the potassium ; but, on opening the stop-cock, the 
 air escapes, the water rushes up, and directly it touches the potassium, 
 combustion ensues. 
 
 Having sufficiently indicated the nature and meaning of impenetra- 
 bility, we may proceed to discuss experimentally three other marked 
 and special qualities of matter — viz., inertia , gravity , and weight. 
 
INERTIA, OR PASSIVENESS. 
 
 Inertia is a power which (according to Sir Isaac Newton) is implanted 
 in all matter of resisting any change from a state of rest. It is sometimes 
 called vis inertia , and is that property possessed by all matter, of re- 
 maining at rest till set in motion, and vice versa ; and it expresses, in 
 brief terms, resistance to motion or rest. 
 
 A pendulum clock wound up and ready to go, does not commence its 
 movements, until the inertia of the pendulum is overcome, and motion 
 imparted to it. On the other hand, when seated in a carriage, should 
 any obstruction cause the horse to stop suddenly, it is only perhaps by 
 a violent effort, if at all, that we can resist the onward movement of our 
 
 Fig. 10. Tin tray, with glass bottom, full of water ; candle placed underneath. 
 
 bodies. To illustrate inertia, construct a metal tray, about three feet 
 long, two feet wide, and two inches deep, with a glass bottom, and 
 arrange it on a framework supported by legs, like a table, and having 
 filled it with water, let the room be darkened, and then place under the 
 tank a lighted candle, at a sufficient distance from the glass to prevent 
 the heat cracking it. If a piece of calico or paper, stretched on a frame 
 work, be now held over the water at an angle of about thirty degrees, 
 all that occurs on the surface of the water will be rendered visible on 
 such screen. Attention may now be directed to the quiescence, or the 
 inertia of the water, while the opposite condition of movement and 
 formation of the waves may be beautifully shown by touching the sur- 
 face of the water with the finger ; the miniature waves being depicted 
 on the screen, and continuing their motion till set at rest by striking 
 against the sides of the tin tray. 
 
10 
 
 BOY’S PLAY'BOOK OF SCIENCE. 
 
 Fig. 11. Same tray, with calico screen ; showing the waves as they are produced by 
 touching the surface of the water with the finger. 
 
 Should the above experiment be thought too troublesome or expen- 
 sive to prepare, inertia may be demonstrated by filling a tea-cup or other 
 convenient vessel with water, and after moving rapidly with it in any 
 direction, if we stop suddenly, the rigidity of all parts of the cup we 
 hold brings them simultaneously to a state of rest; but the mobility of 
 the liquid particles allows of their continuing in motion in their original 
 direction, and the liquid is spilled. Thus, carelessness in handing and 
 spilling a cup of tea (though not to be recommended) serves to illustrate 
 an important principle. The inertia of bodies in motion is further and 
 lamentably illustrated by the accidents caused from the sudden stoppage 
 of a railway train whilst in rapid motion, when heads and knees come in 
 contact with frightful results. — It is more especially demonstrated by 
 the earth, the moon, and the other planets continuing their motion for 
 ever in the absence of any friction or resistance to oppose their onward 
 progress. It is the friction arising from the roughness of the ground, 
 the resistance of the air, and the force of the earth’s attraction, which 
 puts a stop to bodies set in motion about the surface of the earth. 
 
XI 
 
 GRAVITATION. 
 
 Inertia represents a passive force, gravitation , an active condition of 
 matter : and this latter may truly be termed a force of attraction, because 
 it acts between masses at sensible or insensible distances : it is illus- 
 trated by a stone, unsupported, falling to the ground; by the stone 
 pressing with force on the earth, and requiring power to raise it from the 
 ground : indeed, it is commonly reported that it was by an accident — 
 “an apple falling from a tree”— that the great Newton was led to reflect 
 on the universal law of gravitation, and to pronounce upon it in the 
 following memorable w'ords : — 
 
 “ Every particle of matter in the universe attracts every other particle 
 of matter with a force or power directly proportional to the quantity oj 
 matter in each , and decreasing as the squares of the dista?ices ichich sepa- 
 rate the particles increase 
 
 These words may appear very obscure to our juvenile readers ; but 
 when dissected and examined properly, they clearly define the property 
 of gravitation. Tor instance, “every particle attracts every other with 
 a force proportional to the quantity of matter in 
 each.” This statement was verified some years 
 back by Maskelyne, who, having sought out and 
 discovered a steep, precipitous rock in the 
 Schichallion mountains, in Scotland, suspended 
 from it a metal weight by a cord, and going to 
 a convenient distance with a telescope, and ob- 
 serving* the weight, he found that it did not 
 hang perpendicularly, like an ordinary plumb- 
 line, but was attracted, or impelled, to the sides 
 of the rock by some kind of attraction, which, of 
 course, could be no other than that indicated 
 by Newton as the attraction of gravitation. 
 
 This truly wonderful power of attraction per- 
 vades all masses; and being, as before stated, 
 proportional to the quantity of matter, if a man 
 could be transported to the surface of the sun, 
 he would become about thirty times heavier : he 
 would be attracted, or impelled, to the sun with 
 thirty times more gravitating force than on the 
 surface of the earth, and would weigh about two 
 
 tons. Of course, nursing a baby on the sun’s Fig. 12. The Schichallion 
 surface would be a very serious affair with our Rocks. The dotted line and 
 ordinary strength ; whilst on some of the smaller nSf^ition^of" plumb-' 
 planets, such as Ceres and Pallas, we should pro- line, whilst the line of the 
 oably gravitate with a force of a few pounds indicates (of 
 
 only, and with the -same muscular power now ration) the attractive power 
 possessed, we should quite emulate the exploits t h e of t he rock 
 of those domestic little creatures sometimes dicuiarf 1 ° m ei 
 
 2 perpen- 
 
12 
 
 eoy’s playbook of science. 
 
 called “the industrious fleas , 55 and our jumping would be something 
 marvellous. 
 
 There is no very good lecture-table experiment that will illustrate 
 gravitation, although, attention may be directed to the fact of a piece of 
 potassium thrown on the surface of water in a plate generally rushing 
 to the sides, and, as if attracted, attaching itself with great force to the 
 substance of the pottery or porcelain ; or, if a model ship, or lump of 
 wood, be allowed to float at rest in a large tank of water, and a number 
 of light chips of wood or bits of straw be throwm in, they generally col- 
 lect and remain around the larger floating mass. 
 
 A very good idea, however, may be afforded of the universal action of 
 gravity maintaining all things in their natural position on the earth by 
 
GRAVITATION. 
 
 I ** 
 J u 
 
 taking a hoop and arranging in and upon it balls, or a model ship, or 
 other toy, and wires, as depicted in our diagram. 
 
 With this simple apparatus we may illustrate the upward, downward, 
 and sideway movement of bodies from the earth, and the counteraction 
 by the force of gravitation of any tendency of matter to fall away from 
 the globe, which is represented in the model by the india-rubber springs 
 pulling the balls and toys back again to the circumference of the hoop. 
 
 The attraction of gravitation decreases (quoting the remainder of 
 Newton’s definition) as the squares of the distances which separate 
 the particles increase — i.e., it obeys the principle called “inverse pro- 
 portion 55 — viz., the greater the distance, the less gravitating power ; the 
 less the distance, the greater the power of gravitation. Gravitation is 
 like the distribution of light and other radiant forces, and may be thus 
 illustrated. 
 
 Fig. 14. Place a lighted candle, marked a, at a certain distance from No. 1, a board one 
 foot square ; at double the distance the latter will shadow another board, No. 2, four feet 
 square; at three times, No. 3, nine feet square ; at four. No. 4, sixteen feet; and so on. 
 
 To make the comparison between the propagation of light and the 
 attraction of gravitation, we have only to imagine the candle, a , to 
 represent the point where the force of gravity exists in the highest 
 degree of intensity ; suppose it to be the sun — the great centre of this 
 power in our planetary system. A body, as at No. 1, at any given 
 distance will be attracted (like iron-filings to a magnet) with a certain 
 force ; at twice the distance, the square of two being four, and by in- 
 verse proportion, the attraction will be four times less; at thrice 
 the distance, nine times less ; at the fourth distance, sixteen times less ; 
 and so on. With the assistance of this law, we may calculate, 
 roughly, the depth of a well, or a precipice, or a column, by ascer- 
 taining the time occupied in the fall of a stone or other heavy sub- 
 stance. A falling body descends about 16 feet in one second, 61 feet 
 in two seconds, 111 feet in three seconds, 256 feet in four seconds, 
 100 feet in five seconds, 576 feet in six seconds ; the spaces passed over 
 being as the squares of the times. 
 
 Suppose a stone takes three seconds in falling to the surface of the 
 water in a well, then 3x3 = 9x16 = 111 feet would be a rough 
 estimate of the depth. The calculation will exceed the truth in con- 
 sequence of the stone being retarded in its passage by the resistance of 
 the air. 
 
14 
 
 boy’s playbook of science. 
 
 All bodies gravitate equally to the earth : for instance, if an open box, 
 say one foot in length, two inches broad, and two inches deep, be pro- 
 vided with a nicely-fitted bottom, attached by a hinge, a number of 
 substances, such as wood, cork, marble, iron, lead, copper, may be 
 arranged in a row ; and directly the hand is withdrawn, the moveable 
 flap flies open, and if the manipulation with the disengagement of the 
 trap-door is good, the whole of the substances are seen to proceed to the 
 earth in a straight line, as shown in our drawing. 
 
 Fig. 16. 
 
 If a heavy substance, like gold, be greatly extended by hammering 
 and beating into thin leaves, and then dropped from the hand, the re- 
 sistance of the air becomes very apparent ; and a gold coin and a piece 
 of gold-leaf would not reach the earth at the same time if allowed to 
 fall from any given height. This fact is easily displayed by the assis- 
 tance of a long glass cylindrical vessel placed on the air-pump, with suit- 
 able apparatus arranged with little stages to carry the different sub- 
 stances ; upon two of them may be placed a feather and a gold coin, and 
 on the third, another gold coin and a piece of gold-leaf. 
 
 In arranging the experiment, great care ought to be taken that the 
 little stages are all nicely cleaned, and free from any oil, grease, or other 
 matter which might cause the feathers or the gold-leaf to cling to the 
 stages when they are disengaged, by moving the brass stop round that 
 works in the collar of leathers. Sometimes these leathers are oiled, and 
 
GRAVITATION. 
 
 15 
 
 in that case, when the vacuum is made, the oil, by the pressure, is 
 squeezed out, and, passing down, may reach the stages and spoil the 
 experiment, by causing the feathers and gold- 
 leaf to stick to the brass, producing great dis- 
 appointment, as the illustration, usually called 
 the “ guinea aud feather glass experiment ” 
 takes some time to prepare. The air-pump 
 being in good order, the long glass is first 
 greased on the lower welt or edge, and then 
 placed firmly on the air-pump plate. The top 
 edge, or welt, may now be greased, and the 
 gold coins, feathers, and gold-leaf arranged in 
 the drop-apparatus ; this is carefully placed on 
 the top of the glass, and firmly squeezed down. 
 
 The author has always found a tallow candle, 
 rolled in a sheet of paper (so as to leave about 
 half the candle exposed), the best grease to ^ w 
 
 smear the glass it 
 with for air- fjj 
 pump experi- jr 
 ments; if the f 
 weatheriscold, * Fig. 17. 
 the candle may 
 
 be placed for a few minutes before ail 
 ordinary fire to soften the tallow. Po- 
 matum answers perfectly well wTien the 
 surfaces of glass and brass are all nicely 
 ground; but as air-pumps and glasses 
 by use get scratched and rubbed, the 
 tallow seems to fill up better all ordi- 
 nary channels by which air may enter 
 to spoil a vacuum. 
 
 The apparatus being now arranged, 
 the air is pumped out ; and here, again, 
 care must be taken not to shake the 
 gold off the stages. When a proper 
 vacuum has been obtained, which will 
 be shown by the pump-gauge, the stop 
 is withdrawn from one of the stages, 
 and the gold and feather are seen to 
 fall simultaneously to the air-pump 
 plate. Another stage, with the gold- 
 leaf and coin, may now be detaclied ; 
 both showing distinctly, that when the 
 resistance of the air is withdrawn, all 
 bodies, wTiether called light or heavy y 
 gravitate equally to the earth. Then, 
 Fig. is. the screw at the bottom of the pump- 
 
16 
 
 boy’s playbook of science. 
 
 barrels being opened, attention may be directed to the whizzing noise 
 the air makes on entering the vacuum, and when the air is once more 
 restored to the long glass vessel, the last stage may be allowed to fall ; 
 and now, the gold coin readies the pump-plate first, and the feather, 
 lingering behind, loses (as it were) the race, and touches the plate after 
 the gold coin ; thus demonstrating clearly the resistance of the air to 
 falling bodies. 
 
 Another, and perhaps less troublesome, mode of showing the same fact, 
 is to use a long glass tube closed at each end with brass caps cemented 
 on. One cap should have the largest possible aperture closed by a 
 brass screw, and the other may fit a small hand-pump. 
 
 If a piece of gold and a small feather are placed in the tube, it may 
 be shown that the former reaches the bottom of the tube first, whilst it 
 is full of air, and when the air is withdrawn by means of the pump, and 
 the tube again inverted, both the gold and the feather fall in the same 
 time. 
 
 Fig 1 . 19. a b. Glass tube containing’ a piece of gold and a feather, which are placed in at 
 the large aperture a. c. Small hand-pump. 
 
 For this reason, all attempts to measure heights or depths by observing 
 the time occupied by a falling body in reaching the earth must be in- 
 correct, and can only be rough approximations. An experiment tried at 
 St. Paul’s Cathedral, with a stone, which was allowed to fall from the 
 cupola, indicated the time occupied in the descent to be four and a half 
 seconds: now, if we square this time, and multiply by 16, a height of 
 324 feet is denoted; whereas the actual height is only 272 feet, and the 
 difference of 52 feet shows how the stone was retarded in its passage 
 through the air ; for, had there been no obstacle, it would have reached 
 the ground in 4-^tlis seconds. 
 
 The force of gravitation is further demonstrated by the action of the 
 sun and moon raising the waters of the ocean, and producing the tides ; 
 and also by the earth and moon, and other planets and satellites, being 
 prevented from flying from their natural paths or orbits around the sun. 
 It is also very clearly proved that there must be some kind of attractive 
 force resident in the earth, or else all moveable things, the water, the 
 air, the living and dead matters, would fly away from 
 the surface of the earth in obedience to what is called 
 “ centrifugal force.” Our earth is twenty-four hours 
 in performing one rotation on its axis, which is an ima- 
 ginary line drawn from pole to pole, and represented 
 by the wire round which we cause a sphere to rotate. 
 All objects, therefore, on the earth are moving with 
 the planet at an enormous velocity ; and this movement 
 is called the earth’s diurnal, or daily rotation. Now, 
 
 Fig. 20. 
 
CENTRIFUGAL FORCE. 
 
 17 
 
 it will be remembered, that mud or other fluid matter flies off, and is 
 not retained by the circumference of a wheel in motion : when a mop is 
 trundled, or a dog or sheep, after exposure to rain, shake themselves, 
 the water is thrown off by what is called centrifugal force [centrum, a 
 centre, fugio, to fly from). 
 
 CHAPTER II. 
 
 CENTRIFUGAL FORCE. 
 
 That power which drives a revolving body from a centre, and it 
 may be illustrated by turning a closed parasol, or umbrella,’ rapidly 
 round on its centre, the stick being the axis— the ribs fly out, and if 
 there is much friction in the parts, the illustration is more certain bv 
 attaching a bullet to the end of each rib, as shown in our drawing. 
 
 Fig. 21. 
 
 Fir. 22. 
 
 The same fact may be illustrated by a square mahogany rod, say one 
 inch square and three feet long, with two flaps eighteen inches in length, 
 hanging by hinges, and parallel to the sides of the centre rod, which 
 immediately fly out on the rotation of the long centre piece. 
 
 The toy called the centrifugal railway is also a very pretty illustration 
 of the same fact. A glass of water, or a coin, mav be placed in the 
 little carnage, and although it must be twice hanging perpendicular in a 
 line with the earth, the carriage does not tumble away from its ap* 
 pointed track, and the centrifugal force binds it firmly to the interior of 
 the circle round which it revolves. 
 
 J 
 
 c 
 
18 
 
 boy’s playbook of science. 
 
 Another striking and very simple illustration is to suspend a hemi- 
 spherical cup by three cords, and having twisted them, by turning round 
 the cup, it may be filled with water, and directly the hand is withdrawn, 
 the torsion of the cord causes the cup to rotate, and the water describes 
 a circle on the floor, flying off at a tangent from the cup, as may be 
 noticed in the accompanying cut. 
 
 Fig. 24. 
 
 A hoop when trundled would tumble on its side if the force ol gravi- 
 tation was not overcome by the centrifugal force which imparts to it a 
 motion in the direction of a tangent (tango, to touch) to a circle, i 
 same principle applies to the spinning-top-this toy cannot be made to 
 stand upon its point until set in rapid motion. 
 
 Returning again to the subject of gravitation, we may now consider 
 it in relation to other and more magnificent examples which we dis- 
 cover by studying the science of astronomy. 
 
13 
 
 CHAPTER III. 
 
 THE SCIENCE OF ASTEONOMY. 
 
 In a work of this kind, professedly devoted to a very brief and popular 
 view of the different scientific subjects, much cannot be said on any 
 special branch of science; it will be better, therefore, to take up one 
 subject in astronomy, and by discussing it in a simple manner, our young 
 friends may be stimulated to learn more of those glorious truths which 
 are to be found in the published works of many eminent astronomers 
 and especially in that of Mr. Hind, called “ The Illustrated London 
 Astronomy. One ol the most interesting subjects is the phenomenon 
 oi the eclipse of the sun ; and as 1858 is likely to be long remembered 
 for its “ annular eclipse/ 5 we shall devote some pages and illustrations 
 to this subject. 
 
 Eclipses of the sun are of three kinds— partial, annular, and total. 
 Many persons have probably seen large partial eclipses of the sun, and 
 may possibly suppose that a total eclipse is merely an intensified form of 
 a partial one ; but astronomers assert that no degree of partial eclipse 
 even when the very smallest portion of the sun remains visible, gives 
 tne slightest idea of a total one, either in the solemnity and overpower- 
 ing influence of the spectacle, or in the curious appearances which accom- 
 pany it. 
 
 The late Mr. Baily said of an eclipse (usually called that of Thales), 
 winch caused the suspension of a battle between the Lydians and Medes, 
 that only a total eclipse could have produced the effect ascribed to it* 
 Even educated astronomers, when viewing with the naked eye the sun 
 nearly obscured by the moon in an annular eclipse, could not tell that 
 any part of the sun was hidden. 
 
 During the continuance of a total eclipse of the sun, we are permitted 
 a hasty glance at some of those secrets of Nature which are not revealed 
 at any other time — glories that hold in tremulous amazement even 
 veteran explorers of the heavens and its starry worlds. 
 
 The general meaning of an eclipse may be shown very nicely by light- 
 ing a . common oil, or oxy-hydrogen lantern in a darkened room, 'and 
 throwing the rays which proceed from it on a three-feet globe. The 
 lantern may be called the sun, and, of course, it is understood that cor- 
 rect comparative sizes are not attempted in this arrangement; if it were 
 so, the globe representing the earth would have to be a mere speck, for 
 if we make the model of the sun in proportion to a three-feet globe 5 , no 
 ordinary lecture hall would contain it. This being premised, attention 
 is directed to the lantern, which, like the sun, is self-liyninous, and is 
 giving out its own rays ; these fall upon the globe we have designated 
 the earth, and illuminate one-lialf, whilst the other is shrouded in dark- 
 ness, reminding us of the opacity of the earth, and teaching, in a familiar 
 
boy’s playbook of science. 
 
 20 
 
 manner, the causes of day and night. Another globe, sav six inches m 
 diameter, and supported by a string, may be compared to the moon, and, 
 like the earth, is now luminous, and shines only by borrowed light: the 
 moon is simply a reflector of light; like a sheet of white cardboard or 
 a metallic mirror. When, therefore, the small globe is passed between the 
 lantern and the large globe, a shadow is cast on the lantern: it is also 
 seen that only the half of the small globe turned towards the lantern is 
 illuminated, while the other half, opposite the large globe, is m shadow 
 or darkness. And here we understand why the moon appeals to be 
 black while passing before the sun; so also by moving the small globe 
 about in various curves, it is shown why eclipses are only visible at cer- 
 tain parts of the earth’s surface ; and as it would take (roughly speak- 
 ,,,,,'1 fifty globes as large as the moon to make one equal in size to our 
 Sail the shadow it casts must necessarily be small, and cannot obscure 
 the whole hemisphere of the earth turned towards it. An eclipse of the 
 sun is, therefore, caused by the opaque mass of moon passing between 
 the sun and the earth. Whilst an eclipse of the moon is caused by the 
 earth moving directly between the sun and the moon: the large shadow 
 cast bv the earth renders a total eclipse of the moon visible to a greater 
 number of spectators on that half of the earth turned towards the moon. 
 
 AH these facts can be clearly demonstrated with the arrangement already 
 
 described of which we give the following pictorial illustration :— 
 
 in using this apparatus, it should be explained that if the moon were 
 
 as large as the sun, the shadow would be cylindrical like the figure 1, and 
 
 of an unlimited length. If she were of greater magm ude it would 
 precisely resemble the shadow cast in the experiment all eady adduced 
 with the lantern and shown at No. 2 But being so very much smaller 
 than the sun, the moon projects a shadow which converges to a point as 
 shown in the third diagram. 
 
THE SCIENCH OF ASTRONOMY. 
 
 21 
 
 In order to comprehend the difference between an annular and a total 
 eclipse of the sun, it is necessary to mention the apparent sizes of the 
 sun and moon: thus, the former is a very large body — viz., eight 
 hundred and eighty-seven thousand miles in diameter; but then, the sun 
 is a very long way off from the earth, and is ninety millions of miles 
 distant from us; therefore, he does not appear to be very large : indeed, 
 the sun seems to be about the same size as the moon ; for, although the 
 sun’s diameter is (roughly speaking) four hundred times greaterthan 
 that of the moon, he is four hundred times further away from us, and,- 
 consequently, the sun and moon appear to be the same size, and when 
 they come in a straight line with the eye, the nearer and smaller body, 
 the moon, covers the larger and more distant mass, the sun ; and hence, 
 we have either an annular, or a total eclipse, showing how a small body 
 may come between the eye and a larger body, and either partially or 
 completely obscure it. 
 
99 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 With respect to’ an annular eclipse, it mus be remembered, that the 
 paths of all bodies revolving round others are elliptical ; i.e,, they take 
 place in the form of an ellipse, which is a figure easily demonstrated ; 
 and is, in fact, one of the conic sections. 
 
 If a slice be taken off a cone, parallel with the base, we have a circle 
 thus— 
 
 If it be cut obliquely, or slanting, we see at once the figure spoken of, 
 and have the ellipse as shown in this picture. 
 
 Now, the ellipse has two points within it, called “ the foci/’ and these 
 are easily indicated by drawing an ellipse on a diagram-board, in which 
 two nails have been placedina straight line, and about twelve inches apart. 
 Having tied a string so as to make a loop, or endless cord, a circle 
 may first be drawn by putting the cord round one of the nails, and 
 holding a piece of chalk in the loop of the string, it may be extended 
 to its full distance, and a circle described ; here a figure is produced 
 round one point, and to show the difference between a circle and an 
 ellipse, the endless cord is now placed on the two nails, and the chalk 
 being carried round inside the string, no longer produces the circle, but 
 that familiar form called the oval. As a gardener would say, an oval 
 has been struck ; and the two points round which it has been described 
 
THE SCIENCE OF ASTRONOMY. 23 
 
 are called the foci. This explanation enables ns to understand the next 
 diagram, showing the motion of the earth round the sun ; the latter 
 being placed in one of the foci of a very moderate ellipse, and the 
 various points of the earth’s orbit designated by the little round globes 
 marked a, b, c, d, where it is evident that the earth is nearer to the sun. 
 at B than at d. In this diagram the ellipse is exaggerated, as it ought, 
 in fact, to be very nearly a circle. 
 
 A 
 
 0 
 
 C 
 
 Fig. 32. 
 
 We are about three millions of miles nearer to the sun in the winter 
 than we are in the summer ; but from the more oblique or slanting 
 direction of the rays of the sun during the winter season, we do not 
 derive any increased heat from the greater proximity. The sun, there- 
 fore, apparently varies in size ; but this seeming difference is so trifling 
 that it is of no importance in the discussion : and here we may ask, why 
 
24 
 
 boy’s playbook of science. 
 
 docs the earth move round the sun ? Because it is impelled by two 
 forces , one of which has already been fully explained, and is called the 
 centrifugal power, and the other, although termed the centripetal force, 
 is only another name for the “ attraction of gravitation . 55 
 
 To show their mutual relations, let us suppose that, at the creation of 
 the universe, the earth, marked a, was hurled from the hand of its 
 Maker ; according to the law of inertia, it would continue in a straight 
 line, a c, for ever through space, provided it met with no resistance or 
 obstruction. Let us now suppose the earth to have arrived at the 
 point b, and to come within the sphere of the attraction of the sun s ; 
 
THE SCIENCE OF ASTRONOMY. 
 
 25 
 
 here we have at once contending forces acting at right angles to each 
 other ; either the earth must continue in its original direction, A c, or 
 fall gradually to the sun. But, mark the beauty and harmony of the 
 arrangement : like a billiard-ball, struck with equal force at two points 
 at right angles to each other, it takes the mean between the two, or 
 what is termed the diagonal of the parallelogram (as shown in our 
 drawing of a billiard-table), and passes in the direction of the curved 
 line, b d ; having reached d, it is again ready to fly off at a tangent ; 
 the centrifugal force would carry it to 
 e, but again the gravitating force con- 
 trols the centripetal, and the earth 
 pursues its elliptical path, or orbit, till 
 the Almighty Author who bade it move 
 shall please to reverse the command. 
 
 The mutual relations of the centri- 
 petal and centrifugal forces may be 
 illustrated by suspending a tin cylin- 
 drical vessel by two strings, and 
 having filled it with water, the vessel 
 may be swung round without spilling 
 a single drop ; of course, the movement 
 must be commenced carefully, by mak- 
 ing it oscillate like a pendulum. 
 
 The cord which binds it to the finger 
 may be compared to the centripetal 
 force, whilst the centrifugal power is 
 illustrated by the water pressing against the sides and remaining in the 
 vessel. Upon the like principles the moon revolves about the earth, 
 
 but her orbit is more ellip- 
 
 tical than that of the earth 
 
 B around the sun ; and it is 
 evident from our diagram 
 that the moon is much fur- 
 ther from the earth at a 
 than at b. As a natural 
 consequence, the moon ap- 
 pears sometimes a little 
 larger and sometimes 
 smaller than the sun ; the 
 apparent mean diameter of 
 the latter being thirty-two 
 minutes, whilst the moon’s 
 apparent diameter varies 
 from twenty-nine and a 
 half to thirty-three and a half minutes. Now, if the moon passes exactly 
 between us and the sun when she is apparently largest, then a total eclipse 
 takes place ; whereas, if she glides between the sun and ourselves when 
 smallest — i.e., when furthest off from the earth — then she is not suffi- 
 
 Fig. 35. 
 
 Q 
 
 A® 
 
 Fig. 36. 
 
2G 
 
 BOY'S playbook of science. 
 
 ciently large to cover the sun entirely, but a ring of sunlight remains 
 visible around her, and what is called an annular eclipse of the sun 
 occurs. This fact may be shown in an effective manner by placing the 
 oxy-hydrogen lantern before a sheet, or other white surface, and throw- 
 
 Fig. 37. 
 
 ing a bright circle of light upon it, which may be called the sun ; then, 
 if a round disc of wood be passed between the lantern and the sheet, at 
 a certain distance from the nozzle of the lantern, all the light is cut off, 
 the circle of light is no longer apparent, and we have a resemblance to 
 a total eclipse. 
 
 By taking the round disc of wood further from the lantern, and re- 
 peating the experiment, it will be found that the whole circle of light 
 is not obscured, but a ring of light appears around the dark centre, cor- 
 responding with the phenomenon called the annular (ring-shaped) 
 eclipse. 
 
 If a bullet be placed very near to one eye whilst the other remains 
 closed, a large target may be wholly shut out from vision; but if the 
 bullet be adjusted at a greater distance from the eye, then the centre 
 only will be obscured, and the outer edge or ring of the target remains 
 visible. 
 
 When the advancing edge, or first limb , as it is termed, of the moon 
 approaches very near to the second limb of the sun, the two are joined 
 together for a time by alternations of black and white points, called 
 Baily’s beads. 
 
 This phenomenon is supposed to be caused partly by the uneven and 
 mountainous edge of the moon, and partly by that inevitable fault of 
 telescopes, and of the nervous system of the eye, which tends to enlarge 
 the images of luminous objects, producing what is called irradiation. It 
 is exceedingly interesting to know that, although the clouds obscured 
 the annular eclipse of 1858, in many parts of England, we are yet 
 
THE SCIENCE OF ASTK0N03IY. 
 
 27 
 
 Fig. 38. 
 
 ieft the recorded observations of one fortunate astronomer, Mr. John 
 Yeats, who states that — 
 
 “ All the phenomena of an annular eclipse were clearly and beautifully 
 visible on the^Potheringay-Castle-mound', which is a locality easily iden- 
 tified. Baily’s beads were perfectly plain on the completion of the 
 amiulus , which occurrence took place, according to my observation, at 
 about seventy seconds after 1 o’clock; it lasted about eighty seconds. 
 
 ‘ beads/ like drops of water, appeared on the upper and under sides 
 ot the moon, occupying fully three-fourths of her circumference. 
 
 “ Prior to this, the upper edge of the moon seemed dark and rough, 
 and there were no other changes of colour. At 12 '43, the cusps, for a 
 lew moments, bore a very black aspect. 
 
 There was nothing like intense darkness during the eclipse, and less 
 gloom than during a thunderstorm. Bystanders prognosticated rain ; 
 but it was the shadow of a rapidly- declining day. At 12 o’clock, a lady 
 living on the farm suddenly exclaimed, c The cows are coming home 
 to be milked!’ and they came, ail but one; that followed, however, 
 within the hour. Cocks crowed, birds flew low or fluttered about 
 uneasily, but every object far and near was well defined to the eye. 
 
 A singular broadway of light stretched north and south for upwards 
 ol a quarter of an hour ; from about 12*54 to 1*10 p.m. 
 
 If the annular eclipse of the sun be a matter for wonderment, the total 
 eclipse of the same is much pore surprising ; no other expression than 
 that of awfully grand , can give an idea of the effects of totality, and of 
 the suddenness with which it obscures the light of heaven. The dark- 
 u * S Sa ^’ c . omes dropping down like a mantle, and as the moment 
 ot full obscuration approaches, people’s countenances become livid, the 
 horizon is indistinct and sometimes invisible, and there is a general 
 appearance of horror on all sides. These are not simply the invention, [ j 
 
28 
 
 boy’s playbook of science. 
 
 of active human imaginations, for they produce equal, if not greater 
 effects, upon the brute creation. M. Arago quotes an instance of a half- 
 starved dog, who was voraciously devouring some food, but dropped it 
 the instant the darkness came on. A swarm of ants, busily engaged, 
 stopped when the darkness commenced, and remained motionless till 
 the light reappeared. A. herd of oxen collected themselves into a circle 
 and stood still, with their horns outward, as if to resist a common 
 enemy ; certain plants, such as the convolvulus and silk-tree acacia, 
 closed their leaves. The latter statement was corroborated during the 
 annular eclipse of the 15th of March, 1858, by Mr. E. S. Lane, who 
 states, that crocuses at the Observatory, Beeston, had their blossoms 
 expanded before the eclipse ; they commenced closing, and were quite 
 shut at about one minute previous to the greatest darkness ; and the 
 flowers opened partially about twenty minutes afterwards. A “ total 
 eclipse” of the sun has always impressed the human mind with terror 
 and wonder in every age : it was always supposed to be the forerunner 
 of evil ; and not only is the mind powerfully impressed, as darkness 
 gradually shuts out the face of the sun, but at the moment of totality, 
 a magnificent corona, or glory of light, is visible, and prominences, or 
 flames, as they are often termed, make their appearance at different- 
 points round the circle of the dark mass. This glory does not flash 
 suddenly on the eye ; but commencing at the first limb of the sun, 
 passes quickly from one limb to the other. Our illustration shows 
 
 Fig. 39. 
 
 <c the corona” and the “ rose-coloured prominences,” whose nature we 
 shall next endeavour to explain. Professor Airy describes the change 
 from the last narrow crescent of light to the entire dark moon, sur- 
 rounded by a ring of faint light, as most curious, striking, and magical 
 in effect. The progress of the formation of the corona was seen dis- 
 
THE SCIENCE OE ASTRONOMY. 
 
 2d 
 
 tinctly. It commenced on the side of the moon opposite to that at 
 which the sun disappeared, and in the general decay and disease which 
 seemed to oppress all nature, the moon and the corona appeared almost 
 like a local sore in that part of the sky, and in some places were seen 
 double. Its texture appeared as if fibrous, or composed of entangled 
 threads ; in other places brushes, or feathers of light proceeded from 
 it, and one estimate calculated the light at about one-seventh part of a 
 full moon light. The question, whether the corona is concentric with 
 the sun and° moon, was specially mooted by M. Arago, and Professor 
 Baden Powell has produced such excellent imitations of the “corona’’ 
 by making opaque bodies occult, or conceal, very bright points, that it 
 cannot be considered as material or real, although it ought to be re- 
 membered that the best theory of the zodiacal light represents it to be 
 a nebulous mass, increasing in density towards the sun, and yet no 
 portion of this nebulous mass was seen during the totality. . But by far 
 the most remarkable of all the appearances connected with a “ total 
 eclipse” are the rose-coloured prominences, mountains, or flames, pro- 
 jecting from the circumference of the moon to the inner ring of the 
 corona; and, although they had been observed by Vaserius (a Swedish 
 astronomer) in 1733, they took the modern astronomers entirely by 
 surprise in 1842, and they were not prepared with instruments to ascer- 
 tain the nature of these strange and almost portentous forms. In 1851, 
 however, great preparations were made to throw further light on the 
 subject. Professor Airy went to make his observations, and he says, 
 “That the suddenness of the darkness in 1851 appeared much more 
 striking than in 1842, and the forms of the rose-coloured mountains were 
 most curious. One reminded him of a boomerang (that curious weapon 
 thrown so skilfully by the aborigines of Australia) ; this same figure has 
 been spoken of by others as resembling a Turkish scimitar, strongly 
 coloured with rose-red at the borders, but paler in the centre. Another 
 form was a pale- white semicircle based on the moon’s limbs ; a third 
 figure was a red detached cloud, or balloon, of nearly circular form, 
 separated from the moon by nearly its own breadth ; a fourth appeared 
 like a small triangle, or conical red mountain, perhaps a little white in 
 the interior;” and the Professor proceeds to say, “ I employed myself 
 in an attempt to draw roughly the figures, and it was impossible, after 
 witnessing the increase in height ol some, and the disappearance of 
 another, and the arrival of new forms, not to feel convinced that the 
 phenomena belonged to the sun, and not to the moon.” 
 
 Still the question remains unanswered, what are these “'rose- 
 coloured prominences?” If they belong to the sun, and are moun- 
 tains in that luminary, they must be some thirty or forty thousand miles 
 in height. 
 
 M. Paye has formally propounded the theory, that they are caused by 
 refraction, or a kind "of mirage, or the distortion of objects caused by 
 heated air. This phenomenon is not peculiar to any country, though 
 most frequently observed near the margin of lakes and rivers, and on 
 hot sandy plains. M. Monge, who accompanied Buonaparte in his 
 
30 
 
 boy’s playbook of science. 
 
 expedition to Egypt, witnessed a remarkable example between Alex- 
 andria and Cairo, where, in all directions, green islands appeared sur- 
 rounded by extensive lakes of pure, transparent water. M. Monge 
 states that “-Nothing could be conceived more lovely or picturesque 
 than the landscape. In the tranquil surface of the lake, the trees and 
 houses with which the islands are covered were strongly reflected with 
 vdvid and varied hues, and the party hastened forward to enjoy the 
 refreshment apparently proffered them ; but when they arrived, the lake, 
 on whose bosom the images had floated — the trees, amongst whose 
 foliage they arose, and the people who stood on the shore, as if in- 
 viting their approach, had all vanished, and nothing remained but the 
 uniform and irksome desert of sand and sky, with a few naked and 
 ragged J^rabs.” 
 
 If M. Monge and his party had not been undeceived, by actually 
 going to the spot, they would, one and all, have been firmly convinced 
 that these visionary trees, lakes, and buildings had a real existence. 
 This kind of mirage is known in Persia and Arabia by the name of 
 “ serab” or miraculous water, and in the western districts of India by 
 that of “ scheram.” This illusion is the effect of unusual refraction, and 
 M. Eaye attempts to account for the rose-coloured mountains by some- 
 thing of a similar nature. 
 
 It is right, however, to mention, that learned astronomers do not con- 
 sider this theory of any value. 
 
 Lieutenant Patterson, one of the observers of the eclipse of 1851, 
 says, that “ It is very remarkable that the flames or prominences cor- 
 respond exactly (at least as far as he could judge) with the spots on the 
 sun’s surface.” Taking this statement with that of M. Paye, it may 
 be assumed, as a new idea, and nothing more, that these prominences 
 nre, after all, mere aerial pictures of these openings in the sun’s atmo- 
 sphere, or what are called “ sun spots.” In the “ Edinburgh Philoso- 
 phical Journal,” it is said, that although it has lately been shown in the 
 Edinburgh Observatory that it is possible to produce, by certain optical 
 experiments, red flames on the sun’s limb of precisely the rose-coloured 
 tint described, yet, on weighing the whole of the evidence, there does 
 seem a great preponderance in favour of the eclipse flames being real 
 appendages of the sun, and in that case they must be masses of such 
 vast size as to play no unimportant part in the economy of that stupen- 
 dous orb. 
 
 During the last eclipse great disappointment was felt that the dark- 
 ness was so insignificant, although, when we consider the enormous 
 light-giving power of the sun, and know that it was not wholly 
 obscured, we could hardly have expected any other result. There can 
 be no doubt that a decided change in the amount of light is only to 
 be observed during a total eclipse of the sun, one of which occurred 
 on the 7th of September, 1858; but, unfortunately, it was only visible 
 in South America ; we must therefore content ourselves with the de- 
 scriptions of those astronomers who can be fully relied on. From 
 the graphic account given by Piofessor Piazzi Smyth, the astronomer- 
 
THE SCIENCE OF ASTRONOMY”. . 3l 
 
 royal for Scotland, of a total eclipse as seen by him on the western 
 coast of Norway, we may form some notion of the imposing appearance 
 of the surrounding country when obscured during the occurrence of this 
 rare astronomical phenomenon. 
 
 The Professor remarks, “To understand the scene more fully, the 
 reader must fancy himself on a small, rocky island on a mountainous 
 coast, the weather calm, and the sky at the beginning of the eclipse 
 seven-tenths covered with thin aud bright cirro-strati clouds. As the 
 eclipse approaches, the clouds gradually darken, the rays of the sun are 
 no longer able to penetrate them through and through, and drench 
 them with living light as before, but they become darker than the sky 
 against which they are seen. The air becomes sensibly colder, the clouds 
 still darker, and the whole atmosphere murkier. 
 
 “ From moment to moment as the totality approaches, the cold and 
 darkness advance apace ; and there is something peculiarly and terribly 
 convincing in the two different senses, so entirely coinciding in their 
 indications of an unprecedented fact being in course of accomplishment. 
 Suddenly, and apparently without any warning (so immensely greater 
 were its effects than those of anything else which had occurred), the 
 totality supervenes, and darkness comes dozen. Then came into view 
 lurid lights and forms, as on the extinction of candles. This was the 
 most striking point of the whole phenomenon, and made the Norse 
 peasants about us flee with precipitation, and hide themselves for their 
 lives. 
 
 “Darkness reigned everywhere in heaven and earth, except where,, 
 along the north-eastern horizon, a narrow strip of unclouded sky pre- 
 sented a low burning tone of colour, and where some distant snow- 
 covered mountains, beyond the range of the moon’s shadow, reflected 
 the faint mono-chromatic light of the partially eclipsed sun, and exhi- 
 bited all the detail of their structure, all the light, and shade, and 
 markings of their precipitous sides with an apparently supernatural 
 distinctness. After a little time, the eyes seemed to get accustomed to 
 the darkness, and the looming forms of objects close by could be dis- 
 cerned, all of them exhibiting a dull-green hue; seeming to have exhaled 
 their natural colour, and to have taken this particular one, merely by 
 force of the red colour in the north. 
 
 “Life and animation seemed, indeed, to have now departed from 
 everything around, and we could hardly but fear, against our reason,, 
 that if such a state of things was to last much longer, some dreadful 
 calamity must happen to us all ; while the lurid horizon, northward, 
 appeared so like the gleams of departing light in some of the grandest 
 paintings by Danby and Martin, that we could not but believe, in spite 
 of the alleged extravagances of these artists, that Nature had opened 
 up to the constant contemplation of their mind’s -eye some of those 
 magnificent revelations of power and glory which others can only get a 
 glimpse of on occasions such as these.” 
 
 It can be easily imagined, that under such peculiar and awful circum- 
 stances, the careful observation of these effects must be somewhat dif- 
 
32 # boy’s playbook of science. 
 
 ficult, and the only wonder is that the astronomical observations are 
 conducted with any certainty at all. 
 
 In the eclipse of 1842, it was not only the vivacious Frenchman who 
 was carried away in the impulse of the moment, and had afterwards to 
 plead that “ he was no more than a man 33 as an excuse for his unfulfilled 
 part in the observations, but the same was the case with the grave 
 Englishman and the more stolid German. In 1851, much the same 
 failure in the observations occurred ; and on some person asking a worthy 
 American, who had come with his instruments from the other side of 
 the world expressly to observe the eclipse, what he had succeeded in 
 doing ? he merely answered, with much quiet impressiveness, “ That if 
 it was to he observed over again , he hoped he would he able to do some- 
 thing, hit that, as it was, he had done nothing : it had been too much 
 for him. 33 This is not quite so bad as the fashionable lady who 
 had been invited to look at an eclipse of the sun through a grand 
 telescope, but arriving too late, inquired whether “ it could not be shown 
 over again 33 
 
 With this brief glance at the science of astronomy, we once more 
 return to the term “gravity/’ which will introduce to us some new 
 and interesting facts, under the head of what is called “ centre of 
 gravity.” 
 
 CHAPTER IV. 
 
 CENTRE OF GRAVITY. 
 
 That point about which all the parts of a body do, in any situation , 
 exactly balance each other. 
 
 The discovery of this fact is due to Archimedes, and it is a point in 
 every solid body (whatever the form may be) in which the forces of 
 gravity may be considered as united. In our globe, which is a sphere, 
 or rather an oblate spheroid, the centre of gravity will be the centre. 
 Thus, if a plummet be suspended on the surface ol the earth, it points 
 directly to the centre of gravity, and, consequently, two plummet-lines 
 suspended side by side cannot, strictly speaking, be parallel to each 
 other. 
 
 If it were possible to bore or dig a gallery through the whole substance 
 of the earth from pole to pole, and then to allow a stone or the labled 
 Mahomet’s coffin to fall through it, the momentum— i.e., the force of the 
 moving body, would carry it beyond the centre of gravity. This force, how- 
 ever, being exhausted, there would be a retrograde movement, and after 
 many oscillations it would gradually come to rest, and then,. unsupported 
 by anything material, it would be suspended by the force of gravitation, and 
 now enter into and take part in the general attracting force ; and being 
 equally attracted on every side, the stone or coffin must be totally without 
 weight. Momentum is prettily illustrated by a series of inclined planes 
 
THE CENTRE OF GRAVITY. 
 
 33 
 
 Fig 1 . 40. f, The centre, abode. Plummet-lines, all pointing to the centre, and 
 therefore diverging from each other. 
 
 cut in mahogany, with a grooved channel at the top, in imitation of the 
 famous Russian ice mountains : and if a marble is allowed to run down 
 
 BA 
 
 ^ith g a ornnvpTat* £ radua ^ decreasing in height, cut out of inch mahogany, 
 
 Sb^Xch staru from a a. * “ ° rdmary marWc ' B B B - Diffcent of ih. 
 
 D 
 
boy’s playbook of science. 
 
 M 
 
 the first incline, the momentum will carry it up the second, from which 
 it will again descend and pass up and down the third and last miniature 
 
 mounta ^ 0 f un if orm density, the centre of gravity is easily dis- 
 covered, but not so in an irregular mass ; and here, perhaps, an explana- 
 tion of terms may not be altogether unacceptable. 
 
 Mass, is a term applied to solids, such as a mass of lead or sione. 
 
 Bulk , to liquids, such as a bulk of water or oil. 
 
 Volume, to gases, such as a volume of air or oxygen. 
 
 To find the centre of gravity of any mass, as, for example, an ordinary 
 school-slate, we must first of all suspend it from any part ot the frame ; 
 then allow a plumb-line to drop from the point of suspension, and mark 
 
 its direction on the slate. Again, 
 suspend the slate at various other 
 points, always marking the line of 
 direction of the plummet, and at 
 the point where the lines intersect 
 each other, there will be the centre 
 of gravity. 
 
 If the slate be now placed (as 
 shown in Fig. 43) on a blunt 
 
 Fig. 42. a b d. The three points of sus- 
 pension. ’ c, The point of intersection, and. 
 therefore, the centre of gravity, p, The line 
 of plummet. 
 
 wooden point at the spot where the 
 lines cross each other, it will be 
 found to balance exactly, and this 
 ae place is called the centre of gravity, 
 "being the point with which all other 
 particles of t!ie body would move with parallel and equable motion during 
 its fall The equilibrium of bodies is therefore much affected by the 
 position of the centre of gravity. Thus if we cut out an elliptical figure 
 From a board one inch in thickness, and rest it on a flat surface by one 
 of its edges (as at No. 1, fig. 44), this point of contact is called the point 
 of surmort and the centre of gravity is immediately above . 
 
 In this case the body is m a state of secure equilibrium for any 
 motiol on either side will cause the centre of gravity to ascend m these 
 directions and an oscillation will ensue. But if we place it upon the 
 sm^er end! as shown at No. 2 (fig. 441, the position will be one of 
 
THE CENTRE OF GRAVITY. 
 
 35 
 
 equilibrium, but not stable or secure; although the centre of gravity 
 is directly above the point of support, the slightest touch will displace 
 
 N? 2 
 
 the oval and cause its overthrow. The famous story of Columbus and 
 the egg suggests a capital illustration of this fact ; and there are two 
 modes in which the egg may be poised on either of the ends. 
 
 The one usually attributed to the great discoverer, is that of scraping 
 or slightly breaking away a little of the shell, so as to flatten one of the 
 ends, thus • — 
 
 Fig-. 45. a Represents the egg in its natural state, and, therefore, in unstable equilibrium ; 
 n, another egg, with the surface, s, flattened, by which the centre of gravity is lowered, and 
 if net disturbed beyond the extent of the point of support the equilibrium is stable. 
 
 The most philosophical mode of making the egg stand on its end and 
 without disturbing the exterior shell is to alter the position of the yolk, 
 which has a greater density than the white, and is situated about the 
 centre. If the egg is now shaken so as to break the membrane enclosing 
 the yolk, and thus allow it to sink to the bottom of the smaller end, the 
 centre of gravity is lowered ; there is a greater proportion of weight 
 
 D 2 
 
36 
 
 boy’s playbook of science. 
 
 concentrated in the small end, and the egg stands erect, as depicted at 
 fig. 46. 
 
 It is this variable position of the centre of gravity in ivory balls (one 
 
 part of which may be more 
 dense than another) that so 
 frequently annoys even the 
 best billiard-players ; and oil 
 this account a ball will de- 
 viate from the line in which 
 it is impelled, not from any 
 fault of the player, but in 
 consequence of the ivory 
 ball being of unequal den- 
 sity, and, therefore, not hav- 
 ing the centre correspond- 
 ing with the centre of gra- 
 vity. A good billiard-player 
 t 46 -~ No - ^Se^onot egg. c. Centre of gravity. should, therefore, always try 
 i\ T tie yolk. w. The white. xl u n u r i J J 
 
 No. 2. c. Centre of gravity, much lowered, y. The the ball before lie engages 
 yolk at the bottom of the egg. to play for any large sum. 
 
 The toy called the “tombola” reminds us of the egg-experiment, as 
 there is usually a lump of lead inserted in the lower part of the hemi- 
 
 Fig. 47. — No. 1. c. Centre of gravity in the lowest place, figure upright. 
 
 No. 2. c. Centre of gravity raised as the figure is inclined on either side, but falling 
 again into the lowest place as the figure gradually comes to rest. 
 
 sphere, and when the toy is pushed down it rapidly assumes the upright 
 position because the centre of gravity is not in the lowest place to which 
 it can descend ; the latter position being only attained when the figure 
 is upright. 
 
 There is a popular paradox in mechanics — viz., “a body having a 
 tendency to fall by its own weight, may be prevented from falling by 
 adding to it a weight on the same side on which it tends to fall,” and 
 the paradox is demonstrated by another well-known child’s toy as de- 
 picted in the next cut. 
 
THE CENTRE OF GRAVITY. 
 
 37 
 
 Fig. 48. The line of direction falling beyond the base; the bent wire and lead weigl it 
 throwing the centre of gravity under the table and near the leaden weight; the hind legs 
 become the point of support, and the toy is perfectly balanced. 
 
 After wliat has been explained regarding the improvement of the 
 ist ability of the egg by lowering the situation of the centre of gravity, it 
 in ay at first appear singular that a stick loaded with a weight at its 
 upper extremity can be balanced perpendicularly with greater ease and 
 precision than when the weight is lower down and nearer the hand ; 
 and that a sword can be balanced best when the hilt is uppermost ; 
 
 Fig. 49.— -No. 1. Sword balanced on handle : the are from o to d is very small, and if the 
 centre, c, falls out of the line of direction it is not easily restored to the upright position. 
 No 2. Sword balanced on the point : the arc from c to d much larger, and therefore the 
 sword is more easily balanced. 
 
o8 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 but this is easily explained when it is understood that with the 
 handle downwards a much smaller arc is described as it falls than when 
 reversed, so that in the former case the balancer has not time to re- 
 adjust the centre, whilst in the latter position the arc described is so 
 large that before the sword falls the centre of gravity may be restored 
 within the line of direction of the base. 
 
 Eor the same reason, a child tripping against a stone will fall 
 quickly ; whereas, a man can recover himself ; this fact can be very 
 nicely shown by fixing two square pieces of mahogany of different 
 
 Fig. 50. — No. 1. The two pieces of mahogany, carved to represent a man and a boy, one- 
 being 10 and the other 5 inches long, attached to board by hinges at n n. ' * 
 
 Fig. 51. — No. 2. The board pushed forward, striking against a nail, when the 
 short piece falls first, and the long one second. 
 
 lengths, by hinges on a flat base or board, then if the board be pushed 
 rapidly forward and struck against a lead weight or a nail put in the 
 
THE CENTRE OF GRAVITY. 
 
 39 
 
 table, the short piece is seen to fall first and the long one afterwards ; 
 the difference of time occupied in the fall of each piece of wood (which' 
 may be carved to represent the human figure) being clearly denoted by 
 the sounds produced as they strike the board. 
 
 Boat-accidents frequently arise in consequence of ignorance on the- 
 subject of the centre of gravity, and when persons are alarmed whilst 
 sitting in a boat, they generally rise suddenly, raise the centre of gravity, 
 which falling, by the oscillation of the frail bark, outside the line of direc- 
 tion of the base, cannot be restored, and the boat is upset ; if the boat were 
 fixed by the keel, raising the centre of gravity would be of little con- 
 sequence, but as the boat is perfectly free to move and roll to one side 
 or the other, the elevation of the centre of gravity is fatal, and it 
 operates just as the removal of the lead would do, if changed from the 
 base to the head of the “ tombola” toy. 
 
 A very striking experiment, exhibiting the danger of rising in a boat, 
 maybe shown by the following model, as depicted at 'Nos. 1 and 2, figs.. 
 52 and 53. 
 
 N? 1 
 
 Fig. 52. — No. 1. Sections of a toy-boat floating in water, b b b. Three brass wires placed 
 at regular distances and screwed into the bottom of the boat, with cuts or slits at the top 
 so that when the leaden bullets, ul, which are perforated and slide upon them like 
 beads, are raised to the top, they are retained by the brass cuts springing out ; when the 
 bullets are at the bottom of the lines they represent persons sitting in a boat, as shown 
 in the lower cuts, and the centre of gravity will be within the vessel. 
 
 We thus perceive that the stability of a body placed on a base depends 
 upon the position of the line of direction and the height of the centre 
 of gravity. 
 
 Security results when the line of direction falls within the base. In- 
 stability when just at the edge. Incipability of standing when falling 
 without the base. 
 
40 
 
 boy’s playbook of science. 
 
 N? 2 
 
 Fig. 53. — No. 2. The leaden bullets raised to the top now show the result of persons sud- 
 denly rising, when the boat immediately turns over, and either sinks or floats on the 
 surface with the keel upwards. 
 
 The leaning-tower of Pisa is one hundred and eighty-two feet in 
 height, and is swayed thirteen and a half feet from the perpendicular, 
 
 Fig. 54. f. Board cut and painted to represent the leaning-tower of Pisa. g. The centre 
 of gravity and plummet-line suspended from it. h. The hinge which attaches it to the 
 base board, i. The string, sufficiently long to unwind and allow the plummet to hang out- 
 side the base, so that, when cut, the model falls in the direction of the arrow. 
 
 but yet remains perfectly firm and secure, as the line of direction falls 
 considerably within the base. If it was of a greater altitude it could 
 no longer stand, because the centre of gravity would be so elevated 
 that the line of direction would fall outside the base. This fact may 
 be illustrated by taking a board several feet in length, and having cut 
 
THE CENTRE OF GRAVITY. 
 
 41 
 
 it out to represent the architecture of the leaning-tower of Pisa, it may 
 then be painted in distemper, and fixed at the right angle with a hinge 
 to another board representing the ground, whilst a plumb-line may be 
 dropped from the centre of gravity ; and it may be shown that as long 
 as the plummet falls within the base, the tower is safe ; but directly the 
 model tower is brought a little further forward by a wedge so that the 
 plummet hangs outside, then, on removing the support, which may be a 
 piece of string to be cut at the right moment, the model falls, and the 
 fact is at once comprehended. 
 
 The leaning-towers of Bologna are likewise celebrated for their great 
 inclination ; so also (in England) is the hanging-tower, or, more cor- 
 rectly, the massive wall which has formed part of a tower at Bridge- 
 north, Salop ; it deviates from the perpendicular, but the centre of 
 gravity and the line of direction fall within the base, and it remains 
 secure ; indeed, so little fears are entertained of its tumbling down, that 
 a stable has been erected beneath it. 
 
 One of the most curious paradoxes is displayed in the ascent of a 
 billiard-ball from the thin to the thick ends of two billiard-cues placed 
 
 Fig. 55. — No. 1. Two billiard-cues arranged for the experiment and fixed to a board : the 
 ball is rolling up. 
 
 No. 2. Sections showing that the centre of gravity, c, is higher at a than at b, which 
 represents the thick end of the cues ; it therefore, in effect, rolls down hill. 
 
 at an angle, as in our drawing above ; here the centre of gravity ia 
 raised at starting, and the ball moves in consequence of its actually 
 falling from the high to the low level. 
 
 Much of the stability of a body depends on the height through which 
 the centre of gravity must be elevated before the body can be over- 
 thrown. The greater this height, the greater will be the immovability 
 of the mass. One of the grandest examples of this fact is shown in 
 the ancient Pyramids ; and whilst gigantic palaces, with vast columns. 
 
42 
 
 boy’s playbook of science. 
 
 and all, the solid grandeur belonging to Egyptian architecture, have 
 succumbed to time and lie more or less prostrate upon the earth, the 
 
 Fig. 56. c. Centre of gravity, which must be raised to d before it can be overthrown. 
 
 Pyramids, in their simple form and solidity, remain almost as they were 
 built, and it will be noticed, in the accompanying sketch, how difficult, 
 if not impossible, it would be to attempt to overthrow bodily one of these 
 great monuments of ancient times. 
 
 The principles already explained are directly applicable to the con- 
 struction or secure loading of vehicles ; and in proportion as the centre 
 of gravity is elevated above the point of support (that is, the wheels), 
 so is the insecurity of the carriage increased, and the contrary takes 
 place if the centre of gravity is lowered. Again, if a waggon be loaded 
 
 No. 1 . No. 2. 
 
 Fi<r. 57 . No. 1. The centre of gravity is near the ground, and falls within the wheels. 
 
 No. 2. The centre of gravity is much elevated, and the line of direction is outside the wheels. 
 
THE CENTRE OF GRAVITY. 
 
 43 
 
 with a very heavy substance which does not occupy much space, such 
 as iron, lead, or copper, or bricks, it will be in much less danger of an 
 overthrow than if it carries an equal weight of a lighter body, such as 
 pockets of hops, or bags of wool or bales of rags. 
 
 In the one instance, the centre of gravity is near the ground, and falls 
 well within the base, as at No. 1, fig. 57. In the other, the centre of gravity 
 is considerably elevated above the ground, and having met with an ob- 
 struction which has raised one side higher than the other, the line 
 of direction has fallen outside the wheels, and the waggon is over- 
 turning as at No. 2. 
 
 The various postures of the human body may be regarded as so many 
 experiments upon the position of the centre of gravity which w r e are 
 every moment unconsciously performing. 
 
 To maintain an erect position, a man must so place his body as to 
 cause the line of direction of his weight to fall within the base formed 
 by his feet. 
 
 ’ The more the toes are turned outwards, the more contracted will be 
 the base, and the body will be more liable to fall backwards or forwards ; 
 and the closer the feet are drawn together, the more likely is the body 
 to fall on either side. The acrobats, and so-called “ India-Rubber 
 
 Fig. 58. 
 
 Brothers,” dancing dogs, &c., unconsciously acquire the habit of accu- 
 rately balancing themselves in all kinds of strange positions ; but as 
 these accomplishments are not to be recommended to young people, 
 some other marvels (such as balancing a pail of water on a stick laid 
 upon a table) may be adduced, as illustrated in fig. 59. 
 
 Let a b represent an ordinary table, upon which place a broomstick, 
 c d, so that one-half shall lay upon the table and the other extend from 
 
u 
 
 boy’s playbook of science. 
 
 it ; place over the stick the handle of an empty pail (which may possibly 
 require to be elongated for the experiment) so that the handle touches 
 or falls into a notch at 11 ; and in order to bring the pail well under the 
 
 Fig. 59. 
 
 table, another stick is placed in the notch E, and is arranged in the 
 line g F e, one end resting at g and the other at e. Having made these 
 preparations, the pail may now be filled with water ; and although it 
 appears to be a most marvellous result, to see the pail apparently 
 balanced on the end of a stick which may easily tilt up, the principles 
 already explained will enable the observer to understand that the centre 
 of gravity of the pail falls within the line of direction shown by the 
 dotted line ; and it amounts in effect to nothing more than carrying a pail 
 •on the centre of a stick, one end of which is supported at e, and the 
 other through the medium of the table, ab. 
 
 This illustration may be modified by using a heavy weight, rope, and 
 stick, as shown in our sketch below. 
 
 Before we dismiss this subject it is advisable to explain a term re- 
 ferring to a very useful truth, called the centre of percussion ; a know- 
 ledge of which, gained instinctively or otherwise, enables the workman 
 to wield his tools with increased power, and gives greater force to the 
 cut of the swordsman, so that, with some physical strength, he may 
 perform the feat of cutting a sheep in half, cleaving a bar of lead, or 
 
TIIE CENTRE OF GRAVITY. 
 
 45 
 
 neatly dividing, a la Saladin , in ancient Saracen fashion, a silk hand- 
 kerchief floating in the air. There is a feat, however, which does not 
 require any very great strength, but is sufficiently startling to excite 
 much surprise and some inquiry— viz., the one of cutting in half a broom- 
 stick supported at the ends on tumblers of water without spilling the 
 water or cracking or otherwise damaging the glass supports. 
 
 Fig. 61 . 
 
 These and other feats are partly explained by reference to time : the 
 force is so quickly applied and expended on the centre of the stick that 
 it is not communicated to the supports ; just as a bullet from a pistol 
 may be sent through a pane of glass without shattering the whole square, 
 but making a clean hole through it, or a candle may be sent through a 
 plank, or a cannon-ball pass through a half opened door without causin 0, 
 it to move on its hinges. But the success of the several feats depends 
 m a great measure on the attention that is paid to the delivery of the 
 blows at the centre of percussion of the weapon ; this is a point in a 
 moving body where the percussion is the greatest, and about which the 
 impetus or lorce of all parts is balanced on every side. It may be bette- 
 understood by reference to our drawing below. Applying this principle 
 to a model sword made of wood, cut in half in the centre of the blade 
 and then united with an elbow-joint, the handle being fixed to a board 
 by a wire passed through it and the two upright pieces of wood, the 
 lact is at once apparent, and is well shown in Nos. 1, 2, 3, fig. 62. 
 
46 
 
 boy’s playbook of science. 
 
 AB IMM 
 
 Fio- b 01 No 1 . is the wooden sword, with an elbow-joint at c. No. 2. Sword attached to 
 board at ‘k and being allowed to fall from any angle shown by dotted-line it strikes 
 the block w outside the centre of percussion, p, and as there is unequal motion in the 
 s of the sword it bends down (or, as it were, breaks) at the elbow-joint, c. 
 
 P No a displays the same model ; but here the blow has fallen on the block w, precisely 
 at the centre of percussion of the sword, p, and the elbow-jomt remains perfectly firm. 
 
 When a blow is not delivered with a stick or sword at the centre of 
 percussion, a peculiar jar, or what is familiarly spoken of as a stinging 
 sensation, is apparent in the hand; and the cause of this disagreeable 
 result is further elucidated by fig. 63, in which the post, a, corresponds 
 with the handle of the sword. 
 
THE CENTRE OF GRAVITY. 
 
 47 
 
 . A> post to which a rope is attached, b and c are two horses running- round 
 
 m a circle, and it is plain that b will not move so quick as c, and that the latter will have 
 the greatest moving force; consequently, if the rope was suddenly checked by striking 
 against an object at the centre of gravity, the horse c would proceed faster than b, and 
 wouid impart to b a backward motion, and thus make a great strain on the rope at a. But 
 \\ toe obstacle were placed so as to be struck at a certain point nearer c, viz., at or about 
 the little star, the tendency of each horse to move on would balance and neutralize the other, 
 so that there would be no strain at a. The little star indicates the centre of percussion. 
 
 . j mei b and especially those young gentlemen who are 
 
 intended tor the army, should bear in mind this important truth during 
 their sword-practice; and with one of Mr. Wilkinson’s swords, made 
 only ot the very best steel, they may conquer in a chance combat which 
 might otherwise have proved fatal to them. To Mr. Wilkinson, of Pall 
 Mall, the eminent sword-cutler, is due the great merit of improving the 
 quality of the steel employed in the manufacture of officers 5 swords ; 
 and. with one of his weapons, the author has repeatedly thrust through 
 an iron plate about one-eighth ol an inch in thickness without in juring 
 the point, and has also bent one nearly double without fracturing it, the 
 perfect elasticity of the steel bringingthe sword straight again. These, 
 and other severe tests applied to Wilkinson’s swords, show that there is 
 no reason why an officer should not possess a weapon that will bear 
 comparison with, nay, surpass, the far-famed Toledo weapon, instead of 
 submitting to mere army-tailor swords, which are often little better than 
 hoops of beer barrels ; and, in dire combat with Hindoo or Mussulman 
 fanatics Tulwah, may show too late the folly of the owner. 
 
 Fig 61. 
 
48 
 
 boy’s playbook of science. 
 
 CHAPTER Y. 
 
 SPECIFIC GRAVITY, 
 
 It is recorded of the great Dr. Wollaston, that when Sir Humphry 
 Davy placed in his hand, what was then considered to be the scientific 
 wonder of the day — viz., a small bit of the metal potassium, he ex- 
 claimed at once, “ How heavy it is,” and was greatly surprised, when 
 Sir Humphry threw the metal on -water, to see it not only take fire, 
 but actually float upon the surface ; here, then, was a philosopher 
 possessing the deepest learning, unable, by the sense of touch and by 
 ordinary handling, to state correctly whether the new substance (and 
 that a metal), was heavy or light ; hence it is apparent that the pro- 
 perty of specific gravity is one of importance, and being derived from 
 the Latin, means species , a particular sort or kind ; and gravis , heavy 
 or weight — i.e., the particular weight of every substance compared with 
 a fixed standard of water. 
 
 We are so constantly in the habit of referring to a standard of perfec- 
 tion in music and the arts of painting and sculpture, that the youngest 
 will comprehend the office of water when told that it is the philosopher’s 
 unit or starting-point for the estimation of the relative weights of solids 
 and liquids. A good idea of the scope and meaning of the term specific 
 gravity, is acquired by a few simple experiments, thus : if a cylindrical 
 
 Fig. 65. a. A large cylindrical vessel containing water, in which the egg sinks till it 
 reaches the bottom of the glass, n. A similar glass vessel containing half brine and halt 
 water, in which the egg floats in the centre— viz., just at the point where the brine and 
 water touch. 
 
SPECIFIC GRAVITY. 
 
 49 
 
 glass, say eighteen inches long, and two and a half wide, is filled with 
 water, and another of the same size is also filled, one half with water 
 and the other half with a saturated solution of common salt, or what is 
 commonly termed brine, a most amusing comparison of the relative 
 weights of equal bulks of water and brine, can be made with the help 
 of two eggs; when one of the eggs is placed in the glass containing 
 water, it immediately sinks to the bottom, showing that it has a greater 
 specific gravity than water ; but when the other egg is placed in the 
 second glass containing the brine, it sinks through the water till it 
 reaches the strong solution of salt, where it is suspended, and presents 
 a most curious and pretty appearance ; seeming to float like a balloon in 
 air, and apparently suspended upon nothing, it provokes the inquiry, 
 “ whether magnetism has anything to do with it ? ,s The answer, of 
 course, is in the negative, it merely 
 floats in the centre, in obedience to 
 the common principle, that all bodies 
 float in others which are heavier than 
 themselves ; the brine has, therefore, 
 a greater weight than an equal bulk 
 of water, and is also heavier than the 
 egg. A pleasing sequel to this expe- 
 riment may be shown by demonstrat- 
 ing how the brine is placed in the 
 vessel without mixing with the water 
 above it ; this is done by using a glass 
 tube and funnel, and after pouring 
 away half the water contained in the 
 vessel (Fig. 65), the egg can be floated 
 from the bottom to the centre of the 
 glass, by pouring the brine down the 
 funnel and tube. The saturated solu- 
 tion of salt remains in the lower part 
 of the vessel and displaces the water, 
 which floats upon its surface like oil 
 on water, carrying the egg with it. 
 
 The water of the Dead Sea is said 
 to contain about twenty-six per cent, 
 of saline matter, which chiefly con- 
 sists of common salt. It is perfectly 
 clear and bright, and in consequence 
 of the great density, a person may 
 easily float on its surface, like the ^ 
 egg on the brine, so that if a ship 
 could be heavily laden whilst floating on the water of the Dead Sea, 
 it would most likely sink if transported to the Thames. This illus- 
 tration of specific gravity is also shown by a model ship, which being 
 first floated, on the brine, will afterwards sink if conveyed to another 
 vessel containing water. One of the tin model ships sold as a magnetic 
 
50 
 
 boy’s playbook of science. 
 
 toy answers nicely for this experiment, but it must be weighted or 
 adjusted so that it just floats in the brine, a ; then it will sink, when 
 placed, in another vessel containing only 'water. 
 
 Fig. 67. a. Vessel containing brine, upon which the little model floats. 
 b. Vessel containing water, in which the ship sinks. 
 
 Another amusing illustration of the same kind is displayed with gold 
 fish, which swim easily in w*ater, floating on brine, but cannot dive to 
 the bottom of the vessel, owing to the density of the saturated solution 
 of salt. If the fish are taken out immediately after the experiment, and 
 placed in fresh water, they will not be hurt by contact with the strong 
 salt water. 
 
 These examples of the relative weights of equal bulks, enable the 
 youthful mind to grasp the more difficult problem of ascertaining the 
 specific gravity of any solid or liquid substance; and here the strict 
 meaning of terms should not be passed by. Specific weight must not be 
 confounded with Absolute weight ; the latter means the entire amount 
 of ponderable matter in any body : thus, twenty-four cubic feet of sand 
 weigh about one ton, whilst specific weight means the relation that sub- 
 sists between the absolute weight and the volume or space which that 
 weight occupies. Thus a cubic foot of water weighs sixty-two and a half 
 pounds, or 1000 ounces avoirdupois, but changed to gold, the cubic 
 foot weighs more than half a ton, and would be equal to about 19,300 
 ounces — hence the relation between the cubic foot of water and that of 
 
SPECIFIC GRAVITY. 
 
 51 
 
 gold is nearly as 1 to 19’3; the latter is therefore called the specific 
 gravity of gold. 
 
 Such a mode of taking the specific gravity of different substances— 
 viz., by the weight of equal bulks, whether cubic feet or inches, could not 
 be employed in consequence of the difficulty of procuring exact cubic 
 inches or feet of the various substances which by their peculiar proper- 
 ties of brittleness or hardness would present insuperable obstacles to any 
 attempt to fashion or shape them into exact volumes. It is therefore 
 necessary to adopt the method first devised by Archimedes, 600 b.c., 
 when he discovered the admixture of another metal with the gold of 
 King Hiero’s crown. 
 
 This amusing story, ending in the discovery of a philosophical truth, 
 may be thus described : — King Hiero gave out from the royal treasury a 
 certain quantity of gold, which he required to be fashioned into a crown ; 
 when, however, the emblem of power was produced by the goldsmith, 
 it was not found deficient in weight, but had that appearance which 
 indicated to the monarch that a surreptitious addition of some other 
 metal must have been made. 
 
 It may be assumed that King Hiero consulted his friend and philoso- 
 pher Archimedes, and he might have said, “ Tell me, Archimedes, without 
 pulling my crown to pieces, if it has been adulterated with any other 
 metal ?” The philosopher asked time to solve the problem, and going 
 to take his accustomed bath, discovered then specially what he had never 
 particularly remarked before — that, as he entered the vessel of water, 
 the liquid rose on each side of him — that he, in fact, displaced a certain 
 quantity of liquid. Thus, supposing the bath to have been full of water, 
 directly Archimedes stepped in, it w’ould overflow. Let it be assumed 
 that the water displaced was collected, and weighed 90 pounds, whilst 
 the philosopher had weighed, say 200 pounds. Now, the train of 
 reasoning in his mind might be of this kind: — “My body displaces 90 
 pounds of water ; if I had an exact cast of it in lead, the same bulk and 
 weight of liquid would overflow ; but the weight of my body was, say 
 200 pounds, the cast in lead 1000 pounds ; these two sums divided by 
 90 would give very different results, and they would be the specific 
 gravities, because the rule is thus stated : — £ Divide the gross weight by 
 the loss of weight in water, the water displaced, and the quotient gives 
 the specific gravity/ ” The rule is soon tested with the help of an 
 ordinary pair of scales, and the experiment made more interesting by 
 taking a model crown of some metal, which may be nicely gilt and. 
 burnished by Messrs. Elkington, the celebrated electro-platers of Bir- 
 mingham. Eor convenience, the pan of one scale is suspended by 
 shorter chains than the other, and should have a hook inserted in the 
 middle ; upon this is placed the crown, supported by very thin copper 
 wire. Eor the sake of argument, let it be supposed that the crown weighs 
 171 ounces avoirdupois, which are duly placed in the other scale-pan, 
 and witnout touching these weights, the crown is now placed in a 
 vessel of water. It might be supposed that directly the crown enters 
 the water, it would gain weight, in consequence of being wetted,., 
 
 e 2 
 
52 
 
 boy’s playbook of science. 
 
 but the contrary is the case, and by thrusting the crown into the water, 
 it may be seen to rise with great buoyancy so long as the 17£ ounces are 
 retained in the other scale-pan ; and it will be found necessary to place 
 at least two ounces in the scale-pan to which the crown is attached 
 before the latter sinks in the water ; and thus it is distinctly shown that 
 the crown weighs only about 15^ ounces in the water, and has therefore 
 lost instead of gaining weight whilst immersed in the liquid. The rule 
 >v iay now be worked out : 
 
 Ounces. 
 
 Weight of crown in air 17^ 
 
 Ditto in water ]5| 
 
 Less in water 2 
 
 2) 17* 
 
 8-75 
 
 The quotient . 8f demonstrates that the crown is manufactured of 
 copper, because it would have been about 19J if made of pure gold. 
 
SPECIFIC GRAVITY. 
 
 53 
 
 Table of the Specific Gravities of the Metals in common use. 
 
 Platinum 
 
 . 21*5 
 
 Goid 
 
 . 19*4 
 
 Mercury 
 
 . 13*56 
 
 Lead 
 
 . 11*145 
 
 Silver 
 
 . 10*50 
 
 Bismuth 
 
 . 9*83 
 
 Copper 
 
 . S*96 
 
 Iron 
 
 . 7* 79 
 
 Tin 
 
 . 7*28 
 
 Zinc 
 
 6*5 to 7*2 
 
 The simple rule already explained may be applied to all metals of any 
 size or weight, and when the mass is of an irregular shape, having 
 various cavities on the surface, there may be some difficulty in taking 
 the specific gravity, in consequence of the adhesion of air-bubbles ; but 
 this may be obviated either by brushing them away with a feather, or, 
 what is frequently much better, by dipping the metal or mineral first 
 into alcohol, and "then into water, before placing it in the vessel of 
 water, by which the actual specific gravity is to be taken 
 
 The mode of taking the specific gravity of liquids is very simple, and 
 is usually performed in the laboratory by means of a thin globular bottle 
 which holds exactly 1000 grains of pure distilled water at 60° Fahrenheit. 
 A little counterpoise of lead is made of the exact weight of the dry 
 globular bottle, and the liquid under examination is poured into the 
 bottle and up to the graduated mark in the neck ; the bottle is then 
 placed in one scale-pan, the counterpoise and the 1000-grain weight in 
 the other ; if the liquid (such as oil of vitriol) is heavier than water, 
 then more weight will be required — viz., S15 grains — and these figures 
 added to the 1000 would indicate at once that the specific gravity of oil 
 of vitriol was 1*845 as compared with water, which is 1*000. When the 
 liquid, such as alcohol, is lighter than water, the 1000-grain weight will 
 be found too much, and grain weights must be added to the same scale- 
 pan in which the bottle is standing, until the two are exactly balanced. 
 If ordinary alcohol is being examined, it will be found necessary to place 
 ISO grains with the bottle, and these figures deducted from the 1000 
 grains in the other scale-pan, leave S20, which, marked with a dot before 
 the first figure (sic *S20), indicates the specific gravity of alcohol to be 
 less than that of water. 
 
 The difference in the gravities of various liquids is displayed in a 
 very pleasing manner by an experiment devised by Professor Griffiths, 
 to whom chemical lecturers are especially indebted for some of the most 
 ingenious and beautiful illustrations which have ever been devised, 
 the experiment consists in the arrangement of five distinct liquids of 
 various densities and colours, the one resting on the other, and dis- 
 tinguished not only by the optical line of demarcation, but by little balls 
 of wax, which are adjusted by leaden shot inside, so as to sink through 
 
54 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 tlie upper strata of liquids, and rest only upon the one that it is in- 
 tended to indicate. 
 
 The manipulation for this experiment is somewhat troublesome, and 
 is commenced by procuring some pure bright quicksilver, upon which an 
 iron bullet (black-leaded, or painted of any colour) is placed, or one of 
 those pretty glass balls which are sold in such quantities at the Crystal 
 Palace. 
 
 Secondly. Put as much white vitriol (sulphate of zinc) into a half 
 pint of boiling water as it will dissolve, and, when cold, pour off the 
 clear liquid, make up a ball of coloured wax (say red), and adjust it by 
 placing little shot inside, until it sinks in a solution of sulphate of 
 copper and floats on that of the white vitriol. 
 
 Thirdly. Make a solution of sulphate of copper in precisely the same 
 manner, and adjust another wax ball to sink in water, and float on this 
 solution. 
 
 Fourthly. Some clear distilled w r ater must be provided. 
 
 Fifthly. A little cochineal is to be dissolved in some common spirits 
 of wine (alcohol), and a ball of cork painted white provided. 
 
 Finally. A long cylindrical glass, at least eighteen inches high, and 
 two and a half or three inches diameter, must be made to receive these 
 
 five liquids, which are ar- 
 ranged in their proper order 
 Alcoho1, of specific gravity by means 
 
 of a long tube and funnel. 
 The four balls — viz., the 
 Water - iron, the two wax, and the 
 
 cork balls, are allowed to 
 slide down the long glass. 
 Solution of blue vitriol. w hi C b is inclined at an angle ; 
 
 and then, by means of the 
 tube and funnel, pour in the 
 Solution of white vitriol, tincture of cochineal, and 
 all the balls will remain at 
 the bottom of the glass. 
 Quicksilver. The water is poured down 
 
 next, and now the cork ball 
 floats up on the water, and 
 marks the boundary line of 
 the alcohol and water. Then 
 
 Fig. 69. Long cylindrical glass, 18 x 3 inches, con- the solution of blue vitriol, 
 
 taining the five liquids. when a wax ball floats upon 
 
 it. Thirdly, the solution of 
 white vitriol, upon which the second wax ball takes its place ; and lastly, 
 ike quicksilver is poured down the tube, and upon this heavy metallic 
 fluid the iron or glass ball floats like a cork on water. 
 
 The tube may now be carefully removed, pausing at each liquid, so 
 that no mixture take place between them ; and the result is the arrange- 
 ment of five liquids, giving the appearance of a cylindrical glass painted 
 
SPECIFIC GRAVITY. 
 
 &D 
 
 with bands of crimson, blue, and silver ; and the liquids will not mingle 
 with each other for many days. 
 
 A more permanent arrangement can be devised by using liquids which 
 have no affinity, or will not mix with each other — such as mercury, 
 water, and turpentine. 
 
 The specific weight or weights of an equal measure of air and other 
 gases is determined on the same principle as liquids, although a diffe- 
 rent apparatus is required. A light capped glass globe, with stop-cock, 
 from bO to 100 cubic inches capacity, is weighed full of air, then 
 exhausted by an air-pump, and weighed empty, the loss being taken as 
 the weight of its volume of air; these figures are carefully noted, 
 because air instead of water is the standard of comparison for all gases. 
 When the specific gravity of any other gas is to be taken, the glass 
 globe is again exhausted, and screwed on to a gas jar provided with a 
 proper stop-cock, in which the gas is contained ; and when perfect 
 accuracy is required, the gas must be dried by passing it over some 
 asbestos moistened with oil of vitriol, and contained in a glass tube, and 
 the gas jar should stand in a mercurial trough. (Fig. 70.) The stop- 
 
 Fig. 70. a. Glass globe to contain the gas. b. Gas jar standing in the mercurial 
 trough, d. c. Tube containing asbestos moistened with oil of vitriol. 
 
 cocks are gradually turned, and the gas admitted to the exhausted globe 
 from the gas jar ; when full, the cocks are turned off, the globe unscrewed, 
 and again weighed, and by the common rule of proportion, as the weight 
 of the air first found is to the weight of the gas, so is unity (T000, the 
 density of air) to a number which expresses the density of the gas 
 required. If oxygen had been the gas tried, the number would be Till, 
 being the specific gravity of that gaseous element. If chlorine, 2*470. 
 Carbonic acid, 1*500. Hydrogen being much less than air, the number 
 would only be 69, or decimally 0*069. 
 
 A very good approximation to the correct specific gravity (particularly 
 where a number of trials have to be made with the same gas, such as 
 
56 
 
 boy’s playbook of science. 
 
 ordinary coal gas) is obtained by suspending a light paper box, with holes 
 at one end, on one arm of a balance, and a counterpoise on the other. 
 The box can be made carefully, and should have a capacity equal to a 
 
 half or quarter cubic foot ; it is suspended with the holes downward, and is 
 tilled by blowing in the coal gas until it issues from the apertures, and can 
 be recognised by the smell. The rule in this case would be equally simple : 
 as the known weight of the half or quarter cubic foot of common air is 
 to the weight of the coal gas, so is T000 to the number required. 
 (Fig. 71.) 
 
 As an illustration of the different specific weights of the gases, a 
 small balloon, containing a mixture of hydrogen and air, may be so 
 adjusted that it will just sink in a tall glass shade inverted and sup- 
 ported on a pad made of a piece of oilcloth shaped round and bound 
 with list. On passing in quickly a large quantity of carbonic acid, the 
 little balloon will float on its surface ; and if another balloon, containing 
 anly hydrogen, is held in the top part of the open shade, and a sheet of 
 glass carefully slid over the open end, the density of the gases (although 
 they are perfectly invisible) is perfectly indicated ; and, as a climax to 
 the experiment, a third balloon can be filled with laughing gas, and 
 may be placed in the glass shade, taking care that the one full of pure 
 hydrogen does not escape ; the last balloon will sink to the bottom of tho 
 
SPECIFIC GRAVITY, 
 
 jar, because laughing gas is 
 almost as heavy as carbonic 
 acid, and the weight of the 
 balloon will determine its 
 descent. (Fig. 72.) 
 
 A soap-bubble will rest 
 most perfectly on a surface 
 of carbonic acid gas, and the 
 aerial and elastic cushion 
 supports the bubble till it 
 bursts. The experiment is 
 best performed by taking a 
 glass shade twelve inches 
 broad and deep in propor- 
 tion, and resting it on a 
 pad; half a pound of ses- 
 quicarbonate of soda is 
 then placed in the vessel, 
 and upon this is poured a mixture of half a pint of oil of vitriol and half 
 a pint of water, the latter being previously mixed and allowed to cool 
 before use. An enormous quantity of carbonic acid gas is suddenly gene- 
 rated, and rising to the edge, overflows at the top of the glass shade. A 
 well-formed soap-bubble, detached neatly from the end of a glass-tube, 
 oscillates gently on the surface of the heavy gas, and presents a most 
 curious and pleasing appearance. The soapy water is prepared by 
 cutting a few pieces of yellow soap, and placing them in a two-ounce 
 
 (Carbonic acid.) 
 
 Balloon. 
 Laughing gas. 
 
 Fig. 72. Inverted large glass shade, containing half 
 carbonic acid and half common air. 
 
 Fig. 73. a. Inverted glass shade, containing the material, b, for generating carbonic acid 
 gas. c. The soap-bubble. i> d. The glass tube for blowing the bubbles, e. Small lantern, to 
 throw a bright beam of light from the oxy-hydrogen jet upon the thin soap-bubble, which 
 then displays the most beautiful iridescent colours. 
 
 bottle containing distilled water. (Fig. 73.) The specific gravity of the 
 gases, may therefore be either greater, or less than atmospheric air. 
 
58 
 
 boy’s playbook of science. 
 
 which has been already mentioned as the standard of comparison, and 
 examined by this test the vaponrs of some of the compounds of carbon 
 and hydrogen are found to possess a remarkably high gravity ; in 
 proof of which, the vapour of ether may be adduced as an example, 
 although it does not consist only of the two elements mentioned, but 
 contains a certain quantity of oxygen. In a cylindrical tin vessel, two 
 feet high and one foot in diameter, place an ordinary hot-water plate, 
 of course full of boiling water ; upon this warm surface pour about half 
 an ounce of the best ether ; and, after waiting a few r minutes until the 
 whole is converted into vapour, take a syphon made of half-inch pewter 
 tube, and warm it by pouring through it a little hot water, taking care 
 to allow the waterto drain away from it before use. After placing the 
 syphon in the tin vessel, a light may be applied to the extremity of the 
 long leg outside the tin vessel, to show that no ether is passing over 
 rnntil the air is sucked out as with the water-syphon; and after this has 
 been done, several warm glass vessels may be filled w r ith this heavy 
 vapour of ether, which burns on the application of flame. Finally, the 
 remainder of the vapour may be burnt at the end of the syphon tube, 
 demonstrating in the most satisfactory manner that the vapour is 
 flowing through the syphon just as spirit is removed by the distillers 
 from the casks into cellars of the public-houses. (Fig. 74.) 
 
 Fig. 74. a. Tin vessel containing the hot-water plate, B, upon which the ether is 
 poured, c. The syphon, d. Glass to receive the vauour. a. Combustion of the ether 
 vapour in another vessel. 
 
SPECIFIC GRAVITY, 
 
 59 
 
 Before dismissing the important subject of specific gravity (or, as it 
 is termed by the French savants, “ density”), it may be as well to state 
 that astronomers have been enabled, by taking the density of the earth 
 and by astronomical observations, to calculate the gravity of the planets 
 belonging to our solar system ; and it is interesting to observe that the 
 density of the planet Venus is the only one approaching the gravity of 
 
 Lhe earth : — 
 
 The Earth F000 
 
 The Sun *254 
 
 The Moon *742 
 
 Mercury 2*583 
 
 Venus 1*037 
 
 Mars ‘650 
 
 Jupiter ‘25 S 
 
 Saturn *104 
 
 Herschel '220 
 
 CHAPTER VI. 
 
 ATTRACTION OF COHESION. 
 
 In previous chapters one kind of attraction — viz., that of gravita- 
 tion, has been discussed and illustrated in a popular manner, and 
 pursuing the examination of the invisible, active, and real forces of 
 nature, the attraction of cohesion will next engage our attention. 
 There is a peculiar satisfaction in pursuing such investigations, because 
 every step is attended by a reasonable proof; there is no ghostly 
 mystery in philosophic studies ; the mind is not suddenly startled at one 
 moment with that which seems more than natural ; it is not carried away 
 in an ecstasy of wonder and awe, as in the so-called spirit-rapping ex- 
 periments, to be again rudely brought back to the material by the disclo- 
 sure of trickeries of the most ludicrous kind, such as those lately ex- 
 posed by M. Jobert de Lamballe, at the Academy of Sciences at Paris. 
 This gentleman has unmasked the effrontery of the spirit-rappers by 
 merely stripping the stocking from the heel of a young girl of fourteen. 
 M. Velpeau declares that the rapping is produced by the muscles of the 
 heel and knee acting in concert, and quotes the case of a lady once 
 celebrated as a medium, who has the power of producing the most 
 curious and interesting music with the tendons of the thigh. This 
 music is said to be loud enough to be heard from one end of a long 
 room to the other, and has often played a conspicuous part in the reve- 
 lations made by the medium. M. Jules Clocquet also explained the 
 method by which the famous girl pendulum had so long abused the cre- 
 dulity of the Paris public. This girl, whose self-styled faculty is that 
 of striking the hour at any time of the day or night, was attended at 
 the Hospital St. Louis by M. Clocquet, who states that the vibrations in 
 
€0 
 
 BOY'S PLAYBOOK OF SCIENCE. 
 
 this case were produced by a rotatory motion in the lumbar regions of 
 the vertebral column. The sound of these (a la rattlesnake) was so 
 powerful, that they might be distinctly heard at a distance of twenty- 
 mo fee» 
 
 In studying the powers of nature, which the most sceptical mind 
 allows must exist, there is an abundant field for experiment without 
 attempting the exploits of Macbeth’s witches, or the fanciful powers of 
 Manfred ; and, returning to the theme of our present chapter, it may be 
 asked, how is cohesion defined ? and the answer may be given, by 
 directing attention to the three physical conditions of water, which 
 assumes the form of ice, water, or steam. 
 
 In the Polar regions, and also in the Alpine and other mountains 
 where glaciers exist, there the traveller speaks of ice twenty, thirty, forty, 
 nay, three hundred feet in thickness. Here the withdrawal of a certain 
 quantity of heat from the water evidently allows a new force to come 
 into full play. We may call it what we like ; but cohesion, from the Latin 
 cum, together, and hcereo , I stick or cleave, appears to be the best and 
 most rational term for this power which tends to make the atoms or 
 particles of the same kind of matter move towards each other, and to 
 prevent them being separated or moved asunder. That it is not merely 
 hypothetical is shown by the following experiments. 
 
 If two pieces of lead are cast, and the ends nicely scraped, taking 
 care not to touch the surfaces with the fingers, they may by simple 
 pressure be made to cohere, and in that state of attraction may be lifted 
 
 from the table by the ring which is 
 usually inserted for convenience in 
 the upper piece of lead; they may be 
 hung for some time from a proper 
 support, and the lower bit of lead 
 will not break away from the upper 
 one ; they may even be suspended, as 
 
 su; 
 
 oujjpuiu, auu uuc Luwc-i uiu ui. icaut 
 
 will not break away from the upper 
 one ; they may even be suspended, as 
 demonstrated by Morveau, in the va- 
 cuum of an air-pump, to show that the 
 cohesion is not mistaken for the pres- 
 sure of the atmosphere, and no se- 
 paration occurs. And when the union 
 is broken by physical force, it is sur- 
 prising 'to notice the limited number 
 of points, like pin points, where the 
 cohesion has occurred; whilst the 
 weight of the lump of lead upheld 
 against the force of gravitation re- 
 minds one forcibly of the attraction 
 of a mass of soft iron by a powerful 
 magnet, and leads the philosophic in- 
 
 Fig.75. a a. Two pieces oflead, scraped quirer to speculate on the principle 
 
 tion. (Tig. 75.) 
 
ATTRACTION OF COHESION. 
 
 61 
 
 A fine example of the same force is shown in the use of a pair of flat 
 iron surfaces, planed by the celebrated Whitworth, of Manchester. 
 
 A 
 
 B 
 
 Fig. 76. a. Whitworth’s planes, with film of air between them. 
 b. Film of air excluded when cohesion occurs. 
 
 These surfaces are so true, that when placed upon each other, the upper 
 one will freely rotate when pushed round, in consequence of the thin 
 film of air remaining between the surfaces, which acts like a cushion, 
 and prevents the metallic cohesion. When, however, the upper plate is 
 slid over the lower one gradually, so as to exclude the air, then the two 
 may be lifted together, because cohesion has taken place. (Fig. 76.) 
 
 A glass vessel is a good example of cohesion. The materials of which 
 it is composed have been soft and liquid when melted in the fire, and on 
 the removal of the excess of heat it has become hard and solid, in 
 consequence of the attractive force of cohesion binding the particles 
 together ; in the absence of such a power, of course, the material would 
 fall into the condition of dust, and a mere shapeless heap of silicates of 
 potash and lead would indicate the place where the moulded and co- 
 herent glass w'ould otherwise stand. 
 
 A lump of lead, six inches long by four broad, and half an inch 
 thick, may be supported by dexterously taking off a thick shaving 
 with a proper plane, and after pressing an inch or more of the strip on 
 the planed surface of the large lump of lead, the cohesion is so powerful 
 that the latter may be lifted from the table by the strip of metal. 
 
 The bullets projected from Perkins 5 steam- gun, at the rate of three 
 hundred per minute, are thrown with such violence, that, when received 
 on a thick plate of lead backed up with sheet iron, a cold welding takes 
 place between the two surfaces of metal in the most perfect manner, 
 just as two soft pieces of the metal potassium may be squeezed and 
 welded together. The surfaces of an apple torn asunder will not readily 
 cohere, but if cut with a sharp knife, cohesion easily occurs ; so with a 
 wound produced by a jagged surface, it is difficult to make the parts 
 
62 
 
 boy’s playbook of science. 
 
 heal, whereas some of the most desperate sabre-cuts have been healed, 
 the cohesion of the surfaces of cut flesh being very rapid ; hence, if the 
 top of a finger is cut off, it may be replaced, and will grow, in conse- 
 quence of the natural cohesion of the parts. 
 
 The art of plating copper with silver, which is afterwards gilt, and 
 then drawn out into flattened wire for the manufacture of gold lace and 
 epaulets, usually termed bullion, is another example of the wonderful 
 cohesion of the particles of gold, of which a single grain may be ex- 
 tended over the finest plate wire measuring 345 feet in length. 
 
 The process of making wax candles is a good illustration of the 
 attraction of cohesion ; they are not generally cast in moulds, as most 
 persons suppose, but are made by the successive applications of melted 
 wax around the central plaited wick. Other examples of cohesion are 
 shown by icicles, and also stalagmites ; which latter are produced by the 
 gradual dropping of water containing chalk (carbonate of lime) held in 
 solution by the excess of carbonic acid gas ; the solvent gradually 
 evaporates, and leaves a series of calcareous films, and these cohere in 
 succession, producing the most fantastic forms, as shown in various 
 remarkable caverns, and especially in the cave of Arta, in the island of 
 Majorca. 
 
 In metallic substances the cohesion of the particles assumes an im- 
 portant bearing in the question of relative toughness and power of 
 resisting a strain ; hence the term cohesion is modified into that of the 
 property of “tenacity.” 
 
 The tenacity of the different metals is determined by ascertaining the 
 weight required to break wires of the same length and guage. Iron 
 
 Fig. 77. e. Pan supported by leaden wire broken by a weight which the iron 
 wire at a easily supports. 
 
 appears to possess the property of tenacity in the greatest, and lead in 
 the least degree. (Fig. 77.) 
 
ATTRACTION OF COHESION, 
 
 G3 
 
 The tenacity of iron is taken advantage of in the most scientific 
 manner by the great engineers who have constructed the Britannia Tube, 
 and that eighth wonder of the world, the Leviathan , or Great Eastern 
 steain-ship. In both of these sublime embodiments of the genius and 
 industrial skill of Great Britain the advantage of the cellular principle 
 is fully recognised. The magnitude of this colossal ship is bettei 
 realized when it is remembered that the Great Eastern is six times the 
 size of the Duke of Wellington line-of-battle ship, that her length is more 
 than three times that of the height of the Monument, while in breadth 
 it is equal to the width of Pall Mall, and that a promenade round the 
 deck will afford a walk of more than a quarter of a mile. Up to the 
 water-mark the hull is constructed with an inner and outer shell, two 
 feet ten inches apart, each of three-quarter-inch plate ; and between 
 them, at intervals of six feet, run horizontal webs of iron plates, which 
 convert the whole into a series of continuous cells or iron boxes. (Fig. 78.) 
 
 Fig. 78. Transverse section of Great Eastern, showing 1 the cellular construction 
 from keel to water-line, a a. 
 
 This double ship is useful in various ways ; in the first place, the 
 danger arising from collision is diminished, as it is supposed that the 
 outer web only would be broken through or damaged ; so that the water 
 would not then rush into the steam-ship, but merely fill the space 
 between the shells. In the second place, if there should be any difficulty 
 in procuring ballast, the space can be filled with 2500 tons of water, or 
 again pumped out, according to the requirements of the vessel. The 
 strength of a continued cellular construction can be easily imagined, and 
 may be well illustrated by a thin sheet of common tin plate. If the ends 
 be rested on blocks of wood, so as to lap over the wood about one inch, 
 they are easily displaced, and the mimic bridge broken down from its 
 
64 
 
 boy’s playbook of science. 
 
 supports by the addition to the centre of a few ounce weights; whilst 
 the same tin plate rolled up in the figure of a tube, and again rested on the 
 same blocks, will now support many pounds weight without bending or 
 breaking down. (Big. 79.) 
 
 B 
 
 Fiff 79 a. Flat tin plate, breaking down with a few ounce weights. 
 
 B .’ Same tin plate rolled up supports a very heavy weight. 
 
 The deck of the ship is double or cellular, after the plan of Stephenson 
 in the Britannia Tubular Bridge, and is 692 feet in length. The ton- 
 nage register is 18,200 tons, and 22,500 tons builder’s measure; 
 the hull of the Great Eastern is considered, to be of such enormous 
 tenacity, that, if it were supported by massive blocks of stone six feet 
 square, placed at each end, at stem and stern, it would not deflect, curve, 
 or bend down in the middle more than six inches even with all her 
 machinery, coals, cargo, and living freight. 
 
 In adducing remarkable instances of the adhesive power and tenacity ot 
 inorganic matter, it may not be altogether out of place to allude to the 
 strength and force of living matter, or muscular power. It is stated that 
 Dr Georo-e B. Winship, of Roxbury in America, a young physician, twenty- 
 five years old, and weighing 143 pounds, is the strongest man alive ; m 
 fact/quite the Samson of the nineteenth century. He can raise a barrel ot 
 flour from the floor to his shoulders ; can raise himself with either little 
 finder till his chin is half a foot above it ; can raise 200 pounds with 
 either little finger ; can put up a church bell of 141 pounds ; can Mt with 
 his hands 926 pounds dead weight without the aid of straps or belts ot 
 any kind As compared with Topham, the Cornish strong man, who 
 could raise 800 pounds, or the Belgic one, his power is greater ; and 
 as the use of straps and belts increases the power of lifting by about 
 four times, it is stated that Winship could lift at least 2500 pounds 
 
 WC With these illustrations of cohesion we may return again to the ab- 
 stract consideration of this power with reference to water, in which we 
 have noticed that the antagonist to this kind of attraction is the force or 
 power termed caloric or heat. The latter influence removes the frozen 
 bands of winter and converts the ice to the next condition, water. In 
 this state cohesion is almost concealed, although there is just a slighw 
 
ATTKACTION OF COHESION. 
 
 65 
 
 excess to liold even the particles of water in a state of unity, and 
 this fact is beautifully illustrated by the formation of the brilliant dia- 
 mond drops of dew on the surfaces of various leaves, as also in the force 
 and power exercised by great volumes of water, which exert their mighty 
 strength in the shape of breaker-waves, dashing against rocks ancl 
 lighthouses, and making them tremble to their very base by the violence 
 of the shock ; here there must be some unity of particles, or the col- 
 lective strength could not be exerted, it would be like throwing a hand- 
 ful of sand against a window — a certain amount of noise is produced, but 
 the glass is not fractured ; whilst the same sand united by any glutinous 
 material, would break its way through, and soon fracture the brittle 
 glass. It is so usual to see the particles of water easily separated, that it 
 becomes difficult to recognise the presence of cohesion ; but this bond of 
 union is well illustrated in the experiment of the water hammer. The 
 little instrument is generally made of a glass tube with a bulb at one 
 end ; in this bulb the water which it contains is boiled, and as the steam 
 issues from the other extremity, drawn out to a capillary tube, the open- 
 ing is closed by fusion with the heat of a blowpipe flame. As the 
 water cools the steam condenses, and a 
 vacuum, so far as air is concerned, is 
 produced; if now the tube is suddenly 
 inverted, the whole of the water falls en 
 masse, collectively, and striking against 
 the bottom of the tube, produces a me- 
 tallic ring, just as if a piece of wood or 
 metal were contained within the tube. 
 
 If the end to which the water falls is 
 not well cushioned by the palm of the 
 hand, the water hammers itself through 
 and breaks away that part of the glass 
 tube. Hence it is better to construct the 
 water hammer of copper tube, about 
 three-quarters of an inch in diameter and 
 three feet long ; at one end a female screw- 
 piece is inserted, into which a stop-cock 
 is fitted ; when the tube is filled to the 
 height of about six inches with water, and 
 shaken, the air divides the descending 
 volume of water, and the ordinary splash- 
 ing sound is heard ; there is no unity or 
 cohesion of the parts ; if, however, the 
 end of the copper tube is thrust into 
 a fire and the water boiled so that steam 
 issues from the cock, which is then closed, 
 and the tube removed and cooled, a smart 
 blow is given, and distinctly heard when 
 the copper tube is rapidly inverted or 
 shaken so as to cause the water to rise 
 
66 
 
 boy’s playbook of science. 
 
 and fall. The experiment may be rendered still more instructive by 
 turning the cock and admitting the air, which rushes in with a whizzing 
 sound, and on shaking the tube the metallic ring is no longer heard, 
 but it may be again restored by attaching a small air syringe or hand 
 pump, and removing the air by exhaustion. (Eig. 80.) 
 
 In the fluid condition water still possesses a surplus of cohesion over 
 the antagonistic force of heat ; when, however, the latter is applied in 
 excess, then the quasi-struggle terminates; the heat overpowers the 
 cohesive attraction, and converts the water into the most willing slave 
 which has ever lent itself to the caprices of man — viz., into steam — 
 glorious, useful steam : and now the other end of the chain is reached, 
 where heat triumphs ; whilst in solids, such as ice, cohesion is the con- 
 queror, and the intermediate link is displayed in the fluid state of water. 
 If any fact could give an idea of the gigantic size of the Great Eastern, 
 it is the force of the steam which will be employed to move it at the 
 rate of about eighteen miles perhourwith a power estimated at the nominal 
 rate of 2600 horses, but absolutely of at least 12,000 horses. This 
 steam power, coupled with the fact that she has been enormously 
 strengthened in her sharp, powerful bows, by laying down three complete 
 iron decks forward, extending from the bows backward for 120 feet, will 
 demonstrate that in case of war the Great Eastern may prove to be a 
 powerful auxiliary to the Government. These decks will be occupied 
 by the crew of 300 or 400 men, and with this large increase of strength 
 forward, the Great Eastern, steaming full power, could overtake and cut 
 in two the largest wooden line-of-battle ship that ever floated. Should 
 war unhappily spread to peaceful England, and the enormous power of 
 this vessel be realized, her name would not inappropriately be changed 
 from the Great Eastern to the Great Terror of the ocean. The Times 
 very properly inquires, “ What fleet could stand in the way of such a 
 mass, weighing some 30,000 tons, and driven through the water by 
 12,000 horse-power, at the rate of twenty-two or twenty-three miles per 
 hour. To produce the steam, 250 tons of coal per diem will be re- 
 quired, and great will be the honourable pride of the projectors when they 
 see her fairly afloat, and gliding through the ocean to the Ear West/’* 
 
 A good and striking experiment, displaying the change from the 
 liquid to the vapour state, is shown by tying a piece of sheet caoutchouc 
 over a tin vessel containing an ounce or two of water. When this boils, 
 the india-rubber is distended, and breaks with a loud noise ; or in 
 another illustration, by pouring some ether through a funnel carefully 
 into a flask placed in a ring stand. If flame is applied to the orifice, 
 no vapour issues that will ignite, provided the neck of the flask has not 
 been wetted with the ether. When, however, the heat of a spirit-lamp 
 is applied, the ether soon boils, and now on the application of a lighted 
 taper, a flame some feet in length is produced, which is regulated by the 
 
 * For reasons into which it is unnecessary to enter here, these anticipations 
 regarding the Great Eastern have not been realised. But the noble ship has 
 done good service in laying the submarine cables which connect the Old World 
 with the New. 
 
ADHESIVE ATTRACTION. 
 
 67 
 
 spirit-lamp below, and when this is removed, the length of the flame 
 diminishes immediately, and is totally extinguished if the bottom of the 
 flask is plunged into cold water ; the withdrawal of the heat restores the 
 power of cohesion. Another illustration of the vast power of steam 
 is displayed in the Steam Hammer invented by Mr. Nasmyth. The 
 progress of modern engineering rendered necessary the employment of 
 some means of beating into shape the enormous masses of iron which 
 are so largely used in constructive works. It is true that steam was 
 applied to this purpose before Mr. Nasmyth took the matter up, but it 
 was done in such a roundabout fashion, that very little advantage 
 accrued thereby. Nasmyth’s steam hammer consists of an anvil sup- 
 ported upon a very strong foundation of masonry. Above this anvil 
 rises a hugh arm supporting a steam cylinder — to the piston rod of 
 which is attached a block of iron forming the head of the hammer. 
 The steam is admitted below the piston to raise the hammer, and above 
 it as it delivers its blow, the force of which is of course greatly aug- 
 mented by the weight of the falling mass of iron. 
 
 CHAPTER VII. 
 
 ADHESIVE ATTRACTION. 
 
 The term cohesion must not be confounded with that of adhesion, which 
 refers to the clinging to or attraction of bodies of a dissimilar kind. The 
 late Professor Daniel! defines cohesion to be an attraction of homogeneous 
 (opoy, like, and yeW, kind) or similar particles ; adhesion to be an at- 
 traction subsisting between particles of a heterogeneous, erepoy, different, 
 and yeVoy, kind. 
 
 There are numerous illustrations of adhesion, such as mending china, 
 and the use of glue, or paste, in uniting different surfaces, or mortar, in 
 building with bricks ; it is also well shown at the lecture table by means 
 of a pair of scales, one scale-pan of which being well cleaned with alkali at 
 the bottom, may then be rested on the surface of water contained in a 
 plate ; the adhesion between the water and the metal is so perfect, that 
 many grain weights may be placed in the other pan before the adhesion 
 is broken ; and after breakage, if the pan be again placed on the water, 
 and a few grains removed from the other, so as to adjust the two pans, 
 and make them nearly equal, a drop of oil of turpentine being added, in- 
 stantly spreads itself over the water, and breaking the adhesion between 
 the latter and the metal, the scale-pan is immediately and again broken 
 away, as the adhesion between the turpentine and the metal is not so great 
 as that of water and metal. The adhesion of air and water is well dis- 
 played in an apparatus recommended for ventilating mines, in which a 
 constant descending stream of water carries with it a quantity of air, 
 which being disengaged, is then forced out of a proper orifice, the same 
 kind of adhesion between air and water is displayed in the ancient 
 
68 
 
 boy’s playbook of science. 
 
 Spanish Catalan forge, where the blast 
 is supplied to the iron furnace on a simi- 
 lar principle, only, a natural cascade is 
 taken advantage of instead of an artificial 
 fall of water through a pipe. 
 
 The adhesion of air and water be- 
 comes of some value when a river 
 flows through a large and crowded city, 
 because the water in its passage to. and 
 fro, must necessarily drag with it, a 
 continuous column of air, and assist 
 in maintaining that constant agitation of 
 the air which is desirable as a preventive 
 to any accumulation of noxious air 
 charged with foetid odours, arising from 
 mud banks or from other causes. The 
 fact of adhesion, existing between water 
 and air, is readily shown, by resting one 
 end of a long glass tube, of at least one 
 inch diameter, on a block of wood one 
 foot high. If water is allowed to flow 
 down the tube, so as to leave a sufficient 
 space of air above it, the adhesion be- 
 tween the two ancient elements becomes 
 apparent, directly a little smoke is pro- 
 duced, near the top end of the glass tube 
 resting on the block of wood. The 
 smoke, which has a greater tendency to 
 rise than to fall, is dragged down the 
 glass tube, and accompanies the water 
 as it flows from the higher to the lower 
 level. The same truth is also illustrated 
 in horizontal troughs or tubes through 
 
 Fig. 81. Model of the apparatus 
 for drawing down air. a, cistern of level. 
 
 •water, supplied by ball-cock, and kept in horizontal uuugiio ui uuuc 
 
 tWA 1 which water is caused to flow. 
 
 The adhesion between air and glass is 
 so great, that it is absolutely necessary 
 to boil the mercury in the tubes of the 
 best barometers; and if this is not 
 
 draws down the air in the centre, i 
 c. The vessel to which the air and 
 water are conveyed by a gutta-percha 
 tube, t. There is another ball- 
 
 cock to permit the waste water to ucou UM1U mv«v lu , - ** — 
 
 leTertherXLTpe e aiwa" carefully attended to, the adhering air 
 some inches into this water, whilst between the glass and mercury gra- 
 the air escapes from the jet, d. dually ascends to, and destroys, the 
 
 Torricellian vacuum at the top of the barometer tube. Even after 
 the mercury is boiled, the air will creep up in course of years ; and 
 in order to prevent its passage between the glass and quicksilver, it 
 has been recommended, that a platinum ring should be welded on to the 
 end of the glass tube, because mercury has the power of wetting or en- 
 filming the metal platinum, and the two being in close contact, would, as it 
 were, shut the only door by which the air could enter the barometer tube. 
 
69 
 
 CHAPTER VIII. 
 
 CAPILLARY ATTRACTION. 
 
 This kind of attraction is termed capillary, in consequence of tubes, of 
 a calibre, or bore, as fine as hair, attracting and retaining fluids. . 
 
 If water is poured into, a glass, the surface is not level, but cupped 
 at the edges, where the solid glass exerts its adhesive attraction for the 
 liquid, and draws it from the level. If the glass be reduced to a very 
 narrow tube, having a hair-like bore, the attraction is so great that the 
 water is retained in the tube, contrary to the force of gravitation. 
 Two pieces of flat glass placed close together, and then opened like a 
 book, draw up water between them, on the same principle. A mass of 
 salt put on a plate containing a little water coloured with indigo displays 
 this kind of attraction most perfectly, and the water is quickly drawn up, 
 as shown by the blue colour on the salt. A little solution of the ammonio- 
 sulphate of copper imparts a finer and more distinct blue colour to the 
 salt. A piece of dry Honduras mahogany one inch square, placed in a 
 saucer containing, a little turpentine, is soon found to be wet with the 
 oil at the top, which may then be set on fire. 
 
 Almost every kind of wood possesses capillary tubes, and will float, on 
 account of these minute vessels being filled with air ; if, however, the air is 
 withdrawn, then the wood sinks,' and by boiling a ball made of beech wood 
 in water, and then placing it under the vacuum of an air pump in 
 other cold water, it becomes so saturated with water that it will no 
 longer float. A remarkable instance of the same kind is mentioned by 
 Scoresby, in which a boat was pulled down by a whale to a great depth 
 in the ocean, and after coming to the surface it was found that the wood 
 would neither swim nor burn, the capillary pores being entirely filled 
 with salt water. 
 
 A piece of ebony sinks in water on account of its density, closeness, 
 and freedom from air. A gauge made of a piece of oak, with a hole 
 bored in it of one inch diameter, accurately receives a dry plug of willow 
 wood which will not enter the orifice after it is wetted. Millstones are 
 split by inserting wedges of dry hard wood, which are afterwards wetted 
 and swelled, and burst the stone asunder. One of the most curious 
 instances of capillary attraction is shown in the currying of leather, a 
 process which is intended to impart a softness and suppleness to the 
 skin, in order that it may be rendered fit for the manufacture of boots, 
 harness, machine bands, &c. The object of the currier is to fill the 
 pores of the leather with oil, and as this cannot be done by merely 
 smearing the surface, he prepares the way for the oil by wetting the 
 leather thoroughly with water, and whilst the skin is damp, oil is 
 rubbed on, and it is then exposed to the air ; the water evaporates 
 at ordinary temperatures, but oil does not ; the consequence is that the 
 
70 
 
 boy's playbook of science. 
 
 pores of the leather give up the water, which disappears in evaporation, 
 and the oil by capillary attraction is then drawn into the body of the 
 leather, the oil in fact takes the place vacated by the water, and renders 
 the material very supple, and to a considerable extent waterproof. In 
 paper making, the pores of this material, unless filled up or sized, cause 
 the ink to blot or spread by capillary attraction. The porosity of soils is 
 one of the great desideratums of the skilful agriculturist, and drainage 
 is intended to remove the excess of water which would fill the pores of 
 the earth, to the exclusion of the more valuable dews and rains con- 
 veying nutritious matter derived from manures and the atmosphere. 
 
 A cane is an assemblage of small tubes, and if a piece of about six 
 inches in length (cut off, of course, from the joints) be placed in a bottle 
 of turpentine, the oil is drawn up and may be burnt at the top ; it is on 
 this principle that indestructible wicks of asbestos, and wire gauze 
 rolled round a centre core, are used in spirit lamps. Oil, wax, and 
 tallow, all rise by capillary attraction in the wicks to the flame, where 
 they are boiled, converted into gas, and burnt. 
 
 The capillary attraction of skeins of cotton for water was known 
 and appreciated by the old alchemists; and Geber, one of the most 
 ancient of these pioneers of science, and who lived about the seventh 
 century, describes a filter by which the liquid is separated from the 
 solid. This experiment is well displayed by putting a solution of 
 acetate of lead into a glass, which is placed on the highest block of a 
 series of three, arranged as steps. Into this glass is placed the short end 
 
 sulphuric acid. c. The clear liquid, sepa- 
 rated from the sulphate of lead in b. 
 
CAPILLARY ATTRACTION. 
 
 71 
 
 of a skein of lamp cotton, previously wetted with distilled water ; the long 
 end dips into another glass below, containing dilute sulphuric acid, anil 
 as the solution of lead passes into it, a solid white precipitate of sulphate 
 of lead is formed; then another skein of wetted cotton is placed in 
 this glass, the long end of which passes into the last glass, so that the 
 clear liquid is separated and the solid left behind. (Fig. 82.) 
 
 In this filter the lamp cotton acts as a syphon through the capillary 
 pores which it forms. On the same principle, a prawn may be washed 
 in the most elegant manner (as first shown by the late Duke of Sussex), 
 by placing the tail, after pulling off the fan part, in a tumbler of water, 
 and allowing the head to hang over, when the water is drawn up by 
 capillary attraction, and continues to run through the head. (Fig. 83.) 
 The threads of which linen, cotton, and woollen cloths are made are small 
 cords, and the shrinkage of such textile fabrics, is well known and 
 usually inquired about, when a purchase is made ; here again capillary 
 attraction is exerted, and the fabric contracts in the two directions of 
 the ware and woof threads ; thus, twenty-seven yards of common Irish 
 linen will permanently shrink to about twenty-six yards in cold water. 
 In these cases the water is attracted into the fibres of the textile 
 material, and causing them to swell, must necessarily shorten their 
 length, just as a dry rope strained between two walls for the purpose of 
 supporting clothes, has been known to draw the hooks after being sud- 
 denly wetted and shortened by a shower of rain. 
 
 In order to tighten a bandage, it is only necessary to wind the dry 
 linen round the limbs as close as possible, and then wet it -with water, 
 when the necessary shrinkage takes place. 
 
 If a piece of dry cotton cloth is tied over one end of a lamp glass, the 
 other may be thrust into, or removed from the basin of water very easily, 
 but when the cotton is wetted, the fibres contract and prevent air from 
 entering, so that the glass retains water just as if it were an ordinary 
 gas jar closed with a glass stopper. 
 
 A Spanish proverb, expressing contempt, says, “ go to the well with 
 a sieve,” but even this seeming impossibility is surmounted by using a 
 cylinder of wire gauze, which may be filled with water, and by means of 
 the capillary attraction " r 
 
 between the meshes of 
 the copper-wire gauze 
 and the water, the whole 
 is retained, and may be 
 carefully lifted from a 
 basin of water ; the ex- 
 periment only succeeds 
 when the air is com- 
 pletely driven out of the 
 interstices of the gauze, 
 and the little cylinder 
 
 fomnlptrlv fillrrf with Fi ?- 84 * A * Basin of water - B * Cylinder of wire gauze 
 completely nnea witn closed at both endg with gauze When full of water it may 
 
 water ; this may be done be lifted from the basin by the handle, c. 
 
72 
 
 boy’s playbook of science. 
 
 by repeatedly sinking and drawing out the cylinder, or still more 
 effectually, by first wetting it with alcohol and then dipping the cylinder 
 in water. 
 
 A balloon, made of cotton cloth, cannot be inflated by means of a pair 
 of bellows, but if the balloon is wetted with water, then it may be swelled 
 out with air just as if it had been made of some air-tight material ; 
 hence the principle of varnishing silk or filling the pores with boiled oil, 
 when it is required in the manufacture of balloons. 
 
 Biscuit ware, porous tubes for voltaic batteries, alcarrazas, or water 
 coolers, are all examples of the same principle. 
 
 Whilst speaking most favourably of the benevolent labours of many 
 gentlemen (beginning with Mr. Gurney) who have erected “ Drinking 
 Fountains” in London’s dusty atmosphere and crowded streets, it must 
 not be forgotten that pious Mohammedans have, in bygone times, already 
 set us the example in this respect ; and in the palmy days of many of 
 the Moorish cities, the thirsty citizen could always be refreshed by a 
 draught of cool water from the porous bottles provided and endowed by 
 charitable Mussulmans, and placed in the public streets. 
 
78 
 
 F ig. 86. Crystals of snow. 
 
 The term crystal was originally applied by the ancients to silica in the 
 form of what is usually termed rock crystal, or Brazilian pebble ; and 
 they supposed it to be water which, had been solidified by a remarkable 
 intensity of cold, and could not be thawed by any ordinary or summer 
 heat. Indeed, this idea of the ancients has been embodied (to a certain 
 extent) in the shape of artificial ice made by crystallizing large quan 
 tities of sulphate of soda, which was made as flat as possible, and upon. 
 
 CHAPTER IX. 
 
 CRYSTALLIZATION. 
 
 It has been already stated that the force of cohesion binds the similar 
 particles of substances together, whether they be amorphous or shape- 
 less, crystalline or of a regular symmetrical and mathematical figure.. 
 
74 
 
 boy’s playbook of science. 
 
 which skaters were invited to describe the figure of eight, at the usual 
 admittance fee, representing twelve pence. A crystal is now defined to 
 be an inorganic body, which, by the operation of affinity, has assumed 
 the form of a regular solid terminated by a certain number of planes or 
 smooth surfaces. 
 
 Thousands of minerals are discovered in the crystallized state — such as 
 cubes of iron pyrites (sulphuret of iron) and of fiuor spar (fiuoride of 
 calcium), whilst numerous saline bodies called salts are sold only in the 
 form of crystals. Of these salts we have excellent examples in Epsom 
 salts (sulphate of magnesia), nitre (nitrate of potash), alum (sulphate of 
 alumina), and potash ; the term salt being applied specially to all sub- 
 stances composed of an acid and a base, as also to other combinations 
 of elements which may or may not take a crystalline form. Thus, nitre 
 is composed of nitric acid and potash ; the first, even when ' much 
 diluted, rapidly changes paper, dipped in tincture of litmus and stained 
 blue, to a red colour, whilst potash shows its alkaline nature, by changing 
 paper, stained yellow with tincture of turmeric, to a reddish-brown. The 
 latter paper is restored to its original yellow by dipping it into the 
 dilute nitric acid, whilst the litmus paper regains its delicate blue colour 
 by being passed into the alkaline solution. An acid and an alkali com- 
 bine and form a neutral salt, such as nitre, which has no action whatever 
 on litmus or turmeric; whilst the element iodine, which is not an acid, 
 unites with the metallic element potassium, and therefore not an 
 alkali, and forms a salt that crystallizes in cubes called iodide of 
 potassium. Again, cane sugar, which is composed of charcoal, oxygen, 
 and hydrogen, crystallizes in hard transparent four-sided and irregular 
 six-sided prisms, but is not called a salt. Silica or sand is found crystal- 
 lized most perfectly in nature in six-sided pyramids, but is not a salt ; 
 it is an acid termed silicic-acid. Sand has no acid taste, because it is 
 insoluble in water, but when melted in a crucible with an alkali, such as 
 potash, it forms a salt called silicate of potash. Magnesia, from being 
 insoluble, or nearly so, in water, is all but tasteless, and has barely any 
 alkaline reaction, yet it is a very strong alkaline base ; 20*7 parts of it 
 neutralize as much sulphuric acid as 47 of potash. A salt is not always a 
 crystallizable substance, and vice versa. The progress of our chemical 
 knowledge has therefore demanded a wider extension and application of 
 the term salt , and it is not now confined merely to a combination of an 
 acid and an alkali, but is conferred even on compounds consisting only 
 of sulphur and a metal, which are termed sulphur salts. 
 
 So also in combinations of chlorine, iodine, bromine, and fluorine, 
 with metallic bodies, neither of which are acid or alkaline, the term 
 haloid salts has been applied by Berzelius, from the Greek (aX?, sea salt, 
 and ctSo? form), because they are analogous in constitution to sea salt ; 
 and the mention of sea salt again reminds us of the wide signification of 
 the term salt, originally confined to this substance, but now extended 
 into four great orders, as defined by Turner : — 
 
 Order I. The oxy -salts . — This order includes no salt the acid or 
 base of which is not an oxidised body (ex., nitrate of potash). 
 
CRYSTALLIZATION. 
 
 75 
 
 Order II. The hydro-salts . — This order includes no salt the acid or 
 base of which does not contain hydrogen (ex., chloride of ammonium). 
 
 Order III. The sulphur salts . — This order includes no salt the 
 electro-positive or negative ingredient of which is not a sulphuret (ex., 
 hydrosulphuret of potassium). 
 
 Order IY. The haloid salts . — This order includes no salt the electro- 
 positive or negative ingredient of which is not haloidal. (Exs., iodide of 
 potassium and sea salt). To fix the idea of salt still better in the youthful 
 mind, it should be remembered that alabaster, of which works of art are 
 constructed, or marble, or lime-stone, or chalk, are all salts, because they 
 consist of an acid and a base. 
 
 In order to cause a substance to crystallize it is first necessary to 
 endow the particles with freedom of motion. There are many methods 
 of doing this chemically or by the application of heat, but we cannot by 
 any mechanical process of concentration, compression, or division, per- 
 suade a substance to crystallize, unless perhaps we except that remark- 
 able change in wrought or fibrous iron into crystalline or brittle iron, 
 by constant vibration, as in the axles of a carriage, or by attaching a 
 piece of fibrous iron to a tilt hammer. 
 
 If we powder some alum crystals they will not again assume their 
 crystalline form ; if brought in contact there is no freedom of motion. It 
 is like placing some globules of mercury on a plate. They have no 
 power to create motion ; their inertia keeps them separated by certain 
 distances, and they do not coalesce ; but incline the plate, give them 
 motion, and bring them in contact, they soon unite and form one 
 globule. The particles of alum are not in close contact, and they have 
 no freedom of motion unless they are dissolved in water, when they 
 become invisible; the water by its chemical power destroys the 
 mechanical aggregation of the solid alum far beyond any operation of 
 levigation. The solid alum has become liquid, like water ; the particles 
 are now free to move without let or hindrance from friction. A solution, 
 (from the Latin solvo , to loosen) is obtained. The alum must indeed be 
 reduced to minute particles, as they are alike invisible to the eye 
 whether assisted by the microscope or not. No repose will cause the 
 alum to separate ; the solvent power of the water opposes gravitation ; 
 every part of the solution is equally impregnated with alum, and the 
 particles are diffused at equal distances through the water ; the heavy 
 alum is actually drawn up against gravity by the water. 
 
 How, then, is the alum to be brought back again to the solid state ? 
 The answer is simple enough. By evaporating away the excess of 
 water, either by the application of heat or by long exposure to the 
 atmosphere in a very shallow vessel, the minute atoms of the alum are 
 brought closer together, and crystallization takes place. The assumption 
 of the solid state is indicated by the formation of a thin film (called a 
 pellicle) of crystals, and is further and still more satisfactorily proved by 
 taking out a drop of the solution and placing it on a bit of glass, which 
 rapidly becomes filled with crystals if the evaporation has been carried 
 sufficiently far (Fig. 87). 
 
76 
 
 boy’s playbook of science. 
 
 After evaporating away sufficient water, the dish is placed on one 
 side and allowed to cool, when crystals of the utmost regularity of form 
 
 Tig:. 87. r r. Eing-stand. s s. Spirit-lamps. 
 a. Flask containing boiling solution of alum.— 
 Solution, b. Funnel, with a bit of lamp-cotton 
 stuffed in the bottom.— Filtration, c. Evapo- 
 rating dish. — Evaporation, d. Drop on glass. 
 Crystallization. 
 
 are produced, and, denoted by a geometrical term, are called octohedral 
 or eight-sided crystals, when in the utmost state of perfection (Fig. ooj. 
 
 The science of crystallography is too elaborate to be discussed at 
 length in a work of this kind; the various terms connected with crystals 
 win therefore only be explained, and experiments given m illustration of 
 the formation of various crystals. «. ,, 
 
 When the apices—^., the tips or points of crystals— are cut oil, they 
 are said to be truncated; and the same change occurs on the edges ot 
 
 numerous crystals. . , 
 
 If some of the salt called chloride of calcium m the dry and amor- 
 phous state is exposed to the air, it soon absorbs water, or what is termed 
 deliquesces : the same thing occurs with the < crystals of carbonate 
 of potash, and if four ounces are weighed out m an evaporating dish, 
 and then exposed for about half an hour to the air, a very perceptible 
 increase in weight is observed by the assistance of the scales and grain 
 weights. Deliquescence is a term from the Latin deliqueo, to melt, ana 
 is in fact a gradual melting, caused by the absorption of water from 
 the atmosphere. The reverse of this is illustrated with various crystals, 
 such as Glauber’s salt (sulphate of soda), or common washing soda 
 (carbonate of soda); if a fine clear crystal is taken out of the solution, 
 called the mother liquor, in which it has been crystallized, wiped dry, 
 and placed under a glass shade, this salt may remain for a long period 
 
CRYSTALLIZATION. 
 
 77 
 
 without change, but if it receive one scratch from a pin, the door is 
 opened apparently for the escape of the water which it contains, chemi- 
 cally united with the salt, and called water of crystallization; the 
 white crystal gradually swells out, the little quasi sore from the pin- 
 scratch spreads over the whole, which becomes opaque, and crumbling 
 down falls into a shapeless mass of white dust ; this change is called 
 efflorescence, from effloresco , to blow as a flower — caused by the 
 abstraction from them of chemically-combined water by the atmosphere. 
 With reference to the preservation of crystals, Professor Griffiths re- 
 commends them to be oiled and wiped, and placed under a glass shade, 
 if of a deliquescent nature ; or if efflorescent, they are perfectly pre- 
 served by placing them under a glass shade with a little water in a cup 
 to keep the air charged with moisture and prevent any drying up of the 
 crystal. 
 
 Deliquescent crystals may be preserved by placing them, when dry, 
 in naphtha, or any liquor in which they are perfectly insoluble. Some 
 salts, like Glauber’s salts, contain so much water of crystallization that 
 when subjected to heat they melt and dissolve in it, and this liquefac- 
 tion of the solid crystal is called “ watery fusion.” Other salts, such as 
 bay salt, chlorate of potash, &c., when heated, fly to pieces, with a 
 sharp crackling noise, which is due sometimes, to the unequal expansion 
 of the crystalline surface, or the sudden conversion of the water (retained 
 in the crystal by capillary attraction) into steam ; thus nitre behaves in 
 this manner, and frequently retains water in capillary fissures, although 
 it is an anhydrous salt, or salt perfectly free from combined water. The 
 crackling sound is called decrepitation , and is well illustrated by 
 throwing a handful of bay salt on a clear fire ; but this property is 
 destroyed by powdering the crystals. 
 
 Many substances when melted and slowly cooled concrete into the most 
 perfect crystals ; in these cases heat alone, the antagonist to cohesion, 
 is the solvent power. Thus, if bismuth be melted in a crucible, and 
 when cooling, and just as the pellicle (from pellis, a skin or crust) is 
 forming on the surface, if two small holes are instantly made by a 
 rod of iron and the liquid metal poured out from the inside (one of the 
 holes being the entrance for the air, the other the exit for the metal) ; on 
 carefully breaking the crucible, the bismuth is found to be crystallized 
 in the most lovely cubes. Sulphur, again, may be crystallized in pris- 
 matic crystals by pursuing a similar plan; and the great blocks of 
 spermaceti exhibited by wax chandlers in their windows, are crys- 
 tallized in the interior and prepared on the same principle. 
 
 There are other modes of conferring the crystalline state upon sub- 
 stances — viz., by elevating them into a state of vapour by the process 
 called sublimation (from sublimis , high or exalted), the lifting up and 
 condensation of the vapour in the upper part of a vessel ; a process 
 perfectly distinct from that of distillation , which means to separate 
 drop by drop. Both of these processes are very ancient, and were in- 
 vented by the Arabian alchemists long antecedent to the seventh century. 
 Examples of sublimation are shown by heating iodine, and especially 
 
78 
 
 boy’s playbook of science. 
 
 benzoic acid ; with, the latter, a very elegant imitation of snow is pro- 
 duced, by receiving the vapour, on some sprigs of holly or other ever- 
 green, or imitation paper snow- 
 drops and crocuses, placed in a 
 tasteful manner under a glass 
 vessel. The benzoic acid should 
 first be sublimed over the sprigs 
 or artificial flowers in a gas jar, 
 which may be removed when the 
 whole is cold, and a clear glass 
 shade substituted for it. (Fig. 89.) 
 
 All electro deposits on metals 
 are more or less crystalline ; and 
 copper or silver may be deposited 
 in a crystalline form by placing 
 a scraped stick of phosphorus in 
 a solution of sulphate of copper 
 or of nitrate of silver. The phos- 
 phorus takes away the oxygen 
 from the metal, or deoxidizes the 
 solution, and the copper or silver 
 reappears in the metallic form. 
 The surface of the phosphorus 
 must not be scraped in the air, 
 but under water, when the opera- 
 tion is perfectly safe. 
 
 A singular and almost instan- 
 taneous crystallization can be 
 produced by saturating boiling 
 water with Glauber’s salt, of 
 which one ounce and a half of 
 water will usually dissolve about two ounces ; having done this, pour 
 the solutiou, whilst boiling hot, into clean oil . flasks, or vials of any 
 kind, previously warmed in the oven, and immediately cork them, or tie 
 strips of wetted bladder, over the orifices of the flasks or vials, or pour 
 into the neck a small quantity of olive oil, or close the neck with a 
 cork through which a thermometer tube has been passed. When cold, 
 no crystallization occurs until atmospheric air is admitted ; and it was 
 formerly believed that the pressure of the air effected this Qbject, until 
 some one thought of the oil, and now the theory is modified, and crystal- 
 lization is supposed to occur in consequence of the water dissolving 
 some air which causes the deposit of a minute crystal, and this being 
 the turning point, the whole becomes solid. However the fact may be 
 explained, it is certain that when the liquid refuses to crystallize on the 
 admission of air, the solidification occurs directly a minute crystal of 
 sulphate of soda, or Glauber’s salt, is dropped into the vessel. 
 
 When the crystallization is accomplished, the whole mass is usually 
 so completely solidified, that on inverting the vessel, not a drop of liquid 
 falls out. 
 
 Fig 1 . 89. a. Gas-jar, with stopper open 
 first, to be shut when the lamp is withdrawn. 
 b. Wooden stand, with hole to carry the cup c, 
 containing the benzoic acid, heated below by 
 the spirit-lamp, s. * f. Flowers or sprigs ar- 
 ranged on pieces of rock or mineral. 
 
CRYSTALLIZATION. 
 
 79 
 
 It may be observed that the same mass of salt will answer any 
 number of times the same purpose. All that is necessary to be done, is 
 to place the vial or flask, in a saucepan of warm water, and gradually 
 raise it to the boiling point till the salt is completely liquefied, when the 
 vessel must be corked and secured from the air as before. When the 
 solidification is produced much heat is generated, which is rendered 
 apparent by means of a thermometer, or by the insertion of a copper 
 wire into the pasty mass of crystal in the flask, and then touching an 
 extremely thin shaving or cutting of phosphorus, dried and placed on 
 cotton wool. Solidification in all cases produces heat. Liquefaction 
 produces cold. 
 
 In Masters’s freezing apparatus certain measured quantities of crystal- 
 lized sal-ammoniac, nitre, and nitrate of ammonia, are placed in a 
 metallic cylinder, sur- 
 rounded with a small 
 quantity of spring water 
 contained in an outer 
 vessel. Directly the 
 crystals are liquefied by 
 the addition of water, in- 
 tense cold is produced, 
 which freezes the water 
 and forms an exact cast 
 of the inner cylinder in 
 ice, and this may after- 
 wards be removed, by 
 pouring away the lique- 
 fied salts, and filling the 
 inner cylinder, with water 
 of the same temperature 
 as the air, which rapidly 
 thaws the surrounding 
 ice, and allows it to slip 
 off into any convenient 
 vessel ready to receive it. (Eig. 90.) 
 
 Eor an ingenious method of obtaining large and perfect crystals of 
 almost any size, experimentalists are indebted to Le Blanc. His method 
 consists in first procuring small and perfect crystals — say, octohedra of 
 alum — and then placing them in a broad flat-bottomed pan, he pours 
 over the crystals a quantity of saturated solution of alum, obtained 
 by evaporating a solution of alum until a drop taken out crystallizes on 
 cooling. The positions of the crystals are altered at least once a day 
 with a glass rod, so that all the faces may be alternately exposed to the 
 action of the solution, for the side on which the crystal rests, or is in 
 contact with the vessel, never receives any increment. The crystals 
 will thus gradually grov r or increase in size, and wdien they have done so 
 for some time, the best and most symmetrical, may be removed and 
 placed separately, in vessels containing some of the same saturated 
 
 
 Fig 1 . 90. a. The inner cylinder which contains the 
 freezing mixture, e b. The outer one containing spring 
 water, c c. The ice slipping away from the inner cylinder. 
 
so 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 solution of alum, and being constantly turned they may be obtained of 
 almost any size desired. 
 
 Unless the crystals are removed to fresh solutions, a reaction takes 
 place, in consequence of the exhaustion of the alum from the water, and 
 the crystal is attacked and dissolved. This action is first perceptible on 
 the edges and angles of the ciystal ; they become blunted and gradually 
 lose their shape altogether. By this method crystals may be made to 
 grow in length or breadth — the former when they are placed upon their 
 sides, the latter if they be made to stand upon their bases. 
 
 On Le Blanc’s principle, beautiful crystal baskets are made with alum, 
 sulphate of copper, and bichromate of potash. The baskets are usually 
 made of covered copper wire, and when the salts crystallize on them as a 
 nucleus or centre, they are constantly removed to fresh solutions, so 
 that the whole is completely covered, and red, white, and blue sparkling 
 crystal baskets formed. They will retain their brilliancy for any time, 
 by placing them under a glass shade, with a cup containing a little 
 water. 
 
 The sketch below affords an excellent illustration of some of Nature’s 
 remarkable concretions in the peculiar columnar structure of basalt. 
 
81 
 
 CHAPTER X. 
 
 CHEMISTRY. 
 
 There is hardly any kind of knowledge which has been so slowly 
 acquired as that of chemistry, and perhaps no other science has offered 
 such fascinating rewards to the labour of its votaries as the philosopher’s 
 stone, which was to produce an unfailing supply of gold ; or the elixir 
 of life , that was to give the discoverer of the gold-making art the time, 
 the prolonged life, in which he might spend and enjoy it. 
 
 Hundreds of years ago Egypt was the great depository of all learning, 
 art, and science, and it was to this ancient country that the most cele- 
 brated sages of antiquity travelled. 
 
 Hermes, or Mercurius Trismegistus, the favourite minister of the 
 Egyptian king Osiris, has been celebrated as the inventor of the art of 
 alchemy, and the first treatise upon it has been attributed to Zosymus, 
 of Chemnis or Panopolis. The Moors who conquered Spain were re- 
 
 G 
 
82 
 
 boy’s playbook of science. 
 
 markable for their learning, and the taste and elegance with which they 
 designed and carried out a new style of architecture, with its lovely 
 Arabesque ornamentation. They were likewise great followers of the 
 art of alchemy, when they ceased to be conquerors, and became more 
 reconciled to the arts of peace. Strange that such a people, thirsting 
 as they did in after years for all kinds of knowledge, should have 
 destroyed, in the persons of their ancestors, the most numerous collection 
 of books that the world had ever seen: the magnificent library of 
 Alexandria, collected by the Ptolemies with great diligence and at an 
 enormous expense, was burned by the orders of Caliph Omar ; whilst it 
 is stated that the alchemical works had been previously destroyed by 
 Diocletian in the fourth century, lest the Egyptians should acquire by 
 such means sufficient wealth to withstand the Roman power, for gold 
 was then, as it is now, “ the sinews of war.” 
 
 Eastern historians relate the trouble and expense incurred by the suc- 
 ceeding Caliphs, who, resigning the Saracenic barbarism of their an- 
 cestors, were glad to collect from all parts the books which were to 
 furnish forth a princely library at Bagdad. How the learned scholar 
 sighs when he reads of seven hundred thousand books being consigned 
 to the ignominious office of heating forty thousand baths in the capital 
 of Egypt, and of the magnificent Alexandrian Library, a mental fuel for 
 the lamp of learning in all ages, consumed in bath furnaces, and affording 
 six months 5 fuel for that purpose. The Arabians, however, made amends 
 for these barbarous deeds in succeeding centuries, and when all Europe 
 was laid waste under the iron rule of the Goths, they became the pro- 
 tectors of philosophy and the promoters of its pursuits ; and thus we 
 come to the seventh century, in which Geber, an Arabian prince lived, and 
 is stated to be the earliest of the true alchemists whose name has reached 
 posterity. 
 
 Without attempting to fill up the alchemical history of the intervening 
 centuries, we leap forward six hundred years, and now find ourselves in 
 imagination in England, with the learned friar, Roger Bacon, a native of 
 Somersetshire, who lived about the middle of the thirteenth century : and 
 although the continual study of alchemy had not yet produced the 
 “ stone, 55 it bore fruit in other discoveries, and Roger Bacon is said, 
 with great appearance of truth, to have discovered gunpowder, for he 
 says in one of his works : — “ Erom saltpetre and oilier ingredients we 
 are able to form a fire which will burn to any distance ; 55 and again 
 alluding to its effects, “ a small portion of matter, about the size of the 
 thumb, 'properly disposed , will make a tremendous sound and corusca- 
 tion, by which cities and armies might be destroyed. 55 The exaggerated 
 style seems to have been a favourite one with all philosophers, from the 
 time of Roger Bacon to that of Muschenbroek of the University of Leyden, 
 who accidentally discovered the Leyden jar in the year 17 16, and re- 
 ceiving the first shock, from a vial containing a little water, into which 
 a cork and nail had been fitted, states that “he felt himself struck in 
 his arms, shoulders, and breast, so that he lost his breath, and was 
 two days before he recovered from the effects of the blow and tho 
 
CHEMISTRY. 
 
 83 
 
 terror adding, that “ he would not take a second shock for the kingdom 
 of France.” Disregarding the numerous alchemical events occurring 
 from the time of Boger Bacon, we again advance four hundred years — 
 viz., to the year 1662, when, on the 15th of July, King Charles II. 
 granted a royal charter to the Philosophical Society of Oxford, who 
 had removed to London, under the name of the Boyal Society of London 
 for Promoting Natural Knowledge, and in the year 1665 was published 
 the first number of the Philosophical Transactions ; this work contains 
 the successive discoveries of Mayow, Hales, Black, Leslie, Cavendish, 
 Lavoisier, Priestley, Davy, Faraday ; and since the year 17 62 has been 
 regularly published at the rate of one volume per annum. With this 
 preface proceed we now to discuss some of the varied phenomena of 
 chemical attraction, or what is more correctly termed 
 
 CHEMICAL AFFINITY. 
 
 The above title refers to an endless series of changes brought about 
 by chemical combinations, all of which can be reduced to certain fixed 
 laws, and admit of a simple classification and arrangement. A me- 
 chanical aggregation, however well arranged, can be always distinguished 
 from a chemical one. Thus, a grain of gunpowder consists of nitre , 
 which can be washed away with boiling water, of sulphur , which can be 
 sublimed and made to pass away as vapour, of charcoal , which remains 
 behind after the previous processes are complete; this mixture has 
 been perfected by a careful proportion of the respective ingredients, it 
 has been wetted, and ground, and pressed, granulated, and finally 
 dried; all these mechanical processes have been so well carried out 
 that each grain, if analysed, would be similar to the other ; and yet it 
 is, after all, only a mechanical aggregation, because the sulphur, the 
 charcoal, and the nitre are unchanged. A grain of gunpowder mois- 
 tened, crushed, and examined by a high microscopic power, would 
 indicate the yellow particles of sulphur, the black parts of charcoal, 
 whilst the water filtered from the grain of powder and dried, would 
 show the nitre by the form of the crystal. On the other hand, 
 if some nitre is fused at a dull red heat in a little crucible, and two 
 or three grains of sulphur are added, they are rapidly oxidized, and 
 combine with the potash, forming sulphate of potash ; and after this 
 change a few grains of charcoal may be added in a similar manner, when 
 they burn brightly, and are oxidized and converted into carbonic acid, 
 which also unites in like manner with the potash, forming carbonate of 
 potash ; so that when the fused nitre is cooled and a few particles 
 examined by the microscope, the charcoal and sulphur are no longer 
 distinguishable, they have undergone a chemical combination with 
 portions of the nitre, and have produced two new salts, perfectly dif- 
 ferent in taste, gravity, and appearance from the original substances 
 employed to produce them. Hence chemical combination is defined 
 to be “ that property which is possessed by one or more substances % 
 of uniting together and producing a third or other body perfectly dif 
 
84 boy’s playbook of science. 
 
 ferent in its nature from either of the two or more generating the new 
 compound” 
 
 To return to our first experiment with the gunpowder : take sulphur, 
 place some in an iron ladle, heat it over a gas flame till it catches fire, then 
 ascend a ladder, and pour it gently, from the greatest height you can 
 reach, into a pail of warm water : if this experiment is performed in a 
 darkened room a magnificent and continuous stream of fire is obtained, 
 of a blue colour, without a single break in its whole length, provided 
 the ladle is gradually inclined and emptied. The substance that drops 
 into the warm water is no longer yellow and hard, but is red, soft, and 
 plastic ; it is still sulphur, though it has taken a new form, because that 
 element is dimorphous (dig twice, and pop(pTj a form), and, Proteus-like, 
 can assume two forms. Take another ladle, and melt some nitre in it at ’ 
 a dull red heat, then add a small quantity of sulphur, which will burn as 
 before ; and now, after waiting a few minutes, repeat the same experiment 
 by pouring the liquid from the steps through the air into water ; observe 
 it no longer flames, and the substance received into the water is not 
 red and soft and plastic, but is white, or nearly so 5> and rapidly dis- 
 solves away in the water. The sulphur has united with the oxygen of 
 the nitre and formed sulphuric acid, which combines with the potash 
 and forms sulphate of potash ; here, then, oxygen, sulphur, and potas- 
 sium, have united and formed a salt in which the separate properties 
 of the three bodies have completely disappeared ; to prove this, it is 
 only necessary to dissolve the sulphate of potash in water, and after 
 filtering the solution, or allowing it to settle, till it becomes quite clear 
 and bright, some solution of baryta may now be added, when a white 
 precipitate is thrown down, consisting of sulphate of baryta, which is in- 
 soluble in nitric or other strong acids. The behaviour of a solution of 
 sulphate of potash with a nitrate of baryta may now be contrasted with 
 that of the elements it contains ; on the addition of sulphur to a solu- 
 tion of nitrate of baryta no change whatever takes place, because the 
 sulphur is perfectly insoluble. If a stream of oxygen gas is passed from 
 a bladder and jet through the same test, no effect is produced; the nitrate 
 of baryta has already acquired its full proportion of oxygen, and no 
 further addition has any power to change its nature ; finally, if a bit of 
 the metal potassium is placed in the solution of nitrate of baryta it does 
 not sink, being lighter than water, and it takes fire ; but this is not in 
 any way connected with the presence of the test, as the same thing will 
 happen if another bit of the metal is placed in water — it is the oxygen 
 of the latter which unites rapidly with the potassium, and causes it to 
 become so hot that the hydrogen, escaping around the little red-hot 
 globules* takes fire ; moreover, the fact of the combustion of the potas- 
 sium under such circumstances is another striking proof of the opposite 
 qualities of the three elements — sulphur, oxygen, and potassium — as 
 compared with the three chemically combined and forming sulphate of 
 potash. The same kind of experiment may be repeated with charcoal r 
 if some powdered charcoal is made red-hot, and then puffed into the air 
 with a blowing machine, numbers of sparks are produced, and the char 
 
CHEMISTRY. 
 
 85 
 
 ccal burns away and forms carbonic acid gas, a little ash being* left 
 behind; but if some more nitre be heated in a ladle, and charcoal 
 added, a brilliant deflagration (< deflagro , to burn) occurs, and the charcoal, 
 instead of passing away in the air as carbonic acid, is now retained in 
 the same shape, but firmly and chemically united with the potash of the 
 nitre, forming carbonate of potash, or pearl-ash, which is not black and 
 insoluble in water and acids like charcoal, but is white, and not only 
 soluble in water, but is most rapidly attacked by acids with effer- 
 vescence, and the carbon escapes in the form of carbonic acid gas. Thus 
 we have traced out the distinction between mechanical aggregation and 
 chemical affinity, taking for an example the difference between gun- 
 powder as a whole (in which the ingredients are so nicely balanced that 
 it is almost a chemical combination), and its constituents, sulphur, 
 charcoal, and nitre, when they are chemically combined ; or, in briefer 
 language, we have noticed the difference between the mechanical mix- 
 ture, and some of the chemical combinations, of three important elements. 
 Our .very slight and partial examination of three simple bodies does not, 
 however, afford us any deep insight into the principles of chemistry ; we 
 have, as it were, only mastered the signification of a few words in a lan- 
 guage ; we might know that chien was the French for dog, or clieval 
 horse, or liomme man ; but that knowledge would not be the acquisition of 
 the French language, because we must first know the alphabet, and 
 then the combination of these letters into words ; we must also acquire 
 a knowledge of the proper arrangement of these words into sentences, 
 or grammar, both syntax and prosody, before we can claim to be a 
 French scholar : so it is with chemistry — any number of isolated experi- 
 ments with various chemical substances would be comparatively useless, 
 and therefore the “ alphabet of chemistry , 55 or “ table of simple ele- 
 ments , 55 must first be acquired. These bodies are understood to be 
 solids, fluids, and gases, which have hitherto defied the most elaborate 
 means employed to reduce them into more than one kind of matter. 
 Even pure light is separable into seven parts — viz., red, orange, 
 yellow, green, blue, indigo, and violet ; but the elements we shall 
 now enumerate are not of a compound, but, so far as we know, of an 
 absolutely simple or single nature ; they represent the boundaries, not 
 the finality, of the knowledge that may be acquired respecting them. 
 
 The elements are sixty-four in number, of which about forty are 
 tolerably plentiful, and therefore common; whilst the remainder, twenty- 
 four, are rare, and for that reason of a lesser utility : whenever 
 Nature employs an element on a grand scale it may certainly be called 
 common, but it generally works for the common good of all, and fulfils 
 the most important offices. 
 
86 
 
 BOY'S PLAYBOOK OF SCIENCE. 
 
 CLASSIFICATION OF THE ALPHABET OF CHEMISTEY. 
 
 14 Non-Metallic Bodies. 
 
 
 
 
 Combining 
 
 
 
 Combining; 
 
 
 Name. 
 
 Symbol. 
 
 proportion 
 or atomic 
 
 Name. 
 
 Symbol. 
 
 proportion 
 or atomic 
 
 
 
 
 weight. 
 
 
 
 weight. 
 
 1. 
 
 Oxygen . 
 
 . 0 
 
 = 16-0 
 
 8. Carbon 
 
 . c 
 
 = 12-0 
 
 2. 
 
 Hydrogen 
 
 . H 
 
 = 1*0 
 
 9. Boron . . 
 
 . B 
 
 = 11*0 
 
 3. 
 
 Nitrogen . 
 
 . N 
 
 = 14-0 
 
 10. Sulphur . 
 
 . S 
 
 = 32*0 
 
 4. 
 
 Chlorine . 
 
 . Cl 
 
 = 35.5 
 
 11. Phosphorus 
 
 . P 
 
 = 31*0 
 
 5. 
 
 Iodine . . 
 
 . I 
 
 = 127-0 
 
 12. Silicon 
 
 . Si 
 
 — 235- 
 
 6. 
 
 Bromine . 
 
 . Br 
 
 = 80-0 
 
 13. Selenium . 
 
 . Se 
 
 = 79*5- 
 
 7. 
 
 Fluorine . 
 
 . F 
 
 = 19-0 
 
 14. Tellurium. 
 
 . Te 
 
 = 128*0 
 
 50 Metals . 
 
 1. Aluminum . 
 
 A1 
 
 
 
 • 
 
 27-5 
 
 26. Mercury . . 
 
 Hg 
 
 _ 
 
 200R 
 
 2. Antimony 
 
 Sb 
 
 = 
 
 122-0 
 
 27. Molybdenum 
 
 Mo 
 
 
 96-0 
 
 3. Arsenic . . 
 
 As 
 
 — 
 
 75-0 
 
 28. Nickel. . . 
 
 Ni 
 
 — 
 
 58*3 
 
 4. Barium . . 
 
 Ba 
 
 — 
 
 137'0 
 
 29. Niobium . . 
 
 Nb 
 
 — 
 
 97-6 
 
 5. Bismuth . . 
 
 Bi 
 
 
 210-0 
 
 30. Osmium . . 
 
 Os 
 
 — 
 
 199*0 
 
 6. Cadmium . . 
 
 Cd 
 
 — 
 
 112-0 
 
 31. Platinum . . 
 
 Pt 
 
 — 
 
 197*4 
 
 7. Calcium . . 
 
 Ca 
 
 = 
 
 40-0 
 
 32. Potassium 
 
 K 
 
 
 39*0 
 
 8. Caesium . . 
 
 Cs 
 
 — 
 
 133-0 
 
 33. Palladium 
 
 Pd 
 
 — 
 
 106-5 
 
 9. Cerium . . 
 
 Ce 
 
 = 
 
 92*0 
 
 34. Rhodium . . 
 
 Rh 
 
 — 
 
 104*3 
 
 10. Chromium . 
 
 Cr 
 
 — 
 
 52*5 
 
 35. Bimthenium . 
 
 Ru 
 
 — 
 
 104-4 
 
 11. Cobalt . . 
 
 Co 
 
 — 
 
 58-8 
 
 36. Rubidium 
 
 Rb 
 
 — 
 
 85-4 
 
 12. Copper . . 
 
 Cu 
 
 = 
 
 63*5 
 
 37. Silver . . . 
 
 Ag 
 
 — 
 
 108*0 
 
 13. Didymiutn . 
 
 l)i 
 
 
 96-0 
 
 38. Sodium . . 
 
 Na 
 
 
 23-0 
 
 14. Erbium . . 
 
 , E 
 
 = 
 
 112-6 
 
 39. Strontium 
 
 Sr 
 
 — 
 
 87-6 
 
 15. Gallium . . 
 
 , Ga 
 
 — 
 
 69*9 
 
 40. Tin . . . 
 
 Sn 
 
 — 
 
 118-0 
 
 16. Gold . . . 
 
 , Au 
 
 = 
 
 196-7 
 
 41. Tantalum. . 
 
 Ta 
 
 — 
 
 182-0 
 
 17. Glucinum. 
 
 G 
 
 — 
 
 9-5 
 
 42. Thallium . . 
 
 T1 
 
 — 
 
 204-0 
 
 18. Indium . . 
 
 , In 
 
 — 
 
 113-4 
 
 43. Thorium . . 
 
 Th 
 
 — 
 
 231*5 
 
 19. Iron . . . 
 
 Fe 
 
 = 
 
 56*0 
 
 44. Titanium . . 
 
 Ti 
 
 — 
 
 50-0 
 
 20. Iridium . . 
 
 Ir 
 
 — 
 
 198-0 
 
 45. Tungsten . . 
 
 W 
 
 — 
 
 184-0 
 
 21. Lead . . . 
 
 , Pb 
 
 — 
 
 207-0 
 
 46. Uranium . . 
 
 u 
 
 — 
 
 240-0 
 
 22. Lanthanum . 
 
 La 
 
 — 
 
 92-0 
 
 47. Vanadium 
 
 V 
 
 — 
 
 51-3 
 
 23. Lithium . . 
 
 Li 
 
 = 
 
 7-0 
 
 48. Yttrium . . 
 
 Y 
 
 — 
 
 61-7 
 
 24. Magnesium , 
 
 . Mg 
 
 — 
 
 24-0 
 
 ! 49. Zinc . . .• 
 
 Zn 
 
 — 
 
 65-0 
 
 25. Manganese . 
 
 . Mn 
 
 = 
 
 55’0 
 
 ! 50. Zircouium 
 
 Zr 
 
 = 
 
 89*5 
 
 A few words will suffice to explain tlie meaning of the terms which 
 head the names, letters, and numbers of the Table of Elements. The 
 
CHEMISTRY. 
 
 87 
 
 names of the elements have very interesting derivations, which it is not 
 the object of this work to go into; the symbols are abbreviations, 
 ciphers of the simplest kind, to save time and trouble iu the frequent re- 
 petition of long words, just as the signs + plus, and — minus, are used 
 in algebraic formulae. For instance — the constant recurrence of water 
 in chemical combinations must be named, and would involve the most 
 tedious repetition ; water consists of oxygen and hydrogen, and by- 
 taking the first letter of each word we have an instructive symbol, which 
 not only gives us an abbreviated term for water, but also imparts at 
 once a knowledge of its composition by the use of the letters, ELO. 
 
 AgaiD, to take a more complex example, such as would occur in the 
 study of organic chemistry — a sentence such as anhydrous oxide of 
 acetyl is written at once by C 4 H 6 0 3 , the figures referring to the 
 number of equivalents of each element — viz., 4 equivalents of C, the 
 symbol for carbon, G of H (hydrogen), and 3 of 0 (oxygen). 
 
 The long word Naphthylamine, a substance contained in coal tar, is 
 disposed of at once with the symbols and figures C,„H S N. 
 
 The figures in the third column are, however, the most interesting 
 to the precise and mathematically exact chemist. They represent the 
 united labours of the most painstaking and learned chemists, and are 
 the exact quantities in which the various elements unite. To quote one 
 example : if 16 parts by weight of oxygen — viz., the combining propor- 
 tions of that element — are united with 2 parts by weight of hydrogen, 
 also its combining number, the result will *be 1 8 parts by weight of 
 water ; but if 16 parts of oxygen and 3 parts of hydrogen were used, 
 two only of the latter could unite with the former, and the result would 
 be the formation again of IS parts of water, with an overplus of 1 
 equivalent of hydrogen. 
 
 It is useless to multiply examples, and it is sufficient to know that 
 with this table of numbers the figures of analysis are obtained. Sup- 
 posing a substance contained 51 parts of water, and the oxygen in 
 this had to be determined, the rule of proportion would give it at once, 
 IS : 54 : : 16 : 4S. IS parts of water are to 54 parts as 16 of oxygen 
 (the quantity contained in IS parts of water) are to the answer 
 required — viz., 48 of oxygen. The names, symbols, and combining 
 proportions being understood, we may now proceed with the per- 
 formance of many interesting 
 
 CHEMICAL EXPERIMENTS. 
 
 The three gases which head the list will first engage our attention, 
 beginning with the element oxygen — Symbol 0, combining proportion 
 16. There is nothing can give a better idea of the enormous quantity 
 of oxygen present in the animal, vegetable, and mineral kingdoms, 
 than the statement that it represents one-third of the weight of the 
 whole crust of the globe. Silica, or flint, contains about half its weight 
 of oxygen ; lime contains forty per cent. ; alumina about thirty-three 
 per cent. In these substances the element oxygen remains inactive and 
 powerless, chained by the strong fetters of chemical affinity to the 
 
88 
 
 boy’s playbook of science. 
 
 silicium of the flint, the calcium of the lime, and the aluminum of the 
 alumina. If these substances are heated by themselves they will not 
 yield up the large quantity of oxygen they contain. 
 
 Nature, however, is prodigal in her creation, and hence we have but 
 to pursue our search diligently to find a substance or mineral containing 
 an abundance of oxygen, and part of which it will relinquish by what 
 used to be called by the “ old alchemists” the torture of heat. Such a 
 mineral is the black oxide of manganese, or more correctly the binoxide 
 of manganese, which consists of one combining proportion of the metal 
 manganese — viz., 55*0, and two of oxygen — viz., 16 x 2 = 32. If 
 three proportions of the binoxide of manganese are heated to redness 
 in an iron retort, they yield one proportion of oxygen, and all that has 
 just been explained by so many words is comprehended in the symbols 
 and figures below : — 
 
 3 Mn0 2 = Mn 3 0 4 -f 0 2 
 
 Thus the 3 Mn0 2 represent the three proportions of the binoxide of 
 manganese before heat is applied, whilst the sign =, the sign of equation 
 (equal to), is intended to show that the elements or compounds placed 
 before it produce those which follow it ; hence the sequel Mn 3 0 4 -l-0 2 
 shows that another compound of the metal and oxygen is produced, 
 whilst the + 0* indicates the liberated oxygen gas. The iron retort 
 employed to hol3 the mineral should be made of cast iron in preference 
 to wrought iron, as the latter is very soon worn out by contact with 
 oxygen at a red heat. A gun-barrel will answer the purpose for an 
 experiment on the small scale, to which must be adapted a cock and 
 piece of pewter tubing. Such a make-shift arrangement may do very 
 well when nothing better offers ; but as a question of expense, it is 
 probably cheaper in the end to order of Messrs. Simpson and Maule, or 
 of Messrs. Griffin, or of Messrs. Bolton, a cast-iron bottle, or cast-iron 
 retort, as it is termed, of a size sufficient to prepare two gallons of 
 
 Fig. 93. a. The iron bottle, containing the black oxide of manganese, with pipe passing to 
 the pneumatic trough, b b, in which is fixed a shelf, c, perforated with a hole, under winch 
 the end of the pipe is adjusted, and the gas passes into the gas-jar, n. 
 
 oxygen from the binoxide of manganese, which, with four feet of iron 
 conducting-pipe, and connected to the bottle with a screw, does not 
 
PEEP AR ATI ON OF OXYGEN GAS. 
 
 89 
 
 cost more than six shillings — an enormous dip, perhaps, in the juvenile 
 pocket, and therefore we shall indicate presently a still cheaper appa- 
 ratus for the same purpose. (Fig. 93.) 
 
 The oxygen is conveyed to a square tin box provided with a shelf at 
 one end, perforated with several holes at least one inch in diameter, 
 called the pneumatic trough ; any wooden trough, butter or wash-tub, 
 foot-pan or bath, provided with a shelf, may be raised by the same 
 title to the dignity of a piece of chemical apparatus. The gas jar must 
 be filled with water by withdrawing the stopper and pressing it down 
 into the trough, and when the neck is below the level of the water, the 
 stopper is again inserted, and the jar with the water therein contained 
 
 . Fig. 94. a a. Pneumatic trough, with gas jar raised to shelf; bubbles of air are rushing 
 in at b, as the level of the water is below the shelf— viz., at c c. d d. Same trough and 
 gas jar with water kept over the shelf by the introduction of the stone pitcher e, full of 
 water. 
 
 lifted steadily on to the shelf, the entry of atmospheric air being prevented 
 by keeping the lower part of the gas jar, called the welt, under the water. 
 Sometimes > the pneumatic trough contains so small a quantity of water 
 that on raising the gas jar to the shelf the liquid does not cover the bottom, 
 and the air rushes up in large bubbles. Under these circumstances it 
 is better to provide a gallon stone jug full of water, so that when the 
 jar is being raised to the shelf it may be thrust into the trough (on the 
 same principle as the crow and the pitcher in the fable), and thus by its 
 bulk (as the stones in the pitcher) raise the water to the proper level. 
 When the gas jar is about half filled with gas the jug may be withdrawn. 
 This arrangement saves the trouble of constantly adding and baling out 
 water from the pneumatic trough. (Fig. 94.) 
 
 There are other solid oxygenized bodies in which the affinities are less 
 powerful, and hence a lower degree of heat suffices to liberate the 
 oxygen gas, and one of the most useful in this respect is the salt termed 
 chlorate of potash. If the substance is heated by itself, the temperature 
 required to expel the oxygen is almost as high as that demanded for 
 the black oxide of manganese ; but, strange to say, if the two substances 
 are reduced to powder, and mixed in equal quantities by weight, then a 
 very moderate increase of heat is sufficient to cause the chlorate of 
 
90 
 
 boy’s playbook of science. 
 
 potash to give up its oxygen, whilst the oxide of manganese undergoes 
 no change whatever. It seems to fulfil only a mechanical office — possibly 
 that of separating each particle of chlorate of potash from the other, so 
 
 „ _ ,. o n < chlorate of potash, 
 
 Fig. 9o. Preparation of oxygen from [ Qxide of ma i lganese . 
 
 2KC10 3 =30 2 x 2KC1. 
 
 that the heat attacks the substance in detail, just as a solid square of 
 infantry might repel almost any attack, whilst the same body dispersed 
 over a large space might be of little use ; so with the chlorate of potash, 
 which undergoes rapid decomposition when mixed with and divided 
 amongst the particles of the oxide of manganese ; less so with the red 
 oxide of iron, and still less with sand or brick-dust. (Fig. 95.) 
 
 This curious fact is explained usually by reference to what is called 
 catalytic action, or decomposition by contact ( Kara , downwards, and Xvco, I 
 unloosen), being a power possessed by a body of resolving another into a new 
 compound without undergoing any change itself. To make this term still 
 clearer, we may notice another example in linen rags, which may be 
 exposed for any length of time to the action of water without fear of 
 conversion into sugar \ if, however, oil of vitriol is first added to the 
 linen rags, and they are subsequently digested at a proper temperature 
 with water, then the rags are converted into sugar (the author has seen 
 a specimen made of an “ old shirt”) ; but, curious to relate, the oil of 
 vitriol is unchanged in the process, and if the process be commenced with a 
 pound of acid, the same quantity is discoverable at the end of the chemical 
 decomposition of the linen rags, and their conversion into sugar. 
 
 If a mixture of equal parts of oxide of manganese and chlorate of 
 potash is placed in a clean Florence flask, with a cork, and pewter, or 
 glass tube attached, great quantities of oxygen are quickly liberated, on 
 the application of the heat of a spirit lamp. Such a retort would cost 
 about fourpence, and if the flask is broken in the operation it can be 
 easily replaced by another, value one penny, as the same cork and tube 
 will generally suit a number of these cheap glass vessels. Corks may 
 
PREPARATION OF OXYGEN GAS. 
 
 91 
 
 always be softened by using either a proper cork squeezer, or by placing 
 them under a piece of board or a flat surface, and rolling and pressing 
 the cork till quite elastic. 
 
 Whilst fitting the latter into the neck of a flask, it is perhaps safer 
 to hold the thin and fragile vessel in a cloth, so that if the flask breaks 
 the chemical experiment may not be arrested for many days by the- 
 se vere cutting and wounding of the fingers. After the cork is fitted, it 
 is to be removed from the flask and bored with a cork borer. This, 
 useful tool is sold in complete sets to suit all sizes of glass tubes, and 
 the pewter or glass being inserted, the flask and tube will be ready for 
 use, provided the tube is bent to the proper curve. This is easy enough 
 to perform with the pewter, but not quite so easy with the glass tube„ 
 which must be held over the flame of a spirit lamp till soft, and then 
 
 Fig. 96. A. The cork squeezer, b. The cork borers, c. The operation of bending the 
 glass tube over the flame of the spirit-lamp. d. The neck of the flask, with cork and tube 
 bent and fitted complete for use. 
 
 bent very gradually to the proper curve. If a short length of the glass- 
 tube is heated, it bends too sharply, and the convexity of the glass is 
 flattened, whilst the internal diameter of the tube is lessened, so that at 
 least three inches in length should be warmed, and the heat must not 
 be continued in one place only, but should be maintained in the direc- 
 tion of the bend, the whole manipulation being conducted without any 
 hurry. (Tig. 96.) 
 
 Having filled a gas jar with oxygen, it may be removed from the 
 pneumatic trough by sliding it into a plate under the surface of the 
 water, and to prevent the stopper being thrust out accidentally from the 
 jar by the upward pressure of the gas, whilst a little compressed, during 
 the act of passing it into the plate, it is advisable to hold the stopper 
 of the jar firmly but gently, so that it cannot slip out of its place. A 
 number of jars of oxygen may be prepared and arranged in plates, all of 
 which of course must contain a little water, and enough to cover the 
 welt of the jar. 
 
92 
 
 boy’s playbook of science. 
 
 EXPERIMENTS WITH OXYGEN GAS. 
 
 This gas was originally discovered by Priestley, in August, 1774, and 
 was first obtained by heating red precipitate — i.e ., the red oxide of 
 mercury. 
 
 2 Hg0=Hg 2 +0 2 
 
 We leave these symbols and figures to be deciphered by the youthful 
 philosopher with the aid of the table of elements, & c., and return to the 
 experiments. 
 
 There are certain thin wax tapers like waxed cord, called bougies, 
 which can be bent to any shape, and are very convenient for experiments 
 with the gases. If one of these tapers is bent as 
 in Eig. 97, then lighted and allowed to burn for 
 some minutes, a long snuff is gradually formed, 
 which remains in a state of ignition when the flame 
 of the taper is blown out. On plunging this into 
 a jar of oxygen, it instantly re-lights with a sort 
 of report, and burns with greatly increased bril- 
 liancy, as described by Dr. Priestley in his first 
 experiment with this gas, and so elegantly repeated 
 by Professor Brande in his refined dissertation on 
 the progress of chemical science. 
 
 “ The 1st of August, 1774, is a red-letter day in 
 the annals of chemical philosophy, for it was then 
 that Dr. Priestley discovered dephlogisticated # air. 
 Some, sporting in the sunshine of rhetoric, have 
 called this the birthday of pneumatic chemistry ; 
 but it was even a more marked and memorable 
 period ; it was then (to pursue the metaphor) that 
 this branch of science, having eked out a sickly and infirm infancy in 
 the ill-managed nursery of the early chemists, began to display symp- 
 toms of an improving constitution, and to exhibit the most hopeful 
 and unexpected marks of future importance. The first experiment, 
 which led to a very satisfactory result, was concluded as follows : — 
 A glass jar was filled with quicksilver, and inserted in a basin of the 
 same; some red precipitate of quicksilver was then introduced, and 
 floated upon the quicksilver in the jar ; heat was applied to it in this 
 situation with a burning-lens, and to use Priestley’s own words, 1 pre- 
 sently found that air teas expelled from it very readily. Having got 
 about three or four times as much as the bulk of my materials , I ad- 
 mitted water into it , and found that it was not imbibed by it. But 
 what surprised me more than I can well express was , that a candle 
 burned in this air with a remai'lcably vigorous flame , very much like that 
 enlarged flame with which a candle burns in nitrous air exposed to iron 
 or lime of sulphur (i.e. t laughing gas) ; but as I had got nothing like 
 this remarkable appearance from any kind of air besides this peculiar 
 
 Fig. 97. 
 
 * From Phlogiston , a word signifying the principle of inflammability. 
 
EXPERIMENTS WITH OXYGEN GAS. 
 
 93 
 
 modification of nitrous air , and 
 I knew no nitrous acid was used 
 in the preparation of mercurius 
 calcinatus } I was utterly at a loss 
 how to account for it” (Fig. 98.) 
 
 Second Experiment. 
 
 The term oxygen is derived 
 from the Greek ( o£vo ■, acid, and 
 ■y€wa< 0 , I give rise to), and was 
 originally given to this element 
 by Lavoisier, who also claimed 
 its discovery ; and if this honour 
 
 is denied him, surely he has de- Pig 98- A Glasa veasel full of mercurjf) con . 
 served equal scientlhc glorymhis taining the red precipitate at the top, and stand- 
 masterly experiments, through ing in the dish b, also containing mercury, o. The 
 i . i r j- i n j i? burning-glass concentrating the sun s rays on the 
 
 which he discovered that tile red precipitate, being Priestley’s original experi- 
 mixture of forty-two parts by ment. 
 
 measure of azote, with eight parts by measure of oxygen, produced a 
 compound precisely resembling our atmosphere. The name given to 
 oxygen was founded on a series of experiments, one of which will now 
 be mentioned. 
 
 Place some sulphur in a little copper ladle 
 attached to a wire, and called a deflagrating 
 spoon, passed through a round piece of zinc 
 or brass plate and cork, so that the latter 
 acts as an adjusting arrangement to fix the 
 wire at any point required. The combus- 
 tion of the sulphur, previously feeble, now 
 assumes a remarkable intensity, and a pecu- 
 liar coloured light is generated, whilst the 
 sulphur unites with the oxygen, and forms 
 sulphurous acid gas. It produces, in fact, 
 the same gas which is formed by burning an 
 ordinary sulphur match. This compound is 
 valuable as a disinfectant, and is a very im- 
 portant bleaching; agent, being most exten- 
 sively employed in the whitening of straw 
 employed in the manufacture of straw bon- 
 nets. It is an acid gas, as Lavoisier found, 
 and this property may be detected by pour- 
 ing a little tincture of litmus into the bot- 
 tom of the plate in which the gas jar stands. 
 
 The blue colour of the litmus is rapidly 
 changed to red, and it might be thought that no further argument 
 could possibly be required to prove that oxygen was the acidifying 
 agent, the more particularly as the result is the same in the next illustration. 
 
 Fig. 99. a. The deflagrating- 
 spoon, b. The cork. c. The 
 zinc, or brass, or tin plate, d d. 
 The gas jar. 
 
boy’s playbook of science. 
 
 
 Third Experiment. 
 
 Cut a small piece from an ordinary stick of phosphorus under 
 water, take care to dry it properly with a cloth, and after placing it 
 in a deflagrating spoon, remove the stopper from the gas-jar, as there 
 is no fear" of the oxygen rushing away, because it is somewhat heavier 
 than atmospheric air ; and then, after placing the spoon with the phos- 
 phorus in the neck of the jar, apply a heated wire and pass the spoon 
 at once into the middle of the oxygen; in a .few seconds a most 
 brilliant light is obtained, and the jar is filled with a white smoke ; 
 -as this subsides, being phosphoric acid, and perfectly soluble in water, 
 the same litmus test may be applied, when it is in like manner 
 changed to red. The acid* obtained is one of the most important con- 
 stituents of bone. 
 
 Fourth Experiment. 
 
 A bit of bark-charcoal bound round with wire is set on fire either 
 by holding it in the flame of a spirit-lamp, or by attaching a small piece 
 •of waxed cotton to the lower part, and igniting this ; the charcoal may then 
 be inserted into a bottle of oxygen, when the most brilliant scintilla- 
 tions occur. After the combustion has ceased and the whole is cool, 
 n little tincture of litmus may also be poured in and shaken about, 
 when it likewise turns red, proving for the third time the generation 
 of an acid body, called carbonic acid — an acid, like the others already 
 mentioned, of great value, and one which Nature employs on a stu- 
 pendous scale as a means of providing plants, &c., with solid char- 
 coal. Carbonic acid, a virulent poison to animal life, is, when properly 
 diluted, and as contained in atmospheric air, one of the chief alimen- 
 tary bodies required by growing and healthy plants. 
 
 In three experiments acid bodies have been obtained ; can we specu- 
 late on the result of the next ? 
 
 Fifth Experiment. 
 
 Into a deflagrating spoon place a bit of potassium, set this on fire 
 by holding it in the spoon in the flame of a spirit-lamp, and then rapidly 
 plunge the burning metal into a bottle of oxygen. A brilliant ignition 
 occurs in the deflagrating spoon for a few seconds, and there is little or no 
 smoke in the jar. The product this time is a solid, called potash, 
 and if this be dissolved in water and filtered, it is found to be clear 
 and bright, and now on the addition of a little tincture of litmus to 
 one half of the solution, it is wholly unaffected, and remains blue ; 
 but if with the other half a small quantity of tincture of turmeric is 
 mixed, it immediately changes from a bright yellow solution to a 
 reddish-brown, because turmeric is one of the tests for an alkali; and 
 thus is ascertained by the help of this and other tests that the result 
 •of the combustion is not an acid , but an alkali. The experiment 
 is made still more satisfactory by burning another bit of potassium 
 in oxygen and dissolving the product in water, and if any portion of 
 
EXPERIMENTS WITH OXYGEN GAS. 
 
 95 
 
 the reddened liquid derived from the sulphurous, phosphoric, and car- 
 bonic acids taken from the previous experiments, be added to separate 
 portions of the alkaline solution, they are all restored to their original blue 
 colour, because an acid is neutralized by an alkali ; and the experiment is 
 made quite conclusive by the restoration of the reddened turmeric to a 
 bright yellow on the addition of a solution of either of the three acids 
 already named. Moreover, an acid need not contain a fraction of 
 oxygen, as there is a numerous class of /zydracids, in which the acidi- 
 fying principle is hydrogen instead of oxygen, such as the hydrochloric, 
 hydriodic, hydro-bromic, and hydrofluoric acids. 
 
 Sixth Experiment. 
 
 A piece of watch-spring is softened at one end, by holding it in the 
 Same of a spirit-lamp, and allowing it to cool. A bit of waxed cotton 
 is then bound round the softened end, and after being set on fire, is 
 plunged into a gas jar containing oxygen; the cotton first burns away, 
 and then the heat communicates to the steel, which gradually takes fire, 
 and being once well ignited, continues to bum with amazing rapidity, form- 
 ing drops of liquid dross, which fall to the bottom of the plate — and also 
 a reddish smoke, which condenses on the sides of the jar; neither the 
 dross which has dropped into the plate, nor the reddish matter condensed 
 on the jar, will affect either tincture of litmus or turmeric; they are 
 neither acid nor alkaline, but neutral compounds of iron, called the 
 sesquioxide of iron (Fe^0 3 ), and the magnetic oxide (Fe 3 0 4 ). 
 
 Seventh Experiment. 
 
 Some oxygen gas contained in a bladder provided with a proper 
 jet may be squeezed out, and upon, some liquid phosphorus con- 
 
 Fig. 100. a. Bladder containing oxygen, provided with a stop-cock and jet leading to, 
 b, b. Finger glass containing boiling water, c. The cup of melted phosphorus under the 
 water. The gas escapes from the bladder when pressed. 
 
 tained in a cup at the bottom of a finger glass full of boiling water, 
 when a most brilliant combustion occurs, proving that so long as the 
 principle is complied with — viz., that of furnishing oxygen to a com- 
 bustible substance — it will burn under water, provided it is insoluble, 
 and possesses the remarkable affinity for oxygen which belongs to 
 phosphorus. The experiment should be performed with boiling water, 
 to keep the phosphorus in the liquid state ; and it is quite as well to hold 
 
96 
 
 boy’s playbook of science. 
 
 a square foot of wire gauze over tlie finger glass whilst the experiment 
 is being performed. (Fig. 100.) 
 
 Eighth Experiment. 
 
 Oxygen is available from many substances when they are mixed with 
 combustible substances, and hence the brilliant effects produced by 
 burning a mixture of nitre, meal powder, sulphur, and iron or steel 
 filings ; the metal burns with great brilliancy, and is 'projected from the 
 case in most beautiful sparks, which are long and needle-shaped with 
 steel, and in the form of miniature rosettes with iron filings ; it is the 
 oxygen from the nitre that causes the combustion of the metal, the 
 other ingredients only accelerate the heat and rate of ignition of the 
 brilliant iron, which is usually termed a gerb. 
 
 Ninth Experiment. 
 
 A mixture of nitrate of potash, powdered 
 charcoal, sulphuj, and nitrate of strontium, 
 driven into a strong paper case about two 
 inches long, and well closed at the end with 
 varnish, being quite waterproof, may be set on 
 fire, and will continue to burn under water 
 until the whole is consumed ; the only precau- 
 tion necessary being to burn the composition 
 from the case with the mouth downward, and 
 if the experiment is tried in a deep glass jar it 
 has a very pleasing effect. (Fig. 101.) 
 
 The red-fire composition is made by mixing 
 nitrate of strontia 40 parts by weight, flowers- 
 of sulphur 13 parts, chlorate of potash 5 parts, 
 sulphuret of antimony 4 parts. These ingre- 
 dients must first be well powdered separately, 
 and then mixed carefully on a sheet of paper 
 with a paper-knife. They are liable to explode 
 if rubbed together in a mortar, on account of 
 the presence of sulphur and chlorate of potash, 
 burning downwards, and at- and the composition, if kept for any time, is 
 
 b“ onerfen^Tto dnk liable to take fire spontaneously, 
 it. c c. Jar containing water. 
 
 Tenth Experiment. 
 
 Some zinc is melted in an iron ladle, and made quite red hot ; if a 
 little dry nitre is thrown upon the surface, and gently stirred into the 
 metal, it takes fire with the production of an intense white light, whilst 
 large quantities of white flakes ascend, and again descend when cold, 
 being the oxide of zinc, and called by the alchemists the “ Philosopher’s 
 Wool” (ZnO). In this experiment the oxygen from the nitre effects 
 the oxidation of the metal zinc. 
 
THE BUDE LIGHT. 
 
 97 
 
 Eleventh Experiment . 
 
 A mixture of four pounds of nitre with two of sulphur and one and 
 a half of lamp black produces a most beautiful and curious fire, con- 
 tinually projected into the air as sparks having the shape of the rowel 
 of a spur, and one that may be burnt with perfect safety in a room, as 
 the sparks consume away so rapidly, in consequence of the finely divided 
 condition of the charcoal, that they may be received on a handkerchief 
 or the hand without burning them. The difficulty consists in effecting the 
 complete mixture of the charcoal. The other two ingredients must 
 first be thoroughly powdered separately, and again triturated when 
 mixed, and finally the charcoal must be rubbed in carefully, till the 
 whole is of a uniform tint of grey and very nearly black, and as the 
 mixture proceeds portions must be rammed into a paper case, and set 
 on fire ; if the stars or pinks come out in clusters, and spread well 
 without other and duller sparks, it is a sign that the whole is well 
 mixed; but if the sparks are accompanied with dross, and are pro- 
 jected out sluggishly, and take some time to burn, the mixture and 
 rubbing in the mortar must be continued ; and even that must not be 
 carried too far, or the sparks will be too small. N.B. — If the lamp-black 
 was heated red hot in a close vessel, it would probably answer better 
 when cold and powdered. 
 
 Twelfth Experiment. 
 
 Into a tall gas jar with a wide neck project some red-hot lamp-black 
 through a tin funnel, when a most brilliant flame-like fire is obtained, 
 showing that finely divided charcoal with pure oxygen would be suf- 
 ficient to afford light ; but as the atmosphere consists of oxygen 
 diluted with nitrogen, compounds of charcoal with hydrogen, are the 
 proper bodies to burn, to produce artificial light. 
 
 Thirteenth Experiment. The Bude 
 Light. 
 
 This pretty light is obtained by pass - 
 ing a steady current of oxygen gas (es- 
 caping at a very low pressure) through 
 and up the centre pipe of an argand oil 
 lamp, which must be supplied with a 
 highly carbonized oil and a very thick 
 wick, as the oxygen has a tendency to 
 burn away the cotton unless the oil is 
 well supplied, and allowed to overflow 
 the wick, as it does in the lamps of the 
 lighthouses. The best whale oil is 
 usually employed, though it would be 
 worth while to test the value of Price’s 
 “Belmontine Oil” for the same pur- 
 pose. (Pig. 102.) Fig. 102. a. Reservoir of oil. b. Tho 
 
 flexible pipe conveying oxygen to centre 
 of the argand lamp. 
 
 H 
 
boy’s playbook of science. 
 
 98 
 
 Fourteenth Experiment. A Red Light. 
 
 Clear out tlie oil thoroughly from the Bude light apparatus ; or, wnat 
 is better, have two lamps, one for oil, and the other for spirit ; fill the 
 apparatus with a solution of nitrate of strontia and chloride of calcium 
 in spirits of wine, and let it burn from the cotton in the same way as 
 the oil, and supply it with oxygen gas. 
 
 Fifteenth Experiment. A Green Eight. 
 
 Dissolve boracic acid and nitrate of baryta in spirits of wine, and 
 supply the Bude lamp with this solution. 
 
 Sixteenth Experiment. A Yellow Light. 
 
 Dissolve common salt in spirits of wine, and burn it as already de- 
 scribed in the Bude light apparatus. 
 
 Seventeenth Experiment. The Oxy-calcium Light. 
 
 This very convenient light is obtained in a simple manner, either by 
 using a jet of oxygen as a blowpipe to project the flame of a spirit 
 lamp on to a ball of lime ; or common coal-gas is employed instead of the 
 
 Fig. 103.— No. 1. a. Oxygen jet. b. The ball of lime, suspended by a wire. c. Spirit 
 
 ^No*. 2. d. Oxygen jet. e. Gas (jet connected with the gas-pipe in the rear by flexible 
 pipe) projected on to ball of lime, f. 
 
 spirit lamp, being likewise urged against a ball of lime. By this plan 
 one bag containing oxygen suffices for the production of a brilliant light, 
 not equal, however, to the oxy-hydrogen light, which will be explained in 
 the article on hydrogen. (Fig. 103.) 
 
 Eighteenth Experiment. 
 
 To show the weight of oxygen gas, and that it is heavier than air, 
 .he stoppers from two bottles containing it may be removed, one bottle 
 /nay be left open for some time and then tested by a lighted taper, when 
 
EXPERIMENTS WITH OXYGEN GAS. 
 
 99 
 
 it will still indicate the presence of the gas, whilst the other may be 
 suddenly inverted over a little cup in which some ether, mixed with a 
 few drops of turpentine, may be burning — the flame burns with much 
 greater brilliancy at the moment when the oxygen comes in contact 
 with it. 
 
 Nineteenth Experiment. 
 
 The theory of the effect of oxygen upon the system when inhaled 
 would be an increase in the work of the respiratory organs ; and it is 
 stated that after inhaling a gallon or so of this gas, the pulse is raised 
 forty or fifty beats per second : the gas is easily inhaled from a large 
 indiarubber bag thrctagh an amber mouthpiece; it must of course be 
 quite pure, and if made from the mixture of chlorate of potash and 
 oxide of manganese, should be purified by being passed through lime 
 and water, or cream of lime. 
 
 Twentieth Experiment. 
 
 There are certain colouring matters that are weakened or destroyed 
 by the action of light and other causes, which deprive them of oxygen 
 gas or deoxidize them. A weak tincture of litmus, if long kept, oftem 
 becomes colourless, but if this colourless fluid is shaken in a bottle 
 with oxygen gas it is gradually restored ; and if either litmus, turmeric, 
 indigo, orchil, or madder, paper, or certain ribbons dyed with the same 
 colouring matters, have become faded, they may be partially restored by 
 damping and placing them in a bottle of oxygen gas. The effect of the 
 oxygen is to reverse the ^oxidizing process, and to impart oxygen to 
 the colouring matters. By a peculiar process indigo may be obtained 
 quite white, and again restored to its usual blue colour, either by ex- 
 posure to the air or by passing a stream of oxygen through it. 
 
 Twenty-first Experiment. 
 
 Messrs. Matheson, of Torringt on- street, Russell-square, prepare 
 in the form of wire some of the rarest metals, such as magnesium, 
 lithium j &c. A wire of the metal magnesium burns magnificently in 
 oxygen gas, and forms the alkaline earth magnesia. The metal lithium, 
 to which such a very low combining proportion belongs — viz., 6'5, can 
 also be procured in the state of wire, and burns in oxygen gas with an 
 intense white light into the alkaline lithia, which dissolved in alcohol 
 with a little acetic acid, and burnt, affords a red flame, making a curious 
 contrast between the effects of colour produced by the metallic and oxi- 
 dized state of lithium. 
 
 THE ALLOTROPIC CONDITION OE OXYGEN GAS. 
 
 The term allotropy (from aWorponos , of a different nature) was 
 first used by the renowned chemist Berzelius. Dimorphism, or diver- 
 sity in crystalline form, is therefore a special case of allotropy, 
 and is most amusingly illustrated with the iodide of mercury (HgL>) 
 which is made either by rubbing together equal combining proportions 
 
200 boy’s playbook of science. 
 
 of mercurv and iodine (both of which are to be fonnd in the Table 
 of Elements page 86), or bv carefully precipitating a solution ofcor- 
 
 mmMmm 
 
 mmmm 
 
 This experiment may be repeated over and over again with 
 the like results.' If some of the 7 scarlet iodide of mercury is sublimed from 
 
 isSS-ssati 
 
 S » the allotropic 
 state of the element oxygen called 
 
 OZONE. 
 
 “S'XS J «S“d lot™, £ 
 
EXPERIMENTS WITH OZONE. 
 
 101 
 
 little distilled water, into 
 which a piece of clean 
 scraped phosphorus is 
 introduced, so as to ex- 
 pose about one-half of 
 its diameter to the air in 
 the bottle, whilst the 
 other is in contact with 
 the water. (Fig. 104.) 
 
 For the sake of pre- 
 caution, the bottle may 
 stand in a basin or soup 
 plate, so that if the 
 phosphorus should take 
 lire, it may be instantly 
 extinguished by pour- 
 ing cold water into the 
 bottle, and should this 
 crack and break, the 
 phosphorus is received 
 into the plate. 
 
 When the ozone is 
 
 Fig. 104. a. A quart bottle, with the stopper loosely 
 placed therein, b. The stick of clean phosphorus, c. The 
 water level just to half the thickness of the phosphorus. 
 Dr. A soup-plate. 
 
 formed the phosphorus can be withdrawn, and the phosphorous-acid 
 smoke washed out by shaking the bottle; it is distinguishable by its 
 smell, and also by its. action on test paper, prepared by painting with 
 starch containing iodide of potassium on some Bath post paper; when 
 this is placed in the bottle containing ozone, it changes the test blue, 
 or rather a purplish blue. 
 
 Ozone is a most energetic body, and a powerful bleaching agent ; if 
 a point is attached, to the prime conductor of an electrical machine, 
 and the electrified air is received into a bottle, it will be found to smell, 
 and has the power of bleaching a very dilute solution of indigo. Ozone 
 
 „ 7*. ^ voltaic battery standing on the stool with glass legs, s s, and 
 
 capable of heating a thm length of platinum wire about two inches long, and bent to form 
 a point between the conducting wires, w w.—N.B. The voltaic current can be cut off at 
 pleasure, so as to cool the wire when necessary, a is the prime conductor of an ordinary 
 cylinder electrical machine, b is the wire conveying the frictional electricity to the 
 conducting wires of the voltaic battery, where the point p being the sharpest point in the 
 arrangement, delivers the electrified and ozonized air. 
 
102 
 
 boy’s playbook of science. 
 
 is not a mere creation of fancy, as it can not only be produced by certain 
 methods, but may be destroyed by a red heat. If a point is prepared 
 with a loop of platinum wire, and this latter, after being connected with 
 a voltaic battery, made red hot, and the whole placed on an insulating 
 stool, and connected with the prime conductor of an electrical machine, 
 it is found that the electrified air no longer smells, the ozone is destroyed; 
 on the other hand, if the voltaic battery is disconnected, and the electri- 
 fied air again allowed to pass from the cold platinum wire, the smell is again 
 apparent, the air will bleach, and if caused to impinge at once upon 
 the iodide of starch test, changes it in the manner already described. 
 (Fig. 105.) 
 
 Ozone is insoluble in water, and oxidizes silver and lead leaf, finely 
 powdered arsenic and antimony ; it is a poison when inhaled in a con 
 centrated state, whilst diluted, and generated by natural processes, it is a 
 beneficent and beautiful provision against those numerous smells originat- 
 ing from the decay of animal and vegetable matter, which might produce 
 disease or death : ozone is therefore a powerful disinfectant. The test for 
 ozone is made by boiling together ten parts by weight of starch, one of iodide 
 of potassium, and two hundred of water ; it may either be painted on 
 Bath post paper, and used at once, or blotting paper may be saturated 
 with the test and dried, and when required for use it must be damped, 
 either before or after testing for ozone, as it remains colourless when 
 dry , but becomes blue after being moistened with water. 
 
 Paper prepared with sulphate of manganese is an excellent test for 
 ozone, and changes brown rapidly by the oxidation of the proto-salt of 
 manganese, and its conversion into the binoxide of the metal. 
 
 Ozone is also prepared by pouring a little sulphuric ether into a 
 quart bottle, and then, after heating a glass rod in the flame of the spirit 
 lamp, it may be plunged into the bottle, and after remaining there a few 
 minutes ozone may be detected by the ordinary tests. 
 
 NITROGEN, OR AZOTE. 
 
 Ntrpov, nitre ; yewac*, I form ; a, privative ; far), life. Symbol, N > 
 combining proportion, 14. Also termed by Priestley, phlogisticated air. 
 
 In the year 1772, Dr. Rutherford, Professor of Botany in the Uni- 
 versity of Edinburgh, published a thesis in Latin on fixed air, in which 
 he says : — “ By the respiration of animals healthy air is not merely 
 rendered mephitic (i.e., charged with carbonic acid gas), hut also suffers 
 another change . For after the mephitic portion is absorbed by a caustic 
 alkaline lixivium , the remaining portion is not rendered salubrious ; and 
 although it occasions no precipitate in lime-water , it nevertheless extin- 
 guishes flame and destroys lifeF Such is the doctor’s account of the 
 discovery of nitrogen, which may be separated from the oxygen in the 
 air in a very simple manner. The atmosphere is the great storehouse 
 of nitrogen, ana four-fifths of its prodigious volume consist of this 
 element 
 
PREPARATION OF NITROGEN GAS. 
 
 103 
 
 Composition of Atmospheric Air . 
 
 Bulk. 
 
 Oxygen 20 
 
 Nitrogen 80 
 
 Weight. 
 
 22*3 
 
 77*7 
 
 100 100 - 
 
 The usual mode of procuring nitrogen gas is to abstract or remove 
 the oxygen from a given portion of atmospheric air, and the only point 
 to be attended to, is to select some substance which will continue to 
 bum as long as there is any oxygen left. Thus, if a lighted taper is 
 placed in a bottle of air, it will only burn for a certain period, and is 
 gradually and at last extinguished; not that the whole of the oxygen is 
 removed or changed, because after the taper has gone out, some burning 
 sulphur may be placed in the vessel, and will continue to burn for a 
 limited period ; and even after these two combustibles have, as it were, 
 taken their fill of the oxygen, there is yet a little left, which is snapped 
 up by burning phosphorus, whose voracious appetite for oxygen is only 
 appeased by taking the whole. It is for this reason that phosphorus is 
 employed for the purpose of removing the oxygen, and also because the 
 product (phosphoric acid) is perfectly soluble in water, and thus the 
 oxygen is first combined, and then washed out of a given volume of air, 
 leaving the nitrogen behind. 
 
 First Experiment. 
 
 To prepare nitrogen gas, it is only 
 necessary to place a little dry phos- 
 phorus in a Berlin porcelain cup on a 
 wine glass, and to stand them in a 
 soup plate containing water. The 
 phosphorus is set on fire with a hot 
 wire, and a gas jar or cylindrical jar 
 is then carefully placed over it, so that 
 the welt of the jar stands in the water 
 in the soup plate. At first, expansion 
 takes place in consequence of the heat, 
 but this effect is soon reversed, as the 
 oxygen is converted into a solid by 
 union with the phosphorus, forming a 
 white smoke, which gradually disap- 
 pears. (Fig. 106.) 
 
 Supposing two grains of phospho- 
 rus had been placed in a platinum 
 tube, and just enough atmospheric air 
 passed over it to convert the whole 
 into phosphoric acid, the weight of 
 the phosphorus would be increased to 
 4^ grains by the addition of 2 \ grains 
 
 Fig. 106. a. Cylindrical glass vessel, open 
 at one end, and inverted over b, the wine- 
 glass, supporting c, the «up containing 
 the burning phosphorus, and the whole 
 standing in a soup-plate, d d, containing 
 water. 
 
104 
 
 boy’s playbook of science. 
 
 of oxygen ; now one cubic inch of oxygen weighs 0 , 34.19, or about |rd 
 of a grain, hence 7*3 cubic inches of oxygen disappear, which weigh 
 as nearly as possible grains, so that as 36 '5 cubic inches of air con- 
 tain 7*3 cubic inches of oxygen, that quantity of air must have passed 
 over the 2 grains of phosphorus to convert it into 4>b grains of phos- 
 phoric acid. 
 
 For very delicate purposes, nitrogen is best prepared by passing air 
 over finely-divided metallic copper heated to redness ; this metal absorbs, 
 the whole of the oxygen and leaves the nitrogen. The finely-divided copper 
 is procured by passing hydrogen gas over pure black oxide of copper. 
 
 Second Experiment. 
 
 A very instructive experiment is performed by heating a good mass of 
 tartrate of lead in a glass tube which is herme cally sealed, and being 
 
 placed on an iron sup- 
 port, is then covered 
 by a capped air jar 
 with a sliding rod and 
 stamper, the whole 
 being arranged in 
 a plate containing 
 water. When the 
 stamper is pushed 
 down upon the glass 
 the latter is broken 
 (Fig. 107), and the air 
 gradually penetrates 
 to the finely divided 
 lead, when ignition oc- 
 curs, and the oxygen 
 is absorbed, as demon- 
 strated by the rise 
 of the water in the 
 jar. On the same 
 principle, if a bottle 
 is filled about one- 
 third full with a liquid 
 amalgam of lead and 
 mercury, and then 
 stopped and shaken 
 for two hours or 
 more, the finely di- 
 vided lead absorbs 
 the oxygen and 
 
 Fig. 107. a. Glass jar, with collar of leather, through which 
 the stamper, c, works, b b. The tube containing the finely- 
 divided lead, paTt of which falls out, and is ignited, and 
 retained by the little tray just below, being part of the iron 
 stand, d d, with crutches supporting the ends of the glass 
 tube, and the whole stands in the dish of water, e e. 
 
 leaves pure nitrogen. Or if a mixture of equal weights of sulphur 
 and iron filings, is made into a paste with water in a thin iron cup* 
 and then warmed and placed under a gas jar full of air standing on the 
 
EXPERIMENTS WITH NITROGEN GAS. 
 
 105 
 
 slielf of the pneumatic trough, or in a dish full of water, the water 
 gradually rises in the jar in about forty-eight hours, in consequence of 
 the absorption of the oxygen gas. 
 
 Third Experiment . 
 
 Nitrogen is devoid of colour, taste, smell, of alkaline or acid qualities ; 
 and, as we shall have occasion to notice presently, it forms an acid 
 when chemically united with oxygen, and an alkali in union with hydro- 
 gen. A lighted taper plunged into this gas is immediately extinguished, 
 while its specific gravity, which is lighter than that of oxygen or air,, 
 is demonstrated by the rule of proportion. 
 
 Weight of 100 cubic 
 inches of air at 60° 
 Fahr., bar. 29'92 in. 
 
 30*829 
 
 Unity. 
 
 Weight of 100 cubic 
 inches of nitrogen at 
 60° Fahr., bar. 29’92 in 
 
 : 29*952 : 
 
 Specific 
 gravity of 
 nitrogen. 
 
 971 
 
 And its levity may be shown very prettily by a 
 simple experiment. Select two gas jars of the 
 same size, and after filling one with oxygen gas 
 and the other with nitrogen gas, slide glass 
 plates over the bottoms of thejars, and proceed 
 to invert the one containing oxygen, placing 
 the neck in a stand formed of a box open at 
 the top; then place the jar containing nitro- 
 gen over the mouth of the first, withdrawing 
 the glass plates carefully ; and if the table 
 is steady the top gas jar will stand nicely 
 on the lower one. Then (having previously 
 lighted a taper so as to have a long snuff) 
 remove the stopper from the nitrogen j al- 
 and insert the lighted taper, which is im- 
 mediately extinguished, and as quickly re- 
 lighted by pushing it down to the lower 
 jar containing the oxygen. This experi- 
 ment may be repeated several times, and is 
 a good illustration of the relative specific 
 gravities of the two gases, and of the im- 
 portance of the law of universal diffusion 
 already explained at p. 6, by which these 
 gases mix , not combine together, and the 
 atmosphere*remains in one uniform state of 
 composition in spite of the changes going 
 on at the surface of the earth. Omitting 
 the aqueous vapour, or steam, ever present 
 in variable quantities in the atmosphere, ten 
 thousand volumes of dry air contain, ac- 
 cording to Graham 
 
 Fig. 108. a. Gas jar containing- 
 nitrogen, n, standing on b, another 
 jar full of oxygen, o. The taper,, 
 c, is extinguished at w, and re- 
 lighted at o. d d. Stand sup- 
 porting the jars. 
 
106 
 
 BO^’S PLAYBOOK. OF SCIENCE* 
 
 Nitrogen 7912 
 
 Oxygen 2080 
 
 Carbonic acid 4 
 
 Carbnretted hydrogen (CH 4 ) ... 4 
 
 Ammonia a trace 
 
 'Fourth Experiment . 
 
 10,000 
 
 It was the elegant, the accomplished, but ill-fated Lavoisier who dis- 
 covered, by experimenting with quicksilver and air, the compound 
 nature of the atmosphere ; and it was the same chemist who gave the 
 name of azote to nitrogen ; it should, however, be borne in mind that it 
 
 does not necessarily 
 follow because a gas 
 extinguishes flame 
 that it is a poison . 
 Nitrogen extinguishes 
 flame, but w r e inhale 
 enormous quantities 
 of air without any ill 
 effects from the nitro- 
 gen or azote that it 
 contains ; on the other 
 hand, many gases that 
 extinguish flame are 
 specific poisons , such as 
 carbonic acid, carbonic 
 oxide, cyanogen, &c. 
 
 Lavoisier’s experi- 
 ment may be repeated 
 by passing into a mea- 
 sured jar, graduated 
 into five equal vo- 
 lumes, four measures 
 
 Fig. 109. a. Gas jar divided into five equal parts, b b. of nitrogen and One 
 Section of pneumatic trough, to show the decantation of gas measure of OXVgeil ; a 
 from one vessel to another. The gas is being passed from c i *',7 j ± v 
 
 to a, through the water. glass P^te should then 
 
 be slid over the mouth 
 
 of the vessel, and it may be turned up and down gently for some little 
 time to mix the two gases, and when the mixture is tested with a lighted 
 taper, it is found neither to increase nor diminish the illuminating power, 
 and the taper burns as it would do in atmospheric air. (Fig. 109.) 
 
PREPARATION OF. HYDROGEN GAS. 
 
 107 
 
 HYDROGEN. 
 
 j°? en (v 5a) p» water ; ycwaa, I give rise to), so termed by Lavoisier 
 —called by -other chemists inflammable air, and phlogiston. Symbol H • 
 combining properties, 1. The lightest known form of matter. 
 
 Every 100 parts by weight of water contain 11 parts of hydrogen 
 gas ; and as the quantity of water on the surface of the earth represents 
 at least two-thirds of the whole area, the source of this gas, like that of 
 oxygen or nitrogen, is inexhaustible. Van Helmont, Mayow, and 
 iiales had shown that certain inflammable and peculiar gases could be 
 obtained, but it was reserved for the rigidly philosophic mind of Cavendish 
 to determine the nature of the elements contained in, and giving a spe- 
 ciahty to the inflammable gases of the older chemists. By acting with 
 dilute acids upon iron, zinc, and tin, Cavendish liberated an inflammable 
 elastic gas; and he discovered nearly all the properties we shall notice 
 in the succeeding experiments, and especially demonstrated the compo- 
 sition of water m his paper read before the Royal Society in the year 
 17 oL 
 
 First Experiment . 
 
 Hydrogen is prepared in a very simple manner, by placing some zinc 
 cuttings in a bottle, to which is attached a cork and pewter or bent 
 glass tube, and pouring upon the metal 
 some dilute sulphuric or hydrochloric 
 acid. Effervescence and ebullition take 
 place, and the gas escapes in large quanti- 
 ties, water being decomposed ; the oxygen 
 passes to the zinc, and forms oxide of 
 zinc, and this uniting with the sulphuric 
 acid forms sulphate of zinc, which may 
 be obtained after the escape of the hy- 
 drogen by evaporation and crystallization. 
 
 (Fig- HO.) 
 
 Zn-f H 2 S0 4 = ZnS0 4 + H 2 ; 
 
 or 
 
 Zn + 2HC1 = ZnCl 2 + H 2 . 
 
 Li nearly all the processes employed 
 for the generation of hydrogen gas, a 
 metal is usually employed, and this fact 
 nas suggested the notion that hydrogen 
 may possibly be a metal, although it is 
 
 the lightest known form of matter ; and it . Fig. no. a. Bottle containing 
 will be observed in all the succeeding expe- cuttin s s and water and fitted 
 riments that a metallic substance will be con! 
 
 employed to take away the oxygen and v ^ s the sulphuric acid to the zino 
 displace the hydrogen. throughthep^ S c. the gM escapcs 
 
108 
 
 boy’s playbook op science. 
 
 Whenever hydrogen is prepared it should be allowed to escape from 
 the generating vessel for a few minutes before any flame is applied, in 
 order that the atmospheric air may be expelled. The most serious acci- 
 dents have occurred from carelessness in this respect, as a mixture ol 
 Hydrogen and air is explosive, and the more dangerous when it takes 
 fire in any close glass bottle. 
 
 Second Experiment . 
 
 If a piece of potassium is confined in a little coarse wire gauze cage, 
 attached to a rod, and thrust under a small jar full of water, placed 
 on the shelf of the pneumatic trough, hydrogen gas is produced with 
 great rapidity, and is received into the gas jar. The bit of potassium 
 being surrounded with water, is kept cool, whilst the hydrogen escaping 
 under the water is not of course burnt away, as it is whenever the metal 
 is thrown on the surface ol water. 
 
 Third Experiment . 
 
 Across a small iron table-furnace is placed about eighteen inches of 
 1-inch gas-pipe containing iron borings, the whole being red-hot ; and 
 attached to one end is a pipe conveying steam from a boiler, or flask, or 
 retort, whilst another pipe is fitted to the opposite end, and passes 
 the pneumatic trough. Directly the steam passes over the red hot iron 
 borings it is deprived of oxygen, which remains with the iron, forming 
 the rust or oxide of iron, whilst the hydrogen, called in this case water 
 acts, escapes with great rapidity. When steam is passed over red-hot 
 charcoal, hydrogen is also produced with carbonic oxide gas, and this in 
 fact is the ordinary process of making water gas, which being puri- 
 fied is afterwards saturated with some volatile hydrocarbon and burnt. 
 At first sight, such a mode of making gas would be thought extremely 
 profitable, and in spite of the numerous failures the discovery (so called) 
 of water gas is reproduced as a sort of chronic wonder; but experience 
 and practice have clearly demonstrated that water gas is a fallacy, and 
 as long at we can get coal it is not worthwhile going through the 
 round-about processes of first burning coal to produce steam ; secondly , 
 
 t’iff. 111. a- Flask containing toater, and producing steam, which passes to tko ron 
 tube *b b, containing the iron borings heated red hot in the charcoal stove 0. Thu 
 hydrogen passes to the jar d, standing on the shelf of the pneumatic trough. 
 
EXPERIMENTS WITH HYDROGEN GAS. 
 
 109 
 
 of burning coal to heat charcoal, over which the steam is passed to be 
 converted into gas, which has then to be purified and saturated with a 
 cheap hydrocarbon obtained from coal or mineral naphtha ; whilst ordi- 
 nary coal gas is obtained at once by heating coal in iron retorts. 
 
 (M* 111.) 
 
 Thus, by the metals zinc, tin, potassium, red-hot iron (and we might 
 add several others), the oxygen of water is removed and hydrogen gas 
 liberated. 
 
 Fourth Experiment . 
 
 If bottles of hydrogen gas 
 are prepared by all the processes 
 described, they will present the 
 same properties when tested un- 
 der similar circumstances. A 
 lighted taper applied to the 
 mouths of the bottles of hydro- 
 gen, which should be inverted, 
 causes the gas to take fire with a 
 slight noise, in consequence of 
 the mixture of air and hydrogen 
 that invariably takes place when 
 the stopper is removed ; on 
 thrusting the lighted taper into 
 the bulk of the gas it is extin- 
 guished, showing that hydrogen 
 possesses the opposite quality to 
 oxygen — viz., that it takes fire, 
 but does not support combustion. 
 By keeping the bottles contain- 
 ing the hydrogen upright, when 
 the stopper is removed the gas 
 escapes with great rapidity, and 
 atmospheric air takes its place, 
 so much so that by the time a 
 lighted taper is applied, instead 
 ol the gas burning quietly, it fre- 
 quently astonishes the operator 
 with a loud pop. This sudden 
 attack on the nerves may be pre- 
 vented by always experimenting 
 with inverted bottles. (Fig. 112.) 
 
 Fig. 112. a. Bottle opened upright, and 
 hydrogen exploding, b. Bottle opened inverted, 
 and hydrogen burning quietly at the mouth. 
 
 Fifth Experiment . 
 
 Hydrogen is 14*47 lighter than air, and for that reason may be passed 
 into bottles and jars without the assistance of the pneumatic trough. 
 One of the most amusing proofs of its levity is that of filling paper bags 
 or balloons with this gas ; and we read, in the accounts of the fetes at 
 
no 
 
 boy’s playbook of science. 
 
 Paris, of the use of balloons ingeniously constructed to represent animals, 
 so that a regular aerial hunt was exhibited, with this drawback only, 
 that nearly all the animals preferred ascending with their legs upwards, 
 a circumstance which provoked intense mirth amongst the volatile 
 Frenchmen. The lightness of hydrogen may be shown in two ways — 
 first, by filling a little goldbeater’s-skin balloon with pure hydrogen 
 (prepared by passing the gas made from zinc and dilute pure sulphuric 
 acid through a strong solution of potash, and afterwards through one 
 of nitrate of silver), and allowing the balloon to ascend; and then 
 afterwards, having of course secured the balloon by a thin twine or strong 
 thread, it may be pulled down and the gas inhaled, when a most curious 
 effect is produced on the voice, which is suddenly changed from a manly 
 bass to a ludicrous nasal squeaking sound. The only precautions 
 necessary are to make the gas quite pure, and to avoid flame whilst 
 inhaling the gas. It is related by Chaptal that the intrepid (quaere, foolish) 
 but unfortunate aeronaut, Mons. Pilate de Rosio, having on one occasion 
 inhaled hydrogen gas, was rash enough to approach a lighted candle, 
 when an explosion took place in his mouth, which he says “ was so 
 violent that he fancied all his teeth were driven out ” Of course, if it 
 were possible to change by some extraordinary power the condition of 
 the atmosphere in a concert-room or theatre, all the bass voices would 
 become extremely nasal and highly comic, 
 whilst the sopranos would emulate railway 
 whistles and screech fearfully ; and supposing 
 the specific gravity of the air was continu- 
 ally and materially changing, our voices 
 would never be the same, but alter day by day, 
 according to the state of the air, so that the 
 “ familiar voice 55 would be an impossibility. 
 
 A bell rung in a gas jar containing air 
 emits a very different sound from that which 
 is produced in one full of hydrogen — a simple 
 experiment is easily performed by passing ajar 
 containing hydrogen over a self-acting bell, 
 such as is used for telegraphic purposes. 
 (Fig. 113.) 
 
 
 H 
 
 Wm 
 
 _U 
 
 
 Fig. 113. a. Stand and bell. 
 b b. Tin cylinder full of hy- 
 drogen, which may be raised or 
 depressed at pleasure, by lifting 
 it with, the knob at the top, 
 when the curious changes in the 
 sound of the bell are audible. 
 
 Sixth Experiment. 
 
 Some of the small pipes from an organ 
 may be made to emit the most curious sounds 
 by passing heavy and light gases through 
 them ; in these experiments bags containing 
 the gases should be employed, which may 
 drive air, oxygen, carbonic acid, or hydrogen, 
 through the organ pipes at precisely the 
 same pressure. 
 
BALLOONS AND AEROSTATION. 
 
 Ill 
 
 Seventh Experiment. 
 
 One of those toys called “ The Squeak- 
 ing Toy” affords another and ridiculous 
 example of the effect of hydrogen on sound, 
 when it is used in a jar containing this 
 gas. (Fig. 114.) 
 
 Eighth Experiment. 
 
 An accordion played in a large receptacle 
 containing hydrogen gas demonstrates still 
 more clearly what would be the effect of 
 an orchestra shut up in a room containing 
 a mixture of a considerable portion of 
 hydrogen with air, as the former, like 
 nitrogen, is not a poison, and only kills in 
 the absence of oxygen gas. 
 
 Ninth Experiment . 
 
 Some very amusing experiments with 
 balloons have been devised by Mr. Darby, 
 the eminent firework manufacturer, by 
 which they are made to carry signals of three kinds, and thus the 
 motive or ascending power may be utilized to a certain extent. 
 
 Mr. Darby’s attention was first directed to the manufacture of a 
 good, serviceable, and cheap balloon, which he made of paper, cut with 
 mathematical precision; the gores or divisions being made equal, 
 and when pasted toge her, strengthened by the insertion of a string 
 at the juncture; so that the skeleton of the balloon was made of 
 string, the whole terminating in the neck, which was further stif- 
 fened witl_ calico, and completed when required by a good coating 
 of boiled * II. These balloons are about nine feet high and five feet in 
 diameter : the widest part, exactly like a pear, and tapering to the 
 neck in the most graceful and elegant manner. They retain the hydrogen 
 gas remarkably well for many hours, and do not leak, in consequence of 
 the papei* of which they are made being well selected and all holes 
 stopped, and also from the circumstance of the pressure being so well 
 distributed over the interior by the almost mathematical precision with 
 which th 3y are cut, and the careful preparation of the paper with proper 
 varnish. One of their greatest recommendations is cheapness; for 
 whilst a gold-beater’s skin balloon of the same size would cost about 5/., 
 these can be furnished at 5s. each in large quantities. 
 
 A balloon required to carry one or more persons must be constructed 
 of the best materials, and cannot be too carefully made ; it is therefore 
 a somewhat costly affair, and as much as 200/., 500/., and even 1000/. 
 have been expended in the construction of these aerial chariots. 
 t The chief points requiring attention are : — first, the quality of the 
 silk ; secondly, the crecision and scrupulous nicety required in cutting 
 
 Fig. 114. The squeaking toy, used 
 in a jar of hydrogen. 
 
112 
 
 boy’s playbook op science. 
 
 out and joining tlie gores ; thirdly, the application of a good varnish to 
 fill np the pores of the silk, which must be insoluble m water, and suf- 
 ficiently elastic not to crack. ....... 0 . 
 
 The usual material is Indian silk (termed Corah silk), at from 2s. to 
 
 2s. 6 d. per yard. , , „ . , , , 
 
 The gores or parts with which the balloon is constructed require, as 
 before stated, great attention ; it being a common saying amongst 
 aeronauts, “ that a cobweb will hold the gas if properly shaped , the 
 object being to diffuse the pressure equally over the whole bag or 
 
 ^The varnish with which the silk is rendered air-tight can be made 
 according to the private recipe of Mr. Graham, an aeronaut, who states 
 that he uses for this purpose two gallons of linseed oil (boiled), two 
 ditto (raw), and four ounces of beeswax; the whole being simmered 
 together for one hour, answers remarkably well, and the varnish is 
 tough and not liable to crack. 
 
 for repairing holes in a balloon, Mr. Graham recommends a cement 
 composed of two pounds of black resin and one pound of tallow, 
 melted together, and applied on pieces of varnished silk to the apertures. 
 
 The actual cost of a balloon will be understood from information also 
 derived from Mr. Graham. His celebrated “ Victoria Balloon, wlncii 
 has passed through so many hairbreadth escapes, was sixty-five leet 
 highland thirty-eight feet in diameter in the broadest part ; and tfio 
 following articles were used in its construction 
 
 1400 yards of Corah silk, at 2s. 6c?. per yard 
 The netting weighed 70 lbs. . . . • • 
 
 Extra ropes weighed 20 lbs. at 2s. per lb. . 
 
 The car weighed 25 lbs 
 
 Varnish, wages, &c. . 
 
 £ 
 
 175 
 
 20 
 
 2 
 
 7 
 
 16 
 
 d. 
 
 0 
 
 0 
 
 0 
 
 0 
 
 0 
 
 £22C* 0 0 
 
 Thirty-eight thousand cubic feet of coal gas were required to fill this 
 balloon, charged by one company 20/., by others from 9/. to 10/. ; ana 
 ei°*ht men were required to hold the inflated baggy monster. 
 
 Immense journeys have occasionally been sately accomplished by 
 means of balloons, and one of the most noteworthy excursions ot this kind 
 was that undertaken in the year 1836 by the celebrated English aeronaut 
 Green. The distance traversed upon this memorable occasion was no 
 less than 1200 miles, namely, from London to Germany. The balloon 
 rose from the metropolis at noon, and in lour hours time it was above 
 the sea. Not knowing to which quarter of the globe his trail ship 
 might choose to steer, the intrepid voyager had provided himself with 
 passports to different European states, as well as with a supply ot pro- 
 visions in case his descent might have been delayed by untoward cir- 
 cumstances. He was accompanied by two friends. Midnight found 
 the travellers above Liege, the town being visible by the number ot 
 
AEROSTATION. 
 
 113 
 
 twinkling stars which represented the lamps of that busy town One 
 of the travellers thus describes his sensations : “ A biack profound 
 abyss surrounded us on all sides, and, as we attempted to penetrate 
 into the mysterious deeps, it was with difficulty we could beat back the 
 idea and the apprehension that we were making a passage through an 
 immense mass of black marble, in which we were enclosed, and which 
 proach°” W ' m * ^ inches of us, appeared to open up at our ap- 
 
 Alter a long and anxious night, during which, owing to the sinra- 
 lanty of the position sleep was impossible, the day gradually dawned, 
 and the three travelers found themselves placidly sailing above a fertile 
 country through which flowed the beautiful river Rhine. In a few 
 hours they let some of the gas escape, and accomplished a safe descent 
 at Nassau. 1 he entire journey occupied less than twenty hours, and 
 it is worthy of notice that sufficient gas remained in the balloon to have 
 doubled or even treb ed the distance traversed had the aeronauts 
 wished to do so. Balloons of extremely large dimensions have more 
 than once been constructed, but have mostly proved to be wholly un- 
 manageable. One of the largest was made some years back at New 
 Xork, when t ie bold project of crossing the Atlantic by its aid was 
 seriously ente rtained. It was perhaps a fortunate circumstance for the 
 would-be passengers, that the machine, owing to faulty manufacture 
 split into nbl ons during its inflation. ’ 
 
 • S | U Q°^ an0 ^ er jnons tei-baiio°n was the “Geant” contracted for Nadar 
 in 1863. The car ot this balloon, which was subsequently exhibited, 
 at the Crys.al Palace, Sydenham, was a little two-storied house 
 containing every domestic convenience. The immense machine started’ 
 ITh.T °'\f aQda y>p cf - 18th, 1863, and, after sailing over Belgium 
 and Holland, descended m Hanover m such a disastrous manner that it 
 
 his a iif e atter l0r W °“ der that any ° f itS ihirtee “ P assen S ers scaped with 
 
 The voyagers, however, in ignorance of what awaited them seem to 
 
 h I- , j k • r m °%F eartL ln the biggest spirits. After having 
 satiated the..- .ves with the lovely panorama spread out below theni 
 there was a general demand for dinner. Every one eat with unusual 
 appetite, and numberless champagne bottles were speedily emptied. 
 But as darkness iell upon them the travellers found themselves en- 
 veloped m a dense fog, a fog so damp that they were all very SO on 
 
 firill t H r °K U t Sh t0 th f- S u m ' - There ' vaS no moon that ni gH and as arti- 
 
 al lights were disallowed, the gloom of the passengers can be better 
 
 imagined^ than described “ the water,” writes one of these unfor- 
 , W ! nch i ad , c °Ufi°ted on the balloon during its ascent, now 
 F S F F F ake e ,K e ? t ,? ud , caused 'F to desc end with such rapidity into 
 the dark abyss that the ballast, which was immediately thrown over- 
 board, was overtaken m its descent, and fell on our heads again.” The 
 balloon eventually came to the ground with an awful shock, and the 
 passengers narrowly escaped with their lives. 
 
114 
 
 boy’s playbook of science. 
 
 The Geant made one more voyage which had a still more disastrous 
 termination. On this occasion nine passengers occupied the car. They 
 descended during a high wind, and the balloon, dragging away the 
 grappling irons which were thrown out to catch the ground, was 
 bumped along the earth at a terrific speed, carrying away telegraph 
 wires and posts, and indeed everything which offered an obstacle to its 
 fearful career. It was eventually brought to a stop by becoming 
 entangled in a wood at Hanover, and many broken limbs and other 
 serious injuries were received by the passengers as mementoes of 
 their foolhardy enterprise. 
 
 The most perfect, as well as the largest balloon ever constructed, was 
 that which rose during the 1878 Exhibition at Paris. This balloon was 
 designed and owned by M. Henry Giffard, who is perhaps better known 
 by the steam injector of which he is the inventor. It measured more 
 than 100 feet in diameter ; a size which can be better estimated when 
 it is stated that 100 girls were employed for one month in sewing its 
 seams together. It was what is called a “ captive balloon,” that is 
 to say, it was held by a stout rope which was wound on a steam drum. 
 This rope allowed an ascent of 600 metres ; a height sufficient to give 
 an all-round view of the surrounding country for sixty miles. A special 
 fabric was used in the construction of this balloon. It consisted of 
 alternate layers of india-rubber, cloth, and canvas. It \7as filled with 
 pure hydrogen, which is much lighter than the carburet ted hydrogen 
 supplied by the gas companies, and which of course therefore gives 
 greater ascending power. The balloon was capable of lifting a weight 
 of twenty-two tons, and fifty passengers could find accommodation in its 
 car. Our Prince and Princess of Wales were among the passengers 
 during their visit to the Exhibition. 
 
 This balloon, by its daily ascents, earned so much money for its 
 owner, that it was decided that it should again go up the following 
 year. But one day, during an unusually high wind, it w-^s rent from 
 top to bottom. Thus perished the most perfect aerial machine ever 
 made ; its destruction representing a loss of -£90,000. 
 
 Balloons have been more than once used for scientific purposes both 
 in Erance and England. An ascent in the former country was so 
 fruitful in its results, that the Academy of Sciences immediately voted 
 a large sum to cover the expense of another ascent. Accordingly the 
 same balloon ascended with three well-known scientists, namely, 
 M. Tissandier, Captain Sivel, both experienced aeronauts, and M. Croce- 
 Spinelli. By some mischance the balloon was allowed to attain a 
 height where respiration was almost impossible, and in the sequel 
 M. Tissandier returned to the earth with his two companions lying dead 
 at the bottom of the car. 
 
 In this country the most famous scientific ascents have been made 
 by Mr. Glaisher, accompanied by the celebrated balloonist Coxwell. 
 In one of these ascents both of these gentlemqn nearly lost their lives. 
 They both lost the use of their hands for a time, indeed, Mr. Glaisher 
 
AEROSTATION. 
 
 115 
 
 oecame quite insensible. His companion had just enough strength left 
 to grasp the valve cord with his teeth, so as to let out some of the gas, 
 when the descent of course began, and they were eventually saved. On 
 this occasion a height of no less than seven miles was attained. We 
 may therefore note this as the extreme limit to which a man may 
 venture above the earth without sacrificing his life, and we may be 
 quite sure that under no circumstances could he remain there except for 
 an extremely brief period. 
 
 The balloon was recognised at a very early date as an important aid 
 to warfare. As early as the year 1794, the French armies were 
 provided with two companies of aeronauts. Placed in the car of a 
 balloon these men signalled to their comrades below as to the position 
 and movements of the enemy’s troops. France, where the first balloon 
 was made (by the brothers Montgolfier), has perhaps paid more atten- 
 tion to this special application of it than any other country, and her 
 endeavours to make balloons useful in this way never met with 
 more marked success than in the late siege of Paris. At this eventful 
 period a regular balloon post was organised, and by its aid thousands 
 of letters found their way to anxious friends outside the confines 
 of the city. Two of these balloons were carried out to sea and lost, 
 some fell into the enemy’s hand, but the majority escaped to friendly 
 territory. 
 
 Our own war authorities have recently become alive to the importance 
 of using balloons for military purposes, and a select committee was 
 lately appointed to report upon the subject. A series of experiments 
 were also lately carried out at Woolwich under the direction cf Captain 
 Templar, and some of the results recorded are most striking and 
 interesting. Speaking of these experiments the Standard remarks : — 
 “A system of directing the balloon to favourable positions by a rope 
 attached to a wagon drawn by horses has also been tried with success, 
 and all the details of passing through forests, over rivers, and under 
 bridges have been ingeniously provided for.” The generation of 
 hydrogen in the field is accomplished by passing steam over red-hot 
 iron by means of a portable stove ; the manner in which this can be 
 accomplished is sufficiently detailed in the experiment on page 108. 
 As a result of these trials at Woolwich, two balloons have actually been 
 placed in commission. 
 
 Commander Cheyne, who has served on three Arctic explorations, is 
 jonfident, from experiments made in those regions, that the balloon 
 can be made a most useful adjunct to the equipment for a future 
 expedition to the North Pole. It is quite impossible to detail the 
 plans which he has elaborated, but they seem to be feasible. He 
 estimates the _ expense of such an enterprise at £30,000, which he 
 proposes to raise by means of subscriptions throughout the United 
 Kingdom and Canada. With this view he has already organised more 
 than fifty local Arctic committees, and we may do well to wish him all 
 the success which he undoubtedly deserves. 
 
 i 2 
 
116 
 
 boy’s playbook of science. 
 
 A night ascent witnessed at any of the public gardens is certainly a 
 stirring scene, particularly if the wind is rather high. On approaching^ 
 the balloon, swayed to and fro by the breeze, it seems almost capable of 
 crushing the bold individual who would venture beneath it; seen as a 
 large dark mass in the yet dimly-lighted square, it appears to be inca- 
 pable of control ; when the inflation is completed, the aeronaut, all im- 
 portance, seats himself in the car, and blue lights, with other fire- 
 works, display the victim who is to make a “ last ascent,” or perhaps 
 descent . Finally the word is given, the ropes are cast off, and the bulky 
 chariot rises majestically to the sound of the National Anthem. The- 
 crowd see no more, but the day’s Times reports the end of the aerial 
 journey. 
 
 Balloons can never be of any permanent value as means.of locomotion 
 until they can be steered ; and this is a problem, the solution of which is 
 something like perpetual motion. In the first place, a balloon of any 
 size exposes an enormous surface to the pressure and force of the winds ; 
 and when we consider that they move at the rate of from three to 
 eighty miles per hour, it will be understood that the fabric of a balloon 
 itself must give way in any attempt to tear, work, or pull it against 
 such a force. Secondly and lastly, the power has not yet been created 
 which will do all this without the inconvenience of being so heavy that 
 the steering engine fixes the balloon steadily to the earth by its 
 obstinate gravity. 
 
 When engines of power are constructed without the aeronaut s 
 obstacle of weight — when balloons are made of thin copper .or sheet- 
 iron — then we may possibly hear of the voyage of the good ship Aerial , 
 bound for any place, and quite independent of dock, port, and the- 
 host of dues ( quere ) which the sea-going ships have to disburse. 
 It is, however, gratifying to the zeal and perseverance of those who 
 dream of aerial navigation, to know that a balloon is not quite useless ; 
 and here we may return to the consideration of Mr. Darby’s signals, 
 which are of various kinds, and intended to appeal to the senses by 
 night as well as by day ; and first, by audible sounds. Such means 
 have long been recognised, from the . ancient float and bell of the 
 “Inchcape Bock,” to the painful minute-gun at sea, or the shrill- 
 railway whistle and detonating signals employed to prevent the horrors 
 of a collision between two trains. The signal sounds are produced by 
 the explosion of shells capable of yielding a report equal to that of a six- 
 pounder cannon, and they are constructed in a very simple manner. A 
 nail, composed of wood or copper, and made up by screwing together the- 
 two hemispheres, is attached to a shaft or tail of cane or lance-w ood, 
 properly feathered like an arrow ; at the side opposite to that of the 
 arrow — vi^., at its antipodes — is placed a slight protuberance containing 
 a minute bulb of glass filled with oil of vitriol, and surrounded with a 
 mixture of chlorate of potash and sugar, the whole being protected 
 with gutta-percha, and communicating by a touch-hole with the intenor, 
 which is of course filled with gunpowder. These shells are attached 
 
BALLOON SIGNALS. 
 
 117 
 
 to a circular framework by a strong whipcord, which passes to a 
 central fuse, and are detached one after the other as the slow fuse 
 (made hollow on the principle of the argand lamp) burns steadily 
 away. Directly a shell falls to the ground, the little bulb containing 
 the oil of vitriol breaks, and the acid coming in contact with the 
 chlorate of potash and sugar, causes the mixture to take fire, when 
 the gunpowder explodes. During the siege of Sebastopol many 
 
 Fig. 115 . a. Bing attached to balloon, carrying an 
 hexagonal framework with six shells, b. Hollow fuse, 
 which burns slowly up to the strings, and detaches each 
 shell in succession, c. Section of shell. The shaded 
 portion represents the gunpowder. 
 
 similar mines were prepared by the Russians in the earth, so that 
 when an unfortunate soldier trod upon the spot, the concealed mine 
 blew up and seriously injured him; such petty warfare is as bad as 
 shooting sentries, and a cruel application of science, that unnecessarily 
 increases the miseries of war without producing those grand results 
 for which the truly great captains, Wellington and Napoleon, only 
 warred. (Fig. 115.) 
 
118 
 
 BOY’S PLAYBOOK OF SCIENCE. 
 
 The bill distributor consists of a long piece of wood, to which are 
 attached a number of hollow fuses, with packets of bills, protected from 
 being burned or singed by a thin tin plate ; 10,000 or 20,000 bills can 
 thus be delivered, and the wind assists in scattering them, whilst the 
 balloon travels over a distance of many miles. It must be recollected 
 that in each case the shells and the bills are detached by the string 
 burning away as the fire creeps up from the fuse. (Fig. 116.) 
 
 i 
 
 Fig. 116. The bill distributor, consisting of three hollow fuses, 
 with bills attached in packets. 
 
 Another most ingenious arrangement, also prepared by Mr. Darby,, 
 is termed by the inventor, the “ Land and Water Signal,” and may be 
 thus described : — A short hollow ball of gutta-percha, or other con- 
 venient material, five or six inches in diameter, and filled with printed 
 bills, or the information, whatever it may be, that is required to be sent, 
 is attached to a cap to which a red flag, having the words “ Open the 
 shell,” and four cross sticks, canes, or whalebones with bits of cork at 
 equal distances, are fitted. The whole is connected by a string to the 
 fuse as before described. These signals are adapted for land and water : 
 
BALLOON SIGNALS. 
 
 119 
 
 in either case they fall upright, and in consequence of the sticks pro- 
 jecting out they float well in the water, and can be seen by a telescope . 
 at a distance of three miles. (Fig. 117.) Many of these signals were 
 sent away by Mr. Darby from Yauxhall ; one was picked up at Har- 
 wich, another at Brighton, a third at Croydon ; in the latter case it 
 was found by a cottager, who, fearing gunpowder and combustibles. 
 
 Fig. 117. The land and water signal, which remains upright 
 on land, or floats on the surface of water, a. The water-tight 
 
 f utta-percha shell, comaining the message or information, bbb. 
 
 ticks of cane to keep the flag in an upright position : at the 
 end are attached cork bungs. 
 
 did not examine the shell, but having mentioned the circumstance to 
 a gentleman living near him, they agreed to cut it open; and intelli- 
 gence of their arrival, in this and the other cases, was politely forwarded 
 to Mr. Darby at Vauxhall Gardens. 
 
 Balloons, like a great many other clever inventions, have been despised 
 by military men as new-fangled expedients ; toys, which may do very well 
 to please the gaping public, but are and must be useless in the field. 
 Over and over again it has been suggested that a balloon corns for 
 observation should be attached to the British army, but the scheme has 
 
120 
 
 boy’s playbook of science. 
 
 teen rejected, although the expense of a few yards of silk and the gene- 
 ration of hydrogen gas would be a mere bagatelle as compared with the 
 transport and use of a single 32-pounder cannon. The antiquated notions 
 ®f octogenarian generals have, however, received a great shock in the 
 fact that the Emperor Napoleon III. was enabled, by the assistance of 
 a captive balloon, to watch the movements and dispositions of the 
 Austrian troops ; and with the aid of the information so obtained, he 
 made his preparations, and was rewarded by the victory of Solferino ; 
 and as soon as the battle was over Napoleon III. occupied at Cavriana 
 the very room and ate the dinner prepared for his adversary, the Emperor 
 Erancis Joseph. 
 
 Over and over again the most excellent histories have been written of 
 aerostation, but they all tend to one truth, and that is, the great danger 
 and risk of such excursions ; and to enable our readers to form their 
 own judgment, a chronological list of some of the most celebrated 
 aeronauts, &c., is appended. 
 
 1675. Bernair attempted to fly — killed . 
 
 1678. Besnier attempted to fly. 
 
 1772. L 5 Abb6 Desforges announced an aerial chariot. 
 
 1783. Montgolfier constructed the first air balloon. 
 
 „ Roberts freres , first gas balloon, destroyed by the peasantry of 
 
 Geneva, who imagined it to be an evil spirit or the moon. 
 
 1784. Madame Thible, the first lady who was ever up in the clouds; 
 
 she ascended 13,500 feet. 
 
 „ Duke de Chartres, afterwards Egalite Orleans, travelled 135 
 miles in five hours in a balloon. 
 
 „ Testu de Brissy, equestrian ascent. 
 
 „ D’Achille, Desgranges, and Chalfour— Montgolfier balloon. 
 
 „ Bacqueville attempted a flight with wings. 
 
 „ Lunardi — gas balloon. 
 
 „ Rambaud — Montgolfier balloon, which was burnt. 
 
 „ Andreani — Montgolfier balloon. 
 
 1785. General Money — gas balloon, fell into the water, and not rescued 
 
 for six hours. 
 
 „ Thompson, in crossing the Irish Channel, was run into with the 
 bowsprit of a ship whilst going at the rate of twenty miles 
 per hour. 
 
 „ Brioschi — gas balloon ascended too high and burst the balloon ; 
 
 the hurt he received ultimately caused his death. 
 
 „ A Venetian nobleman and his wife — gas balloon — killed. 
 
 „ Pilatre de Roziers and M. Romain — gas balloon took fire^-both 
 killed . 
 
 1806. Mosment — gas balloon — killed. 
 
 „ Olivari — Montgolfier balloon — killed . 
 
 1808. Degher attempted a flight with wings. 
 
 1812. Bittorf — Montgolfier balloon — killed. 
 
 1819. Blanchard, Madame — gas balloon — killed. 
 
BALLOON ACCIDENTS. 
 
 121 
 
 1819. Gay Lussac — gas balloon, ascended 23,040 feet above the level 
 of the sea. Barometer 12*95 inches ; thermometer 14*9 Bah. 
 
 „ Gay Lussac and Biot — gas balloon for the benefit of science. 
 Both philosophers returned safely to the earth. 
 
 1824. Sadler — gas balloon — killed . 
 
 „ Sheldon — gas balloon. 
 
 „ Harris — gas balloon — killed. 
 
 1836. Cocking — parachute from gas balloon — killed. 
 
 1847. Godard. — Montgolfier balloon fell into and extricated from the 
 Seine. 
 
 1850. Poitevin, a successful French aeronaut. 
 
 „ Gale, Lieut. — gas balloon — killed. 
 
 „ Bixio and Barral — gas balloon. 
 
 „ Graham, Mr. and Mrs. — -gas balloon. — Serious accident ascending 
 
 near the Great Exhibition in Hyde Park. 
 
 „ Green, a most successful aeronaut. 
 
 1862. Coxweli — narrow escape. 
 
 „ Glaisner — narrow escape. 
 
 1871. He Groof — flying machine from Chelsea — killed. 
 
 1874. Sivel — killed. . 
 
 „ Croce Spinelli — killed. 
 
 „ Tissandier— escaped. 
 
 Of the 47 persons enumerated, 17 were killed, and nearly all the 
 aeronauts met with accidents which might have proved fatal. 
 
 Fig. 118. Flying machine {theoretical). 
 
122 
 
 boy’s playbook of science. 
 
 Tenth Experiment. 
 
 Soap bubbles blown with hydrogen gas ascend with great rapidity, 
 and break against the ceiling ; if interrupted in their course with a 
 lighted taper they burn with a slight yellow colour and dull report. 
 
 Eleventh Experiment . 
 
 By constructing a pewter mould in two halves, of the shape of a 
 tolerably large flask, a balloon of collodion may be made by pouring the 
 collodion inside the pewter vessel, and taking care that every part is 
 properly covered ; the pewter mould may be warmed by the external 
 application of hot water, so as to drive off the ether of the collodion, 
 and when quite dry the mould is opened and the balloon taken out. 
 Such balloons may be made and inflated witli hydrogen by attaching to 
 them a strip of paper, dipped in a solution of wax and phosphorus, and 
 sulphuret of carbon ; as the latter evaporates, the phosphorus takes fire 
 and spreads to the balloon ; which burns with a slight report. The pewter 
 mould must be very perfectly made, and should be bright inside ; and if 
 the balloons are filled with oxygen and hydrogen, allowing a sufficient 
 excess of the latter to give an ascending power, they explode with a 
 loud noise directly the fire reaches the mixed gases. 
 
 Twelfth Experiment. 
 
 In a soup-plate place some strong soap and water ; then blow out 
 a number of bubbles with a mixture of oxygen and hydrogen ; a loud 
 report occurs on the application of flame, and if the room is small the 
 window should be placed open, as the concussion of the air is likely to 
 break the glass. 
 
 Thirteenth Experiment. 
 
 Any noise repeated at least thirty-two times in a second produces a 
 musical sound, and by producing a number of small explosions of 
 hydrogen gas inside glass tubes of various sizes, the most peculiar 
 sounds are obtained. The hydrogen flame should be extremely small, 
 and the glass tubes held over it may be of all lengths and diameters ; 
 a trial only will determine whether they are fit for the purpose or not. 
 
 Fourteenth Experiment. 
 
 Flowers, figures, or other designs, may be drawn upon silk with a 
 solution of nitrate of silver, and the whole being moistened with water, 
 is exposed to the action of hydrogen gas, which removes the oxygen 
 from the silver, and reduces it to the metallic state. 
 
 In like manner designs drawn with a solution of chloride of gold are 
 produced in the metallic state by exposure to the action of hydrogen 
 gas. Chloride of tin, usually termed muriate of tin, may also be 
 reduced in a similar rnanne care being taken in these experiments that 
 
 
EXPERIMENTS WITH HYDROGEN. 
 
 123 
 
 the fabric upon which the letters, figures, or designs are painted with 
 the metallic solution be kept quite damp whilst exposed to the 
 hydrogen gas. 
 
 Fifteenth 'Experiment. 
 
 A mixture of two volumes of hydrogen with one volume of oxygen 
 explodes with great violence, and produces two volumes of steam, which 
 condense against the sides of the strong glass vessel, in which the 
 experiment may be made, in the form of water. As the apparatus 
 called the Cavendish bottle, by which this experiment only may be 
 safely performed, is somewhat expensive, and requires the use of an 
 air-pump, gas jars with stop-cocks, and anelectrical machine and Leyden 
 jar, other and more simple means may be adopted to show the combi- 
 nation of oxygen and hydrogen, and formation of water. 
 
 If a little alcohol is placed in a cup and set on fire, whilst an empty 
 cold gas jar is held over the flame, an abundant deposition of moisture 
 takes place from the combustion of the hydrogen of the spirits of wine. 
 Alcohol contains six combining properties of hydrogen, with four of 
 charcoal and two of oxygen. If a lighted candle, or an oil, camphine, 
 Belmontine, or gas flame, is placed under a proper condenser, large 
 quantities of water are obtained by the combustion of these substances 
 (Fig. 119). 
 
 Fig. 119. a. A burning candle, or oil or gas lamp. Copper bead and long pipe fitting 
 Into b c, the receiver from which the condensed water drops into d. e e. Two corks 
 fitted, between which is folded some wet rag. 
 
124 
 
 boy’s playbook of science. 
 
 Sixteenth Experiment, 
 
 During the combustion of a mixture of two volumes of hydrogen with 
 one of oxygen, an enormous amount of heat is produced, which is use- 
 fully applied in the arrangement of the oxy-hydrogen blowpipe. The 
 flame of the mixed gases produces little or no light, but when directed 
 on various metals contained in a small hole made in a fire brick, a most 
 intense light is obtained from the combustion of the metals, which is 
 rariously coloured, according to the nature of the substances employed. 
 With cast-iron the most vivid scintillations are obtained, particularly if 
 after having fused and boiled the cast-iron with the jet of the two gases, 
 one of them, viz., the hydrogen, is turned off, and the oxygen only 
 directed upon the fused ball of iron, then the carbon of the iron burns 
 with great rapidity, the little globule is enveloped in a shower of sparks, 
 and the whole affords an excellent notion of the principle of Bessemer’s 
 patent method of converting cast-iron at once into pure malleable iron, 
 or by stopping short of the full combustion of carbon, into cast-steel. 
 
 The apparatus for conducting these experiments is of various kinds, 
 and different jets have been from time to time recommended on account 
 of their alleged safety. It may be asserted that all arrangements pro- 
 posed for burning any quantity of the mixed gases are extremely dan- 
 gerous : if an explosion takes place 
 it is almost as destructive as gun- 
 powder, and should no particular 
 damage be done to the room, there 
 is still the risk of the sudden vibra- 
 tion of the air producing permanent 
 deafness. If it is desired to burn 
 the mixed gases, perhaps the safest 
 apparatus is that of Gurney ; in this 
 arrangement the mixed gases bubble 
 up through a little reservoir of water, 
 and thus the gasholder — viz., a 
 bladder, is cut off from the jet when 
 the combustion takes place. (Big. 
 120.) This jet is much recom- 
 mended by Mr. Woodward, thehighly 
 respected President of the Islington 
 Literary and Scientific Institution, 
 and may be fitted up to show the phenomena of polarized light, the 
 microscope, and other interesting optical phenomena. 
 
 Mr. Woodward states, that a series of experiments, continued during 
 many years, has proved, that while the bladder containing the mixed 
 gases is under pressure, the flame cannot he made to pass the safety 
 chambers, and consequently an explosion is impossible ; and even if 
 through extreme carelessness or design, as by the removal of pressure or 
 4he contact of a spark with the bladder, an explosion occurs, it can 
 produce no other than the momentary effect of the alarm occasioned by 
 
 u 
 
 Fig. 120. Gurney’s jet. a. Pipe with 
 stop-cock leading from the gas-holder. 
 B. The little reservoir of water through 
 which the mixed gases bubble, c. The 
 jet where the gases burn. d. Cork, which 
 is blown out if the flame recedes in the 
 pipe, c. 
 
125 - 
 
 THE OXY-HYDROGEN OR LIME LIGHT. 
 
 Fig*. 121. a. The bladder of mixed gases, pressed by the board, b b, attached by wire 
 supports to another board, c c, which carries the weights, d d. be. Pipe to which the 
 bladder, a, is screwed, and when a is emptied, it is re-filled from the other bladder, k. 
 fpf, Pipe conveying mixed gases to the lantern, g g, where they are burnt from a 
 Gurney’s jet, h. 
 
 the report ; whereas, when the gases are used in separate bags under a 
 pressure of two or three half hundredweights, if the pressure on one of 
 the bags be accidentally removed or suspended, the gas from the other 
 will be forced into it, and if not discovered in time, will occasion an ex- 
 plosion of a very dangerous character ; or if through carelessness one 
 of the partially emp- 
 tied bags should be 
 filled up with the 
 wrong gas, effects of 
 an equally perilous 
 nature would ensue. 
 
 In the oxy-hydro- 
 gen blowpipe usually 
 employed, the gases 
 are kept quite sepa- 
 rate, either in gas- 
 ometers or gas bags, 
 and are conveyed by 
 distinct pipes to a 
 jet of very simple 
 construction, devised 
 by the late Professor 
 Daniell, where they 
 mix in very small volumes, and are burnt at once at the mouth of the 
 jet. (Pig. 122.) 
 
 The gases are stored either in copper gasometers or in air-tight bagsx 
 of Macintosh cloth, capable of containing from four to six cubic feet of 
 gas, and provided with pressure boards. The boards are loaded with 
 two or three fifty-six pound weights to force out the gas with sufficient 
 
126 
 
 boy’s playbook of science. 
 
 pressure, and of course must be equally weighted ; if any change of 
 weight is made, the stop-cocks should be turned off and the light put out, 
 as the most disastrous results have occurred from carelessness in this 
 respect. (Fig. 123.) 
 
 Fig. 123. Gas bag and pressure boards. 
 
 The oxy-hydrogen jet is further varied in construction by receiving 
 the gases from separate reservoirs, and allowing them to mix in the 
 upper part of the jet, which is provided with a safety tube filled with 
 
 Fig. 124. a a. Board to which b b is fixed, o. Oxygen pipe. h. Hydrogen pipe, 
 c c. Space filled with wire gauze, d. Lime cylinder. 
 
 circular pieces of wire gauze. (Fig. 124.) With this arrangement a 
 most intense light is produced, called the Drummond or lime light, and 
 coal gas is now usually substituted for hydrogen. 
 
ANALYSIS AND SYNTHESIS OF WATEPu. 
 
 127 
 
 Seventeenth Experiment. 
 
 There are many circumstances that will cause the union of oxygen and 
 hydrogen, which, if confined by themselves in a glass vessel, may be pre- 
 served for any length of time without change ; but if some powdered glass, 
 or any other finely-divided substance with sharp points, is introduced 
 into the mixed gases at a temperature not exceeding 660° Fahrenheit, 
 then the gases silently unite and form water. 
 
 This curious mode of effecting their combination is shown in a still 
 more interesting manner by perfectly clear platinum foil, which if intro- 
 duced into the mixed gases gradually begins to glow, and becoming red- 
 hot causes the gases to explode. Or still better, by the method first 
 devised by Dobereiner, in 1824, by which finely prepared spongy pla- 
 tinum — i.e ., platinum in a porous state, and exposing a large metallic 
 surface — is almost instantaneously heated red-hot by contact with the 
 mixed gases. When this fact became known, it was further applied to 
 the construction of an instantaneous light, in which hydrogen was made 
 to play upon a little ball of spongy platinum, and immediately kindled. 
 These Dobereiner lamps were possessed by a few of the curious, and 
 would no doubt be extensively used if the discovery of phosphorus had 
 not supplied a cheaper and more convenient fire-giving agent. When 
 the spongy platinum is mixed with some fine pipeclay, and made into 
 little pills, they may (after being slightly warmed) be introduced into 
 a mixture of the two gases, and will silently effect their union. The 
 theory of the combination is somewhat obscure, and perhaps the simplest 
 one is that which supposes the platinum sponge to act as a conductor of 
 electric influences between the two sets of gaseous particles ; although, 
 again, it is difficult to reconcile this theory with the fact that powdered 
 glass at 660°, a bad conductor of electricity, should effect the same 
 object. The result appears to be due to some effects of surface by 
 which the gases seem to be condensed and brought into a condition 
 that enables them to abandon their gaseous state and assume that of 
 water. 
 
 When Sir H. Davy invented the safety-lamp, he was aware that, in 
 certain explosive conditions of the air in coal mines, the flame of the 
 lamp was extinguished, and in order that the miner should not be left 
 in the dreary darkness and intricacies of the galleries without some 
 means of seeing the way out, he devised an ingenious arrangement with 
 thin platinum wire, which was coiled round the flame of the lamp, and 
 fixed properly, so that it could not be moved from its proper place by 
 any accidental shaking. When the flame of the safety-lamp, having the 
 platinum wire attached, was accidentally extinguished by the explosive 
 atmosphere in which it was burning, the platinum commenced glowing 
 with an intense heat, and continued to emit light as long as it remained 
 in the dangerous part of the mine. Sir H. Davy warned those 
 who might use the platinum to take care that no portion of the 
 thin wire passed outside the wire gauze, for the obvious reason 
 that, if ignited outside the wire gauze protector, it would inflame the 
 fire-damp. 
 
128 
 
 boy’s playbook of science. 
 
 Eighteenth Experiment . 
 
 There is a current of 
 electricity passing from 
 and between two plati- 
 num plates decomposing 
 water, offering the con- 
 verse of the Dobereiner 
 
 Water is decomposed 
 by passing a current 
 of voltaic electricity 
 through it by means of 
 two platinum plates, 
 which may be connected 
 with a ten-cell Grove’s 
 battery. The gases are 
 collected in separate 
 tubes, and the experi- 
 ment offers one of the 
 most instructive illus- 
 trations of the composi- 
 tion of water. (Fig. 1 2 5 . ) 
 
 Fig. 125. p p. Two platinum plates connected with experiment, and highly 
 
 wniuu a±su uuutauis unuie suipuuru; aeiu. „ <-> 
 
 improve the conducting power of the water. The wires of lar combination ot OXy- 
 
 ♦.Vip Vmffpw ATP ■nlnoprl in +.V»p mmc and tfhp armwa cTi nur o "L „ J ~ 
 
 num foil, and more especially when we consider the operation of Grove’s 
 gas battery, in which a current of electricity is produced by pieces of 
 platinum foil covered with finely-divided platinum, called platinum black •, 
 each piece is contained in a separate glass tube filled alternately with 
 oxygen and hydrogen, and by connecting a great number of these tubes 
 a current of electricity is obtained, whilst the oxygen and hydrogen arc 
 slowly absorbed and disappear, having combined and formed water,, 
 although placed in separate glass tubes. (Fig. 126.) 
 
 The analysis of water is shown very perfectly on the screen by fitting 
 up some very small tubes and platinum wires in the same manner as 
 shown in fig. 125. The vessel in which the tubes and wires are con- 
 tained with the dilute sulphuric acid must be small, and arranged so as to 
 pass nicely into the space usually filled by the picture in an ordinary 
 magic lantern, or, still better, in one lighted by the oxy-hydrogen or 
 lime light. If the dilute acid is coloured with a little solution of indigo, 
 the gradual displacement of the fluid by the production of the two gases 
 is very perfectly developed on the screen when the small voltaic battery 
 is attached to the apparatus ; and of course a large number of persons 
 may watch the experiment at the same time. 
 
 With respect to the application of the light produced from a jet of 
 
129 
 
 THE SYNTHESIS OF OXYGEN AND HYDROGEN. 
 
 Fig. 12b. Grove s gas battery consists of tubes containing oxygen and hydrogen alternately, 
 and having a thin piece of platinum foil, p, inserted by the blowpipe in each glass tube 
 The foil hangs down the full length of the interior of the glass. Each pair of tubes U 
 contained in a little glass tumbler containing some dilute sulphuric acid and the 
 hydrogen tube, h, of one pair, is connected with the oxygen tube, o, of the next * w w 
 The terminal wires of the series. * vv vv ' 
 
 the mixed gases thrown upon a ball of lime, it may be stated that for 
 many years the dissolving view lanterns, and other optical effects have 
 oecn produced with the assistance of this light ; and more lately Major 
 Fitzmaurice has condensed the mixed gases in the old-fashioned oil 
 gas receivers, and projected them on a ball of lime; and it was this 
 thrown from many similar arrangements that illuminated the 
 British men-of-war when Napoleon III. left her Majesty’s yacht at nWiti 
 m the docks at Cherbourg. ° 
 
 Mr. Sykes Ward, of Leeds, has also proposed a most simple and excel- 
 lent application ot the oxy-hydrogen ligut for illumination under the 
 
 Fig. 127. Cherbourg. 
 
 K 
 
130 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 surface of water, and for the convenience of 
 divers, who are frequently obliged to cease their 
 operations in consequence of the want of light. 
 Mr. Ward’s submarine lamp consists of a series 
 of very strong copper tubes, which are filled 
 with the mixed gases by means of a force-pump ; 
 and in order to prevent the lamp being extin- 
 guished, it burns under double glass shades, 
 which are desirable in order to prevent the glass 
 immediately next to the light cracking by con- 
 tact with the cold water. 
 
 The author tried this lamp at Hyde, and 
 although the coast-guards objected to the pro- 
 duction of a brilliant light at night, which they 
 stated might be mistaken for a signal ana 
 would cause some confusion amongst the war 
 vessels in the immediate neighbourhood, enough 
 experiments were made, to show that the Ward 
 lamp would burn for a considerable time under 
 water, and could be kept charged with the gas 
 by means of a process that was easily work- 
 able in the boat. The gases were taken out 
 mixed in gas bags, and pumped into the reser- 
 voir when required. With a much larger reser- 
 voir greater results could be obtained ; and if 
 nautilus diving bells are to be used in modern 
 warfare, they will require a powerful light to 
 show them their prey, so that they may attach 
 the explosives which are to blow great holes in 
 the men-of-war. 
 
 Fig. 129. Submarine lamp, 
 
 shade, held down by a cap 
 and screw, c. The second 
 glass shade. e e. The 
 handle by which it is low- 
 ered into the water. 
 
THE LIQUIFICATION OF GASES. 
 
 131 
 
 THE LIQITIEI CATION OF GASES. 
 
 The three elements with which we have been just experimenting, 
 namely, hydrogen, oxygen, and nitrogen, have up to the last two years 
 been distinguished by the term “permanent gases” — for every effort to 
 reduce them to a liquid or solid state had previously been attended with 
 failure. But at the close of the year 1877 M. Cailletet, of Paris, and 
 M. Pictet, of Geneva, each working independently of the other, demon- 
 strated that these three gases were no exception to the general law 
 of molecular cohesion. 
 
 The first of these gases which in the hands of M. Pictet was made 
 to give up its vaporous condition was oxygen, and the Journal de 
 Geneve of Dec. 23, 1877, thus refers to the experiments : — 
 
 “ One of the most interesting physical experiments of our time has 
 just been made at Geneva with rare success in the laboratory of the 
 Society for the Manufacture . of Physical Instruments. M. Raoul 
 Pictet has succeeded in obtaining, by means of ingeniously combined 
 apparatus, the liquifaction of oxygen gas. The following is the process 
 by which this curious result was obtained : — 
 
 “By a double circulation oT sulphurous acid and carbonic acid, the latter 
 gas is liquified at a temperature of 65° of cold, under a pressure of from 
 lour to six atmospheres. The liquified carbonic acid is conducted into 
 a tube four metres long ; two combined pumps produce a barometric 
 vacuum over the acid, which is solidified in consequence of the difference 
 of pressure. Into the interior of this .first tube containing solidified 
 carbonic acid is passed a tube of slightly less diameter, in which 
 •circulates a current of oxygen produced in a generator containing 
 chlorate of potash, and the form of which is that of a large shell thick 
 enough to prevent all danger of explosion. The pressure mav thus be 
 carried to 800 atmospheres. 
 
 “Yesterday morning (December 22) all the apparatus being arranged 
 as described, and under a pressure which did not exceed 300 atmospheres, 
 a liquid jet of oxygen issued from the extremity of the tube, at the 
 moment when this compressed and refrigerated gas passed from that 
 high pressure to the pressure of the atmosphere.” 
 
 Strangely enough only twenty days before the interesting experiment 
 above detailed M. Cailletet had in Paris accomplished the same tiling, 
 only he had not then published the fact. There now remained oniv 
 two so-called “permanent” gases, namely hydrogen and nitrogen, and 
 we shall presently see that they too soon yielded to the enormous 
 pressure to which they were subjected. This was realized on the last 
 day of the year at Paris, by M. Cailletet. At a pressure of 200 
 atmospheres nitrogen appeared in the liquid form. Hydrogen was 
 next experimented with, and was reduced to the form of a cloud. 
 Although both the constituents of the atmosphere — oxygen and 
 nitrogen — had been made to succumb, as a matter of scientific interest 
 the apparatus was charged with air, and presently a stream of liquid 
 air was seen issuing from it. 
 
 k 2 
 
132 
 
 CHAPTER XI. 
 
 CHLORINE, IODINE, BROMINE, FLUORINE. 
 
 The four Halogens , or Producers of Substances like Sea Salt. 
 
 Chlorine (x>o>p 0y , green). Symbol, Cl Combining proportion, 35;5. 
 Specific gravity, 2’lf. Scheele termed it dephlogisticated muriatic 
 acid; Lavoisier, oxymuriatic acid ; Davy, chlorine. , 
 
 The consideration of the nature of this important element introduces 
 to our notice one of the most original chemists of the eighteenth 
 century— viz., the illustrious Scheele, who was born at Stralsund, in 1742, 
 and iii spite of every obstacle, fighting his “battle of life with sickness 
 and sorrow, he succeeded in making some of the most valuable dis- 
 coveries in science, and amongst them that of chlorine gas It was m 
 the examination of a mineral solid-viz., of manganese-tliat Scheele 
 made the acquaintance of a new gaseous element; and in a 1 hh 
 original dissertation on manganese, m 1774, lie describes the mode of 
 procuring what he termed dephlogisticated muriatic acid — a name which 
 is certainly to be regretted, from its absurd length, but a title which 
 was strictly in accordance with the then established theory of phlogiston , 
 and if the latter is considered synonymous with hydrogen, quite in 
 accordance with our present views of the nature of this element. 
 Scheele discovered the leading characteristics of chlorine, and especially 
 its power of bleaching, which is alone sufficient to place this gas in a 
 high commercial position, when it is considered that all our linen use 
 formerly to be sent to Holland, where they had acquired great dextenty 
 in the ancient mode of bleaching-viz., by exposure of the fabric to 
 atmospheric air or the action of the damps or dews assisted greatly by 
 the agency of light. Some idea maybe formed of the present value 
 of cldorine, when it is stated that the linen goods were retained by the 
 Dutch bleachers for nine months ; and if the spring and summer hap- 
 pened to be favourable, the, operation was well conducted ; on the othei 
 Land, if cold and wet, the goods might be more or less injured by con- 
 tinual exposure to unfavourable atmospheric changes. At the piesent 
 time as much bleaching can be done in nine weeks as might formerly 
 have beeii conducted in the same number of months ; and the whole ^of 
 the process of chlorine bleaching is carried on independent of external 
 atmospheric caprices, whilst the money paid for the 
 passes to Holland, but remains in the hands of our own diligent 
 bleachers and manufacturers. 
 
 First Experiment. 
 
 As Scheele first indicated, chlorine is obtained by He action of the 
 black oxide of manganese, on “the Spirit of Salt, 
 acid • and the most elementary and instructive experiment showing its 
 preparation can be made in the following manner:— 
 
 J 
 
THE PREPARATION OF CHLORINE GAS. 
 
 133 
 
 Place in a clear Elorence oil-flask, to which a cork and bent tube have 
 been first fitted, some strong fuming hydrochloric acid. Arrange the 
 flask on a ring-stand, and then pass the bent tube either to a Wolfe’s 
 bottle containing some pumice stone moistened with oil of vitriol, or to 
 a glass tube containing 
 either pumice or as- 
 bestos wetted with the 
 same acid. Another 
 glass tube, bent at 
 right angles, passes 
 away from the Wolfe’s 
 bottle into a receiving 
 bottle. (Pig. 130). On 
 the application of heat, 
 the hydrochloric gas is 
 driven off from its so- 
 lution in water, and 
 any aqueous vapour 
 carried up is retained 
 by the asbestos or pu- 
 mice stone wetted 
 with oil of vitriol ; the 
 application of the lat- 
 ter is called drying the 
 gas — i.e., depriving it 
 of all moisture ; some- 
 
 Fig. 130. a. Flask containing the fuming hydrochloric 
 acid, which is gently boiled by the heat of the spirit lamp. 
 b. Tube passing to the Wolfe’s bottle, containing pumice- 
 stone or asbestos moistened with sulphuric acid. c. 
 Second tube passing into a dry empty bottle, which receives 
 the hydrochloric acid gas. 
 
 times the salt called chloride of calcium is used for the same purpose, and 
 it must be understood by the juvenile chemist that gases are not dried 
 like towels, by exposure to heat, or by putting them in bladders before the 
 fire , as we once heard was actually recommended, but by causing the gas 
 charged with invisible steam to pass over some substance having a great 
 affinity for water. The dry hydrochloric gas falls into the bottle, and dis- 
 places the air, being about one-fourth heavier than the latter, and gradu- 
 ally overflowing from the mouth of the vessel, produces a white smoke, 
 which is found to be acid by litmus paper, but has no power to bleach, 
 and is not green ; it is, in fact, a combination of one combining pro- 
 portion of chlorine with one of hydrogen, and to detach the latter, and 
 set the chlorine free, it is necessary to convey the hydrochloric gas to 
 some body which has an affinity for hydrogen. Such a substance is 
 provided in the use of the black oxide of manganese, which is placed 
 either in a small flask or in a tube provided with two bulbs, and when 
 heated with the lamp it separates the hydrogen from the hydrochloric 
 gas, and forms water, which partly condenses in the second bulb. And 
 now the gas that escapes is no longer acid and fuming with a white 
 smoke on contact with the air; but is green, has a strong odour, 
 bleaches, and is so powerful in its action on all living tissues, that it 
 must be carefully avoided and not inhaled ; if a small quantity is acci- 
 dentally inhaled, it produces a violent fit of coughing, which lasts a 
 
134 
 
 coy’s playbook of science. 
 
 considerable time, and is only abated by inhaling the diluted vapour of 
 ammonia, or ether, or alcohol, and swallowing milk and other softe nin g 
 drinks. (Fig. 131). 
 
 i 
 
 — Or 
 
 Fig. 131. a. The flask containing the fuming hydrochloric acid, heated by spirit lamp. 
 b. Tube passing to Wolfe’s bottle, containing the pumice-stone or asbestos wetted with 
 oil of vitriol, c. Second tube, which passes into a wide-mouthed small flask containing 
 black oxide of manganese, partly in powder and partly in lump ; and the third tube 
 conveys the chlorine to any convenient vessel. The double bulb tube, e e, may be substi- 
 tuted for the flask, the oxide of manganese being contained in the bulb m. — N.B. Any tube 
 may be joined on to another by a bit of india-rubber tubing, which is tied by string. 
 
 A C B 
 
 Tube a is joined to tube b by the caoutchouc pipe c, tied with packthread. 
 
 Second Experiment. 
 
 The mode of preparing chlorine, as already given, though very in 
 structive, is troublesome to perform ; a more simple process may there- 
 fore be described : — 
 
 Pour some strong hydrochloric acid upon powdered black oxide of 
 manganese contained in a Florence oil-flask, taking care that the whole 
 of the black powder is wetted with the acid so that none of it clings to the 
 bottom of the flask in the dry state to cause the glass to crack on the 
 application of heat. A cork and bent glass tube is now attached, and 
 conveyed to the pneumatic trough ; on the application of heat to the 
 mixture in the flask the chlorine is evolved, and may be collected in 
 stoppered bottles, the first portion that escapes, although it contains 
 atmospheric air, should be carefully collected in order to prevent any 
 
EXPERIMENTS WITH CHLORINE GAS. 
 
 135 
 
 accident from inhaling the gas, and it will do very well to illustrate the 
 bleaching power of the gas, and therefore need not be wasted. The 
 above process may be described in symbols, all of which are easily deci- 
 phered by reference to the table of elements, page 86. 
 
 Mn0 2 4- IHCl=MnCl 2 + 2 H 2 0 + Cl 2 
 
 Third Experiment. 
 
 Another and still more expeditious mode of preparing a little chlorine, 
 is by placing a small beaker glass, containing half an ounce of chlorinated 
 lime, usually termed chloride of 
 lime or bleaching powder, care- 
 fully at the bottom of a deep and 
 large beaker glass, and then, by 
 means of a tube and funnel, con- 
 veying to the chloride of lime 
 some dilute oil of vitriol, com- 
 posed of half acid and half 
 water ; effervescence immedi- 
 ately occurs from the escape of 
 chlorine gas, and as it is pro- 
 duced it falls over the sides of 
 the small beaker glass into the 
 large one, when it may be dis- 
 tinguished by its green colon r. 
 
 If a little gas be dipped out with 
 a very small beaker glass ar- 
 ranged as a bucket, and poured 
 into a cylindrical glass contain- 
 ing some dilute solution of in- 
 digo, and shaken therewith, the 
 colour disappears almost instan- 
 taneously; and if a piece of 
 Dutch metal is thrown into the 
 beaker glass it will take fire if 
 
 enough chlorine has been gene- Fig . m A A . The large beakcr g]ass . 
 rated, or some very hnely-pow- The small one, containing- the chloride of lime, 
 dered antimony will demonstrate tube and funnel down which the dilute 
 
 41 _ „ _ Si. mi -j.1 sulphuric acid is poured, d d. Sheet of paper 
 
 the same result. lhus, with a over top of large glass, with hole ill centre to 
 few beaker glasses, some clllo- admit the tube. E. The little beaker used as a 
 ride of lime, sulphuric acid, a bucket * 
 
 solution of indigo, and a little Dutch metal, the chief properties of 
 chlorine may be displayed. (Fig. 132.) 
 
 Fourth Experiment . 
 
 Into a little platinum spoon place a small pellet of the metal sodium, 
 and after healing.it in the flame of a spirit lamp, introduce the metal 
 
1S6 
 
 eoy’s playbook of science. 
 
 into a bottle of chlorine, when a most intense and brilliant combustion 
 occurs, throwing out a vivid yellow light, and the heat is frequently so 
 great that the bottle is cracked. After the combustion, and when the 
 bottle is cool, it is usually lined with a white powder, which will be 
 found to taste exactly the same as salt, and, in fact, is that substance, 
 produced by the ' combination of chlorine, a virulent poison, with the 
 metal sodium, which takes fire on contact with a small quantity of 
 water ; and lienee the use of salt for the preparation of chlorine gas 
 when it is required on the large scale. 
 
 Parts. 
 
 Common salt 4 
 
 Black oxide of manganese . . . . i 
 
 Sulphuric acid 2 
 
 Water 2 
 
 Fifth Experiment. 
 
 Some Dutch metal, or powdered antimony, or a bit of phosphorus, 
 immediately takes fire when introduced into a bottle containing chlorine 
 gas, forming a series of compounds termed chlorides, and demonstrating 
 by the evolution of heat and light, the energetic character of chlorine, 
 and that oxygen is not the only supporter of combustion ; chlorine 
 gas has even, in some cases, greater chemical power, because some 
 time elapses before phosphorus will ignite in oxygen gas, whilst it takes 
 fire directly when placed in a bottle of chlorine. 
 
 Sixth Experiment. 
 
 The weight and bleaching power of chlorine are well shown by placing 
 a solution of indigo in a tall cylindrical glass, leaving a space at the 
 top of about five inches in depth. By inverting a bottle of chlorine 
 over the mouth of the cylindrical glass, it pours out like water, being 
 about two and a half times heavier than atmospheric air, and then, after 
 placing a ground glass plate over the top of the glass, the chlorine 
 is recognised by its colour, whilst the bleaching power is demonstrated 
 immediately the gas is shaken with the indigo solution. 
 
 Seventh Experiment . 
 
 As a good contrast to the last experiment, another cylindrical jar of 
 the same size may be provided, containing a solution of iodide of potas- 
 sium with some starch, obtained by boiling a teaspoonful of arrowroot 
 with some water ; any chlorine left in the bottle (sixth experiment) may 
 be inverted into the top of this glass and shaken, when it turns a beautiful 
 purple blue in consequence of the liberation of iodine by the chlorine, 
 whose greater affinity for the base produces this result. The colour is 
 caused by the union of the iodine and the starch, which form together a 
 beautiful purple compound, and thus the apparent anomaly of destroying 
 and producing colour with the same agent is explained. 
 
EXPERIMENTS WITH CHLORINE GAS. 
 
 137 
 
 Eighth Experiment. 
 
 Ninth Experiment. 
 
 A piece of paper dipped in oil of turpentine emits a dense black 
 smoke, and frequently a flash of fire is perceptible, direotly it is plunged 
 into a bottle containing chlorine gas ; here the gas combines only with 
 the hydrogen of the turpentine, and the carbon is deposited as scot. 
 
 Tenth Experiment . 
 
 If a lighted taper is plunged into a bottle of chlorine it continues to 
 burn, emitting an enormous quantity of smoke, for the reason already 
 explained^, and demonstrating the perfection of the atmosphere in which 
 
138 
 
 boy’s playbook of Science. 
 
 we live and breath, and showing that had oxygen gas possessed the 
 same properties as chlorine, the combustion of compounds of hydrogen 
 and carbon would have been impossible, in consequence of the enormous 
 quantity of soot which would have been produced, so that some other 
 element that would freely enter into combination with it must have 
 been provided to produce both artificial light and heat. Chlorine is a 
 gas which cannot be inhaled, and ozone presents the same features, as a 
 mouse confined for a short time with an excess of ozone soon died ; but 
 ozone is the extraordinary condition of 
 oxygen ; the element in the ordinary state 
 is harmless, and is the one which enters 
 _ so largely into the composition of the air 
 
 we breathe. 
 
 ' v 
 
 Eleventh Experiment . 
 
 When one volume of olefiant gas (pre- 
 pared by boiling one measure of alcohol 
 and three of sulphuric acid) is mixed 
 with two volumes of chlorine, and the two 
 gases agitated together in a long glass ves- 
 sel for a few seconds, with a glass plate 
 over the top, which should have a welt 
 ground perfectly flat, they unite on the ap- 
 plication of flame, with the production of a 
 great cloud of black smoke, arising from 
 the deposited carbon, whilst a sort of 
 roaring noise is heard during the time 
 that the flame passes from the top to the 
 foot of the glass. (Fig. 134.) 
 
 Twelfth Experiment. 
 
 Formerly Bandannah handkerchiefs 
 were in the highest estimation, and no 
 gentleman’s toilet was thought complete 
 without one. The pattern was of the 
 simplest kind, consisting only of white 
 spots on a red or other coloured ground. 
 These spots were produced in a very in- 
 genious manner by Messrs. Monteith, of 
 Glasgow, by pressing together many 
 layers of silk with leaden plates perforated 
 Fig. 134. Remarkable deposition with holes ; a solution of chlorine was 
 of carbon during the combustion of then poured upon the upper plate, and 
 one volume of olefiant gas with two 1 i • 1 v j • , 1 1 \ , i 
 
 of chlorine. pressure being applied it penetrated the 
 
 whole mass in the direction of the holes, 
 bleaching out the colour in its passage. This important commercial 
 result may be imitated on the small scale by placing a piece of calico 
 dyed with Turkey red between two thick pieces of board, each of which 
 
EXPERIMENTS WITH IODINE. 
 
 m 
 
 is perforated with a hole two inches in diameter, and corresponding 
 accurately when one is placed upon the other. The pieces of board 
 may be squeezed together in any convenient way, either by weights, 
 strong vulcanized india-rubber bands or screws, and when a strong 
 solution of chlorine 
 gas or of chloride of 
 lime is poured into 
 the hole and perco- 
 lates through the 
 cloth, the colour is 
 removed, and the 
 part is bleached al- 
 most instantaneously 
 by first wetting the 
 calico with a little 
 weak acid, and then 
 pouring on the solu- 
 tion of phWiflp nf Fig. 135. a. Circular hole in the upper piece of wood, a 
 non OI cnio lue . 01 gimil ® r one being perforated in the lower one. b b. The strong 
 lime. Un removing india-rubber bands. The bleaching solution is poured into a 
 and washing the fol- ^ __ 
 
 ded red calico it is found to be bleached in all the places exposed to the 
 solution, and is now covered with white spots. (Tig. 135.) 
 
 IODINE. 
 
 Iodine (I wdrjs, violet coloured). Symbol, I; combining proportion, 
 127*0 ; specific gravity, 4*947- Specific gravity of iodine vapour, 8*716. 
 
 In the previous chapter, devoted to the element chlorine, little or 
 nothing has been said of that inexhaustible storehouse of chlorine, 
 iodine, and bromine — viz., the boundless ocean. Some one has remarked 
 that, as it is possible the air may contain a little of everything capable 
 of assuming the gaseous form, so the ocean may hold in a state of solu- 
 tion a modicum of every soluble substance, in proof of which we have 
 lately read of some very important experiments resulting in the separa- 
 tion of the metal silver from sea water, not certainly in any profitable 
 quantity, but quite enough to prove its presence in the ocean. 
 
 No elaborate research is necessary to ascertain the presence of chlorine,, 
 when it is remembered that Schafhautl has calculated, that all the oceans 
 on the globe contain three millions fifty-one thousand three hundred and 
 forty-two cubic geographical miles of salt, or about five times more than 
 the mass of the Alps. 
 
 Now, salt contains about 60 per cent, of chlorine gas, and therefore 
 the bleachers can never stand still for want of it ; but iodine is not so 
 plentiful, and was discovered by M. Court ois, of Paris, in kelp , a sub- 
 stance from which he prepared carbonate of soda, or washing soda ; but 
 as this is now more cheaply prepared from common salt, the kelp is at 
 present required only for the iodine salts it contains, as also for the 
 chloride of potassium. Kelp is obtained by burning dried sea-weeds in a 
 
140 
 
 boy’s playbook of science. 
 
 shallow pit ; the ashes accumulate and melt together, and this fused mass 
 broken into lumps forms kelp. The ocean bed no doubt has its fertile and 
 barren plains and mountains, and amongst the so-called “ oceanic 
 meadows 5 ’ are to be mentioned the two immense groups and bands of 
 sea-weed called the Sargasso Sea, which occupy altogether a space 
 exceeding six or seven times the area of Germany. 
 
 The iodine is contained in the largest proportion in the. deep sea 
 plants, such as the long elastic stems of the fucus palmatus, &c. The 
 kelp is lixiviated with water, and after separating all the crystallizable 
 salts, there remains behind a dense oily-looking fluid, called “ iodine 
 ley,” to which sulphuric acid is added, and after standing a day or two 
 the acid “ ley” is placed in a large leaden retort, and heated gently 
 with black oxide of manganese. The chlorine being produced very 
 slowly, liberates the iodine, as already de- 
 monstrated in experiment seven, p. 133, 
 and it is collected in glass receivers. 
 
 Iodine, when quite pure and well crys- 
 tallized, has a most beautiful metallic lustre, 
 and presents a bluish-black colour, afford- 
 ing an odour which reminds one at once 
 of the “ sea smell.” 
 
 First Experiment, 
 
 A few grains of iodine placed in a flask 
 may be sublimed at a very gentle heat, and 
 afford a magnificent violet vapour, which 
 can be poured out of the flask into a warm 
 bottle. If the bottle is cold the iodine 
 condenses in minute and brilliant crystals. 
 (Fig. 136.) 
 
 Second Experiment. 
 
 ~ -.o* i Upon a thin slice of phosphorus place a 
 
 iodine heated by spirit lamp. n. lew small particles ot iodine ; the heat pro- 
 Coid flask above to receive the duced by the combination of the two ele- 
 to cutoff the heat spirit “ents soon causes the phosphorus to take 
 
 lamp. fire. 
 
 Third Experiment. 
 
 Heat a brick, and then throw upon it a few grains of iodine ; by 
 holding a sheet of white paper behind, the splendid violet colour of the 
 vapour is seen to great advantage. It was by the discovery of iodine in 
 the ashes of sponge — which had long been used as a remedy for goitre, a 
 remarkable glandular swelling — that this element began to be used for 
 medical purposes, and the important salt called iodide of potassium is 
 now used in large quantities, not only in medicine, but likewise for that 
 most fascinating art, which has made its way steadily, and is now 
 practised so extensively, under the name of photography 
 
THE ART OF PHOTOGRAPHY. 
 
 141 
 
 THE ART OF PHOTOGRAPHY. 
 
 In the year 1556, a philosopher named Fabricius, in his “Book of 
 the Metals,” recorded the fact that if an image from a lens were allowed 
 to fall upon a surface of “ luna cornea ,” or horn silver, that image 
 printed itself in black and white. This horn silver is the old term for 
 chloride of silver, the precipitate which occurs when a solution of 
 common salt (chloride of sodium) is mingled with a solution of nitrate 
 of silver. The preparation of this compound is very easy, and we can 
 easily prove for ourselves that when it is exposed to sunlight it speedily 
 changes from light to dark. 
 
 From this relatively unimportant chemical change has sprung the 
 beautiful art of photography, an industry which finds workers in every 
 part of the habitable globe, and which gives employment to thousands 
 of busy brains and hands. The invention of the “ art science,” as its 
 votaries in justice dignify it, cannot very well be credited to any one 
 man, for many workers contributed to it. And it must be noted that 
 many of these experimenters almost unconsciously added their mite to 
 the general result. For in their restless search after the secrets of 
 the natural world, they recorded facts which have proved of immense 
 service to the photographer, but which had not been sought after with 
 that object. For many of the properties of certain chemicals were 
 discovered and passed over as unimportant by the old alchemists, who 
 may be said to have considered everything unimportant which did not 
 point towards their only goal — the transmutation of the baser metals 
 into those of greater value. The fiction of light upon silver chloride is, 
 however, the most important contribution to photography that was 
 made until quite recent years. 
 
 Another discovery, or invention, which must also be noted as an 
 important link in the chain which was gradually being forged, and which 
 only wanted some clever artificer to join it together and call it photo- 
 graphy, was that of the camera obscura. This invention is credited to an 
 Italian philosopher of the 16th century. He observed that if a lens 
 were fitted into a hole in the shutter of a darkened room, a picture of all 
 that was passing outside, was formed upon the opposite wall of the 
 room, or upon a white screen placed for its reception. 
 
 In walking beneath the shade of trees on a sunny summer’s day, who 
 has not noticed the little rays of light which find their way through the 
 interstices of the leaves overhead, and strike upon the roadway in 
 circular patches? We are so accustomed to see these little spots of 
 light that we do not stop to inquire why they should be round, when the 
 chinks in the foliage through which they find their way are necessarily 
 of varied and irregular form. The answer to the problem will no doubt 
 strike many with surprise. Each of those little circular patches is no 
 less than an image of the round sun itself. The darkened grove of trees 
 forms a rudimentary camera obscura, and the spaces between the leaves 
 where they allow the sun’s rays to penetrate are equal to sc many lens 
 
142 
 
 boy’s playbook of science. 
 
 apertures. To imitate the phenomenon in a small way, we can pierce a 
 piece of cardboard with a knitting needle, and hold it against a candle 
 flame, when the inverted image of the flame can be projected upon another 
 card held near. A more convenient form of camera obscura can be 
 made out of a cigar box, by inserting a lens at one end, and a piece of 
 ground glass at the other end, taking due care that the lens is adapted 
 to the length of the box. 
 
 The camera obscura was at one time a very favourite and common 
 piece of apparatus. A room built for the purpose was often attached to 
 c-ountry houses. It was also to a certain extent used by artists as a 
 help to correct drawing. It was one of these artists — Daguerre, a 
 Parisian scene-painter — who was destined to be one of the first to point 
 out how the camera could be made to yield a photograph. Day by day, 
 he saw the lovely pictures cast in all their natural colours on the screen 
 by the sun ; and as he saw them he wondered whether some means could 
 not be found of preserving them indefinitely. He was soon deep in 
 experiments; but he failed over and over again. At last, a mere 
 accident directed him on the right track. He accidentally left a silver 
 plate which had been treated with iodine, and exposed in the camera, 
 near a bottle of mercury. To his surprise and joy, he found traces of a 
 picture on the plate ; and a few more experiments quickly told him how 
 such pictures could be produced at will. 
 
 The Daguerreotype process, the outcome of these experiments, may be 
 briefly described as follows : — A plate of silvered copper after being 
 carefully cleaned is placed in a box with some crystals of iodine. By 
 this means, its surface becomes coated with a yellow covering of iodide 
 of silver. It is then exposed in the camera, where the light decomposes 
 the iodide. But there is no visible change until the plate is developed 
 by exposure to the vapour of mercury. The mercurial fumes condense 
 upon those parts where the light has acted, and avoid those still covered 
 by the unaltered iodide of silver. The plate is finally fixed by a solution 
 of hyposulphite of sodium. (The discovery of this salt as a fixing agent 
 — a most important one, by the way — is due to a countryman of our 
 own, Sir John Herschell.) 
 
 While Daguerre was busy with his experiments, another Frenchman, 
 by name Niepce, was striving hard to obtain the same end by other means. 
 He was experimenting with a substance called bitumen of Judaea, which 
 when exposed to light becomes insoluble in liquids such as naphtha, in 
 which, under other circumstances, it easily dissolves. It is not necessary 
 to describe his operations, suffice it to say, that he aud Daguerre became 
 acquainted, and finally they entered into partnership with one another. 
 He died just at the time that Daguerre had triumphed over all difficulties 
 and had produced a photographic picture. 
 
 In the meantime Fox Talbot, an English gentleman, was working ^t the 
 problem of obtaining sun pictures by means of silver chloride on paper. 
 He treated ordinary writing paper with a solution of common salt, after- 
 wards washing it over with silver nitrate. By this means he obtained 
 
THE ART OF PHOTOGRAPHY. 
 
 143 
 
 a sensitive surface which speedily blackened under light ; and by placing 
 fern leaves, pieces of lace, and the like above such a surface, he obtained 
 beautiful images of such things — white on a black ground. By taking 
 one of these prints, and placing a sensitive sheet of paper below it, he 
 obtained other copies, as many as he wished— black on a white ground. 
 The first he called a negative , and the second a 'positive \ and these terms 
 are employed in photography to the present day. 
 
 Three years later, namely in 1847, a nephew of Niepce succeeded in 
 producing a negative picture upon a glass plate which had been pre- 
 viously coated with a film of albumen, or white of egg. From such 
 a picture positives could of course be produced by Fox Talbot’s 
 process. A better film for holding the tender image was, however, soon 
 discovered, and the credit of the introduction is due to Archer, who first 
 pointed out the advantages of collodion for that purpose. 
 
 Collodion is made by dissolving gun-cotton in a mixture of alcohol 
 and ether. It is further prepared for the use of photographers by 
 adding to it certain iodides and bromides. In this state it is quite 
 insensitive to light, for the necessary silver compound is not formed 
 until the glass plate bearing it has been bathed in a solution of silver 
 nitrate. Archer’s process, with hardly any variation, is practised to the 
 present time, and 1 cannot do better than at once describe it in detail 
 for the reader’s benefit. Any intending beginner cannot do better 
 than commence with this process, for upon it are founded all other pro- 
 cesses. It is not difficult, and it is sure in its results. 
 
 First a word as to apparatus. Let the beginner first of all fix a 
 definite plan of action. If it be within his means he can have a glass 
 room constructed, and do his best to rival the productions of the pro- 
 fessional photographer. But as it is more likely that he will be content 
 with an occasional portrait of some friend taken in the garden and 
 finished in a cellar for a dark room ; he need 
 not go to much expense. The best plan is to 
 go at once to some reliable dealer, and take his 
 advice as to the outfit required, taking care 
 to state the sum available for the purpose. 
 The cheapest and simplest form of camera is 
 that shown at Fig. 137. It consists of two 
 boxes sliding one within the other so that the 
 picture can be focussed upon the ground glass 
 screen, which is seen in the cut lifted half out 
 of its groove. In the more expensive cameras, 
 the body is of bellows form and made of leather. The focus is gained 
 by a rack motion and a screw, this screw being turned by a handle at 
 the back of the camera as shown in Fig. 138. Many of the modern 
 lenses are fixed in rigid settings, and this form of camera is for them 
 indispensable. A convenient form of tent for landscape work, or where 
 the operator has no dark room, is that shown at Fig. 139, It folds up 
 into small compass, is of light weight, and is furnished with all the 
 
 Fig-. 137. 
 
144 
 
 boy’s playbook of science. 
 
 Fig. 13S. 
 
 necessaries for the work. The curtain at the back of the operator folds 
 
 round him so as to 
 exclude all light, ex- 
 cept that which finds 
 its way through the 
 yellow window with 
 which the tent is 
 furnished. The use 
 of the best chemicals 
 will save the photo- 
 grapher from a host 
 of troubles. These 
 can be purchased in 
 small quantities, and 
 a little will be found 
 to go a very long 
 way. I will now give 
 a brief description of 
 the wet collodion 
 process, but I would 
 refer those who wish 
 to become practical photographers to the capital handbooks published 
 
 on the subject, my remarks being 
 necessarily limited. 
 
 THE WET COLLODION PROCESS. 
 
 This process may rightly be 
 called the sheet-anchor of the 
 photographer, and although, as 
 may be seen from a perusal of the 
 following pages, it may soon be 
 destined to give way to more 
 modern methods, it has certainly 
 up to this time represented the 
 means by which the best photo- 
 graphic results have been attained. 
 It is styled the “wet process’* 
 because the various chemicals 
 employed are used in a liquid 
 state, in contradistinction to those 
 methods where much the same 
 materials are used dry. 
 
 The first operation required is the compounding of the silver bath. 
 Distilled water is generally employed for this purpose, but as there is 
 occasionally some difficulty in procuring this sufficiently pure, I prefer 
 to use ordinary drinking water treated in the following manner. Fid a 
 
 Fig. 139. 
 
THE WET COLLODION PROCESS. 
 
 145 
 
 quart bottle — an ordinary wine bottle will answer the purpose — with 
 water, and drop into it a few crystals of nitrate of silver. As these 
 dissolve, the water will speedily become cloudy by the formation of 
 chloride of silver, caused by chemical action upon the salts which are 
 natural to the water. Stand the 
 bottle in the sun for a few hours, 
 when the deposit will soon settle 
 to the bottom of the bottle, and the 
 water will become perfectly clear, 
 and fit for making the silver bath. 
 
 To thirteen ounces of water thus 
 treated and filtered, add one 
 ounce of triple crystallised nitrate 
 of silver and two drops of nitric 
 acid. Place this mixture in the 
 bath-holder, and it is ready for 
 use. The annexed cut will show 
 the form of bath generally used, 
 together with a glass plate fixed 
 on its holder, and ready for in- 
 sertion into the sensitised solution. 
 
 Before proceeding to take a 
 picture, we must also have some Fig. 140. a. Glass or gutta-percha bath to 
 Other solutions at hand for the hold the sensitising solution, b. Glass, with 
 purpose Of developing and fixino- piece cemented on the end to hold the prepared 
 f] 1 a ° glass plate, c, whilst dipped in the bath, a. 
 
 liie image. The plate c has a eross in one corner to show 
 
 The best way of preparing the best side 
 developer is the following, — take 
 
 Protosulphate of iron . . . | lb. 
 
 Ammonio-sulphate of iron . . | lb. 
 
 Sulphate of copper . . . . -J oz. 
 
 Boiling water 1 pint. 
 
 This will make what we may call the stock solution, from which we may 
 trom time to time take a certain quantity to replenish our bottle of 
 developer, as from time to time it becomes exhausted. This plan lias 
 the merit of certainty about it, to which from personal experience I can 
 fully testify. To compound the developer, take 
 
 Stock solution (filtered) ... 1 oz. 
 
 Glacial acetic acid 3 drs. 
 
 Alcohol (methylated) . . . . £ oz. 
 
 Water 15 oz. 
 
 This will make a capital developer for landscapes and all subjects where 
 there is a tendency to over-expose the sensitised plate, for it is weak in 
 its action ; but for portraiture it is as well to reduce the amount of acid 
 to two drachms, and to double the amount of stock solution. 
 
 L 
 
146 
 
 boy's playbook of science. 
 
 Two solutions will also be required to intensify the image in case it 
 lacks sufficient density. These may be made up thus 
 
 No. 1. — Pyrogallic acid 3 grs. 
 
 Water 1 oz. 
 
 No. 2.— Nitrate of silver 5 grs. 
 
 Citric acid 10 grs. 
 
 Acetic acid \ dr. 
 
 Water (purified as above) . . \ oz. 
 
 The pyrogallic solution should be mixed just before use, but solution 
 No. 2 will keep well, and can be mixed in advance. 
 
 Fixing solution. 
 
 Hyposulphite of soda . . . 4 oz. 
 
 Water i 
 
 Havin" mixed these solutions, we can now proceed to take a photo- 
 graph with some hope of success. One of the most important operations,, 
 which will perhaps strike the mind of the novice as a most simple aflair,. 
 is the cleaning of the glass plate. This plate must not only look clean 
 to the eye, but it must-be chemically clean. The least spot of impurity, 
 or the touch of a finger,, will cause a mark in the finished picture which 
 will quite spoil it. The things required for properly cleaning the g ass 
 plates will be a clean linen rag, a chamois leather (both reserved tor this 
 purpose, and for nothing else), and a bottle of cleaning solution. 
 
 Glass-cleaning solution. 
 
 Alcohol . ... 
 
 Liquid ammonia 
 Water . . . 
 
 Fine tripoli . . 
 
 2 oz. 
 2 drs. 
 i oz. 
 1 oz. 
 
 The plan which I adopt is to clean one or two dozen plates at a time, 
 and to shut them up in a grooved dust-proof box until required for use. 
 Place a little of the solution (shaken up) on a piece of the rag, and well 
 scrub each plate on both sides, as well as the edges. W hen all are thus 
 treated each plate is fixed in a clamp plate-holder, and well polished 
 with the leather. I use a flat camel-hair 
 brush to dust the plate just before 
 the collodion is applied. 
 
 There is a little knack in coating a 
 plate with collodion which is very soon 
 acquired, and which can be well under- 
 stood by a reference to the annexed cut. 
 Hold the plate in the left hand by the 
 corner marked A. Then with the bottle 
 of collodion in the right hand pour a 
 pool of it in the centre of the glass. In- 
 cline the plate so that the liquid runs 
 
THE WET COLLODION PROCESS. 
 
 147 
 
 first towards A, then B, then C, and lastly D, where the surplus amount 
 can be gently returned to the bottle. The whole of the operation must be 
 performed steadily and without any hurry. The plate must now be 
 gently rocked, until the collodion sets, which will be in about half a 
 minute. The plate is now placed on the dipper, or holder, and is slid 
 into the bath with one sure motion ; any hesitation or stoppage in this 
 last action will be recorded on the plate as a straight line. The plate 
 may be gently lifted half up once or twice while in the bath, in order to 
 help the formation of the sensitive surface. 
 
 It must be understood that all operations after the collodion is applied 
 must be conducted by yellow light, for directly the plate is inserted into 
 the bath, an exquisitely sensitive surface commences to form, which can 
 be acted upon by light which is not filtered through a yellow or red 
 medium. A very cheap and good material for dark room windows or 
 lamps is sold by Messrs. Wratten and Wainwright. It consists of an 
 orange coloured paper, which is brushed over with an aniline solution, 
 and afterwards with boiled oil. I have had a frame made, covered with 
 muslin upon which some of this prepared paper is glued, it is fixed above 
 an ordinary window by hinges, and can be let down by a string directly 
 I wish to shut out white light. 
 
 In about three minutes the plate will be ready for removal from the 
 bath, when it must be gently raised and allowed to drain before being 
 taken from the dipper. It should now be drained more 
 thoroughly by letting it rest in a sloping position 
 upon a pad of blotting paper, the back can be gently 
 wiped with a piece of the same material, and the plate 
 can be placed in the dark slide (Fig. 142). 
 
 Now comes the exposure, the length of which can 
 only be gauged by experience, different subjects, 
 different lenses, and different times and seasons modi- 
 fying the period in such a manner that it would be 
 almost impossible to give adequate directions in a 
 mere sketch of photography such as this only professes 
 to be. After exposure the dark slide is taken back to the dark room, 
 the plate removed, and the operation called developing is then proceeded 
 with. It will be noticed that no change whatever is manifest in the 
 appearance of the plate, although a chemical change has been brought 
 about in those parts of it upon which the light has fallen. 
 
 Pour into the developing cup about half an ounce of the iron solution, 
 and turn it on to the plate with such a gentle motion that the stream flows 
 across it in one even wave. Part of the solution may be allowed to run 
 off into the sink, but sufficient should be retained on the plate to flow 
 backwards and forwards as the glass is rocked to and fro. If the image 
 at once flashes out, the exposure has been too prolonged, and the 
 resulting picture will be flat and tame ; but if it gradually comes out, 
 first the brightest parts and then what are called the half tones, we shall 
 have more hope of obtaining a good picture. Should the picture require 
 more intensity than the developer seems to be capable' of giving, it 
 
 
 
 t 
 
 Fig. 142. 
 
148 
 
 boy’s playbook of science. 
 
 should be well washed under the tap, and the intensifying solutions 
 applied in the following mannner. First, sufficient of No. 1 solution to 
 flow over the plate, then return it to the cup, and add one or two drops 
 of No. 2 and re-apply. Wash once more, and drop the plate into the 
 fixing solution, which may for convenience be kept in a dish or tray. 
 White light can now be admitted to the room, and the process of fixing 
 watched as it proceeds. When the picture seems to be thoroughly 
 cleared, remove it from the dish and well wash under the tap. It must 
 now be allowed to dry spontaneously, after which it is gently wa.rmed 
 and varnished. This completes the operation of taking a picture by the 
 wet collodion process. I will now proceed to describe the method by 
 which any number of positives — or pictures on paper — may be made from 
 the glass negative which we have obtained, and which is briefly com- 
 prehended under the term 
 
 PRINTING PROM THE NEGATIVE. 
 
 It will be observed that in the glass picture which we have taken 
 the lights are all reversed, in other words, they are all dark, while the 
 shadows are represented by almost clear glass. It is very evident that 
 if we can place a sensitive surface beneath such a picture, and expose 
 to the light, the resulting picture will be once more reversed, and we 
 shall obtain a photograph more in accordance with our ideas of what a 
 picture should be. For this purpose albumenized paper is floated upon 
 a strong solution of nitrate of silver, and dried in the dark. But the 
 operation is so unpleasant, and so liable to lead to stained hands and 
 linen, that most people now buy their paper ready prepared, which can 
 be done as cheaply, if not cheaper, than it can be made at home. 
 
 The negative is placed in a printing frame (see Figs. 143 and 144) 
 
 Fig. 144. Simple form of 
 printing frame with flat metal 
 springs, suitable for small pic- 
 tures. 
 
 Fig. 143. Printing frame with 
 hinged back; underneath the two 
 bars are metal springs to cause the 
 paper to press closely against the 
 negative. 
 
 which is so arranged that the sensitive paper placed beneath it can be 
 observed from the back without removal. It should be allowed to 
 print much deeper than it is eventually required to be, for the subsequent 
 operations of toning and fixing tend very much to reduce its intensity. 
 Several pictures should, if possible, be printed on the same day, for 
 the other operations can be carried on afterwards in regular order, and 
 the toning and fixing of 50 prints give hardly more trouble than the 
 same treatment of half-a-dozen. 
 
PRINTING FROM THE NEGATIVE. 
 
 149 
 
 When sufficiently printed, the pictures should be placed in one or two 
 changes of water, in order to remove the unaltered nitrate of silver still 
 clinging to them. They must then be transferred, two or three at a 
 time, to the toning bath, which must be prepared at least 1 2 hours 
 before use. 
 
 Toning Solution. 
 
 Choride of gold . . 1 gr. 
 
 Acetate of soda . . 10 grs. 
 
 Distilled water . . 10 oz. 
 
 This mixture must be carefully kept from the light in a stone bottle ; 
 when used it should be poured into a dish, or tray, and care should be 
 taken that the prints while toning do not overlap one another, or they 
 will tone unequally. Have a basin of clean water ready for their 
 reception as they are finished. 
 
 The paper prints must now be transferred to a bath composed 
 thus — 
 
 Hyposulphite of soda . . 3 oz. 
 
 Water \ pint. 
 
 Where they must remain for at least 15 minutes. Several good 
 washings in water must follow ; indeed, for the thorough elimination of 
 the soda, it is better to leave them all night in an open vessel, where 
 the water from a tap can drop upon them. It now only remains for 
 the pictures to be dried, trimmed, and mounted with starch upon 
 cardboard, when they can be preserved in albums. 
 
 One of the chief complaints against photographs is a want of 
 permanency. Many people have valued pictures in their possession 
 which, originally all that they could desire, have gradually faded into 
 sickly yellow phantoms of what they once represented. The fault is 
 attributable to defects in the paper employed, or to the imperfect 
 washing out of the surplus chemicals employed in producing the 
 photograph. Tor this reason I have urged the reader to be liberal in 
 his use of water during the final operation of washing out the soda. 
 
 The so-called Carbon pictures are free from the charge of want of 
 permanency, for they are produced in pigments as lasting as the paper 
 upon which they are laid. The operator can, too, choose the colour in 
 which the finished picture shall appear. A brief outline of this 
 interesting process will not be out of place. It will be observed that 
 it merely applies to the printing of the positive image from a negative 
 taken in the camera in the usual manner. 
 
 THE CARBON PRINTING PROCESS. 
 
 A certain family of chemical salts possess the property of rendering 
 gelatine insoluble after exposure to light. Taking the bichro- 
 mate of potash as a type of these salts, we will follow the various 
 manipulations involved in producing a carbon print. Carbon tissue, 
 consisting of paper covered with a mixture of gelatine and pigment. 
 
150 
 
 boy’s playbook of science. 
 
 can be bought so cheaply, that it is unnecessary to attempt to prepare 
 it, especially as the amateur would most probably fail in such an 
 attempt. It is sold of various tints for different purposes, such tints 
 being purple, brown, black, or red as required. After having cut the 
 tissue to a convenient size, it must be immersed in the following solution 
 in yellow light : — 
 
 Bichromate of potash .... 3 drs. 
 
 Water 12 oz. 
 
 Liquor ammonia 20 drops. 
 
 The solution should be placed in a dish, and the sheet of tissue should 
 Temain in it, face upwards, until it becomes flat and limp, say 30 
 ■seconds. It must then be hung up on a lath, by means of a pin put 
 
 through one corner, until it is per- 
 fectly dry ; an operation which in a 
 warm atmosphere will occupy four 
 or five hours. This constitutes the 
 sensitising operation. When per- 
 fectly dry, it is placed in a printing 
 frame beneath a negative, just as if it 
 were a piece of ordinary sensitised 
 silver paper. We cannot, however, 
 tell how the operation of printing 
 is proceeding, as we can in the latter 
 case, for the colour of the tissue is 
 uniformly dark. But we can judge 
 of the action of the light upon it 
 by exposing at the same time a 
 piece of silver paper, removing the 
 printing frame from the light when 
 that is sufficiently darkened. A 
 useful little instrument called an 
 actinometer has been devised by Mr. 
 Woodbury. It is shown at Fig. 145. By its aid the operator can very 
 well judge how long any particular negative will require to be exposed, 
 in order to yield a satisfactory print. The next operation is to fix the 
 prints on a temporary support during development. For this purpose 
 ordinary glass may be used. It should be coated with a mixture of 
 bees’ wax and ether in the following proportions : — 
 
 Fig. 145. 
 
 Bees’ wax 1 gr. 
 
 Methylated ether .... 1 oz. 
 
 A small quantity of the mixture should be applied to the glass, and 
 wiped off vigorously with a piece of coarse flannel. But enough will 
 remain on the glass to serve the purpose for which it is required, and 
 which will be presently seen. The waxed glass is now coated with thin 
 plain collodion, allowed to set, and is then placed in a dish of cold 
 water. 
 
THE CARBON PRINTING PROCESS. 
 
 151 
 
 The printed tissue is now removed from the frame and placed in 
 another dish of water. When it becomes limp it should be applied to 
 the glass plate, under water, the tissue side being pressed against the 
 collodionised glass, to which it will readily adhere. The tissue and its 
 support are now taken out of the water, and placed under a piece of 
 mackintosh cloth, tissue side uppermost. The cloth is firmly rubbed 
 with a squeegee, (an india-rubber instrument which on a large scale is 
 commonly used for removing mud from the street pavements) after 
 which the glass and adhering tissue are laid aside for ten minutes 
 or so. 
 
 The development of the picture can now be proceeded with, and it 
 will be noticed that it is a very different operation to that which has 
 already been described under the same name in connection with the wet 
 collodion process. Here, the only liquid required is hot water, that is 
 to say, water of such a heat that the hand can be placed in it without 
 inconvenience. Soon after the plate is removed to such a bath, the 
 pigmented gelatine which has not been affected by light, and which is 
 therefore soluble, will begin to ooze out between the paper and the 
 glass. By gently laving the paper with the hand, it will gradually 
 soften, and the unaltered gelatine will come away, a dark, slimy 
 mass, leaving the insoluble gelatine on the glass to constitute the 
 picture. It must now be transferred to a bath of alum and water, and 
 will then be ready for further treatment, i.e ., its transference to paper. 
 
 For this purpose a transfer paper is sold. After soaking in tepid 
 water, it is applied to the print, and left to dry. Now comes apparent 
 the use of the beeswax on the glass ; without it, the transfer paper 
 would resolutely refuse to leave the support, but by its aid, the print 
 will either leave the glass of itself without interference, or will yield to 
 the gentlest persuasion. The gelatine image is thus transferred to the 
 paper, its final support, and the work is done. 
 
 The above is just a brief outline of carbon printing, without which 
 this chapter upon photography might have been considered incomplete. 
 Those who wish to practise this charming mode of printing, should 
 consult the manual published by the Autotype Company. This company 
 Hold the patent rights of the process, and supply the tissue to the 
 large number of photographers who avail themselves of it. 
 
 Another printing process has lately been introduced, in which the 
 picture flashes out directly it is placed in the developing bath. In 
 this process salts of the rarer metals such as platinum, iridium, palla- 
 dium, &c., are employed. These metals, when in a state of fine sub- 
 division, are black or almost black, and the salts (held in the paper, 
 which is exposed beneath a negative in the usual printing frame) are 
 reduced to the metallic state by the immersion of the print in a hot 
 solution of oxalate of iron and oxalate of potash. The picture is faintly 
 visible when the print is removed from the frame, and, as already 
 remarked, it flashes out directly the developer is applied. The tone of 
 the pictures produced by this process is perhaps rather too cold to suit 
 the taste of most people, but they have the merit of permanence. 
 
152 
 
 boy’s playbook of science. 
 
 DRY PROCESSES. 
 
 When a sensitive plate is taken from the silver bath, it must be used 
 at once in the camera, or it is useless. Many plans have been tried for 
 obviating this, with more or less success, and such plans are grouped 
 under the name of dry process. The most simple dry plate is that 
 known as the " washed plate” process. On removal from the bath it is 
 washed with distilled water, and allowed to dry, when it can be exposed 
 in the camera some few hours afterwards. Before development, 
 however, it is treated with an edging of india-rubber in chloroform, or 
 some such varnish, to prevent the film slipping, and it is again lowered 
 into the silver bath. This process is but seldom used, for it is uncertain 
 in its results, and does not offer the advantages of others which have 
 superseded it. 
 
 It is found that a sensitised plate may be preserved for a much 
 longer period by the addition of some organic material. Many materials 
 have been used with success for this purpose — coffee, tea, beer, albumen, 
 tannin, pyrogallic acid, may be named among the number. A solution 
 of any one of these of a certain strength is poured over the plate after 
 its removal from the silver bath, and is allowed to dry upon it sponta- 
 neously. The exposure in the camera is as a rule greatly prolonged, 
 but it is certain that plates prepared by some of these methods, now 
 almost obsolete, have yielded wonderfully fine results. Of late years, 
 however, processes have been invented in which the use of the silver 
 bath is entirely done away with. With this bath, always a difficult 
 thing to keep in order even in the hands of experienced photographers, 
 disappears a host of annoyances and inconveniences. 
 
 These dry plate processes have not only come to the aid of pro- 
 fessional photographers, but they have placed in the hands of tourists a 
 new and interesting pursuit, without entailing upon them the soiled 
 linen and stained fingers which have long ago labelled the photographer 
 with dealing with the “ black art.” Of course there are many who will 
 plead that photographs of different places can always be bought at 
 shops, and that therefore it is useless to go to the trouble and expense 
 of manufacturing them. But such people forget that there is a pleasure 
 in contemplating, as there is in executing one’s own productions, a 
 pleasure which money cannot purchase. The amateur botanist, ento- 
 mologist, or artist, each understands this feeling, for every object, or 
 sketch in his collection will remind him of difficulties overcome, or of 
 pleasant episodes which he would not care to forget. 
 
 The advantages of working by the dry method comprehend something 
 more than the release from dirty shirt cuffs and soiled fingers, for the 
 apparatus required for a day’s work in the field is reduced to what may 
 easily be carried in one hand. A worker by the wet process, on the 
 other hand, must have a tent of some kind, besides a host of bottles, 
 and the tiresome, dirty bath. He must also be provided with a good 
 supply of water for the various operations required, so that under the 
 
THE DRY PROCESS. 
 
 153 
 
 old system it was almost impossible for any one to undertake a photo- 
 graphic journey without a horse and trap, as well as an assistant. 
 
 The impedimenta required for a dry plate worker in the field com- 
 prise a small fold-up camera, (Figs. 146 and 147) its tripod stand, and a 
 batch of dry plates. These can either be carried in double dark slides ( i.e ., 
 two plates in each slide) ready for insertion into the camera, or they may 
 be placed in what is called a changing box. Perhaps the most ingenious 
 changing box ever made is that invented by Mr. Hare. It contains a 
 dozen or more plates, which are placed in grooves within the box. By 
 a very clever contrivance the dark slide is, when required, clamped to 
 the top of the box, turned upside down, and immediately one of the 
 prepared plates runs into the dark slide, ready for exposure in the 
 
 Fig. 146. Tourist’s camera 
 ready for use. 
 
 camera. A little index on the outside of the box registers each 
 plate as removed, so that the mistake of exposing the same plate twice 
 is all but impossible except in very careless hands. 
 
 Another very ingenious plan which still further reduces the burden 
 of a modern photographer is the negative tissue process of Mr. Warnerke. 
 In this case the sensitised material is supported upon a long ribbon of 
 paper. . An ordinary camera is employed, into the back of which fits a 
 dark slide which forms the most novel feature of the process. Inside 
 this box are two rollers, one at each side. On these rollers is wound, 
 panorama fashion, the paper already alluded to. The picture is 
 focussed in the usual manner, the dark slide is then adjusted to the 
 camera, and a section of the prepared paper receives the image. The 
 rollers are then turned until a fresh portion of the paper is in front of 
 the exposing shutter ready for the next picture, and the operation is 
 repeated again and again until the length of the prepared tissue is 
 exhausted. The tissue has of course to undergo development, but this 
 can be postponed for a long time if necessary. With this apparatus it 
 would be possible for the special correspondent of an illustrated news- 
 paper to send home latent images of the scenes which he described, 
 which could be developed into pictures as soon as they reached their 
 journey’s end. For it is clear that such photographs could be sent 
 home in an ordinary envelope, provided, of course, that it was light-tight. 
 The great objection to this process seems to be the difficulty of pre 
 
154 
 
 boy’s playbook of science. 
 
 paring the tissue, a work next to impossible except in skilled hands. 
 Most amateurs like to have the satisfaction of preparing their own 
 plates, so that they can feel that the resulting pictures owe their 
 parentage to them from first to last. Peeling certain that this is the 
 case, I will now give directions by which such an end can be attained 
 without any very difficult or tedious operations. At the same time I 
 can inform those of my readers who are so placed that they cannot 
 afford the time, or do not possess the necessary space and conveniences 
 for the home production of dry plates, that they can purchase them ready 
 prepared ; and naturally better prepared than anything they could 
 produce themselves. In the collodion emulsion process, which I shall 
 first describe, the trouble is reduced to a minimum, by purchasing the 
 mixture ready made, when it merely has to be poured like collodion 
 over the glass plates shortly before they are wanted for use. But 
 for those who prefer to be self-dependent, I give the recipe. 
 
 COLLODION EMULSION PROCESS. 
 
 The following process originally appeared in the “ British Journal 
 Photographic Almanac” under the heading, “ A sure and simple method 
 of making standard dry plates,” by Canon Beechey. As I have tried 
 this method myself with the best results, I place it before my readers 
 with every confidence that it will, with due care, succeed in their 
 hands : — 
 
 “ To be able to make in a few hours, and with little trouble, a batch 
 of dry plates of uniform quality, fairly rapid, easily developed, and 
 needing no intensifying, but of a bright wet-plate character, appears to 
 me to be more useful to the generality of landscape photographers than 
 complicated formula for such delicate and very rapid plates as are 
 difficult of preparation, not easy to intensify, and liable to failure in all 
 but very skilful hands. 
 
 1. Prepare the following chloro-bromide solution : — 
 
 A. 
 
 Anhydrous bromide of cadmium . . 400 grs. 
 
 Absolute alcohol ....... 10 ozs. 
 
 The solution will be mil^y. Let it stand till quite clear. Decant 
 it carefully and add — 
 
 Strong hydrochloric acid . . 80 minims or drops. 
 
 Label this “ Chloro-Bromide Solution.” This is the staple basis ot 
 all your emulsion. 
 
 2. When you require dry plates prepare the day before, by yellow 
 light, the following emulsion for two dozen dry plates — 
 
 Take of A i oz. 
 
 Absolute ether ... 9 drs. 
 
 Proved gun-cotton . . 10 or 12 grs., as thickness requires. 
 
COLLODION EMULSION PROCESS. 
 
 155 
 
 The gun-cotton should entirely dissolve. This is your chloro- 
 bromised collodion. 
 
 To sensitise the above, dissolve by heat forty grains of fused nitrate 
 of silver in powder in one ounce of alcohol *820. When entirely 
 dissolved put the collodion into a clean four-ounce measure, and pour 
 the hot solution of silver steadily in, stirring rapidly with a clean slip 
 of glass. Now you have your chloro-bromide emulsion. It should be 
 very smooth and rather milky ; but after having been kept in the dark 
 twenty-four hours, and shaken once or twice, it will become beautifully 
 creamy. The above quantity for two dozen half-plates will enable you 
 to judge for other sizes.” 
 
 Canon Beechey then proceeds to explain that the glass plates should 
 be thoroughly cleaned, and coated with a substratum of albumen or 
 gelatine, before the emulsion is applied to them. (I may here remark 
 that all the dry processes, with the one exception of gelatine plates, 
 require a substratum of this kind, or the film is sure to slip off during 
 subsequent operations.) Canon Beechey recommends that the glass 
 should be cleaned with the following solution : — 
 
 Hydrochloric acid 
 Water .... 
 
 2 drs. 
 1 oz. 
 
 This should be applied with a tuft of cotton wool made into a brush by 
 being pulled through a piece of glass tubing with a string, so that 
 the wool forms a pad at the top. As each plate is rubbed over with 
 this . mixture, edges and all, it is rinsed under the tap and immediately 
 receives a coating of gelatine. Soak five grains of Nelson’s Opaque 
 Gelatine in one ounce of cold water for an hour ; then add three ounces 
 of boiling water. It will at once dissolve. Each plate should be 
 flooded while wet with the gelatine, but the mixture should be filtered 
 before use. The first application will carry off the water which remains on 
 the washed plate, and a second dose will leave an even film which 
 must be allowed to dry upon the plate. 
 
 To coat and prepare your dry plates have ready two large, flat, 
 china dishes, capable of holding each six plates together side by side. 
 Into one put as much filtered rain water as it will hold, and into the 
 other put of clear (not sour) bitter table beer thirty ounces, in which 
 dissolve thirty grains of pyrogallic acid. This is your preservative, and 
 the simplest and best I know of. It is better made and put in the dish 
 an hour or two before you want it, that it may be quite flat and free 
 from any little bubbles, as they produce pinholes. Next filter your 
 emulsion, after well shaking it, through clean cotton wool in the usual 
 collodion filter. Coat six plates in succession, putting each as it is 
 coated into the water. By the time the sixth is in, the first is ready 
 to he placed in the preservative. Then coat another plate, and place 
 it in the water where No. 1 was. 
 
 As the preservative bath becomes full of plates they are taken out 
 one by one and put in a drying box, or allowed to dry on a rack 
 spontaneously. 
 
156 
 
 boy’s playbook of science. 
 
 The exposure in the camera varies from 30 to 60 seconds, according 
 to the subject and the light. 
 
 Development. 
 
 Pyrogallic acid . . . 
 
 . . 96 
 
 grs. 
 
 Methylated alcohol 
 
 . . 1 
 
 oz. 
 
 Bromide of potassium 
 
 . . 12 
 
 grs. 
 
 Water (distilled) . . 
 
 . . 1 
 
 oz. 
 
 Carbonate of ammonia 
 
 . . 60 
 
 grs. 
 
 Hot water . . . . 
 
 . . 1 
 
 oz. 
 
 Mix of A . . . . 
 
 . . 30 
 
 drops 
 
 „ B (in winter 30 
 
 will do) 60 
 
 a 
 
 C . . . . 
 
 . . 2 
 
 drs. 
 
 Wet the plate well under the tap until no longer greasy. Pour on the 
 developer and let it run well over until the first trace of sky is visible ; 
 then pour back into the measure, and wait to see the development go 
 on. This will both surprise and please you, and will enable you to 
 judge as to exposure. If the detail appear slowly but regularly, pour 
 the developer again on to the plate, and proceed to full development. 
 If the picture flash out rapidly, wash it at once , add to the developer 
 thirty drops or more of B, and again pour it on till all is out. If the 
 detail appear very slowly, do not fear to add another drachm of C. 
 You cannot fog these plates if you try. They generally require no 
 intensifying ; if they do, one dash of the usual acid pyro and silver will 
 suffice. Pix as usual with hyposulphite of soda. 
 
 These plates keep as well as any dry plates I know of ; but never 
 use old plates if you are going on an expedition and want the best 
 results. Fresh plates are so easily made as above, and are always so 
 active and lively, that it is foolish to make more at once than you think 
 you will want. 
 
 Until within very recent times the professional photographer has 
 fought shy of anything in the shape of a dry plate. This is not to be 
 wondered at, for hitherto these plates have not afforded that certainty of 
 result which was yielded by the wet process. But of late a great 
 change has occurred in the opinion of many experienced professionals, 
 and many photographers publish the notice, “Portraits taken in 
 any weather by the new process.” This new process is one in which 
 gelatine supersedes collodion, and there is every reason to suppose 
 that it will ultimately form the standard process by which photographs 
 are produced. 
 
 Its adoption is due not only to the fact that it offers all the usual 
 advantages of a dry process, but because it is, unlike most dry pro- 
 cesses, extremely rapid — far more rapid, indeed, than the collodion 
 process. In order to show that this is actually the case, I may mention 
 that I have now in my possession a photograph of an express train 
 moving at full speed, with a cloud of steam issuing from the funnel. I 
 have seen another taken by the same process of the last Oxford and 
 Cambridge boat race on the Thames, whioh shows not only the com- 
 
THE GELATINE EMULSION PROCESS. 
 
 157 
 
 peting crews, but the crowd of boats and steamboats which accompany 
 them, every ripple on the water being plainly marked. 
 
 I have myself produced some hundreds of photographs by the gelatine 
 process, and have tried nearly every commercial plate that can be 
 bought; I find none so good, or reliable, as those prepared by Messrs. 
 Wratten and Wainwright, by whose plates the two rapid photographs 
 above described were taken. 
 
 For those who prefer to prepare their own plates I give full direc- 
 tions. They are gleaned from the various published ideas of many 
 operators, and if followed with ordinary care, will lead to success. It 
 must be remembered that these dry plates are so much more sensitive 
 to light than wet plates, that they can only be prepared, and handled, by 
 red light. One thickness of ruby glass will be sufficient to protect 
 them from lamp or candle light, but two thicknesses must be used for 
 daylight. 
 
 THE GELATINE EMULSION PROCESS. 
 
 The operations comprised in this process are: — 1. The preparation of 
 the emulsion. 2. Washing the emulsion to free it from the nitrate of 
 ammonia which has not combined with it. 3. Coating the glass plates. 
 
 Procure a large new tin saucepan, and solder to its bottom inside a 
 piece of tin in the form of a triangle, so that it will stand about one inch 
 high, and form the support for a lesser sized gallipot. The saucepan 
 thus prepared should be placed above a small lamp or gas flame. 
 Half fill both the saucepan and the bottle with water, and so regulate 
 the flame beneath that the water remains at one uniform temperature, 
 say 95° Fah. Now procure a wide-mouthed bottle of about six ounces 
 capacity, which will stand easily inside the jar, with plenty of space 
 round it for the water. The bottle should have a good cork, with a 
 string attached, so that it can be easily removed when necessary. Into 
 this bottle put the following mixture : — 
 
 Bromide of ammonia . . 210 grs. 
 
 Nelson’s gelatine ... 87 grs. 
 
 Distilled water .... 3 oz. 
 
 Shake well and put aside for the gelatine to swell, which it will do in 
 about twenty minutes. When this is done place the bottle in the jar, 
 close the lid of the saucepan, and adjust the lamp flame so that the 
 heat will not rise above 90°. 
 
 In a narrow four-ounce bottle put this sensitising mixture : — 
 
 Nitrate of silver . . 130 grs. 
 
 Distilled w r ater . . 3 oz. 
 
 When dissolved, place this bottle in the jar, by the side of the gelatine 
 mixture. In half an hour’s time remove both bottles from the water, 
 and take them into the dark room. Give the gelatine mixture a final 
 shake, then remove the cork, and pour the silver solution into it, after- 
 
158 
 
 boy’s playbook of science. 
 
 wards shaking the compound vigorously for a minute or two. It is 
 now advisable to cover the bottle, cork and all, with thick brown paper, 
 fastened on with sealing-wax. This is a precaution against any acci- 
 dental ray of light, which would utterly spoil the emulsion. The bottle 
 is now returned to the jar, and is kept at the same temperature as 
 before for from four to eight days. It is a curious fact that the sensi- 
 tiveness of the resulting plates is altogether dependent upon the length 
 of time that this cooking operation occupies. The longer the time, the 
 more rapid the plates ; during the whole time, night and day, the lamp 
 must be kept burning so as to preserve the temperature above mentioned, 
 and the bottle must be shaken twice every day while the operation is 
 proceeding. 
 
 At the end of the allotted time, the emulsion must be taken into the 
 dark room, and turned into a porcelain dish. Here it will speedily set 
 into a jelly, but must in the meantime be carefully covered from all light. 
 
 While this operation is going forward, make a bag of that kind of 
 canvas which is used as a backing for berlin wool work. Into this bag 
 scrape the jelly-like emulsion, with a piece of glass, or with a bone paper 
 knife. Now close the opening of the bag, and squeeze the emulsion 
 with the hands, so that it oozes out of the numberless pores in the 
 coarse canvas. By this means it is so subdivided that the water which 
 is afterwards applied to it thoroughly removes all the unaltered nitrate 
 of silvej. , 
 
 The emulsion should be squeezed into a wooden tray with a calico 
 bottom. This tray can afterwards be put into a large trough, or wash- 
 ing tub, and allowed to float, the water being changed every three or 
 four minutes. In a quarter of an hour the emulsion can again be scraped 
 together, put back into a bottle, which has in the meantime been 
 thoroughly cleansed, and once more covered over in the saucepan. By 
 the time that it is again liquid under the influence of the heat applied 
 to it, we shall be ready to proceed to the next operation, the coating of 
 the plates. 
 
 The plates having been perfectly cleaned, are held one by one in the 
 left hand, preferably on a pneumatic plate-holder, while the emulsion 
 is applied in much the same manner as collodion. A pool is poured on 
 the centre of the plate, and is helped to cover it by the guidance of a 
 glass rod. As each plate is coated, it is laid on a sheet of thick glass, 
 or a slab of marble, which has been previously brought to a true level.. 
 The plate must be allowed to dry spontaneously, which in a dry 
 atmosphere will take about six hours, they can then be packed away 
 in grooved, light-tight boxes ready for use. 
 
 I invariably develop gelatine plates by the method recommended by 
 Messrs. Wratten and Wainwright, which is as follows : — 
 
 Stock Solution A # . 
 
 Ammonia liquor fort . . . 
 
 Bromide of potash . . . 
 
 Water 
 
 1 oz. 
 60 gr. 
 
 2 oz. 
 
THE GELATINE EMULSION PROCESS. 
 
 15$ 
 
 Developer. 
 
 Pyrogallic acid 6 gr. 
 
 Stock solution A* 20 drops. 
 
 Water 2oz. 
 
 “ Lay the exposed plate in a dish of cold water while the pyrogallic 
 acid is mixed. Eor each J or 5 X 4 plate use six grains of pyro diluted 
 with two ounces of water. Eirst pour off the water from the plate, 
 and apply the pyro solution, then add five drops of stock solution A*, 
 and keep this weak developer on the plate until the highest lights are 
 pretty well visible. Then add from fifteen to twenty drops more of 
 A* to finish development. Whenever any of the solution A # is to be 
 added to the pyro solution, it should be first dropped into the develop- 
 ing cup, and then, if the solution which is in the dish be poured back 
 to the cup, a perfect mixture will be the result, without the necessity 
 of stirring.” 
 
 Those who prefer a developer even more simple may use the 
 following : — 
 
 Neutral oxalate of potash . . 1 oz. 
 
 j Water (boiling) . . . . 4 oz. 
 
 When dissolved stir in about a quarter of an ounce of oxalate of iron, 
 and when cold, it may be filtered, or the clear portion decanted for use. 
 If enough be made to use in a dish, the plate may be dropped into it 
 without preliminary soaking, and left until all the details are out. It 
 will be seen that by this latter plan of development the photograph 
 simply develops itself without any interference on the part of the 
 operator. This is all very well when a plate has received accurate 
 exposure ; but when from any cause it has been over or under exposed, 
 the alkaline developer before described gives far greater control over 
 the operation. As far as cleanliness is concerned, the ferrous-oxalate 
 developer is simply perfection, for the fingers may be moved about in 
 the solution with impunity. It will doubtless prove a great boon 
 to the fair sex, who have hitherto eschewed photography on account 
 of its unpleasant adjuncts in the shape of blackened fingers. 
 
 In cases where, from unavoidable over-exposure, it has been im- 
 possible to obtain density with the alkaline developer, a most careful 
 washing should be given after fixing (the fixing bath being hyposulphite 
 of soda, as in the wet process), with a view to remove the last trace of 
 the alkali (ammonia). Intensification can then be effected by the use of 
 the following formula : — 
 
 A. 
 
 Protosulphate of iron 15 grs. 
 
 Gelatine acid solution, (as presently described) . . 40 drops. 
 Water 1 oz. 
 
ICO 
 
 boy’s playbook of science. 
 
 B. 
 
 Nitrate of silver 10 grs. 
 
 Acetic acid, glacial, 50° .... 10 drops 
 Water „ . 1 oz. 
 
 The gelatino -acetic solution is compounded as under : — 
 
 Gelatine 15 grs. 
 
 Acetic acid, glacial, 50° .... 3 drs. 
 
 Water 5 drs. 
 
 It is as well to prepare a stock of this, and also of A, as they are both 
 better for keeping. 
 
 To proceed — first flood the plate with water, and then with a solution 
 of iodine and iodide of potassium of the colour of pale sherry for one 
 minute ; rinse it off, and apply enough of A to cover the plate for about 
 the same time. Now drop into the cup a drachm of B, and bring the 
 A back from the plate to the cup to mix them together. Re-apply 
 and keep the mixture moving over the surface until the density is 
 sufficient. 
 
 Both development and intensification should be performed in a dish. 
 When the plate is again dry, warm and varnish as usual. 
 
 Fig. 143. First effect of peripatetic photography on the rural population. 
 
CHEMISTRY. 
 
 161 
 
 BROMINE. 
 
 Bromine (fipcopos, a bad odour). Symbol, Br. Combining propor- 
 tion, 80. Specific gravity, 3187. 
 
 In a previous portion of this work, the connexion between chlorine, 
 iodine, and bromine has been pointed out ; and as we have to notice the 
 colour of the element bromine, the chromatic union of the triad may 
 be alluded to. These elements present very nearly all the colours of 
 the spectrum : 
 
 Bromine red to orange. 
 
 Chlorine yellow to green. 
 
 Iodine blue, indigo, violet. 
 
 These three elements also furnish examples of the three conditions of 
 matter ; iodine being a solid, bromine a fluid, chlorine a gas ; the 
 relation of their combining proportions is also curious : as might be ex- 
 pected, the fluid bromine takes an intermediate position, and (according 
 to the axiom that half the sum of the extremes is equal to the mean) 
 by dividing the combining proportions of iodine and chlorine, and 
 adding them together, we have, as nearly as possible, the combining 
 proportion of bromine. 
 
 Chlorine 35*5 - 4 - 2 = 17*75 
 
 Iodine 127 4- 2 = 63 50 
 
 81-25 
 
 The combining proportion of bromine is 80, but 81*25 is so near, 
 that it may reasonably be conjectured future experiments will reduce the 
 number of the three elements, and may prove that they are only modifi- 
 cations of a single one. This is the only kind of alchemy which is 
 tolerated in the nineteenth century, and any philosopher who will reduce 
 the number of elements, and prove that some of them are only modi- 
 fications of others, will achieve a renown that must transcend the eclat 
 of all previous discoverers. 
 
 Bromine was discovered by Balard, in 1826, and, like chlorine and 
 iodine, is a constituent of sea water. The chief source of bromine is 
 a mineral spring at Kreutznach, in Germany. The process by which it 
 is obtained offers a good example of chemical affinity ; the water of the 
 mineral spring is evaporated, all crystallizable salts removed, and a current 
 of chlorine gas passed through the remaining solution, which changes 
 to a yellow colour, in consequence of the liberation of the bromine by 
 the combinations of chlorine with the bases previously united with the 
 former ; the liquid is then shaken with ether, which dissolves out the 
 bromine. In the next place, the etherial solution is agitated with 
 .strong solution of potassa, and is thus obliged to part with the bromine 
 which is converted into bromate of potassa; this is ultimately changed 
 by fusion to bromide of potassium ; and by distillation with black oxide 
 of manganese and sulphuric c-icid, the bromine is finally obtained. Six 
 
 M 
 
162 
 
 boy’s playbook of science. 
 
 processes are therefore necessary before the small quantity of bromine 
 contained in the mineral spring-water, is separated. 
 
 First Experiment. 
 
 Bromine is a very heavy fluid, which should be preserved by keeping 
 it in a bottle covered with water ; when required, a few drops may be 
 removed by means of a small tube, and dropped into a warm bottle, 
 which is quickly filled with the orange-red vapour. If some phosphorus 
 is placed in a deflagrating spoon, and exposed to the action of bromine 
 vapour, it takes fire spontaneously. 
 
 Second Experiment. 
 
 Powdered antimony sprinkled into the vapour of bromine immediately 
 takes fire. 
 
 Third Experiment. 
 
 A burning taper immersed in a bottle containing the vapour of bromine 
 A gradually extinguished. 
 
 Fourth Experiment. 
 
 Liquid bromine exposed to a freezing mixture of ice and salt, or 
 reduced to a temperature of about eight degrees below zero, solidifies 
 into a yellowish-brown, brittle, crystalline mass. 
 
 Fifth Experiment. 
 
 A solution of indigo shaken with a small quantity of the vapour of 
 bromine is quickly bleached. Many substances, when brought in contact 
 with liquid bromine, combine with explosive violence, and therefore 
 experiments with liquid bromine are not recommended, as all the most 
 instructive and conclusive results can be obtained by the use of the 
 vapour of bromine, which is easily procured by allowing a few drops to 
 fall into a warm, dry bottle. 
 
 Bromine, as already mentioned, is used in the art of photography. 
 
 FLUORINE. 
 
 Symbol, P. Combining proportion, 19. 
 
 This singular element seems almost to embody the ancient idea of 
 the alchemists, being a sort of alkahest , or universal solvent ; or in 
 plainer language, its affinities for other bodies are so powerful, that it 
 attacks every substance (not even excepting gold), at the moment of 
 its liberation, and combines therewith, so that its isolation has not 
 yet been effected. Chemists who assert that they have been able to 
 obtain fluorine in the elementary condition, pronounce it to be a gas 
 which possesses the colour of chlorine ; but the experiments, as hitherto 
 conducted, render that statement extremely doubtful. 
 
ETCHING ON GLASS. 
 
 163 
 
 The only interesting fact connected with fluorine, is the remarkable 
 property of attacking glass and other silicious bodies, belonging to its 
 combination with hydrogen gas, called hydrofluoric acid. This acid is 
 easily obtained and used by placing some powdered fluorspar in a leaden 
 tray six inches square and two inches deep. If sulphuric acid is now mixed 
 with the powdered spar, so as to form a thin paste, and heat applied, 
 the vapour of the hydrofluoric acid quickly rises, and can be employed 
 to etch a glass plate upon which a drawing may have been previously 
 traced by scratching away the wax, with which it is first coated. By 
 heating the glass plate before a fire, a sufficient quantity of wax is soon 
 melted on to it by merely rubbing the wax against the glass plate ; any 
 excess should be avoided, if a well-executed drawing is required to be 
 etched on its surface. (Eig. 149.) 
 
 Fig. 149. aaa. The glass plate, with the waxed side downwards, placed on the 
 leaden tray containing the fluorspar and sulphuric acid. b. Spirit lamp. 
 
 The wax plate must not remain too long over the leaden tray, as the 
 heat is apt to melt the wax, when the acid not only attacks those parts 
 from which the wax has been removed by the etching needle, but also 
 the surface of the glass generally, and thus the clearness of the design 
 is spoilt.’ After exposure — and it is as well to prepare two or three 
 glass plates for the experiment — the wax is quickly removed by rubbing 
 and washing with oil of turpentine, and the design (beautifully etched 
 into the glass) is then apparent. 
 
 CHAPTER XII. 
 
 CARBON, BORON, SILICON, SELENIUM, SULPHUR, PHOSPHORUS. 
 
 This group of non-metallic elements has been frequently styled 
 “ Metalloids , 55 meaning substances allied to, but not possessing, all the 
 properties belonging to a metallic substance; and therefore perhaps 
 the expression, non-metallic solids, is the best that can be adopted. They 
 may be subdivided into two classes of three each, which have properties 
 more or less allied to each other — viz., 
 
 Carbon, Boron, Silicon; and 
 Selenium, Sulphur, Phosphorus. 
 
 M 2 
 
164 
 
 boy’s playbook of science. 
 
 carbon. 
 
 Symbol, C; Combining proportion, 12*0. 
 
 This element has almost the property of ubiquity, and is to be found 
 not only in ail animal and vegetable substances, in common air, sea, and 
 fresh water, but also in various stones and minerals, and especially in 
 chalk and limestone. 
 
 There is, perhaps, no element which offers a greater variety of amusing 
 experiments and elementary facts than carbon, whether it be considered 
 either in its simple or combined state. 
 
 A piece of carbon, in the shape of the Koh-i-Noor, was one of the 
 chief attractions at the first Exhibition in Hyde Park. The diamond is 
 the hardest and most beautiful form of charcoal ; how it was made in 
 the great laboratory of nature, or how its particles came together, seems 
 to be a mystery which up to the present time has not yet been solved, 
 at all events no artificial process has yet produced the diamond. 
 
 Sir D. Brewster, speaking of the Koh-i-Noor, remarks that on placing 
 it under a microscope, he observed several minute cavities surrounded 
 with sectors of polarized light, which could only have been produced 
 by the expansive action of a compressed gas or fluid , that had existed in 
 the cavities when the diamond was in the soft state. 
 
 Now it is known that bamboo, which is of a highly silicious nature, 
 has the property of depositing in its joints a peculiar form of silica, 
 called tabasheer. Silicon is one of the triad with carbon — i.e ., it is allied 
 to carbon on account of certain analogies ; may it not then be supposed 
 that, in times gone by, ages past, when the atmosphere was known to 
 be highly charged with carbonic acid gas, there might possibly have 
 existed some peculiar tree which had not only the power of decomposing 
 carbonic acid (possessed by all plants at the present period), but was 
 enabled, like the bamboo, to deposit, not silica, which is the oxide of 
 silicium, but carbon, the purest form of charcoal — viz., the diamond ? 
 Speculation in these matters is ever more rife than stern proof, and it 
 may be stated, that all attempts to manufacture this precious gem 
 (like those of the alchemists with gold and silver) have most signally 
 failed. 
 
 First Experiment. 
 
 Box and various woods, dried bones, and different organic matters, 
 placed in a nearly close iron or other vessel, and heated red hot, so that all 
 volatile matter may escape, leave behind a solid black substance called 
 charcoal. If that kind obtained from bones, and termed bone black or 
 ivory black, is roughly powdered, and placed in a flask with some solu- 
 tion of indigo or some vinegar, or syrup obtained by dissolving common 
 moist sugar in water, and boiled for a short period, the colour is re- 
 moved, and on filtering the liquid it is found to be as clear and colour- 
 less as water, provided sufficient ivory black has been employed. 
 
COMBUSTION OF THE DIAMOND. 
 
 165 
 
 Second Experiment. 
 
 Charcoal is a disinfectant, and is used for respirators ; it has even been 
 recommended medically, and charcoal lozenges can be bought at various 
 chemists shops. . If a few drops of a strong solution of hydrosulphuret 
 of ammonia (which has the agreeable odour belonging to putrid eggs) 
 is mixed with half a pint of water, it will of course smell strongly, and 
 likewise precipitate Goulard water, or a solution of acetate of lead 
 black ; but on shaking the water with a few ounces of charcoal, it no 
 longer smells of sulphuretted hydrogen, and if filtered and poured into 
 a solution of lead does not turn it black. This chemical action of 
 charcoal, independent of Its seeming mechanical attraction for colouring 
 matter, would appear to show that the pores of charcoal contain oxygen, 
 which in that peculiar condensed state destroys colouring matter, and 
 oxidizes other bodies. 
 
 Third Experiment. 
 
 A very satisfactory experiment, proving that the diamond and plum- 
 bago or black lead are identical with charcoal, although differing in 
 outward form and purity, can be made at a little cost, 
 by purchasing a fragment of refuse diamond, called 
 “ boart” of Mr. Tennant of the Strand. A small 
 piece costs about five shillings. The fragment should 
 be carefully supported by winding some thin platinum 
 wire round it, as, if the wire is too thick, it cools 
 down the heat of the bit of diamond and prevents it 
 kindling m the oxygen gas. A difficulty may arise in 
 preparing the fragment, in consequence of the wire 
 continually slipping off. The “ boart” should there- 
 fore be grasped by the thumb and first finger, and the 
 wire wound round ; then it must be carefully turned 
 and again wound across with the platinum wire, as 
 m the sketch below. (Fig. 350.) 
 
 A piece of black lead (so called) may now be taken 
 from a lead pencil and also supported by platinum 
 wire ; likewise a bit of common bark charcoal or hard 
 coke. Ihree bottles of oxygen should now be pre- 
 paied from chlorate of potash and oxide of manga- 
 nese, an extra bottle being provided for the diamond 
 in case there should be any failure in its ignition. 
 
 e bark charcoal can be first ignited by holding a corner in the spirit 
 rf 1 ?! t0r \ seconds ; when plunged into oxygen it immediately 
 kindles a nd burns with rapidity, and if the cork is well fitted, the 
 pioduct of combustion— —viz., carbonic acid gas— is retained for future 
 examination The small piece of black lead is next heated red hot in 
 f ame ° ^lie s P ln ^. lamp, and being attached by its platinum sup- 
 port to a stiff copper wire thrust through a cork, which fits the bottle 
 
 mifililf 115 1S § aC ml W i^ st rec ^ the g as > an d continues to glow 
 
 onsumed. The fragment of diamond is by no means, however so 
 
 Fig-. 150. a. The 
 platinum wire. B.The 
 fragment of “boart" 
 or refuse diamond. 
 
166 
 
 boy's playbook of science. 
 
 easily ignited, the flame of the spirit lamp must be urged upon it with 
 the blowpipe ; when quite red hot, an assistant may remove the stopper 
 from the bottle of oxygen, and the person heating the diamond should 
 plunge it instantly into the gas ; if this is dexterously managed, the 
 fragment of boart glows like a little star, and the combustion frequently 
 continues till the piece diminishes so much that it falls out of its platinum 
 support. 
 
 Sometimes the diamond cools down without igniting, the same pro- 
 cess must therefore be repeated, and a few extra bottles of oxygen 
 will prevent disappointment, as every failure destroys the purity of the 
 gas bv admixture with atmospheric air when the stopper is removed. 
 (Fig. 151.) 
 
 Fig. 151. a. Bottle containing bark charcoal, b. Ditto the plumbago or 
 black lead. c. Ditto the diamond. 
 
 The combustion having ceased in the three bottles, the corks are 
 removed, and the glass stoppers again fitted for the purpose of testing 
 the products , which offer no apparent indication of any change, as oxygen 
 and carbonic acid gas are both invisible. In each bottle a new com- 
 bination has been produced ; the charcoal, the black lead, the diamond 
 have united with the oxygen, in the proportion of six parts of carbon to 
 sixteen parts of oxygen, to form twenty-two parts of carbonic acid gas, 
 which may be easily detected by pouring into each bottle a small quan- 
 tity of a solution of slacked lime in water, called lime water. This 
 test is easily made by shaking up common slacked lime with rain or 
 distilled water for about an hour, and then passing it through a calico 
 or paper filter. The test, though perfectly clear when poured in, be- 
 comes immediately clouded with a white, precipitate, usually termed a 
 milkiness , no doubt in allusion to the London milk, which is supposed to 
 contain a notable proportion of chalk and water, for in this case the 
 precipitate is chalk, the carbonic acid from the diamond and the charcoal 
 having united with the lime held in solution by the water and formed 
 carbonate of lime, or chalk, a substance similar in composition to 
 marble, limestone, Iceland or double refracting spar, these three being 
 nearly similar in composition, and differing only, like carbon and the 
 diamond, in external appearance. 
 
PREPARATION OF CARBONIC ACID GAS. 
 
 167 
 
 The milkiness, however, must not be held . as conclusive of the pre- 
 sence of carbonic acid gas until a little vinegar or other acid, such as 
 hydrochloric or nitric, has been finally added; if it now disappears 
 with effervescence (like the admixture of tartaric acid, water, and car- 
 bonate of soda), the little bubbles of carbonic acid gas again escaping 
 slowly upwards, leaving the liquid in the three bottles quite clear, then 
 the experimentalist may sum up his labours with these effects, which 
 prove in the most decisive manner that common charcoal, black lead, 
 and the diamond, are formed of one and the same element — viz., 
 carbon. 
 
 Fourth Experiment. 
 
 Having effected the synthesis (or combining together) of the diamond 
 and oxygen, it is no longer possible to recover it in its brilliant and 
 beautiful form. If the product of combustion is retained in a flask 
 made of thin, hard glass, and two or three pellets of the metal potassium 
 are placed in directly after the diamond has ceased to burn, and the 
 flame of a spirit lamp applied till the potassium ignites, then the metal, 
 by its great affinity for oxygen, takes away and separates it again from 
 that which was formerly the diamond ; but instead of the jewel being 
 deposited, there is nothing but black , shapeless, and minute particles of 
 carbon obtained, if the potash produced is dissolved in water, and the 
 charcoal separated by a filter. 
 
 Fifth Experiment. 
 
 Chalk is made by uniting carbonic acid gas with lime ; it may there- 
 fore be employed as a source of the gas, by placing a few lumps of 
 chalk, or marble, or limestone, in a bottle such as was used in the gene- 
 ration of hydrogen gas ; on the addition of some water and hydrochloric 
 acid, effervescence takes place from the escape of carbonic acid gas, and 
 the cork and pewter pipe being adapted, it may be conveyed by its own 
 gravity into glasses, jugs, or any other vessels, and a pneumatic trough 
 will not be required. Carbonic acid gas has a specific gravity of 1*529, 
 and is therefore rather more than half as heavy again as atmospheric air. 
 
 Sixth Experiment . 
 
 In order to satisfy the mind of the operator that the gas obtained 
 from chalk is similar to the product of combustion from the diamond , some 
 lime-water may be placed in a glass, and the gas from the bottle allowed 
 to bubble through it ; instantly the same milkiness is apparent, which 
 again vanishes on the addition of acid. And this experiment is rendered 
 still more striking if a lighted taper be placed in the glass just after the 
 addition of the acid, when it will be immediately extinguished. 
 
 Seventh Experiment. 
 
 If a lady’s muff-box, supported by threads or chains, is hung on one end 
 of a scale-beam, and counterbalanced by a scale pan and a few shot, it is 
 
168 
 
 boy’s playbook of science. 
 
 immediately depressed on pouring into the muff-box a quantity of car- 
 bonic acid gas, which may have been previously collected in a large tin 
 vessel. After showing the weight of the gas, the box is detached 
 from the scale-beam, and the contents poured upon a series of lighted 
 candles, which are all extinguished in succession. (Fig. 152.) 
 
 Fig. 152. a. Carbonic acid gas poured out of the tin box into b, the muff-box. 
 a b. Detached muff-box, and candles extinguished by the carbonic acid gas poured from it. 
 
 Eighth Experiment. 
 
 The property of carbonic acid gas of extinguishing flame, as com- 
 pared with the contrary property of oxygen, is nicely shown by first 
 passing into a large and tall gas jar one half of its volume of oxygen 
 gas; a large cork perforated with holes may be introduced, so as 
 to float upon the surface of the water in the gas jar, and is usefully 
 employed to break the violence with which the carbonic acid enters the 
 gas jar, as it is passed in to fill up the remaining half volume of the gas 
 jar, which now contains oxygen at the top, and carbonic acid gas at the 
 bottom. On testing the contents of the jar with a lighted taper, it 
 burns fiercely in the oxygen, but is immediately extinguished in the 
 
EXPERIMENTS WITH CARBONIC ACID GAS. 
 
 1G9 
 
 carbonic acid gas, being alternately lighted and put out as it is raised or 
 depressed in the gas jar. 
 
 Ninth Experiment. 
 
 A little treacle, water, and a minute portion of size, may be placed 
 with some yeast in a quart bottle, to which a cork and pewter or glass 
 pipe is attached; directly the fermentation begins, quantities of car- 
 bonic acid gas may be collected, and tested either with lime-water or the 
 lighted taper. 
 
 Tenth Experiment. 
 
 Some clear lime-water placed in a convenient glass is quickly rendered 
 milky on passing through it the air from the lungs by means of a glass 
 tube; thus proving that respiration and (as shown by the ninth ex- 
 periment) fermentation, as well as the combustion of charcoal, produce 
 carbonic acid gas. 
 
 Eleventh Experiment. 
 
 Carbonic acid gas is not only generated by the above processes, but 
 is liberated naturally in enormous quantities from volcanoes, and from 
 certain soils : hence the peculiar nature of the air in the Grotto del 
 Cane. Dogs thrust into this cave drop down immediately, and are 
 immediately revived by the tender mercies of the guides, who throw 
 them into the adjoining lake. This natural phenomenon is well imitated 
 by taking a box, open at the top, and nailing on to it a frame of card- 
 
 Fig. ]53. a a. The box model of the Grotto del Cane, b b. Cardboard fixed in front 
 of box, and painted to imitate rocks, c. Carbonic acid gas bottle, with bent tube passing 
 through hole in the side of the box. A taper introduced at d burns in the upper, and is 
 extinguished in the lower, part of the model. 
 
170 
 
 boy’s playbook of science. 
 
 board, which may be painted to represent rocks, taking care that a portion 
 (about three inches deep) at the lower part is well pasted to the box at 
 the edges, so that the gas may be retained ; a hole is perforated at the 
 top side to admit a lighted taper, and another at the side for the pipe 
 from the carbonic acid bottle ; when the bottom is filled with gas, a 
 taper is applied, which is found to burn in the upper part, but is imme- 
 diately extinguished when it reaches the lower division, where the three 
 inches of pasteboard prevent it falling out : thus showing in a simple 
 manner why a guide may enter the cave with impunity, whilst the dog 
 is rendered insensible because immersed in the gas. (Eig. 353.) 
 
 Twelfth Experiment . 
 
 Many fatal accidents have occurred in consequence of the air in deep 
 pits, graves, &c., becoming unfit for respiration by the accumulation of 
 carbonic acid gas, which may arise either from cavities in the soil, where 
 animal matter has undergone decomposition, or it may happen from the 
 depth and narrowness of the hole or well preventing a proper draught 
 or current of air, so that it becomes foul by the breathing of the man 
 who is digging the pit. Air which contains one or two per cent, of 
 carbonic acid will support the respiration of man, or maintain the flame 
 
 a candle; but it produces the most serious results if inhaled for 
 any length of time ; a lighted candle let down into a well (suspected 
 to contain foul ah) before the descent of the person who is to work 
 in it, may burn, but does not indicate the presence of the small 
 percentage of the poison, carbonic acid. Erequently no trouble is taken 
 to test the air with a lighted candle ; a man is lowered by his com- 
 panions, who see him suddenly become insensible, another is then lowered 
 quickly to rescue him, and lie shares the same fate ; and indeed cases 
 have occurred where even a third and a fourth have blindly and igno- 
 rantly rushed to their death in the humane attempt to rescue their fellow 
 creatures. What is to be done in these cases? Are the living to 
 remain idle whilst the unfortunate man is suffocating rapidly at the 
 bottom of the pit ? No ; provided they do not venture themselves into 
 the pit, they may try every known expedient to alter the condition of 
 the foul air, so as to enable them to descend to the rescue. One should 
 be despatched to any neighbouring house or cottage for a pan of burning 
 coals ; if any slacked lime is to be had, it may be rapidly mixed with 
 water, and poured down the side of the pit ; a bundle of shavings set 
 on fire and let down, keeping it to one side, so as to establish a current ; 
 or even the empty buckets constantly let down empty and pulled up full 
 of the noxious air, may appear a somewhat absurd step to take, but 
 under the circumstances any plan that will change the air sufficiently to 
 enable another person to descend must be adopted ; in proof of which 
 the following experiments may be adduced : 
 
 Eill a deep glass jar with carbonic acid, and ascertain its presence 
 with a lighted taper ; if a beaker glass to which a string is attached is 
 let down into the vessel and drawn up, and then inverted over a lighted 
 
EXPERIMENTS WITH CARBONIC ACID GAS. 
 
 171 
 
 taper, the utility of 
 this simple plan is at 
 once rendered appa- 
 rent ; the beaker glass 
 represents the empty 
 bucket, and can be let 
 down and pulled up 
 full of carbonic acid 
 until a sensible change 
 in the condition of the 
 atmosphere is pro- 
 duced. The best plan, 
 however, is to set the 
 air in motion by heat 
 obtained from burning 
 matter, or even a kettle 
 of boiling water, low- 
 ered by a cord, and 
 this fact is Avell shown 
 by putting a small flask 
 full of boiling water, 
 and corked, at the bot- 
 tom of the deep glass 
 jar containing the car- 
 
 Eig. 154. a. Deep jar containing carbonic acid gas, which 
 is being removed by the little glass bucket, b. Jar con- 
 taining corked flask of boiling water on a pad ; the heated 
 gas rises and the cold air descends to take its place. 
 
 bonic acid gas, which rises like other gases when sufficiently heated, and 
 passing away, mixes with the surrounding air. (Eig. 154.) 
 
 Thirteenth Experiment. 
 
 Carbonic acid gas dissolved in water under considerable pressure, 
 forms that most agreeable drink called soda-water ; the gas is not only 
 useful in this respect, but has been applied most successfully by Mr. 
 Gurney to extinguish a fire on a gigantic scale, which had been burning 
 for years in the waste of a coal mine in Scotland. The same gas, gene- 
 rated suddenly by the combustion of a mixture of nitre, coke dust, and 
 clay, or plaster of Paris, in vessels of a peculiar construction, has 
 formed the subject of a patent by Phillips, since merged into the Eire 
 Annihilator Company. The instrument is peculiarly adapted for ship- 
 ping, and might, if properly used, be the means of saving many ships and 
 valuable lives. (Eig 155.) 
 
 Its practical value is established by the test of actual use : in the 
 streets, by the Leeds Eire Brigade, and by firemen of the Eire Anni- 
 hilator Company, temporarily stationed at Liverpool and Manchester. 
 
 The Eire Annihilator has been formally recognised by the Government 
 Emigration Commissioners, who introduced into the Passengers 5 Act, 
 1852, in § 24, the alternative, “ Or other apparatus for extinguishing fire” 
 with distinct reference to this invention, and subsequently by formal 
 order authorized their officers to pass ships carrying Eire AnnihilatOi's. 
 
172 
 
 boy’s PLAYBOOIv of science. 
 
 Fio. 155 a A carriage with six fire annihilators, No. 5 size, fitted with moveable pipes. 
 The bodv of the carriage forms a tank for forty gallons ot water; the tank is filled at a 
 bun-hole in the platform ; a patent tap is fitted to the rear of the carnage ; a spigot is 
 Sd near the end upright of the rail; a hand-pump is placed m the box at rear of 
 Srrfncr^ a leather bucket with foot-holds and three canvas buckets are hung on the 
 
 ASffltotf onehorse l poleS provided to fir across the 
 shafts, so that the battery may be drawn by hand. 
 
 Monsieur Adolphe Girard has proposed that 
 provided with an apparatus for the generation 
 
 all houses should be 
 of carbonic acid gas, 
 
 v-'tr 156 a Tank containing acid, communicating by a pipe with n, half (hied with 
 chalk ^ and water, c c c c. Pipes conveying carbonic acid from the generator b, to the 
 ceiling, where it is discharged from numerous holes on the fire beneath. 
 
CHEMISTRY. 
 
 173 
 
 placed outside the building, which is to be conveyed along the ceiling 
 by means of pipes perforated with numerous holes, and to be put in 
 operation directly a fire breaks out. This plan, however ingenious, 
 could hardly supply the carbonic acid gas with sufficient rapidity, and 
 it is to be feared would utterly fail in practice. (Fig. 150.) 
 
 BORON. 
 
 Symbol, B ; combining proportion, 11*0. 
 
 Discovered by Davy, in 1807, in borax, which is a biborate of 
 soda (Na 2 B 4 0 7 ) and is used very extensively in the manufacture of 
 glass ; also for glazing stoneware and soldering metals ; it is also a 
 valuable flux in various crucible operations, whilst in testing minerals 
 with the blowpipe it is invaluable. Borax is made either from tincal, a 
 substance that occurs naturally in some parts of India, China, and 
 Persia, or by the addition of carbonate of soda to boracic acid, a sub- 
 stance obtained from the volcanic districts of Tuscany, whence it is 
 imported to this country, and used in the manufacture of borax. 
 
 The element boron may be obtained by placing some pure boracic 
 acid and some small bits of potassium in a tube together, and applying 
 the flame of a spirit-lamp, a glow of heat takes place, and when the tube 
 is cold the potash may be washed away, and the boron remains as a 
 dark brownish powder somewhat resembling carbon. M. St. Claire 
 Deville and Wohler have lately made some important discoveries with 
 respect to this element, and disproved the statement that it is uncrystal- 
 lizable. Their researches prove it to be producible under three forms 
 and of various colours, such as honey -yellow and garnet-red, the crystals 
 in some cases being like diamonds of the purest water — /.«?., limpid 
 and transparent. A new combination of aluminium and boron is 
 stated to possess the most remarkable properties. It is harder than 
 the diamond, and in the state of powder will cut and drill rubies, and 
 even the diamond itself, with more facility than diamond powder. 
 Deville and Wohler incline to the belief that the diamond is dimorphous, 
 and capable (in conditions yet to be described) of assuming the same forms 
 as boron. At a high temperature, boron, like titanium, absorbs nitrogen 
 only from the atmosphere, and rejects the oxygen. (Query, may not 
 some of those remarkably hard black diamonds prove to be boron ?) 
 
 SILICON. 
 
 Symbol, Si ; combining proportion, 28*5. 
 
 The great Davy was the first to obtain this element in 1807. 
 Silicon in the pure state is a dark brown powder; if ignited at a very 
 high temperature it assumes a chocolate colour, which is supposed to 
 be the allotropic condition, because it no longer burns when heated 
 moderately in oxygen or air, and is not attacked by hydrofluoric acid. 
 
174 
 
 eoy’s playbook of science. 
 
 The most interesting combination of silicon is the dioxide called 
 silica (Si 2 0). Silicon is next to oxygen so far as regards its plen- 
 tifulness, and is found in the state of silica in nearly every mineral, 
 but especially in rock crystal, quartz, flint, sand, jasper, agate, and 
 tripoli. It is largely used in the manufacture of glass, and a most 
 useful “ soluble glass” is obtained by melting together in a crucible 
 fifteen parts of sand, ten parts of carbonate of potash, and one part of 
 charcoal. 
 
 Cold water merely washes away the excess of alkali, and after this is 
 done the powdered soluble glass may be boiled with water in the pro- 
 portion of one of the former with five of the latter, when it gradually 
 dissolves ; the solution may be evaporated to a thick pasty fluid, which 
 looks like jelly when cool, and on exposure to the air in thin films 
 changes to a transparent, colourless, brittle, but not hard glass. Wood, 
 cotton, and linen fabrics are rendered less combustible when coated 
 with this glass, which excludes the oxygen of the air, and it has lately 
 been employed to fill up the porous and capillary openings in stone 
 exposed to the atmosphere, and is stated to be very efficacious as a 
 preservative of the stone in some cases. 
 
 SULPHUR. 
 
 Symbol, S ; combining proportion, 16. 
 
 Sulphur, like charcoal, is of common occurrence in nature, and is 
 chiefly supplied from the volcanic districts of Tuscany and Sicily : there 
 is an abundance of this element in the United Kingdom, but then it is 
 locked up in combination with iron, copper, and lead, under the name 
 of iron pyrites, copper pyrites, galena ; and whilst Sicily and Tuscany 
 supply thousands of tons weight in the uncombined state, it is not, of 
 course, worth while to go through expensive operations at home for the 
 separation of sulphur from the ores. During the dispute between Sicily 
 and England, several patents were secured for new and economical pro- 
 cesses by which sulphur was obtained from various minerals ; and had 
 this country been excluded from a supply of native sulphur, no doubt 
 some of these patents would now be in active operation. 
 
 It is almost possible to estimate the commercial prosperity of a country 
 by the sulphur it consumes, not, happily, by their warlike operations, but 
 in the manufacture of oil of vitriol or sulphuric acid, which is the starting 
 point of a great number of useful arts and manufactures. 
 
 First Experiment. 
 
 Some very curious results may be obtained by heating sulphur at cer- 
 tain temperatures ; in the ordinary state it is a pale yellow solid, and 
 when subjected to a temperature of 226° Eahr. it melts to a brownish • 
 yellow, transparent, thin fluid ; according to all preconceived notions of 
 the properties of substances which liquify bv an increase of heat, it 
 might be imagined that every additional degree of heat would only 
 
EXPERIMENTS WITH SULPHUR. 
 
 175 
 
 render the melted sulphur still more liquid, but strange to say, when it 
 reaches a temperature of about 320° Fahr. it changes red, and thick 
 like treacle ; and as the heat rises it becomes so tenacious, that the ladle 
 in which it is contained may be inverted, and the sulphur will hardly 
 flow out : at about 482° Faiir. it again becomes liquid, but not so fluid 
 as at the lower temperature. If allowed to cool from 482° Faiir., the 
 above results are simply inverted; the sulphur becomes thick, again 
 liquid, and finally crystallizes in long, thin, rhombic prisms, which are 
 seen most perfectly by first allowing a crust of sulphur to form on the 
 liquid portion, and then having made two holes in this crust, the sulphur 
 is poured out, when the remainder is found in the interior of the crucible 
 crystallized in the form already mentioned. Sulphur takes fire in the 
 air w T hen exposed to a heat of about 560° Fahr., and burns with a pale 
 blue flame ; and, as already stated, it may be poured from a considerable 
 height on a still dark night, and produces a continuous column of blue 
 fire, just like an unbroken current of electricity. If the melted and 
 burning sulphur is received into a vessel containing boiling water, it is 
 no longer yellow, but assumes a curious allotropic state, in which it is a 
 reddish-brown, transparent, shapeless mass, that may be easily kneaded 
 and used for the purpose of taking casts of seals, which become yellow 
 in a few days, and are found then to be hard and crystallized. 
 
 Second Experiment. 
 
 Sulphur vapour, in one sense, may be regarded as a supporter of com- 
 bustion : if a clean Florence oil-flask is filled with copper turnings, and a 
 little roughly-powdered sulphur sprinkled in, and heat applied, the copper 
 glows with an intense heat, and burning in the vapour of the sulphur, pro- 
 duces a sulphuret of copper ; from this compound the sulphur maybe again 
 obtained by boiling the powdered sulphuret with weak nitric acid, which 
 oxidizes and dissolves the copper, leaving the greater part of the sul- 
 phur behind, which may be collected, melfed, and burnt, and will be 
 found to display all the properties belonging to that element. This 
 experiment is a very good example of simple analysis; and if the 
 copper is weighed and likewise the combined sulphur, a good notion may 
 be formed of the principles of combining proportions. 
 
 Third Experiment. 
 
 A little sulphur burnt under a gas jar, or in any convenient box (a 
 hat-box, for instance), produces sulphurous acid (S0 2 ), which will bleach , 
 a wetted red rose or dahlia, and many other flowers. This gas is em- 
 ployed most extensively in bleaching straw, and sundry woollen goods, 
 such as blankets and flannel, and likewise silk, and is perhaps one of the 
 best disinfectants that can be employed; when fever has been raging in 
 the dwellings of the poor, as in cottages, &c., all metallic substances 
 should be removed, the doors and windows closed, the bedding, &c., well 
 exposed, and then a quantity of sulphur should be burnt in an old fry- 
 
176 
 
 boy’s playbook of science. 
 
 ing-pan placed on a brick, taking care to avoid the chance of setting the 
 place on fire ; after a few hours the doors and windows may be opened, and 
 the disinfectant will be found to have done its work cheaply and surely. 
 
 Fourth Experiment. 
 
 The presence of sulphur in various organic substances, such as hair, 
 the white of egg, and fibrine, is easily detected by heating them in a 
 solution of potash, and adding acetate of lead as long as the precipi- 
 tate formed is redissolved ; finally the solution must be heated to the 
 boiling point, when it instantly becomes black by the separation of sul- 
 phuret of lead. 
 
 Fifth Experiment. 
 
 Sulphuric acid, H 2 S0 4 , or oil of vitriol, is made in such enormous 
 quantities that it is never worth while to attempt its preparation on a small 
 scale. In consequence of its great affinity for water, many energetic 
 changes are produced by its action. Oil of vitriol poured on some loaf 
 sugar placed in a breakfast-cup with the addition of a dessert-spoonful of 
 boiling water, rapidly boils and deposits an enormous quantity of black 
 charcoal. If a word be written on a piece of white calico with dilute 
 sulphuric acid, and then rapidly and thoroughly washed out, no visible 
 change occurs ; but if the calico is exposed ^o heat, so that the excess 
 of water is driven off, the remaining and now concentrated oil of vitriol 
 attacks the calico, and the word is indelibly printed in black by the 
 decomposition of the fabric of cotton. A very remarkable process has 
 lately been introduced by Mr. Warren de la Rue, by which paper is con- 
 verted into a sort of tough parchment-like material, called ametastine, by 
 the action of oil of vitriol and water of a certain fixed strength ; and any 
 departure from the exact proportions destroys the toughness of the paper. 
 After the paper has been acted upon by the acid, it becomes extremely 
 tenacious, and will support a considerable weight without breaking. Mr. 
 Smee has used this ametastine in the construction of an hygrometer, and 
 states that it may save many a traveller from catching a severe rheu- 
 matism in a damp bed. 
 
 Sixth Experiment. 
 
 When the vapour of sulphur is passed over red-hot charcoal and the 
 product carefully condensed, a peculiar liquid is obtained, called bisul- 
 phide of carbon (CS 2 ), which possesses a peculiar odour, is extremely 
 transparent and brilliant-looking, and enjoys a high refractive power. 
 This liquid is used as a solvent for phosphorus and other substances, and 
 is extremely volatile and combustible, and burns silently with a pale 
 blue flame. The combustion of its vapour, mixed with certain gases, 
 offers a good example of the fact that slow burning may be a peaceful 
 experiment, whilst very rapid combustion often resolves itself into an 
 explosion. Thus, if a few drops of bisulphide of carbon are dropped into 
 a narrow-mouthed dry quart bottle containing common air, and flame 
 applied, the combustion takes place with rapidity, a rushing or 
 
EXPERIMENTS WITH SULPHUR. 
 
 177 
 
 roaring sound being audible, in consequence of the diffused vapour beino- 
 supplied with more oxygen, and burning more rapidly than it would do 
 if simply consumed from a stick or glass rod wetted with the fluid. A 
 still greater rapidity of combustion is ensured by dropping some bisul- 
 phide of carbon into a long stout cylindrical jar, fifteen inches long 
 and three inches in diameter, containing nitric oxide gas (NO) ; when 
 flame is applied the mixture burns with a bright flash and some noise 
 and if burnt in a narrow mouthed bottle would most likely blow it to 
 atoms. 
 
 The greatest rapidity of combustion, and of course the loudest noise 
 is obtained by shaking some bisulphide of carbon in a similar stout and 
 strong cylindrical jar filled with oxygen gas, but in this case the jar 
 must be protected w*ith a double cylinder of stout wire gauze • it does 
 not always break, but if it is blown to fragments each particle ’becomes 
 a lancet-shaped piece of glass, which is capable of producing the most 
 dangerous wounds. (Fig. 157.) 
 
 Fig. 157. a. Air and bisulphide of carbon, b. Nitric oxide and ditto, c. Oxygen and 
 ditto, d d. Stout cylinder of double wire gauze, open top and bottom. 
 
 SELENIUM. 
 
 Selenium (o-eX^r), the Moon*) ; symbol, Se: combining 
 proportion, 79 '5. 
 
 This new metallic dement is allied to sulphur, and is a species of 
 chemical curiosity, being found in minute quantities in various minerals ; 
 it may be melted and cast into any form. Medallions of the discoverer 
 (Berzelius) of selenium, in little cases, are imported from Germany, 
 for the cabinets of the curious. 
 
 * Called selenium on account of its strong analogy to tellurium (tellus, the earth). 
 
 N 
 
178 
 
 boy’s playbook of scien.ce. 
 
 PHOSPHORUS. 
 
 Phosphorus (< poos , light ; cpspcLu , to bear ; symbol, P ; combining 
 proportion, 3L) 
 
 Monsieur Salverte, in his work on the Occult Sciences of the 
 Ancients, quotes a remarkable story respecting the probable discovery 
 of the nature of phosphorus in 1761: — “A Prince San Severo, at 
 Naples, cultivated chemistry with some success ; he had, for example, 
 the secret of penetrating marble with colour, so that each slab sawed 
 from the block presented a repetition of the figure imprinted on its 
 external surface. In 1761, he exposed some human skulls to the action 
 of different reagents, and then to the heat of a glass furnace, but paying 
 so little attention to his manner of proceeding, that he acknowledged 
 he did not expect to arrive a second time at the same result. Prom the 
 product he obtained a vapour, or rather a gas was evolved, which 
 kindling at the approach of a light, burned for several months 
 without the matter appearing to die or diminish in weight. San 
 Severo thought he had found the impossible secret of the inextin- 
 guishable lamp, but he would not divulge his process, for fear that 
 the vault in which were interred the princes of his family should 
 lose the unique privilege with which he expected to enrich it, of being 
 illuminated with a 'perpetual lamp ” Had he acted like a philosopher of 
 the present day, San Severo would have attached his name to the im- 
 portant discovery of the existence of phosphorus in the bones , and made 
 public the process by which it might be obtained. 
 
 This element, formerly sold at four or five shillings the ounce, has now 
 fallen so much in price, from the greater demand and larger production, 
 that it may be bought for a few shillings the pound, and is imported in 
 tin cases in large quantities from Germany. It was discovered about 
 two hundred years ago by Brandt, a merchant of Hamburg, and may 
 be prepared on a small scale by distilling at a red heat phosphoric 
 acid previously fused with one-fourth of its weight of powdered 
 charcoal. 
 
 First Fxperiment. 
 
 Phosphorus, when pure, is without taste or colour, but generally of a 
 very pale buff-colour, and semi-transparent ; it is extremely combus- 
 tible, and is usually preserved under the surface of water ; when per- 
 fectly dry, a thin slice will take fire at 60° Fall., and burns with 
 great brilliancy. Considering the heat produced during the com- 
 bustion of phosphorus, it might be thought that it would infallibly set 
 fire to any ordinary combustible, such as paper or wood, but this is not 
 the case when phosphorus is employed by itself, as may be proved by 
 the following experiment. 
 
 Cut five very small pieces of phosphorus, and place them like the 
 five of diamonds on a sheet of cartridge-paper laid upon the table, set 
 the bits of phosphorus on fire, when they will be rapidly burnt away 
 
EXPERIMENTS WITH PHOSPHORUS. 17^ 
 
 leaving only five black spots, but not firing the paper, as would be the 
 case if some red-hot coals or charcoal were placed in the same position. 
 The cause is very simple. Phosphorus in burning produces phosphoric 
 acid, which is an anti-combustible, and coats the surface of the paper 
 round the spot where the combustion occurs, and acting as a kina of 
 .glaze or glass, excludes the oxygen of the air, and prevents the fire 
 spreading. 
 
 If some powdered sulphur is sprinkled round the spot where the bit 
 of phosphorus is to be burnt, the case is very different ; the heat melts 
 and sets fire to the sulphur, which being uncoated with the phosphoric 
 acid, communicates to the paper ; and it is on this principle that lucifer- 
 matches can be used as instantaneous lights. The tip of the wood of 
 which they are composed is first dipped in sulphur, and then the phos- 
 phorus composition made of gum, chlorate of potash, vermilion, and 
 phosphorus, is placed over it ; and if the latter were used alone without 
 the sulphur, not one match in a hundred would take fire properly. 
 
 Second Experiment. 
 
 Common phosphorus is perfectly and rapidly dissolved by bisulphide 
 4>f carbon. The solution must be carefully preserved, as it is a liquid 
 combustible, which takes fire spontaneously after the bisulphide of 
 carbon evaporates ; so that wherever it is dropped, a flame, arising from 
 the spontaneous combustion of the finely-divided phosphorus, is sure to 
 be produced. This liquid was recommended many years ago to the 
 Government for the purpose of setting sails of ships or other combus- 
 tible matter on fire. The solution of phosphorus alone did not answer 
 the purpose, as already explained in the first experiment ; but when wax 
 was dissolved with the phosphorus, it then became a most dangerous 
 fluid, which it was recommended should be used in shells, and discharged 
 from a mortar or howitzer in the ordinary manner. Dr. Lyon Playfair 
 .was the first to make this proposed application of the solution, and it 
 lias since, we believe, been recommended by Captain Norton inhis liquid- 
 fire shells. 
 
 Third Experiment. 
 
 One of the most curious facts in connexion with phosphorus, 
 is its assumption of the allotropic state in what is termed amorphous 
 (shapeless) or red phosphorus. This substance, when handled for the 
 first time, might be mistaken for a lump of badly-made Venetian red. 
 There is no risk of its taking fire like the common phosphorus, and it 
 does not (according to Schrotter, of Berlin, who discovered this peculiar 
 condition) exhale those fumes which are so prejudicial to the lucifer- 
 match makers. When the vapour of common phosphorus is continually 
 inhaled, it is said to cause a peculiar and disgusting disease, which 
 terminates in the destruction of the jaw-bone ; whilst the bones in other 
 parts of the body become brittle, and arm-bones thus affected are 
 fractured with the slightest blow. 
 
 The difference between common and red phosphorus is well shown— 
 
 k 2 
 
180 
 
 BOY’S PLAYBOOi*. „ SCIENCE. 
 
 first, by placing* a few small pieces of both kinds in separate bottles or 
 vials containing bisulphide of carbon ; the common phosphorus, as 
 already explained, quickly dissolves in the liquid, and if poured on a 
 sheet of paper, and hung up, is soon on fire ; whilst the red variety is 
 wholly unaffected, and if the bisulphide of carbon is poured off on to 
 paper, it merely evaporates, and no combustion occurs. 
 
 The similarity in composition, though not in outward form, is further 
 shown by filling two jars with oxygen gas, and having provided two 
 deflagrating spoons, some common phosphorus is placed in one, and red 
 phosphorus in the other; a wire, gently heated by dipping it into 
 some boiling water, is now applied to the former, which immediately 
 takes fire, and may be plunged into the jar of oxygen gas, when it burns 
 with the usual brilliancy. The red phosphorus, however, must be brought 
 to a much higher temperature (500° Fall.) before it will even shine in 
 the dark, and then with a still further increase of heat it takes fire, and on 
 being placed in the other jar of oxygen burns up much more slowly than 
 the yellow phosphorus, but at last exhibits that brilliant flash of light 
 which is so characteristic of the combustion of phosphorus in oxygen. 
 
 The amorphous or red phosphorus is employed in the manufacture of 
 safety chemical matches , and M. A. Meunons has secured a patent in 
 England for an improvement in lucifer matches, with a view to obviate 
 the risks of accidental ignition. To attain this end the matches are first 
 cut by a machine from cubes of wood, the cut being stopped at a 
 short distance from the end of each cube, so as to leave the lower ex- 
 tremities adherent. The upper or free extremity of each packet of 
 splints thus formed being coated with wax or sulphur, is dipped in one 
 of the following preparations: — Chlorate of potash, two parts; pul- 
 verized charcoal, one part ; umber, one part ; or, chlorate of potash* 
 sulphur, and umber, in equal parts, thoroughly mixed with glue. The 
 opposite extremity or “ cut” of each packet is then painted over with 
 amorphous phosphorus blended with size, so that on separating the 
 matches the phosphorus is only found on the top of each. The matches 
 thus prepared are ignited by breaking off a small piece of the phos- 
 phorised end and rubbing it on the opposite extremity covered with the 
 inflammable preparation. 
 
 Loud exploding and dangerous lucifer s were formerly made by dipping 
 bundles of matches, previously coated with sulphur at the tips, into a 
 thick solution of gum, at a temperature of 104° Eahr., coloured with 
 smalt or red lead, in which was dissolved a certain proportion of chlorate 
 of potash, and also containing finely divided particles of phosphorus ob- 
 tained by the constant stirring and rubbing of the materials in a mortar. 
 When dry the matches exploded if rubbed against a gritty surface, and 
 there was always a risk of a fragment flying off and entering the eye. 
 To obviate this danger, silent or noiseless lucifer matches were invented, 
 and the composition used (according to Bottger) is as follows : — Gum 
 arable, 16 parts by weight; phosphorus, 9 parts; nitre, 14 parts ; pow- 
 dered black oxide of manganese, 16 parts. The above ingredients are 
 worked up in a mortar wfth water, at 104° Eahr., and the matches pre- 
 viously tipped with sulphur are dipped therein and afterwards dried. 
 
EXPERIMENTS WITH PHOSPHORUS. 
 
 181 
 
 Fourth 'Experiment. 
 
 The combustion of 
 phosphorus under 
 water is easily de- 
 monstrated by plac- 
 ing some ordinary 
 stick phosphorus in 
 a metallic cup, and 
 then plunging it ra- 
 pidly under the sur- 
 face of boiling water. 
 If a jet of oxygen 
 gas is now directed 
 upon the liquid phos- 
 phorus, it burns 
 with great brilliancy, 
 
 Fig. 158.. a a. Finger-glass of boiling water containing 
 a metallic cup with melted phosphorus, c. Jet of oxygen 
 gas. d d. Sheet of wire gauze. 
 
 When the oxygen escapes too rapidly from the jet, it causes some small 
 particles to be thrown out of the water, so that it is advisable to defend 
 the face with a sheet of wire gauze held a few inches above the glass 
 whilst the experiment is being conducted. (Fig. 158.) 
 
 Fifth Experiment. 
 
 Phosphorus burns and emits beautiful 
 flashes of light in the presence of the 
 gas called tetroxide of chlorine (C1 2 0 4 ), 
 which must be very carefully generated 
 under the surface of water by first placing 
 some cut phosphorus and chlorate of pot- 
 ash at the bottom of a long and stout 
 cylindrical glass nearly full of water ; 
 sulphuric acid is then conveyed to the 
 chlorate of potash by means of a syphon, 
 the end of which must be drawn out to a 
 small opening, or else the oil of vitriol 
 will descend too rapidly, and the glass 
 will be cracked by the heat. Immediately 
 the peroxide of chlorine comes in contact 
 with the phosphorus it explodes, and 
 passes again to its original elements, 
 oxygen and chlorine. These bubbles en- 
 velope minute particles of phosphorus, 
 which rapidly ascend, like water-spiders, 
 to the surface, and burn as they pass up- 
 wards, producing a continual series of 
 sparks of fire, which have an extremely 
 pretty effect. (Fig. 159.) The syphon is of 
 course first filled with water, and as that is 
 displaced, the oil of vitriol takes its place. 
 
 Fig. 15°. a a. Tall glass Dearly 
 full of water ; at the bottom are the 
 chlorate of potash and phosphorus. 
 b. Wolfe’s bottle and syphon, con- 
 veying the oil of vitriol to bottom 
 
 of A A. 
 
182 
 
 boy’s PL ai book of science. 
 
 Sixth Experiment . 
 
 If a little phosphorus is placed in a small copper boiler, and the 
 steam allowed to escape from a jet, it is observed to be luminous, in 
 consequence of a minute portion of phosphorus being carried up mecha- 
 nically with the steam. The same fact is showm very prettily by boiling 
 water in a flask containing some phosphorus. 
 
 Fig. 160. a. The iron mortar con* 
 taining the phosphorus and chlorate of 
 potash, b. The pestle, with the shield, 
 c c, composed of a circle of wire gauze, 
 covered with one of cardboard. 
 
 Seventh Experiment. 
 
 Phosphorus explodes violently when 
 rubbed with a little chlorate of potash* 
 and in order to perform this experi- 
 ment safely, it should be made in a 
 strong iron mortar, the pestle of which 
 must be surrounded with a large circle- 
 of cardboard and wire gauze ; so that 
 when it is brought down upon the 
 phosphorus and chlorate of potash,, 
 any particles that may fly out are de- 
 tained by the shield. Without this 
 precaution the experiment is one of 
 the most dangerous that can be made. 
 (Pig. 160.) 
 
 Eighth Experiment. 
 
 Fig. 161. a. The flask containing the phosphide of calcium 
 and water, and placed in a water-bath heated to 140° Fah. 
 b. Bent tube conveying the gas to c c, the U-shaped tube, 
 to which it is attached by india-rubber tubing, c c. The U- 
 shaped tube, surrounded with a freezing mixture, d d. Bent 
 tube, passing into a cup of water to prevent contact with air. 
 
 Phosphuretted hy- 
 drogen owes its pro- 
 perty of spontaneous 
 combustion to the 
 presence of the va- 
 pour of a liquid, 
 phosphide of hydro- 
 gen (P 2 Ii 4 ), which 
 may be prepared by 
 placing some phos- 
 phide of calcium into 
 a flask with water 
 heated to a tempera- 
 ture of 110° Pali., 
 and conveying the 
 gas into a U-shaped 
 tube surrounded with 
 
 4-* wAivluvn AT TOO QYln 
 
 salt. The liquid obtained is colourless, and must be preserved from 
 contact with air, as it takes Are spontaneously directly it is exposed 
 ro the atmosphere. (Pig. 161 .) 
 
EXPERIMENTS WITH PHOSPHORUS, 
 
 183 
 
 Ninth Experiment. 
 
 Phosphide of calcium is quickly prepared by placing some small 
 pieces of lime in a crucible and making them red-hot ; if lumps of dry 
 phosphorus are thrown into the crucible, and the cover placed on 
 quickly, and immediately after the phosphorus, the latter unites with 
 the calcium, and forms a brown substance which produces gaseous 
 phosphide of hydrogen (PH 3 ) when placed in water, and the gas takes 
 fire spontaneously when it comes in contact with the air. 
 
 Tenth Experiment. 
 
 Phosphorus placed in a retort with a tolerably strong solution of 
 potash, and a small quantity of ether, affords a large quantity of phos- 
 phide of hydrogen (commonly called phosphuretted hydrogen) when 
 boiled. The neck of the retort must dip into a basin of water, and the 
 object of the ether is to prevent the combustion of the first bubbles of 
 gas inside the retort, which by their explosion would probably break the 
 glass. If the neck of the retort is kept under water in which potash is 
 dissolved, the gas may be generated for many days at pleasure, although 
 it is not a desirable experiment to renew too often, on account of the 
 disagreeable odour produced. (Fig. 162.) 
 
 Eleve7ith Experiment. 
 
 When a jar of oxygen is held over the neck of the retort generating the 
 phosphuretted hydrogen, a bright flash of light and explosion are ob- 
 served ; and if the experiment is performed in a darkened room, it is just 
 like a sudden flash of lightning. A bottle of chlorine held over the neck 
 
184 
 
 boy’s playbook of science. 
 
 of the retort, and dipping of course in the water of the basin, produces 
 a green flame every time the bubble of gas passes into it. That curious 
 appearance of light, sometimes seen in marshy districts, called will-o?-the- 
 wisp, is supposed to be due to the escape, from decomposing matter, of 
 bubbles of hydrogen, nitrogen, &c., through which the spontaneously 
 inflammable phosphide of hydrogen is diffused. 
 
 At a place called Dead Man’s Island, near Sheerness, magnificent 
 effects of this kind are sometimes apparent when the mud banks are 
 accidentally stirred at night by a boat-hook. A credible observer says, 
 lie once saw there a flash of yellowish-green light, accompanied with 
 noise, about thirty feet in height. The apparent height might be due to 
 the duration of the impression of the flash on the eye, as the light from 
 the burning phosphuretted hydrogen ascended rapidly upwards. The 
 source of this gas appears to be due to the fact, that during the time some 
 Russian ships were watched by the Brest fleet, a number of the sailors 
 died of cholera, and were buried in the banks ; the decomposition of the 
 bone containing phosphorus would account for the appearance of light 
 already described. 
 
 With the discussion of some of the most interesting properties of the 
 thirteen non-metallic elements we take leave of the subject of chemistry, 
 reserving the consideration of the metals for another popular juvenile 
 work, of which they will form the subject. 
 
 In answer to the oft-repeated question, “ Where can I get the things 
 for the experiments ?” it may be stated that every kind of glass vessel 
 and the chemicals mentioned in this chapter, can be procured either of 
 Messrs. Simpson, Maule, and Co., Kennington, or of Griffin and Co., 
 B unhill-row, or Bolton and Co., High Holborn. 
 
 Fig. 163. Will-o’-the-wisp. 
 
185 
 
 Fig. 164. Franklin and his kite. 
 
 CHAPTER XIII. 
 
 riilCTIONAL ELECTRICITY. 
 
 Of all the agents with which man is acquainted, not one can afford a 
 greater source of wonderment to the ignorant, of meditation to the 
 learned, than the effects of that marvellous force pervading all matter 
 called electricity. We look at matter endowed with life, and matter 
 wanting this divine gift, with some degree of interest, depending on our 
 various tastes and occupations ; we know at a glance a bird, a beast, or 
 a fish ; we observe with pleasure and admiration the wonderful changes 
 of nature, and know that a few seeds thrown into the broken clods and 
 well-tilled earth may become either the waving, golden corn-field or in 
 time may grow from the tender little shrub to the stately forest-tree ; 
 we know all these things because they belong to the visible world, and 
 are continually passing before our eyes : but in looking at the visible, 
 we must not forget and ignore the invisible. It may with truth be 
 
186 
 
 boy’s playbook of science. 
 
 stated that the greatest powers of nature are all concealed, and if any 
 truth would lead us from Nature to Nature’s God, it is the fact that 
 no visible, solid, tangible agent can work with so much force and 
 power as invisible electricity. Many centuries passed away since the 
 commencement of the Christian era, before the human mind was pre- 
 pared to appreciate this great power of nature ; other forces had claimed 
 attention, and the difference in the presence or absence of two of the 
 imponderable agents, heat and light, as derived from the sun, in the 
 effects of the change of the seasons, and other common facts, had led 
 philosophers to speculate early upon their nature ; but electricity, from 
 its peculiar properties, long escaped observation, and it was not until 
 the beginning of the eighteenth century (about 1730) that any material 
 facts had been discovered in this science, when Mr. Stephen Grey, a 
 pensioner of the Charterhouse, discovered what he termed electrics 
 and non-electrics , and also the use of insulating materials, such as silk, 
 resin, glass, hair, &c. ; and it is obvious that, until the latter fact was 
 discovered, the science would remain in abeyance, because there would 
 be no mode of preserving the electrical excitement in the absence of 
 non-conductors of this force. 
 
 The year 1750 was remarkable for Yolta’s discoveries and Dr. Frank- 
 lin’s identification of the electricity of the machine with the stupendous 
 effects of the thunderstorm. Sir Humphry Davy, in 1800, with his 
 commanding genius, threw fresh light upon the already numerous 
 electrical effects discovered. In 1821, Faraday commenced his studies 
 in this branch of philosophy ; which he has since so diligently followed 
 up, that he has been for some years, and is still the first electrician of 
 the age. From the commencement of the present century, discoveries 
 have succeeded each other in regular order and with the most amazing 
 results ; and now electricity is regularly employed as a money-getting 
 agent in the process of the electrotype aud electro-silvering and gilding ; 
 also in the electric telegraph ; and in a few years we may possibly see 
 it commonly employed as a source of artificial light. 
 
 The nature of electricity, says Turner, like that of heat, is at present 
 involved in obscurity. Both these principles, if really material, are so 
 light, subtle, and diffuse, that it lias hitherto been found impossible to 
 recognise in them the ordinary characteristics of matter ; and therefore 
 electric phenomena may be referred, not to the agency of a specific sub- 
 stance, but to some property or state of common matter, just as sound 
 and light are produced by a vibrating medium. But the effects of 
 electricity are so similar to those of a mechanical agent, it appears so 
 distinctly to emanate from substances which contain it in excess, and 
 rends asunder all obstacles in its course so exactly like a body in rapid 
 motion, that the impression of its existence as a distinct material sub- 
 stance sui generis forces itself irresistibly on the mind. All nations, 
 accordingly, have spontaneously concurred in regarding electricity as a 
 material principle ; and scientific men give a preference to the same 
 view, because it offers an easy explanation of phenomena, and suggests 
 a natural language intelligible to all. 
 
SOURCES OF ELECTRICITY. 
 
 187 
 
 There are five well-ascertained sources of electricity, and three which 
 are considered to be uncertain. The five sources are friction, chemical 
 action, heat, magnetism, peculiar animal organisms. The three uncertain 
 sources are contact, evaporation, and the solar rays. 
 
 First Experiment. 
 
 A stick of sealing-wax or a bit of glass tube, perfectly dry, rubbed 
 against a warm piece of flannel, has 
 elicited upon its surface a new power, 
 which will attract bits of paper, straw, or 
 other light materials; and after these sub- 
 stances are endowed with the same force, 
 a repellent action takes place, and they 
 fly off. One of the most convenient ar- 
 rangements for making experiments with 
 the attractive and repellent powers of 
 electricity is to fix with shell-lac varnish 
 round discs of gilt paper, of the size of 
 a half-crown, at each end of a long straw 
 that is supported about the centre with 
 a silk thread, which may hang from the 
 ceiling or any other convenient support. 
 
 (Fig. 165.) . 
 
 The varnish is easily prepared by 
 placing four or eight ounces of shell- 
 lac in a bottle, and pouring enough 
 pyroxylic spirit (commonly termed wood 
 naphtha) upon the lac to cover it. After 
 a short time, and by agitation, solu- 
 tion takes place. In a variety of ways 
 friction is proved to be a source of 
 electricity, and forms a distinct branch 
 of the science, under the name of fric- 
 tional electricity. 
 
 Fig. 165. a. The glass pillar sup* 
 port. b. Straw with discs, hanging 
 a silk thread. 
 
 Second Experiment. 
 
 The nature of chemical action has been already explained, and is 
 alluded to here as a source of electricity of which the proof is very 
 simple. Apiece of copper and a similar-sized plate of zinc have attached 
 to ithem copper wires ; these plates are placed opposite to, but do not 
 touch each other, in a vessel containing water acidulated with a small 
 quantity of sulphuric acid. When the wires are brought in contact, a 
 current of electricity circulates through the arrangement, but has no 
 power to attract bits of paper, straw, &c. In order to ascertain whether 
 the current of electricity passes or not, a piece of covered copper wire 
 is bent several times round a magnetic needle, so that it has freedom of 
 motion inside the core or hollow formed by twisting the copper wire. 
 This arrangement, properly constructed, is called the galvanometer 
 
188 
 
 boy’s playbook of science. 
 
 needle, and is invaluable as a means of ascertaining the passage of 
 electricity derived from chemical action. (Fig. 166.) 
 
 Fig. 166. A. The galvanometer needle, b. Vessel containing weak acid and the zinc and 
 copper plates. The arrows show the path of the electric current. 
 
 When the wires leading from the metal plates are connected with the 
 extremities of the coil in the galvanometer, the needle is deflected or 
 pushed aside to the right hand or to the left, according to the direction 
 •of the current. 
 
 Third Experiment, 
 
 The third source of electricity is heat, and the effect of this agent is 
 >fell shown by twisting together a piece of platinum and silver wire, so 
 as to form one length. If the silver end is attached to any screw of the 
 galvanometer, and the platinum end to the second screw, no movement 
 of the magnetic needle takes place until the heat of a spirit-lamp is 
 applied for a moment to the point of juncture between the silver and 
 platinum wires, when the magnetic needle is immediately deflected. 
 
 juncture, +. 
 
 Fourth Experiment . 
 
 The fourth source of electricity — viz., magnetism — requires a some- 
 what more complicated arrangement ; and a most delicate galvanometer 
 needle must be provided, to which is attached the extremities of a long 
 spiral coil of copper wire covered with cotton or silk. Every time a 
 bar magnet is introduced inside the coil, so that the conducting wire cuts 
 the magnetic curves, a deflection of the galvanometer needle takes place. 
 
SOURCES OF ELECTRICITY. 
 
 189 * 
 
 and the same effect is produced on the withdrawal of the magnet, the 
 needle being deflected in the opposite direction. 
 
 The magnetic spark can be obtained by employing a magnet of suffi- 
 cient power ; and the arrangement for this purpose is very simple. A 
 cylinder of soft iron is provided, and round its centre are wound a few 
 feet of covered thin copper wire, one end of which is terminated with a 
 copper disc well amalgamated, and the other end, after being properly 
 cleaned and coated with mercury, is brought into contact with the disc. 
 Directly this cylinder is laid across the poles of the magnet, and as 
 quickly removed, the point and disc, from the elasticity of the former, 
 separate for the moment, the contact is broken between the point and’ 
 disc, and a brilliant but tiny spark is apparent. 
 
 Fig. 168 . a b. Horse-shoe magnet, c. Cylinder of soft iron. n. Coil of copper 
 wire and contact breaker. 
 
 Fifth Experiment. 
 
 The fifth mode of procuring electricity would require the assistance 
 of an electrical eel, a fine specimen of which (forty inches in length) was 
 exhibited at the Adelaide Gallery some years ago. Various experiments 
 were made with this animal, and the author had the pleasure of wit- 
 nessing all the ordinary phenomena of frictional electricity, illustrated 
 by Dr. Faraday, with the assistance of the animal electricity derived 
 from this curious creature. . Recent experiments have, however, proved 
 that the electric current is induced through the agency of the nervous 
 
190 
 
 boy’s playbook of science. 
 
 system. This important fact lias been communicated by M. Dubois- 
 Raymond, whose experiment is thus recorded:— A cylinder of wood is 
 firmly fixed against the edge of a table ; two vessels filled with salt and 
 water are placed on the table, in such a position that a person grasping 
 the cylinder may, at the same time, insert the fore-finger of each hand 
 in the water. Each vessel contains a metallic plate, and communicates, 
 by two wires, with an extremely sensitive galvanometer. In the instru- 
 ment employed by M. Dubois-Raymond, the wire is about 3J miles in 
 length. The apparatus being thus arranged, the experimenter grasps 
 the cylinder of wood firmly with both hands, at the same time dipping 
 the fore-finger of each hand in the saline water. The needle of the 
 galvanometer remains undisturbed ; the electric currents passing by the 
 nerves of each arm, and being of the same force, neutralize each other. 
 Now, if the experimenter grasp with energy the cylinder of wood with 
 the right hand, the left hand remaining relaxed and free, immediately the 
 needle will move from west to south, and describe an angle of 30°, 40°, 
 and even 50°; on relaxing the grasp, the needle will return to its original 
 position. The experiment may be reversed by employing the left arm, 
 and leaving the right arm free : the needle will, in this case, be deflected 
 from west to north. The reversing of the action of the needle proves the 
 influence of the nervous force. The conditions, it may be added, 
 essential to the success of the experiment are : 1st, Great muscular and 
 nervous energy ; 2nd, The contraction of only one arm at a time ; 3rd, 
 Dryness and cleanliness of skin ; and 4th, Freedom from any kind of 
 Wound on the immersed part. 
 
 Sixth Experiment, 
 
 In making electrical experiments of the simplest kind, it soon becomes 
 apparent that certain substances, such as glass, sealing-wax, & c., retain 
 the condition of electrical excitement ; whilst other bodies, and especially 
 the metals, seem wholly incapable of electrical excitation : hence the 
 classification of bodies into conductors and non-conductors of electricity. 
 This arrangement is not strictly correct, because no substance can be 
 regarded as absolutely a conductor, or vice versa. It is better to con- 
 sider these terms as meaning the two extremes of a long chain of inter- 
 mediate links, which pass by insensible gradations the one into the other. 
 In the manufacture of electrical apparatus, glass is of course largely 
 •employed, and this substance, with brass and wood, constitute the usual 
 materials. One of the most instructive pieces of apparatus is the elec- 
 troscope, which can be made with a gas jar, a cork, a piece of glass 
 tube, brass wire and ball, or a flat disc of brass, with some Dutch metal, 
 or still better, gold leaf. The latter is first cut into strips by retaining 
 the leaf between a sheet of well-glazed paper and cutting through the 
 paper and the copper or gold leaf, otherwise it would be impossible to 
 •cut the metal, on account of its excessive thinness, except with a gilder’s 
 knife and cushion. The cork is next fitted to the gas jar, and perforated 
 with a hole to admit the glass tube, which must be thoroughly dry, and 
 
THE ELECTROSCOPE. 
 
 191 
 
 is best coated both inside and out with the shell-lac varnish described 
 at page 175. Some dry silk is wound round the 
 brass wire, so that it remains fixed and upright in 
 the glass tube, the end outside the jar having a 
 ball, or still better, a flat disc of brass attached, 
 and the other extremity being split so as to act 
 like a pair of forceps, to retain a piece of card to 
 which the gold leaves are attached. By removing 
 the cork, tube, and brass wire bodily from the neck 
 of the gas jar, and then in a perfectly still atmo- 
 sphere carefully bringing the card, slightly wetted 
 with gum at the extremity, on two of the cut 
 gold leaves, they may be stuck on, and the whole 
 is again arranged inside the dry gas jar, and forms 
 the important instrument called tlm electroscope. 
 
 (Fig. 169.) With the help of this arrangement, 
 a number of highly instructive experiments are 
 performed. 
 
 Seventh Experiment. 
 
 First, the difference between conductors and 
 non-conductors is admirably shown by rubbing a 
 bit of sealing-wax against a piece of woollen cloth 
 or flannel ; on bringing the wax to the brass disc of ^ re > wit £ flat out- 
 the electroscope the gold leaves no longer hang gold a feaf ° b C mside the 
 quietly side by side, but stand out and repel each jar. c c. The glass 
 other, in obedience to the law <c that bodies simi- tube * 
 larly electrified repel each other E If the brass cap is touched whilst the 
 leaves are in this electrical state, they fall again to their original posi- 
 tion, showing that sealing-wax, after being excited, retains its electrical 
 condition, as also the gold leaves, because they are supported on glass, 
 or what is termed insulated — i.e. } cut off from conducting con mi unica- 
 tion with surrounding objects. When, however, the sealing-wax is 
 passed through a damp hand, or the brass disc of the electroscope 
 touched, the electricity is conveyed away to the earth, because the human 
 body is a conductor of electricity. 
 
 Eighth Experiment. 
 
 When a brass wire is rubbed and brought to the electroscope, the 
 leaves do not move, inconsequence of the electricity passing away to the 
 earth through the body as fast as it is generated : it is just like pouring 
 water into a leaky cistern ; but if the brass wire is tied to a long stick 
 of sealing-wax, and this latter held in the hand whilst the wire is rubbed 
 with a bit of flannel, then the gold leaves of the electroscope are affected, 
 on account of the insulation of the metal, as every substance which can 
 be rubbed (even fluids, as water) produces electricity. 
 
192 
 
 boy’s playbook of science. 
 
 Ninth Experiment. 
 
 An insulating stool is merely apiece of strong square board, supported 
 on glass legs, which should be well varnished. It’ the assistant stands 
 on this stool and touches the disc of the electroscope, no movement of 
 the leaves takes place until his coat is briskly struck with a piece of dry 
 silk or skin, when the usual repulsion occurs. 
 
 Tenth Experiment . 
 
 If a little powdered chalk is placed inside a pair of bellows, and then 
 forcibly ejected on to the disc of the electroscope, the friction of the 
 particles of chalk against the inside of the nozzle of the bellows and 
 against the disc of the instrument soon liberates sufficient electricity to 
 cause the gold leaves to stand out and repel each other. 
 
 Eleventh Experiment. 
 
 Whilst the leaves of the electroscope aie repelled from each other by 
 the application of a bit of rubbed sealing-wax, they may be again caused 
 to approach each other on bringing a dry glass tube previously rubbed 
 with a silk-handkerchief ; because the electricity obtained from sealing- 
 wax is different from that procured from glass : the former is called 
 resinous or negative electricity, the latter positive or vitreous electricity 
 Either, separately, is repulsive of its own particles, but attractive of the 
 
ELECTRICAL EXPERIMENTS. 
 
 193 
 
 other. No electrical excitation can occur without the separation of 
 these two curious states of electricity, and electrical quiescence takes 
 place when the two electricities are brought together ; hence the fall of 
 the gold leaves repelled by rubbed wax when the excited glass is brought 
 towards the disc of the electroscope. This experiment may be reversed 
 by repelling the leaves first with the excited glass, and then bringing the 
 rubbed wax, when the same effect takes place. 
 
 Twelfth Experiment. 
 
 To show the important elementary truth, that in all cases of electrical 
 excitation the two kinds of electricity are generated, take a dry roll of 
 flannel, and holding it as lightly as possible, rub it against a bit of wax. 
 If the flannel is brought to the electroscope, the leaves repel each other, 
 and they immediately fall when the wax is now approached, because the 
 flannel is in the positive or vitreous state of electricity, whilst the 
 sealing-wax is in the negative or resinous condition. 
 
 Thirteenth Experiment. 
 
 Any kind of friction generates electricity. A little roll brimstone 
 placed in a dry mortar and powdered, and then thrown on to the electro- 
 scope, quickly causes the repulsion of the leaves. 
 
 Fourteenth Experiment. 
 
 A sheet of dry brown paper laid on a flat surface, and vigorously 
 rubbed with a piece of india-rubber, produces so much electricity 
 that sparks and flashes of light are apparent in a dark room when it 
 is lifted from the table ; and it affects the leaves of the electroscope 
 ver^ powerfully, so much so that care must be taken to apply it very 
 carefully to the disc, or the violence of the repulsion may cause the 
 fracture of the gold leaves, and then a great deal of time is wasted 
 before they can be put on again. 
 
 Fifteenth Experiment. 
 
 A dry wig or bunch of horse- hair when combed becomes electrical, 
 and likewise affects the leaves of the electroscope. 
 
 Sixteenth Experiment. 
 
 Two dry silk ribbons, the one white and the other black, passed 
 rapidly together through the fingers, exhibit sparks anJ flashes of 
 light when drawn asunder, and also cause the gold leaves to repel each 
 other. 
 
 Seventeenth Experiment. 
 
 Much instructive amusement is afforded by testing the gold leaves 
 when separated from each other during either of the former experiments 
 
 o 
 
104 
 
 boy’s playbook of science. 
 
 with an excited piece of sealing-wax. If the electricity produced is 
 negative, they repel each other further when the excited wax is ap- 
 proached ; if positive, they fall when the excited wax is brought near 
 them. 
 
 Eighteenth Experiment. 
 
 When fresh, dry, ground coffee is received on to the disc of the elec- 
 troscope, as it falls from the mill, powerful electrical excitation is 
 displayed, and this is sometimes so apparent, that the particles cling 
 around the lower part of the mill or to the sides of the cup or basin 
 held to catch it. 
 
 Nineteenth Experiment. 
 
 After playing a tune on a violin, hold the bow (well rosined) to the 
 electroscope, when the usual divergence of the leaves will be apparent. 
 
 Twentieth Experiment. 
 
 Cut some chips from a piece of wood with a knife attached to a glass 
 handle, and as they fall on to the electroscope the leaves are repelled. 
 
 Twenty-first Experiment. 
 
 Warm a piece of bombazine by the fire and then draw out some of the 
 threads (which are of two kinds— viz., silk and wool), and place them 
 on the electroscope, when divergence of the leaves immediately takes 
 place. 
 
 Twenty-second Experiment. 
 
 Put upon the same leg a worsted stocking and over that a silk one, 
 if the latter is now quickly rubbed all over with a dry hand and near 
 the fire, and then suddenly slipped off, the sides repel each other, and 
 the silk stocking retains very much the same shape as if the leg still 
 remained in it, and of course collapses as the electricity passes away. 
 
 Twenty-third Experiment. 
 
 Electrical machines consist only in the better arrangement of larger 
 pieces of glass and a more convenient mechanical contrivance for rubbing 
 them, and are of two kinds — viz., the cylinder and plate machines ; it is 
 usual to give directions for the manufacture of an electrical machine 
 from a common bottle, and doubtless such rude instruments have been 
 made, but as Messrs. Elliott Brothers, of 30, Strand, now supply excel- 
 lent small machines at a very low cost, it is hardly worth while to incur 
 •.even a small expense for an instrument that must at the best be a very 
 imperfect one and frequently out of order. (Pig. 171.) 
 
ELECTRICAL MACHINES. 
 
 105 
 
 Fig. 17] . A cylinder electrical machine. 
 
 Plate machines are somewhat more expensive than cylinder ones, but 
 at the same time are more quickly prepared for experiments, and Mr. 
 Ilearder, of Plymouth, states, that the secret in obtaining the greatest 
 amount of electricity from a cylinder machine, is to keep the inside of 
 the glass absolutely clean, dry, and free from dust. Sometimes the 
 glass of which electrical machines are made is wholly unfit for elec- 
 
 Fig. 172. The ordinary plate electrical machin*. 
 
 o 2 
 
196 
 
 boy’s playbook of science. 
 
 trical purposes, in consequence of the decomposition of the surface 
 from imperfect manufacture and the liberation of the alkali. (Figs, 
 172, 173.) 
 
 Fig-. 173. Woodward’s double plate electrical machine, giving a much larger 
 quantity of electricity than Fig. 167. 
 
 Twenty-fourth Experiment. 
 
 Cylinder and plate machines are furnished with proper rubbers, and 
 before using the instrument it is usual to remove them, and after care- 
 fully cleaning the glass with a dry silk handkerchief before a fire, 
 the rubbers are scraped with a paper-knife to remove the old amalgam, 
 and fresh applied by first melting the end of a tallow candle slightly, 
 and after passing this over the rubber, the finely powdered amalgam is 
 now dusted on to it. Electrical amalgam is prepared by fusing one part 
 of zinc with one of tin, and then agitating the liquid mass with two 
 parts of hot mercury placed in a wooden box; when cold it should 
 be carefully powdered and kept in a well-stoppered bottle for use. 
 When the amalgam has been applied, the rubbers are again screwed 
 in their places, and the machine when turned (if the atmosphere is 
 tolerably dry) will emit an abundance of bright sparks. 
 
 Twenty-fifth Experiment . 
 
 Attraction and repulsion are shown on a larger scale, with the as- 
 sistance of electrical machines, by placing a fishing rod (the last joint of 
 
ATTRACTION AND REPULSION. 
 
 197 
 
 which is made of glass) in an erect position, and attaching to the ex- 
 tremity a long tassel of paper from 
 which a thin wire passes to the prime 
 conductor of the electrical machine ; 
 
 the 
 
 on turning the instrument, 
 strips of paper all stand out and 
 repel each otner. (Fig. 174.) 
 
 Twenty-sixth Experiment. 
 
 Suspend from the prime conductor 
 by a chain a circular brass plate 
 
 Fig. 174. a a. The glass joint of the 
 fishing-rod, from which the last joint, 
 carrying the paper tassel, b, projects, c. 
 The electrical machine. 
 
 b and c. 
 
 and under this place another supported by a brass adjusting stand. 
 If pith figures of men and women are placed on the lower plate, they rise 
 directly the machine is turned, although sometimes, in consequence of 
 irregularity in the adjustment of the centre of gravity, they perversely 
 dance on their heads instead of the usual position ; out of half a dozen 
 figures, one only perhaps will be found to dance well, by alternately 
 jumping to the upper plate and falling to the lower one to discharge the 
 excess of electricity; and indeed the experiment will be found to 
 succeed better with one or two only on the plate instead of a number, 
 as they cling together and impede each other’s movements. (Fig. 175.) 
 
198 
 
 boy’s playbook of science. 
 
 Twenty -seventh Experiment. 
 
 An assistant provided with a wig of well-combed hair presents a 
 most ridiculous appearance when standing on the insulating stool and 
 connected by a wire with the prime conductor of the electrical 
 machine, every hair, when not matted together, standing out in the most 
 absurd manner, when the machine is put in motion. 
 
 Twenty-eighth Experiment. 
 
 Whilst standing on the stool, sparks may be obtained from his body,, 
 and if some tow is tied over a brass ball, and moistened with a little 
 ether, and presented to the tip of his finger, a spark flies off which 
 quickly sets fire to the inflammable liquid. 
 
 Twenty-ninth Experiment. 
 
 If small discs of tinfoil, cut out with a proper stamp, are pasted in 
 continuous lines over plate glass, or spirally round glass tubes, a very 
 
 A 
 
 Fiff 176 a a a. A ring 1 of brass wire supported on a glass pillar inside which the spiral 
 tube b, revolves, and produces beautiful and ever-changing circles of light, when connected 
 with the conductor, c, of the electrical machine. 
 
EFFECTS OF INDUCTION. 
 
 199 
 
 pretty effect is produced when they receive the sparks from the electrical 
 machine, and the passage of the electrieity from one disc to the other 
 produces a vivid spiral or other line of light. When the tube is 
 mounted in a proper apparatus, so as to revolve whilst the sparks pass 
 down the spiral tube, the effect of the continuous electric sparks is much 
 heightened. (Fig. 176.) 
 
 Thirtieth Experiment. 
 
 A great variety of experiments, depending on the proper arrangement 
 of discs of tinfoil on various tubes of coloured glass are manufactured, 
 and some in the form of windmills, the sails being made luminous by the 
 passage of the electricity. The names of illustrious electricians, beautiful 
 crescents, stars, and even profile portraits, have been produced in con- 
 tinuous streams of electric sparks. 
 
 Thirty-first Experiment. 
 
 When an electrified body is brought towards another which is not 
 electrical, the latter is thrown into the opposite state of electricity as 
 long as the excited body remains in its neighbourhood ; and this con- 
 dition of electrical disturbance, set up without any contact or supplv of 
 electricity, is called induction , and involves a vast number of interesting 
 facts, which are thoroughly discussed in Dr. Noad’s excellent work on 
 electricity, but can only be briefly alluded to here. 
 
 If a number of lengths of brass wire, supplied with balls at the ex- 
 tremities, are supported on glass legs and arranged in a line, with a 
 little pitli ball attached to a thread hanging from each end of the length 
 of brass wire, the effect of induction is shown very nicely ; and when an 
 excited glass rod is brought towards one end of the series, the rising of 
 the pith balls to each other betrays the change which has occurred in 
 
 Fig 1 . 177. The lengths of brass wire supported on glass rod pillars indented by blowpipe, 
 so as to retain the brass wires with the pith balls hanging from each series, the letters- 
 p and it mean Positive and Negative, and the signs for these terms are placed above. 
 The letters p and ir are painted on the blocks which support the glass rods. 
 
 the electrical state of the brass wires by the mere neighbourhood of the 
 excited glass tube. The glass tube is electrified positively, and attracts 
 the negative electricity from the brass wire towards the end nearest i*> 
 
200 
 
 BO\’s PLAYBOOK OF SCIENCE. 
 
 it; the other extremity of the brass wire is found to be in the positive 
 state, and this re-acting on the next, and so on throughout the lengths, 
 completes the electrical disturbance in the whole series. (Fig. 177.) 
 
 Thirty-second Experiment. 
 
 If an insulated brass rod (such as has been described in the last 
 experiment) is touched by the finger whilst under induction, it remains 
 permanently electrified on the removal of the disturbing electrified body • 
 -and it is on this principle that the useful electrical machine called the 
 Electrophorus is constructed. This constant electrical machine— for it 
 will remain in action during weeks and months if kept sufficiently dry— 
 was invented by Volta in the year 1774, and has been brought to great 
 perfection by Mr. Lewis M. Stuart, of the City of London School ; so that 
 with a little additional apparatus the whole of the fundamental prin- 
 ciples of electricity can be demonstrated. It consists of a flat brass or 
 tm circular dish about two feet in diameter and half an inch deep, which 
 is filled with a composition of equal parts of black rosin, shell-lac, and 
 Venice turpentine; the rosin and the Venice turpentine being first 
 melted together, and the shell-lac added afterwards, care of course being 
 taken that the materials do not boil over and catch fire, in which case 
 the not must be removed from the heat, and a piece of wet baize or other 
 woollen material thrown over it. Another tin or brass circular plate of 
 twelve inches diameter, and supported in the centre with a varnished 
 glass handle nine inches long, is also provided, and the resinous plate 
 being first excited by several smart blows with a warm roll of flannel, 
 the plate held by the glass handle is now laid upon the centre of the 
 resinous one, and if removed directly afterwards, does not afford the 
 electric spark ; but if, whilst standing upon the excited resinous plate, 
 it is touched, and then removed by the glass handle, a powerful electric 
 spark is obtained ; and this may be repeated over and over again with 
 the like results, provided the plate w r ith the glass handle is touched with 
 the finger just before lifting it from the resinous plate. (Fig. 178.) 
 
 Fig- 118. a a. Large circular tin or brass disc with turned-up edge half an inch deep, 
 &nd containing the resinous mixture n, which is rubbed with the warm flannel, c c The 
 upper plate supported by the glass handle d, a pith ball attached to a wire show’s the 
 electrical excitation, and the spark is supposed to be passing to the hand e. 
 
THE ELECTROPHORUS. 
 
 201 
 
 The electricity excited on the resinous plate is not lost, and by induc- 
 tion sets up the opposite condition in the plate with the glass handle. 
 The resinous plate, being excited with negative electricity, disturbs the 
 electrical quiescence of the upper plate, and positive electricity is found 
 on the surface touching the resinous plate, and negative electricity on 
 the upper one, so that when it is removed without oeing touched, the 
 two electricities come together again, and no spark is obtained ; but if, 
 as already described, the upper plate is touched whilst under induction, 
 then positive electricity appears to pass from the finger to the negative 
 electricity on the upper side of the plate, when the two temporarily 
 neutralize each other, and then, when the plate is removed, the excess 
 of electricity derived from the earth through the finger becomes appa- 
 rent. Induction requires no sensible thickness in the conductors, and 
 can be just as well produced on a leaf of gold as on the thickest plate of 
 metal ; and it should be remembered that non-conductors do not retain 
 their state of electrical excitation when the disturbing cause is removed, 
 whereas conductors possess this power, and this fact brings us to the 
 consideration of the Leyden jar. 
 
 Thirty-third Experiment. 
 
 If one side of a dry glass plate is held before and touches a brass ball 
 proceeding from the prime conductor of an electrical machine whilst in 
 action, the other side is soon found to be electrical ; this does not arise 
 from the conduction of the electricity through the particles of the glass, 
 but is produced by induction, the side nearest the ball being in the 
 positive state, and the other side negative : as glass is a non-conductor 
 of electricity, the effect is much increased by coating each side with tin- 
 foil, leaving a margin of about two inches of uncovered glass round the 
 covered portion, then, if one side of such a plate is held to the prime 
 conductor of the electrical machine, and the other connected with the 
 ground, a powerful charge is accumulated ; and if the opposite sides 
 •are brought in contact with a bent brass wire, a loud snapping noise is 
 heard, and the two electricities resident on either side of the glass come 
 together with the production of a brilliant spark, or if the hands are 
 substituted for the bent brass wire, that most disagreeable result is 
 obtained — viz., an electric shock ; hence these glass plates are some- 
 times fitted up as pictures, and when charged and handed to the 
 unsuspecting recipient, he or she receives the electric discharge to the 
 great discomfort of their nervous system. 
 
 Mica is sometimes substituted for glass, and the late Mr. Crosse, the 
 celebrated electrician, constructed a powerful combination of coatea 
 plates of this mineral. It consisted of seventeen plates of thin mica, 
 each five inches by four, coated on both sides with tinfoil within half 
 an inch of the edge. They were arranged in a box with a glass plate 
 between each mica plate, all the upper sides were connected by strips 
 of tinfoil to one side of the box, and all the under surfaces in the same 
 manner with the opposite extremity of the box. They were charged like 
 an ordinary Leyden battery. 
 
202 
 
 boy’s playbook of science. 
 
 Thirty -fourth Experiment. 
 
 If the glass plate coated with tin- 
 foil is charged, and then placed up- 
 right on a stand, it may be slowly dis- 
 charged by placing a bent wire on the 
 edge with the extremities covered with 
 pith balls. The wire balances itself, 
 and continues to oscillate with noise 
 until the electricities of the two sur- 
 faces neutralize each other. (Fig. 17 9 .) 
 
 Thirty-fifth Experiment. 
 
 Fig. 179. a a. Glass plate or stand coated It is easy to imagine the jjlass 
 
 Wilh pith'ballg ^sdiilttag^urSg^the P late ? f t,le iast experiment roue's up 
 discharge of the glass plate. into the more convenient form of the 
 
 Leyden jar, which consists of a glass 
 vessel lined both inside and out with tinfoil, leaving some two or three 
 inches of the glass round the mouth uncovered and varnished with 
 
 Fig 180. The Leyden jar and brass 
 wire discharger. 
 
 shock are obtained by grasping tl 
 the ball with a brass wire held in 
 
 shell-lac ; a piece of dry wood is fitted 
 into the mouth of the jar, through 
 which a brass wire and chain are 
 passed, and the end outside is fitted 
 with a ball. The Leyden jar is 
 charged by holding the ball to the 
 prime conductor of the electrical 
 machine until a sort of whizzing 
 noise is heard, caused by the excess 
 of electricity passing round the un- 
 covered part of the jar and not 
 through it, as the smallest crack in 
 the glass of the Leyden jar would 
 render it useless. Electricity is 
 sometimes called a fluid, and the fact 
 of collecting it like water in a jar, 
 helps us to understand this analogy. 
 The noise, the bright spark, or the 
 outside with one hand and touching 
 le other. (Fig. 180.) 
 
 Thirty-sixth Experiment. 
 
 The jar is silently discharged if the Dalis are removed from the. dis- 
 charger and points used instead ; so, also, the whole of the electricity 
 produced by an electrical machine in full action may be readily drawn 
 off by a pointed conductor, such as a needle, placed at the end of a brass 
 wire. Electricity passes much more rapidly through points than rounded 
 surfaces, hence the reason why all parts of electrical apparatus are free 
 from sharp points and rough asperities. 
 
THE LEYDEN BATTERY. 
 
 203 
 
 Thirty -seventh Experiment. 
 
 Extremely thin wires may be burnt by passing the charge of a lame 
 Leyden jar through them. The show jars, called specie jars, usually 
 decorated and placed in the windows of chemists’ shops, make excel- 
 lent Leyden jars, when not too thick; and with two of the largest, all 
 
 Fig. 181. a. Mahogany board with a sheet of white paper and three pairs of brass wires' 
 and balls fixed in the wire, three on each side. The thin wires are stretched between the 
 calls, and the lower one is in course of deflagration, b b. Charged large Leyden battery 
 of two jars ; the arrovys indicate the path of the electricity. 
 
 the interesting effects produced by accumulated electricity may be dis- 
 played. To pass the discharge through wires, nothing more is required 
 than to strain them across a dry mahogany board, between two brass 
 wires and balls, and if a sheet of white paper is placed under them, most 
 curious markings are produced by the fine particles of the deflagrated 
 metal blown into the surface of the paper. An arrangement of two or 
 more Leyden jars is usually called a Leyden Battery, just as a single 
 cannon is spoken of as a gun, whilst two or more constitute a battery. 
 (Fig. 181.) 
 
 Thirty-eighth Experiment. 
 
 Little models of houses, masts of ships, trees, and towers are sold by 
 the instrument makers, and by placing a long balanced wire on the top 
 of the pointed wire of a large Leyden jar, having one end furnished 
 with wool to represent a cloud, a most excellent imitation of the effects 
 of a charged thunder-cloud is produced. The mechanical effect of a 
 flash of lightning has been analysed, and it has been stated, in one 
 instance, that the power developed through fifty feet was equal to a 
 12,220 horse-power engine, or about the power of the engines of the 
 Great Eastern , and that the explosive power was equal to a pressure of 
 three hundred millions of tons. (Eig. 182.) 
 
204 
 
 boy’s playbook of science. 
 
 end of a house ; the square pieces of wood fly out when the continuity of the conductor is 
 broken. 
 
 It was the learned but humble minded Dr. Franklin who established 
 the identity between the mimic effects of the electrical machines (such 
 as have been described), and the awe-inspiring thunder and lightning of 
 nature. A copper rod, half an inch thick, pointed and gilt at the ex- 
 tremity, and carried to the highest point of a building, will protect a 
 circle with a radius of twice its length. The bottom of the rod must oe 
 passed into the earth till it touches a damp stratum. 
 
 Fis. 1S3. A storm. 
 
205 
 
 CHAPTER XIV. 
 
 VOLTAIC ELECTRICITY. 
 
 In describing the various means by which electricity may be obtained,, 
 it was stated that “ Chemical Action” was a most important source of 
 this remarkable agent ; at the same time it must be understood that it 
 is not every kind of chemical action which is adapted for the purpose ;• 
 there are certain principles to be rigidly adhered to — first, in the' 
 generation of the force ; and secondly, in carrying it by wires so as to 
 be applicable either for telegraphic purposes, or for the highly valuable 
 processes of electrotyping and electro-silvering, plating, and gilding. 
 
 A lighted candle, or an intense combustion of coal, coke, or charcoal, 
 no doubt involves the production of electricity, but there are no means at 
 present known by which it may be collected and conducted ; when that 
 problem is solved, the cheapest voltaic battery will have been constructed, 
 in which the element decomposed is charcoal, and not a metal, such as iron 
 or zinc. The first and most simple experiment that can be adduced in 
 proof^of electrical excitation by chemical means, is to take a bit of clean 
 zinc and a clean half-crown, and placing one on the tongue and the other 
 below it, as long as they remain separate no effect is observed, but 
 directly they are made to touch each other, whilst in that position, a 
 peculiar thrill is rendered evident by the nerves of the tongue, which in 
 this case answers the same purpose as the electroscope already de- 
 scribed, and in a short time a peculiar metallic taste is perceptible. 
 
 It has been stated over and over again that it was to a somewhat 
 similar circumstance we owe the discovery of voltaic electricity, and 
 the story of the skinned frogs agitated and convulsed by an accidental 
 communication with two different metals, or, as some say, with the 
 electricity from an ordinary machine, has been repeated in nearly every 
 work on the science. Professor Silliman, however, asserts that the gal- 
 vanic story is doubtful, and is a fabrication of Alibert, an Italian writer 
 of no repute, and that greater merit is due to Galvani than that of being 
 merely the accidental discoverer of this kind of electricity, because he had 
 been engaged for eleven years in electro-physiological experiments, using 
 frogs’ legs as electroscopes. It was whilst experimenting on animat 
 irritability, Galvani noticed the important fact that when the nerve of a 
 dead frog, recently killed, was touched with a steel needle, and the muscle 
 with a silver one, no convulsions of the limb were produced until the two 
 different metals were brought in contact, and he explained the cause of 
 these singular after-death contortions by supposing that the nerves and 
 muscles of all animals were in opposite states of electricity, and that 
 these nervous contractions were caused by the annihilation, for the time, 
 of this condition, by the interposition of a good conductor between them. 
 
 This theory of Galvani had several opponents, one of whom, the cele- 
 
UOY’s PLAYIiOOK OF SCIENCE. 
 
 206 
 
 brated Volta, succeeded in pointing out its fallacy; lie maintained that 
 the electrical excitement was due entirely to the metals, and that the 
 muscular contractions were caused by the electricity thus developed 
 passing along the nerves and muscles of the dead animal. 
 
 To Volta we are indebted for the first voltaic battery, and the distin- 
 guished philosopher may truly be said to have laid the foundation of this 
 now commercially valuable branch of science. 
 
 First Experiment . 
 
 If a plate of clean bright zinc is placed in a vessel containing some 
 dilute sulphuric acid, energetic action occurs from the oxidation of the 
 metal, and its union as an oxide with the acid, and the escape of a mul- 
 titude of bubbles of hydrogen gas. After the action has proceeded some 
 time, the zinc may be removed, and if a little quicksilver is now rubbed 
 over the surface with a woollen rag tied on the end of a stick, it unites 
 
 with the metal, and the sur- 
 face of the zinc assumes a 
 brilliant silvery appearance, 
 and is said to be amalga- 
 mated. In that condition it 
 is no longer acted upon by 
 dilute sulphuric acid, and for 
 the sake of economy this is 
 the only form in which zinc 
 should be employed hi the 
 construction of voltaic batte- 
 ries or single circles. If a 
 clean plate of copper, with a 
 wire attached, is now placed 
 in the dilute acid opposite to 
 and not touching the amal- 
 gamated zinc plate, which may 
 also be furnished with a con- 
 ducting wire, no bubbles of 
 hydrogen escape until the wires from the two metals are brought in 
 contact, and then, singular to relate, the hydrogen escapes from the 
 copper plate, whilst the oxygen is rapidly absorbed by the zinc, and a 
 current of electricity will now be found to pass from the zinc through 
 the fluid to the copper, and back again through the wire to the starting- 
 point, and if the wires are disconnected, the chemical action ceases, and 
 no more electricity is produced. (Fig. 184.) 
 
 The passage of the current of electricity is not discoverable by the 
 electroscope, because it is adapted only to indicate electricity of high 
 tension or intensity, such as that produced from the electrical machine, 
 which will pass rapidly through a certain thickness of air, and cause 
 pith balls to stand out and repel each other ; such effects are not pro- 
 ducible by a single voltaic circle, or even an ordinary voltaic battery, 
 although one comprising some hundreds of alternations would produce 
 
 Fig. 181 . A single voltaic circle, consisting of a 
 zinc and copper plate (marked z and c) in dilute 
 acid. The arrows show the direction of the 
 current. 
 
THE GALVANOMETER. 
 
 207 
 
 an effect on a delicate electrometer ; hence voltaic electricity is said to 
 be of low intensity, and this property makes it much more useful to 
 mankind, because it has no desire to leave a metallic path prepared for 
 it, and does not seize the first opportunity, like the electricity from the 
 electrical machine, to run away to the earth through the best and 
 shortest conductor offered for it. If electricity had only been producible 
 by friction, we should never have heard of electrotyping, and the other 
 useful applications of electrical force of low intensity. 
 
 Second Experiment. 
 
 To ascertain the 
 passage of a current 
 of voltaic electricity, 
 the instrument called 
 the galvanometer 
 
 needle is provided, Fig. jqs. A galvanometer needle, consisting of a coil of 
 which Consists of a covered copper wire, the ends of which terminate at the 
 ™il nf rnrmpr wirp binding screws. The magnetic needle is suspended on a 
 ' u 1 i point in the centre, and the coil is surrounded with a gradu- 
 
 •surroundmg a mag- ated circle, 
 netic needle, so as to 
 
 leave the latter freedom of motion from right to left, or vice versa. 
 When this coil is made part of the voltaic circle it becomes magnetic, 
 and reacting on the magnetized needle, deflects it to one side or the 
 other, according to the direction of the current. (Eig. 185 .) 
 
 Third Experiment. 
 
 If a number of simple voltaic circles, such as the one described in the 
 first experiment, are connected together, they form a voltaic battery, 
 in which of course the quantity of electricity is greatly increased. 
 Batteries of all kinds, from the original Volta’s pile, consisting of round 
 zinc and copper plates soldered together with interposed cloth moistened 
 with dilute sulphuric acid, or his couronne des tasses } consisting of zinc 
 and silver wires soldered together in pairs, and placed in glass cups 
 containing dilute acid, to the improved batteries of Cruikshank, Wil- 
 kinson, Babington, Wollaston, and the still more perfect arrangements 
 of Daniell, Leclanche, Bunsen, and Grove, have been from time to time 
 recommended for their own peculiar features. 
 
 Amongst these several inventions, none will be found more useful 
 than the constant battery of Daniell for electrotyping, silvering, gilding, 
 and other purposes, and Grove’s battery for all the more brilliant results, 
 such as the deflagration of the metals or the production of the electric 
 light. The construction of the Daniell and Grove batteries will there- 
 fore be described. The former consists of a cylindrical vessel made of 
 copper, in which is suspended or placed (as it is open at the top) a 
 membranous, brown-paper, canvas, or porous earthenware tube, con- 
 taining an amalgamated rod of zinc. To charge this arrangement, a 
 strong solution of sulphate of copper, with some sulphuric acid, is 
 poured into the copper vessel, which is provided usually with a sort o( 
 
208 
 
 BOY S PLAYBOOK OF SCIENCE. 
 
 colander at the top to hold crystals of sulphate of copper, and in the 
 porous tube containing the zinc rod is poured dilute sulphuric acid. A 
 number of these cylinders of copper, twenty inches high and three inches 
 and a half in diameter, arranged in wooden frames to the number of 
 
 Fig. 186. a a. Copper cylindrical vessel with colander to hold the crystals of sulphate 
 of copper, b. The amalgamated zinc rod inside the porous cell c c. d. A series of single 
 cells forming a Daniell’s battery. 
 
 twenty, afford a quantity of electricity sufficient to demonstrate all the 
 usual phenomena. (Eig. IS 6.) 
 
 Professor Grove’s battery consists of a flat glazed earthenware vessel 
 containing a flat porous cell. An amalgamated zinc plate is placed 
 outside the porous cell, and a platinum plate inside the latter. The 
 arrangement is put in action by pouring dilute sulphuric acid round the 
 zinc and strong nitric acid inside the porous cell. A set of Grove’s 
 nitric acid battery, as manufactured by Messrs. Elliott, Brothers, of 
 30, Strand, with fifty pairs of sheet platinum, five inches by Uvo inches 
 and a quarter, and double amalgamated zinc plates, flat porous cells, and 
 separate earthenware troughs for each pair, and stout mahogany stand, 
 arranged in ten series of five pairs, will evolve with a proper voltameter 
 one hundred cubic inches of the mixed gases per minute from the decompo- 
 sition of water, and wall exhibit a most brilliant electric light, when 
 arranged as a single series of fifty pairs of plates. Even thirty pairs 
 exhibit the most splendid effects, whilst forty may be regarded as the 
 happy medium, giving all the results that can be desired. (Eig. 187.) 
 
 The advantage of employing amalgamated zinc is very prominently 
 illustrated whilst using any powerful arrangements of either Daniell's or 
 Grove’s batteries, as they will remain for hours quiescent, like a giant 
 asleep, until the terminal wires of the series are brought in contact 
 
BATTERIES OF DANIELL AND GROVE. 
 
 209 
 
 A. 
 
 either through the intervention of some fluid under decomposition or by 
 means of charcoal points. The author had the pleasure of witnessing 
 at King’s College some of the effects of an enormous battery, prepared 
 by the late Professor Daniell, and consisting of seventy of his cells. 
 
 A continuous arch of flame was produced between two charcoal points, 
 when distant from each other three quarters of an inch, and the light 
 and heat were so intense that the professor’s face became scorched and 
 inflamed, as if it had been exposed to a summer heat. The rays col- 
 lected by a lens quickly fired paper held in the focus.* 
 
 Fourth Experiment. 
 
 It is by “ chemical action” the electricity is produced, and as action 
 and reaction are always equal, but contrary, we are not surprised to find 
 that the electricity from the voltaic battery will in its turn decompose 
 chemically many compound bodies, of which water is one of the most 
 interesting examples. It was in the year 1800, and immediately after 
 Volta’s announcement to Sir Joseph Banks of his discovery of the pile, 
 that Messrs. Nicholson and Carlisle constructed the first pile in England’ 
 consisting of thirty-six half-crowns, with as many discs of zinc and paste- 
 board soaked in salt water. These gentlemen, whilst experimenting 
 with the pile, observed that bubbles of gas escaped from the platinum 
 wires immersed in water and connected with the extremities of the 
 Volta’s pile, and covering the wires with a glass tube full of water, on 
 the 2nd of May, 1800, they completed the splendid discovery of ’the 
 lact tnat the Volta’s current had the power to decompose water and 
 other chemical compounds. 
 
 * By the light from the same battery photogenic drawings were taken and the heitina- 
 power was so great as to fuse with the utmost readiness a bar of platinum o^e e gh h of ail 
 ^ ^S re ^,-l ndallth t ,n0r 1 “foible metals, such as rhodiui, iridium, titmium, 4c 
 tiSrcnt or elSdt“ P “ SmaU Caviti<!s “ hard & ra P hite exposed to tlm 
 
 P 
 
210 
 
 boy’s playbook of science. 
 
 In 1801, Davy had suc- 
 ceeded to a vacant post in 
 the Royal Institution, and 
 on Oct. 6th, 1807, made 
 his transcendent discovery 
 of potassium with the aid 
 of the voltaic battery, and 
 from that and other expe- 
 riments inferred that the 
 whole crust of the globe 
 was composed of the oxides 
 of metals. To exhibit the 
 decomposition of water, 
 two platinum plates with 
 proper connecting wires, 
 passing to small metallic 
 cups full of mercury, are 
 cemented inside a glass 
 vessel, which is then filled 
 with dilute sulphuric acid. 
 Just above the platinum 
 plates and over them, stand 
 two glass tubes also con- 
 taining the same fluid in- 
 contact with the battery. 
 Two measures of hydrogen 
 are found in one tube, and 
 one of oxygen in the other. 
 (Fig. 188.) 
 
 To measure the quan- 
 tity power of the voltaic 
 battery, an important in- 
 strument invented by Fa- 
 raday is used. It consists 
 <x ? separate platinum plates 
 cemented in a wooden 
 stand, and over which a 
 capped air-jar with a bent 
 pipe is also cemented. This 
 apparatus contains dilute 
 sulphuric acid of the same 
 strength as that used in 
 the battery under exami- 
 nation, and by taking the 
 time, the quantity of the 
 mixed Dxygen and hydrogen gases producible by a battery per minute is- 
 accurately determined, the gases of course being collected in a gra- 
 duated jar. (Fig. 189-) 
 
 Fig. 138. a a. A finger glass with two holes drilled 
 to pass the wires through, which are imbedded in 
 cement up to the platinum plates, b b. Glass tubes, 
 closed at one end and open at the other, which are 
 placed over the platinum plates to receive the liberated 
 oxygen and hydrogen. The scale at the side shows 
 the respective volumes of two of H to one of 0. 
 
 Fig. 189 . a. Gas jar with cap and bent tube passing 
 to the graduated tube c; the jar is cemented in the 
 same stand which carries the connecting cups, wires, 
 and platinum plates, which are bent round each other 
 to improve the action of the voltameter. 
 
ELECTRO-CHEMISTRY. 
 
 211 
 
 Fifth Experiment. 
 
 By grouping the simple circles forming a voltaic battery in various 
 numerical relations, the quantity and intensity effects are modified. 
 
 Thus, if a series of thirty pairs of Grove’s battery are all connected 
 together in consecutive order, the smallest quantity and the largest 
 intensity effect is produced. 
 
 If changed to two groups of fifteen each, the quantity is doubled— 
 that is to say, it will produce double the quantity of the mixed gases 
 from the voltameter with half the intensity. 
 
 If arranged in three groups of ten each, it is trebled with a propor- 
 tional loss of intensity, until the grouping reaches six series of five each, 
 when a maximum supply of the mixed gases is obtained from the 
 voltameter. 
 
 In arranging the groups, all the zinc ends of each series are con* 
 nccfed, and all the platinum ends are likewise joined by proper wires. 
 
 Sixth Experiment, 
 
 A plate-glass trough, con- 
 taining a few grains of iodide 
 of potassium dissolved in 
 water with some starch, is 
 quickly decomposed into its 
 elements by placing in two 
 platinum plates and connect- 
 ing them with the wires of 
 the voltaic battery. If the 
 glass trough is divided in the 
 centre with a bit of cardboard, 
 the purple colour of the iodine 
 and starch is shown very beau- 
 tifully on one side, but not on 
 the other, as iodine is libe- 
 rated at one pole and the al- 
 kali at the other. (Eig. 190.) 
 
 Seventh Experiment. 
 
 Some solution of common salt coloured with sulphate of indigo and 
 placed in the trough is decomposed into chlorine, which bleaches one 
 side of the indigo solution, and the alkali liberated on the other does 
 not affect it. 
 
 Eighth Experiment. 
 
 Some nitrate of potash dissolved in water and coloured with litmus 
 placed in the glass trough, changes red on one side of the cardboard by 
 the liberation of acid, and is not affected on the other. 
 
 In these experiments the oxygen, iodine, chlorine, and nitric acid are 
 liberated at the electro-positive pole, and are hence termed electro- 
 negative bodies, whilst hydrogen and the alkalies are set free at the 
 electro-negative pole, and are therefore called electro-positive bodies*- 
 
 p 2 
 
 Fig. 190. a a. A glass trough containing the 
 salt dissolved in water, and divided temporarily 
 with a bit of cardboard, b. c c are the two platinum 
 plates connected with the battery, and the shaded 
 side is supposed to represent the liberation of the 
 iodine. 
 
212 
 
 boy’s playbook of science. 
 
 Faraday has modified these terms, and calls the two classes “ a?iions” 
 and “ cat Mans” and the two poles “anodes 55 and “ cathodes. 55 
 
 Anode, from ava , up, and 656?, a way : the way which the sun rises. 
 Anions, from ava , up, ei/zi, to go : that which goes up ; a substance 
 which passes to the anode during the passage of a current of elec- 
 tricity. Cathode, from Kara, down, and 656?, a way : the way which 
 the sun sets. Cathion, from Kara , down, and et/u, to go : that which 
 goes down ; a substance which passes to the cathode during the passage 
 of electricity from the anode to the cathode. 
 
 Ninth Experiment. 
 
 In the process of the electrotype is presented a valuable application 
 of the chemical power of the voltaic circle or battery, and it may be 
 conducted either as a single cell operation or by distinct batteries. In 
 the former case the most simple arrangement will suffice ; the *only 
 articles necessary are — a large mug or tumbler ; some brown paper and 
 a ruler ; a bit of amalgamated zinc, four inches long and half an inch 
 wide ; a short length of copper wire ; some black lead, blue vitriol, and 
 oil of vitriol. 
 
 The mould from which the electrotype is to be taken can be made 
 of common sealing wax, plaster of Paris, white wax, gutta percha, 
 or fusible alloy. Supposing the first to be selected — viz., a common 
 seal, it is first thoroughly black-leaded,* 
 then one end of the copper wire is bent 
 round the top of the amalgamated zinc, 
 and the other is gently warmed and 
 melted into the side of the seal, leaving 
 a small portion uncovered by the wax, 
 which is then well black-leaded. A few 
 ounces of blue vitriol are dissolved in 
 boiling water, and when cold the solu- 
 tion is poured into the tumbler, and the 
 porous cell to contain the mixture of 
 eight parts water to one of sulphuric 
 acid is made by rolling the brown paper 
 three or four times round the ruler and 
 closing the end, and fixing the side with 
 a little sealing wax. The porous cell of 
 brown paper is now filled with the di- 
 lute acid, and placed in the tumbler 
 containing the solution of blue vitriol, 
 the amalgamated zinc being arranged in 
 the paper cell, and the attached seal in 
 the copper solution ; in about twelve 
 hours a good deposit of copp< 
 duced, and a perfect cast in 
 the seal obtained. (Fig. 191.) 
 
 * The application of plumbago, or bT&ck lead, for electrotype purposes, was first made 
 by the late lamented Mr. Robert Murray. 
 
 r is pro- 
 metal of 
 
 Fig. 191. a a. The tumbler con- 
 taining the solution of sulphate of 
 copper, b b. The brown paper cell 
 containing the dilute sulphuric acid, 
 inside which is the amalgamated zinc 
 with wire attached to the seal d. 
 
THE ELECTROTYPE. 
 
 213 
 
 Messrs. Elliott provide every kind of convenient vessel for the pur- 
 pose, and in the picture below it will be noticed that the single cell appa- 
 ratus, though not so economical as the simple tumbler arrangement already 
 described, is perhaps more convenient for electrotyping. (Fig. 192.) 
 
 Fig. 192. a. Single cell apparatus with proper vessel, porous tube, and binding screws* 
 b. A large trough divided by a diaphragm of biscuit- ware or very thin porous wood. 
 
 Tenth Experiment . 
 
 A single cell apparatus is only adapted to produce small electrotypes, 
 but when larger ones are required, a separate battery of three or four 
 
 Fig. 193. a. A single cell, Daniell’s, attached to b, the trough containing the mould 
 and the plate of copper. Below is a Smee’s battery ready to be attached to a larger tough 
 for the purpose of electrotyping a great number of moulds at the same time. 
 
214 
 
 boy’s playbook of science. 
 
 Darnell’s or Smee’s cells is required; and it is usual to place the mould 
 to be copied in a separate wooden trough, attaching it to the cathode 
 wire, whilst a copper plate is connected with the anode, so that as the 
 solution of sulphate of copper undergoes decomposition by the passage 
 of the electricity, it is kept almost in a normal state, in consequence of 
 the oxygen of the water and the acid passing to the copper plate, which 
 they attack and dissolve as fast as the oxide of copper and hydrogen 
 are liberated at the cathode, where the latter deoxidizes the oxide of 
 copper, and by a secondary action deposits metallic copper; the object 
 being to dissolve fresh metal as the copper is deposited on the mould. 
 (Fig. 193.) 
 
 Eleventh Experiment. 
 
 To silver electrotypes or other brass and copper articles, the first 
 attention must be paid to the cleanness of them ; and when an electrotype 
 is just removed from the copper solution, and washed in clean water, 
 it is at once ready to receive the coating of silver ; otherwise, if it has 
 been handled, or is slightly greasy, it should be first boiled in a solution 
 of common washing soda, and then the oxide removed by passing it 
 rapidly in and out of some “ Dipping Acid,” which is prepared by 
 mixing together equal parts of oil of vitriol and nitric acid; when 
 removed from the “ Dipping Acid,” it must be well washed in water, 
 and may remain under the surface of the water until the silvering 
 solution is ready. A silver solution may be prepared by dissolving a 
 sixpence in some nitric acid contained in a flask ; it is then poured into 
 a solution of common salt, which precipitates the chloride of silver, and 
 leaves the copper in solution — the latter is poured off when the chloride 
 has subsided, and after being well washed in some boiling water, is 
 dissolved in a solution of cyanide of potassium. If a clean electrotype 
 is plunged into this solution, it is imme- 
 diately covered with a very thin coating of 
 silver, which of course would soon wear off, 
 and in order to increase the thickness of 
 the silver deposit, a single cell arrangement 
 may be constructed of a large gallipot con- 
 taining a wide porous cell and a circle of 
 amalgamated zinc around it ; the arrange- 
 ment is set in action by pouring a solution 
 of salt (or, still better, sal ammoniac) into 
 and around the porous vessel, and the sil- 
 vering solution into the latter ; a connect- 
 ing wire passes from the zinc, and the ar- 
 ticle being attached to it, is now plunged 
 into the porous cell, when a current of 
 electricity slowly passes and deposits the 
 silver on the copper article. (Fig. 194.) 
 
 Fig. 194. 
 
 The gallipot con- 
 taining tne solution of sal ammo- 
 niac, with the circular amalga- 
 mated zinc with wire and binding 
 screw to which the medal is 
 attached, and contained in the 
 porous vessel holding the silvering 
 solution and medal* 
 
ELECTRO-SILVERING AND GILDING 
 
 215 
 
 Twelfth Experiment. 
 
 Separate batteries and large troughs containing a solution of cyanide 
 of silver in cyanide of potassium are used on a grand scale in the electro- 
 plating establishment of Messrs. Elkington of Birmingham, where the 
 finest specimens of the art are to be obtained ; a plate of silver being 
 attached J;o the anode to supply the loss of silver in these troughs. 
 
 Thirteenth Experiment. 
 
 The art of gilding by the agency of electricity is quite as simple as 
 the processes already described, although greater care is necessary to 
 avoid any loss of the precious metal. A small bit of gold is dissolved 
 in a mixture of three parts muriatic acid and one of nitric acid, which 
 forms the chloride of gold. This is then digested with an excess of 
 calcined magnesia, and the gold is precipitated as an oxide of the metal; 
 the latter is collected and washed, and then boiled in strong nitric acid 
 to remove the magnesia clinging to it, and being again thoroughly washed 
 with water, is dissolved in a solution of cyanide of potassium, forming 
 a solution of cyanide of gold and potassium, which may be placed in 
 the porous cell of the single cell arrangement already described in 
 the Eleventh Experiment. 
 
 Fourteenth Experiment . 
 
 The safest and surest mode of making a gilding solution is to dissolve 
 some cyanide of potassium in water in a gallipot, and having placed a 
 porous vessel therein containing the same solution, put a plate of copper 
 into the porous cell, and some thin foil of pure gold into the gallipot ; 
 connect the gold with the anode of a single cell of Daniell, and the 
 copper in the porous cell with the cathode, and in a few hours sufficient 
 gold will be dissolved for the purpose of gilding. 
 
 It is usually recommended to warm the gilding solution till it reaches 
 a temperature of about 150° Eahr., and a very moderate battery power 
 is employed in Electro Gilding. Indeed the same arrangement, shown 
 in the Eleventh Experiment, Eig. 189, will also answer for the gilding 
 solution. After being gilt, the articles may be rubbed with a little 
 tripoli, or burnished (with taste) by the handle of a key. 
 
 Fifteenth Experiment. 
 
 Passing on to the more brilliant results obtainable from a powerful 
 voltaic battery (of at least thirty pairs of Grove), the beautiful incan- 
 descence of platinum wire may first be noticed. If a wire of this metal 
 is stretched between the brass standards of two ring stands, the length 
 must be proportioned to the power of the battery ; the adjustment can 
 be made very conveniently by twisting the platinum wire on one ring 
 stand, and then leaving the other end loose, the second ring stand may 
 be brought nearer and nearer to the first, until the desired intensity of 
 
216 
 
 boy’s playbook of science. 
 
 Fig. 195. a a. Two ring stands with the battery- 
 wires b b (which should be a convenient length) at- 
 tached. c. Platinum wire, fixed end. d. The other 
 end held in one hand and shortened as the stand is 
 moved by the other hand. 
 
 light from the incandescent 
 wire is obtained. (Fig. 195.) 
 If the wire is contained in 
 a glass tube the cooling 
 effect of currents of air is 
 prevented, and a much 
 greater length of* wire can 
 be made hot. 
 
 Sixteenth Experiment. 
 
 • With the same arrange- 
 ment, a chain composed of 
 alternate links of silver and 
 platinum wire presents a 
 very pretty effect, every 
 alternate link of platinum 
 being incandescent, whilst 
 the silver, from its excellent 
 conducting power, remains 
 comparatively cool. 
 
 Seventeenth Experiment. 
 
 Fireworks or gunpowder, arranged 
 in proper cases, are fired at a great 
 distance from the voltaic battery by 
 heating a thin iron or platinum wire 
 contained within them by the pas- 
 sage of the electricity; and sub- 
 marine and other explosions of gun- 
 powder by the same agency have 
 become a common engineering ope- 
 ration. (Fig. 196.) 
 
 During the operation of blasting 
 the hard marl rocks in ’the River 
 Severn by Mr. Edwards, C.E., a 
 number of holes were made side by 
 Fig. i9fi. a. A Gerb firework with two side in the bed of the river, and 
 holes punctured, through which the bit of car t r idges formed of strong duck OL* 
 iron wire passes, and is wound loundthe o , o . 
 
 battery wires tied to the outside of the case. Ccllivas, tapeiCCi at tile bottom, 
 c. A gut bladder containing the thin wire were filled with charges of powder 
 and nowder for a miniature submarine r c ° i 1 i 
 
 PVTfinSrm from two to four pounds, accord- 
 
 ing to the depth of the marl ; 
 thus, two pounds for four feet, three pounds for four feet six inches, and 
 fou/pounds for five feet. Into the bag were conveyed the wires of the 
 voltaic battery, or Bickford’s fuse, and being then coated with pitch and 
 tallow, and finally greased all over and dusted with whitening, they 
 rarely failed, and were all fired simultaneously under water. The pitch 
 and tallow first, and afterwards the simple tallow, effectually excluded 
 the water from the gunpowder contained in the canvas bag. 
 
THE ELECTRIC LIGHT. 
 
 217 
 
 'Eighteenth Experiment. 
 
 The burning of various 
 metals by the battery is 
 displayed with great effect 
 by De la Rue’s discharger, 
 as also the incandescence 
 of the charcoal points pro- 
 ducing the electric light . 
 
 The illuminating power 
 derived from a forty-cell 
 Grove’s battery of the or- 
 dinary size is about equal 
 to the light of 500 candles. 
 
 Tizeau and Foucault 
 have made a careful com- 
 parison of the light ob- 
 tained from 92 carbon couples as arranged in a Bunsen’s battery, and 
 of the oxy-hydrogen, or Drummond Light, as compared with that of 
 the sun, and they state that “ On a clear August day, with the sun two 
 hours high, the electric light (assuming the sun as unity) bore to it the 
 ratio of one to two and a half— i.e. } the sun was two and a half times 
 more powerful, while the Drummond Light was only j^th that of the 
 sun.” Bunsen found the light from 48 carbons equal to 572 candles. 
 In Bunsen’s battery carbon is substituted for the platinum in Grove’s 
 arrangement; and simultaneously with Bunsen, Cooper (in England) 
 had applied charcoal for the same purpose. 
 
 Fig 1 . 197. De la Rue discharger, containing a series 
 of six pairs of different substances, such as charcoal, 
 iron, lead, zinc, copper, antimony, in six pair of crayon 
 holders, and turning on a centre, so as to be charged at 
 pleasure. 
 
 Fig. 198. Great Eastern, with electric light. 
 
218 
 
 boy’s playbook of science. 
 
 CHAPTER XY. 
 
 MAGNETISM AND ELECTRO-MAGNETISM. 
 
 If a small helix, or coil of covered wire, is arranged with an uiimag. 
 .netized steel needle within it, so that the discharge of a large Leyden 
 
 jar may take place 
 B B through the coil, the 
 
 needle will be found 
 strongly magnetic af- 
 ter the discharge of 
 the electricity. (Pig. 
 194.) Many years 
 before this was 
 known, it had been 
 noticed that when a 
 ship was struck by 
 lightning, the com- 
 passes were generally 
 reversed; and in a 
 special case, where a 
 house was struck, the 
 electricity entered a 
 Fig. 199. a a. A glass tube supported on two uprights of q£ knives fusing 
 wood, with coil of copper wire passing round it, terminating in , ’ ? • tl 
 
 the balls b b. c. Needle to place inside glass tube. some, tearing tile 
 
 handles off others, 
 
 but leaving them strongly magnetic. Electricians tried to repeat the 
 effect by sending the discharge of powerful Leyden batteries through 
 bars of steel without any important result ; and it was not until 
 Oersted, in the year 1819, made his important discovery that the copper 
 vire conveying the electricity possessed peculiar magnetic power, that 
 
 the principle began 
 to be understood, and 
 then the electricians 
 succeeded in imitat- 
 ing the effects of 
 lightning on steel, as 
 already described in 
 the beginning of this 
 chapter. (Fig. 199.) 
 
 When the electri- 
 city has passed away 
 from the Leyden jar 
 through the coil of 
 
 Fig. 20J. 
 
THE LOADSTONE. 
 
 219 
 
 copper wire, it no longer possesses any power to affect a piece of steel 
 or iron, but if the wires of the voltaic battery are now connected with 
 the coil of copper wire, which should be covered with cotton or silk, 
 and many yards in length, then a bar of steel or soft iron is not only 
 rendered magnetic, but remains permanently so, as long as the current 
 of electricity continues to pass along the coil of wire, so that if some 
 nails or iron filings are brought to the bar of iron, one end of which 
 projects from the coil, they cling to it with great force, and a great 
 number of nails may be hung on in this manner, but they imme- 
 diately fall off when the contact is broken with the battery. (Fig. 200.) 
 
 Electricity thus becomes a source of magnetism, and the discoverer. 
 Oersted, found that only needles or bars of steel or iron were thus 
 affected, and not those of brass, shell-lac, sulphur, and other substances ; 
 he termed the conducting wire “ a conjunctive wire,” and described the 
 effect of the electric current or “ electric conflict ,” as he called it, as 
 resembling a Helix (from eXiao-co, to turn round; a screw or spiral), and 
 that it is not confined to the conducting wire, but radiates an influence 
 at some distance. This latter statement is exactly in accordance with 
 our present notions, and hence the coil conveying the current is said to 
 induce magnetism in the iron or steel, just as the phenomena of induction 
 are produced with frictional electricity. The effect of Oersted’s disco- 
 very, says Silliman, was truly electric ; the scientific world was ripe 
 for it, and the truth he thus struck out was instantly seized upon by 
 Arago, Ampere, Davy, Faraday, and a crowd of philosophers in all coun- 
 tries. The activity with which this new field of research has been cul- 
 tivated, has never relaxed even to this hour, while it has borne fruit in 
 a multitude of theoretical and practical truths, and above all, in the 
 electro-magnetic telegraph, truly called, and especially in connexion 
 with the Atlantic telegraph wire, “ the great international nerve of 
 sensation .” 
 
 Magnetism is not only the result of a current of electricity through 
 any good conductor, but there are certain 
 oxides of iron, called magnetic iron ores, 
 which have the property of attracting iron 
 filings, and are mostly found in primitive 
 rocks, being abundant at Roslagen, in 
 Sweden, and called the loadstone, from its 
 always pointing, when freely suspended, to 
 the Polar, North, or Load Star. If a tole- 
 rably large specimen of this mineral is exa- 
 mined, there will be found usually two points 
 where the iron filings are attracted in larger 
 quantities than in other parts of the same 
 specimen. These attractive points are called 
 
 poles, and the loadstone bein<? properly on i A , . . 
 
 J: i i ..i ■ v j & / i 1 i J Fig. 201. A loadstone 
 
 mounted with soft iron bars, termed cheeks, mounted in brass or silver, 
 
 bound round it (in old-fashioned loadstones) * he iron cheeks b b at- 
 with silver plate and duly ornamented with iron^aUedthe 6 ° f ‘ 
 
220 
 
 boy’s playbook of science. 
 
 engraving, has its magnetic power greatly increased, and is then said to 
 be endowed with magnetic polarity; and to prevent the loss of power, a 
 soft piece of iron, called the armature, is placed across and attracted 
 to the poles of the loadstone. (Fig. 201.) 
 
 Second 'Experiment . 
 
 If a needle of tempered steel (fitted with a little brass cup in the 
 centre to work upon a point) is rubbed with the loadstone in one direc- 
 tion only, it is rendered permanently magnetic, and will now be found 
 to take a certain fixed position, pointing always in a direction due north 
 and south. The end which points towards the north is called the north 
 pole, and the other extremity the south pole, and it is usual to mark 
 the north pole with an indent or scratch to distinguish it at all times. 
 
 Fig 1 . 202. A magnetic needle, the north poie rr being at- 
 tracted to the south pole of the bar magnet s, and repelled from 
 the north end. 
 
 Third Experiment. 
 
 If another bar of steel is magnetized, and the north pole duly marked, 
 and then brought towards the same pole of the suspended magnet, in- 
 stant repulsion takes 
 place; the magnet, of 
 course, grasped in 
 the hand is not free 
 to move, but the 
 small magnet imme- 
 diately shows the 
 same fact noticed 
 with electricity, viz., 
 “ that similar magne- 
 tisms repel .” Two 
 noi th poles repel each 
 other, but when the bar of steel is reversed, the opposite effect occurs, 
 and the suspended magnet is attracted, showing that dissimilar mag- 
 netisms attract , and a north will attract a south pole. (Fig. 202.) 
 
 Fourth Experiment. 
 
 Bv contact, the magnetic power is transferred from the magnet to a 
 
 piece of unmagnetized 
 steel, and it is stated 
 that the highest magnet- 
 izing effect is that pro- 
 duced by the simple me- 
 thod of Jacobi. A horse- 
 shoe magnet has its poles 
 brought in contact with 
 the intended poles of an- 
 
 Fig. 203. The horse-shoe magnet, and another one other bar of steel, Fke- 
 immagnetized, placed end to end ; the one shaded and bent in the lorm 
 
 lettered n and s is the magnet, a a. The piece of soft « horseshoe and by 
 iron moved in the direction of the arrow. 01 a UOrsebiiue, 3 
 
ELECTilO-MAGNETS. 
 
 221 
 
 drawing the feeder over the unmagnetized horse-shoe in the direction of 
 the arrow in the cut, and when it reaches the curve, bringing it back 
 again to the same place, say at least twelve times, and after turning 
 the whole over without separating the poles, and repeating the same 
 operation on the other side likewise twelve times, the steel* is then 
 powerfully magnetized ; and it is said that a horse-shoe of one pound 
 weight may be thus charged so as to sustain tw r enty-six and a half 
 pounds, and that by the old method of magnetizing it would only have 
 sustained about twenty-two pounds. (Eig. 203.) 
 
 Fifth Experiment. 
 
 If the horse-shoe magnet is placed on a sheet of paper, and some iron 
 tilings are dusted between the poles, a very beautiful series of curves are 
 formed, called the magnetic curves, which indicate the constant passage 
 of the magnetic power from pole to pole. 
 
 Sixth Experiment. 
 
 The magnetic force 
 exerted by a horse- 
 shoe-shaped piece of 
 soft iron, surrounded 
 with many strands of 
 covered copper wire 
 in short lengths, is 
 extremely powerful 
 (Eig. 201), and enor- 
 mous weights have 
 been supported by an 
 electro-magnet when 
 connected with a vol- 
 taic battery. Sup- 
 posing a man were 
 dressed in complete 
 armour, he might be 
 held by an electro- 
 magnet, without the 
 power of disengaging 
 himself, thus realiz- 
 ing the fairy story of 
 the bold knight who 
 w r as caught by a rock 
 of loadstone, and, 
 in full armour, de- 
 tained by the un- 
 friendly magician. 
 
 Fig. 204. a. Powerful electro-magnet supporting a great 
 weight, b. The battery. 
 
222 
 
 boy’s playbook of science. 
 
 Seventh Experiment. 
 
 When a piece of soft iron is held sufficiently near one of the pole^- 
 of a powerful magnet, it becomes by induction endowed with magnetic 
 poles, and will support another bit of soft iron, such as a nail, brought 
 in contact with it. When the magnet is removed, the inductive action 
 ceases, and the soft iron loses its magnetic power. This experiment 
 affords another example of the connexion between the phenomena of 
 electricity and magnetism. It is in consequence of the inductive action 
 of the magnetism of the earth that all masses of iron, especially 
 when they are perpendicular, are found to be endowed with magnetic 
 polarity ; hence the reaction of the iron in ships upon the compasses, 
 which nave to be corrected apd adjusted before a voyage, or else serious 
 errors in steering the vessel would occur, and there is no doubt that many 
 shipwrecks are due to this cause. No other metals beside iron, steel, 
 nickel, cobalt, and possibly manganese, can receive or retain magnetism 
 after contact with a magnet. 
 
 The remarkable effect of magnetism upon all matter, so ably investi- 
 gated by Faraday and others, will be explained in another part of this- 
 Book — viz., in the article on Dia-Magnetism. 
 
 Fig. 20c. Magician and his loadstone-rock. — Vide Fairy Tale . 
 
223 
 
 CHAPTER XVX 
 
 ELECTRO-MAGNETIC MACHINES, 
 
 .L 
 
 
 
 c 
 
 1 
 
 s c 
 
 1 1 
 
 1 
 
 The experiments already described in illustration of some of the phe- 
 nomena of electro-magnetism are of such a simple nature that they 
 may be comprehended without difficulty ; but it is not such an easy 
 task to appreciate the curious fact of an invisible power producing 
 motion. It has already been explained that a copper or other metallic 
 wire conveying a current of electricity becomes for the time endowed 
 with a magnetic power, and if held 
 above, or below, or close to, a sus- 
 pended magnetized steel needle, 
 affects it in a very marked degree, 
 causing it to move to the right or 
 left, according to the direction of 
 the electric current ; and in order 
 to form some notion of the con- 
 dition of a metallic wire whilst the 
 electricity is passing through it, Fig< 2O6. Portion of a square copper con* 
 the annexed diagrams may be re- ductor, in which a b represents the direction 
 f erred to (Ti°-S 206 207 of the electricity, and the small arrows s,cccc, 
 
 lerrea. to. ycigs. ^U0,z-u/.j the magnetic current or whirl at right angles 
 
 Hr. iioget says : I he magnetic to the electrical current, and exercising a 
 force which emanates from the elec- tangential action, 
 trical conducting wire is entirely 
 different in its mode of operation 
 from all other forces in nature with 
 which we are acquainted. It does 
 not act in a direction parallel to 
 that of the current which is pass- 
 ing along the wire, nor in any plane directl °? <}f the large dart a b, , and the small 
 passing through that direction. It force, 
 is evidently exerted in a plane per- 
 pendicular to the wire, but still it has no tendency to move the poles of 
 the magnet in a right or radial line, either directly towards, or directly 
 from, the wire, as in every other case of attractive or repulsive agency. 
 The peculiarity of its action is that it produces motion in a circular 
 direction all round the wire — that is, in a direction at right angles to 
 the radius, or in the direction of the tangent to’ a circle described round 
 the wire in a plane perpendicular to it ; hence the electro-magnetic force 
 exerts a tangential action, or that which Hr. Wollaston called a vertigi- 
 nous or whirling motion. 
 
 Fig. 207. A round conducting wire, in 
 which the electrical current is flowing in the 
 
224 
 
 BOY S PLAYBOOK OF SCIENCE. 
 
 Dr. Faraday concluded that there is no real attraction or repulsion 
 between the wire and either pole of a magnet, the action which imitates 
 these effects being of a compound nature ; and he also inferred that the 
 wire ought to revolve round a magnetic pole of a bar magnet, and a 
 
 magnetic pole round a wire, 
 if proper means could be de- 
 vised for giving effect to 
 these tendencies, and for 
 isolating the operations of a 
 single pole. For the first 
 idea of electro-magnetic ro- 
 tation the world is indebted to 
 Dr. Wollaston; but Dr. Fara- 
 day, with his usual ingenuity, 
 was the first who carried out 
 the theory practically. The 
 rotation of a wire (conveying 
 a current of voltaic electri- 
 city) round one of the poles 
 of a magnet is well displayed 
 with the simple contrivance 
 devised by him. (Fig. 208.) 
 
 By a careful observation of 
 the complex action of an 
 electrified wire upon a mag- 
 netic needle, Dr. Faraday was 
 enabled to analyse the phe- 
 nomena with his usual pene- 
 tration and exhaustive ability, 
 and he found, as Daniell 
 relates, — 
 
 ‘ That if the electrified wire is 
 placed in a perpendicular position, 
 and made to approach towards one 
 
 Fig 1 . 208. N. A small bar magnet cemented into 
 a wineglass, the north pole being at n. a is a 
 moveable wire looped over the hook, which is the 
 positive ( +) pole of the battery ; the free extremity 
 rotates round the pole of the magnet when the cur- 
 rent of electricity passes. The dotted line repre- 
 sents the level of the mercury which the glass con- 
 tains. The electricity passes in at a, and out at 
 
 the wire b, as shown by the arrows, c is connected . . ,. - .. . ... 
 
 with the negative, and d with the positive, pole of P°* e . °* needle, the pole will not 
 the battery. be simply attracted or repelled, but 
 
 J * will make an effort to pass off on 
 
 one side in a direction dependent 
 upon the attractive or repulsive power of the pole ; but if the wire be continually made to 
 approach the centre of motion by either the one or the other side of the needle, the ten- 
 dency to move in the former direction will first diminish, then become null, and ulti- 
 mately the motion will be reversed, and the needle will principally endeavour to pass in 
 the opposite direction. The opposite extremity of the needle will present similar phe- 
 nomena in the opposite direction ; hence Dr. Faraday drew the conclusion that the direc- 
 tion of the forces was tangential to the circumference of the wire, that the pole of the 
 needle is drawn by one force, not in the direction of a radius to its centre, but in that of 
 a line touching its circumference, and that it is repellpd by the other force in the opposite 
 direction. In this manner the northern force acted all round the wire in one direction, 
 and the southern in the opposite one. Each pole of the needle, in short, appeared to have 
 a tendency to revolve round the wire in a direction opposite to the other, and, conse- 
 quently, the wire round the poles. Each pole has the power of acting upon the wire by 
 itself, and not as connected with the opposite pole, and the apparent attractions and 
 repulsions are merely exhibitions of the revolving motions in different parts of their 
 eircles.” 
 
faraday’s experiments. 
 
 225 
 
 The same fact il- 
 lustrated at Fig. 203, 
 is also demonstrated in 
 a still more striking 
 manner by means of 
 wire bent into a 
 rectangular form, and 
 so arranged that whilst 
 the current of electri- 
 city passes, it is free 
 to move in a circle ; 
 and when the poles of 
 a magnet are brought 
 towards the electrified 
 wire, it may be at- 
 tracted or repelled at 
 pleasure, and in fact 
 Fig. 209. a a a a. The rectangular wire covered with silk pecomes a magnetic 
 and varnished, one end of which being pointed, rests on the indicator and places 
 little cup b, connected with a covered wire passing down the i+o P ]f l] 
 centre of the brass support to the binding screw c let into 1Lseil v 11 careiUiiy SUS- 
 ivory. d. The other extremity of the rectangular wire ; this pended) at right angles 
 being covered and varnished, is not in metallic contact with + n rnAV ; 
 
 the end b, but is likewise pointed, and dips into the mercury “V lI1G 3“ meu ~ 
 contained in the large cup e e. The upper and lower cups Clian. (Dig. 2Uy.) 
 do not touch, and are separated by ivory, marked by the These Curious move- 
 shaded portion, and the cup e e is in metallic communication _ ± r + V 1 
 
 with the brass pillar, and is connected with the negative pole menTS 01 a magnetized 
 of the battery at f, whilst c is connected with the positive needle, and rotations 
 pole of the battery, and the electricity circulates round the w i VPe nnr j 
 
 wire in the direction of the arrows. When a bar magnet, n, is Wil t ^ magnets, 
 
 brought towards the wire, the latter is immediately set in brought about by tile 
 motion, and by alternately presenting the opposite poles of ap’Pnov of an npfivp 
 the magnet, the rectangular wire rotates freely round the ^ c i , • . , 
 
 cupB. current or electricity, 
 
 have induced Sir David 
 
 Brewster to advance his admirable theory, which supposes the affection 
 of the mariner’s compass needle, and all other suspended pieces of 
 steel, to be due to the agency of electrical currents continually circu- 
 lating around the globe ; and Mr. Barlow contrived the following expe- 
 riment in illustration of Brewster’s theory. A wooden globe, sixteen 
 inches in diameter, was made hollow, for the purpose of reducing its 
 weight, and while still in the lathe, grooves one-eighth of an inch deep 
 and broad were cut to represent an equator, and parallels of latitude 
 at every four and a half degrees each way from the equator to the poles. 
 A groove of double depth was also cut like a meridian from pole to pole, 
 but only half round. The grooves were cut to receive the copper wire 
 covered with silk, and the laying on was commenced by taking the 
 middle of a length of ninety feet of wire one-sixteenth of an inch in 
 diameter, which was applied to the equatorial groove so as to meet in the 
 transverse meridian ; it was then made to pass round this parallel, re- 
 turned again along the meridian to the next parallel, and then passedround 
 this again, and so on, till the wire was thus led in continuation from pols 
 
 Q 
 
;226 
 
 boy’s playbook of science. 
 
 to pole. The length of wire still remaining at each pole was returned 
 from each pole along the meridian groove to the equator, and at this 
 point, each wire being fastened down with small staples, the wires from 
 the remaining five feet were bound together near their common ex- 
 tremity, when they opened to form separate connexions for the poles of 
 a voltaic battery. When the battery was connected, and magnetic 
 needles placed in different positions, they behaved precisely as they 
 would do on the surface of the earth, the induction set up by the elec 
 trifled wire being a perfect imitation of that which exists on the globe. 
 
 The opposite effect to that 
 
 already described — viz., the 
 rotation of one pole of a 
 magnet round the electri- 
 fied wire, was also arranged 
 by Faraday in the following 
 manner. (Fig. 210.) 
 
 In the examination of the 
 magnetic phenomena ob- 
 tained from wires trans- 
 mitting a current of elec- 
 tricity, it should be borne 
 in mind that any conducting 
 medium which forms part of 
 a closed circuit — i.e., any 
 conductor, such as charcoal, 
 saline fluids, acidulated 
 water, which form a link 
 in the endless chain re- 
 quired for the path of the 
 electricity, — will cause a 
 magnetic needle placed near 
 it to deviate from its natu- 
 ral position. 
 
 These positions of the 
 electrified wire and the 
 magnetic needle are of 
 course almost unlimited, 
 and in order to assist the 
 memory with respect to the 
 fixed laws that govern these 
 relative movements, Monsieur Ampere has suggested a most useful 
 mechanical aid, and he says “ Let the observer regard himself as the 
 conductor, and suppose a positive electric current to pass from his head 
 towards his feet, in a direction parallel to a magnet ; then its north 
 pole in front of him will move to his right side, and its south pole to 
 
 bis left. ...... . 
 
 “The plane in which the magnet moves is always parallel to tlie plane 
 in which the observer supposes himself to be placed. If the plane of Ilia 
 
 Fig. 210. N s. A little magnet floating in mercury 
 contained m the glass a a; the north pole is allowed 
 to float above the surface of the quicksilver, and the 
 south pole is attached to the wire passing through 
 the bottom of the glass vessel. The electricity passes 
 in at b, and taking the course indicated by the arrows 
 travels through the glass of quicksilver to the other 
 pole of the battery at c. Directly contact is made 
 with the battery, the little magnet rotates round the 
 electrified wire, w. The dotted line shows the level of 
 the mercury in glass. 
 
ELECTRO-MAGNETIC ROTATION. 
 
 227 
 
 .chest is horizontal, the plane of the magnet’s motion will be horizontal, 
 but if he lie on either side of the horizontally-suspended magnet, his 
 lace being towards it, the plane of his chest will be vertical, and the 
 magnet will tend to move in a vertical plane.” 
 
 This very lucid comparison will be seen to apply perfectly to the 
 direction of the rotations in Tigs. 208 and 210. 
 
 The whole of this apparatus is 
 made in the most elegant and 
 finished manner by Messrs. Elliott, 
 of 30, Strand; and by a modi- 
 fication of the latter arrangement 
 (Fig. 206), the opposite rotations 
 of the opposite poles of the mag- 
 nets round the electrified wire, are 
 shown in the most instructive 
 manner. The apparatus (Fig. 
 
 211) was devised by the late Mr. 
 
 Francis Watkins, and consists of 
 two fiat bar magnets doubly bent 
 in the middle, and having agate 
 •cups fixed at the under part of 
 the bend (by which they are sup- 
 ported) upon upright pointed 
 wires, the latter being fixed 
 upright on the wooden base of 
 the apparatus, and the magnets 
 turn round them as upon an axis. 
 
 Two circular boxwood cisterns, 
 to contain quicksilver, are sup- 
 • ported upon the stage or shelf 
 above the base. A bent pointed wire is directed into the cup of each 
 magnet, the ends of which dip into the mercury contained in the box- 
 wood circular troughs on the stage. By using a battery to each magnet, 
 and taking care that the currents of electricity flow precisely alike, they 
 will then rotate in opposite directions. 
 
 Directly after the ingenious experiments of Faraday became known, a 
 great number of electro- magnetic engine models were constructed, and 
 many thought that the time was fast approaching when steam would 
 be superseded by electricity; and really, to see the pretty electro- 
 magnetic models work with such amazing rapidity, it might be supposed 
 that if they were constructed on a larger scale, a great amount of hard work 
 could be obtained from them. This idea, however, has been proved to be a 
 fallacy, for reasons that will be presently explained. The figure on p. 216 
 displays two of these engines, one of which represents the rotation 
 of electro-magnets within iom fixed steel magnets , and the other the 
 rotation of steel magnets by the fixed electro-magnets > The latter 
 (No. 2) moves with such great velocity, that unless the strength of the 
 battery is carefully adjusted, the connexions are soon destroyed. (Fig. 212.) 
 
 q 2 
 
 Fig-. 211. a. Wire conveying the current 
 of electricity, b b. The magnets balanced on 
 points rotating round the wires. 
 
228 
 
 boy’s playbook of science. 
 
 Fig. 212— No. 1 consists of vertical permanent steel magnets and horizontal soft-iroa 
 
 electro-magnets which rotate. c4 . nn1 
 
 No. 2 consists of two fixed soft-iron electro-magnets, and four bent permanent steel 
 magnets, which rotate, in both cases of course, only when connected with the battery. 
 
 Considering the prodigious power or pull of a soft-iron electro- 
 mao-net, and its capability of supporting considerable weight, the most 
 reasonable expectations of success might be entertained with machines 
 acting by the direct pull. It was, however, discovered that they soon 
 became inefficient, from the circumstance that the repeated blows re- 
 ceived bv the iron so altered its character, that it eventually assumed 
 the quality of steel, and had a tendency to retain a certain amount of 
 permanent magnetism, and thus to interfere with the principle of making 
 and unmakin 0 * a magnet. It was this fact that induced Pi of essor Jacobi, 
 of St, Petersburg, "after a large expenditure of money, to abandon 
 arrangements of this kind, and to employ such as would at once produce 
 a rotatory motion. The engine thus arranged was tried upon a tolerably 
 large scale on the Neva, and by it a boat containing ten or twelve 
 people was propelled at the rate of three miles an hour. 
 
 Various engines have been constructed by Watkins, Botta, Jacotn, 
 Armstrong, Page, Hjorth; the engine made by the latter (Hjorth) ex- 
 cited much attention in 1851-52, and consisted of an electro-magnetic 
 piston drawn within or repelled from an electro-magnetic cylinder; and 
 l)v this motion it w T as thought that a much greater length of stroke 
 could be secured than by the revolving wheels or discs, but the loss ot 
 power (not onlv in this engine, but in others) through space is > verv 
 great, and the "lifting power of any magnet is greatly reduced and 
 
ELECTRO-MAGNETIC MACHINES. 
 
 229 
 
 altered at the smallest possible distance from its poles. This loss of 
 power is therefore a great obstacle in the way of the useful application 
 of electro-magnetic force, and can be appreciated even with the little 
 models, all of which may be stopped with the slightest friction, although 
 they may be moving at the time with great velocity. 
 
 In the second place, supposing the reduced force exerted by the two 
 magnets, a few lines apart, was considered available for driving 
 machinery, the moment the magnets begin to move in front of one 
 another there is again a great loss of power, and as the speed increases, 
 there is curiously a corresponding diminution of available mechanical 
 power, a falling-off in the duty of the engine as the rotations become 
 more rapid. In the third place, the cost of the voltaic battery, as com- 
 pared with the consumption of coal in the steam-engine, is very startling, 
 and extremely unfavourable to electro-magnetic engines. 
 
 Mr. J. P. Joule found that the economical duty of an electro-magnetic 
 engine at a given velocity and for a given resistance of the battery is 
 proportioned to the mean intensity of the several pairs of the battery. 
 With his apparatus, every pound of zinc consumed in a Grove’s battery 
 produced a mechanical force (friction included) equal to raise a weight 
 of 331,400 pounds to the height of one foot, when the revolving magnets 
 were moving at the velocity of eight feet per second. Now, the duty of 
 the best Cornish steam-engine is about one million five hundred thousand 
 pounds raised to the height of one foot by the combustion of each pound 
 of coal, or nearly five times the extreme duty that could be obtained 
 from an electro-magnetic engine by the consumption of one pound of 
 zinc. This comparison is therefore so very unfavourable, that the idea 
 of a successful application of electricity as an economic source of power, 
 is almost, if not entirely abandoned. 
 
 By instituting a comparison between the different means of producing 
 power, it has been shown that for every shilling expended there might be 
 raised by 
 
 Pounds. 
 
 Manual power . . . 600,000 one foot high in a day. 
 
 Horse ..... 3,600,000 „ ,, 
 
 Steam 56,000,000 „ „ 
 
 Electro-magnetism . 900,000 „ „ 
 
 A powerful magnet has been compared to a steam-engine with an 
 enormous piston but with an exceedingly short stroke. Although 
 motive power cannot be produced from electricity and applied success- 
 fully to commercial purposes, like the steam-engine, yet the achievements 
 of the electric telegraph as an application of a small motive power must 
 not be lost sight of, whilst the fall of the ball at Deal and other places, 
 by which the chronometers of the mercantile navy are regulated, as also 
 the means of regulating the time at the General Post Office and various 
 railway stations, are all useful applications of the power which fails to 
 compete in other ways with steam. 
 
230 
 
 CHAPTER XVII. 
 
 THE ELECTRIC TELEGRAPH. 
 
 The engineering and philosophical details of this important instrument 
 have grown to such formidable dimensions, that any attempt (short of 
 devoting the whole of these pages to the subject) to give a full account 
 of the history and application of the instrument, the failures and successes 
 of novel inventions, and the continued onward progress of this mode 
 of communication, must be regarded as simply impossible, and there- 
 fore a very brief account of the principle only will be attempted in these 
 pages. 
 
 Eor the complete history of the discovery and introduction of the 
 principle of the Electric Telegraph the reader is referred to the Society 
 of Arts Journal (Nos. 34S-9, vol. viii.), where it is stated that it is half 
 a century , dating from August, 1859, since the first galvanic telegraph 
 was made. “ It was the Russian Earon Schilling’s electro-magnetic 
 telegraph which, without its being known to be his, was brought to 
 London, and caused the establishment of the first practically useful 
 telegraph lines, not only in Great Britain, but in the world.” Dr. 
 Hamel says: “The small sprout nursed on the Neva, which had been 
 exhibited on the Rhine, and thence brought to the Thames, grew up 
 here to a mighty tree, the fruit-laden branches of which, along with 
 those from trees grown up since, extend more and more over the lands 
 and seas of the Eastern hemisphere, whilst kindred trees planted in the 
 Western hemisphere have covered that part of the world with their 
 branches, s'ome of which will, ere long, be interwoven with those in our 
 hemisphere.” 
 
 The first telegraph line in England was constructed by Mr. Cooke 
 from Paddington along the Great Western Railroad to West Drayton 
 in 1838-39 ; and it must be remembered that it was in Eebruary,’I837, 
 that Mr. Cooke first consulted Professor Charles Wheatstone, having 
 previously visited Dr. Earaday and Dr. Roget, and on the 19th 
 November, 1837, a partnership contract was concluded between Messrs. 
 Cooke and Wheatstone. 
 
 To the distinguished philosopher, Professor Wheatstone, the merit of 
 the ingenious construction of the vertical-needle telegraph is due; 
 whilst Mr. Cooke’s name will always be associated with the practical 
 establishment of the first telegraph lines in England. The first line in 
 the United States, from Washington to Baltimore, was completed in 
 1841, being arranged and worked by Professor Morse. 
 
 In British India, in April and May, 1839, the first long line of 
 telegraph, twenty-one miles in length, and embracing 7000 feet of 
 river surface, was constructed bv Dr. (now Sir William) O’Shaughnessy 
 
THE ELECTRIC TELEGRAPH. 
 
 231 
 
 The construction of the electric telegraph may be considered under 
 three heads : 
 
 1st. The Battery, the motive power. 
 
 2nd. The Wires, the carriers of the force. 
 
 3rd. The Instruments to be worked — the hell and the needle telegraph. 
 
 THE BATTERY. 
 
 The construction and rationale of the batteries generally in use have 
 been explained in another part of this work ; those used for telegraphic 
 purposes consist of one or more couples, of which zinc is one, the second 
 being copper, silver, platinum, or carbon. Each couple is termed an 
 element, and a series of such couples a battery. 
 
 The batteries employed chiefly on the English lines consist of a plate 
 of cast-zinc four inches square and ygtlis of an inch thick, attached by a 
 copper strap one inch broad to a thin copper plate four inches square. 
 The zinc is well amalgamated with mercury. Twelve of these couples 
 are arranged in a trough of wood, porcelain, or gutta-percha, divided by 
 partitions into twelve water-tight cells, ly inch wide. The zinc and 
 copper preserve the same order and direction throughout, and when 
 arranged, the trough is filled with the finest white sand, and then 
 moistened with water previously mixed with five per cent, by measure of 
 pure sulphuric acid. This mode of applying the acid is the clever prac- 
 tical improvement of Mr. Cooke, and prevents any inconvenience from 
 the spilling of the acid, and at the same time renders the battery quite 
 portable. The voltaic arrangement thus prepared is found to remain 
 in action for several weeks, or even months, with the occasional addition 
 of small quantities of acid, and answers well for working needle tele- 
 graphs in fine and dry weather. In fogs and rains, at distances ex- 
 ceeding 200 miles at most, their action is not so perfect, and a vast 
 number of couples must be employed, 144 to 288 being frequently in 
 use. In Erance, Prussia, and America, sand batteries do not appear to 
 answer, and Daniell’s arrangement is preferred. Sixty couples suffice in 
 Erance for some of the long lines— viz., from Paris to Bordeaux, 284 
 miles; Paris to Brussels, 231y miles; and in fact, the advantages of 
 the Daniell’s battery have become so apparent, that they are now being- 
 used on English lines. In Prussia, Bunsen’s carbon battery is much 
 used; in India, a modification of Grove’s battery is preferred, the zinc 
 being acted upon by a solution of common salt in w'ater. Two of these 
 elements were found sufficient to work a line of forty miles totally un- 
 insulated, and including the sub-aqueous crossing of the Hooghlv River, 
 6200 feet wide. 
 
 The continual energy of the battery, whatever may be its construc- 
 tion, depends on the circulation of the electricity, the object being to 
 pass the force from the positive end of the series through the wires, 
 back again to the negative extremity of the voltaic series. 
 
 The wire (the carrier of the force) must be continuous throughout, 
 unless, of course, water or earth forms a part of the endless conducting 
 chain. 
 
282 
 
 boy’s playbook of science. 
 
 THE CONDUCTING WIRES. 
 
 These roads for the electricity may be of any convenient metal, and 
 the. one preferred and used is iron, which is well calculated from its 
 great tenacity (being the most tenacious metal known) and cheapness 
 
 to convey the electricity, al- 
 though it is not such a good 
 conductor as copper, and 
 offers about six times more 
 resistance to the flow of the 
 current than the latter metal. 
 The wire does not appear to 
 be made of iron, because 
 it is galvanized or passed 
 through melted zinc, which 
 coats the surface and defends 
 it from destructive rust, 
 at the same time does not 
 destroy its valuable property 
 of tenacity or power of re- 
 sisting a strain. About one 
 ton of wire is required for 
 every five miles, and to sup- 
 port this weight, stout post s 
 of fir or larch are erected 
 about fifty yards apart, and 
 from ten to twenty-five feet 
 high ; At every quarter 
 mile, on many lines, are 
 straining - posts with 
 ratchet wheel winders, 
 for tightening the 
 wires. On some of the 
 lines the wires are at- 
 tached to the posts by 
 side brackets carrying 
 the insulators invented 
 by Mr. C. Y. Walker, 
 which are composed 
 of brown salt-glazed 
 stoneware of the hour- 
 glass shape, as shown 
 in the drawing. (Fig. 
 213 .) 
 
 There are some ob- 
 jections to the hour- 
 glass insulators, and 
 they have been modi- 
 Fig. zii, Clark’s insulator. lied by Mr. Edwin 
 
 Fig-. 213. Walker’s insulator. 
 
THE ELECTRIC TELEGRAPH. 
 
 2 33 
 
 Clark, who employs a very strong stone-ware hook open at the side, 
 so that the wire can be placed on the hook without threading, and the 
 hooks can be replaced in case of breaking, without cutting the tele- 
 graph wire, which is securely fastened to each insulator by turns of 
 thinner wire. An inverted cap of zinc is used to keep the insulator 
 dry. (Fig. 214.) 
 
 In India the conductor is rather a rod than a wire, and weighs about 
 half a ton per mile ; it is erected in the most substantial manner, and 
 many miles of the rod are supported on granite columns, other portions 
 on posts of the iron-wood of Arracan, or of teak. 
 
 The number of wires required by the electric telegraph often puzzles 
 the railway traveller, and people ask why so many wires are used on 
 some lines and so few on others ? The answer is very simple : they are 
 for convenience. Two wires only are required for the double needle 
 telegraph, and one for the single needle instrument. But as so many 
 instruments are required at the terminal stations, an increased number 
 of wires, like rails for locomotives, must be provided; thus, on the 
 Eastern Counties, seven wires are visible, and are thus employed. The 
 two upper wires pass direct from London to Norwich ; the next pair 
 connect London, Broxbourne, Cambridge, Brandon, Chesterfield, Ely; 
 the third pair all the small stations between London and Brandon ; and 
 the seventh wire is entirely devoted to the bell. 
 
 If the eartli was not a conductor of electricity, and employed in the 
 telegraphic circuit, four wires would be required for the double needle 
 telegraph, and two for the single instrument. To understand this, let 
 us suppose a battery circuit extending from Paddington to the instru- 
 ment at Slough, and the wire returning from Slough to Paddington, it 
 is evident that one wire would take the electricity to Slough, and the 
 other return it to London, as in the diagram below. (Fig. 215.) 
 
 Fig. 215. a. The battery, b. The instrument. The arrows show the passage of the 
 electricity to the single needle telegraph instrument by one wire, and the return current 
 by the other. 
 
 If the whole of the return wire is cut away except a few feet at each 
 end, which are connected by plates of copper with the damp earth, the 
 current not only passes as before, but actually has increased m intensity, 
 and will cause a much more energetic movement of the needle in the 
 telegraph instrument. (Fig. 216.) These plates are called “ Earth 
 Plates and Steinheil, in 1837, was the first who proved that the earth 
 might perform the function of a wire. 
 
234 
 
 boy’s playbook of science. 
 
 Fig. 21tf. a. The battery, b. The instrument, c. Earth plate at Slough, d. Earth 
 plate at London. The arrows show the direction of the electric current. 
 
 It must be obvious that a message may be received at any station 
 without a battery, but in order to be able to return an answer, every 
 station must have its own battery. 
 
 Ingeniously-constructed lightning-conductors are attached to the posts 
 which carry the wires, so that in case of a storm, the natural electricity 
 is conveyed to the earth, whilst the voltaic electricity artificially pro- 
 duced pursues its own course without deviation. Protectors are also 
 required for the instruments at the stations, and the plan devised by 
 Mr. Highton is thus described by the inventor : — 
 
 “ A portion of the wire circuit — say for six or eight inches — is enve- 
 loped in blotting-paper or silk, and a mass of metallic filings, in con- 
 nexion with the earth, is made to surround it. This arrangement is 
 placed on each side of the telegraph instrument at a station. When a 
 flash of lightning happens to be intercepted by the wires of the tele- 
 graph, the myriads of infinitesimally fine points of metal in the filings 
 surrounding the wire at the station, on having connexion with the 
 earth, at once draw off nearly the whole charge of lightning, and carry 
 it safely to the earth.” 
 
 THE INSTRUMENTS TO BE WORKED — THE BELL. 
 
 A form of telegraphic apparatus, now but seldom used, was intro- 
 duced some years ago by Sir Charles Bright. In this instrument, two 
 bells took the place of the more common dial needles, and they were 
 sounded by the movement of the armatures of two electro magnets. 
 In every system of telegraphy, bells are used at each end of the line, 
 to call the attention of the clerks in charge. They are also largely 
 used for railway signalling. There are three kinds of electric bells : — 
 Firstly, those connected with a train of clockwork, which is set in 
 motion by the removal of a trigger attached to the armature of an 
 electro magnet ; secondly, those where the hammer of the bell is itself 
 attached to the armature, and which give a single stroke each time the 
 circuit is completed by the depression of a key at the distant station 
 
THE BELL OR ALARUM. 
 
 235 
 
 and lastly, tli q trembler, in which the action of the hammer makes and 
 breaks contact several times in a second, for as long as the current is 
 caused to pass. 
 
 The latter form is the most common of all, and is now largely used 
 for domestic purposes, especially in hotels,. 
 
 1U98II1I ill! ill lllllll (Sillll clubs, and other large buildings, where it en- 
 
 JMI991 III lllllilll tirely supersedes the wires and cranks which 
 
 so constantly require the attentions of the bell- 
 hanger. The annexed cut will enable the 
 reader to understand the way in which it 
 works ; the dotted white lines showing the 
 outline of the case with which it is usually 
 covered to protect it from the dust. In order 
 to avoid the confusion which would arise from 
 the ringing of different bells in a house, without 
 some way of ascertaining from which apart- 
 ment the call arises, it is usual to employ an 
 instrument called an indicator. This consists 
 of a mahogany case, somewhat like a picture- 
 frame, enclosing so many numbered square 
 spaces, each space denoting a certain room. 
 Each space is connected with an electro- 
 magnet having an armature with a cardboard 
 disc attached to it. Upon ringing the bell the 
 disc drops across the space denoting the room where the button was 
 pressed. By this plan one bell will serve for a number of rooms. 
 
 The ordinary electric bell push is too common to require description, 
 it being hardly necessary to say that the act of pressing it completes 
 the electrical circuit, and so the electro-magnet ot 
 the bell is called into action. A great many forms 
 of burglar alarms are constructed on the same 
 principle, contact being made by the opening ot 
 a window, or of a door, or by the pressure of a 
 footstep on a particular board of the flooring. 
 
 These bells are almost invariably worked by & 
 Leclanehe battery, a single cell of which is hem 
 shewn. The outer cell is of glass, containing a 
 solution of sal ammoniac, in which a rod of zinc 
 is placed, the inner vessel being a porous pot, 
 containing a stick of carbon, round which is tightly 
 packed a mixture of peroxide of manganese an 0 
 coke. These cells if properly made will last foi 
 
 217. Electric bell. 
 
 Eig. 218 . Leclanehe cell' 
 
 several months without attention. 
 
 cooke and Wheatstone’s double needle telegraph. 
 
 The principle of this instrument, as already explained, is involved in 
 the elementary experiment of Oersted — viz., the deflection of a mag- 
 
236 
 
 BOY S PLAYBOOK OF SCIENCE, 
 
 netic needle from the inside of a coil of 
 current of electricity, and as it is difficult 
 
 wire conveying a 
 
 to 
 
 give a good 
 description 
 and drawing 
 of the in- 
 terior of the 
 i n st rument 
 that can 
 really be un- 
 derstood, it 
 may be suffi- 
 cient to state 
 that the han- 
 dles give the 
 operator the 
 power of re- 
 versing the 
 current of 
 electricity, so 
 that the 
 needles are 
 deflected with 
 the utmost 
 certainty to 
 one side or 
 the other, 
 either sepa- 
 rately or 
 simultaneous- 
 ly. (Fig. 219.) 
 
 Fig 1 . 219. The letters of the alphabet, figures, and a variety of conventional signals, are 
 indicated by the single and combined movements of the needles on the dial. The left- 
 hand needle moving once to the left indicates the +, which is given at the end of a word. 
 Twice in the same way, a ; thrice, b ; first right, then left, c ; the reverse, d. Once direct 
 to the right, e ; twice, r ; thrice, g. In the same order with the other needle for h, i, k, 
 l, m, n, o, p. The signals below the centre of the dial are indicated by the parallel move- 
 ments of both needles simultaneously. Both needles moving once to the left indicate r ; 
 twice, s ; thrice, t. First right, then left with both, u ; the reverse, v. Both moving once 
 to the right, w; twice, x; thrice, y. The figures are indicated in the same way as the 
 letters nearest to which they are respectively placed. To change from letters to figures the 
 operator gives h, followed by the +, which the recipient returns to signify that he under- 
 stands. If, after the above signs (n and +) were given, c r h l were received, 1845 would 
 be understood. A change from figures to letters is notified by giving i, followed by the +, 
 which the recipient also returns. Each word is acknowledged. If the recipient under- 
 stand, he gives e ; if not, the +, in which case the word is repeated. Attention to a com- 
 munication by this instrument is called by the ringing of a bell (of any size), which is 
 effected through the agency of an electric current. The upper case contains the bell. 
 
 Sir W. O’Shaughnessy, in bis excellent work on the electric telegraph 
 in British India, gives a description of a telegraphic instrument of re- 
 markable simplicity, which is successfully employed in India, and is 
 
o'shaughnessy's simple telegraph instrument. 237 
 
 highly spoken of by Mr. E. Y. Walker and other gentlemen practically 
 acquainted with the working of telegraphs. It consists of a coil of fine 
 wire on a card or ivory frame, a magnetic needle with a light index of 
 paper pasted across it ; two stops of thin sheet lead to limit the vibra- 
 tions of the index ; a supporting board eight inches square, and a square 
 of glass in a frame of wood, or a common glass tumbler placed over it as 
 a shade, to prevent the index being moved by currents of air. It is 
 stated that the office boys, with the assistance of a native Indian 
 carpenter, make up these telegraphs at a price not exceeding two 
 shillings each. 
 
 In England of course they would be more expensive ; but the 
 simplicity and perfection of the arrangement are so much to be com- 
 mended that we give the details for the benefit of those boys who might 
 wish to establish a telegraph on a small scale for amusement. 
 
 THE FRAME. 
 
 This is a piece of mahogany eight inches square and one inch thick, 
 with a hollow groove cut in its centre two inches and a half long, half an 
 inch wide, and a quarter of an inch deep ; a ledge of the same wood 
 one inch wide and half an inch deep surrounds the frame, leaving the 
 inner surface seven inches square ; this is stained black with ink to 
 make the motions of the index more conspicuous. 
 
 THE COIL. 
 
 This consists of fifty feet of the finest silk-covered copper wire wound 
 on a frame of card two inches long, half an inch broad, three-eighths 
 deep in the open part. 
 
 An edge or flange of card, three-eighths of an inch wide, is attached 
 to it at each side to keep the wire in its place. The frame may be of 
 thin wood or ivory, and the winding of the wire commences at the 
 lower left corner, and it is coiled from left to right, as the hands of a 
 watch would move in the same plane. (Fig. 220.) 
 
 Fig. 220. The coil. 
 
 Two inches of each end of the coil wire are now stripped of their silk 
 covering by being rubbed with sand-paper. The coil is mounted in the 
 frame by inserting its lower edge or flange in the groove, so that the 
 lower part or floor of the inside of the coil is level with that of the 
 
238 
 
 BOY S PLAYBOOK OF SCIENCE. 
 
 frame, as shown below, and it is now ready to receive the magnetized 
 needle. (Fig. 221.) 
 
 Fig. 221. The coil fitted into frame. 
 
 THE NEEDLE. 
 
 This is one inch long, one-twelfth of an inch wide, of the thinnest 
 -steel, and fitted with a little brass cap turned to a true cone to receive 
 the point on which it is balanced. These needles are of hard tempered 
 steel, and are magnetized by a single contact with the poles of an 
 electro-magnet or other ordinary powerful magnet. 
 
 The ma°*net is now to be balanced on a steel point one-eighth of an 
 inch high ;°these are nipped off with cutting pliers from common sewing 
 needles, and soldered into a slip of thin copper three inches long, half 
 an inch wide. (Fig. 222.) 
 
 Fig. 222. a. The needle, b. The point on the slip of copper. 
 
 As the north end of the needle will be found to dip, it is advisable to 
 counteract this by touching the south end with a little shell-lac varnish, 
 which dries rapidiy, and soon restores the needle to a perfect equilibrium. 
 
 The needle is completed for use by fixing to it an index of paper (cut 
 from glazed letter paper) two inches long, tapering from one-eighth of 
 
 an inch to a point, and 
 fastened at right angles 
 on to the needle with 
 lac varnish, so as to 
 be truly balanced, and 
 pointing the sharp end 
 to the east, when the 
 needle placed on the 
 point settles due north 
 and south, its . north 
 pole being opposite the 
 observer’s right hand, 
 the observer facing west. 
 
 Fig. 223. The needle with the paper index. 223 ) 
 
o’shaughnessy’s simple telegraph instrument. 239 
 
 The coil frame is placed north and south, and the needle is now intro- 
 duced by sliding the end of the slip of copper into the opening in ‘the 
 frame. 
 
 To limit the vibrations of the paper index a stop is placed at each 
 side. The stops are made of a strip of thin sheet-lead or copper, a 
 quarter of an inch broad, one inch and a half long, and turned up at a 
 right angle, so that one inch rests on the board and half an inch is 
 vertical. Tor ordinary practice these stops are placed each at half an 
 inch from the index. 
 
 The telegraph is placed in a box, which may have a piece of looking- 
 glass in the lid, so that the readings can be taken with the needle in .the 
 vertical instead of the horizontal position, if required. (Fig. 224.) 
 
 Fig. 224. Box containing the telegraph, with the looking-glass in the lid. A small 
 €teel magnet is placed on or near the frame, if required, the south pole of this magnet 
 oeing opposite to the north pole of the needle in the telegraph coil. The bar is four inches 
 long, half an inch broad, three-sixteenths of an inch thick, and it is only used to counteract 
 any local deviation which may arise in using the instrument with miles of wire. It would 
 not be required under ordinary circumstances. The alphabet used is shown to the left. 
 
 The ends of the fine wire of the telegraph coil are joined on to the 
 wires from the reversing instrument, and this is connected with a voltaic 
 series of one or more elements, so that by the employment of the 
 reverser the needle is caused to move right or left at pleasure. The 
 
 / 
 
240 
 
 boy’s playbook of science. 
 
 white paper index on the black ground can be followed with the greatest 
 certainty, and Sir W. O’Shaughnessy states that with this instrument a 
 telegraph clerk may read at the rate of twenty words per minute with a 
 double needle wire, being equal to forty words per minute. 
 
 THE REVERSED 
 
 consists of a block of wood, two inches and a half square, in which 
 four hollows, half an inch deep, are cut, and these hollows are joined 
 diagonally by copper wires let into the substance of the wood, and most 
 carefully insulated from each other by melted cement, but exposing 
 a clean metallic surface in each cell, which is filled with mercury. 
 (Fig. 225.) 
 
 Fig. 225. Block of wood with four holes; the positive terminal is connected with the 
 holes a and b, the negative with c and d ; the hollows are filled with mercury, t t are the 
 wires from the telegraph box, and it is obvious that by dipping them alternately into c b 
 and a i) the current is reversed, and the needle deflected right or left at pleasure. 
 
 In practice a more elaborate reverser is employed, but to demonstrate 
 the principle the simple block above described is quite sufficient. 
 
 With the telegraph placed at the top of a house, or in a distant 
 cottage, and a single cell of Grove’s battery, or at most two, for any 
 short distances, with the reverser, messages may be passed with great 
 rapidity from the bottom of the house to the top, or from a mansion to 
 the lodge, it being understood that a battery, reverser, and telegraph, 
 are required at both places where messages are received and answered ; 
 hut if no answers are required, the battery and reverser are placed at 
 one end of the wire in the house, and the telegraph at the other ex- 
 tremity in the cottage, and earth plates may be arranged to return the 
 current, or another wire used for that purpose. 
 
 The alphabet for the needle telegraph in use in this country differs 
 from that given upon the former page, but it is unnecessary to quote it 
 at length, for the characters are of course made up of the right and left 
 movements of the needle, and their nature will be readily understood. 
 
 Another form of instrument which has of late years been largely used 
 
THE ELECTRIC TELEGRAPH. 
 
 241 
 
 in telegraphy is that known as the Morse system. In this method 
 the alphabet is made up of dots and dashes, the dot answering to a left- 
 hand deflection in the needle instrument, and the dash corresponding 
 with a right-hand deflection. A person therefore who has learnt to 
 work the needle instrument can very soon acquire a proficiency in the 
 Morse system. The alphabet is as follows, the short lines representing 
 dots and the long ones dashes : — 
 
 A [as] 
 
 E I" 
 
 h in in ~ 
 
 i __ 
 
 Full stop [.] 
 
 Note of interrogation [?] . 
 
 Note of Admiration [!] - — 
 
 Apostrophe [’] 
 
 Parenthesis [(] 
 
 Inverted commas 
 
 o _ _ 
 
 o » — — 
 
 Dashes and dots similar to these are printed in ink by the action of 
 the current. The transmitting instrument consists of a key (Fig. 226 ), 
 which being pressed for a long or short duration of time, makes at the 
 receiving end of the circuit a dash or a dot. This is brought about in 
 the following manner, — at the receiving end is an electro-magnet, the 
 armature of which is connected with a little roller, which is constantly sup- 
 plied with printing ink. Just above this roller is a slipof paper which travels 
 along by clockwork. Directly the current passes, the magnet attracts the 
 
 s 
 
242 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 armature, the little ink roller is brought against the slip of paper, and 
 makes a dot or a dash, according to the length of time it rests there. 
 
 Fig. 226. Speciality key. 
 
 Another means of recording the Morse signals is by Bain’s chemical 
 telegraph, in which the electro-magnet is not used. The travelling slip 
 of paper is soaked in a certain chemical solution, which is decomposed 
 directly the electric current is passed through it. A steel pointer rests 
 against the paper, and every time the circuit is completed, it leaves a 
 mark, which may be short or long as the transmitter may wish. 
 
 Sometimes the recording instrument is dispensed with altogether, and 
 
 Fig. 227. Morse sounder. 
 
 the operator depends altogether on his hearing faculties for understanding 
 
THE ELECTRIC TELEGRAPH. 
 
 243 
 
 the signals sent. In this case a Morse sounder is used (Fig. 227). In 
 the annexed cut the electro-magnet of the sounder is shewn standing 
 upright in the centre, the armature above it being so adjusted that 
 every time it is attracted to the magnet it gives an audible click. In 
 using the sounder, the dashes are expressed by double clicks and the 
 dots by single clicks. Thus with these two little instruments (the key 
 and the sounder), a battery, and a line wire, communication between 
 two distant persons is accomplished, provided they are acquainted with 
 the Morse alphabet. 
 
 In many cases it is found desirable to use some kind of telegraphic 
 system, where the signals given are not of a conventional form, as in the 
 Morse and needle instruments, but are represented by the ordinary 
 letters of the alphabet. The best known form of instrument which 
 accomplishes this is Wheatstone’s magnetic alphabetic- dial telegraph, 
 which is extensively used on private lines, and more especially in 
 connecting business firms who have premises in different parts of one 
 city. The great advantage of such a system is that anybody possessing 
 ordinary intelligence can work the instrument, provided he has learnt 
 his alphabet. 
 
 Another instrument which must not pass unnoticed is Hughes’ printing 
 telegraph, in which the message sent is actually printed in ordinary 
 type as it arrives at its destination. In this system two type wheels — 
 having the letters of the alphabet on their edges — revolve, one at each 
 station, with equal velocity. The required letters are brought above a 
 slip of travelling paper by the revolution of the type wheel, and are im- 
 pressed thereon in printers’ ink. 
 
 A great many plans have been from time to time suggested for trans- 
 mitting handwriting. The first of these was Bakewell and Casselli’s 
 copying telegraph. It depends, as in Bain’s telegraph, upon the 
 decomposition of certain chemical salts by the passage of the electric 
 current. These phenomena were first pointed out by Sir Humphrey 
 Davey, but were not acted upon for the use of the telegraph until 1850, 
 when Bakewell produced his copying telegraph. The message is 
 written in resinous ink, such as sealing-wax dissolved in spirit, or tin 
 foil. This foil is then attached to a cylinder, so arranged that a pointer 
 traverses every part of its surface as it revolves, the action being similar 
 to the travelling tool of a screw-cutting lathe. Another cylinder with a 
 similar pointer forms the recording instrument, but in this case the foil 
 is replaced by chemical paper. By clockwork the two cylinders are 
 caused to revolve at exactly the same pace. An electric current passes 
 through the pointers to the cylinders which they touch. Supposing that 
 no interruption occur, the two pointers will make spiral lines on each 
 cylinder, one being indicated by a slight depression upon the tin-foil, 
 and the other by a coloured continuous line caused by the decomposition 
 of the salt employed. (A solution of prussiate of potash and ammonia 
 gives a blue mark — the well-known prussian blue — but a mixture of 
 iodide of potash and starch will give a brown mark, owing to the libera- 
 tion of iodine.) The resinous ink, however, on the sending cylinder 
 
244 
 
 boy’s playbook of science. 
 
 forms a barrier through which the electricity cannot venture ; whenever, 
 therefore, the pointer passes over a piece of the writing, the current is 
 stopped, and so the recording pointer on the chemical paper ceases to 
 act. The result is a white writing upon a background made up of a 
 multitude of fine lines, like the engraved sky of a good wood block. 
 
 A somewhat similar plan was lately tried at the General Post Office. 
 It was the invention of M. d’Arlincourt, and contained many features 
 which represented improvements upon Bakewell’s system. .By its aid 
 drawings could be executed, and it was supposed that it might prove 
 useful in war time in the transmission of plans of fortifications, maps, 
 and the like. It has not come into use, however, and may be regarded 
 as one of those scientific toys which from time to time make their 
 appearance suddenly, and as suddenly disappear from view. 
 
 On a wholly different principle is the writing telegraph of Mr. h. A. 
 Cowper, of Westminster, which is likely to have an extended use. . It 
 has already been tried for some months on the South-Western line, 
 working from London to Woking, a distance of more than twenty-six 
 miles, and giving every satisfaction. An ordinary pencil serves as the 
 transmitting instrument, and the receiving instrument is bound to lollow 
 and transcribe its every movement. The inventor has kindly sent me 
 a slip of the writing, which has been transferred to a wood block and 
 
 
 Fig. 228 . 
 
 engraved. (See Fig. 228.) He lias also sent me a description of the 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 245 
 
 communicated by one wire, and the position horizontally being com- 
 municated by the other wire. 
 
 “ The pencil of the operator has two light f contact rods 3 jointed to 
 it, and one of these slides over the edges of a series of ‘ contact plates/ 
 having various resistances interposed between them and the line wire, 
 while the other rod slides over a second set of such plates connected to 
 the other line wire. At the receiving end of the line, each of these 
 wires actuates its own needle. 
 
 “The two needles (which are placed at right angles to each other, 
 and are provided with light springs), actuate one writing pen, this pen 
 moving up or down, and backwards or forwards, in exact obedience to 
 the motions of the pencil in the hand of the operator at the distant 
 station. 
 
 “ Both the paper written upon in pencil by the operator at the send- 
 ing station and that written upon in ink by him at the receiving station 
 move along as the writing proceeds, and the messages have only to be 
 cut off from time to time, wound round a piece of card, and sent out to 
 their destination, or put into an envelope and despatched. 3 ’ 
 
 With this description of the latest development of modern telegraphy 
 I must bring this section to a close. I shall next point out how in the 
 invention of that wonderful instrument called the telephone, modern 
 telegraphic instruments may become altogether superseded by the 
 sound of actual speech. 
 
 Fig 1 . 229. One of the ideas of telegraphic communication. 
 
 THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 
 
 The announcement that it is actually possible to transmit the sounds 
 of the human voice through a telegraphic wire is perhaps the most 
 
246 
 
 boy’s playbook of science. 
 
 startling information which any one ignorant of the march of physical 
 science could conceive. The first intimation that such a feat had been 
 accomplished came from Sir William Thompson, in his opening address 
 to the British Association at Glasgow in the year 1876, who recorded 
 how he had so heard the well-known speech from “ Hamlet,” “ To be 
 or not to be,” etc. Since that time many forms of telephones have 
 appeared and have met with different degrees of success, until at the pre- 
 sent day one or two which surpass all others in their action are coming 
 into actual use for purposes of intercommunication. 
 
 Long before it became possible to convey speech by means of the 
 telephone, more than one inventor had produced instruments by which 
 it was possible to transmit musical sounds by means of a telegraphic 
 wire. To go back to the very beginning of these experiments, we must 
 note some curious phenomena which were first discovered by Pagein the 
 year 1837. He found that the operation of magnetizing and demagnetizing 
 an iron bar, by sending an electric current through the helix of wire 
 surrounding it, was accompanied by an audible sound, a kind of click. 
 By making and breaking the current several times in a second these clicks 
 were made to follow one another so rapidly that they constituted a 
 musical note, the greater the number of such sounds in a given time, 
 the higher the pitch of the note produced. (To understand this the 
 reader should refer to some work on acoustics, where he will find 
 described an instrument called Sav art’s wheel, the cogs of which beat 
 against a piece of card. The greater the velocity at which the wheel is 
 turned, the greater the number of beats against the card in a given 
 time, and the higher in pitch the resulting note. This proves that a 
 musical note is simply a succession of noises which follow one another 
 periodically. To constitute a note they must occur at least sixteen 
 times in every second, or the ear will not acknowledge them but as a 
 series of distinct taps.) 
 
 In the year 1860, Philip Reiss, of Germany, took advantage of Page’s 
 discovery by the construction of a transmitter by which he was enabled 
 to control the number of electrical contacts by the action of a vibrating 
 diaphragm. This instrument consisted of a box into the side of which 
 was fitted a mouthpiece not unlike the mouthpiece of any ordinary 
 speaking-tube. At the top of the box was an orifice filled in with a 
 parchment diaphragm. In the centre of the diaphragm was a small 
 piece of metal, over which, but not actually touching it, was a metallic 
 point. Upon singing a note into the mouthpiece of the box, the parch- 
 ment above was thrown into vibration, and every such vibration caused 
 the piece of metal to touch the point hanging above it. So that ac- 
 cording to the number of vibrations in any given note, a similar 
 number of contacts were made, and as both pieces of metal were joined 
 up with a battery and a line wire, these contacts were electrical and 
 effected the magnetization of an iron bar, which formed the receiving 
 instrument at the distant station. 
 
 Some years later another form of telephone was devised, in which the 
 action of the common tuning-fork was taken advantage of to make and 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 247 
 
 break the current. Mr. Cromwell Varley produced an instrument of this 
 nature., which I believe was the first form of telephone ever publicly 
 exhibited in this country. It was placed in the Queers Theatre, Long 
 Acre, the other end of the line wire being at a music hall on the Surrey 
 side of the river, and music played at the latter place was plainly 
 heard in the theatre. 
 
 Mr. Elisha Gray, of Chicago, was the next inventor who came upon 
 the scene. In 1874 this gentleman produced an instrument of some- 
 what. the same character as the one just described, but far more perfect 
 in its action. In this telephone metal reeds were employed of the same 
 form as those used in harmoniums. These reeds were governed by 
 pianoforte keys, and were so arranged that electro-magnets at the dis- 
 tant station actuated similar reeds, and so the original sounds were 
 reproduced. 
 
 All these instruments were capable only of producing musical notes, 
 not speech, and they are distinguished from the more recent inventions 
 as “Tone Telephones,” the latter being called “Articulating Tele- 
 phones. ” 
 
 U p to the year 1876 no instrument had been devised for transmitting 
 speech, except a little toy called the thread telephone, which was sold, I 
 believe, some twenty years ago, and forgotten, but revived within the 
 last year or two. It is however something more than a mere toy, for it 
 teaches us how wonder- 
 fully sounds and even 
 articulate speech can be 
 converted into motion, 
 and again produced at a Bjj|jjjji 
 distance as speech. This 
 form of telephone is 
 shown at fig. 230. It 
 consists of two little 
 boxes made of wood, card, or metal, open at one end, and closed at the 
 other with a diaphragm of parchment. To the centre of each diaphragm 
 is knotted the two ends of a piece of twine. With this simple con- 
 trivance people a hundred yards apart can keep up a conversation with- 
 out difficulty. The action of the instrument is as follows : — the speaker 
 into one box throws the diaphragm into vibration by the vibration of 
 his voice, these vibrations constitute so many pulls upon the cord lead- 
 ing to the other diaphragm, and so the latter is made to describe 
 similar movements, and the sounds become audible to the listener there. 
 It is evident then that if we can find some means of throwing a dia- 
 phragm into motion at a distance, so as to correspond with the move- 
 ments of a diaphragm agitated by the voice, we can reproduce the 
 original sounds given. Twine will of course only answer the purpose 
 for a few yards, and although experiment has shown that this distance 
 can be greatly increased by the use of fine copper wire, still such 
 distance is limited to a few hundred yards. It was reserved for Pro- 
 fessor Graham Bell to solve the problem by the use of magnetism. 
 
248 
 
 boy’s playbook of science. 
 
 Professor Bell’s first form of articulating telephone made its appear- 
 ance at the Philadelphia Centennial Exhibition of 1876, but the 
 instrument then shewn has since been considerably modified. Want 
 of space will compel me to leave out many interesting details as to the 
 manner in which Professor Bell, step by step, surmounted every 
 difficulty until the end which he had in view was attained. And I must 
 content myself by simply describing the instrument, and by briefly 
 explaining to my readers the principles involved in its construction. 
 
 Fig. 231. Prof. Bell’s telephone, in elevation and seetion. 
 
 Eig. 231 shows Bell’s telephone in elevation and section. Its out- 
 ward form has been compared to the handle of a skipping rope, which .it 
 much resembles both in appearance and size, its total length being only 
 about six inches; Referring to the section, A is the mouthpiece of the 
 instrument, which also serves as ear-piece (for this form of telephone 
 both receives and transmits sounds), c.c. is a metallic diaphragm made 
 of that very thin enamelled iron upon which photographs are taken 
 under the name of Ferrotypes. The principal part of the instrument is 
 the bar-magnet D, which passes through its centre, the north pole of 
 which is surrounded by a coil of silk-covered copper wire. This end. of 
 the magnet all but touches the iron diaphragm, its other end being 
 fitted with a screw by which its exact position can be regulated to a 
 nicety. The ends of the coil are carried down to the back of the case. 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 249 
 
 where they are connected with two binding-screws, to which the line 
 wires can be readily adjusted. On short circuits it is as well to use 
 two wires, but where the distance is considerable the earth-current 
 should be taken advantage 
 of, as explained in a former 
 page. In this latter case the 
 instrument will be joined 
 up in the manner shown at 
 Big. 232, the letters C and 
 Z indicating the copper and 
 zinc elements of the battery 
 for ringing the call-bell. 
 
 So far as the telephone 
 itself is concerned, it re- 
 quires no battery whatever, 
 its action being dependent 
 upon the magnet contained 
 within it. The sonorous 
 vibrations set up in the air 
 by the voice are projected 
 upon the diaphragm, which 
 also vibrates in sympathy. 
 
 These vibrations, by con- 
 stantly varying the distance 
 between the centre of the 
 iron disc and the magnet 
 behind it, cause variations 
 in the current of electricity 
 which is induced in the coil 
 of wire, and such variations 
 are telegraphed to the dis- 
 tant telephone, where the 
 corresponding diaphragm is 
 brought into similar move- 
 ments, and gives out the 
 spunds conveyed. In the 
 next chapter it will be seen 
 how a current can be in- 
 duced in a coil of wire by r 
 the approach of a magnet ; I 
 and when we know by ex- 
 periment that this is the 
 case, it is not difficult to 
 understand how this current 
 must be varied in its con- 
 
 Fig. 232. Diagram showing manner of joining up 
 a telephone circuit. 
 
 dition by the movement of a piece of iron placed near the end of the 
 magnet. Such movements are brought about by the vibrating .iron 
 diaphragm in Bell’s telephone. 
 
250 
 
 boy’s playbook of science. 
 
 I have no doubt that my readers will be glad to learn that a pair of 
 these telephones can be very easily constructed by those who can use 
 their fingers with neatness and intelligence. Shortly after Bell’s tele- 
 phone was first brought to England, I published in one of the magazines 
 full directions for making a pair of instruments. The case was con- 
 structed from a penny pop-gun, glued into a wooden tooth-powder box. 
 I had the satisfaction of hearing that the editor of the periodical 
 received dozens of letters from boys who had followed my direc- 
 tions, and had met with success which altogether surpassed their 
 expectations. 
 
 A very convenient form of bell for use with this telephone is shown 
 at Eig. 233, which has the advantage of dispensing with a battery. 
 The box contains a small magneto-electric machine, which is set in 
 
 Fig-. 233. Telephone bell and shunt. 
 
 motion by the handle on the left-hand side. The other handle is a 
 shunt by which the bell or the telephone can be thrown into circuit 
 as required. Without some such contrivance as this, it would be 
 necessary to have a separate line wire to work the bell. 
 
 The sounds reproduced by this form of telephone are very perfect, 
 but unfortunately extremely weak, so that it is necessary for the 
 transmitter to speak very distinctly, and for the hearer to hold the 
 instrument close to his ear. Notwithstanding these defects the 
 instrument is largely used, especially in the United States; and in 
 order to show the marvellous distance through which it will act, I 
 may state that it is upon record that conversation has been easily carried 
 on between Boston and New York, a distance of 260 miles. 
 
 A modification by which Bell’s telephone has been vastly improved 
 has lately been introduced by Mr. E. A. Gower. The bar-magnet is 
 discarded, and is replaced by one formed like the letter D. The two 
 poles are thus brought close together, and each is furnished with a coil. 
 The sounds are greatly augmented by this arrangement, while the 
 articulation is improved. There is little doubt that this form of telephone 
 will meet with extended use. 
 
 It is quite impossible to notice here the various forms of telephones 
 which have been devised since Professor Bell pointed out how articula- 
 tion could be reproduced at a distant point. Their name is legion, 
 but.it is doubtful whether the majority will ever come into practical 
 use. 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 251 
 
 We now arrive at the name of one who, long well known as an 
 inventor in America, has of late years attained a celebrity which can 
 only be described as world-wide. Thomas Alva Edison was born at 
 Milan, Erie County, Ohio, in 1 847. He began his career as a news* 
 paper boj on the Grand Trunk Railroad. Even at this early period 
 his active mind was constantly turned towards scientific pursuits, for 
 we learn that he fitted up a disused car as a chemical laboratory, and 
 advanced so far in his experiments as to nearly set the train on fire. 
 He shortly afterwards became employed as a telegraph operator, and in 
 this capacity he had opportunities of gaining a thorough practical* 
 knowledge of the principles of electric communication. In a few years 
 the instruments which he invented replaced those in use at the office with 
 which he became connected; and at the present time he is engaged' 
 in working out various wonderful instruments in his large experimental 
 laboratory and factory at Menlo Park, near New York. He is the 
 proprietor of some 120 different patents, the majority of which relate 
 to improvements in telegraphy. But the instrument which first 
 made his name famous beyond his own country was the speaking 
 phonograph. 
 
 The first published description of this marvellous, yet simple piece 
 of mechanism, appeared in a London paper in January, 1878, the account 
 being copied from the Scientific American of Dec. 22nd, 1877. 
 
 “ Mr. Thomas A. Edison recently came into this office, placed a little 
 machine on our desk, turned a crank, and the machine enquired as to 
 our health, asked how we liked the phonograph, informed us that it was 
 well, and bid us a cordial good night. These remarks were not only 
 perfectly audible to ourselves, but to a dozen or more persons gathered 
 around, and they were produced by the aid of no other mechanism than 
 the simple little contrivance explained and illustrated below. 
 
 Fig-. 234. Edison’s phonograph. 
 
 “ There is, first, a mouthpiece E, across the inner orifice of which is 
 a nietal diaphragm, and to the centre of this diaphragm is attached a 
 point, also of metal. Behind this mouthpiece is a brass cylinder, C, 
 supported on a shaft which is screw-threaded, and turns in a nut for a 
 
252 
 
 boy’s playbook of science. 
 
 bearing, so that when the cylinder is caused to revolve by the crank D, 
 it also has a horizontal travel behind the mouthpiece. It will be clear 
 that the point on the metal diaphragm must, therefore, describe a spiral 
 trace over the surface of the cylinder C. On the latter is cut a spiral 
 groove of like pitch to that on the shaft, and around the cylinder is 
 attached a strip of tinfoil. When sounds are uttered in the mouthpiece, 
 the diaphragm is caused to vibrate, and the point thereon is caused to 
 make contacts with the tinfoil at the portion where the latter crosses 
 the spiral groove. Hence, the foil, not being there backed by the solid 
 metal of the cylinder, becomes indented, and these indentations are 
 necessarily an exact record of the sounds which produced them. 
 
 “A and B are the bearings in which the shaft turns, G is the base- 
 board of the instrument. H is a lever for adjusting the position of the 
 mouthpiece, I being the nut on which it works. The heavy flywheel 
 E is to equalise the motion of the cylinder.” 
 
 So far the phonograph is simply a recorder of sounds, which record 
 is inscribed on a piece of tinfoil, as a series of indentations dug into it 
 by the point of the vibrating metallic diaphragm. Other instruments 
 have long ago been invented which produce such records, notably the 
 phonautograph of M. Leon Scott, a full description of which is given 
 in Ganot’s Physics. But now comes the marvellous part of Edison’s 
 invention, the reproduction from the tinfoil record of the sounds which 
 produced it. 
 
 In the first form of phonograph constructed, the reading or talking 
 mechanism consisted of a duplicate diaphragm held in a tube at the other 
 side of the cylinder, but in the perfected instrument one diaphragm is 
 made to act both as recorder and talker. The cylinder is pushed back 
 to its first position, and the crank is again turned so that it travels once 
 more over the same ground. The little point on the diaphragm once 
 more finds its way into the indentations in the tin-foil, and as it thus 
 steps in and out of its own footprints the diaphragm vibrates and gives 
 out the sounds originally spoken. The details of construction of this 
 curious instrument are shown in the section. (Eig. 235.) 
 
 It is not surprising that a machine capable of such wonderful doings 
 should have attracted the notice of every person who could read or 
 think ; and its first appearance in this country created quite an excite- 
 ment. As usual in cases of the kind, the most absurd notions as to the 
 capabilities of the little machine were speedily promulgated, and even 
 thoughtful people were induced to raise wondrous dreams as to its 
 possibilities in the future. I quote once more from the article before 
 alluded to : — “ We have already pointed out the startling possibility of 
 the voices of the dead being reheard through this device, and there is no 
 doubt but that its capabilities are fully equal to other results quite as 
 astonishing. When it becomes possible, as it doubtless will, to magnify 
 the sound, the voices of such singers as Parepa and Titiens will not die 
 with them, but will remain as long as the metal in which they may be 
 embodied will last. The witness in court will find his own testimony 
 repeated by machine, confronting him on cross-examination, the 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 253 
 
 testator will repeat his lost will and testament into the machine, so that 
 it will be reproduced in a way that will leave no question as to his 
 devising capacity or sanity. It is already possible, by ingenious optical 
 contrivances, to throw stereoscopic photographs of people on screens in 
 full view of an audience. Add the talking phonograph to counterfeit 
 
 Fig. 235. Section of phonograph, r, the mouthpiece secured in the frame, b, b, a, 
 diaphragm, p, metallic point or stylus to indent tinfoil on the cylinder, c. e, spring 
 support to hold the stylus rigidly in position. The two round cushions seen above the 
 stylus are pieces of india-rubber tubing to deaden the sound, which otherwise would be too 
 metallic in character, s, adjustment screw. 
 
 their voices, and it would be difficult to carry the illusion of real 
 presence much further.” 
 
 Such ideas as these have been eopied and re-copied into various papers, 
 until many people believe in them. But those who have actually heard 
 the phonograph will acknowledge that very much has yet to be done 
 before any particular voice, however familiar, could be recognised by its 
 aid. There is no doubt whatever but that it is a marvellous invention, 
 but beyond being a wonderful curiosity, it is not likely in its present 
 form to be of any particular use to mankind. 
 
254 
 
 boy’s playbook. of science. 
 
 The London Stereoscopic Company, to whom I am indebted for the 
 use of the cuts, Tigs. 234 and 235, have the exclusive right to exhibit 
 and sell the phonograph in this country. 
 
 It seems but natural that Mr. Edison should have early turned his 
 attention to telephonic phenomena. His first experiments in this direc- 
 tion were guided by the previous attempts of Reiss, but he soon struck 
 out into a fresh track, and produced an instrument which is known as 
 Edison’s carbon transmitter. Its main feature is a button of carbon 
 made of compressed lamp-black. In common with other imperfect 
 conductors of electricity, carbon possesses the property of varying its 
 resistance with variations of pressure. And in this telephone such 
 variations are caused by the action of sonorous vibrations upon a 
 diaphragm placed above the carbon button. The latest form of this 
 instrument is that of an ebonite ring, about the size and shape of 
 those old turnip watches which our grandfathers used to carry in their 
 fobs. In practice it is placed in circuit with a battery and a receiving 
 instrument at the further end of the line wire. I have often used this 
 transmitter with a Bell telephone as receiver, and the resulting sounds 
 have been most distinct. Mr. Edison has produced some other instru- 
 ments in which the same principle is employed, notably the micro- 
 tasimeter, which is so exquisitely sensitive, that the heat of the hand 
 held ten yards from it will cause the deflection of a galvanometer needle 
 placed in circuit with it. 
 
 But the latest form of telephone produced by this fertile inventor is 
 that known as the “ loud-speaking telephone.” This instrument I had 
 the honour of lecturing upon at the Polytechnic Institution for many 
 weeks, and the astonishment which its performance created among the 
 audience was immense. My assistant was stationed at a house in 
 Cavendish Square, and the sole communication between us was a fine 
 copper wire. The sounds given out by the instrument were easily 
 heard by everybody in the large theatre, and it was not an unusual 
 circumstance for one of the audience to suggest that some one was 
 hidden near the instrument, and that the voice came from him , and not 
 from the telephone. On more than one occasion my assistant at the 
 further station sang a song, or played a cornet solo which wms accom- 
 panied on the piano at the receiving end. This will show how really 
 loud the sounds must have been, to allow of such treatment ; indeed, 
 the instrument has more than once been called “the shouting tele- 
 phone,” and that term by no means conveys an exaggerated idea of its 
 capabilities. 
 
 The action of the instrument is entirely different to every telephone 
 which preceded it, and is three-fold — namely, electrical, chemical, and 
 mechanical. To understand the principle upon which its action is 
 based, I must briefly refer to a little experiment which any one in the 
 possession of a battery cell cau easily try for himself. 
 
 A slip of blotting paper moistened with a weak solution of caustic 
 potash is laid upon a metallic plate. This plate is connected with the 
 positive pole of the battery. The negative pole is connected with a slip 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 255 
 
 of brass, tipped with a facing of platinum. A key (like that used in the 
 Morse sounder) is included in the circuit so that contact may be made 
 or unmade whenever desired. Upon dragging this metallic slip upon 
 the surface of the paper, and exercising some little pressure upon it, 
 there is necessarily a certain amount of friction which would under any 
 circumstances manifest itself between two surfaces rubbed together. 
 But directly the key is depressed so that the current is allowed to pass, 
 this friction seems to vanish, and the metal glides over the paper as it 
 would traverse a piece of ice. 
 
 There are two ways in which this strange phenomenon can be ex- 
 plained, or rather, perhaps I ought to say, two theories have been 
 advanced to account for it. Possibly they may both be wrong, but in 
 the absence of anything more plausible we may for the present give 
 them consideration. The first is, that the potash employed may under 
 the action of the electric current give off minute bubbles of gas, and 
 that these bubbles form so many cushions of vapour upon which the 
 metal slips. The other theory -suggests that the salt may in infinitesimal 
 quantities be reduced to the metallic state, and that the friction is thus 
 greatly reduced. 
 
 Whatever be the true explanation of this curious phenomenon, Mr. Edison 
 has turned it to excellent account in his loud-speaking telephone, the interior 
 arrangements of which may be under- 
 stood by a reference to the diagram (Fig. 
 
 236). A is a cylinder of chalk which is 
 moulded upon a metallic roller or reel, 
 and which is rotated upon a handle 
 which projects outside the instrument. 
 
 This chalk is impregnated with caustic 
 potash, or some other chemical prepara- 
 tion which acts under the electric current 
 in the manner described in the experi- 
 ment just noted. This chalk cylinder, 
 in fact, takes the place of the blotting 
 paper there mentioned. Pressing upon 
 the cylinder, by means of the india- 
 rubber pad, C, is a little metallic arm, 
 
 B, faced with platinum, the further end „„„ tv * . . 
 
 Ot tills, arm being fastened to the centre action of the loud-speaking telephone, 
 of a 4-inch diaphragm of mica, D. It will 
 
 be evident that when the cylinder is turned on its axis the friction 
 generated between the arm, B, and the surface of the chalk, will cause 
 such a pull upon the mica diaphragm, that it will assume a slightly 
 concave form, but directly the electric current is caused to pass between 
 A and B the friction is reduced by that curious slippery effect already 
 alluded to, and' the diaphragm springs back to its normal position. This 
 % arrangement is so sensitive to minute variations of friction, that the 
 alterations of the strength of the current caused by a voice speaking to 
 a carbon transmitter are immediately translated into corresponding 
 
boy’s playbook of science. 
 
 256 
 
 variations of friction, the mica diaphragm vibrates to every such varia- 
 tion, and the sounds are reproduced. It must be noted, too, that the 
 sounds, are increased rather than diminished in their intensity by their 
 transmission through the system. In the first instruments produced it 
 was found necessary to constantly moisten the surface of the chalk, 
 but in the later form which has been adopted this inconvenience is 
 altogether obviated. 
 
 Fig. 237. Exterior view of EdiBon’s loud-speaking telephone. 
 
 I will now explain how the Edison telephone system is adapted to the 
 wants of every-day business life in London. At a central station in 
 the city is situated the telephone exchange, to which the various 
 wires connected with different offices where the telephone has been 
 adopted are carried. These wires are joined up to what is called a 
 switch-board, in front of which sits the clerk in charge. We will stand 
 by his side for a few minutes and notice how the work is carried on. 
 Presently a bell rings, and a little disc, one of a number on the upper part 
 of the board, drops down and exposes a number, sayi No. 12. The 
 clerk immediately switches his telephone on to the line denoted by this 
 figure, and asks the applicant what he wants. The reply comes audibly 
 through the telephone as the clerk turns the little handle, “ Put me on 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 257 
 
 to number 27.” By the simple insertion of a little metallic pee; in a 
 particular hole in the board, the clerk places No. 12 and No. 27 
 into communication. Now No. 12 may represent some merchant at 
 the west end of the city, and No. 27 may be his agent at the east end, 
 and possibly they may be three or four miles apart ; but by the insertion 
 of that little peg in the switch-board, they converse as easily as if they 
 were in the same room. In the meantime the clerk at the exchange is 
 unable to hear a single word they say to each other. When they have 
 finished speaking they ring the exchange bell, and both their numbers 
 drop as a signal to the clerk that they have done talking. In this wonderful 
 manner is conversation carried on between two distant people by means 
 of Edison’s loud-speaking telephone. 
 
 The chief office of the Edison Telephone Company of London is at 
 11, Queen Victoria Street. The benefits of the exchange system can 
 be secured by a subscription of £12 per annum. Or a special private 
 wire can be purchased for £19 per annum. These charges are extremely 
 moderate for the unusual advantages secured. 
 
 I must now pass on to the consideration of another marvellous instru- 
 ment — namely, the microphone. In first introducing this contrivance 
 to the notice of the Society of Telegraphic Engineers, Mr. Preece, the 
 well-known electrician of the Post Office, made use of the following 
 words : — “ A late member of the present Ministry at a dinner given by 
 the institution whose hospitality we enjoy in this hall, implied, on the 
 authority of one of the leading members of the engineering profession, 
 that invention, like cock-tails, or Colorado beetles, had taken root in 
 America, and deserted Old England. It is therefore to me, as X am 
 sure it is to you, a great gratification to have brought before us an 
 invention which is the offspring of British soil.” I am certain that my 
 readers will sympathize with the sentiment thus expressed, as they follow 
 me in my description of the microphone of Professor Hughes. 
 
 The microphone may be described as an instrument which changes 
 sonorous vibrations, without the intervention of a diaphragm (as in the 
 telephone), into forms of electrical action. It also so magnifies the 
 original sounds, that it acts for the ear much in the same way that the 
 microscope serves the eye, hence its name. At the time when it was 
 first invented, the most exaggerated accounts of its capabilities were 
 published in different newspapers, one especially remarked that the 
 breathing of a fly was heard through the instrument “ as an elephant 
 bellowing through his proboscis in an Indian jungle.” Setting aside this 
 very fanciful notion, it is a fact that the foot-tramps of a commonho use- 
 fly can be heard loudly by means of the microphone, and this no doubt 
 gave rise to the elephantine remark just quoted. 
 
 The microphone is an outcome of the telephone ; indeed, without the 
 latter instrument the former would have been impossible. Nor would 
 the extraordinary sensitiveness of Bell’s magnetic telephone have been 
 appreciated if the microphone had not told us of what it was capable. 
 
 It wall be remembered that the magnetic telephone is quite independent 
 of battery power, but it occurred to Professor Hughes to put it in 
 
 s 
 
258 
 
 boy’s playbook op science. 
 
 V 
 
 
 
 circuit with a weak battery current in order to note how it would behave. 
 We have already seen in previous experiments, and especially in those of 
 Faraday, how intimately connected is electrical action with magnetism, 
 and we shall not therefore be much surprised to find that when the 
 magnetic telephone is attached to a battery current the one reacts upon 
 the other. Professor Hughes included in the circuit with the telephone 
 a fine wire to which he attached weights until it- 
 , broke. On listening through the telephone he 
 
 noticed that just before the break occurred a 
 peculiar rushing sound was manifest. He next 
 tried the experiment of loosely binding the broken 
 ends of the wire together so that the current still 
 passed. He now found to his surprise that by 
 this simple means he had hit upon a sensitive 
 detection of minute sounds, for every noise in the 
 neighbourhood of the joined wires was given out 
 as a louder sound by the connected telephone. 
 Upon modifying the arrangement by placing two 
 nails in the circuit, as shown in Fig. 238, the same results were 
 obtained. He then tried a small pencil of carbon, fitted loosely into 
 holes in two carbon blocks, as shown in section at Fig. 239, 
 and this form gave wonderful results. Astonishing as it 
 may seem, it is a fact that if an arrangement such as 
 this be placed in a room where ordinary conversation is 
 being carried on, the words spoken can be distinctly heard 
 in a distant building by means of a telephone and a battery 
 placed in circuit. This little contrivance need not be more 
 than an inch long, and it is most conveniently used by 
 being attached to a vulcanite plate, and having binding 
 screws fastened on the carbon blocks for the attachment 
 of the wires. (See Fig. 240.) It is also well to mount the 
 arrangement on a small box, which acts as a kind of sound-board for it 
 Thus mounted it appears as shown in Fig. 241. 
 
 Fig. 238. Tlse nail 
 microphone. 
 
 Fig. 240. Microphone on 
 ebonite plate. 
 
 Fig. 241. Microphone 
 mounted on sound-box. 
 
 Another form of microphone from which I have obtained good results, 
 and which perhaps is more sensitive than those already described, com 
 
THE TELEPHONE, PHONOGRAPH, AND MICROPHONE. 259 
 
 Fig. 242 . Horizontal bar microphone. 
 
 sists of a small pencil of carbon so balanced on a brass pivot that its 
 end very lightly touches a fixed block of the same material. With 
 this form of instrument the fly experiment can > be tried. First 
 catch your fly, and imprison him in a match box, which has an opening 
 cut in it for "the insertion of a muslin window. Place this box on the 
 wooden board of the microphone 
 (Fig. 242) (which is purposely pro- 
 longed for the reception of any- 
 thing of the kind), and on listening 
 through the telephone, the little 
 insect is heard tramping about its 
 prison in the vain hope of finding 
 an exit. If a fly cannot be found, 
 which is often the case in winter- 
 time, any other small creature will answer the purpose. A watch 
 placed on the stand will also serve as a convenient test for the 
 powers of the microphone, or a piece of paper written upon with a 
 quill pen will give very loud results. The touch of a feather upon 
 the carbon rod is magnified into quite a loud noise, although the sound 
 made without the microphone would not be evident to the most 
 sensitive ear. These few experiments will show what this marvellous 
 little instrument is capable of. The original microphone and its 
 belongings, which I had the privilege of seeing, were made by its 
 inventor, and were of the most homely character. Indeed, they 
 seemed to be made up of match-boxes, pen-holders, sealing-wax, and 
 string ; the battery consisted of three small pickle bottles, and were 
 also of home manufacture. Thus a wonderful instrument was con- 
 structed and worked out by its inventor with materials the value of 
 which was only a few pence. 
 
 As no doubt some of my readers may be induced to try and construct 
 a microphone, and may find the battery the only difficulty, I will briefly 
 describe the one made by Professor Hughes, one 
 cell of which is depicted at Fig. 243. I have 
 chosen a gallipot for the cell, in lieu of a pickle 
 bottle, because it is easier to fill. At the bottom 
 of the jar is placed a coil of copper wire (C), the 
 end of which projects at the top. The straight 
 part of this wire, where it passes up the jar, must 
 be covered with sealing-wax or gutta-percha, in 
 order to insulate that part of it from the other 
 contents of the battery. Upon the coil must be 
 poured enough water to cover it about half an inch, 
 and in this water must be placed two ounces of 
 sulphate of copper (bluestone), broken into lumps 
 the size of a pea. Above the crystals the jar must be all but filled 
 with wet sawdust, or clay, and upon this is placed a round zinc disc 
 (Z) with a little band projecting from it. Three cells constructed 
 like this are quite sufficient to work a microphone efficiently. And 
 
 s 2 
 
 243. Microphone 
 battery cell. 
 
260 
 
 boy’s playbook of science. 
 
 the way in which the various parts are joined together will be 
 understood from the diagram (Fig. 244). The battery cells must 
 be joined so that the zinc terminal of one is attached to the copper 
 of the next. In the diagram, B, B, B, are the battery cells, so 
 joined, M, the microphone, and T, the telephone. Those who prefer to 
 buy the instrument ready made, can obtain any of the forms here de- 
 scribed of Messrs. Paterson, of Bedford Court. 
 
 Fig. 244. The microphone in circuit with a battery and telephone. 
 
 The microphone has been turned to account in more ways than one. 
 By a special arrangement of it, known as the sphygmophone , doctors are 
 able to hear all over a room the sound of a patient’s pulse, and find it 
 an infallible means of judging of the condition of the heart. (Young 
 people in love, beware !) In another instrument, called the audiometer , 
 the hearing capabilities of different people are accurately gauged. 
 And an aurist can test the progress of his patient from time to time, 
 and ascertain whether the remedies he employs are having the desired 
 effect. There are many other uses to which the microphone can be 
 put, and there is no doubt but that its powers will receive in time to 
 come many new applications. 
 
THE ELECTRO-MAGNETIC COIL MACHINE. 
 
 261 
 
 CHAPTER XVIII. 
 
 ruhmkorff’s, hearder’ s, and bentlev’s coil apparatus. 
 
 In the course of the popular articles on frictional and voltaic electricity, 
 it has already been mentioned that whilst the intensity effects — such aa 
 the capability of the spark to pass through a certain thickness of air, 
 or the production of the peculiar physiological effect of the shock — 
 belong especially to the phenomena of frictional electricity, they are 
 not apparent with the quantity effects i such as may be produced by an 
 ordinary voltaic battery, unless the latter consists of an immense 
 number of elements, such as the famous water battery of the late 
 respected Mr. Crosse, which consisted of two thousand five hundred 
 pairs of copper and zinc cylinders, well insulated on glass stands, and 
 protected from dust and light. If, however, the feeble intensity current 
 of voltaic electricity, from four or five elements, is permitted to pass into 
 a coil of a peculiar construction, fitted with a condenser, and manu- 
 factured either by Ruhmkorff of Paris, or Mr. Hearder of Plymouth, then 
 the most remarkable effects are producible, which have created quite a 
 new and distinct series of phenomena, and further established in the 
 most satisfactory manner the connexion between the electricities derived 
 from friction and chemical action . 
 
 The construction of these coils does not differ very materially, and 
 great merit is due to Messrs. Ruhmkorff, Hearder, and Bentley, who 
 liave separately and independently worked out the construction of the 
 most formidable machines of this class. In a letter to the author 
 Mr. Bentley says : — 
 
 “ I commence the formation of my coil by using as an axis an iron 
 tube ten inches long and half an inch diameter ; around this is placed a 
 considerable number of insulated iron wires the same length as the tube, 
 and sufficiently numerous to form a bundle one inch and three quarters 
 diameter. This core is wrapped carefully in eight or nine layers of 
 waxed silk, the necessity of which will be obvious presently. 
 
 “ My primary helix, which is formed of thirty yards of No. 14 cotton- 
 covered copper wire, is wound carefully on this core, and consists of 
 two layers, each layer being carefully insulated one from the other by 
 waxed silk, for I find that if a wet string or fine platinum wire be con 
 nected with the two ends of the primary wires of an induction coil in 
 action, there is scarcely an indication of an induced current to be 
 obtained from the secondary wire. That this is not owing to any 
 decrease of magnetic power is proved by testing the iron core before 
 and after the experiment, but is simply owing to the central magnet or 
 coil exerting the whole of its inductive powers upon the nearest closed 
 circuit ; it therefore follows that if the two layers of primary wire are 
 connected by the cotton covering becoming moist, the whole of the 
 
262 
 
 BCTX’S PLAYBOOK OF SCIENCE. 
 
 induced current will take this path instead of traversing the secondary 
 wire. 
 
 “ Before describing my secondary wire I must again call attention to 
 the important fact that the magnetism of the iron exerts its inductive 
 power upon the nearest conducting medium ; and I have constructed 
 an instrument to demonstrate this fact. It consists simply of an ordi- 
 nary coil, giving the third of an inch spark, but having the four inner 
 layers of secondary wire brought out separately. Now, I find that 
 when I keep the ends of this wire separate I obtain nearly the third of 
 an inch spark, but when I connect them metallically I can obtain no in- 
 tensity spark whatever from the seventeen coils which surround, them. 
 
 “ It follows from this that before winding the secondary wire the 
 striking distance of a single layer must be ascertained, and I find that with 
 my coil I can get a spark one-tenth of an inch long from one coil of wire, 
 and sufficiently intense to penetrate with facility six layers of waxed silk. 
 
 “ Waxed silk is therefore unsuited for the insulation of large coils, 
 and I find, after numerous experiments, that there is no substance so 
 fitted for the purpose as gutta-percha tissue, and I use five layers of 
 this substance to each layer of wire.^ 
 
 “The secondary helix then consists of three thousand yards of No. 35 
 silk-covered copper wire, and is insulated in the manner described above; 
 but as I do not use cheeks to my coil it assumes the form of a cylinder 
 having rounded ends. 
 
 “For the protection of this instrument I place it in a mahogany box 
 of the proper size, and it is supported and retained in its position by an 
 iron rod, which is thrust through the hollow axis of the core and the 
 two ends of the box, leaving half an inch of the iron projecting to work 
 the contact breaker, which is fixed to one end of the box, while the 
 two ends of the secondary wire are brought out of the other through 
 gutta percha tubes. 
 
 “ The condenser is contained in a separate box, and is formed of one 
 hundred and twenty sheets of tinfoil between double that number of 
 sheets of varnished paper,* the alternate sides of the foil being brought 
 out and connected to appropriate binding screws. 
 
 “ This condenser forms a convenient stand for the coil, and can be 
 used for many interesting experiments.” 
 
 The shock which the condenser gives to the system depends in a 
 great measure on the size of the coatings. The primary wire alone does 
 not produce any physiological results, or at least very feeble ones.. Mr. 
 Hearder’s coil is wound on a bobbin six inches in length, and four inches- 
 and a half thick, and includes three thousand yards of covered wire 
 (No. 35). The iron core consists of a bundle of small wires capped 
 with solid ends, and the sparks obtained from it were five-eighths of an 
 inch in air when the primary coil was excited by four pairs of Grove’s 
 series ; and when connected with the Leyden jar, the most vigorous 
 and brilliant results were produced. The condenser is made of car- 
 tridge paper, coated in the proper manner with tinfoil. The secon- 
 
 * Paper impregnated with parafin is now commonly used for this Purpose. 
 
ruiimkorff’s inductive apparatus. 
 
 263 
 
 dary coil is quite independent of the primary one, which is laid on in 
 different lengths, so that the coil can be adjusted to any battery power, 
 whether for quantity or intensity . 
 
 Por the successful exhibition of the capabilities of the machine, it is 
 required to perform the experiments in a darkened room. (Tig. 245.) 
 
 ivuniuiLuiii o ^ , gmore than a mile of in- 
 
 sulate d* wire. ^ The ^st and it^rests upon, and with which it is in communication, contains 
 the condenser. 
 
 In using this apparatus, eight pairs of Grove’s battery will be quite 
 sufficient to produce the effects, and the greatest care must be taken to 
 avoid the shock, which is most severe and painful, and might do a great 
 deal of liarmto a weakly, 
 sensitive, and nervous 
 person. To avoid any 
 accidents of this kind, 
 the convenient arrange- 
 ment at one end shown 
 in Pig. 246 must be 
 carefully attended to, 
 and when manipulating 
 with any part of the 
 apparatus, if the bat- 
 tery is attached, the 
 contact should first be 
 broken by bringing the 
 ivory (the non-conduct- 
 ing) part of the cy- 
 linder a (Pig. 222) in 
 comnrmnicatiouwith the 
 
 conductors, b b, where the wires from the battery are attached. 
 
 Fig. 246. One end of RuhmkorfFs coil, b b. Con- 
 nexion to receive the battery wires, a is the cylinder, 
 one half of which is ivory and the other metal. In this 
 position no shock can be received, because the electricity 
 is cut off by the ivory from the coil. 
 
 First Experiment. 
 
 It is at the other extremity of the coil that the experiments are per- 
 formed; for instance, if an exhausted globe is connected with the 
 pillars b B (Pig. 223), and the connexion made with the battery, a 
 beautiful faint blue light is apparent on one of the knobs and wires, and 
 by reversing the current the light appears on the other knob and wire. 
 
264 
 
 boy’s playbook of science. 
 
 This effect is supposed to resemble some 
 of those magnificent streaks and undu- 
 lations of coloured light called the Au- 
 rora Borealis; and»if the globe is removed 
 from the foot, and screwed on to the air- 
 pump plate, and a little alcohol, ether, 
 naphtha, or turpentine placed on wool 
 or tow is held to the air-pump screw, 
 where the air usually rushes in, and the 
 cock turned, so that the vacuum is de- 
 stroyed, a quantity of the vapour will 
 necessarily fill the globe ; and if this is 
 once more exhausted, it presents a 
 different appearance, being full of co- 
 loured light (varying according to the 
 spirit employed) but stratified and of 
 a circular form. (Fig. 247.) 
 
 Fig. 247. End of coil where the experiments are performed, b b. Connecting screw* 
 and wires passing to the exhausted globe, c. The screws are supported on insulating 
 glass pillars, p p. 
 
 Second Experiment . 
 
 The appearance of these bands of light is modified by the nature of 
 the glass tubes employed, and the subject has been carefully investigated 
 by Mr. Gassiott. At one of the meetings of the British Association at 
 Aberdeen, Dr. Robinson made various experiments, arranged by Mr. 
 Ladd, for the purpose of showing the connection between these minia- 
 ture effects of bands of light in tubes containing various gases, and the 
 phenomena of the Aurora Borealis. The title of the discourse, which 
 was specially delivered in the Music Hall by the learned Doctor, 
 was “On Electrical Discharges in Highly-rarefied Media,” and it 
 was illustrated by experiments prepared by Mr. Gassiott and Mr. 
 Ladd. 
 
 The kind of tubes employed may be understood from the next figure. 
 They are made in Germany, and by approaching a powerful magnet to 
 
EXPERIMENTS WITH RUHMKORFF’S COIL. 
 
 265 
 
 the outside of any of 
 the glass tubes whilst 
 the bands of light are 
 being produced, the 
 most remarkable mo- 
 difications of them are 
 obtained. Mr. Ladd 
 has mounted one of 
 these tubes in a rota- 
 tory arrangement si- 
 milar to that de- 
 scribed at page 186. 
 When connectedwith 
 the coil and battery 
 it furnishes one of the 
 most lovely “ elec- 
 tric fire-wheels” that 
 can possibly be de- 
 scribed. (Fig. 218.) 
 Mr. Grove placed a 
 piece of carefully- 
 dried phosphorus in 
 a little metallic cup, 
 and covered it with a 
 jar having a cap and 
 wire. On removing 
 the air from the re- 
 ceiver, and passing 
 the current of elec- 
 tricity through it 
 
 Fig. 248. a, b, c, d, e, f. Various tubes of different kinds of 
 glass, and containing gases and vapours. Each tube has a 
 platinum wire inserted at both ends, with which the contact is 
 made with the coil. The tube a contains mercury, which has 
 been boiled in it, and the air expelled. By moving the con- 
 ducting wire to g or h, the light which otherwise passes 
 through the whole of the tubes stops at these points. 
 
 from the Ruhmkorff coil, he obtained a light completely stratified, and 
 blended transversely with straight but vibrating dark bands. 
 
 Third Experiment. 
 
 When two very thin iron 
 wires are arranged in the 
 upright pillars (Fig. 247), 
 and held sufficiently close to 
 each other, as in Eig. 249, 
 light passes from one to the 
 other. The wire from which 
 the light passes remains 
 cold , the other becomes so 
 hot that it melts into a 
 little globule of liquid iron, and if paper is held between the wires it 
 rapidly takes fire. (Eig. 249.) 
 
266 
 
 boy’s playbook of science. 
 
 Fig. 250. The making anti breaking of the circuit. 
 
 Fourth Experiment. 
 
 Remove the break. 
 Attach two wires to 
 X X (Fig. 250). Hold 
 them so as at pleasure 
 to complete and inter- 
 rupt the galvanic circle. 
 Two other wires are at- 
 tached at p p, their 
 ends being about three- 
 quarters of an inch 
 asunder. When the cur- 
 rent is closed or broken 
 at a a, a spark passes 
 between b b. (Fig. 250.) 
 
 Fifth Experiment. 
 
 A Leyden jar may be charged and discharged with, singular rapidity 
 when connected with the coil, and the snapping noise is so rapid that it 
 produces a continuous sharp sound. (Fig. 251.) If a piece of paper 
 
 is held between the ball of the Leyden jar and the wire, it is instantly 
 perforated, but not set on fire. 
 
iiearder’s experiments. 
 
 267 
 
 Sixth 'Experiment, 
 
 When the Leyden jar is coated with spangles of tinfoil, a spark 
 appears at each break, and the whole jar is lit np with hundreds of 
 brilliant sparks each time it is charged and discharged, and as this 
 occurs with amazing rapidity, the light is almost continuous. (No. 1. 
 !Fig. 252.) The larger the Leyden jar, the shorter the spark, and vice 
 versa. By the employment of a nicely-made screw and inch-scale, the 
 distance between the discharging points connected with a Leyden jar 
 can be accurately determined ; and Mr. Hearder states that supposing a 
 Leyden jar has one square foot of charging surface, it will give a spark 
 of one inch in length, but if a smaller jar is used, with only half a square 
 
 Fig. 252. — No. 1. Spangled Leyden jar. No. 2. Hearder’s apparatus for measuring 
 the length of spark for Leyden jar and coil, p p. Glass pillars. No. 3. Two best forms of 
 spangles to paste on a Leyden jar. 
 
 foot of charging surface, the spark would be about one inch and a 
 quarter in length. (Fig. 252.) 
 
 Seventh Experiment . 
 
 The direction and rapidity of the current appear to influence greatly 
 the heating and fire-giving power of the coil, and the following experi- 
 ment, devised by Mr. Hearder, furnishes a curious illustration of this fact. 
 When the current passes in the direction of the arrows (Fig. 253), 
 
268 
 
 boy’s playbook of science. 
 
 the platinum wire remains perfectly cool whilst the gunpowder is fired ; 
 and the contrary takes place if the current is reversed — viz., the gun- 
 
 /" 
 
 Fig. 253. a. The coil. b. Hearder’s discharger, with thin platinum wire, p, hanging 
 between the points, c. Another discharger, and powder going off between the points 
 from the little table. The pillars of the dischargers are glass. The arrows show the 
 direction of the current of electricity. 
 
 powder does not blow up, but the platinum wire is heated. In the 
 second experiment, a Leyden jar is included in the circuit. (Fig. 253.) 
 
 Eighth Experiment . 
 
 Amongst so many beautiful experiments, it is somewhat difficult to 
 say which is the most pleasing, but for softness and exquisite colouring, 
 with the continuous vibrating motion of the flowing current of elec- 
 tricity, nothing can surpass “ the cascade experiment/’ [This beautiful 
 experiment is usually termed “Gassiott’s Cascade,” and is thus de- 
 scribed by that gentleman. Two-thirds of a beaker glass, four inches 
 deep by two inches, are coated with tinfoil, leaving one inch and a half 
 of the upper part uncoated. On the plate of an air-pump is placed a 
 glass plate, and over it the beaker, covering the whole with an open- 
 mouthed glass receiver, on which is placed a brass plate having a thick 
 wire passing through a collar of leather ; the portion of the wire within 
 the receiver is covered with a glass tube ; one end of the secondary 
 coil is attached to this wire, and the other to the plate of the pump. 
 As the vacuum improves the effect is very surprising; at first a faint 
 clear blue light appears to proceed from the lower part of the beaker 
 to the plate ; this gradually becomes brighter, until by slow degrees 
 it rises, increasing in brilliancy until it arrives at that part which is 
 opposite, or on a line with the inner coating, the whole being in- 
 tensely illuminated ; a discharge then commences, as if the electric 
 fluid were itself a material body running over.] This result is ob- 
 tained by coating the inside of a handsome glass goblet with tinfoil, 
 and placing it under a jar fitted with a collar of leather and ball, and 
 arranged in the usual manner on the air-pump. Directly a vacuum is 
 obtained, the ball is moved down to the inside of the goblet, and the 
 wires from the coil being attached, a continuous scries of streams of 
 
HEARDERS EXPERIMENTS. 
 
 269 
 
 electric light seem to overflow the goblet all round the edge, and it 
 stands then the very embodiment of the brimming cup of fire , and 
 emblematical of the dangers of the wine-cup. (Fig. 254.) 
 
 Fig. 254. Gassiott’s Cascade. 
 
 Ninth Experiment. 
 
 If a piece of wood five inches long and half an inch square is placed, 
 on the table of the discharger, and one wire brought on to the top edge 
 and the other ap- 
 proached to within 
 three inches of it, 
 and touching the 
 wood, and the 
 space between them 
 moistened with the 
 strongest nitric acid, 
 a curious effect is 
 visible from' the 
 creeping along of 
 the fire, which gradu- 
 ally carbonizes and 
 
 ( W00 ^* Fig. 255. Burning the piece of wood moistened with the 
 \ ri b* *OQ.) strongest nitric acid. 
 
270 
 
 boy’s playbook of science. 
 
 Tenth Experiment. 
 
 A glass plate wetted with gum, and then sprinkled with various 
 filings of iron, zinc, lead, copper, &c., produces a very pretty effect of 
 deflagration as one of the conducting wires is moved over its surface, 
 the other of course being in contact with the plate. The gum quickly 
 dries by putting the plate in a moderately-heated oven. 
 
 Eleventh Experiment , 
 
 When the continuous discharges from the Leyden jar are made to 
 pass through the centre of a large lump of crystal of alum, blue vitriol, 
 or ferroprussiate of potash, &c., the whole of the crystal is beautifully 
 
 Fig:. 253. a. The Leyden jar. b. Large lump of alum, with a hole bored through it 
 in a line with c d. The discharging wires are brought within three-eighths of an inch of 
 each other, and the whole crystal is lighted up with the brilliant electric sparks. 
 
 lighted up during the passage of the electricity from one wire of the 
 discharger to the other. (Fig. 256.) 
 
 Twelfth Experiment . 
 
 When a piece of paper slightly damped is placed between the wires of 
 the discharger, the spark is increased to a much greater length, on 
 account of the conducting power of the water contained in the pores of 
 the paper ; and taking all things into consideration, the author considers 
 he has witnessed the grandest effects from the coil invented and con- 
 structed by Mr. Hearder, the talented lecturer and electrician of the 
 West of England. 
 
 Thirteenth Experiment . 
 
 Electro-magnetic coil machines have been employed for a very con- 
 siderable time in alleviating certain of “the ills which flesh is heir to,” 
 
hearder’s experiments. 
 
 271 
 
 by the administration of shocks. These may be so regulated as to be 
 hardly perceptible, or may be so powerful that the pain becomes abso- 
 lutely intolerable. 
 
 These coils are now made self-acting, and consist of two coils of 
 covered and insulated wire wound round a bundle of soft-iron wires, 
 with the necessary connecting screws for the voltaic battery. The con- 
 tact with the battery is made and broken with great rapidity by a simple 
 form of break, consisting of a tinned disc of iron held by a spring over 
 the axis of the bundle of iron wires ; and the continual noise of the 
 break, which is alternately attracted down to the bundle and brought 
 back by the spring, when the coil is in contact with the battery, demon- 
 strates (without the pain of taking the shock) when the instrument is in 
 full working order. 
 
 The coil machine is not only useful in a medical point of view, but 
 when properly arranged offers a good reception to a run-away bell- 
 ringer, and is an excellent preventive against illicit attempts at cheap 
 rides by small boys. 
 
 Pig. 257. Roy, evidently shocked , behind doctor’s carriage provided with a 
 small coil machine. 
 
 Most of the experiments detailed, as well as a large' number of others, 
 can be performed on a small scale with the miniature coils now sold 
 by most opticians. A capital battery for use with a small coil is the 
 Bichromate, and the bottle form (Fig. 258) is the most convenient. It 
 consists of an outer glass jar, containing two carbon plates, between 
 which is a plate of zinc. To charge this battery two ounces of bichromate 
 of potash must be dissolved in one pint of hot water. When cold, 
 sulphuric acid is added in the proportion of one part of acid to every 12 of 
 solution. The bottle is filled with this mixture up to the shoulder, the 
 neck being left empty for the reception of the zinc plate when the battery 
 is not in use. The great convenience of this battery lies in the facility 
 
272 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 with which it can be put in action, or left idle as required. Moreover, it 
 gives off no fumes, like those of Grove or Bunsen. 
 
 Yacuum tubes are now constructed in all kinds of ingenious devices, 
 and Messrs. Cetti, of Brooke Street, Holborn, make them to any pattern 
 required. Some of these are shown in Fig. 260. Many 
 of the tubes are made of different kinds of glass, and 
 some are charged with coloured solutions, which greatly 
 increase the effects produced. 
 
 Of late years the construction of the Induction coil 
 has been carried to very great perfection, and several 
 modifications have been adopted by which the results 
 have been much increased. In large coils the wires 
 are generally wound in sections, separated by vul- 
 canite discs. In the annexed cut, the edges of these 
 discs are well seen. 
 
 The most perfect coil in existence is probably 
 that of Mr. Spottiswoode, F.R.S., who recently exhibited 
 some experiments by its aid at the Royal Institution. 
 It has two primary coils, either of which can be used 
 according to the nature of the subject under investiga- 
 tion. One is made of much thicker wire than the other, 
 and gives short, thick sparks, suitable for spectroscopic 
 work. The other is used for more general purposes, and will give a 
 spark 42 inches in length. It weighs 67 lbs. The secondary coil 
 
 Fig. 258. 
 Bichromate Cell. 
 
 Fig. 259. Induction Coil. 
 
hearder’s experiments. 
 
 273 
 
 through which these effects are induced contains wire ol a total length 
 of two hundred and eighty miles, a length which would very nearly 
 cover the distance between London and Carlisle. 
 
 I need hardly say that a shock from a coil of this size would mean 
 instant death. It has more than once been proposed that criminals 
 should suffer the last penalty of the law by such means as this. It has 
 also been suggested that sheep and cattle could be more mercifully put 
 to death by such an instrument than by the usual slaughtering process. 
 But a more ready and far less costly means of attaining the same end 
 is pointed out by some experiments which were lately successfully 
 carried out at Dudley. Two horses and a donkey, who had reached 
 that period in their existence when they are of no further use in a 
 
 living state, were the victims experimented upon. A cartridge ot 
 dynamite (a preparation of that fearfully explosive compound called 
 nitro-glycerine) was tied on to each animal’s forehead. These cartridges 
 were furnished with explosive fuses, and were in circuit with an electric 
 battery. A touch of the wires exploded the cartridges simultaneously, 
 and the three beasts dropped dead. It is much to be wished that such 
 a painless end could be guaranteed to all animals that man is obliged 
 to kill. But it is feared that the general use of such dangerous tools 
 would lead to some of the higher animals being included in the list of slain. 
 
 With the large coil already described, Mr. Crookes has lately carried 
 out some remarkable experiments connected with molecular physics. 
 
 T 
 
CHAPTER XIX. 
 
 ]NI AGNETO-ELECTRICIT Y» 
 
 The correlation of tlie physical forces, heat, light, electricity, magnetism, 
 and motion, is one of the most interesting subjects for study that can 
 be suggested to the lover of science. The examination of the precise 
 meaning of the term correlation, so ably considered by Professor Grove, 
 indicates a necessary mutual or reciprocal dependence of one force on 
 the other. Thus, electricity will produce heat, and vice versa ; motion, 
 such as friction, produces electricity, and the latter, by its attraction 
 and repulsion, establishes itself as a source of motion.. Electricity pro- 
 duces light, also magnetism, and contrariwise light is said to possess 
 
THE MAGNETO-ELECTRICAL MACHINE, 275 
 
 the power of magnetizing steel, whilst magnetism again produces light 
 and electricity. Such are the intimate connexions that exist between 
 these imponderable agents, and we may trace cause and effect and its 
 reversal amongst these forces, until the mind is lost in the examination 
 of the bewildering mazes, and is content to return to the beaten track 
 and work out experimentally the practical truths. We have had occa- 
 sion to notice in another part of this playbook the fact that a current 
 of electricity causes the evolution of magnetism in its passage through 
 various conducting media, and the truth has been specially illustrated oy 
 the various experiments in the chapter devoted to electro-magnetism. 
 In commencing this portion of electrical science, we have no new terms 
 to coin for the title of the discourse, as we merely reverse the other 
 when we examine the nature and peculiarities of 
 
 MAGNETO-ELECTRICITY. 
 
 The source of the power must necessarily be a bar or horseshoe- 
 shaped piece of steel permanently endowed with magnetism. If the 
 former is thrust into a cylinder of wood or pasteboard, around which 
 coils of covered copper wire have been carefully wound, so that the 
 extremities communicate with a galvanometer, an immediate deflection 
 of the needle occurs, which, however, quickly returns to its first posi- 
 tion, but is again deflected in the opposite direction on the withdrawal 
 cf the steel magnet from the coil of copper wire. (Fig. 262.) 
 
 Fig. 262. a b. Coil of copper wire. c. Permanent bar magnet placed inside the 
 coil, when the galvanometer needle, d, is deflected. 
 
 The rapid entrance and exit of the steel magnet in the helix of copper 
 wire would be insufficient to produce any quantity of electricity, and 
 the ingenuity of man has been taxed to arrange a method by which a 
 magnet may be suddenly formed and destroyed inside a coil of insulated 
 copper wire. The difficulty, however, has been surmounted by several 
 ingenious contrivances, based on the principles first discovered by 
 Faraday; and the one especially to be noticed is the revolution of a 
 coil of copper wire enclosing a piece of soft iron, called the armature , 
 before the poles of a powerful magnet. The first machine was invented 
 
 t 2 
 
276 
 
 boy’s playbook of science. 
 
 by M. Hypolyte Pixii, of Paris, and in 1833, Mr. Saxton improved 
 upon this machine, and three years afterwards, Mr. E. M. Clarke de 
 scribed a very ingenious modification of the electro-magnetic machine, 
 which is depicted at page 274 of this chapter. In this picture, the letter 
 a is the permanent fixed horseshoe magnets, which are very appro- 
 priately termed the battery magnets, because they take the position 
 that would otherwise be occupied by a voltaic battery, and they are 
 indeed the prime source of the electrical power that is evoked, d is the 
 intensity armature which screws into a brass mandril seated between 
 the poles of the magnets a, motion being communicated to it by the 
 multiplying wheel, e. This armature or inductor has two coils of fine 
 insulated copper wire of 1500 yards in length, coiled on its cylinders, 
 the commencement of each coil being soldered to the bar d, from which 
 projects a brass stem, also soldered into d, carrying the break-piece h, 
 which is made fast in any position by a small binding-screw in a hollow 
 brass cylinder to which the other terminations of the coils, E p, are 
 soldered, these being insulated by a piece of hard wood attached to the 
 brass stem, o is an iron wire spring pressing against one end of the 
 hollow brass cylinder ; p is a square brass pillar ; q is a metal spring 
 that rubs gently on the break piece H ; T is a copper wire for connecting 
 the brass pieces with the wood l between them, and out of which p 
 and o pass ; r R are two handles of brass with metallic wires, the end 
 of one being inserted into either of the brass pieces connected with p 
 and o, and the other into the brass stem that carries the break H, delivers 
 a most severe shock directly the wheel is set in motion. 
 
 Many other magneto-electric machines followed that of Clarke. In 
 most of these the number of magnets was multiplied, and the effects 
 displayed correspondingly increased ; with the disadvantages of making 
 the machines both cumbrous and costly. Among these I may specially 
 mention the “ Alliance” machine, which is used up to this day in some 
 of the Erench lighthouses ; and Holmes’ machine, which fulfils a similar 
 duty at the South Foreland. In this last machine an electro-magnet 
 was used in conjunction with a so-called “ permanent” magnet. 
 
 A great advance in the construction of magneto-machines was made 
 in the year 1866, when Siemens and Wheatstone simultaneously, but 
 independently, pointed out that permanent magnets need not be em- 
 ployed at ali, because iron always possesses some traces of magnetism 
 which, by proper appliances, can be utilised in the production of the 
 electric current. From this date, therefore (with the exception of 
 those used for medical purposes and for the lecture table), the machines 
 produced have been furnished with electro -magnets only. Three or four 
 new contrivances were framed on this discovery, but they have been 
 altogether eclipsed by more modern machines. 
 
 The period covered by the years 1877-1880 will long be remembered 
 on account of the universal interest suddenly manifested in the question 
 of electric illumination, and it is certain that more specifications 
 bearing upon this subject were filed during 1877 and 1.878 than during 
 all the previous time that the Patent Office had been established. 
 
THE MAGNETO-ELECTRICAL MACHINE. 
 
 277 
 
 This excitement was due in the first case to an extremely simple kind 
 of lamp or regulator, the invention of a Russian engineer, and called 
 after him “The Jablochkoff Candle, 5 ’ which effectively replaced the 
 very costly and complex electric regulators previously used. This con- 
 trivance I shall fully describe later on. But the agitation was also no 
 doubt due to the very perfect magneto-electro machines which had by 
 this time been invented, and by which the most brilliant effects could 
 be obtained. 
 
 One of the most remarkable and perhaps the most commonly used 
 machines of the present day is that of M. Gramme. Pig. 263 represents 
 
 Fig. 263. Experimental Gramme machine. 
 
 one of these, made specially for lecture-room demonstration. It is 
 capable of all the effects which are obtainable from a Grove or 
 Bunsen battery of several cells. More than once I have demonstrated 
 this by performing with the assistance of a battery the experiments 
 detailed in a former chapter, and then repeating them by wires joined 
 up to the machine. Only those who know the labour and unpleasant- 
 ness involved in putting a battery together, and the effect of inhaling 
 
278 
 
 boy’s playbook of science. 
 
 the fumes of the acid employed, can really appreciate one of these 
 machines, which merely requires a little “ elbow grease” to put it 
 into action. 
 
 The principal feature of the Gramme machine is the ring which forms 
 its armature. This ring is bound round With separate coils of insulated 
 copper wire, its core being formed of a bundle of iron wires. The 
 ends of the several coils are brought on to the axis upon which the 
 ring rotates, where they are separated from one another by strips of 
 some non-conducting substance. The electric currents which are 
 generated in these coils, as the ring revolves between the poles of the 
 magnet, are collected by metallic brushes, which rub against the axis of 
 the ring, where the ends of the coils are prolonged. In this manner 
 a continuous stream of electricity . is carried to the terminal wires, 
 which can be used for the production of light, heat, or indeed for any 
 purpose for which a battery current is employed. It will be noticed 
 that in this small machine for manual power a permanent magnet is 
 used. This magnet is of somewhat peculiar construction, for instead 
 of being made of one solid steel horseshoe, it is constructed of 
 several layers of that material, each having been separately mag- 
 netised. By this means the power of the magnet is very much 
 increased. 
 
 Fig. 261 shows another form of Gramme machine in which electro- 
 magnets only are used, the ring being retained, and placed between 
 them. This form of machine is for "steam power, the engine being 
 connected by belting with the wheel on the left-hand side of the 
 drawing. By means of this machine the lamps which now light the 
 Thames Embankment are provided with the necessary current. It 
 is greatly used in France, both for illuminating purposes, and also for 
 electro-plating. 
 
 Another machine which is also much used is the Siemens machine, 
 but it is so constructed that it can only give one light. This would 
 -also be the case with the Gramme machine, if another contrivance, called 
 the distributor, were not employed with it. The Gramme lighting 
 •system is, in short, a double one, the machine last figured pro- 
 viding the current, which is distributed for use by a second machine. . 
 
 The Lontin machine has also been in use both in France and this 
 •country, and is not unlike the more, recent forms of Gramme dis- 
 tributor. It was this machine which gave those brilliant lights which 
 lately appeared in front of the Gaiety Theatre. But the fact that 
 these lights have long ago ceased to exist will show that there was 
 some disadvantage, either in co$t of production or inconvenience, which 
 affected the system. 
 
 The only other machine necessary to mention is that of Mr. F. C. 
 Brush, which, although in extensive use on the other side of the 
 Atlantic, has only just been brought into notice in this country by 
 the Anglo-American Electro-Light Company, who have purchased the 
 patent rights. The patents cover the machine, the lamp, and the 
 manufacture of the carbon pencils consumed in the lamp. 
 
THE MAGNETO-ELECTRICAL MACHINE. 279 
 
 “In construction, the machine differs essentially from all others 
 both in the armature, the arrangement of the field magnets and the 
 commutator, and the novel mode of connection, thereby producing 
 from a given amount of power a larger available current than has 
 hitherto been obtained from any other combination. At the same 
 time, the mechanical construction is such that the wear and tear is 
 reduced to a minimum, the wearing parts (the segments of the commu- 
 tator and brushes) being easily replaced when necessary by an ordinary 
 mechanic, at a trifling cost.” 
 
 Fig. 264. Gramme machine. 
 
 I lately saw one of these machines* (known as No. 7) at work, when 
 it was producing on one circuit 16 powerful lights. The machine was 
 then absorbing 13 -horse power. I believe that the success of this 
 system is greatly due to the clever construction of the lamps or regu- 
 lators, and also to the exceedingly fine quality of the carbon employed 
 in them. Unless some new discovery is made, which completely alters 
 the present mode of utilising electricity in the production of light, we 
 may predict a great future for the Brush machine. 
 
280 
 
 boy’s playbook of science. 
 
 Prom time to time fears have been entertained that we are using up 
 our coal supplies so quickly, that a day must sooner or later arrive 
 when Britain will no longer have fuel for her steam engines. It is 
 almost unnecessary to state that if such a time should arrive, England’s 
 Dower must speedily diminish. Many persons have therefore con- 
 sidered the question of utilising such motive powers as are not 
 dependent upon heat for their production. The natural force of the 
 wind, of falling water, and even the ebb and flow of the tide, have been 
 turned to account for the benefit of man. And although we dwellers' 
 in town have not often the opportunity of seeing windmills and 
 waterwheels, we know that such things are in use. I need hardly 
 say that it is customary to place a windmill in some exposed situation, 
 where the wind will catch its sails, and a waterwheel must be relegated 
 to some stream where there is water to keep it in motion. In other 
 words, the power obtainable by such means is localised. But here 
 comes in a use for the dynamo-electric machine. The waterwheel, or 
 windmill, can be made to turn one of these magnetic machines, the 
 electricity so produced can be carried along wires of great length, 
 these wires can be joined on to another machine, and the electricity 
 is once more turned into motion. Let us for a moment glance at a 
 lecture lately given by Dr. Siemens, which bears upon this subject. 
 
 “Let us suppose,” says he, “ that at some central station 100 horse- 
 power of steam or water-power was employed to give motion to several 
 dynamo-electric machines of the dimensions found most convenient in 
 practice, and that by means of metallic conductors of suitable dimen- 
 sions the electric current produced at the central station was 
 conducted to a number of halls or factories requiring to be lighted, or 
 to utilise mechanical power. If illumination were the only object in 
 view, the total amount of light that could be thus produced would be 
 equal to 125,000 candle power. This would be equivalent to 6250 
 Argand burners, each of 20-candle power, at a consumption per 
 burner of 6 cubic feet of gas per hour, or a total consumption of 
 37,500 cubic feet of gas to produce the same effect of light. This 
 would require 3f tons of coal, and the electric light about as many 
 hundredweights.” 
 
 Dr. Siemens in the same lecture describes his visit to the Falls of 
 Niagara, and how he was struck with the extraordinary amount of force 
 there being wasted so far as the useful purposes of man are concerned. 
 He calculates that the one hundred million tons of water which fall 
 there every hour from a height of 150 feet, represent an aggregate of 
 16,800,000 horse power, producing as their effects no other result than 
 to raise the temperature of the water at the foot of the fall. He goe& 
 on to say: “ It would not be necessary to seek on the other side of the 
 Atlantic for an application of this mode of transmitting the natural 
 force of falling water, as there is perhaps no country where this force 
 abounds to a greater extent than on the west coast of Scotland, with 
 its elevated lands and heavy rainfalls. You have already conducted the 
 water of one of your high-level locks to Glasgow by means of a gigantic 
 
THE MAGNETO-ELECTRICAL MACHINE. 
 
 281 
 
 tube ; and how much easier would it be to pass the water in its 
 descent from elevated lands through turbines, and to transmit the vast 
 amount of force that might thus be collected, by means of stout me- 
 tallic conductors, to towns and villages for the supply of light and 
 mechanical power.” 
 
 At a recent soiree given by the institution of Civil Engineers at 
 the South Kensington Museum, Dr. Siemens exhibited the transmis- 
 sion of mechanical power by means of two dynamo-electric machines. 
 On this occasion a large machine was placed in circuit with a small 
 one by means of a long cable, the smaller machine being connected with 
 a centrifugal pump. By this means the pump was made to lift water 
 from a tank to a height of 10 feet or more. But recently the system 
 has been tested upon a far larger 
 scale both here and in Erance. In 
 the latter country the transmitted 
 power has been applied, with a satis- 
 factory result, to ploughing the 
 fields on the farm of M. Menier. 
 
 We know that steam has long been 
 applied to the culture of the land, 
 but surely the most ardent philoso- 
 pher would never have dreamt that 
 electricity would have been enlisted 
 in such a service. 
 
 Returning once more to the sub- 
 ject of electric lighting, we must now 
 leave the magneto-electric machines, 
 and look to the manner in which 
 the current produced is turned into 
 brilliant illumination. 
 
 It was Sir Humphry Davy who first 
 made the discovery that if the two 
 terminal wires of a powerful battery 
 were furnished with charcoal points, 
 and were then brought together, 
 a briliant arc of light was imme- 
 diately created between them. The 
 heat developed in the operation was 
 so great that the most refractory 
 substances, such as platinum, mag- 
 nesia, lime, &c., were easily melted 
 in the brilliant flame. If, how- 
 ever, the points were separated beyond a certain distance, proportional 
 to the strength of the battery, the light disappeared, and could not be 
 renewed until they were once more caused to touch. Various kinds of 
 regulators or lamps have been devised to meet these conditions. In 
 most of these the two charcoal points (now replaced by pencils of pre- 
 pared gas carbon) are placed vertically, and are caused to move towards 
 
 Fig. 265. Browning’s lamp. 
 
282 
 
 boy’s playbook of science. 
 
 one another as they are gradually consumed. In some, if not most of 
 these regulators, clockwork is used to accomplish this end. Serrin’s 
 lamp is one of the best known, and although reliable, is very expensive, 
 Siemens 5 regulator is another which is in common use, but, like Serrin’s, 
 it has a train of wheel-work, which causes it to be rather complicated 
 and therefore expensive. This form of regulator is, however, much used 
 for the illumination of large spaces, and for lighthouses, where the ques- 
 tion of expense is of course not a matter for consideration. In Fig. 265 is 
 shown Browning’s lamp, which is very much used for experimental work, 
 and in conjunction with a lantern for the exhibition of spectrum analysis 
 on a screen. Figs. 266 and 267 show a much simpler form of regulator by 
 
 t.he same maker, w r ith and without a reflector attached. This regulator 
 will give a small but brilliant light with ten cells of Grove’s battery. 
 The distance of the points are regulated by a screw, the upper carbon 
 being clutched in its place by the electro-magnet on the back post of 
 the lamp. When the space between the carbons becomes, by their con- 
 sumption, too great, the magnet loses its power, and the upper carbon 
 
THE MAGNETO-ELECTRICAL MACHINE. 
 
 283 
 
 drops by its own weight, to be immediately clutched once more by the 
 magnet which governs it. 
 
 In all these lamps provision is made for one carbon being consumed 
 at double the rate of the other, a phenomenon inseparable from a 
 battery, and all machines which give, like a battery, a continuous cur- 
 rent. Many of the modern machines, however, are made to give what is 
 called an alternating current — that is to say, the terminals are alternately 
 positive and negative several times in every second. The principal 
 reason why this alteration has in many machines been adopted, 
 is the invention of the Jablochkoff candle, which, as will be 
 presently seen, cannot be used with a continuous current. 
 
 Tig. 268 shows this new form of electric illuminator. The 
 carbons are not placed one above the other, as in most other 
 forms of regulator, but are placed side by side, with a thin 
 slip of plaster of paris, or other non-conducting medium, 
 between them. Now it stands to reason that if a continuous 
 current were used with this contrivance, one half of the 
 “candle 55 would burn down twice as quickly as the other 
 half, and they would soon be so widely separated at their 
 points that the light would go out. But by alternating the 
 current, so that each carbon is sometimes positive and 
 sometimes negative, they are both subject to the same rate of 
 combustion, and burn down together like a veritable candle. 
 
 The Jablochkoff candle is now being used to a far greater 
 extent than any other form of electric lamp, and, as I before 
 intimated, the present excitement with regard to electric 
 lighting is primarily due to this invention. But it by no 
 means represents a sufficiently perfect system to justify the 
 conclusion that it will be the light of the future. Its success J*bioch- 
 may be attributed to its great simplicity when compared to koff 
 the complicated arrangements before used, but it has many candle, 
 disadvantages in the way of expense, &c., which form serious draw- 
 backs to universal adoption. 
 
 Mr. Wilde, of Manchester, has patented another “candle, 55 which 
 resembles the Jablochkoff arrangement in every respect, only that it 
 has no insulating material between the carbons, in other words, they 
 are merely separated by space. They are so inclined that their points 
 touch, but directly the arc is established, they spring apart by the 
 action of a magnet, and the light is maintained between them. 
 
 A very perfect form of regulator is that of M. Rapieff, now in use at 
 the Times printing office. Tour carbons are used here, two above, and 
 two below, the four points meeting where the light is given out. In 
 the Wallace Tarmer regulator, plates of carbon are used in lieu of rods, 
 but the result is far from satisfactory. 
 
 Another distinct method of employing electricity as a light producer 
 is that of including in the circuit some substance which by its resistance 
 is caused to become incandescent. We have seen by an experiment 
 detailed on a former page, that platinum wire placed between the ter- 
 
284 
 
 boy’s playbook of science. 
 
 minals of a battery will glow with fervent heat, carbon will exhibit the 
 same phenomena, but neither the one nor the other can stand such treat- 
 ment with impunity, they speedily perish. This difficulty has been obvi- 
 ated to some extent by inclosing the incandescent substance in a vacuum, 
 for it must be remembered that the light from electricity is in no way 
 dependent upon oxygen for its support. Thus King’s patent, dated 
 1845, makes use of platinum in thin leaves, which were held in metallic 
 forceps in a glass bulb exhausted of air. The year later another patent 
 was filed of a precisely similar character. In 1872 Konn invented 
 a lamp in which a strip of graphite was rendered incandescent, in a 
 glass vessel charged with nitrogen. 
 
 Although these contrivances have proved barren of result so far as 
 general electric illumination is concerned, they are highly interesting just 
 now, when all kinds of rumours are afloat as to what the wonder-working 
 Mr. Edison is accomplishing in his laboratory at Menlo Park. Al- 
 though some of these rumours are of the most ridiculous character, 
 there seems to be no doubt about one thing, and that is, that Mr. 
 Edison is working with the idea of producing the electric light by the 
 incandescent principle. 
 
 The first notification of this appeared in the publication of a patent 
 specification, in which figured a form of regulator of no novel kind. It 
 consisted of a wire ccm posed of an alloy of platinum and iridium, 
 stretched between a fixed arm and a lever. When by the incandescence 
 of this wire the metal expanded, the lever dropped and touched a 
 metallic button, thereby diverting the current and preventing the wire 
 reaching its fusing point. In this manner light was given out without 
 the risk of the wire being destroyed, but it is obvious that no metallic 
 alloy whatever could withstand such treatment for any lengthened time 
 without destruction. This fact (according to the report published of a 
 statement made by Mr. Edison at the Saratoga meeting of the American 
 Association for Advancement of Science) was shortly afterwards ad- 
 mitted by the inventor himself. “ A platinum wire, rendered incandescent 
 by an electric current, presents before long a shrunken appearance and 
 is full of deep cracks, and if the current be continued for several hours 
 these effects so increase that the wire falls to pieces.” On the same 
 occasion Mr. Edison explained some very interesting experiments by 
 which he succeeded in greatly obviating this difficulty. He caused the 
 platinum, by special treatment under a vacuum, to assume a far more 
 compact condition. “ His mode of procedure was this : — Several platinum 
 spirals were brought to the melting-point by means of an electric current, 
 and the average light of each was then found, by the photometer, equal 
 to four standard candles. Next, one spiral was placed in the receiver 
 of an air-pump, and the air exhausted, a weak current was then sent 
 through the wire to warm it slightly, and so assist the gradual escape of 
 the air from the metal. The temperature was gradually increased (by 
 increase of the current) at intervals of ten minutes, afterwards at inter- 
 vals of fifteen minutes. Before each increase the wire was let cool, and 
 a welding process occurred in it at the points previously containing air. 
 
THE MAGNETO-ELECTRICAL MACHINE. 
 
 285 
 
 In one hour and forty minutes the spiral had reached such a temperature 
 before melting that it was giving a light of twenty -five standard candles, 
 whereas otherwise it would certainly have melted before giving a light 
 of five candles.” Under this treatment the wire seems to have become 
 white as silver, polished, and smaller in diameter. And Mr. Edison is 
 reported to have stated that by use of such material he could produce 
 eight separate jets, each equal to a light of six- 
 teen candles, by the expenditure of one-horse 
 power applied to his dynamo-electric machine. 
 
 Notwithstanding these comforting assurances, 
 the great inventor seems to have forsaken his 
 newly- found fire-proof metal for something which 
 seems on first acquaintance to be of a far more 
 fragile nature. According to a recent telegram, 
 
 “he has discovered that a steady, brilliant light 
 is obtained by the incandescence of mere carbonized 
 paper better than from any other known substance. 
 
 Strips of drawing paper in horse-shoe form are 
 placed in a mould and baked at a very high tem- 
 perature. The charred residuum is then attached 
 to the platinum wires and hermetically sealed in 
 a glass globe from which the air has been exhausted. 
 
 This, attached to a wooden stand, or ordinary gas 
 fixture, is the whole lamp.” The arrangement is 
 shown in Eig. 269. The cost of each lamp is 
 said to be one shilling, although it is difficult to 
 see how such a delicate piece of apparatus could be 
 constructed for such a small sum. It is also not 
 easy to understand how such a fragile thing can 
 ever stand the every-day rough usage to which domestic lamps are 
 exposed. The general use of gas in dwelling houses is greatly due to 
 the ease with which they can be manipulated, and the little risk there is 
 of getting them out of order by rough treatment. We may be quite 
 sure that if they are to be superseded, it must be by something which 
 will bear harder knocks than a bulb of glass. 
 
 Edison’s electric lamp. 
 
 V 
 
286 
 
 CHAPTER XX. 
 
 DIA-MAGNETISM. 
 
 At the end of the chapter devoted to the subject of light, will be found 
 an experiment devised and carried out bj Dr. Faraday, in which it is 
 shown that if a bar of a peculiar glass (called after the inventor, 
 Faraday’s heavy glass , or silicated borate of lead) is subjected to the 
 inductive action of a very powerful electro-magnet, that it has the 
 power of changing the direction of a ray of polarized light transmitted 
 through it. This effect is not confined to the poles of an electro ► 
 magnet, but is also perceptible (though in a diminished degree) with 
 ordinary magnets. 
 
 The result of this important experiment was communicated to the 
 Royal Society by Dr. Faraday on the 27th November, 1845, the enun- 
 ciation of the fact by this learned philosopher being, “ that when ‘ the 
 line of magnetic force 5 is made to pass through certain transparent 
 bodies parallel to a ray of polarized light traversing the same body, the 
 ray of polarized light experiences a rotation. 55 Now, “ the line of mag- 
 netic force 55 means that continual flow of the magnetic current which 
 passes from pole to pole, and is indicated by iron filings sprinkled on 
 paper placed above the poles of a magnet, and usually termed magnetic 
 curves , or the curved lines of magnetic force. (Fig. 270.) 
 
 Fig. 270. The curved lines of magnetic force. 
 
 The heavy glass already alluded to, upon which the magnet exerts a 
 certain influence, is called 
 
 THE DIA-MAGNETIC ; 
 
 and by this term is meant a body through which the lines of magnetic 
 force are passing without affecting it like iron or steel. At page 223 is 
 a picture representing (at Figs. 206 and 207) the direction of the 
 electricity and that of the magnetic current or whirl at right angles to 
 it. If, then, Fig. 207 be considered as a piece of glass, the arrow a b 
 
PHENOMENA OF DIA-MAGNETISM. 
 
 287 
 
 will show “ the line of magnetic force,” the point B being the north 
 pole, and the shaft a the south pole of the magnet, and the arrows 
 traced round will represent direction. This simple drawing expresses 
 the whole of the law of the action of the magnet on the glass, and if 
 kept in view, will give every position and consequence of direction re- 
 sulting from it. 
 
 The phenomenon of the affection of the beam of polarized light is im- 
 mediately connected with the magnetic force, and this is supposed tc 
 be proved by the brightness of the polarized ray being developed 
 gradually , as the iron coiled with wire requires about two seconds to 
 acquire its greatest power after being connected with the battery. 
 
 In another experiment of Baraday’s, where a beam of polarized light 
 was sent through a long glass tube containing water, and introduced as 
 . a core inside a powerful electro-magnetic coil, the image of a candle 
 viewed with a proper eye-piece, appeared or disappeared as the battery 
 connexion was made or broken with the coil ; but this result is not 
 considered by many philosophers to be conclusive of the action of 
 magnetism on light, but rather as an alteration of the refracting power 
 of the medium through which the light passes. These experiments were 
 the precursors of the other effects of magnetism upon different kinds of 
 matter which Baraday discovered, and he commenced his examination 
 with a small bar of heavy glass suspended by a filament of silk between 
 the poles of an electro-magnet, and when the twisting or effects of 
 torsion had ceased, the battery was connected. Directly the current 
 passed, Baraday’s keen eye detected a movement of the glass, and on 
 repeating the experiment, he discovered that the movement was not 
 accidental, but always took place in a certain fixed direction — viz., a 
 direction at right angles to a line drawn across and touching the two 
 poles of a horseshoe-shaped magnet — i.e ., supposing the feeder or bit 
 of soft iron usually placed in contact with the poles of the horseshoe- 
 magnet to represent the “ axial line,” any line drawn across it at right 
 angles would be called the equatorial line , whilst the general space 
 included between the poles of the magnet is called “the magnetic 
 field” The movement of the heavy glass was therefore equatorial , and 
 it pointed east and west instead of north and south, like iron and steel. 
 
 By the use of the apparatus (Big. 271) Baraday proved that every 
 
 Fig. 271. A cube of copper suspended between the poles of a powerful electro-magnet. 
 
•288 
 
 boy’s playbook of science. 
 
 substance, whether solid, fluid, or gaseous, was subject to magnetic 
 influences, assuming either the axial or equatorial position. The appa- 
 ratus consists of a prolongation of the poles of a powerful electro- 
 magnet, between which the cube of copper, weighing from a quarter to 
 half a pound, suspended by a thread, may be set spinning or rotating. 
 If the electro -magnet is connected with the battery, the cube stops 
 immediately, and whilst still in the same position or in the magnetic 
 field , with the magnet in full action, it is impossible to set it spinning 
 or twisting round again. (Fig. 271.) 
 
 A large number of other substances, solid, liquid, and gaseous, were 
 submitted to the action of the magnet, the liquids and gases being 
 hermetically sealed in glass tubes, and some of the results are detailed 
 in the following list : 
 
 Bodies that point axially , or are paramagnetic , like a suspended needle . 
 
 Iron. 
 
 Nickel. 
 
 Cobalt. 
 
 Manganese. 
 
 Chromium. 
 
 Cerium. 
 
 Titanium. 
 
 Palladium. 
 
 Platinum. 
 
 Osmium. 
 
 Paper. 
 Sealing-wax. 
 Fluor spar. 
 Peroxide of lead. 
 Plumbago. 
 
 China ink. 
 
 Berlin Porcelain. 
 
 Red-lead. 
 
 Sulphate of zinc. 
 
 Shell-lac. 
 
 Silkworm-gut. 
 
 Asbestos. 
 
 Vermilion. 
 
 Tourmaline. 
 
 Charcoal. 
 
 All salts of iron, when the latter is 
 basic. 
 
 Oxide of titanium. 
 
 Oxide of chromium. 
 
 Chromic acid. 
 
 Salts of manganese. 
 
 Salts of chromium. 
 
 Oxygen, which stands alone as a 
 paramagnetic gas. 
 
 Bodies that point eqiuitorially, or are diamagnetic , like Faradays 
 heavy glass. 
 
 Bismuth. 
 
 Antimony. 
 
 Zinc. 
 
 Tin. 
 
 Cadmium. 
 
 Sodium. 
 
 Mercury. 
 
 Lead. 
 
 Silver. 
 
 ar 
 
 Arsenic. 
 
 Uranium. 
 
 Rhodium. 
 
 Iridium. 
 
 Tungsten. 
 
 Rock crystal. 
 
 The mineral acids. 
 Alum. 
 
 Glass. 
 
 Litharge. 
 
 Common salt. 
 Nitre. 
 
 Phosphorus. 
 
PHENOMENA OF DIA-MAGNETISM. 
 
 289 
 
 Sulphur. 
 
 Resin. 
 
 Spermaceti. i 
 
 Iceland spar. i 
 
 Tartaric acid. 
 
 Citric acid. 
 
 Water. i 
 
 Alcohol. j 
 
 Ether. > 
 
 Sugar. » 
 
 Starch. J 
 
 Gum-arabic. I 
 
 Wood. J 
 
 Ivory. 
 
 Dried muttoa. 
 
 Eresh beef. 
 
 Dried beef. 
 
 Apple. 
 
 Bread. 
 
 Leather. 
 
 Eresh blood. 
 
 Dried blood. 
 
 Caoutchouc. 
 
 Jet. 
 
 Turpentine. 
 
 Olive oil. 
 
 Hydrogen. 
 
 Carbonic acid. 
 
 Carbonic oxide. 
 
 Nitrous oxide (moderately). 
 Nitric oxide (very slightly). 
 Olefiant gas. 
 
 Coal gas. 
 
 Nitrogen is neither paramagnetic nor diamagnetic, and is equivalent to 
 a vacuum. Magnetically considered, it is like space itself, which may 
 be considered as zero. 
 
 The term magnetic Earaday proposes should be a general one, 
 like that of electricity, and include all the phenomena ana effects pro- 
 duced by the power, and he proposes that bodies magnetic in the sense 
 of iron should be called paramagnetic , so that the division would stand 1 
 
 ^ 1US : iv i- i- f Paramagnetic, 
 
 Magnetic { * 
 
 and it 
 tables. 
 
 is this division which 
 
 \ Diamagnetic ; 
 has been observed in the preceding 
 
 All space above and within the limits of our atmosphere may be 
 regarded as traversed by lines of force, and amongst others are the lines 
 of magnetic force which affect bodies, as shown in the table of para- 
 magnetic and diamagnetic bodies, which have the same relation to each 
 other as positive and negative, or north and south, in electricity and 
 magnetism. 
 
 The lines of magnetic force are assumed to traverse void space with- 
 out change ; but when they come in contact with matter of any kind 
 they are either concentrated upon it or scattered according to the 
 nature of the matter. 
 
 The power which urges bodies to the axial or equatorial lines is not a 
 central force, but a force differing in character in the axial or radial 
 directions. If a liquid paramagnetic body were introduced into the field 
 of force, it would dilate axially, and form a prolate spheroid like a lemon, 
 while a liquid diamagnetic body would dilate equatorially, and form an 
 oblate spheroid like an orange. Pliicker has demonstrated that if mag- 
 netic solutions are placed in watch glasses across the poles of the 
 
 u 
 
290 
 
 boy’s playbook of science. 
 
 electro-magnet, they are heaped up in a very curious manner. The 
 poles of the electro-magnet are pieces of soft iron, which may be drawn 
 away or approached at pleasure, and according as the poles are nearer or 
 further asunder, the magnetic liquids, such as solution of iron, are 
 heaped up in cue or two directions, as shown at b and c in Tig. 272. 
 
 Fig. 272. Glass dish holding magnetic solution of iron, and placed in the magnetic field. 
 
 ! “The diamagnetic power, doubtless,” says Taraday, “ has its appointed 
 loffice, and one which relates to the whole mass of the globe. Tor 
 though the amount of the power appears to be feeble, yet, when it is 
 •considered that the crust of the earth is composed of substances of 
 which by far the greater portion belongs to the diamagnetic class, it 
 must not be too hastily assumed that their effect is entirely overruled 
 by the action of the magnetic matters, whilst the great mass of waters 
 and the atmosphere must exert their diamagnetic action uncontrolled.” 
 
 Pliicker has also announced — what at the time he believed to be true 
 — the highly interesting and important fact that the optic axis of Ice- 
 land or calcareous spar is repelled by the magnet and placed equa- 
 torially — a fact which Pliicker thought true of many other crystals 
 when the magnetic axis is parallel to the longer crystallographic axis. 
 A piece of kyanite, which is a mineral composed of sand, clay, often 
 lime, iron, water, and is used in India, being cut and polished as a gem, 
 and sold frequently as an inferior kind of sapphire, will, it is said, even 
 under the influence of the earth’s magnetism, arrange itself like a mag- 
 netic needle. 
 
 Pliicker believed that he had discovered an existing relation between 
 the forms of the ultimate particles of matter and the magnetic forces, 
 and he imagined that the results he obtained would lead gradually to 
 the determination of crystalline form by the magnet. The experiments 
 of Tyndal and Knoblauch lead, however, to a very opposite series of con- 
 clusions, and by ingeniously powdering the crystals with water, and 
 making them into a paste, which was afterwards dried and suspended 
 
FARADAY’S EXPERIMENTS. 
 
 291 
 
 as a model in “ the magnetic field ;” also' by taking a slice of apple 
 about as thick as a penny -piece, with some bits of iron wire through it, 
 in a direction perpendicular to its flat surface, they were found to set 
 cquatorially not by repulsion but by the attraction of the iron wires ; or 
 instead of the iron by placing bismuth wires, the apple now settled 
 axially, not by attraction but by the repulsion of the bismuth. Ipe- 
 cacuanha lozenges, Carlisle biscuits also, suspended in the magnetic field, 
 exhibited a most striking directive action. The materials in these two 
 cases were diamagnetic ; but owing to the pressure exerted in their 
 formation their largest horizontal dimensions set from pole to pole, the 
 line of compression being equatorial ; and it is a universal law “ that in 
 diamagnetic bodies the line along which the density of the mass has been 
 induced by compression sets equatorial , and in magnetic bodies axial .” 
 Hence they assume, from these and many other conclusive experiments, 
 that crystallized bodies, such as Iceland spar, take their position in the 
 magnetic field without reference to the existence of an“ optic axis.” 
 
 At the conclusion of a brilliant lecture at the Royal Institution by 
 .Dr. Tyndal “ On the influence of material aggregation upon the 
 manifestations of force,” in which Pliicker’s experiments respecting the 
 repulsion of the optic axis were gracefully discussed and his theory 
 refuted, the learned doctor said : “ This evening’s discourse is in some 
 measure connected with this locality; and thinking thus, I am led to 
 inquire wherein the true value of a scientific discovery consists ? Not 
 in its immediate results alone, but in the prospect which it opens to 
 intellectual activity — in the hopes which it excites — in the vigour 
 which it awakens. The discovery which led to the results brought 
 before us to-night was of this character. That magnet* was the 
 physical birthplace of these results ; and if they possess any value they 
 are to be regarded as the returning crumbs of that bread which in 184R 
 was cast so liberally upon the waters. I rejoice, ladies and gentlemen, 
 in the opportunity here afforded me of offering my tribute to the 
 greatest workman of the age, and of laying some of the blossoms of that 
 prolific tree which he planted at the feet of the great discoverer of dia- 
 magnetism. ”f 
 
 It was first observed by Father Bancalari, of Genoa, that when the 
 flame of a candle is placed between the poles of a magnet it is strongly 
 repelled. The flames of combustible gases from various sources are 
 differently affected, both by the nature of the combustible and by the 
 nearness of the poles. Faraday repeated Bancalari’s experiments, and 
 by a certain arrangement of the poles of this magnet he obtained a 
 powerful effect in the magnetic field, and having the axial line of the 
 magnetic force horizontal, he found that when the flame of a wax 
 taper was held near the axial line (but on one side or the other), and about 
 one-third of the flame rising above the level of the upper surface of the 
 
 * Alluding to a splendid magnet made by Logeman, which was sent to the Exhibition in 
 Hyde-park in 1851. It could sustain a weight of 430 pounds, and was pm-chased by th* 
 Royal Institution for Dr. Faraday. 
 
 t Dr. Faraday. 
 
292 
 
 boy’s playbook of science. 
 
 poles, as soon as the magnetic force was exerted the flame receded from 
 the axial line, moving equatorially until it took an inclined position, as 
 if a gentle wind was causing its deflection from the upright position. 
 
 When the flame was placed so as to rise truly across the magnetic 
 axis, the effect of the magnetism was very curious, and is shown at a. 
 
 Fig. 273. . , 
 
 On raising the flame a little more the effect of the magnetic force 
 was to intensify the results already mentioned, and the flame actually 
 became of a jisli-tailed shape , as at c, Fig. 273; and when the flame 
 w&s raised until about two-thirds of it were above the level of the axial 
 line, and the poles approached very close, the flame no longer rose 
 between the poles, but spread out right and left on each side of the 
 axial line, producing a double flame with two long tongues, as at b, 
 Fig. 273. 
 
 It was these experiments that led to the important discovery of the 
 paramagnetic property of oxygen, and proved in a decided manner that 
 gaseous bodies when heated became more highly diamagnetic. Oxygen, 
 which (tried in the air) is powerfully magnetic, becomes diamagnetic when 
 heated. A coil of platinum wire heated by a voltaic . current, and 
 placed beneath the poles of Faraday’s apparatus, occasioned a strong 
 upward current of air ; but directly the magnetic action commences the 
 ascending current divides, and a descending current flows down betioeen 
 the upward currents. 
 
 The discovery, says Silliman, of the highly paramagnetic character of 
 oxygen gas, and of the neutral character of nitrogen, the two con- 
 stituents of air, is justly esteemed a fact of great importance in studying 
 the phenomena of terrestrial magnetism. We thus see that one-fifth ot 
 the air by volume consists of ail element of eminent magnetic capacity, 
 after the manner of iron, and liable to great physical changes of density, 
 temperature, &c., and entirely independent of the solid earth. In this 
 medium hang the magnetic needles used as tests, and as this mag- 
 netic medium is daily heated and cooled by the sun’s rays, its power of 
 
Faraday’s experiments. 
 
 203 
 
 transmitting the lines of magnetic force is then affected, influencing 
 undoubtedly the diurnal changes of the magnetic needle. 
 
 Tor a complete digest of Faraday’s discoveries in diamagnetism the 
 reader is referred to the second edition of Dr. Noad’s comprehensive 
 and learned work entitled “ A Manual of Electricity.” 
 
 Coming always from the highest walks of philosophy to lower and 
 “ common things ,” one cannot help being reminded of the old-fashioned 
 method of drawing up a sluggish fire, and the natural query is suggested 
 whether the poker is to be considered as a weak magnet, and does in- 
 fluence and draw towards the fire a greater supply of magnetic oxygen 
 gas? (Fig, 274.) 
 
 Fig. 274. 
 

 
 294 
 
 Fig 1 , 275. ** The moon shines bright In such a night as this .”— The Merchant of Venice . 
 
 CHAPTER XXI. 
 
 LIGHT, OPTICS, AND OPTICAL INSTRUMENTS. 
 
 “ To gild refined gold, to paint the lily, 
 
 To throw a perfume on the violet, 
 
 To smooth the ice, or add another hue 
 Unto the rainbow, or with taper light 
 To seek the beauteous eye of heaven to garnish, 
 
 Is wasteful and ridiculous excess.” 
 
 Perfection admits of no addition, and it is just this feeling that 
 might check the most eloquent speaker or brilliant writer who attempted 
 to offer in appropriate language, the praises due to that first great 
 creation of the Almighty, when the Spirit of God moved upon the face 
 of the waters and said, “ Let there be light. 0 If any poet might be 
 permitted to laud and glorify this transcendant gift, it should be the 
 inspired Milton; who having enjoyed the blessing of light, and witnessed 
 the varied and beautiful phenomena that accompany it, could, when 
 afflicted by blindness, speak rapturously of its creation, in those sublime 
 strains beginning with— - 
 
 “ * Let there be light,’ said God, and forthwith light 
 Ethereal, first of things, quintessence pure, 
 
 Sprung from the deep : and from her native east 
 To journey through the airy gloom began, 
 
 Sphered in a radiant cloud, for yet the sun 
 Was not; she in a cloudy tabernacle 
 
 
The interior of the optical box at the Polytechnic— looking towards the screen. The assistants are supposed to be showing 
 

THE SOURCES OF LIGHT. 
 
 295 
 
 Sojourn’d the while. God saw the light was good. 
 
 And light from darkness by the hemisphere 
 Divided : light the day, and darkness night. 
 
 He named.” 
 
 There cannot be a more glorious theme for the poet, than the vast 
 utility of light, or a more sublime spectacle, than the varied and beautiful 
 phenomena that accompany it. Ever since the divine command went 
 forth, has the sun continued to shine, and to remain, “ till time shall be 
 no more,” the great source of light to the world, to be the means of 
 disclosing to the eye of man all the beautiful and varied hues of the 
 organic and inorganic world. By the help of light we enjoy the pris- 
 matic colours of the rainbow, tlite lovely and ever changing and ever 
 varied tints of the forest trees, the flowers, the birds, and the insects ; 
 the different forms of the clouds, the lovely blue sky, the refreshing 
 green fields; or even the graceful adornment of “the fair,” their beautiful 
 dresses of exquisite patterns and colours. Light works insensibly, and at 
 all seasons, in promoting marvellous chemical changes, and is now fairly 
 engaged and used for man’s industrial purposes, in the pleasing art of 
 photography; just as heat, electricity, and magnetism, (all imponderable 
 and invisible agents,) are employed usefully in other ways. 
 
 The sources from whence light is derived are six in number. The 
 first is the sun, overwhelming us with its size, and destroying life, 
 sometimes, with his intense heat and light, when the piercing rays are not 
 obstructed by the friendly clouds and vapours, which temper and mitigate 
 their intensity, and prevent the too frequent recurrence of that quick and 
 dire enemy to man, the coup de soldi. 
 
 I may here perhaps introduce a few remarks concerning those curious 
 substances called phosphorescent which retain for a shorter or longer 
 time the light received from the sun or other source of light, and shine 
 like glow-worms in the dark. The light given out in this manner is 
 unaccompanied by heat, and many artificial compounds are now pre- 
 pared which exhibit the phenomenon to an astonistiing extent. One of 
 these has lately formed the subject of a patent under the name of 
 Balmain’s Luminous paint, and as this compound is likely to come into 
 pretty general use it may be of interest to trace in a brief manner 
 the history of phosphorescent bodies. 
 
 In the year 1602 a poor cobbler of Bologna, who was smitten with 
 the gold lever which then prevailed in the form of a continual search 
 alter the fabulous philosopher’s stone, picked up a curious mineral. 
 His attention was attracted by its unusual weight, and he immediately 
 lumped to the conclusion that its heaviness must be due to the presence 
 of gold. In a word, he believed his prize to be the veritable philo- 
 sopher’s stone. Taking it home, he placed it in a crucible with some 
 charcoal and eagerly watched for the appearance of the precious metal. 
 I need hardly say that no gold became apparent, but the stone under- 
 went a strange modification. It had become phosphorescent, and had 
 acquired the property of shining in the dark after insolation—/.^, after 
 being exposed to sunlight. 
 
296 
 
 boy’s playbook of science. 
 
 This stone was sulphate of barium, which by treatment with charcoal 
 was converted to barium sulphide, a well-known substance now pre- 
 pared in a more direct manner. In 1663 an English chemist found 
 that the diamond and other crystals exhibited to a certain extent the 
 same properties. A few years later another experimenter found that a 
 luminous substance could be prepared from nitrate of lime. But in 
 1761 a still more phosphorescent body was compounded by Canton, and 
 this is still known as Canton’s Phosphorus. The formula for it is as 
 
 follows : — 
 
 Sifted, calcined oyster shells ... 3 parts 
 Sulphur 1 part 
 
 This mixture is submitted to a strong heat in a crucible, and the result- 
 ing mass is sulphide of calcium, or, as already stated, Canton’s phos- 
 phorus. It can also be prepared by calcining piaster of Paris (sulphate 
 of lime) with charcoal. It is a white powder, with that strong and 
 extremely unpleasant odour characteristic of rotten eggs. It should be 
 preserved in a well stoppered bottle, when it will retain its luminous 
 property — that is after occasional exposure to light — for many years. 
 Indeed, there is now preserved a tube of the powder, prepared one 
 hundred years ago by Canton himself, which still shines most brilliantly 
 after insolation. 
 
 The composition of Balmain’s paint is not published, but it is no 
 doubt a modification of Canton’s phosphorus so blended with oil and 
 varnish that it can be applied as easily as ordinary pigment. Its basis 
 is a phosphorescent powder, made I believe by an assistant of M. 
 Becquerel, a scientific gentleman who has worked in this particular 
 direction, and has produced compounds far more luminous than any 
 previously known. He has also greatly added to our knowledge of 
 this class of bodies by the invention of a piece of apparatus known as 
 Becquerel’s Phosphoroscope. By this machine many things have been 
 found to be phosphorescent for a few seconds after exposure to sun- 
 light. I have not space to devote to a full consideration of the phos- 
 phoroscope, but I may briefly describe it as a closed box with two 
 openings, one of which admits the sunlight, the other being for obser- 
 vation. The substance under examination is placed within this box, 
 and a rotating screen permits it to be seen several times a second. 
 
 The following are some of the uses to which it is proposed to apply 
 the new compound. The names of streets, numbers of houses, painted 
 with it will easily be decipherable in the darkest night. So also will 
 be such notices as “ Lodgings to Let,” “ Apartments,” and such like 
 advertisements. Eor fancy articles, its applications will be endless, and 
 we may soon hope to see boxes, fans, and all kinds of things decorated in 
 this manner. Mr. Woodbury lately showed me a photographic portrait 
 on glass, which he had backed up with a card covered with phospho- 
 rescent material, and the effect in the dark was most curious, not to say 
 spectral. But far more important uses are prophesied for the new paint, 
 and in its application to life-buoys and belts it is no doubt destined to 
 save many lives. It has also been tried with success in powder magazines. 
 
THE SOURCES OF LIGHT. 
 
 297 
 
 spirit vaults, and other places where 
 the use of ordinary artificial lights 
 is objectionable. The evolution of 
 light is not, however, confined to the 
 sun, and it emanates freely from ter- 
 restrial matter by mechanical action, 
 either by friction, or in some cases by 
 mere percussion. Thus the axles 
 of railway carriages soon become 
 red hot by friction if the oil holes 
 are stopped up ; indeed hot axles 
 are very frequent in railway tra- 
 velling, and when this happens, 
 a strong smell of burning oil 
 is apparent, and flames come 
 out of the axle box The knife- 
 grinder offers a familiar ex- 
 ample of the production 
 of fight by the attrition of 
 iron or steel against his 
 dry grindstone. 
 
 The same result on 
 much grander 
 scale is produced 
 by the apparatus 
 invented by the 
 late J acob Per- 
 kins; the combus- 
 tion of steel ensues 
 
 // 
 
 A /;"/// //' 
 
 ';///. /i / 4' s/ 
 
 under the action, 
 viz., the friction 
 of a soft iron disc revolv- 
 ing with great velocity 
 against a file or other 
 convenient piece of bar* 
 ^ dened steel. (Pig. 276) 
 The stand has a disc of soft 
 iron fixed upon an axis, which 
 revolves on two anti-friction 
 wheels of brass. The disc, by 
 means of a belt worked over a 
 wheel immediately below it, is 
 made to perform 5000 revolu- 
 tions per minute. If tine 
 hardest file is pressed against 
 the edge of the revolving disc, 
 the velocity of the latter pro- 
 duces sufficient heat by the 
 great friction to melt that por- 
 tion of the file which is brought 
 in contact with it, whilst some 
 particles of the file are torn 
 away with violence, and being 
 
 Fig. 276. Instrument for the combustion of steel. 
 
298 
 
 boy’s play book of science. 
 
 projected into the air, bum with that beautiful effect so peculiar to 
 steel. If the experiment is performed in a darkened room, the pe- 
 riphery of the revolving disc will be observed to have attained a 
 luminous red heat. Thirty years ago every house was provided with a 
 “ tinder-box” and matches to “ strike a light.” Since the advent of 
 prometheans and lucifers, the flint and steel, the tinder, and the matches 
 dipped in sulphur, have all disappeared, and now the box might be 
 deposited in any antiquarian museum under the portrait of Guy Fawkes, 
 and labelled, “ an instrument for procuring a light, extensively used in 
 the early part of the nineteenth century.” (Fig, 2779 
 
 Fig, 377- c. The steel, b. The flint. e. The tinder, d. The matches of the 
 old-fashioned tinder-box, a. 
 
 The rubbing of a piece of wood (hardened by fire, and cut to a point) 
 against another and softer kind, has been used from time immemorial 
 by savage nations to evoke heat and light ; the wood is revolved in the 
 fashion of a drill with unerring dexterity by the hands of the savage, 
 and being surrounded with light chips, and gently aided by the breath, 
 the latent fire is by great and incessant labour at last procured. How 
 favourably the modern lucifers compare with these laborious efforts of 
 barbarous tribes ! a child may now procure a light with a chemically 
 prepared metal, and great merit is due to that person who first devised 
 a method of mixing together phosphorus and chlorate of potash and so 
 
THE SOURCES OF LIGHT. 
 
 299 
 
 adjusted these dangerous materials that they are as safe as the “old 
 tinder-box,” and have now become one of our domestic necessaries. 
 Ignition, or the increase of heat in a solid body, is another . source of 
 light, and is well illustrated in the production of illuminating power 
 from the combustion of tallow, oil, wax, camphine or coal . gas. The 
 term ignition is derived from the Latin (ignis, fire), and is quite distinct, 
 and has a totally different meaning from that of combustion. If a glass- 
 jar is filled with carbonic acid gas, and a little tray placed in it containing 
 some gun cotton, it will be found impossible to fire the latter with a 
 lighted taper, i.e. by combustion ( comburo , to burn), because the gas 
 extinguishes flame which is dependent on a 
 supply of oxygen; whereas if a copper or 
 other metallic wire is made red hot or ignited, 
 the carbonic acid has no effect upon the heat, 
 and the red hot wire being passed through 
 the gas, the gun cotton is immediately fired. 
 
 Flame consists of three parts — viz., of an 
 outer film, which comes directly in contact 
 with the air, and has little or no luminosity ; 
 also of a second film, where carbon is deposited, 
 and, first by ignition , and finally by com- 
 bustion, produces the light ; and thirdly, of 
 an interior space containing unburnt gas, 
 which is, as it were, waiting its turn to reach 
 the external air, and to be consumed in the 
 ordinary manner. (Fig. 278.) 
 
 Chemical action and electricity have been 
 so frequently mentioned in this work as a 
 source of heat and light, that it will be un- 
 necessary to do more than to mention them 
 here, whilst phosphorescence (the sixth 
 source of light) in dead and living matter, 
 a spontaneous production of light, is well 
 known and exemplified in the “ glow-worm,” 
 the “ fire-fly,” the luminosity of the water of 
 the ocean, or the decomposing remains of 
 certain fish, and even of human bodies. Phos- 
 phorescence is still more curiously exempli- 
 fied by holding a sheet of white paper, a cal- 
 cined oyster-shell, or even the hand, in the 
 sun’s rays, and then retiring quickly to a 
 darkened room, when they appear to be lu- 
 minous, and visible even after the light has 
 ceased to fall upon them. _. „ 
 
 t or the purpose Ol examining the tempo- l. Outer flame. 2. Inner flame, 
 rary phosphorescence of various bodies, M. which is badly supplied with 
 Becquerel has invented a most ingenious in- “dfposite/Jd'wS TtZ 
 Strument, called the “ phosphorescope. It interior, containing unburnt gas. 
 
300 
 
 boy’s playbook of science. 
 
 consists of a cylinder of wood one inch in diameter and seven inches 
 long, placed in the angle of a black box with the electric lamp inside, 
 so that three-fourths of the cylinder are visible outside, and the re- 
 maining fourth exposed to the interior electric light. 
 
 By means of proper wheels the cylinder, covered with any substance 
 (such as Becquerel’s phosphori), is made to revolve 300 times in a 
 second, and by using this or a lesser velocity, the various phosphori 
 are first exposed to a powerful light and then brought in view of the 
 spectator outside the box. 
 
 It is understood that light is produced by an emanation of rays from 
 a luminous body. If a stone is thrown from the hand, an arrow shot 
 from a bow, or a ball from a cannon, we perfectly understand how either 
 of them may be propelled a certain distance, and why they may travel 
 through space ; but when we hear that light travels from the sun, which 
 is ninety-five millions of miles away from the earth, in about seven 
 minutes and a half, it is interesting to know what is the kind of 
 force that propels the light through that vast distance, and also what is 
 supposed to be the nature of the light itself. 
 
 There are two theories by which the nature of light, and its propaga- 
 tion through space, are explained ; they are named after the celebrated 
 men who proposed them, as also from the theoretical mechanism of their re- 
 spective modes of propulsion : thus we have the Newtonian or corpuscular 
 theory of light, and the Huyghenian or undulatory theory; the first named 
 after Sir Isaac Newton, and the second after Huyghens, another most 
 learned mathematician. Many years before Newton made his grand dis- 
 covery of the composition of light in the year 1672, mathematicians were in 
 favour of the undulatory theory, and it numbered amongst its supporters 
 not only Huyghens, but Descartes, Hook, Malebranche, and other learned 
 men. Mankind has always been glad to follow renowned leaders, it is 
 so much easier, and is in most cases perhaps the better course, to resigii 
 individual opinion when more learned men than ourselves not only adopt 
 but insist upon the truth of their theories ; and this was the case with 
 the corpuscular theory, which had been written upon systematically and 
 supported by Empedocles, a philosopher of Agrigentum in Sicily, who 
 lived some 414 years before the Christian era, and is said to have been 
 most learned and eloquent ; he maintained that . light consisted of 
 particles projected from luminous bodies, and that vision was performed 
 both by the effect of these particles on the eye, and by means of a visual 
 influence emitted by the eye itself. In course of time, and at least 2000 
 years after this theory was advanced, philosophers had gradually rejected 
 the corpuscular theory, until the great Newton, about the middle 
 of the seventeenth century, advanced as a champion to the rescue, and 
 stamping the hypothesis with his approval, at once led away the whole 
 army of philosophers in its favour, so that till about the beginning of the 
 nineteenth century the whole of the phenomena of light were explained 
 upon this hypothesis. 
 
 The corpuscular theory, reduced to the briefest definition, supposes 
 light to be really a material agent, and requires the student to believe 
 
THE THEORIES OF LIGHT, 
 
 301 
 
 that this agent consists of particles so inconceivably minute that they 
 could not be weighed, and of course do not gravitate ; the corpuscles are 
 supposed to be given out bodily (like sparks of burning steel from a 
 gerb firework) from the sun, the fixed stars, and all luminous bodies ; to 
 travel with enormous velocity, and therefore to possess the property of 
 inertia ; and to excite the sensation of vision by striking bodily upon 
 the expanded nerve, the retina, the quasi-mind of the eye. Dr. Young 
 remarks, “that according to this projectile theory the force employed in 
 the free emission of light must be about a million million times as great 
 as the force of gravity at the earth’s surface, and it must either act with 
 equal intensity on all the particles of light, or must impel some of them 
 through a greater space than others, if its action be more powerful, since 
 the velocity is the same in all cases — for example, if the projectile force 
 is w*eaker with respect to red light than with respect to violet light, it 
 must continue its action on the red rays to a greater distance than on 
 the violet rays. There is no instance in nature besides of a simple pro- 
 jectile moving with a velocity uniform in all cases, whatever may be its 
 cause ; and it is extremely difficult to imagine that such an immense force 
 of repulsion can reside in all substances capable of becoming luminous, 
 so that the light of decaying w r ood, or two pebbles rubbed together, may 
 be projected precisely with the same velocity as the light emitted by 
 iron burning in oxygen gas, or by the reservoir of liquid fire on the 
 surface of the sun.” Now one of the most striking circumstances 
 respecting the propagation of light, is the uniformity of its velocity in 
 the same medium. These and other difficulties in the application of the 
 corpuscular theory aroused the attention of the late Dr. Young, and in 
 the year 1801 he again revived and supported the neglected undulatory 
 theory wdth such great ability that the attention of many learned 
 mathematicians was directed to the subject, and now it may be said 
 that the corpuscular theory is almost, it not entirely, rejected, whilst 
 the undulatory theory is once more, and deservedly, uspd to explain 
 the theory of light, and its propagation through space. By this hypo- 
 thesis it is assumed that the whole universe, including the most minute 
 pores of all matter, whether solid, fluid, or gaseous, are filled with a 
 highly elastic rare medium of a most attenuated nature, called ether , 
 possessing the property of inertia but not of gravitation. This ether is 
 not light, but light is produced in it by the excitation on the part of 
 luminous bodies of a vibratory motion, similar to the undulation of 
 water that produces w r aves, or the vibration of air affording sound. 
 Water set in motion produces waves. Air set in motion produces w T aves 
 of sound. Ether, i.e . the theoretical ether pervading all matter, like- 
 wise set in motion, produces light. The nature of a vibratory medium 
 is indeed better understood by reference to that which we know 
 possesses the ordinary properties of matter — viz., the air ; and by tracing 
 out the analogy between the propagation of sound and light, the diffi- 
 culties of the undulatory theory very quickly vanish. To illustrate 
 vibration it is only necessary to procure a finger glass, and having 
 supported a little ebony ball attached to a silk thread by a bent brass 
 
302 
 
 boy’s PLAYBOOIv of science. 
 
 wire directly over it, so that the ball may touch either the outside or 
 the inside of the glass, attention must be directed to the quiescence of 
 the ball when a violin bow is lightly moved over the edge of the glass 
 without producing sound, and to the contrary effect obtained hjso 
 moving and pressing the bow that a sharp sound is emitted, when im- 
 mediately the little ball is thrown off from the edge, the repulsive action 
 being continued as long as the sound is produced by the vibration of 
 the glass. (Fig. 279.) 
 
 Fig. 279. a. The finger glass, b. The violin bow. c. The ebony ball. The dotted ball 
 shows how it is repelled during the vibration of the glass. 
 
 Here the vibrations are first set up in the glass, and being communi- 
 cated to the surrounding air, a sound is produced ; if the same experi- 
 ment could be performed in a vacuum, the glass might be vibrated, but 
 not being surrounded with air, no sound would be produced. This fact 
 is proved by first ringing a bell with proper mechanism fixed under the 
 receiver placed on the air-pump plate ; the sound of the bell is audible 
 until the pump is put in motion and the receiver gradually exhausted, 
 when the ringing noise becomes fainter and fainter, until it is perfectly 
 inaudible. This experiment is made more instructive by gradually 
 admitting the air again into the exhausted vessel, and at the same time 
 ringing the bell, when the sound becomes gradually louder, until it 
 attains its full power. The sun and other luminous bodies may be 
 compared to the finger glass, and are supposed to be endowed 
 naturally with a vibratory motion (a sort of perpetual ague), only 
 instead of the air being "set in motion, the ether is supposed to be 
 thrown into waves, which travel through space, and convey the 
 impress-ion of light from the luminous object. Another familiar 
 example of an undulatory medium is shown by throwing a stone 
 into a pool of water ; the former immediately forces down and displaces 
 a certain number of the particles of the latter, consequently the sur- 
 rounding molecules of water are heaped up above their level ; by the 
 force of gravitation they again descend and throw up another wave, this 
 in subsiding raises another, until the force of the original and loftier 
 
THE THEORIES OF LIGHT. 
 
 S03 
 
 wave dies away at the edge of the pool into the faintest ripples. It 
 must however be understood that it is not the particles of water first 
 set in motion that travel and spread out in concentric circles ; 
 
 Fig. 2S0. Boy throwing stones into water and producing circular waves. 
 
 but the force is propagated by the rising and falling of each separate 
 particle of water as it is disturbed by the momentum of the descending 
 wave before it. When standing at a pier-head, or on a rock against 
 which the sea dashes, it is usual to hear the observer cry out, if the 
 weather is stormy and the waves very high, “ Oh ! here comes a great 
 wave !” as if the water travelled bodily from the spot where it was first 
 noticed, whereas it is simply the force that travels, and is exerted finally 
 on the water nearest the rock. It is in fact a progressive action, just as 
 the wind sweeps over a wide field of corn, and bends down the ears one 
 after the other, giving them for the time the appearance of waves. The 
 principle of successive action is well shown by placing a number of 
 billiard balls in a row, and touching each other ; if the first is struck the 
 motion is communicated through the rest, which remain immovable, 
 whilst the last only flies out of its place. The force travels through all 
 the balls, which simply act as carriers, their motion is limited, and the 
 last only changes its position. Progressive movement is also well dis- 
 
 Fig. 25]. a b. Series of needles arranged as described, c. The bar magnet, with the 
 north pole n towards the needles The dotted lines show the direction gradually assumed 
 by all the needles, commencing at d. 
 
 played by arranging six or eight magnetized needles on points in a row, 
 with all their north poles in one direction. (Pig. 28 ] .) 
 
 On approaching the north pole of a bar magnet to the same pole of 
 
304 
 
 boy’s playbook of science. 
 
 one end of the series of needles, it is very curious to see them turn in the 
 opposite direction progressively, one after the other, as the repulsive 
 power of the bar magnet gradually operates upon the similar poles in the 
 magnetic needles. The undulations of the waves of water are also perfectly 
 shown by using the apparatus consisting of the trough with the glass 
 bottom and screen above it, as described at page 10. . The transmission 
 of vibrations from one place to another is also admirably displayed in 
 Professor Wheatstone’s Telephonic Concert (see page picture), where 
 the musical instruments, as at the Polytechnic, were placed by the 
 author in the basement, and the vibration only conducted by wooden 
 rods to the sounding-boards above, so that the music was laid on like 
 gas or water. These vibrations or undulations in air, water, and the 
 theoretical ether, have therefore been called waves of water, waves of 
 sound, and waves of light, just as if three clocks were made of three 
 different metals, the mechanism would remain the same, though the 
 material, or in this case the medium, be different in each. 
 
 Any increase in the number of vibrations of the air produces acute, 
 whilst a decrease attends the grave sounds, and when the waves succeed 
 each other not less than sixteen times in a second, the lowest sound is 
 produced. Light and colours are supposed to be due to a similar 
 cause, and in order to produce the red ray, no less than 477 millions of 
 millions of vibrations must occur in a second of time ; the orange, 506 ; 
 yellow, 535 ; green, 577; blue, 622; indigo, 658; violet, 699; and 
 white light, which is made up of these colours, numbers 541 millions of 
 millions of undulations in a second. 
 
 Although light travels with such amazing rapidity, there is of course 
 a certain time occupied in its passage through space— there is no such 
 thing as instantaneitv in nature. A certain period of time, however small, 
 must elapse in the performance of any act whatever, and it has been 
 proved by a careful observation of the time at which the eclipses of the 
 satellites of Jupiter are perceived, that light travels at the rate of 
 192,500 miles per second, and by the aberration of the fixed stars, 
 191,515, the mean of these two sets of observations would probably 
 afford the correct rate. Such a velocity is, however, somewhat difficult 
 to appreciate, and therefore, to assist our comprehension of their great 
 magnitude, Sir J. Herschel has given some very interesting comparative 
 calculations, and coming from such an authority we can readily believe 
 them to be correct. 
 
 “A cannon-ball moving uniformly at its greatest velocity would 
 require seventeen years to reach the sun. Light performs the same 
 distance in about seven minutes and a half. 
 
 “ The swiftest bird, at its utmost speed, would require nearly three 
 weeks to make the tour of the earth, supposing it could proceed without 
 stopping to take food or rest. Light performs the same distance in 
 less time than is required for a single stroke of its wing.” 
 
 Dismissing for the present the theory of undulations, it will be 
 necessary to examine the phenomena of light, regarding it as radiant 
 matter, without reference to either of the contending theories. 
 
THE KADIATION OF LIGHT. 
 
 ■ 05 
 
 Light issues from the sun, passes through millions of miles to the 
 earth, and as it falls upon different substances, a variety of effects are 
 apparent. There is a certain class of bodies which obstruct the passage 
 of the rays of light, and where light is not, a shadow is cast, and the 
 substance producing the shadow is said to be opaque. Wood, stone, 
 the metals, charcoal, are all examples of opacity ; whilst glass, talc, and 
 horn allow a certain number of the rays to travel through their par- 
 ticles, and are therefore called transparent. Nature, however, never 
 indulges in sudden extremes, and as no substance is so opaque as not 
 (when reduced in thickness) to allow a certain amount of light to pass 
 through its substance, so, on the other hand, however transparent a 
 body may be, a greater or lesser number of the rays are always stopped, 
 and hence opacity and transparency are regarded as two extremes of a 
 long chain ; being connected together by numerous intermediate links, 
 they pass by insensible gradations the one into the other. 
 
 If a gold leaf, which is about the one two-hundredth part of an inch 
 in thickness, is fixed on a glass plate and held before a light, a green 
 colour is apparent, the gold appearing like a green, semi-transparent 
 substance. When plates of glass are laid one above the other, and the 
 flame of a candle observed through them, the light decreases enor- 
 mously as the number of glass-plates are increased. Even in the air a 
 considerable portion of light is intercepted. It has been estimated that 
 of the horizontal sunbeams passing through about two hundred miles of 
 air, one two-thousandth part only reaches us, and that no sensible light 
 can penetrate more than seven hundred feet deep into the sea ; conse- 
 quently, the vast depths discovered in laying the Atlantic telegraph 
 must be in absolute darkness. 
 
 Light is thrown out on 
 all sides from a luminous 
 body like the spokes of a 
 cart-wheel, and in the ab- 
 sence of any obstruction, the 
 rays are distributed equally 
 on all sides, diverging like the 
 radii drawn from the centre 
 of a circle. As a natural 
 consequence arising from 
 the divergence of each ray 
 from the other, the intensity 
 of light decreases as the 
 distance from the luminous 
 source increases, and vice 
 versa. Perhaps the best me- 
 chanical notion of this law 
 is afforded by an ordinary 
 fan; the point from which 
 the sticks radiate, and where 
 they all meet, may be 
 
 x 
 
806 boy’s playbook of science. 
 
 termed the light; the sticks are the rays proceeding from it. (Fig* 
 282.) 
 
 The fan is held in one hand, and the first finger of the other can be 
 made to touch all the sticks if placed sufficiently near to a ; and sup- 
 posing the sticks are called rays of light, the intensity must be great at 
 that point, because all the rays fall upon it ; but if the finger is removed 
 towards the outer edge — viz., to b, it now only touches some three or 
 four sticks ; and pursuing the analogy, a very few rays fall upon that 
 point — hence the light has decreased in intensity, or to speak correctly, 
 “ Light decreases inversely as the squares of the distance.” This law 
 has already been illustrated at page 13 ; and as an experiment, the 
 rays from the oxy-hydrogen lantern may be permitted to pass out of a 
 square hole (say two inches square), and should be thrown on to a 
 transparent screen divided into squares by dark lines, so that the light 
 at a certain distance illuminates one of them ; then it will.be found that 
 at twice the distance, four may be illuminated, at three times nine, and 
 so on. (Fig. 283.) 
 
 Upon this law is based the use of photometers, or instruments for 
 measuring light, and supposing it was required to estimate roughly the 
 illuminating power of any lamp, as compared with the light of a wax 
 candle six to the pound, the experiment should be conducted in a dark 
 room, from which every other light but that from the lamp and candle 
 under examination must be excluded. 
 
 The lamp, with the chimney only, is now placed say twelve feet from 
 the wall, and a stick or rod is placed upright and about two inches from 
 the latter, so that a shadow is cast on the wall ; if the candle is now 
 lighted and allowed to burn up properly, two shadows of the stick will 
 be apparent, the one from the lamp being black and distinct, and the 
 other from the candle extremely faint, until it is approached nearer tiie 
 
PHOTOMETRY. 
 
 307 
 
 wall — saj to within three feet — when the two shadows may he now 
 equal in blackness. (Pig. 284.) After this is apparent to one or more 
 
 persons, the distances of the lamp and candle from the wall are carefully 
 measured, and being squared, and the greater divided by the lesser 
 number, the quotient gives the illuminating power. Por example : 
 
 The lamp was 12 feet from the wall . . . 12 X 12 = 144. 
 
 The candle was 3 feet „ ... 3x3=9. 
 
 9 ) 144 
 16 
 
 Therefore the illuminating power of the lamp is equal to 16 wax candles 
 six to the pound. 
 
 There are other and more refined means of working out the same 
 fact, but for a rough approximation to the truth, the plan already de- 
 scribed will answer very fairly. 
 
 A most amusing effect can be produced on the principle that every 
 light casts its own shadow, called the “ dance of death,” or the “ dance of 
 the witches either of these agreeable subjects are drawn, and the out- 
 lines cut out of a sheet of cardboard. If a wet sheet is stretched or hung 
 on one side of a pair of folding doors partly open, and between which 
 the cardboard is tacked up, and the space left at the top and bottom 
 closed with a dark cloth, directly the room before the sheet is 
 darkened and a lighted candle held behind the figure cut out in the 
 cardboard, one shadow or image is thrown upon the sheet, and these 
 shadows may be increased according to the number of candles used, and 
 if they are held by two or three persons, and moved up and down, or 
 sideways, the shadows follow the direction of the candles, ami present 
 the appearance of a dance. (Pig. 285.) 
 
Fig. 235. “ Before the curtain.” 
 
SHADOW ILLUSIONS. 
 
 309 
 
 Another very comic effect of shadow is that called “ jumping up to 
 the ceiling,” and when carried out on a large scale by the author on an 
 enormous sheet suspended in the centre transept of the Crystal Palace, 
 Sydenham, it had a most laughable effect, and caused the greatest 
 amusement to the children of all ages. (Fig. 287.) 
 
 Fig. 237. The laughable effect of the shadows at the Crystal Palace. 
 
 This very telling result is produced by placing an oxy-hydrogen light 
 some feet behind a large sheet, and of course if any one passes between 
 the two a shadow of the individual is cast upon the sheet, then by 
 walking towards the light the figure diminishes in size, and by jumping 
 over it the shadow appears to go up to the ceiling, and to come down 
 when the jump is made in the opposite direction over the light and towards 
 the sheet. The rationale of this experiment is very simple, and is 
 
310 
 
 boy’s playbook of science. 
 
 Fig. 288. The rays of light marked abode 
 proceeding from a lighted candle or oxy-hydro- 
 gen light. The arrow pointing to the right 
 shows how these rays are crossed in jumping 
 up to the ceiling ; and the second arrow, point- 
 ing to the left, shows the reverse. 
 
 another proof of the distribution of light from a luminous source being 
 in every direction. By jumping over the light the radii projected from 
 
 the candle over the sheet are 
 crossed, and the shadow rises or 
 v falls as the figure passes upwards 
 
 E or downward. (Fig. 238.) 
 
 A beam of light is defined to 
 be a collection of rays, and it is 
 a convenient definition, because 
 it prevents confusion to speak 
 only of one ray in attempting to 
 explain how light is disposed of 
 under peculiar circumstances. 
 
 The smallest portion of light 
 which it is supposed can be se- 
 parated is therefore called a ray, 
 and it will pass through any me- 
 dium of the same density in a 
 perfectly straight line ; but if it 
 passes out of that medium into 
 another of a different density, or 
 into any other solid, fluid, or 
 gaseous matter, it may be dis- 
 posed of in four different ways, being either reflected, refracted, polar- 
 ized, or absorbed. 
 
 The reflection of light is the first property that will be considered, 
 and it will be found that every substance in nature possesses in a greater 
 or lesser degree the power of throwing off the rays of light which fall 
 upon them. Thus if we go into a room perfectly darkened, containing 
 every kind of work produced by nature or art, such as flowers, birds, 
 boxes of insects, rich carpets, hangings, pictures, statuary, jewellery, 
 &c., they cannot excite any pleasure because they are invisible, but 
 directly a lighted lamp is brought into the chamber, then the rays fall 
 upon all the surrounding objects, and being reflected from their surfaces 
 enter the eye, and there produce the phenomena of vision. 
 
 This connexionbetween luminous and non-luminous bodies becomes very 
 apparent when we consider that the sun would appear only as an intense 
 light in a dark background, if the earth was not surrounded with the 
 various strata of air, in which are placed clouds and vapours that collec- 
 tively reflect and scatterthe light, so as to cause it to be endurable to vision. 
 It is when the sky is very clear during July or August that the heat 
 becomes so intense, directly clouds begin to form and float about, the heat 
 is then moderated. 
 
 Many years ago, Baron Alexander Funk, visiting some silver mines in 
 Sweden, observed, that in a clear day it was as dark as pitch under- 
 ground in the eye of the pit at sixty or seventy fathoms deep; whereas, on 
 a cloudy or rainy day he could even see to read at 106 fathoms deep. 
 Inquiring of the miners, he was informed that this is alwavs the case, and 
 
THE REFLECTION OF LIGHT. 
 
 311 
 
 reflecting upon it he imagined very properly that it arose from this 
 circumstance — that when the atmosphere is full of clouds, light is re- 
 flected from them into the pit in all directions, so that thereby a con- 
 siderable proportion of the rays are reflected perpendicularly upon the 
 earth; whereas when the atmosphere is clear there are no opaque bodies 
 to reflect the light in this manner, at least, in a sufficient quantity, and 
 rays from the sun itself can never fall perpendicularly in Sweden. The 
 use of reflecting surfaces has now become quite common in all crowded 
 cities, and especially in London, where even the rays of light are too few 
 to be lost, and flat or corrugated mirrors are placed at various angles, 
 either to throw the light from the outside on the white-washed ceiling 
 within, and thus obtain a better diffused light through the apartment, 
 or it is reflected bodily to some back room, or rather dark brick box, 
 where perhaps for half a century candles have been required at an 
 early hour in the afternoon. The brilliant cut in diamonds is such an 
 arrangement of the posterior facets, or cut faces of the jewel, that all 
 light reaching them shall be thrown back and reflected, and thus 
 impart an extraordinary brilliancy to the gem. 
 
 The intense glare of snow in the Alpine regions has long been noticed, 
 and the reflected light is so powerful, that philosophers were even 
 disposed to believe that snow possessed a natural or inherent lumi- 
 nosity, and gave out its own light. Mr. Boyle, however, disproved 
 this notion by placing a quantity of snow in a room from which all 
 foreign light w T as excluded, and neither he nor his companion could 
 observe that any light was emitted, although, on the principle of 
 momentary phosphorescence, it is quite possible to conceive that if the 
 snow was suddenly brought into a darkened room after exposure to the 
 rays of the sun, that it would give out for a few seconds a perceptible 
 light. In trying such an experiment, one person should expose the 
 snow to the sun, and bring it into a perfectly darkened room to a second 
 person, whose eyes would be ready to receive the faintest impression of 
 light, and if any phosphorescence existed, it must be apparent. 
 
 The property of reflection is also illustrated on a grand scale in the 
 illumination of our satellite, the moon, and the various planetary bodies 
 which shine by light reflected from the sun, and have no inherent self- 
 luminosity. Aristotle was well aware that it is the reflection of light 
 from the atmosphere which prevents total darkness after the sun sets, 
 and in places where the sun’s rays do not actually fall during the day- 
 time. He was also of opinion that rainbows, halos, and mock suns, 
 were all occasioned by the reflection of the sunbeams in different cir- 
 cumstances, by which an imperfect image of the sun was produced, the 
 colour only being exhibited, but not the proper figure. 
 
 The image, Aristotle says, is not single, as in a mirror, for each dro^ 
 of rain is too small to reflect a visible image, but the conjunction of ail 
 the images is visible. Aristotle ascribed all these effects to the reflection 
 of light, and it will be noticed when we come to the consideration 
 of the refraction of light, that of course his views must be seriously 
 modified. 
 
312 
 
 boy’s playbook of science. 
 
 The reflection of light is affected rather by the condition of the 
 surface than the whole body of a substance, as a piece of coal may 
 be covered with gold or silver leaf and caused to shine, whilst the 
 brightest mirror is dimmed by the thinnest film of moisture. 
 
 From whatever surface light is reflected, it always takes place in 
 obedience to two fixed laws. 
 
 First. The incident and reflected rays always lie in the same plane. 
 
 Second. The angle of incidence is equal to the angle of reflection. 
 
 With a single jointed two-foot rule, both of these laws are easily 
 illustrated. The rule may be held in the hand, and one end being 
 marked with a piece of white paper may be called the incident ray, i.e., 
 the ray that falls upon the surface ; and the other is the reflected ray, 
 the one cast off or thrown back. A perpendicular is raised by holding 
 a stick upright at the joint. (Fig. 289.) 
 
 s 
 
 Fig. 289. ad. A two foot rule ; the end a may be termed the incident ray, and the end 
 d the reflected ray. s. The stick held perpendicularly. The angle a b c is equal to the 
 angle d e p, and the whole may be moved in any direction or plane, either horizontal or 
 perpendicular, g g. The reflecting surface. 
 
 One of the most simple and pleasing delusions produced by the reflec- 
 tion of light, is that afforded by cutting through the outline of a vase, 
 or statuette, or flower; drawn on cardboard, and if certain points are 
 left attached, so that the design may not fall out, all the effect of solidity 
 is given by bending back the edges of the cardboard, so that the light 
 
THE REFLECTION OF LIGHTS 
 
 313 
 
 from a candle placed behind it, may be reflected from the back edge of 
 one cardboard on to the design, which is bent back. The light reflected 
 from one surface on to the other, imparts a peculiarly soft and marble-like 
 appearance, and when the design is well drawn and cut, and placed in 
 p, good position, the illusion is very perfect, and it appears like a solid 
 form instead of a mere design cut out of cardboard. (Eig. 290.) 
 
 Fig. 290. Cardboard design in frame, cut and bent back. The lighted caudle is behind. 
 
 The leaf at the side of the above picture is intended to give an idea of 
 the mode of cutting out the designs, and in this case the leaf would be 
 cut and bent back, and a small attachment slip of cardboard left to 
 prevent it falling out. 
 
 The cardboard design is always bent toward the light, which is 
 placed behind it. As a good illustration of the importance of reflected 
 light and its connexion with luminous bodies, a beam of light from the 
 oxy-hydrogen lantern may be allowed to pass above the surface of a 
 table, when it will be noticed that the latter is lighted up only when the 
 beam is reflected downward by a sheet of white paper. 
 
 By reference to the two laws of reflection already explained, it is easy 
 to trace out on paper, with the help of compasses and rule, the effect of 
 plane, concave, and convex surfaces on parallel, diverging, or converging 
 rays of light, and it may perhaps assist the memory if it is remembered 
 that a plane surface means one that is flat on both sides, such as a 
 looking-glass : a convex surface is represented by the outside of a watch- 
 glass ; a concave surface, by the inside of a watch-glass ; parallel rays 
 are like the straight lines in a copy-book; diverging and converging 
 
314 
 
 boy’s playbook of science. 
 
 rays, are like the sticks of a fan spread out as the sticks separate or 
 diverge ; the sticks of the fan come together, or converge at the handle. 
 
 The reflection of rays from a plane surface may be better understood 
 by reference to the annexed diagram. (Fig. 291.) 
 
 Fig. 291. a i, a k. Two diverging rays incident on the plane surface, d. a d is perpen- 
 dicular, and is reflected back in the same direction, a i is divergent, and is thrown off at 
 i l. The incident and reflected rays forming equal angles, as proved by the perpendicular, h. 
 Any image reflected in a plane mirror appears as far behind it as the object is before it, and 
 the dotted lines meeting at g show the apparent position of the reflected image behind 
 the glass, as seen at g. The same fact is also shown in the second diagram, where the 
 reflected picture, i m, appears at the same distance behind the surface of the mirror as the 
 object, a b, is before it. 
 
 By the proper arrangement of plane mirrors, a number of amusing 
 delusions may be produced, one of which is sometimes to be met with 
 in the streets, and is called “ the art of looking through a four-inch deal 
 board. 5 ’ The spectator is first requested to look into a tube, through 
 which he sees whatever may be passing the instrument at the time ; 
 the operator then places a deal board across the middle of the 
 tube, which is cut away for that purpose, and to the astonishment of 
 the juveniles the view is not impaired, and the spectator still fancies 
 he is looking through a straight tube ; this however is not the case, as 
 the deception is entirely carried out by reflection, and is explained in 
 the next cut. (Fig. 292.) 
 
 During the siege of Sebastopol numbers of our best artillerymen 
 were continually picked off by the enemy’s rifles, as well as by cannon 
 shot, and in order to put a stop to the foolhardiness and incautiousness 
 of the men, a very ingenious contrivance was invented by the Rev. Wm. 
 Taylor, the coadjutor of Mr. Denison in constructing the first “Big 
 Ben” bell. It was called the reflecting spy-glass, and by its simple con- 
 struction rendered the exposure of the sailors and soldiers, who would 
 look over the parapet or other parts of the works to observe the effect 
 of their shot, perfectly unnecessary; whilst another form was constructed 
 for the purpose of allowing the gunner to “ lay” or aim his gun in 
 safety. The instruments were shown to Lord Panmure, who was so 
 convinced of the importance of the invention, that he immediately 
 
OPTICAL ILLUSIONS. 
 
 315 
 
 Pig. &92. a a a a. The apertures through which the spectator first looks, b. The 
 piece of wood, four inches thick, c, d, e, f, are four pieces of looking-glass, so placed that 
 rays of light entering at one end of the tube are reflected round to the other where the 
 eye of the observer is placed. 
 
 commissioned the Rev. Wm. Taylor to have a number of these telescopes 
 constructed ; and if the siege had not terminated just at the time the 
 invention was to have been used, no doubt a great saving of the 
 valuable lives of the skilled artillerymen would have been effected in 
 the allied armies. The principle of the reflecting spy-glass may be 
 comprehended by reference to the next cut. (Eig. 293.) 
 
 Fig. 293. A picture of enemy’s battery is supposed to be on the mirror, a, whence it 
 is reflected to b, and from that to the artilleryman at c. 
 
 By placing two mirrors at an angle of 45°, the reflected image of a 
 person gazing into one is thrown into the other, and of course the effect 
 is sornew'hat startling when a death’s head and cross bones, or other 
 
316 
 
 boy’s playbook of science. 
 
 cheerful subject, is introduced opposite one mirror, whilst some person 
 who is unacquainted with the delusion is looking into the other/ Two 
 adjoining rooms might have their looking-glasses arranged in that 
 manner, provided there is a passage running behind them. (Fig. 294.) 
 
 Fig. 294. a. A mirror at an angle of 45 degrees. The arrows show the direction of the 
 reflected image, b. The second mirror, also at an angle of 45 degrees ; the face of the 
 person looking in at a is reflected at b. c is the partition between the rooms. 
 
 One of the most startling effects that can be displayed to persons 
 ignorant of the common laws of the reflection of light, is called the 
 “ magic mirror,” and is described by Sir Walter Scott in his graphic 
 story of that name. The apparatus for tne purpose must be well 
 planned and fixed in a proper room for that purpose, and if carefully 
 conducted, may surprise even the learned. A long and somewhat 
 narrow room should be hung • with black cloth, and at one end may be 
 placed a large mirror, so arranged that it will turn on hinges like a door. 
 The magician’s circle may be placed at the other end of the chamber in 
 which the spectators must be rigidly confined, and there is very little doubt 
 that the arrangement about to be described was formerly used by clever 
 astrologers who pretended to look into the future, and to hold commu- 
 nication with the supernatural powers. The credulity of the persons 
 who consulted these “ wise men,” is not surprising when we consider 
 the ignorance of the public generally of common physical laws, and of 
 the wonders that may be worked without the assistance of the “ evil 
 one ;” moreover, the initiated took great care to conceal the machinery 
 of their mysteries, never imparting the illusive tricks even to their 
 most faithful dependents except under solemn oaths of secresy, because 
 they derived in many cases considerable profit by their pretended conju- 
 rations and juggling tricks, and therefore were interested in keeping the 
 outer world in ignorance. The wizards were always careful to impress 
 those who came to consult them with the awful nature of the incanta- 
 tions thev were about to perform, and with such a powerful auxiliary as 
 
THE MAGIC MIRROR. 
 
 S17 
 
 fear, and a well-darkened room, they diverted the thoughts of the more 
 curious, and prevented them watching the proceedings too closely. 
 Theatrical effects were not disdained, such as suppressed and dismal 
 groans, sham thunder, and the wizard usually heightened his own 
 inspiring personal appearance by wearing of course a long beard and 
 flowing rooe trimmed with hieroglyphics, and with the assistance of a 
 ponderous volume full of cabalistic signs, a few skulls and cross bones, 
 an hour-glass, a pair of drawn swords, a black cat, a charcoal fire, and 
 sundry drugs to throw into it, a very tolerable collection of imps, 
 familiars, and demons, might be expected to attend without the modern 
 practice of spirit-rapping. As before stated, the delusion must be care- 
 fully conducted, ana a confederate is necessary in order to use the 
 phantasmagoria, or magic lantern. The slides of course were painted to 
 suit the fortune to be unfolded — an easy road to riches for the gentle- 
 men, a tale of love, ending in matrimony, for the ladies. 
 
 The spectators being placed in the magic circle, are directed to look 
 into the mirror ; they mav even be ordered singly to fetch a skull oft 
 the mantel-shelf beside the mirror, and whilst doing so to look full 
 into the mirror, and then return to the circle. Absolute silence is 
 enjoined, and soft music is now heard; the darkened room is lit up for 
 the moment by a little yellow or green fire thrown on to the charcoal 
 fire, and now looking into the mirror, it no longer reflects surrounding 
 objects, but a picture, at first small and faint, and then gradually 
 becoming large and clearer, is apparent. The picture is made visible by 
 the confederate gently drawing the mirror from its position parallel 
 with the frame to an angle of 45 degrees, and then throwing on from 
 the side a picture from a magic-lantern. The picture is small and in- 
 distinct whilst the confederate holds it near the mirror and out of focus, 
 but as he moves backwards and focuses the lenses, the picture gradually 
 increases in size, and the reflecting angles having been well planned 
 beforehand, only those in the circle will be able to see the picture, and 
 great fun may be elicited from the magic mirror by pretending to tell 
 the future fate of a very slim person, and introducing him by a suc- 
 cession of pictures which gradually assume a John Bull rotundity of 
 figure, surrounded by dozens of children ; whilst to young ladies who are 
 engaged, a provoking picture of an old maid may be introduced ; indeed, 
 there is no end to the innocent fun that may be extracted from the 
 magic mirror, and the whole plan of the delusion may be better understood 
 by reference to the next picture. (Fig. 295.) 
 
 Monsieur Salverte very properly remarks that "man is credulous 
 from his cradle to his tomb; but the disposition springs from an 
 honourable principle, the consequences of which precipitate him into 
 
 many errors and misfortunes The novelty of objects, and the 
 
 difficulty of referring them to known objects, will not shock the 
 credulity of unsophisticated men. They arc some additional sensations 
 which he receives without discussion, and their singularity is perhaps a 
 charm which causes him to receive them with greater pleasure. Man 
 almost always loves and seeks the marvellous. Is this taste natural ? 
 
318 
 
 boy’s playbook of science. 
 
 The magic mirror. 
 
 reflected. 
 
THE CONVEX MIRROR. 
 
 319> 
 
 Does it spring from the education which during many ages the human 
 race has received from its first instructors ? A vast and novel question, 
 but with which I have nothing to do. It is sufficient to observe that 
 as the lover of the wonderful always prefers the most surprising to the 
 most natural account, this last has been too frequently neglected, and is 
 irrevocably lost. Occasionally, however (and we shall cite more than 
 one instance), simple truth has escaped from the power of oblivion. 
 Credulous man may be deceived once, or more frequently ; but his 
 credulity is not a sufficient instrument to govern his whole existence. 
 The wonderful excites only a transient admiration. In 1798, the 
 Drench savans remarked with surprise how little the spectacle of 
 
 balloons affected the indolent Egyptian But man is led by his 
 
 passions, and particularly by hope and fear” 
 
 When parallel rays fall upon a convex mirror, they are scattered and 
 dispersed in all directions, and the image of an object reflected in a 
 convex mirror appears to be very small, being reduced in size because 
 the reflected picture i m is nearer the surface of the mirror than the- 
 object a b. No. 1. (Dig. 296.) 
 
 No. 2. 
 
 No. 1. 
 
 \ 
 
 \ 
 
 Fig. 296. a b, d h. (No. 2) represent two parallel rays incident on the convex surface 
 n h, the one (a b) perpendicularly, the other (d h) obliquely, c is the centre of con- 
 vexity. ee is the reflected ray of the oblique incident one, d h j whilst cn is the 
 perpendicular. 
 
 Convex mirrors are not employed in any optical deception on a large 
 scale, although some ingenious delusions are producible from cylindrical 
 and conical mirrors, and are thus described by Sir David Brewster : 
 
 “ Among the ingenious and beautiful deceptions of the seventeenth 
 century, we must enumerate that of the re-formation of distorted 
 pictures by reflection from cylindrical and conical mirrors. In these 
 representations, the original image from which a perfect picture is pro- 
 
320 
 
 boy’s playbook of science. 
 
 duced, is often so completely distorted, that the eye cannot trace in it 
 the resemblance to any regular figure, and the greatest degree of 
 wonder is of course excited, whether the original image is concealed or 
 exposed to view. These distorted pictures may be drawn by strict 
 geometrical rules, and I have shown a simple method of executing 
 them. Let m be an accurate cylinder made of tin-plate or of thick 
 
 pasteboard. Out of the further side of it cut a small aperture, abed , and 
 out of the nearer side cut a larger one, abcd (white letters), the size of 
 the picture to be distorted ; having perforated the outline of the picture 
 with small holes, place it in the openmg abcd (white letters), so that its 
 surface may be cylindrical ; let a candle or a bright luminous object — the 
 smaller the better — be placed at s, as far behind the picture abcd (white 
 letters) as the eye is afterwards to be placed before it, and the light passing 
 through the small holes will represent on a horizontal plane a distorted 
 image of the picture at abcd, which, when sketched in outline with a 
 pencil, shaded, and coloured, will be ready for use. If we now substitute 
 a polished cylindrical mirror of the same size in place of m, then the 
 distorted picture, when laid horizontally at abcd, will be restored to 
 its original state when seen by reflection at abcd (white letters) in 
 the polished mirror.” The effect of a cylindrical mirror on a distorted pic- 
 ture is shown at No. 2, being copied from an old one seen by Sir D. 
 Brewster. 
 
 By looking at a reflection of the face in a dish-cover or the common 
 surface of a bright silver spoon or of a silver mug, the latter truly 
 becomes ugly as the image is seen reflected from its surface, and 
 
PICTURES DISTORTED BY REFLECTION. 321 
 
 assumes the most absurd form as the mouth is opened or shut, and 
 the face advanced or removed from the silver vessel. (Fig. 298.) 
 
 Fig. 2S8. Distorted image produced by an irregular convex surface. 
 
 In the writings of the ancients there are to be found certain indica- 
 tions of the results of illusions produced by simple optical arrange- 
 ments, and the sudden and momentary apparition (from the gloom of 
 perfect darkness) of splendid palaces, delightful gardens, &c., with 
 which — the concurrent voice of antiquity assures us — the eyes of the 
 beholders were frequently dazzled in the mysteries, such as the evocation 
 and actual appearance of departed spirits, the occasional images of thei; 
 umbrae , and of the gods themselves. From a passage in “ Pausanias/' 
 (Boeotic xxx.), when, speaking of Orpheus, he says there was anciently 
 at Aornos, a place wdiere the dead were evoked, vsKvoiiavreiov, we learn 
 that in those remote ages there were places set apart for the evocatior 
 of the dead. Homer relates, in the eleventh book of the “ Odyssey,” the 
 admission of Ulysses alone into a place of this kind, when his interview 
 with his departed friend was interrupted by some fearful voice, and the 
 hero, apprehending the wrath of Proserpine, withdrew ; the priests who 
 managed these deceptive exhibitions no doubt adopted this method of 
 getting rid of their visitor, who might become too inquisitive, and dis- 
 cover the secret of the mysteries. 
 
 Of all the reflectingsurfacesmentioned, none produce more interesting 
 deceptions than the concave mirror, and there is very little doubt that 
 silver mirrors of this form were known to the ancients, and employed in 
 
322 
 
 boy’s playbook of science. 
 
 some of their sacred mysteries. Mons. Salverte has industriously col 
 lected in his valuable work the most interesting proofs of their use, and 
 quotes the following passage of “ Damascus,” in which the results 
 obtainable from a concave mirror are clearly apparent. (Fig. 299.) 
 
 Fig. 299. The picture of a human face, possibly reflected from a concave mirror concealed 
 below the floor of the temple ; the opening being hidden by a raised mass of stone, and 
 the worshippers confined to a certain part of the temple, and not allowed to ap- 
 proach it. 
 
 He says: — “In a manifestation which ought not to be revealed 
 
 there appeared on the wall of the temple a mass of light which 
 
 at first seemed very remote ; it transformed itself in coming nearer into 
 a face evidently divine and supernatural, of a severe aspect, but mixed 
 with gentleness, and extremely beautiful. According to the institution 
 of a mysterious religion, the Alexandrians honoured it as Osiris and 
 Adonis/ 5 
 
 Parallel rays thrown upon a concave surface are brought to a focus 
 or converge, and when an object is seen by reflection from a concave 
 surface, the representation of it is various, both with regard to its mag- 
 
THE CONCAVE MIRROR. 
 
 323 
 
 nitude and situation, according as the distance of the object from the 
 reflecting surface .is greater or less. (Fig. 300.) When the object is 
 placed between the focus of parallel rays 
 and the centre, the image falls on the 
 opposite side of the centre, and is larger 
 than the object, and in an inverted po- 
 sition. The rays which proceed from 
 any remote terrestrial object are nearly 
 parallel at the concave mirror — not 
 strictly so, but come diverging to it in 
 separate pencils, or, as it were, bundles 
 
 No. l. 
 
 Fig. 300. No. 1. A b, d h represent two parallel rays incident on the concave sur- 
 face b n, whose centre of concavity is c. bp and h p are the reflected rays meeting each 
 other in f, and a b being perpendicular to the concave surface, is reflected in a straight line. 
 No. 2. a b. The object, i m. The image. 
 
 of rays, from each point of the side of the object next the mirror; 
 therefore they will not be converged to a point at the distance of half 
 the radius of the mirror’s concavity from its reflecting surface, but in 
 separate points at a little greater distance from the concave mirror. 
 The nearer the object is to the mirror, the further these points will be 
 from it, and an inverted image of the object will be formed in them, 
 which will seem to hang pendant in the air, and will be seen by an eye 
 placed beyond it (with regard to the mirror), in all resnects like the 
 object, and as distinct as the object itself. No. 2. (Fig. 300.) 
 
 Fig. 301. a b represents the object, s v the reflecting 
 surface, f its focus of parallel rays, and c its centre. 
 Through a and b, the extremities of the object, draw 
 the lines c e and c n, which are perpendicular to the 
 surface, and let a e, a g, be a pencil of rays flowing 
 from a. These rays proceeding from a point beyond 
 the focus of parallel rays, will, after reflection, con- 
 verge towards some point on the opposite side of the 
 centre, which will fall upon the perpendicular, e c, pro- 
 duced, but at a greater distance from c than the radiant 
 a from which they diverged. For the same reason, 
 rays flowing from b will converge to a point in the 
 perpendicular n o produced, which shall be further from 
 c than the radiant b, from whence it is evident that the 
 image i m is larger than the object a b, that it falls on 
 the contrary side of the centre, and that their positions 
 are inverted with respect to each other. 
 
824 
 
 boy’s playbook of science. 
 
 It appears, from a circumstance in the life of Socrates, that the 
 effects of burning-glasses were known to the ancients ; and it is pro- 
 bable that the Romans em- 
 ployed the concave speculum 
 for the purpose of lighting the 
 “sacred fire.” This is very 
 likely to be true, considering 
 that the priests who conducted 
 the heathen worship of Osiris 
 and Adonis were acquainted 
 with the use of concave metallic 
 specula, as already described at 
 page 282. The effects that can 
 be produced with the aid of con- 
 cave mirrors are very impres- 
 sive, because they are not 
 merely confined to the reflec- 
 tion of inanimate objects, but 
 life and motion can be well 
 displayed by them ; thus, if a 
 man place himself directly be- 
 fore a concave mirror, but fur- 
 ther from it than its centre of 
 
 Fig. 302. A concave mirror, showing the ap- concavity, he will see ail in- 
 the^r 06 ° f the inveited and reflected image 111 verted image of himself in the 
 
 air between him and the mirror 
 of a less size than himself; and if he hold out his hand towards the 
 mirror the hand of the image will come out towards his hand and 
 coincide with it, being of an equal bulk when his hand ism the centre 
 of concavity, and he will imagine he may shake hands with his image. 
 
 (Fig. 302.) „ J . n . x 
 
 By using alarge concave mirror of about three feet m diameter, the author 
 was enabled to show all the results to a large audience that were usu- 
 ally visible to one person only. Whilst experimenting with a concave 
 mirror, by holding out the hand in the manner described, a bystander 
 will see nothing of the image, because none of the reflected rays that 
 form it enter his eyes. This circumstance is well illustrated by placing 
 a concave mirror opposite the fire, and allowing the image of the flames 
 projected from it to fall upon a well-polished mahogany table. If the 
 door of the room opens towards the mirror, and a spectator unacquainted 
 with the properties of concave mirrors should enter the apartment, the 
 person would be greatly startled to see flames apparently playing over 
 the surface of the table, whilst another spectator might enter from 
 another door and see nothing but a long beam of light, rendered visible 
 by the floating particles of dust. To give proper effect to this experi- 
 ment the concave mirror should be large, and no other light must 
 illuminate the room except that from the fire. 
 
 On the same polished table the appearance of a planet with a re- 
 
illusions with concave mirrors. 
 
 325 
 
 solving satellite may be prettily shown by darkening the fire with a 
 screen, and placing a lighted candle before it, which will be reflected by 
 the concave mirror, and appear on the table as a brilliant star of light, 
 and the satellite may be represented by the flame of a small wax taper 
 moved around the large burning candle. The following is the arrange- 
 ment used by the author at the Polytechnic Institution for the purpose 
 of exhibiting the properties of the concave mirror, A lantern enclosing 
 a very brilliant light, such as the electric or lime light, is required for 
 the illumination of the objects which are to be projected on to the 
 screw. The lantern and electric lamp of Duboscq was preferred, 
 although, of course, any bright light enclosed in a box, with a plain 
 convex lens to project the beam of light when required, will answer the 
 purpose. (Fig. 303.) 
 
 Fig. 303. a B.Portable screen of light framework, covered with black calico, cccc. 
 Square aperture just above the shelf, d d, upon which the object — viz., a bottle half full of 
 water— is placed, e. Duboscq lantern to illuminate the object at d d. 
 
 By removing the diaphragm required to project the picture of the 
 charcoal points on to the screen, a very intense beam of light is ob- 
 tained, which may be focussed or concentrated on any opaque object 
 by another double convex lens, conveniently mounted with a telescope 
 stand, so that it may be raised or lowered at pleasure. This lens is 
 independent of the lantern, and may be used or not at the pleasure of 
 the operator. 
 
 The object is now placed on a shelf fixed to the screen, with a 
 square aperture just above it. The object of the screen is to cut off all 
 extraneous rays of light reflected from the mirror, or to increase the 
 sharpness of the outline of the picture of the object. The screen and 
 object being arranged, and the light thrown on from the lantern, the 
 next step is to adjust the concave mirror, and by moving it towards the 
 
326 
 
 boy’s playbook of science.' 
 
 object, or backwards, as the case requires, a good image, solid and quasi- 
 stereoscopic, is projected on to tlie screen. (Fig. 304.) 
 
 The act of filling the bottle with water, or better still with mercury, 
 is one of the most singular effects that can be shown ; and if all the 
 apparatus is enclosed in a box, so that the picture on the screen only is 
 apparent, the illusion of a bottle being filled in an inverted position is 
 quite magical, and invariably provokes the inquiry, how can it be done ? 
 The study of numismatics, the science of coins and medals, is generally 
 considered to be limited to the taste of a very few persons, and any de- 
 scription of a collection of coins at a lecture would be voted a great bore, 
 unless the members of the audience happened to be antiquaries ; great 
 light, however, may be thrown on history by a study of these interesting 
 remains of bygone times, and a lecture on this subject, illustrated with 
 pictures of coins thrown on to the disc by a concave mirror in the 
 manner described, might be made very pleasing and instructive.* 
 
 Coins, or plaster casts of coins gilt , flowers, birds, white mice, the 
 human face and hands, may all, when fully illuminated, be reflected by 
 the concave mirror on to the disc. A Daguerreotype picture at a 
 certain angle appears, when reflected by the concave mirror, to be like 
 anv ordinary collodion negative, and all the lights and shadows are 
 reversed, so that the face of the portrait apears black, whilst the black 
 coat is white. On placing the Daguerreotype in another position, easily 
 found by experiment, it is now reflected in the ordinary manner, showing 
 an enlarged and perfect portrait on the disc. In using the Daguerreo- 
 type the glass in front of it must be removed. The pictures from the 
 concave mirror may be aisp projected on thick smoke procured from 
 
 * These effects can be more easily produced by the use of the opaque lantern, hereafter 
 described. 
 
EXPERIMENTS WITH MIRRORS. 
 
 327 
 
 smouldering damped brown paper, or from a mixture of pitch and a little 
 chlorate of potash laid on paper, and allowed to burn slowly by wetting 
 it with water. 
 
 An image reflected from smoke would be visible to a number ot 
 spectators, just as the light from the furnace fires of the locomotive is 
 frequently visible at night, being reflected on the escaping column ot 
 steam. 
 
 It was probably with the help of some kind of smoke and the concave 
 speculum that the deception practised on the worshippers at the temple 
 of Hercules at Tyre was carried out, as it is mentioned by Pliny that a 
 consecrated stone existed there “from which the gods easily rose.” 
 At the temple of Esculapius at Tarsus, and that of Enguinum in Sicily, 
 the same kind of optical delusions were exhibited as a portion of the 
 religious ceremonies, from which nq doubt the priests obtained a very 
 handsome revenue, much more than could be obtained in modern times 
 by the mere exhibition of such wonders at Adelaide Galleries, Poly- 
 technics, or Panopticons. 
 
 The smoke from brown paper is very useful in showing the various 
 directions of the rays of light when reflected from plane, convex, and 
 concave surfaces. The equal angles of the incident and reflected rays 
 may be perfectly shown by using the next arrangement of apparatus. 
 (Fig. 305.) 
 
 A very dense white smoke is obtained by boiling in separate flasks 
 (the necks of which are brought close together) solutions of ammonia 
 and hydrochloric acid. 
 
 The opposite properties of convex and concave mirrors — the former 
 scattering and the latter collecting the rays of light which fall upon 
 them — are also effectively demonstrated by the help of the same ilium! 
 
328 
 
 BOY S PLAY BOOK OF SCIENCE. 
 
 nating source and proper mirrors, the smoke tracing out perfectly the 
 direction of the rays of light. (Fig. 306.) 
 
 Fig-. 306. The smoke shows the rays of light falling on a convex mirror, and rendered 
 still more divergent. 
 
 The smoke developes the cone of rays reflected from a concave 
 mirror in the most beautiful manner, and by producing plenty of 
 
 vergent rays meet. 
 
LOUD ROSSE S TELESCOPE. 
 
 829 
 
 umoke, and turning the mirror about — the position of the focus ( focus , a 
 fire-place), is indicated by a brilliant spot of light, and the reason the 
 images of objects reflected by the concave mirror are reversed, may be 
 better understood by observing how the rays cross each other at that 
 point. (Fig. 307.) 
 
 ^ One of the most perfect applications of the reflection of light is 
 shown in the “ Gregorian reflecting telescope,” or in that magnificent 
 instrument constructed by Lord Rosse, at Parsonstown, in Ireland. 
 (Fig. 30S.) 
 
 Fig. 308. Lord Rosse’s gigantic telescope. 
 
 The description of nearly all elaborate optical instruments is some- 
 what tedious, but we venture to give one diagram, with the explana- 
 tion of the Gregorian reflecting telescope. (Fig. 309.) 
 
 At the bottom of the great tube mi, (Fig. 309), is placed the 
 large concave mirror Dtvi, whose principal focus is at m; and in its 
 middle is a round hole p, opposite to which is placed the small mirror 
 l, concave towards the greater one, and so fixed to a strong wire si, that 
 it may be moved farther from the great mirror or nearer to it, by means 
 ot a long screw on the outside of the tube, keeping its axis still in the 
 same line r m n with that of the great one. Now since in viewing a 
 very remote object we can scarcely see a point of it but what is at least 
 as broad as the great mirror, we may consider the rays of each pencil, 
 which flow from every pomt of the object, to be parallel to each other. 
 
380 
 
 boy’s playbook of science. 
 
 and to cover the whole reflecting surface dtvp. But to avoid confusion 
 in the figure, we shall only draw two rays of a pencil flowing from each 
 
 T 
 
 T 
 
 Fig. 309. The Gregorian reflecting telescope. 
 
 extremity of the object into the great tube, and trace their progress 
 through all their reflections and refractions to the eye f, at the end of 
 the small tube 1 1, which is joined to the great one. 
 
 Let us then suppose the object a b to be at such a distance, that the 
 rays e flow from its lower extremity b, and the rays c from its upper 
 extremity a. Then the rays c falling parallel upon the great mirror at 
 D, will be thence reflected by converging in the direction d g ; and by 
 crossing at i in the principal focus of the mirror, they will form the 
 upper extremity i of the inverted image i K, similar to the lower extre- 
 mity b of the object a b ; and passing on the concave mirror l (whose 
 focus is at n) they will fall upon it at g and be thence reflected, con- 
 J1 1 ’ 1 e g m is longer than g n; and passing 
 
 mirror, they would meet somewhere 
 
 about r, and form the lower extremity d of the erect image a d, similar 
 to the lower extremity b of the object a b. But by passing through 
 the plano-convex glass u in their way they form that extremity of the 
 image at b. In like manner the rays e which come from the top of the 
 object a b and fall parallel upon the great mirror at e, are thence re- 
 flected converging to its focus, where they form the lower extremity K of 
 the inverted image i k, similar to the upper extremity a, of the object 
 a B ; and passing on to the smaller mirror l and falling upon it at h, 
 they are thence reflected in the converging state h o ; and going on 
 through the hole P of the great mirror, they would meet somewhere 
 about q, and form there the upper extremity a of the erect image a d, 
 similar to the upper extremity a of the object A B; but by passing- 
 through the convex glass u in their way, they meet and cross sooner, as 
 at a, where that point of the erect image is formed. The like being 
 understood of all those rays which flow from the intermediate points of 
 the object, between a and b, and enter the tube t t, all the intermediate 
 points of the image between a and b will be formed ; and the rays 
 passing on from the image through the eye-glass s, and through a small 
 bole e in the end of the lesser tube 1 1, they enter the eye f which sees 
 
THE BURNING MIRROR OF ARCHIMEDES. S3 i 
 
 the image a d (bv means of the eye-glass), under the large angle ced, 
 and magnified in length, under that angle, from c to d. 
 
 To find the magnifying power of this telescope, multiply the focal 
 distance of the great mirror by the distance of the small mirror, from 
 the image next the eye, and multiply the focal distance of the small 
 mirror by the focal distance of the eye-glass ; then divide the product 
 of the latter, and the quotient will express the magnifying power, 
 (Fig. 309.) 
 
 We now come to that much disputed and often quoted experiment of 
 Archimedes, who is stated to have employed metallic concave specula or 
 some other reflecting surface by which he was enabled to set fire to the 
 Roman fleet anchored in the harbour of Syracuse, and at that time be- 
 sieging their city, in which the great and learned philosopher was shut up • 
 with the other inhabitants. The story handed down to posterity was not 
 disputed till about the seventeenth century, when Descartes boldly 
 attacked the truth of it on philosophical grounds, and for the time 
 silenced those who supported the veracity of this ancient Joe Miller. 
 Nearly a hundred years after this time, the neglected Archimedes fiction 
 was again examined by the celebrated naturalist Buffon, and the account 
 of his experiments detailed by the author of “Adversaria, 5 ’ in Chambers’ 
 Journal, is so logical and conclusive, that we give a portion of it verbatim. 
 
 “For some years prior to 1747, the French naturalist Buffon had 
 been engaged in the prosecution of those researches upon heat which 
 he afterwards published in the first volume of the Supplement to his 
 ‘Natural History. 5 Without any previous knowledge, as it would 
 seem, of the mathematical treatise of Anthemius (n epi napabo^cov prj- 
 Xavrj pciTtov), in which a similar invention of the sixth century is de- 
 scribed,* Buffon was led, in spite of the reasonings of Descartes, to 
 conclude that a speculum or series of specula might be constructed 
 sufficient to obtain results little, if at all, inferior to those attributed to 
 the invention of Archimedes. 
 
 “ This, after encountering many difficulties, which he had foreseen 
 with great acuteness, and obviated with equal ingenuity, he at length 
 succeeded in effecting. In the spring of 17 47, he laid before the French 
 Academy a memoir which, in his collected works, extends over upwards 
 of eighty pages. In this paper, he describes himself as in possession of 
 an apparatus by means of which he could set fire to planks at the distance 
 of 200, and even 210 feet, and melt metals and metallic minerals at 
 distances varying from twenty-five to forty feet. This apparatus lie 
 describes as composed of 168 plain glasses, silvered on the back, each 
 six inches broad by eight inches long. These, he says, were ranged in 
 a large wooden frame, at intervals not exceeding the third of an inch ; 
 so that, by means of an adjustment behind, each should be moveable in 
 all directions independently of the rest — the spaces between the glasses 
 being further of use in allowing the operator to see from behind the 
 point on which it behoved the various disks to be converged. 
 
 See Gibbon’? “ Decline and Fall,” chap. xl„ section v., note g . 
 
332 
 
 boy’s playbook of science. 
 
 “ These results ascertained, Buffon’s next inquiry was how far they 
 corresponded with those ascribed to the mirrors of Archimedes — the 
 most particular account of which is given by the historians Zonaras and 
 Tzetzes, both of the twelfth century.* ‘ Archimedes/ says the first ot 
 these writers, ‘ having received the rays of the sun on a mirror, by the 
 thickness and polish of which they were reflected and united, kindled a 
 flame in the air, and darted it with full violence on the ships which 
 were anchored within a certain distance, and which were accordingly 
 reduced to ashes/ The same Zonaras relates that Proclus, a celebrated 
 mathematician of the sixth century, at the siege of Constantinople, set 
 on fire the Thracian fleet by means of brass mirrors. Tzetzes is yet 
 more particular. He tells us, that when the Homan galleys were within 
 a bow-shot of the city-walls, Archimedes caused a kind of hexagonal 
 speculum, with other smaller ones of twenty-four facets each, to be 
 placed at a proper distance ; that he moved these by means of hinges 
 and plates of metal ; that the hexagon was bisected by e the meridian of 
 summer and winter / that it was placed opposite the sun ; and that a 
 great fire was thus kindled, which consumed the Homan fleet. 
 
 “From these accounts, we may conclude that the mirrors of Archimedes 
 and BulFon were not very different either in their construction or effects. 
 No question, therefore, could remain of the latter having revived one of 
 the most beautiful inventions of former times, were there not one cir- 
 cumstance which still renders the antiquity of it doubtful : the writers 
 contemporary with Archimedes, or nearest his time, make no mention 
 of these mirrors. Livy, who is so fond of the marvellous, and Polybius, 
 whose accuracy so great an invention could scarcely have escaped, are 
 altogether silent on the subject. Plutarch, who has collected so many 
 particulars relative to Archimedes, speaks no more of it than the former 
 two ; and Galen, who lived in the second century, is the first writer by 
 whom we find it mentioned. It is, however, difficult to conceive how 
 the notion of such mirrors having ever existed could have occurred, if 
 they never had been actually employed. The idea is greatly above the 
 reach of those minds which are usually occupied in inventing falsehoods; 
 and if the mirrors of Archimedes are a fiction, it must be granted that 
 they are the fiction of a philosopher.” 
 
 Supposing that Archimedes really did project the concentrated rays 
 of the sun on the Homan vessels, one cannot help pitying the ignorance 
 of the Admiral Marcellus. Had this officer been acquainted with the 
 laws of the reflection of light, he might have laughed to scorn the 
 power of Archimedes, and by receiving the unfriendly rays on one of 
 the bright brazen convex shields of his soldiers, Marcellus could have 
 scattered the concentrated rays, and prevented the burning of his 
 vessels. 
 
 In these days of learning it therefore appears strange to find any one 
 advocating the possible use of specula or reflecting mirrors for the 
 purposes of offence or defence, but M. Peyrard a few years ago proposed 
 
 • Quoted by Fabricius in his "Biblioth. Gnec.,” vol. ii., pp. 551, 552. 
 
THE BURNING MIRROR OF ARCHIMEDES. 
 
 to produce great effects by mounting each mirror in a distinct frame, 
 carrying a telescope so that one person could direct the rays to the 
 object intended to be set on fire, and he gravely calculated, presuming 
 on the ignorance of the attacked, that with 590 glasses of about twenty 
 inches in diameter, he could reduce a fleet to ashes at the distance of 
 a quarter of a league ! and with glasses of double that size at the dis- 
 tance of half a mile ! What effect a shell or shot would produce upon 
 this ancient weapon is not stated ; this we may safely leave our readers 
 to determine for themselves. The experiment of Archimedes has long 
 been a favourite one with the boys. (Fig. 310.) 
 
 Fig. 310. One of the “ miseries of reflection .” 
 
 The total internal reflection of light by a column of water is an ex- 
 periment that admits of great variety so far as colour is concerned, and 
 is one of the most novel and beautiful experiments with light presented 
 to the public within the last few years. The author had the pleasure 
 of introducing it in the first place at the Polytechnic Institution, where 
 the optical novelty excited the greatest attention, and received the 
 approbation of her Most Gracious Majesty, and his Royal Highness 
 the Prince Consort, with the Royal Family, who were pleased to pay a 
 private evening visit to the Polytechnic, and amongst other things 
 minutely examined the “ Illuminated Cascade,” which had been erected, 
 by Mons. Duboscq of Paris. 
 
 The illumination of the descending columns of water was obtained by 
 converging the rays from a powerful electric light upon the orifice from 
 
334 
 
 boy’s playbook of science. 
 
 which, the water escaped, the Duboscq lantern already explained being 
 employed, and in front of it were placed three cylinders, each having a 
 circular window behind and opposite the lens, and an aperture of about 
 one inch in diameter on the opposite side for the escape of water. The 
 
 lantern and the cistern of water. 
 
 lantern used was of a peculiar shape, and had three sides, the electric 
 light being in the centre of them, and passing through three separate 
 plano-convex lenses to the three cylinders from which the water escaped. 
 
 Attention may be directed to the fact that the light merely passes 
 out of the orifices as a diverging beam of light until the flow of water 
 commences, when the rays are immediately taken up and reflected from 
 
THE ILLUMINATED CASCADE. 
 
 335 
 
 point to point inside tlie arched column of water, and illuminating the latter 
 m the most lovely manner, it appears sometimes like a stream of liquid 
 metal from the iron furnace, or like liquid ruby glass, or of an amethyst 
 or topaz colour, according to the colours of the plates of glass held 
 between the mouths of the lantern and the circular windows in the 
 cylinders of water. The same experi- 
 ment created quite a furore at the 
 Crystal Palace when it was introduced 
 in one of the author’s lectures deli- 
 vered in .that noble place of amuse- 
 ment. In order that our readers may 
 understand the arrangement of the 
 apparatus, we have given at page 291 
 a ground plan view of it, as also the 
 appearance of the cascade when exhi- 
 bited at the Polytechnic to the Royal 
 party. (Pig. 313.) 
 
 Another curious effect observed with 
 the illuminated cascade, is the descent 
 of balls of light as the reflection is cut 
 off for a moment by passing the 
 finger through the stream of water, 
 showing that a certain time is occupied 
 in the reflection^ of light from one end 
 of the cylinder of water to the other ; 
 indeed the best idea of the rationale 
 
 of the experiment is formed by substi- „ x 
 
 fnhW iri imacririnHnn « dWpr tnKp JH 1 ! 011 of . onl y two rays of the beam of 
 xuimg in imagination a Sliver tube light passing down inside the water. 
 
 highly polished m the interior, for the 
 
 descending jet of water. The reflection of sound takes plaoe precisely 
 in the same manner, and the vibrations of the air are reflected from plane, 
 concave, and convex surfaces. It is on this principle that waves of sound 
 thrown off from different surfaces (as of hard rocks), produce the effect 
 of the echo . The sounds arrive at the ear in succession, those reflected 
 nearest the ear being first, and the reflecting surfaces at the greatest 
 distance sending the waves of sound to the ear after the former. At 
 Lurley Palls on the Rhine, there is an echo which repeats seventeen 
 times. Whispering galleries, again, illustrate the reflection of sound 
 from continuous curved surfaces, just as the arched column of water 
 reflects from its interior curved surfaces the rays of light. 
 
 Speaking-tubes are well known in which the waves of sound are 
 successively reflected from the sides, exactly like the “ Illuminated 
 Cascade” (Pig. 312). The speaking-trumpet is also another and familiar 
 example of the same principle. Probably when Albertus Magnus con- 
 structed the brazen head, which had the power of talking, it was nothing 
 more than a metallic head with a few wheels and visible mechanism 
 inside, but connected with a lower apartment by a hollow metal tube, 
 where Albertus Magnus descended, and astonished the ignorant with 
 
 Fig. 312. a b. The sides of the cas- 
 cade. The dotted lines show the re- 
 
336 
 
 boy’s playbook of science. 
 
 the then unknown principle of the speaking tubs. Light entering at 
 one end of a bright metallic tube is reflected from the sides of the tube 
 till it reaches the other, and precisely the same effect occurs in the 
 interior of the cascade of water. (Fig. 313). 
 
 Fig. 313. End of Polytechnic Hall, where the illuminated cascade was displayed to her 
 Majesty, H.R.H. the Prince Consort, and Itoyal party. The cascades issued from behind 
 some artificial rock-work. 
 
 THE KALEIDOSCOPE. 
 
 If this article on light and optics had gone minutely into the mat he- 
 matical and purely scientific portion of the subject, \ve should have had 
 frequent occasion to mention the name of Sir David Brewster, a dis- 
 tinguished philosopher, whose name is peculiarly identified with tins 
 interesting branch of physics. It is always pleasing to find men of such 
 standing not only devoting themselves to arguments which college 
 wranglers would study with pleasure, but also descending to a lower 
 level, and inventing optical instruments that delight and amuse the 
 non-scientific and juvenile part of the community. The names of Sir 
 David Brewster and Professor Wheatstone have been connected during 
 the last few years with the invention of the stereoscope, an instrument 
 
THE KALEIDOSCOPE. 
 
 337 
 
 that will be noticed in another part of this book, but here we shall 
 describe one of the most original optical instruments ever devised, and 
 although it is now regarded as a mere toy, its merits are very great. 
 The title of the instrument is borrowed from the Greek kciXo?, beautiful, 
 €*do?, a form or appearance, a-Koneco , to see; and the public certainly 
 endorsed the name when they purchased 200,000 of these instru- 
 ments in London and Paris during the space of three months. It is 
 said that the sensation it excited in London, throughout all ranks 
 of the community, was astonishing, and people were everywhere seen, 
 even at the corners of the streets, looking through the kaleidoscope. 
 The essential parts of this instrument are two mirrors of unsilvered 
 black parallel glass, or plate glass painted black on one side, which 
 should be from six to ten inches in length, and from one inch to an inch 
 and a half in breadth at the object end, while they are made narrower 
 at the other end, to which the eye is applied. The mirrors are united 
 at their lower edges by a strip of black calico fixed with common glue, 
 and are left open at the upper edges, and retained at the proper angle 
 by a bit of cork properly blackened. The angles are 36°, 30°, 25°f, 
 22°^, 20°, 18°, which divide the circumference into 10, 12, 14, 16, 18* 
 20 parts, thus 36 x 10 = 360, or 18 x 20 = 360, and the strictest 
 attention must be paid to this part of the adjustment, or the figures 
 produced will not be symmetrical. After the mirrors are adjusted to 
 
 Fig. 314. a b. The tube containing the two mirrors, shown by dotted lines, a is the 
 small end where the eye is placed, b. The object end. c d. Another view of the mirrors 
 arranged to place in the tube; the shaded portion represents the black velvet. e. Double 
 convex lens, r. Box to contain obieets, and usually fitted with ground glass outside. 
 
 Z 
 
338 
 
 boy’s playbook of science. 
 
 the proper angle, the space between the two upper edges should be 
 covered across with black velvet and the mirrors placed in a tin or 
 brass tube, so that the broad ends shall barely project beyond the 
 end, while the narrow end is placed so that the angle formed by the 
 junction of the mirrors shall be a little below the middle of that end of the 
 tube. A cover with a circular aperture in the centre is then to be fitted 
 to the narrow end of the mirrors, which should in general be furnished 
 with a convex lens whose focal length is an inch or two greater than 
 the length of the mirrors. A case for holding the objects, and for com- 
 municating to them a revolving motion, is fitted to the object end of the 
 tube. The objects best suited for producing pleasing effects are small 
 fragments of coloured glass, wires of glass, both spun and twisted, and of 
 different colours and shades of colours, and of various shapes, in curves, 
 angles, circles ; also, beads, bugles, fine needles, small pieces of lace, and 
 fragments of fine sea-weed are very beautiful. M. Sturm, of Prague, has 
 lately fixed the images of the kaleidoscope, so that they are available for the 
 production of patterns in every branch of silk, cotton, and mixed fabrics. 
 Photographs could be taken of the most beautiful of these accidental 
 designs, which only occur once, and if not copied are lost. 
 
 FLASHING SIGNALS. 
 
 The mirror with which naughty boys have from time immemorial 
 annoyed “ the maid hanging out the clothes” and any other unfortunate 
 within convenient distance, has of late been put to good account in 
 warfare. And strangely enough, it has been used in precisely the 
 manner depicted in Pig. 310; namely, to cast a beam of sunlight in a par- 
 ticular direction. In the first experiments, I believe a shaving glass 
 was used, but this gave place to an instrument called the 7ieliograph> 
 its function being to transmit signals by means of flashes. 
 
 In warfare, it frequently happens that one corps of an army becomes 
 separated from another, without any means of communication. Such a 
 thing occurred lately in Zululand, when Colonel Pearson was shut up in 
 an extemporized fort, surrounded on all sides by the enemy. He was in 
 fact in a trap, he had gone in, but could not get out, at least, not 
 without being, with his gallant baud, cut to pieces in the attempt. He 
 knew well that his comrades would not allow him to starve at Ekowe. 
 And as he expected, a force was soon sent to his relief. 
 
 Now long before- the relieving column reached their goal, they were 
 enabled to carry on constant communication with those in the fortress, 
 and they accomplished this by means of flashing signals sent by the 
 heliograph. Imagine a round mirror with a little of the quicksilver 
 scratched away from its back in the centre, and you will have a very 
 good idea of this instrument. It is swung in a frame, not unlike an 
 ordinary toilet glass, and the whole arrangement is supported on a 
 tripod stand to bring it up to the level of the operator’s eye. A few 
 feet in front of the mirror is planted a stick having a stop upon it 
 which can be adjusted to any height. This stop answers to the sight 
 upon a gun barrel, and is used to take aim with the mirror upon any 
 desired spot. So that if the operator wishes his flashes to be seen at a 
 
FLASHING SIGNALS. 
 
 339 
 
 Fig. 315. Heliograph. 
 
 distant place, lie will first of all arrange his apparatus so that the stop 
 will just come between his line of sight through the mirror and the 
 place to which he wishes to aim the flashes. When this is once 
 arranged, the mirror can be so adjusted that it will always fall to the 
 desired angle, except when a lever at the back is depressed to interrupt 
 and separate the flashes. 
 
 In the diagram Eig. 315, 
 these arrangements are 
 shown, and can be 
 readily understood. 
 
 A system such as this, 
 only worked by means 
 of flags, has long been 
 in use on shipboard, 
 and each ship is fur- 
 nished with a code by 
 which the crew can trans- 
 mit, and understand, 
 signals transmitted to 
 them by other ships. ' 
 
 Different coloured flags, 
 placed in different rela- 
 tive positions to one another, signify different numbers, and these numbers 
 in the code will mean different sentences. Thus an Admiral’s ship may 
 run up a few coloured flags to the masthead. The other ships of the 
 squadron immediately refer to their code, and find the number to which 
 that particular combination of flags is attached is, say 243. Then against 
 these figures they see the order “ weigh anchor” and they act ac- 
 cordingly. This is merely an imaginary case in order to demonstrate 
 the application of the system. 
 
 The heliograph comprehends a system of the same kind, only instead 
 of flags, we have here to deal with flashes, and I will now explain how 
 these flashes are converted into intelligible language. First we have 
 an alphabet, which like the Morse telegraph alphabet already detailed on 
 another page, is a system of longs and shorts, or dots and dashes. Only 
 in this case we have an alphabet of numbers, instead of letters. Thus : — 
 
 1 is expressed by a short flash _ 
 
 2 „ „ two „ flashes — 
 
 3 -)-) three ;; ;; — - — 
 
 4 „ „ four „ „ 
 
 & „ „ 
 
 6 „ one long flash — 
 
 7 „ „ a short and a long — _ 
 
 8 „ „ the reverse of 7 
 
 9 „ „ by — 
 
 10 „ „ by the reverse of 9 — 
 
 z 2 
 
340 
 
 BOY’S PLAl r BOOK OF SCIENCE. 
 
 An answering signal meaning that the receiver of the message 
 understands whatsis sent is expressed by alternate long and short 
 flashes, thus : — 
 
 The code is made up of hundreds of different sentences, of a nature 
 most likely to be required in warfare. And these sentences are 
 numbered consecutively. We may suppose that on opening the 
 code book we find the following at the top of one of the pages 
 
 1671. Send on cavalry at once. 
 
 1672. Our ammunition is failing. 
 
 1673. The enemy is preparing to attack. 
 
 The first sentence here quoted would be expressed in flashes thus 
 
 7 T ~7~ 1 
 
 On receiving such a signal, the officer in charge of the heliograph would 
 refer to the code, and immediately report to his commanding officer the 
 message conveyed. . 
 
 Not only in Zululand has this system proved of service, but it has 
 flashed signals across the wild passes of Afghanistan, and has done 
 much to mitigate the horrors of warfare in that country as well as in 
 
 other regions. . . .. . . , 
 
 It may be urged that without sunshine the heliograph is useless. 
 This has been provided for in the construction of a hugh timber frame 
 filled in with louvre boards like a Venetian blind. I he movement of 
 these boards is governed by a lever, on depression of which they take up 
 a horizontal or vertical position. When horizontal, their edges only 
 are in view of the distant observer, so that he can hardly see them at 
 all ; but when, by the action of the lever, they are placed edge to edge, 
 they form a dense square mass which is easily seen. By depressing 
 the lever for long or short periods, the long and short flashes are 
 mimicked, and so correspondence is carried on in the absence of sunshine. 
 
 We Londoners well know what a fog means, and it is evident that 
 no system such as this could be worked in one of those thick November 
 days such as we often have in the metropolis. This difficulty is also 
 met. Powerful fog horns, such as are used on our coasts, and on 
 ship-board in thick weather, are here called into play. The lungs, or 
 some other bellows, pump into the fog-horn sufficient wind to yield a 
 short or long sound, and once more the dot and dash system is rendered 
 available. I may here without any great digression introduce a story 
 about Mr. Edison, which is a good instance of the ready tact with 
 which he adapts to his wants anything that may be at hand. 
 
 The telegraph wire across one of the broad American rivers, for some 
 reason or other, suddenly refused to work. It was essential that 
 directions how to act should be immediately conveyed across. No boat 
 or other means of crossing was at hand. But on a railway line near, 
 stood a locomotive engine. Edison jumped on to the foot-plate, and in 
 another moment the whistle was shrieking dots and dashes to those 
 
THE REFRACTION OF LIGHT. 341 
 
 on the further side. Not long after an answering whistle was heard, 
 and arrangements were quickly made to repair the disaster. 
 
 At night, the flash system is of course easily carried on by means of 
 xamps. One of these constructed for the purpose is especially worthy 
 of notice. If consists essentially of a spirit lamp enclosed in a lantern. 
 Now a spirit lamp gives but a feeble blue flame, which cannot be seen 
 from any distance ; but it possesses plenty of heat, and this heat is 
 utilized for the flash system, by igniting a pyrotechnic mixture which 
 is blown into the flame when required. This mixture includes pow- 
 dered magnesium, and gives a most brilliant light. It is contained in 
 a small receptacle in the body of the lantern, and is urged into the 
 flame by means of an indiarubber tube which passes outside the lamp 
 to the operator’s mouth. A long breath or a short breath will here 
 once more illustrate the alphabet of dots and dashes. 
 
 The flashes from the heliograph can be seen and understood for at 
 least twenty miles. At night if the electric light be employed as 
 transmitter, this distance can be quadrupled, provided that the light 
 is placed sufficiently high to clear the convexity of the earth between 
 the sender and receiver. One more allusion to Mr. Edison and the 
 Morse system. He has two little children, and their nicknames are 
 “Dot” and “Dash.” 
 
 CHAPTER XXII. 
 
 THE REFRACTION OF LIGHT. 
 
 This term appears to be often confounded with that of reflection, and 
 signifies the bending or breaking back of a ray of light (re, back, and 
 frango, to break) ; and it will be remembered that when light falls on 
 the surface of a solid (either liquid or gaseous) body, it may be reflected 
 (re, back, and flecto, to bend), refracted, polarized, or absorbed. In the 
 previous chapter the property of the reflection of light has been fully 
 investigated, and in this one refraction only will be considered. It is 
 a property which has been, and will continue to be, of the greatest 
 practical utility in its application to the construction of all magnifying 
 glasses, whether belonging to the telescope, microscope, magic lantern, or 
 the dissolving views ; or the minor refracting instruments — such as spec- 
 tacles, opera-glasses, &c.; and it should be remembered that their 
 magnifying power depends solely on the property of refraction. 
 
 If substances such as glass had not been endowed with this property, 
 it . would be difficult to understand how the great discoveries in the 
 science of astronomy could have been made, or what information we 
 could have gained respecting those interesting truths so constantly 
 revealed by the aid of the microscope. Numerous instances might be 
 quoted of the value of this latter instrument in the detection of 
 adulteration, and the examination of organic structures. When so 
 many talented and industrious scientific men are at work with this 
 
342 
 
 boy’s playbook of science. 
 
 instrument, it is perhaps invidious to point to one singly, though we 
 must make an exception in favour of Professor Ehrenberg, of Berlin, 
 whosemicroscope did such good service in procuring undeniable proof of 
 the Simonides* fraud ; he has made use of it again to detect the thief 
 that stole a barrel of specie, which had been purloined on one of the 
 railways. One of a number of barrels, that should have contained 
 coin, was found on arrival at its destination to have been emptied of its 
 recious contents, and refilled with sand. On Professor Ehrenberg 
 eing consulted, he sent for samples of sand from all the stations along 
 the different lines of railway that the specie had passed, and by means 
 of his microscope identified the station from which the sand must have 
 been taken. The station once discovered, it was not difficult to hit 
 upon the culprit in the small number of employes on duty there. 
 
 The simplest case of refraction occurs in tracing the course of a ray 
 
 of light through the air, and into 
 the medium water; in this case it 
 passes from a rare to a dense me- 
 dium, and the fact itself is well 
 illustrated by the next diagram, in 
 which the shaded portion repre- 
 sents water, and the paper that it 
 is drawn upon the air. The line 
 a r is a perpendicular ray of light, 
 which passes straight from the air 
 into and through the water, with- 
 out being changed in its direction. 
 The line c d is another ray, inclined 
 from the perpendicular, and enter- 
 ing the water at an angle, does not 
 pass in the straight line indicated by the dotted line, but is refracted or 
 bent towards the perpendicular at d e. 
 
 This fact reduced to the brevity of scientific laws is thus expressed : — 
 When a ray of light falls perpendicularly on a refracting surface, it does 
 not experience any refraction or change of direction. When light passes 
 out of a rare into a dense medium, as from air into water, the angle of 
 incidence is greater than the angle of refraction. And when light passes 
 from a dense into a rare medium, as out of water into air, the reverse 
 takes place , and the angle of incidence is smaller than the angle of re- 
 fraction. 
 
 In order to illustrate these laws, a zinc-worker or tinman may con- 
 struct a. little tank, with glass windows in the front and sides, the 
 latter being as deep as the half-circle described on the back metal plate 
 of the tank, which of course rises higher, in order to show the full 
 circle ; this should be japanned white, and a perpendicular and hori- 
 zontal black line described upon it — the whole, with the exception of 
 the circle, being japanned black. If the Duboscq lantern is arranged 
 with the little mirror, as described in fig. 305, page 327, the ray of 
 light may be thrown perpendicularly, or at an angle, through the water, 
 
THE REFRACTION OF LIGHT, 
 
 343 
 
 and the actual breaking back of the ray of light is rendered distinctly 
 apparent. (Fig. 317.) 
 
 The refraction of light is also well displayed by Duboscq’s apparatus, 
 with the plano-convex lens, and a brass arrow as an object, with another 
 double convex lens to focus it. When a good sharp outline of the 
 arrow is obtained on the disc, a portion of the rays of light producing it 
 may then be truly broken out or refracted by laying across the brass 
 arrow a square bar of plate glass. (Fig. 318.) 
 
 the disc, and portion refracted at e. 
 
 There are many simple ways in which the refraction of light is dis- 
 played, such as the apparent breaking of an oar where it enters the 
 water, or the remarkable manner in which the bottom is lifted up when 
 we look, at any angle, through the clear water of a deep river or lake ; 
 the latter circumstance has unhappily led to most serious accidents, in 
 consequence of children being induced by the apparent shallowness of 
 
344 
 
 boy’s playbook of science. 
 
 the water to get in and bathe. Fish, again, unless &een perpendicularly 
 from a boat, always appear nearer than their true position, and the 
 Indians, when they spear fish, always take care to strike as near the 
 perpendicular as possible ; experienced shots know they must aim a 
 little lower and nearer than the apparent position of a fish in order to 
 hit it. 
 
 Having learnt that light is bent from its course, it might be supposed 
 that all objects looked at through plate glass should appear distorted ; 
 but it must be remembered that the sides of the glass being nearly 
 parallel, an equal amount of refraction occurs in every direction — so 
 that, unless the window is glazed with uneven wavy glass, the object, 
 for all practical purposes, does not apparently change its position, being 
 neither moved to the right or the left, or upward or downward. In 
 order to bend the rays of light in the required direction, the glass must 
 be cut into certain figures called prisms, plane glasses, spheres, and 
 lenses, some of which are shown in the annexed cut. (Fig. 319.) 
 
 Fig. 319. 
 
 It would be tedious to trace out, by a regular series of diagrams, the 
 passage of light through the variety of combinations of lenses ; and as 
 
 the plane, convex, and concave 
 
 D ^ surfaces have been examined with 
 
 respect to their effect on the re- 
 flection of light, they may be re- 
 ferred to again with regard to 
 their influence in refracting light. 
 In the latter it will be found that 
 convex and concave lenses have 
 Fig. 320. a b. A double convex lens, c is a just the opposite properties of 
 ray of light, which falls perpendicularly on a b, m j rrnrq . t u s a nnnvpx lens re- 
 and therefore passes on straight to f, the focus. , IUUS, a convex leilS re 
 
 d d. Bays falling at an angle on a b, refracted ceiVing parallel rays Will Cause 
 to focus, f. them to converge to a focus. 
 
 (Fig. 320.) The case of short-sighted persons arises from too great a 
 convexity of the eye, which makes a very near focus ; and that of old 
 people is a flattening of the eye, by which the focus is thrown to a 
 greater distance. The remedy for the latter is a convex spectacle glass, 
 whilst a concave lens is required for the former, to scatter the rays and 
 prevent their coming to a point too soon. 
 
GLASS LENSES. 
 
 315 
 
 The action of a concave re- 
 fracting surface is again the op- 
 posite to a concave reflecting 
 surface — the former disperses 
 the rays of light, whilst the latter 
 collects them. A concave lens, 
 as might be expected, produces 
 exactly the contrary effect on 
 light to that of a concave mirror. 
 
 (Eig. 321.) Fig. 321. a b. A double concave lens, c Isa 
 
 These facts are well shown raj 'of light which falls ; perpendicularly on a b. 
 
 .j „ , and passes through without any alteration of its 
 
 Wltll the aid 01 the lantern and course, d d. Rays falling at an angle on a b. 
 
 electric light. The rays of light are refracted and diverged 
 
 are refracted in a visible manner when received on a concave or convex 
 lens, provided a little smoke from paper is employed, as in the mirrot 
 experiments. (Fig. 322.) 
 
 Bearing these elementary truths in mind, it will not be difficult to 
 follow out a complete set of illustrations explanatory of the construc- 
 tion and use of various popular optical contrivances. 
 
346 
 
 CHAPTER XXIII. 
 
 RETRACTING OPTICAL INSTRUMENTS. 
 
 I. The Magic Lantern . 
 
 The most popular of all optical instruments is undoubtedly the magic 
 lantern. Unlike the microscope, telescope, and other contrivances which 
 uan only be used by one person at a time, the lantern can be made the 
 medium of amusement or instruction for large audiences. And since the 
 introduction of photographic pictures to replace the coarsely painted 
 slides hitherto in use, it has become a valuable educational help. 
 
 The common toy lantern (Eig. 323) consists of a tin box crowned 
 with a bent chimney, so that the hot air can be carried off without any 
 escape of light. Within this box is an oil lamp and a reflector. The 
 lenses are placed opposite the reflector, 
 and consist of a condenser — to illuminate 
 the glass picture or slide— and the objec- 
 tive, which magnifies the picture upon the 
 sheet or screen placed for its reception. 
 This form of lantern is but a toy, and the 
 effects produced by it are only fit for the 
 amusement of very little folk. Still its 
 description, so far as the relative positions 
 of the glasses and lamps are concerned, 
 would apply generally to the arrange- 
 ments of the most perfect instruments 
 made. 
 
 The magic lantern was much improved 
 by the introduction of the Argand lamp, 
 Fig. 323. ‘ The magic lantern, in which ordinary coal gas was burnt. 
 
 But of late years parafin oil has been 
 applied to magic lantern lamps, and seems to have caused quite a 
 revolution in both lamps and lanterns. The first lantern constructed 
 to burn this oil was named the sciopticon (or caster of shadows), 
 and it still deservedly holds the first place among instruments of this 
 class. As will be seen by the following cut, its outward form differs 
 materially from what we have been accustomed to look for in a magic 
 lantern. Instead of being square, it is cylindrical, its various parts 
 being so adjusted that there is no wasted space. Erom experience I can 
 testify to its general excellence. It can be used with the oil lamp or with 
 the oxy-hydrogen burner, each lantern being so arranged that either form 
 of light can be adopted. The lamp consists of a double flame from two 
 wicks placed edgeways, and the light given is so great that an eight-foot 
 disc can be illuminated with great brilliancy. This will be sufficiently 
 
THE MAGIC LANTERN. 
 
 347 
 
 large for any ordinary room. 
 The general arrangement 
 of the instrument can be 
 readily understood from 
 the sectional cut shown at 
 Ti g. 325. 
 
 In the most recent form 
 of sciopticon, the lamp and 
 flame chamber are remov- 
 able, and take the form 
 shown in Tigs. 326 and 
 327. A great improve- 
 ment has also been effected 
 in the focussing arrange- 
 ment, which the company 
 thus describe. “The im- 
 provement consists in aban- 
 doning the old-fashioned 
 
 wju.ttawcK.ssJl 
 Fig-. 324. Sciopticon 
 
 Fig. 325. p q. Condensing lens. s. Body of lamp containing the paratin oil. t. Nozzle 
 to screw off to replenish oil supply, w w. Buttons to adjust height of wicks g g. Front 
 and back of flame chamber, e' e" e"'. Bottom of flame chamber, h. Reflector — forming 
 back of instrument, b. Chimney, j. Chimney cap, to prevent escape of light, o. Stage 
 for slides, with arched wire spring to keep them firmly in position. For showing photo- 
 graphic slides a carrier is used, the glass pictures running in a groove and following one 
 another as required. 
 
348 
 
 boy’s playbook of science. 
 
 Fig. 326. Lamp uncovered. ' 
 
 plan of fixing the slide in the same place, and focussing with the lens* 
 lor the scientific optical principle of first adjusting the front lens so that 
 the whole of the cone of light coming from the 
 condensers passes through it on to the screen, 
 and then focussing with the slide. The advantage 
 is twofold — first, the slide being in its correct 
 optical position almost perfect sharpness is ob- 
 tained all over the disc; secondly, the slide 
 being brought forward into the cone, it is better 
 lighted. By adjusting the distance from the 
 screen so that the slide when in focus is in that 
 part of the cone which has the same diameter as 
 the mount of the slide, it is evident that the whole of the light will 
 pass through the picture. 
 
 The lantern slides produced by the Sciopticon 
 Company are of very excellent quality. They are 
 printed on glass by the Woodbury process, an inge- 
 nious method of reproducing a photographic picture 
 by an ordinary printing press. A brief outline of the 
 process by which these Woodbury slides are produced 
 will not be out of place. 
 
 In the chapter on photography we have already 
 seen that gelatine impregnated with the dichromate 
 of an alkali becomes insoluble after exposure to light. 
 It is, so to speak, tanned. A gelatine film thus 
 treated is placed under a negative and exposed to 
 light, with the result that those parts of the negative 
 through which the light passes with the least inter- 
 ruption are reproduced upon the gelatine as places of 
 insolubility. The film is then placed in hot water* 
 when the non-protected parts are melted out, leav- 
 ing the picture in relief. Although this film is 
 so delicate that 300 pictures placed one above the other will measure 
 scarcely an inch in thickness, it will bear enormous pressure. The 
 Sciopticon Company thus describe the rest of the operations required 
 in producing the slide. “ It is in relief, that is, the darkest parts are 
 the thickest. To produce the prints or slides, an intaglio mould is 
 required. Upon a prefectly true steel plate the film is laid, upon that 
 a piece of lead, the whole is then subjected to enormous pressure in a 
 hydraulic press till every part of the relief is crushed into the metal, the 
 result being a perfect intaglio mould, with every gradation of shadow 
 accurately represented by a proportionate depth of hollow. The 
 gossamer web or relief is uninjured, and will serve again and again. 
 
 “ Upon this mould a coloured, hot, gelatinous ink is poured, a piece of 
 perfectly true plate glass pressed down upon it, squeezing out all the 
 superfluous ink. In a few minutes it is cold, the glass is removed with 
 the coloured gelatine adhering to it — the slide is made.” 
 
 Fig. 327. 
 Lamp complete. 
 
screen at the Polytechnic during the exhibition of the dioramic effects 
 
THE MAGIC LANTERN. 
 
 349 
 
 inch. Less will suffice, even the g-J^th. This represents the deepest 
 .shadows, and yet every possible gradation of tone is faithfully repro- 
 duced. How fine the colour must be may be judged from the fact, that a 
 Woodbury lantern slide will not contain more than a fiftieth of a grain of 
 carbon, which is the principal colouring matter, many not the half of that.” 
 
 The next form of lantern to which I will direct attention is the bi- 
 unial (Fig. 328). This is one of the most convenient forms for ex- 
 
 Fig. 328. Biunnial lantern. 
 
 hibitions of dissolving views. I am in the habit of using such a lantern 
 for illustrating my lectures. It was made for me by Mr. J. H. Steward, 
 406, Strand, and I have every reason to be satisfied with it. It consists of 
 a mahogany body lined with sheet iron, with openings at the back through 
 which the ends of the lime jets are seen protruding. In the front are two 
 stages made of brass, for the reception of the slides, and these stages can 
 be so adjusted by screws that the two luminous discs upon the screen are 
 made concentric. In front of these stages are the object glasses, the 4-inch 
 condensers fitting into cells placed behind them. 
 
 The effect of one view dissolving into another had long a mystery 
 attached to it, for the inventor kept the manner of its production a secret. 
 But this secret, like many others, has long ago become public property. 
 The original plan was to cause a toothed screen to gradually cover the 
 opening of. one lens, while a similar screen uncovered the orifice of the 
 other. This plan has given place to another which has the advantage of 
 
350 
 
 boy’s playbook of science. 
 
 savin" fifty per cent, of the gas used, for the dissolving is now effected 
 by turning down one jet, while the other is gradually turned up. The 
 manipulation of four taps to attain this end, would be rather a formid- 
 able task for one operator, so the plan of a dissolving tap governing the 
 whole gas system is now universally adopted. This tap is shown, at 
 Tig. 329. 
 
 To 
 
 oxygen 
 of 
 
 bottom 
 jet. 
 
 To 
 
 oxygen 
 
 of 
 
 top jet. 
 
 Supply 
 pipe 
 from 
 oxygen 
 bag. 
 
 Fig. 329. Dissolving tap. 
 
 When the handle of the dissolver is placed upright as shown, both 
 lanterns are furnished with light, but shifted to the right or left, only 
 one lens is illuminated. The small upright pipes which cross the others 
 on each side of the centre of the instrument, are by-passes for the 
 gas, so that neither light is ever actually turned out. 
 
 Many exhibitors use a triple lantern. The capabilities of this instru- 
 ment are indeed enormous. The two lower lenses are used for ordinary 
 dissolving views, whilst that above is reserved for what are known as 
 “effects.” Thus, suppose a summer landscape in the lowest lantern is 
 dissolved into a winter picture placed in the next above ; the topmost 
 stage can then be employed in the production of falling snow. This 
 last effect is managed by rolling up a ribbon of opaque material pierced 
 with needle pricks, the upward motion being inverted by the lens into 
 a downward movement upon the screen. Effects of lightning, moving 
 smoke, explosions and the like, can all be easily portrayed by this 
 splendid apparatus. 
 
 At the Polytechnic sometimes six lanterns are in use at one and the 
 same time ; besides a host of accessory apparatus behind the screen for 
 the production of noise — thunder, wind, cannon shots, the roars of 
 hungry beasts, &c., &c., are all imitated with great success. A plate is 
 appended representing the efforts to imitate the horrors of war during 
 the exhibition of the siege of Delhi. 
 
 To 
 
 hydrogen 
 of top jet. 
 
 To 
 
 hydrogen 
 of bottom 
 jet. 
 
 Supply 
 pipe from 
 hydrogen 
 bag. 
 
THE MAGIC LANTERN. 
 
 351 
 
 The best form of oxyhydrogen, or limelight for the magic lantern is 
 undoubtedly that known as the “ mixed jet” in which the two gases 
 are combined just before they are projected upon the cylinder of lime. 
 
 Eig. 330. 
 
 The two gases must in this instance be under equal pressure, and a 
 most ingenious form of double pressure board lias been devised by 
 Mr. Malden to attain this end. In inexperienced hands, however, the 
 mixed jet has an element of danger in its use which it is as well to 
 avoid. If the pressure upon one bag become by any accident reduced, 
 the other gas is forced into it, and a most dangerous explosion may 
 
552 
 
 boy’s playbook of science. 
 
 ensue. The difficulty is altogether obviated by using the blow* through 
 jet, shown at Eig. 331. If ordinary care be used, this form of jet is 
 
 absolutely safe, for the two gases do not make acquaintance until they 
 meet at the lime cylinder. This cylinder is placed upon the upright 
 wire which passes through a hole in its centre. A milled screw at the 
 back communicates by a spiral spring, with a little metallic disc upon 
 which the lime rests. A half turn of this screw will expose a fresh 
 part of the cylinder to the flame when necessary. Ordinary house gas, 
 (carburetted hydrogen) is used with this burner, and it is supplied 
 direct to the lantern by means of an indiarubber tube from the nearest 
 gas bracket or chandelier. The oxygen alone is under pressure, and 
 this may be supplied from a bag between weighted pressure boards, from 
 a charged iron bottle, or it can be generated as it is wanted in the way 
 to be presently described. > . 
 
 Perhaps the most convenient way to obtain oxygen ready made (it is 
 hardly worth while to make it at home, but if this be preferred the 
 operation is described in a former page) is to buy it compressed in an 
 iron cylinder (see Eig. 332). Eor a long time nitrous oxide, for the use 
 
 Fig. 332. Orchard’s gas bottle. 
 
 of dentists, has been supplied in this manner. Mr. Orchard, of 100, High 
 Street, Kensington, has turned his attention to the manufacture of 
 gases, and supplies oxygen for lantern work in such a compressed 
 state, that 15 feet of gas are contained in a bottle little more than two 
 feet long, and five inches in diameter. This quantity will serve for two 
 evening’s entertainment. An indiarubber tube is connected with the 
 nozzle of the bottle, the other end being forced over the oxygen supply 
 pipe of the lantern. A key is then inserted in an orifice in the side ot 
 the nozzle, a half turn of which will cause the gas to steadily flow out. 
 Care must be taken to leave the jet tap open, and to regulate the 
 supply from the bottle itself, or the connecting tube may burst from the 
 gas confined within it. As the pressure is gradually reduced by con- 
 sumption of gas, it will be necessary to turn the key a little more once 
 or twice during an exhibition. This mode of using oxygen gas is most 
 convenient as well as economical, for it is supplied at a very cheap rate. 
 
THE MAGIC LANTERN. 
 
 353 
 
 The method of generating the gas as required is the device of Mr. 
 Chadwick. The retort used (Fig. 333) is of very ingenious construc- 
 tion. In the orifice on the right hand side is placed a Bunsen burner, 
 which heats a plate of iron above. Upon this plate is placed a moulded 
 cake of oxygen mixture (four parts of chlorate of potash to one of man- 
 ganese). As the gas is generated, it is passed off by the pipe above to a 
 -gas-holder. Should this outlet pipe by any means become stopped up, 
 the lid of the retort hung upon spiral springs, seen at the side, rises by 
 the pressure of the gas, and thus all risk of explosion is obviated. 
 
 Fig. 334. 
 
 Fig. 333. 
 
 The next illustration (Fig. 334) 
 represents a sciopticon filled to tin 
 top of a gas-holder, which can be 
 supplied with oxygen in the way just 
 described. 
 
 A form of lamp for using incan- 
 descent lime without oxygen, except 
 that supplied by atmospheric air, has 
 been introduced by Mr. Woodbury (see Fig. 335). In this lamp com- 
 mon house gas is used and fulfils a double office. At the top is a larn-e 
 Bunsen burner which heats a coil of pipe, which finds its outlet in the 
 iarger pipe which projects above a disc of lime. The other end of the 
 coiled pipe is attached to a foot bellows. The air from this source 
 therefore gets intensely heated before projecting a blowpipe flame upon 
 the lime The light given, while not so bright as the oxyhydiogen 
 name, is beautifully white, and one cannot help thinking that a modification 
 ot the arrangement would be most useful in many other fields. The 
 
354 
 
 boy’s playbook of science. 
 
 magnesium lamp has also been suggested for lantern work, but, although 
 it gives a magnificent light, there are one or two great objections to its 
 use. It is not only expensive, but the fumes given off require an 
 outlet pipe to the open air. It is occasionally 
 used by photographers where a bright light is 
 now and then required for enlarging pictures. 
 I may here mention that the sciopticon oil 
 lamp fulfils this last office admirably. 
 
 II. The Oxy -Hydrogen Microscope. 
 
 The oxyhydrogen microscope is one of the 
 most instructive, as well as entertaining instru- 
 ments which has yet been added to the capa- 
 bilities of the lantern. It introduces us to a 
 world of wonders and fairy forms that altogether 
 surpass the greatest efforts of the imagination. 
 Indeed the old saying that “Truth is stranger 
 than fiction” receives here a startling confirma- 
 tion. The instrument is now to be had in a most 
 convenient form (see Tig. 336). It can be 
 readily screwed on to the lantern in place of 
 the usual lens, and it has an opening above 
 through which microscopic slides, or a live tank can be admitted for 
 projection upon the screen. 
 
 Fig. 335. 
 
 Fig. 336. Browning’s new lantern microscope. J 
 
 The pleasure in using this instrument is much enhanced by the con- 
 sideration that the objects it shows can be collected and prepared by the 
 operator himself, an occupation which will afford him many a pleasant 
 ramble over hill and dale. There is no difficulty in finding subjects for 
 examination, the difficulty lying rather in deciding which to select from 
 such a museum of curiosities as everything in Nature affords. The animal, 
 vegetable, and mineral kingdoms are all open to such investigations, 
 and the more we come to examine them in detail by means of the 
 microscope, the more shall we wonder at the inexhaustive beauty of 
 their minute component parts. e . . 
 
 Should the inquirer into Nature’s secrets wish to begin upon living 
 things, he has merely to visit the nearest pond, and fish lor specimens. 
 A bottle with a piece of string attached to its neck is all the fishing 
 tackle he requires. This bottle held upside down is carefully lowered 
 towards the unsuspecting insect whose capture is desired. It is then 
 turned a little on one side, the water flows in, and with it the prisoner. 
 
THE CHOREUTOSCOPE. 
 
 355 
 
 In this way rotifers and many other interesting creatures can be readily 
 bottle 116 SpeClmens as they are ca P tured being put into a reserve 
 
 The mud from the bottom of any pool will also furnish abundant 
 material tor the microscope. A small portion of this mud should be 
 placed in a test tube and covered with nitric acid with extreme care — 
 lor the acid is fearfully corrosive and gives off deleterious fumes— 
 
 aD Hi be rru r ?7 e . r a lamp for some minut es and allowed to 
 
 settle. The liquid is carefully poured off, and a second dose of nitric 
 acid applied and treated as before. The residue is then carefully washed 
 and some of it examined under a microscope. It will be found to con’ 
 tam innumerable flinty skeletons of former inhabitants of the pond. The 
 -Jrj of these can be mounted in Canada balsam and used as ordinary 
 slides. Wings of flies, butterflies, and moths, wing-cases of beetles,, 
 scales of fishes, and host of other things will also furnish beautiful 
 subjects for examination. 
 
 In the vegetable kingdom, the leaves and petals of flowers, ferns, and 
 mosses, Ornish inexhaustible subjects for study. Sections of different 
 
 objects^ W °° d ’ CUt Wlth ° r aCr ° SS the grain ’ are als ° m0st interestin g 
 
 The limits of this. work will only allow me to briefly refer to the 
 capabilities of the microscope, but those who would wish to learn more 
 about the matter, and to gain a knowledge regarding the preparation of 
 objects, cannot do better than consult the admirable little manual by the 
 Rev J G Wood “Common Objects of the Microscope.” Although, 
 this book deals only with the more usual form of instrument, the greater 
 part of the information which it contains can be well applied to the oxy- 
 hydrogen microscope. J 
 
 III. The Choreutoscope. 
 
 This instrument, the invention of Mr. John Beale, of Greenwich is- 
 one of the most ingenious and diverting adjuncts to the lantern which 
 has ever been devised. Like the thaumatrope, it is dependent for its 
 eflect upon the duration of impressions of light upon the retina. It 
 consists of a slide upon which is depicted a figure in six or eight different 
 positions. This slide is held in a metal frame, and by the motion of a 
 handle the various figures painted upon it are brought opposite an 
 opening which corresponds with the lens orifice of the lantern By a 
 clever contrivance, a little shutter falls in front of this opening between 
 the exhibition of every successive figure, and when the instrument is 
 properly worked the various figures appear upon the screen in such quick 
 succession that they present the appearance of a single being endowed 
 with endless motion. One of the best designs for the choreutoscope is 
 a skeleton, not painted upon glass, but cut out stencil fashion from a 
 sheet of thin brass. By this means the whole of the light from the 
 lantern js carried through the perforations to the disc, and a wonderfully 
 brilliant image is the result. The annexed illustrations have been copied, 
 direct from the stencil figures in my possession, so that they represent 
 the exact size of those actually used. I need hardly say that they da 
 
 A A 2 
 
356 boy’s playbook of science. 
 
 not pretend to be anatomically correct, but are merely conventional 
 representations of a skeleton. They answer their purpose admirably, 
 and the roars of laughter which their appearance always calls forth must 
 be beard to be appreciated. 
 
 £• 0 ^ 1 f /l|>\ 
 
 A If A 
 
 I -YJsiA.il. 
 
 Fig. 337. 
 
 Mr. Beale is also the inventor of another quaint conceit for the lantern 
 which must not pass unnoticed, and which he has christened The 
 Rinker.” As its name implies it consists of a skating figure, which is 
 
 A®/\ 
 
 m'w'rm 
 
 rr 
 
 i \ 
 
 
 n 
 
 Fig. 338 . 
 
 so contrived that it throws its arms and legs about, and tumbles down 
 in the most amusing manner. This figure is cut out of thin metal, 
 
THE OPAQUE LANTERN. 
 
 357 
 
 having at its upper part grooves into which a piece of glass is inserted. 
 Upon this slip of glass is painted the face and shirt front. The annexed 
 cut will explain the manner in which the various parts are jointed 
 together, the levers shown at the left-hand side giving the figure 
 apparent life.. The arrangement is backed by a glass slide upon which 
 is painted a wintry landscape, and the effect when seen upon the disc is 
 very comical. 
 
 IV. The Opaque Lantern . 
 
 A great many attempts have been made, with more or less success, to 
 cast, the image of opaque objects upon the screen. The first instrument 
 devised for this purpose was Chadburn’s lantern, in which the light from 
 the condenser was concentrated upon the object, the objective being 
 placed at such an angle as to magnify the image upon the screen. It is 
 usual with this form of lantern to use a large jet, for the amount of light 
 lost in transmission is considerable. Such a lantern has long been used 
 at the Polytechnic, and some very curious effects are produced by it. 
 The moving works of a watch appear on the screen in Brobdingnagian 
 proportions. A . squeezed lemon also forms a favourite subject for 
 exhibition. . As the cells burst under the pressure applied to them, the 
 pips and juice are forced out, and fly upwards, for of course in this in- 
 strument everything is reversed. 
 
 A modification of this lantern has also been used with success under 
 the name of the Physioscope, in which the inversion of the image is 
 corrected. This apparatus is large enough to admit the human face, 
 and the same magnified to colossal size is seen upon the screen. The 
 effect of this immense countenance winking and blinking at the audience 
 was always productive of considerable amusement. The exhibition 
 usually finished with the image drinking off a glass of wine. This was 
 not only relished by the audience, but also by the unfortunate being 
 who had been for some minutes exposing his features to the fierce heat 
 of two large limelights. 
 
358 
 
 boy’s playbook of science. 
 
 A recent adaptation of the opaque lantern to fit on an ordinary 
 lantern, or better still to a pair of lanterns, has recently been introduced 
 under the name of the “ Aphengescope. ,, With this all the effects 
 named in connection with Chadburn’s lantern can be obtained, carte 
 de visite of friends or public characters being shown by it to great 
 advantage. Collections of coins or medals are peculiarly w r eli adapted 
 for exhibition, for their bright surfaces and points of relief catch the 
 rays of light with a very pleasing effect upon the screen. 
 
 According to a New York paper of recent date our American friends 
 have lately discovered a new use for the opaque lantern. “ During the 
 recent trial of the Whittaker will case in Philadelphia, it became 
 necessary to show the differences between a genuine signature and an 
 imitation or forgery of the same. Eor this purpose Dr. Charles M. Cresson 
 brought into court a powerful reflecting magic lantern. The room was 
 darkened, and images of the two signatures, enormously magnified, were 
 thrown side by side upon a screen before the judge and jury. The false 
 signature was at once revealed. In the ordinary magic lantern the 
 object to be thrown on the screen is photographed or painted on a slide 
 of glass, and the light passes through the slide to the screen ; in the 
 reflecting (or opaque) lantern the light is thrown against the face of the 
 object itself, and as the reflected rays from the object appear on the 
 screen, a stronger light is required for the opaque lantern than for the 
 ordinary instrument. In the present case the illumination of the 
 writing was effected by means of two powerful limelights contained 
 within the lantern.” 
 
 “The peculiar arrangement of the lights and screen enables the 
 examiner to discover the surface of the paper through the ink, so that 
 patching or shading or painting of letters becomes evident the instant 
 it is brought under the focus of the lantern. An arrangement of screens, 
 by which the light is cut off alternately from either side of the instru- 
 ment, discovers any tampering with the surface of the paper, either by 
 scratching or washing by chemicals. The instrument is of sufficient 
 •capacity to view at once two bank notes placed side by side, and the 
 pictures are of such fineness that the image is produced without colour 
 from chromatic aberration, or distortion from spherical aberration.” 
 
 I need hardly point out that this useful field for the opaque lantern 
 ds capable of great extension. It will not only act as a check upon 
 fraudulent documents, but will perhaps act as a stimulus to those 
 people who endeavour to shirk the duty of serving upon juries. Surely 
 no one could refuse to act when there is the prospect of a “ lantern 
 •show” before him ! 
 
 Y. Lantern Experiments. 
 
 There are some experiments both in chemistry and physics which can 
 perhaps be better seen by means of the lantern than in any other way. 
 Indeed, the number of delightful experiments that can be performed in 
 miniature but shown largely magnified upon the screen is very great. 
 Thus, suppose we take magnetism to begin with. Take a piece of thin 
 
LANTERN EXPERIMENTS. 
 
 359 
 
 glass, the size to fit the slide holder, and cover it with a solution of 
 common gum. When perfectly dry, place it above the poles of an 
 ordmary sixpenny horseshoe magnet, so that the ends of the magnet 
 are just under its centre. Now from a fine muslin bag scatter upon the 
 glass iron filings. Tap the glass gently with the finger, and the parti- 
 cles of iron will assume definite positions, showing most beautifully the 
 magnetic curves. Upon breathing upon the glass, the gum will be so 
 softened as to cause the filings to retain their position when placed 
 vertically in the lantern, and the curves in all their beauty will appear 
 greatly magnified upon the screen. 
 
 By another arrangement we can show the electro-magnet upon the 
 screen. The slide for this is shown in Big. 340. It consists of a 
 
 
 Fig 1 . 340. Lantern slide to show effects of magnetism. 
 
 wooden frame to which is fastened a piece of soft iron, bent so that its 
 ends nearly approach one another. Several thicknesses of covered 
 C0 PP. ® r wire are wound round each end, their extremities being carried 
 outside the frame for ready attachment to a small bichromate battery 
 ce . * "" .^°P ls a through both frame and iron, through 
 
 which the various metals, &c., under examination can be introduced 
 between the magnetic poles. Having focussed the image of the 
 magnet sharply upon the screen, we can scatter filings through the 
 hole, when we shall obtain much the same result as in the previous 
 experiment Or we may fasten small discs of different metals to fila- 
 ments or silk, and watch the effect of the magnet upon them Thus 
 iron will assume a different position to a disc of copper, or bismuth, 
 the lormer being a magnetic substance, and the two latter diamagnetic. 
 
 the decomposition of water by the electric current is also an effective 
 experiment for the lantern. For this as well as for several chemical 
 experiments which I shall presently describe, a water-tight glass cell 
 33 necessar f- A very ingenious cell has recently been devised by 
 
360 
 
 boy’s playbook of science. 
 
 Mr. Smith of the Sciopticon Company, (see Fig. 341). It consists of a 
 mahogany frame, inserted into the round opening of which are two 
 
 glass plates, separated by a piece 
 of red indiarubber tubing. The 
 pressure of the glass surfaces 
 against theflexible rubber makes 
 the cell perfectly water-tight, and 
 the ease with which the glasses 
 can be removed, cleaned, and 
 replaced in a few seconds, makes 
 this a most useful piece of ap- 
 Fig. 341. Chemical-tank. parat.us. . For showing the de- 
 
 composition of water this tank 
 will require an adjunct which can easily be constructed. Take a piece of 
 mahogany which will just fit between the glasses, and which is the same 
 width as the tank. Bore two holes in its centre about one inch apart. 
 These holes are for the reception of copper wires, to the ends of which 
 pieces of platinum foil must be soldered. The wood should be soaked 
 in melted parafin, so that it may resist the action of the acidulated 
 water with which the tank is afterwards filled. The wires also coated 
 with parafin are carried outside the lantern to a battery, two Groves’ 
 or Bunsen’s being sufficient. When connection is made, bubbles of 
 oxygen will appear at one pole, and hydrogen at the other. The 
 apparatus may be made still more complete by crowning the electrodes 
 with small test tubes in which the gases will collect, that devoted 
 to the hydrogen filling with gas at double the rate of the oxygen 
 tube, thus proving the truth of the chemical symbol for water H 2 0. 
 
 The formation of hydrogen alone, can be shown by dropping a few 
 pieces of granulated zinc to the bottom of the tank when filled with 
 acidulated water (i.e., water soured by sulphuric acid). Or should we 
 wish to obtain carbonic acid, we can readily do so by replacing the 
 sulphuric by a dilute solution of hydrochloric acid, and dropping in 
 pieces of lime instead of zinc. 
 
 Fig. 342. 
 
 Fig. 343. 
 
 Capillary attraction is well shown by the slides shown at Figs. 342 
 and 343. In Fig. 342 a series of glass tubes of different diameter are 
 
LANTERN EXPERIMENTS. 361 
 
 suspended above the water, when the liquid — which should be coloured 
 or darkened with ink — will attain different levels in the different tubes. 
 In Pig. 313, two slanting glass-plates are adjusted, and the water rises 
 between them in a regular curve. 
 
 For many of the chemical experiments pipettes furnished with an 
 indiarubber ball, will be found useful if not indispensable. (See 
 Pig. 314.) 
 
 Eig. 344. Pipette for chemical experiments. 
 
 1 . Pill the tank with a solution of sulphate of iron, then add to it by 
 means of the pipette a solution of prussiate of potash for the formation 
 of prussian blue. 
 
 2. To a weak solution of sulphate of copper, add a few drops of strong 
 ammonia — beautiful blue clouds will become apparent on the screen. 
 
 3. Sulphate of iron on the addition of gallic acid will give dense 
 clouds of ink. 
 
 4. Into an infusion of red cabbage drop some alum : it will change 
 the colour to purple. A solution of potash will turn it green, and 
 muriatic acid crimson. By dropping the three solutions into different 
 parts of the tank, the three colours will appear at the same time. 
 
 5. A solution of salt dropped into one of nitrate of silver will show 
 the formation of insoluble chloride. 
 
 This last experiment might well form the first of a series illustrating, 
 the art of photography. Thus a plate can be coated with collodion 
 emulsion, dried and exposed under a negative to a gaslight for a few 
 seconds, and developed in the glass cell. To do this the cell must 
 have a piece of ruby glass inserted between it and the light. It is now 
 filled with the alkaline developer (see article on Photography) when the 
 details of the picture will be gradually formed on the plate placed within 
 it. The process is completed by filling the tank with a solution of 
 hyposulphite of soda, to clear and fix the image. In this last operation the 
 ruby glass can be omitted, for the plate is no longer sensitive to light 
 after development. The photograph so taken can afterwards be mounted 
 and used as an ordinary slide. In mounting a slide, a piece of thin glass 
 must be placed in front of the film, with a paper mask between them. 
 This mask is usually cut out of black paper, and may be round, cushion- 
 shaped, or square in outline. The best and quickest way to cut any 
 number is to use a brass pattern, to place the black paper beneath it, 
 and then cut the paper with the ingenious 
 little tool shown at Pig. 345, which is 
 supplied by the Sciopticon Company for 
 that purpose. The slide is completed by 345 - 
 
 being bound round with a strip of needle paper, which holds the two glasses 
 together, and protects the picture from that enemy of the lanternist— dust. 
 
362 
 
 BOY S PLAYBOOK OF SCIENCE. 
 
 The formation of ice flowers can be beautifully seen by inserting a 
 thin slab of ice into the slide aperture, when the effect is observable as 
 the ice slowly melts under the heat from the condensers. 
 
 By filling the tank with methylated alcohol and adding a few drops of 
 Judson’s dyes of different colours, some very fine effects can be obtained. 
 
 Slips of glass brushed over with solutions of different salts in gum 
 water, will speedily crystallize ; and the varying forms of different 
 crystals can be well studied by this means. Sal-ammoniac yields very 
 fine results when treated in this way. And a solution of urea in 
 alcohol will show crystals of a totally different kind. I merely mention 
 these two as being good specimens to contrast with one another. 
 
 Another experiment I borrow from an excellent little manual 
 called “ Science at Home,” by Mr. Woodbury. He says “Coat a piece 
 of glass with a strong solution of chloride of cobalt, to which a little 
 gelatine has been added. When dry, introduce this with an ordinary 
 photographic slide ; at first the effect will be to give a rosy tint to the 
 view, which, as the cobalt becomes thoroughly desiccated by the 
 warmth from the lantern, will gradually change to a bright blue. On 
 again placing in a damp place, the slide will assume its normal pink 
 state, and may be used over and over again. This experiment may be 
 varied by painting a picture on glass with a solution of cobalt and gum, 
 which from a pink will change to a blue ; or by using a much weaker 
 solution the picture will be invisible, but on warming gradually, will 
 develop itself on the screen. Other chemicals will show a similar 
 action, but cobalt is the most effective.” 
 
 I may well conclude this chapter with a few words respecting the 
 colouring of magic lantern slides. Most amateur efforts in this line of 
 
 Fig. 346. 
 
 art are attended with utter failure, the reason being that too much is 
 attempted. It is quite certain that he who cannot produce a satis- 
 factory result upon paper, need not hope for success in working upon 
 the smooth surface of a glass plate. The resulting picture has more- 
 over to be reproduced upon the screen so magnified that every defect is 
 
THE ANALYSIS OF LIGHT. 
 
 363 
 
 exaggerated. A speck of dust or a hair from the paintbrush is quite 
 enough to spoil a sky, and unless the greatest care is exercised such 
 accidents are frequent. Although few are able to originate a picture, 
 there are many who can tint a photograph satisfactorily. I use the 
 word tint advisedly, for a photograph loses its beauty by any approach 
 to full colouring. Water colours may be used, but they are somewhat 
 difficult of manipulation. I have found Messrs. Barnard’s varnish 
 colours, which are made for the purpose, to answer all requirements. 
 Bull instructions are issued with each box of colours, and to these I 
 must refer any aspirant to artistic honours. 
 
 YI. The Decomposition of Light — “ its Analysis and Synthesis .” 
 
 It is in the Italian language that the bride, the emblem of purity, is 
 called Lucia {Lux, light) ; and surely if an illustration were required of 
 beauty and singleness, light would be named 
 poetically as appropriate; but physically it is 
 not of a single nature, it is composite, and made 
 up of seven colours. The instrument required 
 to refract a ray of light sufficiently to break it 
 into its elementary colours is called the prism, 
 and is a solid having two plane surfaces, called 
 its refracting surfaces, with a base equally in- 
 clined to them. (Big. 347.) 
 
 It was in 1672 that Sir Isaac Newton made B Moi 347 The rigm The 
 his celebrated analysis of light, by receiving basefi equaUyYnSined to 
 a sunbeam (as it passed through a hole in a the refracting surfaces, ca,cb. 
 shutter) on to the refracting surface of a 
 
 prism, and throwing the image or spectrum on to a screen, where he 
 observed the seven colours, red, orange, yellow, green, blue, indigo, and 
 violet, and thus proved “ that there are different species of light, and that 
 each species is disposed both to suffer a different degree of refrangibility in 
 passing out of one medium into another , and to excite in us the idea of a 
 different colour from the rest; and that bodies appear of that colour which 
 arises from the composition of those colours the several species they reflect 
 are disposed to excite .” 
 
 Sir Isaac Newton’s name would have been immortalized by this dis- 
 covery alone, even if he had not possessed that transcendent ability 
 which raised him above all other mathematicians and physicists. 
 It is at the same time interesting to know that the ancient author 
 Claudian (a d. 420) inquires “ whether colour really belongs to the sub- 
 stances themselves, or whether by the reflection of light they cheat the 
 eye — enquires sitve color proprius rerum lucisne repulsa eludant aciem 
 
 Sir Isaac Newton determined that the spectrum could be divided 
 into 360 equal parts, of which red occupied 45, orange 27, yellow 48, 
 green 60, blue 60, indigo 40, violet 80. He also discovered that if the 
 highly refracted rays, the seven colours, or spectrum were received into 
 •a concave mirror or a double-convex lens, that they again unitH and 
 
364 
 
 boy’s PLAYBOOIi of science. 
 
 formed white light. In order to demonstrate the properties of the 
 prism in various positions, the next diagram may be adduced. (Fig. 348.) 
 
 Fig. 348. a. The ray of light passing through two prisms b placed base to base. In 
 this position the light passes through to the second prism, c, without alteration. At c 
 the decomposition of light occurs, and the spectrum is shown at d d. The top prism 
 at b used singly would reflect the ray to e without decomposing it into the coloured rays. 
 
 The rainbow is the most beautiful natural optical phenomenon with 
 which we are acquainted ; it is only seen in rainy weather when the sun 
 illuminates the falling rain, and the spectator has the sun at his back. 
 There are frequently two bows seen, the interior and exterior bow, or 
 the primary and secondary, and even within the primary rainbow, and 
 in contact with it, and outside the secondary one, there have been seen 
 other bows beyond the number stated. 
 
 The primary or inner rainbow consists of seven different coloured 
 bows, and is usually the brightest, being formed by the rays of light 
 falling on the upper parts of the drops of rain. The exterior bow is 
 formed by the rays of light falling on the lower parts of the drops of 
 rain ; and in both cases the rays of light undergo refraction and reflec- 
 tion, hence the opinion of Aristotle, that the rainbow is caused only by 
 the reflection of light, is not correct. 
 
 The first refraction occurs when the rays of light enter, and the 
 second wdien they emerge from the spheroids of water in the first bow ; 
 the refracted rays undergo only one reflection, whereas in the second 
 the brilliancy of the colours is impaired by two reflections. 
 
 The spectrum from the electric light is one of the most gorgeous ex- 
 hibitions of colour that can be conceived ; and the instruments required 
 for the purpose are illustrated in Fig. 349. 
 
THE ANALYSIS AND SYNTHESIS OF LIGHT. 
 
 365 
 
 On the left of the woodcut is seen a lantern furnished inside with an 
 electric lamp. The light from this lantern passes through a narrow 
 slit, thence through a lens and prism, after which it appears upon the 
 screen placed for its reception as a band or ribbon of brilliant colours. 
 In this way is repeated the experiment which Sir Isaac Newton first 
 performed more than two hundred years ago. 
 
 Fig. 349. Apparatus for showing spectrum on screen. 
 
 It is important to observe that whereas the great philosopher used a 
 mere hole in his window-shutter for the purpose, a narrow slit is now 
 employed. Dr. Wollaston at the beginning of the present century was 
 the first to use this slit for observing the appearance of the spectrum, 
 and by doing so he arrived at unexpected results. He found, by this 
 substitution of a narrow aperture for a round one, that the coloured 
 ribbon of light no longer showed itself as a continuous unbroken band, 
 but that it was intersected by innumerable dark lines, for which he 
 could not account. Many other scientists tried to make out what these 
 lines signified, but they did not succeed in doing so. Frauenhofer, an 
 optician of Munich, was the first to point out that these mysterious 
 lines of darkness occupied a certain fixed position in the spectrum. He 
 succeeded in mapping them to the number of several hundred, and 
 they are in consequence known as “ Frauenhofer’ s lines.” 
 
 By means of improved apparatus, Bunsen and Kirchhoff in 1860 
 investigated these lines of Frauenhofer, and by their researches laid the 
 foundation of a new science which is comprehended in the term 
 spectrum analysis. 
 
 Herschell some years before had experimented with different metals 
 under the blowpipe, and had pointed out that each metal gave a charac- 
 teristic tinge of colour to the flame. He further suggested that it 
 might be possible by a modification of the means employed to found a 
 new method of analysis. He little knew how well his words would 
 be verified. 
 
 Bunsen and his co-worker made the strange discovery by means of 
 
36G 
 
 boy’s playbook op science. 
 
 special apparatus that burning metals gave a spectrum having bright 
 lines — so many lines for each metal. They further found that these 
 bright lines had their counterparts as dark lines in the solar spectrum as 
 mapped out by Frauenhofer. It was evident then that some sort of 
 mysterious connection existed between the metals ignited in the 
 laboratory and the dark lines which for so long a time had puzzled 
 Wollaston and other scientists. What could this connection mean ? 
 
 The question was not answered until the vapours of some burning 
 metals were observed through the prism, when it was seen that what 
 before were bright lines, were now dark. And so the law came to be 
 established that “ vapours of metals at a lower temperature absorb ex 
 actly those rays which they emit at a higher ” To simplify this we may 
 suppose that we throw a piece of some metal into a furnace and imme- 
 diately view its spectrum, when we shall see the bright lines peculiar to 
 that metal. But on looking at the spectrum of its vapour with the 
 sunlight as a background, we shall see dark lines only, but these will 
 occupy precisely the same position as the bright lines we before 
 observed. Here then the philosopher has a new power placed in his 
 hands, and one so marvellously sensitive, that the presence of a minute 
 particle of a substance, far too small to be seen by the eye, can be 
 readily detected. 
 
 Sir Isaac Newton’s primitive arrangement has now long ago given 
 place to the wonderful instrument called the spectroscope, which in its 
 simplest form is shown at Big. 350. Here the darkened room is repre- 
 
 Fig. 350. Browning’s Direct Vision Spectroscope. 
 
 sented by a little tube, and the hole in the window-shutters by the tiny 
 slit seen at the end of it. This miniature form of spectroscope contains 
 what is known as a compound direct-vision prism. This is placed 
 in a sliding drawer, at the end of which is a lens to magnify the image 
 of the slit upon the retina of the eye. The opening of the slit is ad- 
 justable by a screw motion, a very necessary provision in the case of 
 delicate examinations. This little contrivance, only a few inches in 
 length, will show many of Frauenhofer’ s lines — the bright lines peculiar 
 to different metals and gases — as well as absorption bands in coloured 
 gases or liquids. 
 
 In using this instrument it should be held like a spyglass, and 
 directed to any source of light, a bright gasflame for instance, when a 
 continuous spectrum, like a piece cut out of a rainbow, will be plainly 
 seen. But supposing that we wish to observe the bright lines of the 
 
THE ANALYSIS AND SYNTHESIS OF LIGHT. 
 
 367 
 
 metals, a different mode of proceeding must be observed. (I might 
 here mention that it is a matter of great convenience to have the tube 
 dipped into some kind of stand, so that the hands are at liberty to 
 carry out necessary manipulations). A spirit lamp, or Bunsen flame, 
 must be placed opposite the slit, and as near to it as is possible without 
 injury to the instrument. A piece of platinum wire must now be pro- 
 cured, and bent into a loop at one end. Into this loop can be fused a 
 small bead of the substance or metallic salt to be examined. The wire is 
 now supported above the lamp, so that the bead at its end is just within 
 the front edge of the flame, opposite the slit of the spectroscope. If 
 these directions be complied with, the lines due to the substance under 
 examination will be plainly seen on looking through the eye-piece. 
 Where very minute portions of a substance are only available, it is 
 usual to dissolve it, and apply a drop of the solution to the platinum loop. 
 
 The exceeding delicacy of this mode of analysis is almost beyond 
 belief. In experiments carried on at the Royal Mint, having for their 
 object the examination of different mixtures of metal for coining pur- 
 poses, the difference of one ten-thousandth part in an alloy was made 
 evident. Blood in a most dilute form can be readily recognised, and 
 there is no doubt but that the spectroscope would have proved a useful 
 detective in certain criminal investigations if the microscope had not 
 already furnished readier services in that connection. The sodium 
 lines can be observed in the instrument when a solution containing not 
 more than of a grain of sodium is employed. 
 
 Fig. 351. Spectroscope with two prisms. 
 
 A higher class of spectroscope is shown at Fig. 351. On the left- 
 hand side is seen the dark tube with the slit at its end. In the centre two 
 
368 
 
 BOY S PLAYBOOK OF SCIENCE. 
 
 prisms (the use of which gives a longer spectrum than a single prism), 
 and on the right a telescope to magnify the image. In using this 
 instrument the lamp or other light source is placed opposite the slit, a 
 piece of black cloth, or velvet, being thrown over the prisms. 
 
 The apparatus for showing spectra on a screen so that the phenomena 
 can be observed by a number of persons simultaneously, is identical with 
 that shown at Tig. 349, page 365. It consists of an electric lantern 
 furnished with a slit, in lieu of condensers, a convex lens mounted upon 
 a stand, and a bottle prism filled with bisulphide of carbon. The sub- 
 stance under examination is placed in a hollow cup formed in the lower 
 carbon of the lamp, and is thus exposed to the intense heat of the 
 voltaic arc. The results thus obtained cannot approach in delicacy the 
 observations which can be made by the forms of spectroscopes previously 
 described, impurities in the carbon points, as well as the bright lines 
 due to incandescent carbon, interfering more or less with the general 
 result. With care, however, these difficulties can be partly obviated, 
 and the effects produced, if not perfect, are very beautiful and 
 wonderful. 
 
 In using this apparatus it is usual to place the different substances 
 under examination in separate crucibles, which so revolve upon a stand 
 that each can successively be brought under the upper carbon of the 
 lamp. By this means the audience is not kept waiting between each 
 display. By burning a small piece of sodium in an iron spoon, inside 
 the lantern, so as to fill it with vapour, and placing another piece of the 
 same metal in the voltaic arc, the reversal of the bright yellow line due 
 to sodium can be well observed. Salts of silver, zinc, copper, or little 
 pieces of the metals themselves, will also afford brilliant spectra by 
 means of this apparatus. Liquids placed in a small wedge-shaped cell 
 in front of the slit, may also be compelled to give up their secrets. In 
 such manner can be examined solutions of blood, chlorophyll (the green 
 colouring matter of plants), cochineal, and many other substances too 
 numerous to mention. 
 
 The discovery of no less than four elementary bodies is due to 
 spectrum analysis. Thus in 1860 Bunsen found, when operating upon 
 the residue of a certain mineral water, certain lines in the spectroscope 
 which did not coincide with any previously noticed ; these were due 
 to the two metals caesium and rubidium. Mr. Crookes not long after- 
 wards noticed a bright green line in the spectrum given by some 
 specimens of pyrites. Thus was discovered thallium , which takes its 
 name from the characteristic colour which led to its detection. The 
 fourth metal which owes its discovery to the prism was indium , which 
 like the other three already mentioned is named after the colour of 
 its most characteristic lines. 
 
 A curious, but very useful, application of the spectroscope is found in 
 the Bessemer process for converting iron into steel. In this process air 
 is driven through the molten iron, from apertures at the bottom of the 
 vessel in which it is melted. At the moment of conversion, the bril- 
 liant flame from the molten mass, undergoes a change which is very 
 
THE ANALYSIS AND SYNTHESIS OF LIGHT. 
 
 369 
 
 difficult to detent by the unaided eye. But viewed through the 
 spectroscope the moment at which this change occurs, and when there- 
 fore it is all-important that the process should be stopped, the flame 
 gives unerring indications for the guidance of the workmen. The 
 spectrum given consists of numerous bright lines, the most brilliant of 
 which are green. At the moment when the process becomes complete 
 these green lines suddenly vanish. Thus can an inexperienced workman 
 be made competent by this wonderful instrument to detect a change 
 which otherwise would cost him years of practice. 
 
 The most wonderful applicationof the spectroscope is however evidenced 
 in the means which it affords of analysing the constituents of the heavenly 
 bodies. Kirchhoff by means of the prism demonstrated the existence in 
 the sun of iron, barium, copper, zinc, magnesium, chromium, calcium, 
 and iron. With improved apparatus modern astronomers have increased 
 the number of elements in the sun to about twenty-two, whilst they are 
 in doubt about the presence of some ten others. The last solar discovery 
 of this nature was that of Dr. Henry Draper, of New York, who was the 
 first to detect the lines due to oxygen. The^solar spectroscope is used 
 with an astronomical telescope, and takes the place of the usual eye- 
 piece. 
 
 Still more interesting are the discoveries which have been rendered 
 
370 
 
 boy’s playbook or science. 
 
 lines given by terrestrial substances astronomers are ab L^fto uS on 
 
 IFlra= 
 
 vapour, at a temperature to which we can only 
 has done in the past. A most interesting and 
 
 by means of the spectroscope has been initiated by Mr. • tru _ 
 
 a gentleman whose previous discoveries and labours with the nstru 
 me S nt must give any conclusions at which he ar rives gr eat we gh t. A 
 the close of the year 1878 a letter appeared m one ot itej* 
 giving news of a most startling discovery, for effected 
 
 Lock?., had realized the alche— 
 
 the transmutation ol several metals. II f chemistry niust 
 
 therefore not elementary and that the whole system o J 
 
 ’^Thisiettor’ezoked a reply from Mr. Lockyer, 
 
 ssts-as ss J r s “ tio " 
 
 hich Mr. Lock jer himself brought before the Royal Sociey. ^ 
 
 In this paper Mr. Lockyer hazards the assertion that many^ 
 called elements are in reality compound he 
 
 »j^raV A fSS£ i: fs to - i = 
 
 r2^m.«'l'fo£ed l i“"^ “f 1 “ , "V"«VdT.ri'rh"™- 
 
 the nroblem. We must remember that it is not so very long ft 
 men believed in the existence of four etements on y^name y . ^ f h( I 
 
 water, and fire. From these four supposed elements everyth g 
 
 sfss Si. s' 
 
 IfalSS m U .l' .‘„S". n Zt, Kre-d .. dimi.Lhed 
 
THE ANALYSIS AND SYNTHESIS OF LIGHT. 
 
 371 
 
 as time goes on. The general acceptance of any new doctrine is always 
 a difficult matter, and the history of discovery will show how learned 
 men have been laughed at for notions which, in the end, have been 
 universally accepted. We must therefore look upon our list of 
 elements as the best that can be tabulated as far as present knowledge 
 goes, and we may look to the spectroscope to tell us more hereafter. 
 
 Another use to which this wonderful instrument is being applied 
 with most successful results, is in medicine. The lines in the spectrum 
 afforded by blood are quite different to those of other substances. And 
 the quantity necessary to show the effect is so excessively minute that 
 the least trace can be readily detected. In this way the presence of 
 blood in any of the secretions of the body where it has no business to 
 be can be easily made out, and the lurking disease is detected. A 
 morsel of dried blood weighing less than the fifty thousandth of a grain, 
 is sufficient to give evidence of its presence to the spectroscopist. The 
 detection of minute quantites of different metallic salts, together with 
 their rapid diffusion through the body after administration, has also 
 been studied by the same agency, and is likely to lead to valuable 
 physiological results. It need not be imagined that spectrum analysis is, 
 on account of the expense of the apparatus, out of reach of ordinary folk, 
 for of Mr. Browning can be obtained the direct vision instrument already 
 described, with all necessary appliances, for little more than a guinea. 
 It is difficult to imagine how a guinea could be more profitably spent. 
 
 VII. Duration of the Impression of Light. 
 
 If a circular disc is painted with the prismatic colours taken in the 
 same proportion with respect to each other in which they are exhibited 
 in the spectrum made by the prism, and the wheel is turned swiftly, then 
 the individual colours disappear, and nearly white light is apparent. 
 The cause is due to the same principle that creates the appearance of a 
 complete circle of fire when a burning squib is moved quickly round 
 before it is thrown away to burst, and as it is evident that the burning 
 squib cannot be in every part of the circle at the same moment, there 
 must be some inherent faculty belonging to the human eye which 
 enables it to retain for a definite period the impression of images that 
 may fall upon it ; and this principle has been so far pressed, as it were, 
 beyond its limits, that it is gravely asserted the image of a man’s mur- 
 derer “might be discovered on the retina of the eye-ball if that could be 
 examined sufficiently quick after death.” The fixture of the picture is 
 said to be due to a sort of natural photographic process; but such fanciful 
 statements often lead the mind into dreamland only, and so we will 
 return to the fact of the duration of the impression of light on the eye 
 as evidenced by several ingenious optical instruments, and especially by 
 the scientific inventions of Dr. Earaday, Dr. Paris, and of Mr. Thomas 
 Bose of Glasgow. 
 
 By careful experiment M. D’Arcy found that the light of a live coal, 
 moving at the distance of 165 feet, maintained its impression on the 
 b b 2 
 
boy’s playbook of science. 
 
 retina during the seventh part of a second. Hence the cause of thg 
 recomposition of white light when the colours on the disc are cpiickly 
 rotated. Each colour at any point succeeds the other before the impres- 
 sion of the last is gone from the eye, and provided the colours move 
 round within the seventh part of a second, they are all impressed toge- 
 ther on the eye, and meeting on the retina, produce the effect of white 
 light. 
 
 VIII. The PhenaJcistiscope. 
 
 This amusing instrument consists of a turning wheel upon which figures 
 appear to jump, walk, or dance. The disc or wheel is of cardboard, 
 upon which are painted (towards the peri- 
 phery) figures in eight, ten, or twelve 
 postures/ Thus, if it is desired to repre- 
 sent clowns turning round in a circle, twelve 
 different positions of the figure in the act of 
 turning are painted on the disc, and above 
 each of the figures on the wheel a slit is cut 
 about one inch long, and a quarter of an 
 inch wide in a direction corresponding with 
 the radii of the circle. This simple form of 
 the instrument is used by placing the figured 
 side towards a looking-glass and then causing 
 it to revolve at a certain speed, which is 
 ascertained by experiment ; and as the spec- 
 tator looks through the slits into the looking- 
 glass, the clowns appear to turn round. At 
 the Polytechnic Institution there are two 
 of these wheels with looking-glasses, and 
 although the same designs have done duty 
 for many years, they still attract the public 
 attention. (Eig. 353.) 
 
 In the “ Journal of the Royal Institution” Mr. Earaday has de- 
 scribed some very interesting experiments and optical illusions produced 
 by the revolution of wheels in different directions and velocities. The 
 wheels are made of cardboard, and by cutting cut two cog wheels of an 
 equal size, and placing one above the other on a pin, the usual hazy 
 tint when the cogs are acting is apparent when they are whirled round ; 
 but if the two cog wheels are made to move in opposite directions, 
 there will be the extraordinary appearance of a fixed spectral wheel. 
 If the cogs are cut in a slanting direction on both wheels, the spectral 
 wheel will exhibit slanting cogs ; but if one wheel is turned so that the 
 cogs shall point in opposite directions, then the spectral wheel will have 
 straight cogs. A number of such wheels set in motion in a darkened 
 room, and illuminated suddenly with the light from the electric spark, 
 appear to stand perfectly still, although moving with a great velocity. 
 An expensive instrument has been constructed by Dubo3cq, for the 
 
 Fig. 353. Design for the phe- 
 nakistiscope. The spectator is 
 supposed to be looking towards 
 a mirror through the slits. It is 
 supported by a handle through 
 the centre, round which it is 
 twirled by the other hand. 
 
THE PHENAKISTISCOPE. 
 
 373 
 
 purpose of showing the usual phenakistiscope effects on the screen 
 with the magic lantern ; a very limited picture, however, is shown, and 
 there is still great room for the improvement of the apparatus. (Fig. 354.) 
 
 No. 1. 
 
 No. 2. 
 
 Fig. 354. Phenakistiscope madu by Duboscq, of Paris. No. 1. Apparatus in elevation 
 with the condensers. No. 2. Section of the apparatus, a. The light, b. Condenser, or 
 plano-convex lens. c. Round glass disc with design painted on it. d. Wooden disc with 
 four double-convex lenses placed at equal distances from each other, so as to coincide 
 with c, whilst rotating. Both the latter and c rotate, and the picture is focussed on the dist 
 by the lenses F. No. 3. Glass plate, with device painted thereon. 
 
boy’s playbook of science. 
 
 «7 /t 
 
 < -JC 
 
 IX. The Thaumatrope. 
 
 This ver^ simple toy was invented by the late Dr. Paris, who gave it 
 an appropriate name, compounded of the Greek words, Savfia , wonder, 
 rpeVo), to turn. The duration of the impressions of lm-lit on the eye 
 is very apparent whilst using this toy, which is usually made of a 
 circular piece of cardboard, having on one side a painting of a man’s 
 head, and on the other a hat ; or a picture of a lighted candle on one 
 face of the cardboard, and an extinguisher on the other; or a 
 gate, and a horseman leaping it. Each pair of designs painted on 
 opposite sides of the cardboard appear to be one when twisted round 
 by strings tied to the opposite edges of the cardboard circle. The 
 rationale of this experiment being, that the picture of one design — 
 such as the head and face — is retained by the eye until the hat appears, 
 and being mutually impressed upon the nerve of vision at very nearly 
 the same instant of time, they appear as one picture. 
 
 X. The Kalotrope. 
 
 This is an optical arrangement by Mr. Thomas Rose, of Glasgow, 
 primarily designed for showing the illusions of the phenakistiscope and 
 kindred devices to a numerous audience ; but more remarkable for its 
 presentations of very beautiful spectra, composed of the multiplication, 
 combination, and involution of simple figures disposed around a disc. 
 The arrangement consists of a movement for giving considerable 
 velocity to two concentric wheels, working nearly in contact, and 
 moving in contrary directions. But the only part of the apparatus that 
 requires special explanation and illustration is the device disc and the 
 disc of apertures ; the first of which is placed on the hinder wheel, and 
 the second on the front wheel. We give figures of the two discs, 
 premising, however, that each is capable of an almost infinite variety 
 of characters. No. 1 (Eig. 355) presents in its four quadrants the 
 perforations for four distinct discs of apertures ; and No. 2 is a device 
 disc, consisting of twelve equidistant black bails. Under a the balls 
 will be presented as twenty-four ovals ; under b, as forty-eight involved 
 figures, beautifully variegated ; under c , as an elaborate lacework ; and 
 under d, as a rich variegation of form and colour. Every fresh disc of 
 devices and disc of apertures of course opens up a new field of effect. 
 Thus, if we take a disc bearing twelve repeats of a ball in the in- 
 terior of a ring, each repeat being so painted that its position is ad- 
 vanced in the ring until it reaches in the twelfth ring the point whence 
 it started, and place this on the back disc of the kalotrope, having pre- 
 viously removed the first one, no effect is observed when the wheel 
 is rotated beyond the spreading out of the design and general appear- 
 ance of hazy black circles. When, however, the disc, with twelve slits 
 or apertures, is now placed on the front wheel, and the two rotated in 
 opposite directions, then the whole figure starts as it were into exist- 
 ence, and each ball apparently moves round the interior of its circle. 
 
MR. ROSE’S KALOTROPE AND PHOTODROME. 875 
 
 The apparatus was produced at the Royal Polytechnic Institution by 
 the author, and excited much interest. (Pig. 355.) 
 
 Pig. 355. Nos. 1 and 2 are the discs. No 3. Kalotrope in elevation. No. 4. Side view 
 of kalotrope, showing the multiplying wheels and the perforated and painted discs moving 
 in opposite directions. 
 
 % 
 
 XI. The Photodrome. 
 
 This is a second optical arrangement by Mr. Rose for showing spec- 
 tral illusions ; and it is superior to the last, inasmuch as it offers to the 
 public lecturer a most effective means of presenting these deceptions to 
 a large audience. It differs from the kalotrope in several important 
 points. It dispenses with the discs of apertures, and leaves the device 
 disc with its face fully exposed to the spectators. The effects are pro- 
 duced by a powerful light, thrown through the tube of a lantern, and 
 broken by a wheel working across it. The apparatus, Sts it at present 
 stands in the inventor’s possession, consists of two distinct parts ; the 
 one a movement for the device discs, and the other for the light. A 
 wheel four feet in diameter is connected with a train of movement 
 capable of giving it five hundred or six hundred revolutions per minute. 
 On this wheel the device disc is placed, in full view of the spectators, 
 and set in motion. Prom an opposite gallery the light is thrown, and 
 
376 
 
 boy’s playbook of science. 
 
 broken by a wheel of such diameter and number of apertures as will 
 admit the velocity of the photodrome (or light-runner) to be at least 
 six times the velocity of the device disc ; whilst the apertures are of 
 such width as to restrict the duration of the light- flash to about one- 
 two-thousandth of a second. The wheel working across the light has a 
 train of movement for raising the velocity to two thousand revolutions 
 per second. The management of the apparatus is very simple. The 
 device-wheel is brought to a steady, rapid rotation, and the operator on 
 the light then works his wheel with gradually increasing velocity, until 
 he overtakes the figures of the device, where, by mere delicacy of touch, 
 he is able to hold them stationary or give them motion, at pleasure. 
 
 Theories of light and colour still agitate the scientific world, although 
 that man must be bold who will assert that his hypothesis is fitted to 
 explain every difficult point that arises as our experimental knowledge 
 increases. Mr. G. J. Smith, of the Perth Academy, has propounded a 
 very ingenious theory of light and colour, supported by some clever 
 experiments. But, as Solomon says, “ there is nothing new under the 
 sun,” and in an able paper Mr. Bose, of Glasgow, lays claim to the 
 anticipations of Mr. Smith’s theory as follows : — 
 
 “ My attention has been directed to a paper entitled e The Theory of 
 Light/ by G. John Smith, Esq., M.A., of Perth Academy. I think it 
 is now nearly two years since I communicated an interesting fact to 
 Professor Faraday, and to a member of our local Philosophical Insti- 
 tution, which may fairly claim to have anticipated Mr. Smith’s theory. 
 The fact was this : that if a piece of intensely white card be held in one 
 hand, with the light of a powerful gas-jet falling upon it, and if the 
 other hand has command of the gas-tap, as the light is gradually reduced, 
 the card will assume the prismatic colours down to intense blue, and as 
 the light is restored the colours will present themselves in inverse 
 order. The experiment showed, very conclusively to my mind, that light 
 is homogeneous, and that what we name colour is only the various 
 affection of the optic nerve by a greater or lesser radiation of light from 
 a focal point in an imperfect reflector — say, in the instance, a white 
 card. I apprehend that Mr. Smith confuses his theory when he speaks 
 of alternations of light and shadow producing colour. Shadow, or 
 darkness, is mere negation of light. We do not see mixtures of light 
 and darkness, or blackness and whiteness, but light in its several degrees 
 of intensity. Mr. Smith’s experiments present only what my kalotrope 
 has done, and what my later device, the photodrome (now nearly three 
 years old) is doing in a much more perfect manner. It is one of the 
 mysteries intelligible only to the initiated, that whilst Mr. Smith’s paper 
 seems to have been received with great favour by the British Association, 
 my communication relative to the photodrome was voted ‘ not sufficiently 
 practical .’ 
 
 “ Since I have come before the public with an experiment, which in 
 any view is an interesting one, permit me to reproduce it under several 
 distinct conditions, and to add a brief narrative of remarkable presen- 
 tations of colour that have come before me, and which, so far as I am 
 
rose's experiments. 
 
 377 
 
 aware, are perfectly novel, or known only through the more recent 
 experiments of Mr. Smith. Professor Paraday very courteously 
 acknowledged my communication of the experiment with the card, but 
 said that it only partially succeeded with him, and added that probably 
 this was owing to some decay of sensitiveness in his eyes. More likely 
 I failed to state with sufficient clearness the conditions of the ex- 
 periment, since I have always found nine persons out of ten perfectly 
 agreed as to the effects produced when they have been at my side. The 
 transitions from white to yellow, orange, red, and thence to intense 
 blue, are, I may say, invariably admitted. Success depends on a very 
 slow and regular reduction and restoration of the light. I have given 
 one method of performing the experiment, and will add other two. 
 Allow the light to remain undisturbed, and begin by holding the card 
 near to it ; then keep the hand steady and the eye intently fixed upon 
 the card, and retire gradually with your back to the light, and the 
 colours will change in the order of the prismatic spectrum from yellow 
 to intense blue. On returning backwards towards the light the colours 
 will again present themselves, but in inverse order. In this form of 
 the experiment we are certain that the light remains precisely the same 
 throughout. The third method is this : Place a circle of white card, 
 about three inches in diameter, in the centre of a black board, and let a 
 spectator stand within twelve inches of the board, with his eyes fixed 
 upon the card. Let an operator be provided with a light so covered 
 that it shall not fall on the eye of the spectator ; then, as he retires 
 with the light or returns with it, the spectator will see the colours as 
 before. This arrangement evidently subjects the experiment to a severe 
 test, since the black board enhances the whiteness of the card, and 
 
 tends to preserve it Whilst pursuing my principal object, 
 
 I frequently noticed most remarkable presentations of colour ; but, as 
 the conditions were for the most part unsuitable to the lecture-room, I 
 gave them only a passing regard. Allow me to instance a few of the 
 experiments. 
 
 “ The first refers to the kalotrope, which may be briefly described as 
 an arrangement of two concentric wheels, working nearly in contact and 
 in contrary directions. Discs of various devices are provided for the 
 hinder wheel, and a number of perforated black discs for the one 
 in frcnt. When a disc charged with twelve black radii is placed on 
 the hinder wheel, the six spokes of the front wheel, in passing rapidly 
 across it, convert the twelve black radii into twenty-four apparently 
 stationary white radii upon a tinted ground. Here is a remarkable 
 presentation of the complementary, inasmuch as it is placed permanently 
 before the eye by persistence. 
 
 " The second experiment is performed with the photodrome, which 
 consists of an independent wheel to receive the device discs, and an 
 apparatus (altogether apart, and, if desired, out of sight) by which 
 flashes of light are thrown upon the disc in rapid and regular succession. 
 How, if a disc charged with twelve dark blue balls, nearly in contact, 
 be placed upon the wheel, and a little natural light be allowed to fall 
 
378 
 
 boy’s platbook of science. 
 
 upon it, so soon as it is thrown into rapid revolution, and flashes of 
 artificial light (insulated in a lantern) are duly measured out upon it, 
 we see twelve apparently stationary light-blue balls upon a zone of 
 bright orange. Here, again, there is nothing for which we > are not 
 prepared; the complementary is suddenly presented, and it is main- 
 tained permanently before the eye by persistence. 
 
 “A third experiment may prove interesting in its relation to Mr. 
 Smith’s ingenious theory. Place the kalotrope opposite a bright 
 northern noonday sky, remove the front wheel, and affix to the hinder 
 wheel one of the perforated black discs used for the kalotropic effects. 
 The experimentalist stands at the back of the instrument, and can see 
 the sky only through the apertures in the black disc. Cause these 
 apertures to pass the eye at intervals varying from one-half to one-sixth 
 of a second, and very remarkable presentations of colour are seen. 
 Under the lower velocities the sky flashes, and assumes an unnatural 
 brilliancy, and the intervals of the fourth and fifth of a second give it 
 sometimes a crimson, at others a deep purple colour. Now, what are 
 w T e to infer from this experiment ? Certainly not that the pulsations 
 have absolutely produced variety of colour. At every pulsation the 
 full natural light falls upon the eye, and the intervals between the 
 pulsations give time for the reaction necessary to the suggestion of 
 complementary colour, and that under manifold modifications arising 
 out of the ever-changing condition of the eye during the experiment. 
 If the apertures pass the eye with a velocity exceeding one-sixth of a 
 second, the effect ceases. There is then perfect persistence, and the 
 eye apprehends nothing but the ordinary light of the sky, reduced in 
 intensity, with nothing to break its uniformity or give it a chromatic 
 character. 
 
 “A fourth experiment is kindred to the last. Place the kalotrope 
 under the same adjustment and management as before, in front of a 
 brilliant sunset, and the spectator will see, with more than a poet’s 
 
 vision, 
 
 * The rich hues of all glorious things.’ ” 
 
 XII. The Kaleidoscopic Colour-top. 
 
 This invention by John Graham, of Tunbridge, is designed to show that 
 when white or coloured light is transmitted to the eye through small 
 openings cut into patterns or devices, and when such openings are made 
 to pass before the eye in rapid successive jerks, both form and colour are 
 retained upon the nerve of the visual organ sufficiently long to produce 
 a compound pattern, all the parts of which appear simultaneously, 
 although presented in succession. The instrument forms, therefore, a 
 pleasing illustration of the law that the eye requires an almost inappre- 
 ciably short space of time to receive an impression, and that such 
 impression is not directly effaced, but remains for an assignable though 
 very limited period. The results are obtained by rotating two discs on 
 a wheel, the lower disc containing colours, and the upper one the 
 
CHEAP MICROSCOPES AND TELESCOPES. 379 
 
 openings ; this latter disc is made to vibrate as well as to rotate, thus- 
 allowing the eye to receive the coloured light reflected from below, 
 which light assumes, at the same time, the forms of the patterns through 
 which it has been transmitted. The instrument serves also to illustrate 
 most of the important phenomena of colour. 
 
 XIII. Simple Microscopes and Telescopes. 
 
 The Stanhope lenses are now sold at such a cheap rate, and are so 
 useful as simple portable microscopes, that it is hardly worth while to 
 detail any plan by which a cheap single-lens magnifier may be obtained. 
 Eloquent vendors of cheap microscopes are to be found in the streets, 
 who make their instrument of a pill-box perforated with a pin-hole, in 
 which a globule of glass fixed with Canada balsam is placed ; and the 
 spherical form of the drop affords the magnifying power : or a thin 
 platinum wire may be bent into a small circular loop, and into this may 
 be placed a splinter of flint-glass ; if the flame of a spirit-lamp is urged 
 upon the loop of platinum wire and glass by the blowpipe until it melts, 
 a small double-convex lens may be obtained, which will answer very 
 well as a magnifying-glass. Practice makes perfect, and after two or 
 three trials, a good single lens may be obtained, which can be mounted 
 between two small pieces of lead, brass, or cardboard, properly fixed 
 together, with holes through them just large enough to retain the edge 
 of the tiny lens. A prism can be made of two small pieces of window- 
 glass stuck together with a lump of soft beeswax, and if a few drops 
 of water are placed in the angle, they are retained by capillary attraction. 
 The prism is used by holding it against a large pin-hole or small slit in 
 a bit of card, and directing them towards the sky, when the beautiful 
 colours of the spectrum will be apparent if the card and prism are 
 brought close to the eye. 
 
 The most simple form of the refracting telescope is made with a lens 
 of any focal length exceeding six inches, placed at one end of a tin or 
 cardboard tube, which must be six inches longer than the focal length 
 of the lens ; the tube may be in two parts, sliding one within the other, 
 and when the eye is placed at the other end, an inverted image of the 
 object looked at, is apparent. By using two double-convex lenses, a 
 more perfect simple astronomical telescope is obtained. The object- 
 glass, i.e. } the lens next the object looked at, must be placed at the end 
 of a tin or pasteboard tube larger than its focus, and the second lens, 
 called the eye-glass, because next the eye, is a smaller tube, termed the 
 eye-tube ; and if the focal length of the object-glass is three feet, the 
 eye-glass must have a one-inch focus, and of course the eye-tube and 
 glass must slide freely in the tube containing the object-glass. An 
 object-glass of forty feet focus will admit of an eye-glass of only a four- 
 inch focus, and will, therefore, magnify one hundred and twenty times. 
 A tube of forty feet in length would of course be very troublesome to 
 manage, and therefore it is usual to adopt the plan originally devised by 
 Huygens, viz., that of placing the object-glass in a short tube on the 
 
380 
 
 boy’s playbook of science. 
 
 top of a high pole 
 brought into the 
 
 Fig. 356. A com- 
 pound achromatic 
 Ions, composed of 
 <3 c, the double-con- 
 vex lens of crown- 
 glass, and f f, the 
 plano-concave lens of 
 flint-glass. 
 
 compound lens, 
 together, and use 
 
 with a ball-and-socket joint, whilst the eye-glass is 
 same line as the object-glass, and focused with a tube 
 and rack-work properly supported. In an ordinary 
 terrestrial telescope there are four lenses, in order 
 that the objects seen by its assistance shall not be 
 inverted ; and whenever objects are examined by a 
 common telescope, they are found to . be fringed, or 
 surrounded with prismatic colours. This disagreeable 
 effect is corrected by the use of achromatic lenses, in 
 which two kinds of glass are united ; and the light 
 decomposed by one glass, uniting with the colours 
 produced by the other form white light, thus a douple 
 convex lens of crown glass, c c, may be united with 
 a plano-convex lens of flint glass, F F, which must 
 have a focus about double the length of that of the 
 crown-glass lens. The concave lens corrects the 
 colour or chromatic aberration of the other, and 
 leaves abont one-half of the refracting power of the 
 convex lens as the effective magnifying power of the 
 The Trench opticians cement the lenses very neatly 
 them in ordinary spy and opera glasses. (Fig. 356.) 
 
 XIV. The Stereoscope. 
 
 This instrument has now attained a popularity quite equal to, if it 
 does not surpass, that formerly enjoyed by the kaleidoscope, and without 
 entering upon the much-vexed question of priority ot discovery, it is 
 sufficient again to mention with the highest respect the names ot 
 Sir David Brewster and Professor Wheatstone as identified with the 
 discovery and use of this most pleasing optical instrument. 
 
 The principle of the stereoscope (meaning, solid I see) is copied 
 from nature : i.e., when both eyes are employed in the examination ot an 
 object, two separate pictures, embracing dissimilar forms, are impressed 
 upon the retinae, and produce the effect of solidity; if the pictures formed 
 at the back of the eyes could be examined by another person with a 
 stereoscope, they would come together, and also produce the effect ot 
 
 ^Stereoscopic pictures are obtained by exposing sensitized films in 
 the camera to the picture of an object taken in two positions, or two 
 cameras are employed to obtain the same result. It tne latter mode is 
 adopted, the stereoscopic pictures must not be taken from positions too 
 widely separated from each other ; or else, when the two pict'jrcs are 
 placed in the stereoscope, they will stand out with a relief that is quite 
 unnatural, and the object will appear like a very reduced solid mode 
 instead of having the natural appearance presented by pictures which 
 have been taken at positions too distant from each other. 
 
 Sir David Brewster says, “ In order to obtain photographic pictures 
 mathematically exact, we must construct a binocular camera which will 
 
Wheatstone’s stereoscope. 
 
 381 
 
 take the pictures simultaneously, and of the same size ; that is, by a 
 camera with two lenses of the same aperture and focal length, placed at 
 the same distance as the two eyes. As it is impossible to grind and 
 polish two lenses, whether single or achromatic, of exactly the same 
 focal lengths, even if we had the very same glass for each, I propose to 
 bisect the lenses, and construct the instrument with semi-lenses, which 
 will give us pictures of precisely the same size and definition. These 
 lenses should be placed with their diameters of bisection parallel to one 
 another, and at a distance of 2^ inches, which is the average distance of 
 the eyes in man ; and when fixed in a box of sufficient size, will form a 
 binocular camera, which will give us at the same instant, with the same 
 lights and shadows, and of the same size, such dissimilar pictures ot 
 statues, buildings, landscapes, and living objects, as will reproduce 
 them in relief in the stereoscope.” Thus with a single camera provided 
 with semi-lenses, or two lenses of the same focal length, stereoscopic 
 pictures can be obtained. 
 
 To bring the images of the two pictures together, and produce 
 the effect of solidity ; either of two instruments may be employed. The 
 reflecting stereoscope is the invention of Professor Wheatstone. The 
 refracting or lenticular stereoscope that of Sir David Brewster. 
 
 The former is constructed by placing two upright boards on a wooden 
 stand at a moderate distance from each other; the stereoscopic pictures 
 are attached to these boards, which may be made to move up or down, 
 and if the pictures are held in grooves, they may be pulled right or left 
 at pleasure, and thus four movements are secured — viz., upward, down- 
 ward, right, or left. Between the two stereoscopic pictures are placed 
 two looking-glasses, so adjusted that their backs form an angle of ninety 
 degrees with each other. (Fig. 357.) 
 
 The pictures are illuminated at night by a lamp or gas flame placed at 
 the back of the mirrors, which, when fixed together, have the same shape 
 as a prism; indeed, Professor Wheatstone substituted a prism for the 
 mirrors, and thus paved the way for the invention of the lenticular 
 stereoscope. 
 
382 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 The stereoscopic effect is obtained by bringing the eyes close to the 
 inclined mirrors, so that the two reflected images coincide at the inter- 
 •section of the optic axis ; the coincidence of the images is further secured 
 by moving either picture a little to the right or left, and if the upright 
 boards move bodily in grooves to or from the centre mirror, the greatest 
 nicety of adjustment is procured. 
 
 During the last three years of the author’s directorship of the Poly- 
 technic — viz., in 1856, 1857, 1858 — nearly the whole of the pictures 
 shown by the dissolving- view apparatus were coloured photographs from 
 Mr. Hine’s original pictures, painted two feet square in blue and white, 
 and reduced on the glass to about six inches square. The collodion 
 film being frequently thick and difficult to penetrate with light, was 
 etched and scratched away where required, and filled in with colour, and 
 when these pictures were looked at with one eye only, they appeared to 
 be almost solid or stereoscopic on the disc. 
 
 The lenticular stereoscope consists of a box of a pyramidal shape, 
 open at the base, and provided with grooves in which are placed the 
 stereoscopic pictures; if the latter are taken 
 on glass the base of the box is held directly 
 against the light, but if they are daguerreotypes 
 or paper pictures, then a side light is reflected 
 upon them by means of a lid covered in the 
 inside with tinfoil, which is raised or lowered 
 at pleasure from the top part of the box. Two 
 semi-lenses are now fitted into the narrow part 
 of the box, and are placed at such a distance 
 from each other that the centres of the semi- 
 leuses correspond with the pupil of the eyes, 
 and this distance has already been stated to 
 amount to 2^ inches. (Eig. 358.) 
 
 The principle of the lenticular stereoscope is 
 perhaps better seen by reference to the next 
 diagram, in which the centres of the semi-lenses 
 ( i.e ., a lens cut in half) are placed at 2J inches 
 apart, with their thin edges towards each other, 
 and marked, a b, Eig. 359. The centres of the 
 two stereoscopic pictures c d correspond with 
 the centres of the lenses, and the rays of light 
 diverging from c d fall upon the semi-lenses, 
 and being refracted nearly 'parallel are, by the prismatic form of the semi- 
 lenses, deflected from their course, and leave the surfaces of the lenses 
 in the same direction as if they actually emanated from E ; and as all 
 images of bodies appear to come in a straight line from the point whence 
 they are seen, the two pictures are superimposed on each other, and 
 together produce the appearance of solidity, so that a stereoscopic 
 result is obtained when the spectral images of the two stereoscopic 
 pictures are made to overlap each other. By taking one of the semi- 
 lenses in each hand, and looking at the two pictures, the over-lapping 
 
 Fig. 358. Brewster’s len- 
 ticular stereoscope. 
 
BREWSTER S STEREOSCOPE. 
 
 883 
 
 of the spectral images becomes very apparent, so that the combined 
 spectral images , and not the pictures themselves, are seen when we look 
 into a stereoscope. (Fig. 359.) 
 
 Sir David Brewster says, “ In order that the two images may coalesce 
 without any effort or strain on the part of the eye, it is necessary that 
 the distance of the similar parts of the two drawings be equal to twice 
 the separation produced by the prism. For this purpose measure the 
 distance at which the semi-lenses give the most distinct view of the 
 stereoscopic pictures, and having ascertained by using one eye the 
 amount of the refraction produced at that distance, or the quantity by 
 which the image of one of the pictures is displaced, place the stereo- 
 scopic pictures at a distance equal to twice that quantity — that is, place 
 the pictures so that the average distance of similar parts in each is equal 
 to twice that quantity. If this is not correctly done, the eye of the 
 observer will correct the error by making the images coalesce, without 
 being sensible that it is making any such effort. When the dissimilar 
 stereoscopic pictures are thus united, the solid will appear standing as 
 it were in relief between the two plane representations.” 
 
 XY. The Stereomonoscope. 
 
 M. Claud et, whose name has long been celebrated in connexion with 
 the art of photography, has described an instrument by which a single 
 picture is made to simulate the appearance of solidity, and he states that 
 by means of this arrangement a number of persons may observe the 
 effect at the same time. The apparatus required is very simple, con- 
 sisting of a large double convex lens, and a screen of ground glass. The 
 
£84 
 
 boy’s playbook of science. 
 
 object a, Eig. 360, is highly illuminated, and placed in the focus of a 
 double convex lens B, when an image of the object is projected, and will 
 
 Fig 1 . 360. Tlie stereomonoscope. 
 
 be found suspended in the air in the conjugate focus of the lens at c, 
 and from this point the rays of light will diverge as from a real object, 
 which will be seen by separate spectators at d d and e e ; and it the 
 screen of ground glass is placed at g g, the image will appear with all 
 the effect of length, breadth, and depth, which belong to solid bodies. 
 
 (Eig. 360.) . . . , . 
 
 An image formed on ground glass in this manner can be seen only m 
 the direction of the incident rays, and the stereoscopic effect is not 
 apparent when the image is received on a calico pr transparent screen, on 
 account of the rays being scattered in all directions. 
 
 XYI. The Stereomoscope. 
 
 This arrangement is an important modification of the other, and 
 consists of a screen of ground glass (a b, Eig. 361), and two convex 
 
Wheatstone’s pseudoscope. 
 
 885 
 
 lenses (c d, and e e) arranged in such a manner that they will project 
 images of the stereoscopic pictures, g h, at the same point on the 
 screen, A b. 
 
 • It might be thought that a confusion of images would result from 
 projecting two pictures on one point, r — viz., the focus of the two 
 lenses ; but as each photograph can be seen only in the direction of its 
 own rays, it follows that if the eyes are so placed that each receives the 
 impression of one stereoscopic picture, the two images must coalesce, 
 and a stereoscopic effect will be the result, as is apparent at k k and 
 l l ; so that several persons may look at the stereoscope at one time. 
 (Fig. 361.) 
 
 XVII. The Pseudoscope. 
 
 This curious optical instrument, as its name implies, produces a false 
 image by the refracting power of prisms, and is the invention of 
 Professor Wheatstone. When used with both eyes, the same as the 
 stereoscope, it inverts the relief of a solid body, and makes it appear 
 exactly as if it were an intaglio, or sunk beneath the line surrounding it. 
 For instance, a terrestrial globe when looked at through the pseudoscope 
 appears to be concave, instead of convex. A vase with raised ornaments* 
 upon it looks as if it had been turned (to reverse the usual expression) 
 
 Fig. 362. Horizontal section of the pseudoscope, showing at a b two prisms placed 
 against a block of wood about two inches long and one inch and a half wide, and 
 cut out in the centre to admit the nose at d. The eyes are supposed to be looking at the 
 globe, c, in the direction of the arrows, e e. Brass plates blackened, which shut out tha 
 side light, and assist in keeping the prisms in position. 
 
386 
 
 boy’s playbook of science. 
 
 Dutside in, and the whole of its convexity is turned to concavity; 
 and of course a face seen under these circumstances looks very curious. 
 (Fig. 362.) The cause is perhaps somewhat difficult to understand; 
 but by taking other and more simple examples of the same effect, the* 
 principle may be gradually comprehended. 
 
 Sir David Brewster, in his “Letters on Natural Magic,” remarks 
 that “ one of the most curious phenomena is that false perception in 
 vision by which we conceive depressions to be elevations, and elevations 
 depressions — or by which intaglios are converted into cameos, and 
 cameos into intaglios. This curious fact seems to have been observed 
 t one of the early meetings of the Royal Society of London, when 
 one of the members, in looking at a guinea through a compound 
 microscope of new construction, was surprised to see the head upon 
 the coin depressed, while other members could only see it embossed, as 
 
 it really was The best method of observing this deception 
 
 is to view the engraved seal of a watch with the eye-piece of an achro- 
 matic telescope, or with a compound microscope, or any combination 
 .of lenses which inverts the objects that are viewed through it ; a single 
 convex lens will answer the purpose, provided we hold the eye six or 
 eight inches behind the image of the seal formed in its conjugate focus.” 
 
 After bringing forward various interesting experiments in further 
 explanation of the cause, Sir D. Brewster states it to be his belief that 
 the illusion is the result of an operation of our own minds, whereby 
 we judge of the forms of bodies by the knowledge we have acquired of 
 light and shadow. Hence, the illusion depends on the accuracy and 
 extent of our knowledge on this subject ; and while some persons are 
 under its influence, ethers are entirely insensible to it. This statement 
 is borne out by experience, as the author, whilst Resident Director of 
 the Polytechnic, had four of Wheatstone’s pseudoscopes placed in the 
 gallery, with proper objects behind them ; and he frequently noticed 
 that some visitors would look through the instrument and see no 
 alteration of the convex objects, whilst others would shout with delight, 
 and call their friends to witness the strange metamorphosis, who in 
 their turn might disappoint the caller by being perfectly insensible to 
 its strange effects. 
 
 The pseudo-effects of vision are not confined to the results already 
 explained, but are to be observed especially whilst travelling in a coach, 
 when the eyes may be so fixed as to give the impression of movement to 
 the trees and houses, whilst the coach appears to stand still. In railway, 
 carriages, after riding for some time and then coming to a stand still, if 
 another train is set slowly in motion by the one at rest, it frequently 
 happens that the latter appears to be moving instead of the former. 
 
387 
 
 CHAPTER XXIV. 
 
 THE ABSORPTION OP LIGHT. 
 
 The analysis of light has been explained in a previous chapter, and it 
 has been shown how the spectrum is produced. Colour, however, may 
 be obtained by other means, and the property enjoyed by certain bodies, 
 of absorbing certain coloured rays in preference to others, offers another 
 mode of decomposing light. 
 
 Until very recent times red, yellow, and blue have been regarded as 
 the three primary colours. But the investigations of Helmholtz have 
 shown that this choice has been based upon a consideration of painters’ 
 pigments, and not of coloured light. He has, therefore, found reason 
 to name red, green, and violet as primaries. For further information 
 upon this matter the reader must refer to the works of Helmholtz ; or 
 to Professor Tyndall’s recent lectures upon light. The subject is rather 
 too abstruse to warrant its introduction here. 
 
 Connected with this property is the remarkable effect produced by 
 coloured light on ordinary colours, and the sickly hue cast upon the 
 ghost in a melodrama, or the fiery complexion imparted to the hair 
 of Der Ereischutz, or the jaundiced appearance presented by every 
 member of a juvenile assembly when illuminated with a yellow light 
 from the salt and burning spirit of “ snapdragon,” are too well known 
 to require a lengthened description here. 
 
 If a number of colours are painted on cardboard, or groups of plants, 
 flowers, flags, and shawls, are illuminated by a mono-chromatic light, and 
 especially the light procured from a large tow torch well supplied with 
 salt and spirit, the effect is certainly very remarkable ; at the same time 
 it shows how completely substances owe their colour to the light by 
 which they are illuminated, and it also indicates why ladies cannot 
 choose colours by candle-light, unless of course they propose to wear 
 the dress only at night, when it is quite prudent to see the colours in 
 a room lit with gas ; and this fact is so well known that, at the chief 
 drapers, a darkened room lit with gas is provided during the daytime to 
 enable purchasers of coloured dresses to judge of the effect of artificial 
 light upon them. Whilst the flowers, &c., are lighted up with the yellow 
 light, a magical change is brought about by throwing on suddenly the 
 rays from the oxy-hydrogen light, when the colours are again restored ; 
 or if the latter apparatus is not ready, the combustion of phosphorus in 
 a jar of oxygen will answer the same purpose. The light obtained from 
 the combustion of gas affords an excess of the yellow or red rays of 
 light, which causes the difference between candlelight and daylight 
 colours already alluded to. 
 
 c c 2 
 
388 
 
 boy’s playbook of science 
 
 CHAPTER XXV. 
 
 THE INFLECTION Oil DIFFRACTION OF LIGHT. 
 
 In this part of the subject it is absolutely necessary to return to the 
 theory of undulations with which the present subject was commenced. 
 The inflection of light offers a third method by which rays of light may 
 be decomposed and colour produced. The phenomena are extremely 
 beautiful, although the explanation of them is almost too intricate for a 
 popular work of this kind. 
 
 The cases where colour is produced by inflection are more numerous 
 than might at first be supposed; thus, if we look at a gaslight or the 
 setting sun through a wire gauze blind, protecting the eye with a little 
 tank of dilute ink, a most beautiful coloured cross is apparent. An 
 extremely thin film of a transparent matter, such as a little naphtha or 
 varnish dropped on the surface of warm water or soap bubbles, or a very 
 thin film of glass obtained by blowing out a bulb of red-hot glass till it 
 bursts, or an exquisitely thin plate of talc or mica, all present the 
 phenomena of colour, although they are individually transparent, and in 
 ordinary thicknesses quite colourless. 
 
 Sir Isaac Newton brought his powerful intellect to bear on these 
 facts, and as a preliminary step invented an instrument for measuring 
 the exact thickness of those transparent substances that afforded colour, 
 and the apparatus displaying Newton’s rings is still a favourite optical 
 experiment. It consists of a plano-convex lens, a. (Eig. 363) a slice. 
 
 C 
 
 B 
 
 Fig. 363. The two lenses, with the plate or film of air between them, and producing 
 seven coloured rings when the lenses are brought sufficiently close to each other by the 
 screws. 
 
 as it were, from a globe of glass twenty-eight feet in diameter, or the 
 radius of whose convex surface is fourteen feet. This plano-convex lens 
 is placed on another double convex lens, b., whose convex surfaces have 
 a radius of fifty feet each, consequently the lenses are very shallow, and 
 the space (c c) included between them being filled with air, can of course 
 be accurately measured. (Eig. 363.) It is usual to mount the lenses in 
 brass rings which are brought together with screws, when the most 
 beautiful coloured rings are apparent, and are produced by the extreme 
 thinness of the film or plate of air enclosed between the two lenses ; and 
 
COLOURS CF THIN PLATES. 
 
 389 
 
 the relative thicknesses of the plates of air at which each coloured light 
 is reflected are as follows : 
 
 Red 
 
 . . . 133 10 millionths of an inch. 
 
 Orange 
 
 ... 120 
 
 99 
 
 Yellow . 
 
 . . . 113i 
 
 99 
 
 Green . 
 
 . . • 105* 
 
 99 
 
 Blue 
 
 ... 98 
 
 99 
 
 Indigo . 
 
 ... 92* 
 
 99 
 
 Yiolet . 
 
 ... 83* 
 
 99 
 
 By dividing an inch into ten millions of parts, and by taking 133 of such 
 parts, the thickness of the film of air required to reflect the red ray is 
 obtained, and in like manner the other colours require the minute thick- 
 nesses of air recorded in the table above. When the thickness of the 
 film of air is about tt8. 2 ooo^^ s °f an inch, colours cease to become 
 visible, owing to the union of all the separate colours forming white 
 light, but if the Newton rings are produced in mono-chromatic light, 
 then a greater number of rings are apparent, but of one colour only, 
 and alternating with black rings, i.e., a dark and a yellow succeeding 
 each other ; this fact is of great importance as an illustration of the 
 undulatory theory, and demonstrates the important truth, that two rays 
 of light may interfere with each other in such a manner as to produce 
 darkness . 
 
 Sir David Brewster remarks that, “From his experiments on the 
 colours of thin and of thick plates, Newton inferred that they were 
 produced by a singular property of the particles of light, in virtue of 
 which they possess, at different points of their paths, fits or dispositions 
 to be reflected from or transmitted by transparent bodies. Sir Isaac 
 does not pretend to explain the origin of these fits , or the cause which 
 produces them, but terms them fits of transmission and fits of reflexion .” 
 
 Sir Isaac Newton objected to the theory of undulations because ex- 
 periments seemed to show that light could not travel through bent tubes, 
 which it ought to do if propagated by undulations like sound ; and it was 
 reserved for the late Dr. Young to prove that light could and would turn 
 a corner, in his highly philosophical experiments illustrating the inflection 
 or bending in of the rays of light. 
 
 Dr. Young placed before a hole in a shutter a piece of thick paper 
 perforated with. a fine needle, and receiving through it the diverging 
 beams on a paper screen, found that when a slip of cardboard one- 
 thirtieth of an inch in breadth was held in such a beam of light, that 
 the shadow of the card was not merely a dark band, but divided into 
 light and dark parallel bands, and instead of the centre of the shadow 
 being the darkest part, it was actually white. Dr. Young ascertained 
 that if he intercepted the light passing on one side of the slip of card 
 with any opaque body, and allowed the light to pass freely on the other 
 side of the slip of cardboard, that all the bands and the white band 
 in the centre disappeared, and hence he concluded that the bands 
 or fringes within the shadow were produced by the interference 
 
390 
 
 boy 7 s playbook op science. 
 
 of the rays bent into the shadow by one side of the card , with the rays benb 
 into the shadow by the other side. (Tig. 364). 
 
 7; 
 
 In order to show how two waves may interfere so as to exalt or destroy 
 each other, two sets of waves may be propagated on the surface of a still 
 tank or bath of water, from the two points a a (Tig. 364), the black 
 lines or circles representing the tops of the waves. It will be seen 
 that along the lines b b the waves interfere just half way between each 
 other, so that in all these directions there will be a smooth surface, 
 provided each set of waves is produced by precisely the same degree of 
 disturbing force, so as to be perfectly equal and alike in every respect, 
 and the first wave of one set exactly half a wave in advance of the first 
 wave of the other, while at the curve in the direction of all the line c c, 
 the waves coincide, and produce elevations or undulations of double 
 extent ; in the intermediate spaces, intermediate effects will, of course, 
 be produced. 
 
 Professor Wheatstone has invented some very simple and beautiful 
 acoustic apparatus for the purpose of proving that the same laws of 
 interference exist also in sound, which, as already stated, consists in 
 the vibrations or undulation of the particles of air. 
 
WOODWARDS MODELS. 
 
 391 
 
 The nature and effects of interference are also admirably illustrated 
 by the following models of Mr. Charles Woodward, President of the 
 Islington Scientific Institution, and to whom we have already alluded. 
 
 Fig. 365— No. 1. A model of waves with moveable rods— No. 2. A model of fixed waves.— 
 No. 3. Intensity of waves doubled by the superposition and coincidence of two equal 
 systems. — No. 4. Waves neutralized by the superposition and interference of two equal 
 systems, the raised part of one wave accurately fitting into and making smooth the hollow 
 of the other, illustrating the fact that two waves of light or sound fhay destroy each other. 
 
 Returning again to the coloured rings, we find that Newton discovered 
 that at whatever thickness of the film of air the coloured ring first ap- 
 peared, there would be found at twice that thickness the dark ring, at three 
 times the coloured, at four times the dark, and so on, the coloured rings 
 regularly occurring at the odd numbers , and the dark ones at the even 
 numbers. This discovery is well illustrated by the models (Fig. 365) ; and 
 it jnay be noticed at No. 3 that the highest and the lowest parts of the waves 
 
392 
 
 boy’s playbook of science. 
 
 interfere, but coincide and produce a wave of double intensity ; the lifctia 
 crosses of the upper model are in a straight line with the numbers 1, 3, 
 5, 7, and are supposed to represent the coloured rings, whilst in No. 4 
 the upper series of waves is half an undulation in advance of the lower ; 
 and if the eye is again directed from the little crosses downward, the 
 figures 2, 4, G, 8, even numbers, are apparent, and represent the dark 
 rings, when the waves of light destroy each other. The phenomena of 
 thin plates, such as colours from soap bubbles, and the films of varnish, 
 are well explained by the law of interference. The light reflected from 
 the second surface of the film of air (which must of course, however 
 thin, have two surfaces, viz., a upper and a lower one) interferes with 
 the light reflected from the first, and as they come from different points 
 of space, one set of waves is in advance of the other, No. 4, Eig. 365 ; they 
 
 Fig. 366. Appearance of Newton’s rings when produced in yellow light, 1, 3, 5, 7, being 
 the yellow rings, and 2, 4, 6, 8, the dark rings. Light by the odd numbers ; darkness by 
 the even numbers. The central spot, where the two surfaces are in contact, is dark. 
 
 reach the eye with different lengths of paths, and by their interference 
 form alternately the luminous and dark fringes, bands, or circles. 
 Bridge’s diffraction apparatus, manufactured only by Elliott Brothers, 
 offers itself specially as a most beautiful drawing-room optical instru- 
 ment. The purpose of this apparatus is to illustrate in great variety, 
 and in the most convenient and compact form, the phenomena of the 
 diffraction or interference of light. This is attained by the assistance 
 of photography. Transparent apertures in an opaque collodion film are 
 produced on glass, and a point of light is viewed through the apertures. 
 
elliott’s diffraction apparatus. 
 
 393 
 
 The forms of the apertures are exceedingly various, — triangles, squares, 
 circles, ellipses, parabolas, hyperbolas, and combinations of them, besides 
 many figures of fanciful forms, are included in the set. When an 
 image of the sun is viewed through these apertures, figures of extra- 
 ordinary beauty, both of form and colour, are produced ; and of eacli 
 of these many variations may be obtained by placing the eye-glass of 
 the telescope at different distances from the object glass. Many of the 
 figures produced, especially when the telescope is out of focus, might 
 suggest very useful hints to those concerned in designing patterns. 
 Although the phenomena are chiefly of interest to the student of science, 
 in consequence of their bearing on theories of light, yet their beauty and 
 variety render them amusing to all. A few words on the mode of using 
 the apparatus may be of service. (Pig. 367.) 
 
 Choose a very bright day, for then only can the apparatus be used. 
 Place the mirror in the sun, and let the light be reflected on the back 
 of the blackened screen. The lens which is inserted into this screen 
 will then form an exceedingly bright image of the sun. Then at the 
 distance of not less than twelve feet, clamp the telescope to a table in 
 such a position as to view the image thus formed. Put the eccentric 
 cap on the end of the telescope, clean the glass objects carefully, and 
 attach them to the cap so that they may be turned each in order before 
 the telescope. In this manner, all those which consist of a series of 
 figures may be viewed. Then detach the eccentric cap, and replace it 
 by the other. Into it place any of the single objects. In viewing some 
 of the figures, brightness is advantageous — in others, delicacy ; in the 
 former case, let the lens of long focus be inserted in the screen — in the 
 latter case, that of shorter focus. In every case, let the phenomena be 
 observed not only when the telescope is in focus, but also when the 
 eye-glass is pushed in to various distances. 
 
 Mr. Warren de la Hue has ingeniously taken advantage of the colours 
 produced by thin films of varnish, and actually fixed the lovely iridescent 
 colour produced in that manner on highly polished paper, which is 
 termed “ iridescent paper A tank of warm water at 80° Pahr., about 
 
394 
 
 boy’s playbook of science. 
 
 six inches deep, and two feet six inches square, is provided, and a highly 
 glazed sheet of white or black paper being first wetted on a perforated 
 metallic plate, is then sunk with the plate below its surface, care being 
 taken to avoid air bubbles. A peculiar varnish is then allowed to 
 trickle slowly down a sort of tongue of metal placed in the middle of 
 one of the sides of the tank, and directly the varnish touches the surface 
 of the water it begins to spread out in exquisitely thin films, and by 
 watching the operation close to a window and skimming away all the 
 imperfect films, a perfect one is at last obtained, and at that moment the 
 paper lying on the metal plate is raised from the bottom of the tank, and the 
 delicate film of varnish secured. When dry, the iridescent colours are 
 apparent, and the paper is employed for many ornamental purposes. 
 
 An extremely simple and 
 pretty method of producing 
 Newton’s rings has been in- 
 vented by Reade, and is called 
 “ Reade’s iriscope.” A plate 
 of glass of any shape (perhaps 
 circular is the best) is painted 
 on one side with some quickly 
 drying black paint or varnish, 
 and after the other side has 
 been cleaned, it is then rubbed 
 over with a piece of wet soap, 
 and this is rubbed off with a 
 clean soft duster. A tube of 
 about half an inch in diameter, 
 and twelve inches iong, is pro- 
 vided, and is held about one 
 inch above the centre of the soaped side of the glass plate, and directly 
 the breath is directed down the tube on the glass, an immense number 
 of minute particles of moisture are deposited on the glass, and these by 
 inflection decompose the light, and all the colours of the rainbow are 
 produced. (Fig. 368.) 
 
 The iridescent colours seen upon the surface of mother-of-pearl , which 
 Mr. Simonds’ excellent commercial dictionary tells us is “ the name for 
 the iridescent shell of the pearl oyster, and other molluscs,” are refer- 
 rible to fine parallel lines formed by its texture, and are reproducible, 
 according to Brewster’s experiments, by taking impressions of them in 
 soft wax. The gorgeous colours of certain shells and fish, the feathers 
 of birds, Barton’s steel buttons, are not due to any inherent pigment or 
 colouring matter that could be extracted from them, but are owing either 
 to the peculiar fibrous, or parallel -lined, or laminated (plate-like) surfaces 
 upon which the light falls, and being reflected in paths of different lengths, 
 interference occurs, and coloured light is produced. 
 
 Fig. 368. Reade’s iriscope. 
 
395 
 
 CHAPTER XXYI. 
 
 THE POLARIZATION OF LIGHT. 
 
 This branch of the phenomena of light includes some . of the most 
 remarkable and gorgeous chromatic effects ; at the same time, regarded 
 philosophically, it is certainly a most difficult subject to place in a 
 purely elementary manner before the youthful minds of juvenile phi- 
 losophers, and unless the previous chapter on the diffraction of light is 
 carefully examined, the rationale of the illustrations of polarized light 
 will hardly be appreciated. We have first to ask, “ What is polarized 
 light ?” The answer requires ns again to carry our thoughts back to 
 the consideration of the undulatory theory of light, already illustrated 
 and partly explained at pages 302, 390 v 
 
 After perusing this portion of the subject, it might be considered 
 that waves of light were constituted of one motion only, and that an 
 undulation might be either perpendicular or horizontal, according to 
 circumstances. (Eig. 369.) 
 
 No. 1. 
 
 No. 2. 
 
 Fig. 369.— No. 1. A wire bent to represent a perpendicular vibration, which if kept 
 In the latter position, will only pass through a perpendicular aperture.— No. 2. A wire 
 bent to represent a horizontal wave which will only pass through a horizontal aperture. 
 
 This simple condition of the waves of light could not, however, be 
 reconciled theoretically with the actual facts, and it is necessary in 
 regarding, a ray of light, to consider it as a combination of two vibrating 
 motions, one of which, for the sake of simplicity, may be considered as 
 perpendicular, and the other horizontal ; and this idea of the nature of 
 
396 
 
 BOY'S PLAYBOOK OF SCIENCE. 
 
 an undulation of light originated with the late Dr. Young, who while 
 considering the results of Sir D. Brewster’s researches on the laws of 
 double refraction, first proposed the theory of transversal (cross-wise) 
 vibration. Dr. Young illustrated his theory with a stretched cord, 
 which if agitated or violently shaken perpendicularly, produces a wave 
 that runs along the cord to the other end, and may be often seen illus- 
 trated on the banks of a river overhung; with high bushes; the bargemen 
 who drive the horses pulling the vessel by a rope, would be continually 
 stopped by the stunted thick bushes, but directly they approach them, 
 they give the horse a lash, and then violently agitate the rope vertically, 
 which is thrown into waves that pass along the rope, and clear the 
 bushes in the most perfect manner. (Fig. 370-) 
 
 Fi{ar. 3 70. Bargeman throwing his tow-rope into waves to get it over the thick bushes. 
 
 / 
 
 / 
 
 
 ( 
 
 
 Fig. 371. A section of a 
 
 Now if a similar movement is made 
 with the stretched rope from right to 
 left, another wave whI be produced, 
 which will run along the cord in an 
 horizontal position, and if the latter 
 is compared with the perpendicular 
 undulation, it will be evident that each 
 set of waves will be in planes at right 
 angles to and independent of each 
 other. This is supposed to be the 
 mechanism of a wave of common light, 
 so that if a section is taken of such 
 an undulation, it will be represented 
 by a circle abcd (Fig. 37l)> with 
 wave of t wo diameters a b, and c d; or a better 
 
 thetransversaI mechanical notion of a wave of com- 
 
THE POLARIZATION OF LIGHT. 
 
 3a: 
 
 moil light is acquired from the inspection of another of Mr. Woodward's 
 cardboard models. (Pig. 372.) 
 
 Fig. 372. Model of a wave of common light. 
 
 The existence of an alternating motion of some hind at minute intervals 
 along a ray is, says Professor Baden Powell, “ as real as the motion of 
 translation by which light is propagated through space. Both must 
 essentially be combined in any correct conception we form of light. 
 That this alternating motion must have reference to certain directions 
 transverse to that of the ray is equally established as a consequence of 
 the phenomena ; and these two principles must form the basis of any 
 explanation which can be attempted.” A beam of common light is 
 therefore to be regarded as a rapid succession of systems of waves in 
 which the vibrations take place in different planes. 
 
 If the two systems of waves are separated the one from the other, 
 viz., the horizontal from the perpendicular, they each form separately 
 a ray of polarized light, and as Presnel has remarked, common light is 
 merely polarized light , having two planes of polarization at right angles 
 to each other. To follow up the mechanical notion of the nature of 
 polarized light, it is necessary to refer again to Woodward's card 
 wave model (Pig. 372), and by separating the two cards one from 
 the other it may be demonstrated how a wave of common light reduced 
 to its skeleton or primary form is reducible into two waves of polarized 
 light, or how the two cards placed together again in a transversal position 
 form a ray of common light. (Pig. 373.) 
 
 No. l. No. 2. No. 3. 
 
 \ 
 
 HB 
 
 Fig. 373.— No. 1. Common light, made up of the two waves of polarized 
 light, Nos. 2 and 3. 
 
 The query with respect to the nature of polarized light being answered, 
 it is necessary, in the next place, to consider how the separation of these 
 transversal vibrations may be effected, and in fact to ask what optical 
 arrangements are necessary to procure a beam of polarized light ? Light 
 may be polarized in four different ways — viz., by reflection, single refrac- 
 tion, double refraction, and by the tourmaline — viz., by absorption. 
 
398 
 
 boy’s playbook of science. 
 
 Polarization by Reflection , and by Single Refraction. 
 
 In the year 1810, the celebrated French philosopher, Mons. Malus, 
 while looking through a prism of Iceland spar, at the light of the setting 
 sun, reflected from the windows of the Luxemburg palace in Paris, 
 discovered that a beam of light reflected from a plate of glass at an 
 angle of 56 degrees, presented precisely the same properties as one of the 
 rays formed by a rhomb of Iceland spar, and that it was in fact polarized. 
 One of the transversal waves of polarized light of the common light, 
 being reflected or thrown off from the surface of the glass, whilst the 
 other and second transversal vibration passed through the plate of 
 glass, and was likewise polarized in another plane, but by single refrac- 
 tion, so that the experiment illustrates two of the modes of polarizing 
 light — viz., by reflection, and by single refraction. This important ele- 
 mentary truth is beautifully illustrated by Mr. J. T. Goddard’s new 
 form of the oxy-hydrogen polariscope, by which a beam of common 
 light traverses a long square tin box without change ; but directly a 
 bundle of plates of glass composed of ten plates of thin flattened crown 
 glass, or sixteen plates of thin parallel glass plates used for microscopes, 
 are slid into the box at an angle of 56° 45', then the beam of common 
 
 Fig. 374.— No. 1. a is the lime light, b. The condenser lenses, c. The beam of common 
 light. Here the glass plates are removed. — No. 2. a. Lime light, b. The condenser 
 lenses, c c. The bundle of plates of glass at an angle of 56° 45'. d is the ray of light 
 polarized by reflection from the glass plates, c c, and e is the beam of polarized light by 
 single refraction, having passed through the bundle of plates of glass, c c. 
 
goddard’s polariscope. 
 
 399 
 
 light is split into two 
 beams of polarized light, 
 which pursue their re- 
 spective paths, one pass- 
 ing by single refraction 
 through the glass, and the 
 other being reflected, and 
 rendered apparent by 
 opening an aperture over 
 the glass plates, and then 
 again by using a little 
 smoke from brown paper, 
 the course of the rays 
 becomes more apparent. 
 
 Fig*. 375. a a. Model in wood of a bundle of plates 
 ± x of glass at an angle of 56° 45'. b. Beam of common 
 
 Tile same truth is well with transversal vibration, c. Light polarized by 
 reflection, n. Light polarized by refraction. 
 
 illustrated by the card- 
 board model wave and a wooden plane with horizontal and perpendicuL 
 slits, placed at an angle of 56° 45', as at Tig. 375. 
 
 POLARIZATION BY DOUBLE REPRACTION. 
 
 The name of Do^/^-refracting or Iceland Spar is given to a very 
 clear, limpid, and perfectly transparent mineral, composed of carbo- 
 nate of lime, and found on the eastern coast of Iceland* Its crystal- 
 lographic features are well described by the Rev. Walter Mitchell 
 in his learned work on mineralogy and crystallography, and it is suffi- 
 cient for the object of this article to state that it crystallizes in rhombs, 
 and modifications of the rhomboidal system. It must not be confounded 
 with rock or mountain crystal, which, under the name of quartz, crystal- 
 lizes in six-sided prisms with six-sided pyramidal tops; quartz being 
 composed of silica, or silicic acid and calcareous spar of carbonate of 
 lime. Yery large specimens of the latter mineral are rare and valuable, and 
 the lion oi specimens of calcareous, or double-refracting spar, is now in the 
 possession of Professor Tennant, the eminent mineralogist of the Strand. 
 It is nine inches high, seven and three-quarters inches broad, and five 
 and a half inches thick ; its estimated value being 100/. This beautiful 
 specimen has been photographed, and its stereograph illustrates in a 
 very striking manner the double refracting properties of the spar. 
 
 If a printed slip of paper is placed behind a rhomb of Iceland spar, 
 two images of the former are apparent, and the stereograph already 
 alluded to shows this fact very perfectly, at the same time illustrates 
 the value of the stereoscope. Out of the stereoscope the words “ Stereo- 
 scopic Magazine ” appear doubled, but seem to lie in the same plane; 
 but directly the picture is placed in the instrument, then it is clearly 
 seen that one image is evidently m a very different plane from the other. 
 The double-refracting power of this mineral is illustrated by holding a 
 small rhomb of Iceland spar, placed in a proper brass tube before 
 the orifice as at Tig. 327, from which the rays of common light are 
 
400 
 
 boy’s playbook of science. 
 
 passing ; if an opaque screen of brass perforated with a small hole is 
 introduced behind the rhomb, then, instead of one circle of light 
 being apparent on the screen, two are produced, and both the rays 
 issuing in this manner are polarized, one being termed the ordinary and 
 the other the extraordinary ray. (Fig. 376.) 
 
 A 
 
 light. 
 
 The polarizing property of the rhomb is perhaps better shown by 
 the next diagram, where a b represents the obtuse angles of the Iceland 
 spar, and a line drawn from a to b, would be the axis of the crystal. 
 The incidental ray of common light is shown at c, and the oppositely 
 polarized transmitted rays called the ordinary ray o, and extraordinary 
 ray e, emerge from the opposite face of the rhomboid. If a black line is 
 ruled on a sheet of paper as at k k, and examined by the eye at c, it 
 appears double as at k k and j j. (Fig. 377.) 
 
 The cardboard model is again useful in demonstrating the polarization 
 of light by double refraction, and if a model of a rhomb of Iceland 
 
THE TOURMALINE. 
 
 401 
 
 spar is made of glass plates, one face of which has an aperture like a 
 cross, and the other a horizontal and perpendicular slit, as at Nos. 1 
 and 2 (Fig. 378), the production of the ordinary and extraordinary rays 
 is demonstrated in a familiar manner, and is easily comprehended. 
 
 
 Fig. 378.— No. 1. One face of the model rhomb to admit the transversal vibration repre- 
 sented by the cardboard model.— No*. 2. The opposite face of the rhomb, from which issue 
 the polarized, ordinary, and extraordinary rays.— No. 3. Side view of the model. 
 
 In Newton’s “ Optics” we find the following description of Iceland 
 spar “ This crystal is a pellucid fissile stone, clear as water or crystal 
 
 of the rock (quartz), and without colour Being rubbed on cloth 
 
 it attracts pieces of straw and other light things like amber or glass, and 
 with aquafortis it. makes an ebullition If a piece of this crys- 
 
 talline stone be laid upon a book, every letter of the book seen through 
 it will appear double by means of a double refraction.” 
 
 POLARIZATION BY THE TOURMALINE. 
 
 This mineral was first discovered during the sixteenth century, in 
 the island of Ceylon, afterwards in Brazil, and since that period at 
 various localities in the four quarters of the globe. In the Grevillian 
 collection purchased many years ago by government for the British 
 Museum, there is a fine specimen of red ^tourmaline valued at 500/. 
 The green tourmaline is named Brazilian emerald, and the Berlin blue 
 tourmaline is called Brazilian sapphire ; the mineral chiefly consists of 
 sand (silica) and alumina, with a small quantity of lime, or potash, or soda, 
 boracic acid, and sometimes oxide of iron or manganese. When light 
 is. passed through a slice of this mineral it is immediately polarized, one 
 of the transversal vibrations being absorbed, stopped, or otherwise dis- 
 posed of, the other only emerging from the tourmaline, consequently it 
 is one of the most convenient^ polarizers, although the polarized light 
 partakes of the accidental colour of the mineral. Green, blue, and 
 yellow tourmalines are bad polarizers, but the brown and pink varieties 
 
402 
 
 boy’s playbook of science. 
 
 are very good, and it is a most curious fact that white tourmaline does 
 not polarize. (Fig. 379.) 
 
 Fig. 379. Crystal of tourmaline slit (parallel to the axis) into four plates, which when 
 ground and polished, may be used for the polarization of light. 
 
 The mineral crystallizes in long prisms, whose primitive form is the 
 obtuse rhomboid, having the axis parallel to the axis of the prism. The 
 term axis with reference to the earth, as shown at page 16, is an 
 v imaginary single line around 
 
 which the mass rotates, but in a 
 crystal it means a single direction 9 
 because a crystal is made up of 
 a number of similar crystals, each 
 of which must have its axis, thus 
 the whitest Carrara marble re- 
 duced to fine powder, moistened 
 with water and placed under a 
 microscope, is found to consist 
 chiefly of minute rhomboids, simi- 
 lar to calcareous spar. The 
 smallest crystal of this mineral is 
 divisible again and without limit 
 into other rhombs, each of which 
 possesses an axis. (Fig. 380.) 
 
 If a plate of tourmaline is held 
 before the eye whilst looking at 
 the sun (like the gay youth in 
 Hogarth’s picture who is being 
 arrested whilst absorbed with the 
 wonders of a tourmaline, which 
 was, in the great painter’s time, a 
 popular curiosity,) it may be turned round in all directions without the 
 slightest difference in the appearance of the light, which will be coloured 
 by the accidental tint of the crystal, but if a second slice of tourmaline 
 is placed behind the other, there will be found certain directions in which 
 the light passes through both the slices, whilst in other positions the light 
 is completely cut off. 
 
 J 
 
 y/ 
 
 3 
 
 j 
 
 '\c 
 
 
 F 
 
 \ 
 
 * 
 
 
 
 
 B 
 
 Fig. 380 represents a crystal, tlie axis of 
 which is the direction a b. The dotted lines 
 show the division of the large crystal into 
 four other and smaller ones, each of which has 
 its axis, a c, c b, d e, f g ; and every line 
 within the large crystal parallel to a b is an 
 axis, consequently the term is employed usually 
 in the plural number axes. 
 
THE TOURMALINE. 
 
 403 
 
 When the axes of both plates coincide, the light polarized by one 
 tourmaline will pass through the other, but if the axes do not coincide,, 
 and are at right an- 
 gles to each other, 
 then the polarized 
 light is entirely 
 stopped, and the ra- 
 tionale of this will be 
 appreciated at once 
 if a tourmaline is re- 
 garded (mechanical- 
 ly) as if it were like a 
 grating with perpen- 
 dicular bars through 
 which the polarized 
 light will pass. Any 
 number of such grat- 
 ings with the bars 
 parallel would not 
 stop the polarized 
 light, but if the second grating is turned round ninety degrees, the bars 
 will be at right angles to those of the first grating, and the perpen- 
 dicular wave of polarized light cannot pass. (Fig. 381 .) 
 
 Fig 1 . 381. a. Model of the first slice of tourmaline into 
 which the transversal vibrations, b, are passing; the horizontal 
 wave is absorbed, and the perpendicular polarized one proceeds 
 to the second slice of tourmaline, c, where the bars (the axes' 
 being at right angles to those of a, it is stopped, and cannot 
 pass through until the bars of c are parallel with a. 
 
 Splendid Chromatic effects produced by Polarized Light. 
 
 Having discussed the various modes of obtaining polarized light, the 
 next step is to arrange an apparatus by which certain double refracting 
 crystals, and other bodies, shall divide a ray of polarized light, and then 
 by subsequent treatment with another polarizing surface, the divided 
 rays are caused to interfere with each other, and afford the phenomena 
 of colour. Bodies that refract light singly, such as gases, vapours or 
 liquids, annealed glass, jelly, gums, resins, crystallized bodies of the 
 tessular system, such as the cube and octohedron, do not afford any of 
 the results which will be explained presently, except by the influence 
 of pressure, as .in unannealed glass, or a bent cold glass bar. By compres- 
 sion or dilatation, they are changed to double refractors of light. The 
 bodies that possess the property of double refraction (though not to the 
 visible extent of Iceland spar), are all other bodies such as crystallized 
 chemicals, salts, crystallized minerals, animal and vegetable substances 
 possessing a uniform structure, such as horn and quill; all these sub- 
 stances divide the ray of polarized light into two parts, and by placing 
 a tliiii film of a crystal of selenite (which is one of the best minerals that 
 can be used for the purpose) in the path of the beam of polarized lmht,. 
 coming either from the glass plates, as in No. 2, (Fig. 325), page 338* 
 or from a slice of tourmaline, and then receiving it through the ordinary- 
 focusing lenses or object-glasses of the oxy-hydrogen microscooe, no 
 colour is yet apparent in the image of the selenite on the screen, until 
 
 i)j)2 
 
404 
 
 boy’s playbook of science. 
 
 another tourmaline, or a bundle of glass plates, is placed at an angle of 
 56° 45', and at right angles to the plane of reflection of the first set of 
 plates ; then the most gorgeous colours suddenly appear over all parts of 
 the film of selenite as depicted on the screen, like other objects shown 
 by the oxy-hydrogen microscope. (Fig. 382.) 
 
 Fig. 382. Duboscq’s polarizing apparatus, a. The light and the condenser lens. 
 B. The plates of glass at the proper angle, c. The selenite object, d. The focusing 
 lens. e. The second bundle of plates of glass called the analyser, f. A stop for ex- 
 traneous’rays of light, g. The image of the film of selenite most beautifully coloured. 
 
 Goddard’s oxy-hydrogen polariscope is one of the most convenient, 
 because either tiie reflected or refracted polarized rays can be rendered 
 available ; it consists of the apparatus shown at Fig. 374, and to 
 this is added a low microscope power, and stage to hold the selenite 
 or other objects, with another bundle of sixteen plates of the thin 
 microscopic glass or mica, called the analyser. A slice of tourmaline, 
 or a Nicol’s prism may be employed, instead of the second bundle of 
 reflecting plates. When the ray of polarized light reflected from the 
 first set of glass plates enters the doubly refracting film of selenite, 
 which is about the fortieth or fiftieth part of an inch in thickness, it is 
 split into the ordinary and extraordinary rays, and is said to be dipola- 
 rized, and forms two planes of polarized light, vibrating at right angles 
 to each other. When the latter are received on another bundle of plates 
 of glass called the analyser, at an angle of 56° 45', but at right angles 
 to the first set of glass plates, they interfere, because in the passage of 
 the two rays from the selenite they have traversed it in different direc- 
 tions, with different velocities ; one of these sets of waves will therefore, 
 on emerging from the opposite face of the selenite be retarded, and lie 
 
THE POLARIZATION OF LIGHT. 
 
 405 
 
 behind the other ; but being polarized in different planes, they cannot 
 interfere until their planes of polarization are made to coincide, which is 
 
 Fig 1 . 383. The electric lamp and lantern of Duboscq, showing the projection of the 
 carbon poies on the disc. This experiment is performed with the help of the plano-convex 
 lens, a, and the rays pass through a very narrow aperture at b. 
 
 Fig. 384. a a. Card model of a beam of polarized light coming from the first bundle ol 
 plates of glass, shown at Fig. 326, p. 339. b. Model of the film of selenite, which divided 
 or dipolarizes the ray a a into c and n, which, interfering by means of the second bundle* 
 of plates of glass called the analyser z, produce reflected chromatic ellects by interference 
 at e, and refracted elfects at p.. 
 
406 
 
 boy’s playbook of science. 
 
 effected by means of the second bundle of glass plates called the analyser ; 
 and when this is brought into a position at right angles to the first set 
 of reflecting glass plates, half the ordinary wave interferes with half the 
 extraordinary wave; and being transmitted through the analyser, 
 produces, say red and orange, whilst the remaining halves also interfere, 
 and being reflected, afford the complementary colours green and blue. 
 (Fig. 3S3.) The term complementary is intended to define any two 
 colours containing red, yellow, and blue, because the three combined 
 together produce white light ; for example, the complementary colour to 
 red would be green, because the latter contains yellow and blue ; the 
 complementary colour to orange would be blue, because the former 
 contains red and yellow. Any two colours, therefore, which together 
 contain red, yellow, and blue are said to be complementary ; and if this 
 principle was better understood, ladies would never commit such 
 egregious blunders as they occasionally do in the choice of colours for 
 bonnets and dresses, and select a blue bonnet to be worn with a 
 green dress, or vice versa. By rotating the analyser, the reflected 
 and refracted rays change colours, and if the former is red and the 
 latter green, by moving the analyser round 90°, the reflected rays change 
 to green and the refracted to red; at 180° the colours again change 
 places ; at 270° the reflected ray will be again green, and the refracted 
 red; to be once more brought back at 360° to the original position, viz., 
 reflected rays red, refracted green. The thickness of the films of 
 selenite determines the particular colour produced. 
 
 If the selenite is of a uniform thickness, one colour only is obtained, 
 and by ingeniously connecting pieces of various thicknesses (in the same 
 forms as stained glass for cathedral windows), the most beautiful designs 
 were made by the late Mr. J. T. Cooper, jun., which have since been 
 manufactured in great quantity and variety by Mr. Darker, of Paradise- 
 street, Lambeth. The colours of these selenite objects are seen by 
 placing them in front of a piece of black glass, fixed at the polarizing 
 angle, and then examining the design with a slice of tourmaline, or still 
 better with a single-image Nicol prism, when the most brilliant colours 
 are obtained, and varied at every change of the angle of the analyser. 
 
 Selenite, or sparry-gypsum, is the native crystallized sulphate of lime, 
 which contains water of crystallization (CaO, S0 3 , 2HO). It frequently 
 occurs imbedded in London clay, and is called quarry glass by the 
 labourers who find it at Shotover Hill, near Oxford, and also in the 
 Isle of Sheppey. 
 
 At a very early period, before the discovery of glass, selenite was used 
 for windows ; and we are told that in the time of Seneca, it was im- 
 ported into Rome from Spain, Cyprus, Cappadocia, and even from 
 Africa. It continued to be used for this purpose until the middle ages, 
 for Albinus informs us, that in his time, the windows of the dome of 
 Merseburg were of this mineral. The first greenhouses, those invented 
 by Tiberius, were covered with selenite. According to Pliny, bee- 
 hives were encased in selenite, in order that the bees might be seen at 
 work. 
 
CHROMATIC EFFECT OF FOLARIZED LIGHT. 
 
 407 
 
 The late Dr. Pereira has placed the phenomena already described in 
 the form of a most instructive diagram, which we borrow from hi 3 
 elaborate work on “ Polarized Light/’ (Pig. 385.) 
 
 F ] g. 38o. a. A ray of common or unpolarized light, incident on b. b. The polarizer (a 
 plate of tourmaline), c. A ray of plane polarized light, incident on d. d. The doubly- 
 reiractmg film of selenite, e. The extraordinary ray. o. The ordinary ray, produced by the 
 double refraction of the ray c. g. The analyser (or doubly-refracting or NicoTs prism). 
 ® °* + e °™ mar y ra y* E E - The extraordinary ray, produced by the double refraction of 
 tne extraordinary ray, e. o o. The ordinary ray, o e. The extraordinary ray, produced by 
 
 the double refraction of the ordinary ray, o. J 
 
 The chromatic effects described are not confined to selenite objects 
 only, but are obtained from glass, provided the particles are in a state 
 of unequal tension, as in masses of unannealed glass of various forms. 
 (Pig. 386.) Consequently, polarized light becomes a most valuable 
 
 l\!° 1 
 
 Fig. 3S6. No. 1. Unanncaled glass for the polariscope. Nos. 2 and 3. Appearance of the 
 clack cross and coloured circles in a square and circular piece of unannealed glass in the 
 
 means for ascertaining the condition of particles otherwise invisible and 
 inappreciable. One of the most beautiful experiments can be mada 
 
408 
 
 boy’s playbook of science. 
 
 with a bar of plate-glass, which refracts light singly until pressure is 
 applied to the centre, in order to bend it into an arch or curve, when 
 
 the appearance pre- 
 sented in Fig. 387 is 
 apparent. 
 
 A quill placed in the 
 polarizing apparatus is 
 also discovered to be 
 in a state of unequal 
 tension by the appear- 
 ance of coloured fringes 
 within it, which change 
 colour at every move- 
 ment of the analyser. 
 
 Another series cf 
 beautiful appearances 
 present themselves 
 when a ray of white 
 polarized light is made 
 
 Fig. 337. a b. Bar of glass under the pressure of the 
 screw c, and appearance of bands or fringes of coloured 
 light, which entirely disappear on the removal of the screw. 
 An effect, of course, only visible by polarized light. 
 
 to pass perpendicularly through a slice of any crystallized substance 
 with a single axis ; if the analyser consist of a slice of tourmaline, a, 
 
 number of concentric 
 coloured rings are ren- 
 dered visible with a 
 black cross in the cen- 
 tre, which is replaced 
 with a white one on 
 moving the tourmaline 
 through each quadrant 
 of the circle. 
 
 Crystals of Iceland 
 spar present this phe- 
 nomenon in great 
 beauty; and if the 
 crystal (such as nitre) 
 lias two axes of double- 
 refraction, a double- 
 system of coloured 
 rings is apparent, with 
 the most curious 
 changes and combina- 
 tions of the black and white crosses with them. (Fig. 388.) 
 
 Mr. Goddard has recommended the optical arrangement (Fig. 389) for 
 showing the rings with great perfection, as also the number of rings 
 that increase in some crystals (the topaz, for example), with the 
 divergence of the rays of polarized light passing through them. 
 
 Mr. Woodward’s table and oxv-hydrogen polariscope and microscope, 
 made by Smith and Beck, of Coleman-street, is well adapted, from its 
 
 Fig. 388. Crystal of nitre with two axes, as seen in 
 polarized light. 
 
UTILITY OF POLARIZED LIGHT. 
 
 409 
 
 simplicity and perfection, to exhibit all the varied and beautiful effe cts 
 of polarized light ; and we only regret that want of space prevents us 
 
 Fig. 389. aaa. Polarized light, b b. A lens of short focus, transmitting a cone of 
 light with an angle of divergence for its rays, c c, of 45°. d d. The crystal of topaz, 
 Iceland spar, or nitre, e e. The slice of blue tourmaline for analysing. 
 
 describing it in detail, although the reader may see the body of the 
 apparatus at page 125, where the .modifications of the oxy-hydrogen 
 light are described and figured ; and the polarizing apparatus would be 
 placed, of course, in front of the light issuing from the lantern. 
 
 Finally, the question of utility (the cm bono) may be considered in 
 answer to the query, What is the use of polarized light ? 
 
 The value to scientific men of a knowledge of the nature of this 
 modification of common light cannot be overrated. It has given the 
 philosopher a new kind of test, by which he discovers the structure of 
 things that would otherwise be perfectly unknown ; it has given the 
 astronomer increased data for the exercise of his reasoning powers ; 
 whilst to the microscopist the beauty of objects displayed by polarized 
 light has long been a theme of admiration and delight, and has served 
 as a guide for the identification of certain varieties of any given sub- 
 stance, such as starch. 
 
 A tube provided with a polarizer of tourmaline, or a single-image 
 INficol prism, is invaluable to the look-out at the mast-head in cases 
 where vessels are navigating either inland or sea water, where the 
 presence of hidden rocks is suspected, because the polarizer rejects ail 
 the glare of light arising from unequal reflection at the surface of water, 
 and enables the observer to gaze into the depths of the sea and to 
 examine the rocks, which can only be perfectly visible by the refracted 
 light coming from their surfaces through the water. 
 
 Professor Wheatstone has invented an ingenious polarizing clock foi 
 showing the hour of the day by the polarizing power of the atmosphere. 
 Birt, Powell, and Leeson have each invented instruments for examining 
 the circular polarization of fluids, by which a more intimate knowledge 
 of the relative values of saccharine solutions may be obtained, besides 
 unfolding other truths important to investigators in this branch ot 
 science. 
 
 And last, but not least, it was with the assistance of polarized light 
 
410 
 
 boy’s playbook of science. 
 
 that Dr. Faraday established the relation that exists between light and 
 magnetism, and through the latter, with the force of electricity; and 
 the next figure indicates the necessary apparatus required to repeat this 
 highly important physical truth — viz., the deviation of the plane of 
 polarization of light by the influence of the magnetic force from a 
 powerful electro-magnet. (Fig. 390.) 
 
 Fig. 390. a. The light and condenser lens. b. Single-image Nicol prism, c. Rock crystal 
 of two rotations, d. A double-convex lens, e e. Faraday’s heavy glass, f f. The 
 powerful electro-magnet connected with battery. G-. Double-refracting prisms, h. 
 Image, or screen where the deviation of the plane of polarization by the magnetic force 
 is shown. 
 
 By another and equally beautiful experiment at the London Institu- 
 tion, Professor Grove demonstrated the production of all the other kinds 
 of force from light, using the following arrangement for the purpose : 
 
 A prepared daguerreotype plate is enclosed in a box full of water 
 having a glass front with a shutter over it ; between this glass tnd the 
 plate is a gridiron of silver wire ; the plate is connected with one ex- 
 tremity of a galvanometer coil, and the gridiron of wire with one 
 extremity of a Breguet’s helix ; the other extremities of the galva- 
 nometer and helix are connected by a wire, and the needles brought to 
 zero. As soon as a beam of either daylight or the oxy-hvdrogen light is, 
 by raising the shutter, permitted to impinge upon the plate, the needles 
 are deflected. Thus, light being the initiatory force, we get ~ 
 
 Chemical action on the plate, 
 
 Electricity circulating through the wires. 
 
 Magnetism in the coil, 
 
 Heat in the helix, 
 
 Motion in the needle. 
 
 Such, then, are some of the glorious phenomena that we have en- 
 deavoured to explain in this and the preceding chapters on light. 
 Here we have noticed specially how completely we owe their appre- 
 ciation to the sense of sight operating through the eye, the organ of 
 vision. Well may those who have lost this divine gift speak of their 
 darkness as of a lost worid of beauty to be irradiated only by better 
 
THE LOSS OF SIGHT. 
 
 411 
 
 and more enduring light; and most feelingly does Sir J. Coleridge 
 speak on this point when he says : — 
 
 “ Conceive to yourselves, for a moment, what is the ordinary enter- 
 tainment and conversation that passes around any one of your family 
 tables ; how many things we talk of as matters of course, as to the 
 understanding and as to the bare conception of which sight is abso- 
 lutely necessary. Consider* again, what an affliction the loss of sight 
 must be, and that when we talk of the golden sun, the bright stars, the 
 beautiful flowers, the blush of spring, the glow of summer, and the 
 ripening fruit of autumn, we are talking of things of which we do not 
 convey to the minds of these poor creatures who are born blind, anything 
 like an adequate conception. There was once a great man, as we all 
 know, in this country, a poet — and nearly the greatest poet that 
 England has ever had to boast of — who was blind; and there is a 
 passage in his works which is so true and touching that it exactly 
 describes that which I have endeavoured, in feeble language, to paint. 
 Milton says : — 
 
 * Thus with the year 
 Seasons return ; but not to me returns 
 Day, or the sweet approach of even, or morn, 
 
 Or sight of vernal bloom, or summer’s rose, 
 
 Or flocks, or herds, or human face divine ; 
 
 But cloud instead, and ever- during dark 
 Surrounds me ; from the cheerful ways of men 
 Cut off, and for the book of knowledge fair 
 Presented with a universal blank 
 Of Nature’s works, to me expunged and rased. 
 
 And wisdom at one entrance quite shut out. 
 
 So much the rather, thou, celestial light, 
 
 Shine inward, and the mind through all her powers 
 Irradiate ; there plant eyes ; all mist from thence 
 Purge and disperse, that I may see and tell 
 Of things invisible to mortal sight.’ 
 
 The great poet, when intent upon bis work, sought for celestial light to 
 accomplish it. And this brings me to that part of the labours of our 
 Blind Institutions upon which I dwell the most and which, after all, is 
 the greatest compensation we can afford to the inmates for the affliction 
 they suffer ; and that is, the means we provide for them to read the 
 blessed Word of God, which they can read by day as well as by night, 
 for light in their case is not an essential.” 
 
412 
 
 boy’s playbook of science. 
 
 Fig. 3&1. James Watt. 
 
 CHAPTER XXVII. 
 
 HEAT. 
 
 Throughout the greater number of the preceding chapters it will be 
 evident that the active properties of matter may be summed up under 
 one general head, and may be considered as varieties of attraction — such 
 as the attraction of gravitation, cohesive attraction, adhesive attraction, 
 attraction of composition (or chemical attraction), electrical attraction, 
 magnetical attraction. 
 
 The absolute or autocratic system does not, however, prevail in the 
 works of nature; and she seems ever anxious, whilst imparting 
 great and peculiar powers to certain agents, to create other forces 
 which may control and balance them. Thus, for instance, the 
 great force of cohesive attraction is an ever-present power dis- 
 cernible, as nas been shown, in solids and liquids ; but if this agent 
 
THE SOURCES OF HEAT. 
 
 413 
 
 were allowed to run riot in its full strength and intensity, it would 
 tyrannically hold in subjection all liquid matter, and every drop of water 
 which is at present kept in the liquid state, would succumb to its iron 
 rule, and retain the solid state of ice. Hence, therefore, the wise 
 creation of an antagonistic force— viz., heat ; which is not provided in 
 any niggardly manner, but is liberally bestowed upon the globe from that 
 all-sufficient and enormous source, the sun. And it is by the softening 
 and liquifying influence of his rays that tne greater proportion of the 
 water on the surface of the globe is maintained in the fluid condition, 
 and is enabled to resist the power of cohesion, that would otherwise 
 turn it all, as it were, to stone. 
 
 Cohesion, electricity, and magnetism fully embody the notion of 
 powers of attraction, or a drawing together ; whilst heat stands almost 
 alone in nature as the type of repulsion, or a driving hack. 
 
 Mechanically, repulsion is demonstrated by the rebound of a ball from 
 the ground ; the parts which touch the earth are for the moment com- 
 pressed, and it is the subsequent repulsion between the particles in those 
 parts which causes them to expand again and throw off the ball. 
 
 The development of heat is produced from various causes, which may 
 be regarded as at least four in number. Thus, it was shown by Sir 
 Humphrey Davy, that even when two lumps of ice are rubbed together, 
 sufficient heat is obtained to melt the two surfaces which are in contact 
 with each other. Eriction is therefore an important source of heat, 
 and one of the most interesting machines at the Paris Exposition con- 
 sisted of an apparatus by which many gallons of water were kept in the 
 boiling state by means of the heat obtained from the friction of two 
 copper discs against each other. The machine attracted a good deal of 
 attention on its own merits, and especially because it supplied boiling 
 water for the preparation of chocolate, which the public was duly 
 informed was boiled by the heat rubbed out of the otherwise cold discs 
 of copper. When cannon made on the old system are bored with a 
 drill, it is necessary that the latter should be kept quite cool with a 
 constant supply of water, or else the hard steel might become red-hot, 
 and would then lose its temper, and be no longer capable of performing 
 its duty. 
 
 Count Rumford endeavoured to ascertain how much heat was actually 
 generated by friction. When a blunt steel bore, three inches and a 
 half in diameter, was driven against the bottom of a brass cannon seven 
 inches and a half in diameter, with a pressure which was equal to the 
 weight of ten thousand pounds, and made to revolve thirty-two times in 
 a minute, in forty-one minutes 837 grains of dust were produced, and 
 the heat generated was sufficient to raise 113 pounds of the metal 70° 
 Fahrenheit— a quantity of heat which is capable of melting six pounds 
 and a half of ice, or of raising five pounds of water from the freezing 
 to the boiling point. When the experiment was repeated under water, 
 two gallons and a half of water, at 60° Eah., were made to boil in two 
 hours and a half. 
 
 Chemical affinity has been so often alluded to in these pages, that it 
 
411 
 
 boy’s playbook op science. 
 
 may be sufficient to mention only one good instance of its almost magical 
 power in evoking heat. When a bit of the metal sodium is placed on 
 the tip of a knife, and thrust into some warm quicksilver, or if a pellet 
 of sodium and a few globules of mercury are placed on a hot plate just 
 taken from the oven, and then gently squeezed together, a vivid pro- 
 duction of heat and light is apparent ; and when the mixture of the 
 two metals is cold, it will be found that the quicksilver has lost its 
 fluidity, and a solid amalgam of sodium and mercury is obtained, which 
 gradually, by exposure to the air, returns to the liquid state, the 
 mercury being set free, whilst the sodium is oxidized, and forms soda. 
 Just as an ordinary alloy of copper and gold used by jewellers wmuld 
 lose its colour and brilliancy by the oxidation of the copper ; and when 
 the rusty, dirty film is removed by rubbing and polishing, the surface is 
 again brilliant, and remains so until another film of the exposed copper 
 is attacked : in like manner the sodium is attacked and changed by the 
 oxygen of the air, whilst the mercury being unaffected retains its bril- 
 liancy, and at the same time regains its fluidity. The evolution of heat 
 in the above case indicates that a chemical union has taken place between 
 the two metals. 
 
 Examples of the production of heat by electricity and magnetism 
 have been abundantly shown in the chapters on these subjects ; and one 
 of the best illustrations of this fact has been shown on the occasion of 
 the opening of the telegraphic communication between Erance and Eng- 
 land by means of the submarine cable, when cannon were fired alternately 
 at both ends of the conducting cable by means of electricity, and the 
 event thus inaugurated in both countries. 
 
 That heat is a product of living animal organization is shown, as it 
 were, visibly by the marvellous phenomena that proceed in our own 
 bodies. People do not very often trouble themselves to ask where the 
 heat comes from, or even to think that this invisible power must be 
 maintained in the body, and that slow combustion, or, as Liebig terms 
 it, eremacausis , must continually go on inside our frail mortal tenements ; 
 and more than this, that we cannot afford to waste our heat. If the 
 body is deprived of heat faster than it can be generated, death must 
 inevitably occur ; and a very melancholy instance of this remarkable 
 mode of death has lately occurred in Switzerland to a Russian gen- 
 tleman. 
 
 Such another instance of a man being slowly frozen to death within 
 sight and sound of other beings, through whose veins the blood was 
 flowing at its accustomed temperature (about 90° Eahr.), it would be 
 difficult to find, and it stands forth, therefore, as a marked example and 
 illustration of the statement already made, that living animal organisms 
 are truly a source of heat, which is as essential to the well-being of the 
 body as meat, drink, and air. 
 
 Heat is of two kinds, and may be either apparent to our senses, and 
 therefore called sensible heat; or it may be entirely concealed, although 
 present in solids, liquids, and gases, and is then termed insensible or 
 latent heat. 
 
PANSION OF SOLIDS. 
 
 415 
 
 Sensible Heat. 
 
 The first effect of this force is a demonstration of its repulsive agency* 
 and the dilatation or expansion of the three forms of matter whilst under 
 the influence of heat, admits of very simple illustrations. The expansion of 
 a solid substance, as, for instance, a metal, on the application of heat, 
 
 simply means the absence of heat. 
 
 Solid bodies do not expand equally on the application of the same 
 amount of heat ; thus, a bar of glass one inch square and one thousand 
 inches long would only expand one inch whilst heated from the freezing 
 to the boiling point of water. A bar of iron one inch square and eight 
 hundred inches long would expand one inch in length, through the same 
 degrees of heat ; and a bar of lead one inch square and three hundred 
 and fifty inches long would also dilate one inch in length. Hence, 
 
 Lead expands in volume . 
 
 Iron 
 
 Glass 
 
 . i fL 
 3 5 0 lU * 
 
 800 ^* 
 
 TnVntll. 
 
 The unequal expansion of the metals is well illustrated by an experi- 
 ment devised by Dr. Tyndal, the respected Professor of Natural Philo- 
 sophy in the Royal Institution of Great Britain, and is arranged as 
 follows : — A long bar of brass and another of iron are supported on the 
 
416 
 
 BOY ? S PLAYBOOK OF SCIENCE. 
 
 edges of two pieces of wood placed at an angle, and resting against the 
 sides of a mahogany framework. The metallic bars only touch one end 
 
 of the frame, and are 
 in metallic commu- 
 nication with a piece 
 of brass inserted 
 there, and forming 
 part of a conducting 
 chain connected with 
 a voltaic battery ; 
 when heat is applied 
 to both bars they ex- 
 pand unequally ; the 
 brass bar dilates first, 
 and filling up the mi- 
 nute space left be- 
 Fig. 393. a a. The brass bar which has expanded by the tween the two ends 
 heat from the gas jet b, and making the contact between the f f , 
 
 brass plates in connexion with the bmdmg screws c c, the 01 me lrame, tuueues> 
 voltaic circuit is completed, and a coil of platinum wire in the another brass plate 
 glass tube d, is immediately ignited. The iron bar at e e has not j inctnntlv mm 
 
 expanded sufficiently, which is shown afterwards by removing dll ~ mM'diiiry . 
 
 the angular wooden supports k k, when the iron falls off, and pietes the VOltaiC Cir- 
 the brass remains on the two ledges of the mahogany frame- when a Coil of 
 
 work l l l. platinum wire be- 
 
 comes ignited, showing the fact of expansion ; and secondly, the diffe- 
 rence in the power of dilatation possessed by each is clearly shown by 
 removing the two angular supports of wood, when the iron falls away, 
 whilst the brass remains and still completes the voltaic circuit. (Fig. 393.) 
 
 The force exerted by the expansion of solids is enormous, and reminds 
 us again of the amazing power of all the imponderable agents ; and it is 
 truly wonderful to notice how the entry of a certain amount of heat into 
 and between the particles of metals, or other solids, endues them with 
 a mechanical force which is almost irresistible, and is capable of working 
 much harm. Kussne made an experiment with an iron sphere, which 
 he heated from a temperature of 32° Falir. to 212° Fahr., and he found 
 that the expansion of the ball exerted a force equal to 4000 atmospheres 
 —i.e. 4000x15 — on every square inch of surface, ora pressure equal to 
 thirty millions of pounds ; the entry of only 180° of heat into the iron 
 sphere produced this remarkable result, just as Faraday has calculated that 
 a single drop of water contains a sufficient quantity of electricity to pro- 
 duced result equal to the most powerful flash of lightning, provided, the 
 electricity of quantity in the drop of water is converted into electricity 
 of high tension or intensity. 
 
 The practical applications of this well-known property of solids with 
 respect to heat are very numerous ; thus, the iron bullet-moulds are 
 always made a little larger than the requisite size, in order to allow for 
 the expansion of the hot liquid lead, and the contraction of the cold 
 metal. The tires of wheels and the hoops of casks are usually placed on 
 whilst hot, in order that the subsequent contraction may bind the spokes 
 
EXPANSION OF SOLIDS. 
 
 417 
 
 and fellies, or the staves, closely together. If an allowance was not 
 made for the expansion and contraction of the iron rails on the perrna* 
 nent ways of railroads, the- regularity of the level would be constantly 
 destroyed, and the position of the rails, chairs, and sleepers w'ould be 
 most seriously deranged ; indeed it is calculated that the railway bars 
 between London , 
 and Manchester 
 are five hundred 
 feet longer in the 
 summer than in the 
 winter. 
 
 The walls of the 
 Cathedral of Ar- 
 magh, as also those 
 of the Conserva- 
 toire des Art et Me- 
 tiers, were brought 
 back to a nearly 
 perpendicular po- 
 sition, by the in- 
 sertion(throughthe 
 opposite walls) of 
 great bars of iron, 
 which being alter- 
 nately heated, ex- 
 panded, and screw- 
 ed up tight then Fig. 394. The iron frame, with c c, wrought-iron bar heated by 
 i J , putting on the semicircular piece of iron e e, which is first made 
 
 COOieu and contract- red-hot, and as the heat is communicated to the wrought iron; 
 ed, gradually cor- rod c c, it is screwed up tight by the nut k. g g. The index 
 rpptprl thp Vmlcrino* attached to the iron frame screwed up when hot ; the arms come 
 itLicu. tilt? uuigm 0 t 0 g e th er at p, and separate further to n n as the contraction 
 Out Oi the wails or takes place by cooling the bar c d. 
 main supports of 
 
 these buildings. The principle of these famous practical experiments is 
 neatly illustrated by means of an iron framework with a bar of iron placed 
 through both its uprights, and screwed tight when hot ; on cooling, con- 
 traction occurs, which is shown by a simple index. (Fig. 394.) 
 
 It has often been remarked that there is no rule without an excep- 
 tion, and this applies in a particular instance to the law that “ bodies 
 expand by heat and contract by cold” — viz., in the case of Hose’s 
 fusible metal, which consists of 
 
 Two parts by weight of bismuth, 
 
 One part „ lead, 
 
 One part „ tin. 
 
 To make the alloy properly, the lead is first melted in an iron ladle, 
 and to this are added first the tin, and secondly the bismuth ; the 
 whole is then well stirred with a wooden rod, and cast into the shape 
 of a bar. 
 
 P 
 
418 
 
 boy’s PLAY'BOOK OF SCIENCE. 
 
 When placed in the pyrometer and heated, the bar expands pro- 
 gressively till it reaches a temperature of 111° Fahr. ; it then begins to 
 contract , and is rapidly shortened , until it arrives at 156° Fahr., when it 
 attains a maximum density, and occupies no more space than it would 
 do at the freezing-point of water. The bar, after passing 156°, again 
 expands, and finally melts at about 201°, which is 11° below the 
 boiling-point of water. Fusible metal is sometimes made into tea- 
 spoons, which soften and melt down when stirred in a cup of hot tea or 
 basin of soup, to the great surprise and bewilderment of the victim of 
 the practical joke. 
 
 Unequal expansion is familiarly demonstrated with a bit of toasted 
 bread, which curls up in consequence of the surface exposed to the fire 
 contracting more rapidly than the other ; and the same fact is illus- 
 trated with compound flat and thin bars of iron and brass, which are 
 fixed and rivetted together ; when heated, the compound bar curves, 
 because the iron does not expand so rapidly as the brass, and of course 
 forms the interior of the curve, whilst the brass is on the exterior. 
 
 The experiment with the compound bar is made more conclusive and 
 interesting by arranging it with a voltaic battery and platinum lamp. One 
 of the wires from the battery is connected with the extremity of the 
 compound bar, and as long as it remains cold, no curve or arch is pro- 
 duced, but when heat is applied, the bar curves upwards, and touching 
 the other wire of the battery, the circuit is completed, and the platinum 
 lamp is immediately ignited. (Fig. 395.) 
 
 A 
 
 Fig. 395. a b. Compound bar resting on two blocks of wood. The end a is connected 
 with one of the wires from the battery. The circuit is completed and the platinum lamp 
 d ignited directly the bar curves upwards by the heat of the spirit lamp, and touches the 
 wire c c connected with the opposite pole of the battery. 
 
 The expansion and contraction of liquids by heat and cold is also 
 another elementary truth which admits of ample illustration, and 
 indeed introduces us to that most useful instrument called the ther- 
 mometer. 
 
 If a flask is fitted with a cork through which a long glass tube, open 
 
EXPANSION OF LIQUIDS. 
 
 419 
 
 at botli ends, is passed, and then carefully filled with water coloured 
 with a little solution of indigo, so that when the cork and tube are 
 placed in the neck, all the air is excluded, a rough thermometer is thus 
 constructed, which, if placed in boiling water, quickly indicates the in- 
 creased temperature by the rising or expansion of the coloured water 
 inside the flask. (Fig. 39G.) 
 
 Eig. 'P®* Expansion of liquids shown at a by the coloured water rising* in the tube from 
 the flask, which is quite full of liquid, and heated by boiling water, n. The expansion of 
 the water heated by the spirit-lamp is shown by the rising of the piston and rod c c. 
 d represents a retort filled up like a to show the expansion of a liquid by heat. 
 
 The thermometer embraces precisely the same principle as that 
 already described in Fig. 396, with this difference only, that the tube is 
 of a much finer bore, and the liquid employed, whether alcohol or 
 mercury, is boiled and hermetically sealed in the tube, so that the air is 
 entirely excluded. To make a thermometer, a tube with a capillary 
 bore is selected of the proper length ; it is then dipped into a glass con- 
 taining mercury, so that the tube is filled to the length of half an inch 
 with that metal. The half-inch is carefully measured on a scale, and 
 the place the mercury fills in the tube marked with a scratching 
 diamond ; the mercury is then shaken half an inch higher, and ao-ain 
 marked, and this proceeding is continued until the whole tube is divided 
 into half inches. The object of doing this is to correct any inequalities 
 
 E £ 2 
 
420 
 
 boy’s PLAY-BOOK of science. 
 
 ill the diameter of the bore of the glass tube, because if wider at one 
 part than another, the spaces filled with the mercury are not equal ; 
 as the bore is usually conical, the careful measurement of the tube 
 with the half inch of mercury in the first place gives the operator 
 at once a view of the interior of his tube, and enables him to graduate 
 it correctly afterwards, (hi g. 397.) 
 
 Fi* 397 AB. Magnified view of the bore of one of the thermometer tubes which are 
 made’ by ‘rapidiy drawing out a hollow mass of hot glass whilst soft and ductile, 
 consequently the bore must be conical, and larger at one end than the other. 
 
 The next step is to heat one extremity by the lamp and blowpipe, and 
 whilst hot, to blow out a ball upon it ; if this operation were per- 
 formed with the mouth, moisture from the breath would deposit inside 
 the fine bore of the glass tube, and injure the perfection of the ther- 
 mometer afterwards. In order to prevent any deposit of water, the 
 bulb is blown out, whilst red-hot, with the air from a small caoutchouc 
 
 N?l 
 
 o= 
 
 
 P : t , 393 a —No 1 First bulb. The intended length of the thermometer is shown at the 
 3 ' * little cross .—No. 2 is the second bulb placed above the cross. 
 
 Fig. 393 b. Heating and expanding 
 the air in the top bulb, so that when 
 cool the mercury in the giass a, may 
 rise into the tube and fill the bulb b. 
 
 bag fitted on to the other extremity of 
 the tube. The operator now marks off 
 the intended length of his thermometer, 
 and above that point the tube is again 
 softened with the flame and blowpipe, and 
 a second bulb blown out. (Fig. 398 a.) 
 
 The open end of the tube is now placed 
 under the surface of some pure, clean, dry 
 quicksilver, and heat being applied to the 
 upper bulb, the air expands and escapes 
 through the mercury, and as the tube 
 cools a vacuum is produced, into which 
 the mercury passes. By this simple me- 
 thod, the mercury is easily forced into 
 the tube, as otherwise it would be impos- 
 sible to pour the quicksilver into the ca- 
 pillary bore of the intended thermometer. 
 (Fig. 398 b.) 
 
 The tube is now taken from the glass 
 containing the mercury, and simply in- 
 verted; but in consequence of the very 
 narrow diameter of the bore the air will 
 not pass out of the first bulb until heat 
 is applied, when the air expands, and the 
 
THE CONSTRUCTION OF THE THERMOMETER. 
 
 421 
 
 mercury, first stationary in tne second bulb, will now displace the air, 
 and fall into the first bulb when the tube is again cool. 
 
 The ball, No. 1 (Fig. 398 a ), is now full of mercury, and there is also 
 some left in No. 2 ; in the next place, the tube is supported by a wire, 
 and held over a charcoal fire, when it is heated throughout its entire 
 length, and the mercury being boiled expels the whole of the air , so 
 that there is nothing inside the bulbs and capillary bore but mercury 
 and its vapour. (No. 1, Fig. 399.) The open end of the intended ther 
 mometer is now temporarily closed with sealing-wax, and the whole 
 allowed again to cool with the sealed end uppermost, so that the ball 
 No. 2, Fig. 399, and the tube above it, are quite filled with quicksilver. 
 
 After cooling, the tube is placed at an angle with the sealed end 
 uppermost, and, guided by experience, the operator heats the lower 
 bulb so as to expand enough mercury into the upper one to leave space 
 for the future expansion and contraction of the mercury in the tube, 
 which has now to be hermetically sealed. This is done by dexterously 
 heating the tube at the cross whilst the mercury in the first bulb is still 
 expanded ; and by drawing it out rapidly with the help of the heat obtained 
 from the lamp and blowpipe, the second bulb is separated from the first 
 at the little cross (b, No. 3, Fig. 399), and the thermometer tube at last 
 properly filled with quicksilver, and hermetically closed. (No. 4, Fig. 399.) 
 
 = ■ - j =g^ 
 
 Fig. 399.— No. 1. Boiling quicksilver in the tube with two bulbs. — No. 2. Tube cooled, 
 with the sealed end uppermost. — No. 3. Mercury in first bulb expanded by lamp a, and at 
 the proper moment hermetically sealed by the flame urged by the blowpipe at b. The 
 upper bulb and tube to the cross being drawn away and separated. — No. 4. Thermometer 
 tube containing the requisite quantity of mercury, hermetically sealed, and now ready to* 
 graduation. 
 
 
422 
 
 BOYS PLAYBOOK OF SCIENCE. 
 
 In order to procure a fixed starting-point, the thermometer tube is 
 placed in ice, with a scale attached ; the temperature of ice never varies, 
 it is always at 32 degrees. When, therefore, the mercury has sunk to 
 the lowest point it can do by exposure to this degree of cold, the place 
 is marked off in the scale, and represents that position in the graduated 
 scale where the freezing point of water is indicated. 
 
 The tube is placed in the next place in a vessel of boiling water, care 
 being taken that the whole tube is subject to the heat of the water and; 
 the steam issuing from it, and when the mercury has risen to the highest 
 position attainable by the heat of boiling water, another graduation is 
 made which indicates 212 degrees — viz., the boiling point of water. This 
 graduation should be made when the barometer stands at 30 inches, 
 because the boiling point of water varies according to the weight of the 
 superincumbent air pressing upon it. 
 
 Between the graduation of the freezing and the boiling point of water 
 the space is divided into ISO parts, which added to 32 make up the 
 boiling point of water to 212 degrees, being the graduation of Fahrenheit, 
 who was an instrument-maker of Hamburg. Why he divided the space 
 between the freezing and boiling point of water nobody appears to know, 
 unless he took a half circle of 180 degrees as the best division of space. 
 If the thermometer contains air the mercury divides itself frequently 
 into two or three slender threads, each separated from the other in the 
 capillary bore, and thus the instrument is rendered useless until the 
 threads again coalesce. If the thermometer has been well made, and 
 is quite free from air, it may be tied to a string and swung violently 
 round, when the centrifugal force drives the slender threads of mercury 
 to their common source — viz., the bulb containing the quicksilver, and 
 the whole is again united. The string must be attached, of course, to 
 the top of the thermometer scale. 
 
 When travelling on the Continent it is sometimes desirable to be 
 able to read the thermometers which are graduated in a different manner 
 to that of Fahrenheit. In France the Centigrade scale is preferred, and 
 in many parts of Germany Reaumur’s graduation The difference of 
 the graduation is seen at a glance. 
 
 In the Centigrade the freezing point is 0, the boiling point 100°. 
 
 801 
 
 212°. 
 
 Reaumur 
 
 Fahrenheit 
 
 The number of degrees, therefore, between boiling and freezing is 
 100 in the Centigrade, 80 in Reaumur, and (212 — 32, that is) 180 in 
 Fahrenheit. 
 
 If, then, the letters C, R, F, be taken to denote the number of degrees 
 from the freezing point at which the mercury stands in the Centigrade, 
 Reaumur, and Fahrenheit thermometers, we have the following pro- 
 portions : — 
 
 (1.) 100 : SO :: C : R, whence C = f of R, or R = a 0 f C. 
 
 (2.) 180 : 100 :: F : C, whence F = f of C, or C = f of F. 
 
 (3.) 180: 80 :: F . R, whence F = § of R, or R = § cf F. 
 
EXPANSION OF WATER BY COLD. 
 
 423 
 
 The following examples will show how to apply these formulae : — 
 
 (1) . — Suppose the Reaumur stands at 28°, at what height does the 
 Centigrade stand ? We have C = f of R (in this case), f of 28 = 35 : 
 that is, the Centigrade stands at 35°. 
 
 (2) . — Suppose Fahrenheit to stand at 41°, what will Reaumur stand 
 at ? R = f of (41 — 32) (that is, the number above freezing in Fahr.) 
 = £ of 9 = 4. Reaumur stands at 4. 
 
 (3) . — Suppose Fahrenheit stands at 23°, what will the Centigrade 
 stand at ? C = -J of F = J- of (32 — 23) =-§■ of 9 = 5 below, freezing 
 (or — 5). 
 
 (4) . — If Fahrenheit stands at 4 below 0, what will Reaumur indicate ? 
 R = f of F = f of (32 + 4) = | of 36 = 16 below 0 (or —16). 
 
 The only liquid which has the exceptional property of expanding by 
 cold is water, and it will be seen presently that this curious anomaly is 
 of the greatest importance in the economy of nature. 
 
 If a box containing a mixture of ice and salt is placed round the top 
 of a long cylindrical glass containing water at a temperature of 60° 
 Fahr., the intense cold of the freezing mixture, which is zero — that is 
 to say, 32° below the freezing point of water — very soon reduces the 
 temperature of the water contained in the glass, and as it becomes 
 colder it contracts, is rendered heavier, and sinks to the bottom of the 
 vessel, and its place is taken 
 by other and warmer water. 
 
 This circulation commencing 
 downwards, proceeds till the 
 water has attained a tempe- 
 rature of about 40° Fahr., 
 when the maximum density 
 is obtained and the circula- 
 tion stops, because after sink- 
 ing below 40° the cold water 
 becomes lighter , and conti- 
 nues to be so until it freezes, 
 and of course, being of a 
 less specific gravity than the 
 warrfier water, it floats (like 
 oil on water) upon its surface; 
 so that a small thermometer 
 placed at the bottom of the 
 jar indicates only 40° Fahr., 
 whilst the solid ice enveloping 
 the other or second thermo- 
 meter placed at the top may 
 be as low as 29°, or even 
 
 lower according- to the mian- Fi =*400. AB. Long cylindrical glass containing 
 1U u ei, ciCLOi umg LO me quail- water ancl two thermometers ; the one at the bottom 
 
 tlty OI ice and salt used in the shows a temperature of 40°; the other at the top 32°, 
 box surrounding the top of <F e T en lo wer. c C F c - Section of box containing 
 tbo rvlnoc /-c the lce and salt > and standing on four legs, two of 
 the glass. (I lg. 400.) which are shown at d d. 
 
424 
 
 boy’s playbook of science. 
 
 The importance of this curious anomaly cannot be overrated. If 
 water did not possess this rare property, all the seas, rivers, canals, 
 lakes, &c., would gradually become impassable from the presence of 
 enormous blocks of ice formed during the winter. The whole bulk of 
 water contained in them would have to sink below 32° before it could 
 solidify, provided water increased in density or continued to contract by 
 cold. Having once solidified, the warmth of the rays from a summer’s 
 sun would certainly melt a great deal of the ice, but not the whole, and 
 winter would come again before the solid masses had disappeared. The 
 ocean could not be navigated in safety even near our own shores, in 
 consequence of the vast icebergs that would be formed, and float about 
 and jostle each other even in the British Channel. 
 
 The earth has been wonderfully prepared for God’s highest work — 
 Man, and in nothing is this supreme wisdom more apparent than in the 
 fact that water offers the only known exception to the law “ that bodies 
 expand by heat and contract by cold.” 
 
 The expansion of gases by heat and contraction by cold take place in 
 obedience to a law to which there is no exception, except in degree. It 
 was discovered in 1801 by M. Gay Lussac, of Paris, and also about the 
 same period by the famous English philosopher who established the 
 atomic theory — viz., by Hr. Dalton. Since these experiments ana 
 calculations Budberg, Magnus, and Begnault have made other researches, 
 and their successive experiment^ give the following results : — 
 
 Vols. of air. Volumes. 
 
 Dalton, Gay Lussac 1000 heated from 32° to 212° became 1375 
 
 Budberg .... 1000 „ „ „ 1365 
 
 Magnus, Begnault . 1000 „ „ „ 13 66 ‘5 
 
 As a natural result, air at 32° Ealir. expands - 4 -|y part of its volume 
 for every degree of heat on the scale of Eahrenheit ; and a volume of 
 air which measures 491 cubic inches at 32° will measure 492 at 33°, 
 493 at 34°, and so on. The exception is only in . degree, and Magnus 
 and Begnault discovered by their searching experiments that the gases 
 easily liquified are more expansible by heat than air and those gases 
 (such as oxygen, hydrogen, and nitrogen) which have never* been 
 liquified. 
 
 The expansion of air is easily shown by placing the open end of a 
 tube with a large bulb blown at the other extremity, under the surface 
 of a little coloured water ; on the application of heat the air expands 
 and escapes, and its place is taken, when cool, by the coloured liquid. 
 Such an arrangement represents the first thermometer constructed by 
 Sanctorio about a.d. 1600, which might certainly answer for rough 
 purposes, but as the ascent and descent of the fluid depend on the 
 bulk of air contained in the bulb, and as this is affected by every change 
 of the height of the barometer, no satisfactory indication of an increase 
 ,or decrease of temperature could be obtained with it, although the 
 instrument itself is interesting in an historical point of view, and in a 
 
THE EXPANSION OF GASES. 
 
 425 
 
 modified form as an air thermometer has been employed by Sir John 
 Leslie, under the name of the “Differential Thermometer,” in his 
 refined and delicate experiments with heat. (Tig. 401.) 
 
 Fig. 401. a. Sanctorio’s original air thermometer; the expansion and contraction of the 
 air in the bulb indicate the rise or fall of the temperature. The cork is merely a support, 
 and is not fitted into the bottle air-tight, b c. The differential thermometer. When both 
 bulbs are subjected to a uniform temperature, no movement of the fluid shown at d occurs ; 
 but if the bulb b is put into any place warmer than the position of the bulb c, then the air 
 expands in b, and drives the coloured liquid, which consists of carmine dissolved in oil of 
 vitriol, up the scale attached to the stem of the bulb c. 
 
 Tire balloons are a good example of the expansion of gases, and the 
 levity of the air thus increased in bulk was taken advantage of by 
 Montgolfier in the construction of his famous balloon, winch, with a 
 cage containing various animals, ascended, in the presence of the King 
 and royal family of Trance, at Versailles ; and in spite of huge rents in 
 two places, it rose to a height of 1440 feet, and after remaining in- the 
 air for eight minutes, fell to the ground at the distance of 10,200 feet 
 from the place whence it started, without injury to the animals. 
 When it is considered that a volume of air heated from 32° to 491° is 
 doubled, and tripled when heated to 982°, it will at once be understood 
 how great must be the ascending power of such balloons, provided the 
 air within them is kept sufficiently hot. 
 
 That gallant aeronaut, Pilate de Rozier, offered himself to be the 
 first aerial navigator ; and having joined Montgolfier, they made three 
 successful ascents and descents with a large oval-shaped balloon, forty- 
 eight feet in diameter, and seventy-four feet high. On the fourth 
 occasion he ascended to a height of 262 feet, but in the descent a gust 
 of wind having blown the machine over some large trees of an adjoining 
 garden, the situation of the brave aeronaut was extremely dangerous, 
 and if he had not possessed the strongest presence of mind, and at once 
 
426 boy’s playbook of science. 
 
 given the balloon a greater ascending power, by rapidly supplying his 
 stove with some straw and chipped wood, he might on this occasion 
 have met with that untimely end which subsequently, in another rash 
 aeronautic adventure, befel this brave but foolhardy Frenchman. 
 
 On descending again, he once more, and without the slightest fear 
 raised himself to a considerable height by feeding his fire with cnopped 
 straw. Some time after he ascended, in company with M. Giroud de 
 Yilette, to the height of 330 feet, hovering over Paris at least nine 
 minutes, m sight of all the inhabitants, and the machine keeping all the 
 while perfectly steady. ° 
 
 The d 5?ger in using this method of inflating the balloon arises from 
 the possibihty of generating gas, which escaping unburnt into the body 
 ol the balloon, may accumulate and blow up, or burn afterwards. 
 
 Fire balloons, as 
 usually made, are very 
 dangerous toys, and 
 may sometimes prove 
 rather costly to the 
 person who may send 
 them off, in conse- 
 quence of their being 
 blown by the wind on 
 a hay or corn rick, of 
 other combustible sub- 
 stances. The safest 
 . mode of using fire bal- 
 loons is to fill them 
 with hot air from a 
 lighted gas stove (Wes- 
 sel’s, for instance) ; 
 the balloons may then 
 be used in large rooms, 
 or out in the air, with- 
 out fear of doing any 
 harm to neighbouring! 
 property, as of course 
 the stove and the fire 
 remain behind, and 
 will fill any number of 
 air balloons. (Fig. 402.) 
 
 After all the fuss 
 made about the novelty 
 . . # of the Americanhot-air 
 
 engine, it is somewhat amusing to look back to the records of civil 
 engineering, and in the “ Transactions of the Institution of Civil 
 Engineers, to. read Mr. James Stirling’s account of his improved air 
 engine, in which the. great expansion of air mentioned at p. 365 has 
 been successfully applied. The engine was constructed about the year 
 
 . Fig. 402. a b. Wessel’s gas stove, with ring of gas jets 
 lighted inside ; the air rashes in the direction of the arrows, 
 c .c, and escaping at the top of the chimney, d d, soon fills the 
 air or fire balloon, which is usually made of paper. 
 
THE HOT-AIR ENGINE, 
 
 427 
 
 1843, and the principle, discovered thirty years before by Mr. R» 
 Stirling, will be comprehended by reference to the cut. (Fig. 403.) 
 
 Fig. 403. Stirling’s air engine. 
 
 Two strong air-tight vessels are connected with the opposite ends of 
 a cylinder, in which a piston works in the usual manner. About four- 
 fifths of the interior space in these vessels is occupied by two similar 
 air-tight vessels or plungers, which are suspended to the opposite 
 extremities of a beam, and capable of being alternately moved up and 
 down to the extent of the remaining fifth. By the motion of these 
 interior vessels, which are filled with non-conducting substances, the air 
 to be operated upon is moved from one end of the exterior vessel to the 
 ether, and as one end is kept at a high temperature, and the other as 
 cold as possible, when the air is brought to the hot end it becomes 
 heat ed, and has its pressure increased ; and when it is brought to the 
 cold end, its heat and pressure are diminished. Now, as the interior 
 vessels necessarily move in opposite directions, it follows that the pressure 
 of the enclosed air in the one vessel is increased, while that of the other 
 is diminished. A difference of pressure is thus produced upon the 
 opposite sides of the piston, which is thereby made to move from 
 the one end of the cylinder to the other, and by continually reversing the 
 motion of the suspended bodies or plungers, the greater pressure is 
 successively thrown upon a different side, and a reciprocating motion of 
 
428 
 
 boy’s playbook of science. 
 
 the piston is kept up. The piston is connected with a fly-wheel in any 
 of the usual modes ; and the plungers, by whose motion the air is heated 
 and cooled, are moved in the same manner, and nearly at the same 
 relative time, with the valves of a steam engine. 
 
 The pressure is greatly increased and made more economical by using 
 somewhat highly-compressed air, which is at first introduced, and is 
 afterwards maintained, by the continued action of an air-pump. The 
 pump is also employed in filling a separate magazine with compressed 
 air, from which the engine can be at once charged to the working 
 pressure. Mr. Stirling’s chief improvement consists in saving all or 
 nearly all the heat of the expanded air after it has done its work, by 
 passing it from the hot to the cold end of the air vessel through a 
 multitude of narrow passages, whose temperature is at the beginning 
 of the tubes nearly as great as that of the hot air, but gradually 
 declines till it becomes nearly as low as the coldest part of the air 
 vessel. The heat is therefore retained by these passages, so that when 
 the mechanism is reversed, the cold air returns again through these hot 
 pipes, and is thus made nearly hot enough by the time it reaches the 
 heating vessel to do its work. Thus, instead of being obliged to supply 
 at every stroke of the engine as much heat as would be sufficient to 
 raise the air from its lowest to its highest temperature, it is necessary 
 to furnish only as much as will heat it the same number of degrees by 
 which the hottest part of the air vessel exceeds the hottest part of the 
 intermediate passages. This portion of the engine may be called the 
 economical process , and represents the foundation of all the success to 
 which it has attained in producing power with a small expenditure of 
 fuel. No boiler being required, of course the danger of explosions is 
 much lessened. The higher the pressure under which the engine was 
 worked the greater was the effect produced. A small engine on this 
 principle was worked to a pressure of 360 pounds on the square inch ; 
 and perhaps the best popular notion of the novelty in the arrangement 
 is that suggested by Mr. George Lowe, who compared the economical 
 part of the machine to a “ Jeffrey’s Respirator” used by consumptive 
 patients. The heat from the air expired being retained by the laminae, 
 and again used when cold air is inspired or drawn into the lungs. Mr. 
 Stirling states that the consumption of fuel as compared to the steam 
 engine which the air engine had replaced was as 6 to 26 ; the same 
 amount of work being now performed by about six cwt. of coals which 
 had formerly required about twenty-six cwt., though he ought to have 
 stated that the steam engine removed was not of the best construction, 
 nor had the boiler any close covering. (Fig. 403.) 
 
 Conduction of Heat. 
 
 This property of heat with reference to matter, and the consideration 
 of the curious manner in which it creeps, as it were, through solid sub- 
 stances, brings the thoughtful mind at once to the bold question of 
 What is heat ? Is it to be regarded as something real or material ? or 
 
THEORIES OF HEAT. 
 
 429 
 
 must it be considered only as a property or state of matter ? These 
 questions are not to be solved easily, and they demand a considerable 
 amount of experiment and reasoning even to appreciate their meaning. 
 
 If a red-hot ball is placed in the focus of a concave metallic speculum, 
 it gives out certain emanations that are quite invisible, but which are re- 
 flected from the surface of the mirror in the same manner as visible rays 
 of light, and may be collected in the focus of another and second con- 
 cave speculum, when they can be concentrated on to a bit of phosphorus, 
 and will cause the combustion of that substance. If the air from a pair 
 of bellows is blown forcibly across the rays of heat as they are being con- 
 centrated upon the phosphorus, the rays are not moved from their 
 course, they are no more blown away than a sunbeam darting through 
 an aperture in a cloud on a stormy, windy day. The heat has, therefore 
 nothing to do with 
 the air, and is wholly 
 independent of that 
 medium in its pas- 
 sage from one mirror 
 to the other. Such 
 an experiment as that 
 described would at 
 once suggest the idea 
 that heat is a matter 
 
 j a compo- 
 nent part of all bo- 
 dies, and given off 
 from incandescent 
 matter, the sun, &c., 
 and that it may be 
 propagated through 
 space much in the 
 same manner as light. 
 (Fig. 404.) The me- 
 chanism may be very 
 much like the cor- 
 
 Fig. 404. Heat reflected by mirror, but not blown away by 
 air from bellows. 
 
 puscular movement of light as defined by Sir Isaac Newton, and already 
 ™ an °ther portion of this book. Hence it has been supposed 
 that heat is propagated through the air, water, and solid substances by 
 ftift emlssl ? n °, f material particles from the heat-giving agent, and 
 that these molecules of heat force their way into, or along, or throuo-h 
 them, according to circumstances. 
 
 Certain bodies are almost transparent to heat rays, such as air, 
 wlnlst others take an mtermedial position, and only stop a certain quan- 
 
 a i at m I jl f U ! es ’ Sl ! ch as rock crystals, mirror glass, and alum. 
 
 A third class of bodies absorbs the heat plentifully, such as char- 
 coal, black cloth, &c. ; and a fourth, when polished and placed at the 
 proper angle, reflects or throws off the heat, as in the case of polished 
 mirrors. I he transparency or opacity of substances (so far as light is 
 
430 
 
 boy’s playbook of science. 
 
 concerned) does not affect the transmission of heat. Light of every 
 colour and from all sources is equally transmitted by all transparent 
 bodies in the liquid or solid form, but this is not the case with 
 heat. 
 
 The rays of heat emitted by the sun and other luminous bodies have 
 properties quite different to the rays of light with which they are accom- 
 panied. From these statements it will be evident that the material 
 theory of heat is surrounded with difficulties and anomalies that cannot 
 be reconciled the one with the other, or neatly adapted, fitted in, and 
 dovetailed with all the puzzling phenomena that arise. Our knowledge 
 of the theory of heat has been greatly assisted by the researches of 
 Melloni, who has demonstrated that different species of rays of heat are 
 given off by the same body at different temperatures, which may be dis- 
 tinctly sifted and separated from each other. Long before the experi- 
 ments of Melloni philosophers had endeavoured to weigh heat; trains 
 of the most delicate levers were exposed, without effect, to the action 
 of heat rays ; and all attempts, experimental as well as theoretical, to 
 define heat by the material theory, are imperfect, crude, and unsatis- 
 factory. We are perforce obliged to adopt another theory, and the one 
 that obtains the greatest favour, as offering the best definition of heat, 
 is the dynamical theory, which is more or less analogous to the undula- 
 tory theory of light. At pages 302,388, 395, this theory has been partly 
 explained, and in speaking of it again, great care must be taken not to 
 confuse the undulations of heat with those of light. The sun and the 
 stars swim in a molecular medium, and 39,180 vibrations or waves must 
 occur in one inch to produce the sensation of red light, and 57,490 
 undulations in the space of one inch to produce a violet light. As vibra- 
 tions of the ethereal molecules affect the eye, so there may be other 
 nerves in our bodies which are peculiarly sensitive to the waves of heat. 
 It requires eight vibrations of the air to occur in a second to produce 
 an audible sound ; whilst if the vibrations of the air amount to 25,000 
 per second they cannot be appreciated by the human ear, although it is 
 possible to conceive that the ears of certain animals may be so suscep- 
 tible of rapid vibrations that they may be able, for certain wise purposes 
 of the Creator, to appreciate sounds which are inaudible to human 
 ears. 
 
 Melloni exhibited a spectrum to a number of persons, and found that 
 there was more light apparent to some eyes than to others. Lubeck 
 put a scarlet cloth on a donkey, and found that the two were frequently 
 confounded together by the eyes of many spectators. These facts indi- 
 cate that there may be vibrations of molecules that produce the sensation 
 of heat, but which do not affect the nerves that are sensitive to the 
 action of light waves, and vice versa; and it is also probable that all these 
 different undulations, some affording heat and some light, may be gene- 
 rated and propagated through space, as from the sun ; or through shorter 
 distances, as from burning lamps and fires, without in any way inter- 
 fering with or impeding each other’s progress. 
 
 The dynamical theory seems to offer the best idea of the transmission 
 
THE CONDUCTION OF HEAT. 
 
 431 
 
 of heat which is carried, conducted, or propagated through solids with 
 variable rapidity, either by the vibration of the constituent molecules of 
 the body itself, or by the undulation of a rare subtle fluid which per 
 vades them. If a copper and iron wire of the same length and diameter 
 are bound together and heated at the point of union, the waves of heat 
 travel faster through the copper than the iron, and the former is said to 
 be the best conductor of heat ; and the fact itself is demonstrated by 
 placing a bit of phosphorus at the end of each metallic wire, and it will 
 be found by experiment that the combustible substance melts first and 
 takes fire on the copper, and that a considerable interval of time elapses 
 before the phosphorus ignites on the iron. 
 
 Fig. 405. c. Copper wire bound at a to i, an iron wire. After the heat of the lamp has 
 been applied for about five minutes the heat travels to c first, and ignites the bit of phos- 
 phorus placed there. After some time has elapsed the phosphorus at i also ignites. 
 
 The same fact is exhibited in a most striking manner by inserting a 
 series of rods of equal lengths and thicknesses in the side of a rectan- 
 gular box, allowing them to pass across the interior to the opposite 
 side. The rods are composed of wood, porcelain, glass, lead, iron, zinc, 
 copper, and silver, and have attached to each of their extremities, by 
 wax or tallow, a clay marble. When the water placed in the box is made 
 to boil, the heat passes along the different rods, and melting the wax or 
 tallow, allows the marble to drop . off. Consequently the first marble 
 -would drop from the silver rod, the next from the copper, the third 
 from the iron, the fourth from the zinc, the fifth from the lead, 
 whilst the porcelain, glass, and wooden rods would hardly conduct (in 
 several hours) sufficient heat to melt the wax or tallow, and discharge 
 the marbles. 
 
 Gold . 
 Silver 
 Copper 
 Iron . 
 Zinc . 
 Lead - 
 
 1000 
 
 973 
 
 898*2 
 
 374*3 
 
 363 
 
 179*6 
 
 Conduction of Metals. 
 
432 
 
 boy’s playbook of science. 
 
 The experiment is made 
 more striking if the marbles 
 are allowed to fall on a lever 
 connected with the detent of 
 a clock alarum, which rings 
 every time a marble falls from 
 one of the rods. (Fig. 406.) 
 
 During a cold frosty day, 
 if the hand is placed in con- 
 tact with various substances, 
 some appear to be colder than 
 others, although all may be 
 precisely the same tempera- 
 ture ; this circumstance is due 
 to their conducting power: 
 and a piece of slate seems 
 colder than a bit of chalk, because the former is a much better con- 
 ductor than the latter, and carries away the heat from the body with 
 greater rapidity, and diffuses it through its own substance. 
 
 The gradual passage 
 of heat along a bar of 
 iron as compared with 
 one of copper, is well 
 illustrated by sup- 
 porting the ends of 
 the two bars on the 
 top of the chimney of 
 an argand lamp, whilst 
 the other extremities 
 
 Fig. 407. a. Section of an argand gas lamp, with a copper held ill a liorizon- 
 chimney supporting the ends of the bars of copper and iron tal position by little 
 marked c and i. The balls have fallen from c, the copper blocks of wood If 
 
 marbles are attached 
 
 by wax to the under side, they fall off as the heat travels along the 
 metallic bars, and more rapidly from the copper than the iron, because 
 the former is a better conductor of heat than the latter. (Fig. 407 ) 
 From the experiments of Mayer, of Erlangen (“ Ann. de Ch.,” xxx.), 
 it would appear that the conducting powers of different woods are to a 
 certain extent to be regarded as in the inverse proportion to their 
 specific gravities — i.e., the greater the density of the wood the less con- 
 ducting power, and the contrary. 
 
 If a cylindrical bar or thick tube of brass, six inches long, and about 
 cwo inches in diameter, is attached to a wooden cylinder of the same 
 size, the conducting powers of the two substances are well displayed 
 by first straining a sheet of white paper over the brass, and then holding 
 it in the flame of a spirit lamp. The heat being conducted rapidly away 
 by the metal will not scorch the paper, until the whole arrives at a 
 uniform high temperature ; whereas the paper is rapidly burnt when 
 
 Fig. 406. a b. Trough containing boiling water, 
 heated by gas jets below, c. The eight rods and 
 marbles attached, one of which has fallen, d. The 
 tray to receive the marbles. 
 
THE CONDUCTION OF HEAT. 
 
 433 
 
 strained over the wooden 
 cylinder, because the heat of 
 the flame of the lamp is con- 
 centrated upon one point, 
 and is not diffused through 
 the mass of the wood. (Eisr. 
 
 408.) 
 
 In the course of the 
 highly philosophical experi- 
 ments of SirH. Davy, which 
 led him gradually to the dis- 
 covery of the construction 
 of the safety lamp, he con- 
 nected together, by a copper 
 tube of a small bore, two 
 vessels, each containing an 
 explosive mixture composed 
 of fire damp and air. When 
 the mixture was fired in one 
 vessel he found that the 
 
 rlirl not armpnr fn hp Fig. 408. Cylinder, half brass and half wood. The 
 name cua not appear 10 oe paper strained over the wood is taking fire# The 
 
 able to travel, as it were, Other extremity, shaded, is the brass portion. 
 
 across the bridge — viz., the 
 
 copper tube — and communicate with the other magazine, because it was 
 deprived of its heat whilst passing through t'he tube, and was no longer 
 flame, but simply gaseous matter at too low a temperature to effect the 
 inflammation of the mixture in the second box. 
 
 A mass of cold metal may be suddenly applied to a small flame, such 
 as that of a night light, and depriving it rapidly of heat (like the case 
 of the unfortunate Kussian described at page 354), it is almost imme- 
 diately extinguished (fig. 360), not by the mere exclusion of the oxygen 
 
 Fig. 409. a. Small flame from night light, b c. Large mass of cold copper wire- open at 
 both ends to place over flame, and by conduction of the heat to extinguish it. 
 
 of the air, but on account of the withdrawal of the heat necessary for 
 the maintenance of the combustion. 
 
 Sir H. Davy first thought of making his safety lamp with small tubes, 
 which would supply fresh air, and carry off the burnt or foul air, at tflo 
 
434 
 
 boy’s playbook of science. 
 
 same lime they were to be so narrow that no flame could pass out of hislanrp 
 to communicate with an outer explosive atmosphere; and in speaking 
 of his lamp with tubes he says “ I soon discovered that a few apertures, 
 even of very small diameter, were not safe unless their sides were very 
 deep ; that a single tube of one-twenty-eighth of an inch in diameter, 
 and two inches long, suffered the explosion to pass through it ; and that 
 a great number of small tubes, or of apertures, stopped explosion, even 
 when the depths of their sides was only equal to their diameters. And 
 at. last I arrived at the conclusion that a metallic tissue , however thin 
 and fine, of which the apertures filled more space than the cooling 
 surface, so as to be permeable to air and light, offered a perfect barrier 
 to explosion, from the force being divided between, and the heat com- 
 municated to an immense number of surfaces. I made several attempts 
 to construct safety lamps which should give light in all explosive mixtures 
 of fire damp, and after complicated combinations, I at length arrived at 
 one evidently the most simple, that of surrounding the light entirely by 
 wire gauze , and making the same tissue feed the flame with air and emit 
 
 light ” . , . . 
 
 If a number of square metallic tubes of a fine bore are placed upright 
 side bv side, and a section cut off horizontally, it would represent the 
 wire gauze which possesses such marvellous > powers of sifting away 
 the heat from a flame, so that it is destroyed in its attempted passage 
 through the metallic meshes ; and of this fact a number of proofs may 
 be adduced. . 
 
 A gas jet delivering coal gas may be placed under a sheet of wire 
 gauze, the gas permeates the gauze, and may be set on fire at the upper 
 
 side, but the flame is cut off from 
 the mouth of the jet by the cooling 
 action of the wire gauze. The same 
 experiment reversed, by holding the 
 gauze over the gas burning from the 
 jet, shows still more decidedly that 
 flame will not pass through the me- 
 tallic tissue, (fig. 410.) 
 
 Sir H. Davy again says : “ Though 
 all the specimens of fire damp which 
 I had examined consisted of carbu- 
 retted hydrogen mixed with different 
 small proportions of carbonic acid 
 and common air, yet some pheno- 
 mena I observed in the combustion 
 of a blower induced me to believe 
 that small quantities of olefiant gas may be sometimes evolved in coal 
 mines with the carburetted hydrogen. I therefore resolved to make 
 all lamps safe to the test of the gas produced by the distillation oj coal , 
 which, when it has not been exposed to water, always contains ole- 
 fiant gas. I placed my lighted lamps in a large glass receiver through 
 which there was a current of atmospherical air, and by means oi a 
 
 Fig. 410. a a. A number of square tubes 
 placed upright. The arrow shows the 
 direction of the section to obtain a figure 
 like wire gauze. 
 
THE DAVY LAMP. 
 
 435 
 
 gasometer filled with coal gas, I made the current of air which passed 
 
 into the lamp more or less explosive, and caused it to change rapidly or 
 slowly at pleasure, so as to produce all possible varieties of inflammable 
 and explosive mixtures, and I found that iron gauze wire composed of 
 wires from one-fortieth to one-sixtieth of an inch in diameter, and con- 
 taining twenty-eight wires or seven hundred and eighty-four apertures 
 to the inch, was safe wider all circumstances in atmospheres of this hind ; 
 and I consequently adopted this material in guarding lamps for the 
 coal-mines, when in January, 1816, they were immediately adopted, and 
 have long been in general use.” 
 
 The remarkable conducting power of wire gauze is further shown oy 
 placing some lumps of camphor on a piece of this material, and when 
 the heat of a spirit-lamp is applied on the under side of the gauze, the 
 camphor volatilizes, and as the vapour is remarkably heavy, it falls 
 through the meshes of the gauze, and takes fire ; but the most curious 
 and further illustration of the conducting power of the wire meshes is 
 shown in the fact that the fire does not communicate through the thin 
 film of gauze to the lumps of camphor placed upon it. 
 
 The camphor may be ignited by applying flame to the upper side of 
 the gauze, showing that, although this substance is so exceedingly com- 
 bustible, it will not take fire even if placed at no greater distance from 
 flame than the thickness of the wire gauze, provided the latter mate- 
 rial is interposed between it and the 
 
 flame. 
 
 A square box made of wire gauze, 
 with a hole at the bottom to admit a 
 candle or spirit-lamp, may have a con- 
 siderable jet of coal gas forced upon 
 
 it from the outside, or a large jug 1 
 
 * ~ , — — p ~ 
 
 of ether vapour poured upon it ; and 
 
 although the box may be full of flame, 
 arising from the combustion of the gas 
 or ether, the fire does not come out of 
 the wire box or communicate with the 
 jet or the ether vapour as it is poured 
 from the jug. (Tig. 411.) 
 
 Sir Humphrey Davy’s safety lamp 
 consists of a common oil-lamp, f with 
 a wire through the cistern for the pur- 
 pose of raising or depressing the cot- 
 ton wick without unscrewing the wire 
 gauze ; h is the male screw fitting the 
 screw attached to the cylinder of wire 
 
 - — — — ~r IT spirit lamp ngniea. a not jug' run oi 
 
 the platinum coil which Sir H. Davy the vapour of ether may be poured on 
 
436 
 
 boy’s PLAYBOOIv of science. 
 
 cage of platinum consists of 
 wire of one-seventieth to one- 
 eightieth of an inch in thick- 
 ness, fastened to the wire for 
 raising or depressing the cot- 
 ton wick, and should the lamp 
 be extinguished in an explo- 
 sive mixture, the little coil of 
 platinum begins to glow, and 
 will afford sufficient light to 
 guide the miner to a safe part 
 of the mine. With respect to 
 this platinum coil. Sir II. 
 Davy gives a careful charge, 
 and says : — “ The greatest 
 care must be taken that no 
 filament or wire of platinum 
 protrudes on the exterior of 
 the lamp, for this would fire 
 externally an explosive mix- 
 ture?* 
 
 Since the invention of the 
 Davy lamp, a great number 
 of modifications have been 
 brought forward, some of 
 which for a short time have 
 occupied the public attention, but whether from increased cost or a 
 sort of inertia that arrests improvement, it is certain that the lamp 
 originally devised by Sir Humphrey Davy is still the favourite. It was 
 perhaps unfortunate that the lamp w^as called the safety lamp, because 
 it is not so under every circumstance that may arise, unless it happens 
 to be in the hands of persons who have taken the trouble to study it 
 and understand how to correct the faults. The lamp might have escaped 
 the incessant attacks that have been made upon its just merits, if the 
 name had simply been that of its illustrious inventor — “ a Davy lamp/’ 
 No one could carp at that, whilst “ safety ” was held to mean perfect 
 immunity from every possible and probable danger that might arise in 
 the coal-pits. The lamps are now usually placed under the charge of 
 one man, who trims them and ascertains that the wire gauze is in perfect 
 order ; this latter is usually locked upon the lamp, and as it is a penal 
 offence, and punishable by a heavy fine and imprisonment, to remove the 
 wire gauze from safety lamps in dangerous parts of the mine, of course 
 the miners are being gradually brought to a sense of the obligations they 
 owe themselves and their brother-miners, and the rash, ignorant, and 
 foolhardy offences of breaking open safety lamps for more illumination, 
 or to light pipes, are becoming much less frequent than formerly. One 
 of the most ingenious “detector lamps” is that of Mr. Symons, of 
 Birmingham. (Fig. 413.) It consisted of the old-fashioned Davy, but 
 
symons’ detector lamp. 
 
 437 
 
 inside the rim of the wire gauze is 
 placed a small extinguisher and spring, 
 which does not move so long as the 
 gauze is screwed on to the lamp, but 
 directly the gauze is unscrewed, the 
 reversed movement releases the detent, 
 and the extinguisher falls upon the 
 light. In spite of the manifest inge- 
 nuity of this lamp, it is not adopted, 
 because it costs a trifle more than the 
 ordinary “ Davy . 55 To show the re- 
 markable perfection of the wire gauze 
 principle, some turpentine may be 
 poured upon a lighted safety lamp, 
 when a great smoke is produced by the 
 evaporation of the spirit, but no flame 
 passes through to the outside, although 
 the turpentine burns inside the lamp. 
 
 If some coarse gunpowder is laid upon 
 two thicknesses of fine wire gauze, it 
 may be heated from below with the 
 flame of the spirit lamp, and the sulphur 
 will gradually volatilize without setting 
 fire to the mass of powder. To show 
 tne security of the Davy lamp, it may 
 be lighted and hung in a large box 
 with glass sides, open at the top, and a 
 jet of coal gas supplied at the bottom; 
 as this rises and diffuses in the air, the 
 mixture becomes explosive, and the 
 fact is at once evident by the altera- 
 tion in the appearance of the flame 
 of the lamp, which enlarges, flickers, and frequently goes out, in conse- 
 quence of the suddenness with which the explosion of the mixture takes 
 place inside the lamp, producing a concussion that extinguishes the 
 flame. In this case the utility of the platinum coil is very apparent, 
 and it continues to glow with a red heat until the explosive character 
 of the air in the box is changed. 
 
 If a large washhand-basin is first warmed by some boiling water, 
 which is then poured away, and a drachm of ether thrown in, a highly- 
 combustible atmosphere is obtained, and when a lighted Davy lamp is 
 placed into the basin so prepared, the flame inside the lamp immediately 
 enlarges and flickers, but is not extinguished, and does not communicate 
 to the combustible vapour outside. The contrast between the safety 
 lamp and an unprotected flame is very striking ; if a lighted taper is 
 thrust into the basin, the ether catches fire, and burns with a very 
 large flame. The solid conductors of heat, which are said to enjoy this 
 property in the highest degree, are the metals, marble, stone, slate, and 
 
 Fig. 113. Symons’ self-extinguishing 
 Davy lamp. 
 
438 
 
 boy’s playbook of science. 
 
 other dense and compact solid substances; whilst the opposite quality 
 of being non-conductors, or nearly so, is possessed by fur, wood, silk, 
 cotton, wool, eider and swansdown, paper, sand, charcoal, and every 
 substance which is of a light or porous nature. The practical applica- 
 tion of this knowledge is very apparent in the affairs of every-day life. 
 Thus we rise in the morning, and immediately after the necessary ablu- 
 tions, if it is winter time, proceed to encase the body in non-conductors, 
 such as flannel and wool. . When we sit down to the breakfast table to 
 make tea, we may notice the contrivances for preventing the handle of 
 the top of the urn, or that of the teapot, from becoming too hot for the 
 fingers, by the interposition of ivory or wood. If asked to place water 
 in the teapot from the kettle, we instinctively seek for the well-worn 
 kettle-holder made of Berlin wool, and therefore a bad conductor. As 
 we cut our meat or fish at the same meal, we may shiver with cold, but 
 our fingers are not quite frozen by contact with the steel knives, as we 
 hold them by ivory handles ; and we are agreeably reminded that some 
 metals are good conductors of heat, by the pleasant warmth of the 
 silver teaspoons, as we stir our tea or coffee. 
 
 Even the polish of the well-rubbed mahogany is protected from the 
 heat of the dishes by non-conducting mats, and plates are handed about, 
 if “ nice and hot,” with a carefully-wrapped non-conducting linen 
 napkin. Supposing we prefer a bit of fresh-made toast, the fork is 
 provided with a non-conducting handle; and should we peep out of window 
 some wintry morn whilst the baker delivers his early work in the shape 
 of hot rolls, we notice they come out of nicely-wrapped flannel or baize, 
 which being a bad conductor is employed to retain their heat. We read, 
 occasionally, in the military intelligence, statements respecting some 
 newly-constructed shells which are to burst and scatter melted iron (! !); 
 and of course the idea of the interposition of a good non-conductor of heat 
 between the bursting charge and the molten metal must be realized in 
 their construction. 
 
 The central heat of our globe is a reality that cannot be disputed, and 
 after digging beyond a depth of twenty feet the thermometer gradually 
 rises at the rate of one degree of Fahrenheit’s scale for every fifteen 
 yards. The bad conducting power of the crust of the earth must, there- 
 fore, be apparent, as it is easy, knowing the diameter of our globe, to 
 calculate that the increase of heat downwards amounts to 116° for each 
 mile, consequently at a depth of thirty and a half miles below the sur- 
 face, there will be a temperature most likely equal to 3500°, or a heat 
 that might easily melt cast-iron, and would help to account for the 
 earthquakes and eruptions of volcanoes, which still remind us by their 
 terrible warnings, that we live only on the bad conducting upper crust 
 of a globe, the inside of which is still, perhaps, in a liquid and molten 
 state. Monsieur Fourier has demonstrated the non-conducting power 
 of this shell by calculating that, supposing the globe was wholly com- 
 posed of cast-iron, the central heat would require myriads of years to be 
 transmitted to the surface from a depth of 150 miles; and by inverting 
 the process of reasoning, we may come to the conclusion that the in- 
 
THE CONDUCTION OF HEAT. 
 
 439 
 
 ternal heat must be excessive, because it is confined and shut out from 
 those influences that would carry off and weaken the intensity. 
 
 There are no two words, says Tyndal, with which we are more familiar 
 than matter and force. The system of the universe embraces two things, 
 an object acted upon , and an agent by which it is acted upon ; the object 
 we call matter and the agent we call force. Matter, in certain respects, 
 may be regarded as the vehicle of force ; thus, the luminiferous ether is 
 the vehicle or medium by which the pulsations of the sun are transmitted 
 to our organs of vision. Or, to take a plainer case, if we set a number 
 of billiard balls in a row, and impart a shock to one end of the series in 
 the direction of its length, we know what will take place ; the last ball 
 will fly away, the intervening balls having served for the transmission of 
 the shock from one end of the series to the other. Or we might refer to 
 the conduction of heat. If, for example, it be required to transmit heat 
 from the fire to a point at some distance from the fire, this may oe 
 effected by means of a conducting body — by a poker, for instance ; thrust- 
 ing one end of a poker into the fire, it becomes heated, the heat makes 
 its way through the mass, and finally manifests itself at the other end. 
 Let us endeavour to get a distinct idea of what we here call heat ; let 
 us first picture it to ourselves as an agent apart from the mass of the 
 conductor, making its way among the particles of the latter, jumping 
 from atom to atom, and thus converting them into a kind of stepping 
 stones to assist its progress. It is a probable conclusion, even had we 
 not a single experiment to support it, that the mode of transmission 
 must, in some measure, depend upon the manner in which those little 
 molecular stepping stones are arranged. But we must not confine our- 
 selves to the molecular theory of heat. Assuming the hypothesis, which 
 is now gaining ground, that heat, instead of being an agent apart from 
 ordinary matter, consists in a motion of the material particles; the con- 
 clusion is equally probable that the transmission of the motion must be 
 influenced by the manner in which the particles are arranged. Does 
 experimental science furnish us with any corroboration of this inference P 
 It does. More than twenty years ago MM. De la Rive and De Can- 
 dolle proved that heat is transmitted through wood with a velocity 
 almost twice as great along the fibre as across it. This result has been 
 recently expanded, and it has been proved that this substance possesses 
 three axes of calorific conduction; the first and greatest axis being 
 parallel to the fibre ; the second axis perpendicular to the fibre and to 
 the ligneous layers ; while the third axis, which marks the direction in 
 which the greatest resistance is offered to the passage of the heat, is 
 perpendicular to the fibre and parallel to the layers. 
 
 If many solids are bad conductors of heat, they are at all events 
 greatly surpassed by fluids, and especially by water. The conduction of 
 heat by that fluid is almost imperceptible, so much so, that it has even 
 been questioned whether liquids do really conduct heat downwards at all. 
 It has, however, been found that liquid mercury will conduct heat down- 
 wards, and therefore by analogy it may be assumed that other liquids 
 must possess a conducting power, although it may be exceedingly limited. 
 
440 
 
 boy’s playbook of science. 
 
 In order to prove that water is an exceeding bad conductor of heat, a 
 tube with a large glass bulb blown at one end is partly filled with 
 tincture of litmus, until it will just sink below the surface of water 
 placed in a tall cylindrical or open jar. If a copper basin, containing 
 burning ether, is now lioated on the top of the water, so as to leave 
 about a quarter of an inch between the top of the air thermometer — 
 viz., the bulb containing the coloured liquid — and the bottom of the 
 copper pan, it will be noticed that whilst the water surrounding the 
 latter almost boils, not the slightest effect arising from the conduction 
 •of heat can be perceived in a downward direction. After the ether has 
 burnt out of the copper vessel, it may be removed, and the boiling water 
 stirred down and around the air thermometer, when the air within it 
 expands, drives out the colouring liquid, and the bulb becoming spe- 
 cifically lighter, rises to the top of the containing glass. (Fig. 414 .) 
 
 Fig. 414. a a. Cylindrical glass full of water, b. The glass air thermometer containing 
 the coloured liquid just standing upright, the mouth of the tube at c being open, d d is 
 the copper basin containing the burning ether, e shows how the glass bulb and tube 
 rise after the upper basin is removed, and the hot water comes in contact with and 
 expands the air, making the thermometer light, and causing it to rise. 
 
 Again, if the tube of an air thermometer is placed through a cork in 
 the neck of a gas jar, inverted and standing on a ring stand, and the 
 
THE CONDUCTION OF HEAT BY FLUIDS. 
 
 44* 
 
 jar is then filled with 
 water, and boiled at 
 the top with a red- 
 hot iron heater, tiio 
 heat does not pass 
 downwards and af- 
 fect the thermome- 
 ter. By introducing 
 a syphon the water 
 surrounding the 
 thermometer at the 
 bottom of the jar 
 may be drawn off, 
 until the hot water 
 is within a fraction 
 of an inch of the air 
 thermometer, and 
 still no heat is con- 
 ducted, and the li- 
 quid in the latter 
 remains stationary. 
 (Fig. 415.) 
 
 The diffusion of 
 heat through water 
 does not take place 
 like that of solids, 
 but is effected by the 
 motion of the parti- 
 cles of the w'ater. 
 When heat is applied 
 to the bottom of a 
 vessel containing 
 water, such as an 
 inverted glass shade, 
 the first effect is to 
 expand the layer of 
 water which is first 
 affected by the heat; 
 this expanded layer 
 being specifically 
 lighter than the cold 
 water above, it rises 
 
 Fig. 415. aaa. Inverted gas jar supported by the ring 
 
 ' “"'y- Fig. 415. aaa. inverted gas j 
 
 to the upper part of stand, b. The red-hot urn heater, c c. The air thermometer, 
 flip o-l ncc chnrlp nnrl with the coloured liquid stationary at c. d. The syphon for 
 iuc biiciue, anu. drawi off the cold water> ^ bringing the hot down close to 
 
 its place is immedi- the bulb of c c. 
 ately taken by other, 
 
 colder and heavier, water, which in like manner moves upwards, and is 
 again succeeded by a fresh portion. Now, the first and succeeding strata 
 
442 
 
 boy’s playeook of science. 
 
 of water all carry off so much 
 heat, and thus by the con- 
 vective or carrying power of 
 the water the heat is diffused 
 finally in the most perfect 
 manner through the whole 
 bulk of fluid; and indeed, 
 the movement itself of the 
 particles of water may easily 
 be watched by putting a little 
 paper pulp at the bottom of 
 the inverted glass shade con- 
 taining the water. (Fig. 416.) 
 
 This bad conducting power 
 is not merely confined to 
 water, blit is likewise appa- 
 rent with oil and other fluids, 
 and if some water is frozen 
 at the bottom of a long test- 
 tube by means of a freezing 
 mixture, oil may then be 
 poured upon it, and some 
 alcohol above the latter. If 
 the flame of a spirit-lamp is 
 now applied to the alcohol at 
 the top of the tube it may be 
 entirely boiled away, and no 
 heat will travel down the oil 
 and communicate with the 
 ice, and even after the alcohol 
 has been evaporated away 
 the tube can be filled up 
 with water ; this may also be boiled, and whilst demonstrating the bad 
 conducting power of the oil, the curious anomaly is observed of a vessel 
 or tube containing ice at the bottom and boiling water at the top, and 
 further showing the tvisdom of the Supreme Creator in preventing the 
 freezing of the water of lakes, rivers, and seas, by the exceptional law of 
 the expansion of water by cold. It is evident from what has been 
 stated that liquids acquire and lose their heat by means of those cur- 
 rents and movements of the particles of water which have already been 
 partly explained. Whatever interferes with this movement must pre- 
 vent the passage of heat, and consequently thick viscous liquids are 
 always difficult to boil, and in consequence of their motion being im- 
 peded they rise to too high a temperature and are burnt. This fact is 
 remarkably apparent in the manufacture of nice white lump sugar ; as 
 the syrup is evaporated it becomes very thick, and if boiled over a fire 
 might frequently be burnt, but it is boiled by the heat of steam, and 
 under a vacuum produced by an air-pump, and thus the sugar-boiler is 
 enabled to avert all danger from burning. 
 
 Fig. 416. a a. Inverted glass shade containing 
 water and some paper pulp. b. Burning spirit lamp 
 placed under one side of the glass ; the pulp shows 
 the rising of the heated water and the sinking of 
 the cold, in the direction indicated by the arrows. 
 
THE CONVECTION OF HEAT. 
 
 443 
 
 It is, then, by a continual and perpetual motion, involving circulation 
 of the particles, that heat travels through water ; and the fact already 
 described is still further 
 elucidated by one of Pro- 
 fessor Griffith’s simple but 
 telling experiments. A 
 glass tube, about three feet 
 in length and half an inch 
 in diameter, is bent as at a 
 (Pig. 417), and then being 
 filled with water, is sus- 
 pended by a string attached 
 to any convenient support 
 inside a copper dish con- 
 taining water, so that the 
 straight end is at the top 
 of the water, and the curved 
 end at the bottom. Just 
 before it is used some ink 
 or other colouring matter 
 is poured into the copper 
 pan of water ; and it 
 should not be added till 
 the moment the experi- 
 ment is to begin, as any 
 rise of temperature in the 
 room promotes circulation, 
 and interferes with the co- 
 lourlessness of the water 
 in the tube, which is com- 
 pared with the inky fluid 
 in the basin. Directly heat 
 is applied the hot water 
 rises to the top of the 
 copper vessel, and thence 
 gradually up the tube ; and 
 this movement is rendered visible by the hot coloured liquid matter 
 creeping slowly up the tube, and displacing the colourless water, whicli 
 falls gradually into the copper pan. (Fig. 417 •) 
 
 The principle of the circulation of the particles of water being once 
 understood, it is easy to comprehend how it is applied to the heating of 
 buildings by what is called the “Hot Water Apparatus. 55 A coil of 
 pipe is enclosed in a proper furnace, and the bottom end communicates 
 with a pipe coming from a second tube or set of coils, placed above it in 
 another apartment, whilst the top of the latter coil communicates with 
 the top pipe of the first coil. When the fire is lighted, the circulation 
 through the first coil of pipe commences, and is communicated to the 
 second, and from that back again to the first ; so that the “ hot water 
 
 Fig. 417. a. The bent glass tube full of water. 
 B b. The copper pan containing coloured water. The 
 arrows show the circulation of the water. 
 
444 
 
 boy’s playbook of science. 
 
 system” involves an endless chain of pipes of water, provided with 
 proper safety valves to allow for the escape of any expanded air or 
 steam ; and serious accidents have occurred in consequence of persons 
 neglecting to look after the perfection of this safety valve. The fearful 
 accident which occurred to the hot w T ater casing around one of the 
 funnels of the Great Eastern offers a painful but memorable example of 
 the heating of water, and of the dangers that must arise if the pipe, 
 casing, or other vessel which contains it, is not provided with an escape 
 or safety valve, which must always be in good working order. 
 
 Mr. Jacob Perkins, in 1824, made his name remarkable for experi- 
 ments with the circulation of water through tubes, and his account of 
 
 the invention and im- 
 provement of the 
 “ Steam Gun,” in 
 which the improve- 
 ment consists chiefly 
 in the circulation of 
 water through coils of 
 pipe, is so important 
 that we give it verba- 
 tim, with a drawing of 
 the steam gun; and 
 the author is enabled 
 to vouch for the accu- 
 racy of the statements 
 made in the description 
 of the apparatus, as lie 
 purchased one of the 
 improved steam guns, 
 and exhibited it at the 
 Polytechnic Institu- 
 tion, where it dis- 
 charged three hundred 
 bullets per minute. 
 
 “ The expansive 
 power of steam has 
 often been proposed as 
 a substitute for gun- 
 powder, for discharging 
 balls and other pro- 
 jectiles ; the greal 
 danger, however, which was formerly thought to be inseparably con- 
 nected with the generation and use of steam, at so extraordinary a 
 pressure as appeared necessary to produce an effect approximating to 
 that of gunpowder, prevented scientific men from testing the power of 
 this new agent by experiment. It was also apparent that the appa- 
 ratus which was ordinarily used for generating steam for steam-engines 
 was wholly inadequate to sustain the necessary pressure, and that one 
 
 Fig. 418. The charging tube and gun-barrel 
 of steam gun. 
 
THE STEAM GUN. 
 
 445 
 
 of a totally different character .must be contrived before steam could 
 be sufficiently confined to come into competition with its powerful rival. 
 
 “In the year 1824, Mr. Jacob Perkins succeeded in constructing a 
 generator of such form and strength, as allowed him to carry on his 
 experiments with highly elastic steam without danger, although sub- 
 jected to a pressure of 100 atmospheres. The principle of its safety 
 consisted in subdividing the vessel containing the water and steam into 
 chambers or compartments, so small, that the bursting of one of them 
 was perfectly harmless in its effects, and only served as an outlet, or 
 safety valve, to relieve the rest. 
 
 “ Although Mr. Perkins’ generator was originally intended for working 
 steam engines (it having long been evident to him that highly elastic 
 steam used expansively would be attended with considerable economy), 
 the idea occurred to him, in the course of his experiments, that he had 
 already solved the problem of safely generating steam of sufficient 
 power for the purposes of steam gunnery ; and that the steam which 
 daily worked his engine possessed an elastic force quite adequate to the 
 projection of musket balls. He therefore caused a gun to be imme- 
 diately constructed, and connected by a pipe to the generator, the first 
 trial of which fully realized his most sanguine anticipations. Its per- 
 formance, indeed, was so extraordinary and unexpected, that it gave rise 
 to a paradox, which was difficult of explanation — viz., that steam, at a 
 'pressure of only forty atmospheres , produced an effect equal to gunpowder ; 
 whereas it was known that the combustion of gunpowder was attended 
 with a pressure of from 500 to 1000 atmospheres. 
 
 “ Mr. Perkins gives the following explanation of this apparent dis- 
 crepancy, by referring to the small effect produced by fulminating 
 powder, compared to gunpowder, although many times more powerful ; 
 he supposes that the action of fulminating powder, however intense, 
 does not continue sufficiently long to impart to the ball its full power. 
 The explosion of gunpowder, although not so powerful at the instant of 
 ignition , is nevertheless, in the aggregate, productive of greater effect 
 than that of fulminating powder, because the subsequent expansion 
 continues in action upon the ball (but with decreasing effect), until it 
 has left the barrel. The action of steam differs from either of these 
 agents, inasmuch as it continues in full force until the ball has left the 
 barrel ; and to this is assigned the cause of its superiority. 
 
 “ In the year 1826, Mr. Perkins had so perfected the mechanism of 
 the gun and generator that, at an exhibition and trial of its power, in 
 the presence of the Duke of Wellington and other distinguished officers 
 of the Ordnance Department, balls of an ounce weight were propelled, 
 at the distance of thirty-five yards, through an iron plate one-fourth of 
 an inch in thickness ; also, through eleven hard planks, one inch in 
 thickness, placed at distances of an inch from each other. Continuous 
 showers of balls were also projected with such rapidity, that when the 
 barrel of the gun was slowly swept round in a horizontal direction, a 
 plank, twelve feet in length, was so completely perforated, that the line of 
 holes nearly resembled a groove cut from one of its ends to the other. 
 
446 
 
 boy’s playbook of science. 
 
 Fig. 419. Perkins’s steam gun. 
 
THE STEAM GUN. 
 
 447 
 
 “ a is an iron furnace, containing a continuous coil of iron tubing, 80 feet in length, 
 1 inch of external and fth inch of internal diameter, within which the fire is made ; the 
 upper end of this tube, b, called the flow-pipe, is extended any required distance to the top 
 of the generator. 
 
 “The furnace is provided with a very ingenious heat governor or regulator, by which the 
 intensity of the fire is always proportionate to the temperature which it may be requisite 
 to maintain in the tubes. 
 
 “ h is an iron box, containing a series of levers, h h l ; c, a nut screwed upon the flow- 
 pipe, and in contact with the short arm of the lowest of the levers, e. A lever, from one 
 end of which is suspended the damper f, and from the other end the rod g, which rests 
 upon the long arm of the highest of the levers, hhh. When the apparatus has arrived at 
 the required temperature, the nut c is screwed down until it bears upon the lever. Any 
 farther increase of temperature will expand or lengthen the flow-pipe, and depress the 
 short arm of the lever, which is in contact with the nut. The combined and multiplied 
 action of the levers will then elevate the rod g, and the damper f will descend to check 
 the draught. When the fire slackens, and the apparatus cools, the action of the levers will 
 be reversed, and the damper will open. The space through which the damper moves, com- 
 pared with the nut c, is as 200 to 1. 
 
 “ c is the generator, composed of a strong iron tube, 3 inches diameter and 6 feet in 
 length, within which are eight smaller tubes, having their ends welded to the ends of the 
 larger tube. These small tubes communicate at the top with the flow-pipe b, and at the 
 bottom with the return-pipe n, which is continued to the bottom of the furnace-coil of 
 tubing. The circulation in the tubes is occasioned by the difference in the specific gravities 
 of the water composing the ascending and descending currents ; the portion contained in 
 the flow-pipe and fire coil becoming expanded by the heat, ascends by its superior levity ; 
 while that contained in the small tubes of the generator, having given off its heat, acquires 
 increased density, and descends through the return-pipe d to the bottom of the furnace- 
 coil, to take the place of the ascending current. When the hot-water current has arrived 
 at a temperature of 212° and upwards, cold water is injected into the generator, and 
 becomes converted into steam by its contact with the small tubes ; the rapidity of evapo- 
 ration and the pressure of the steam depending, of course, upon the temperature of the 
 hot-water current, which at 500° will cause a pressure within the tubes of 50 atmospheres, 
 or 750 lbs. upon the square inch. The whole apparatus is proved to be capable of sustaining 
 a pressure of 200 atmospheres, or 3000 lbs. upon the square inch. 
 
 “ g. A force pump for injecting water into the generator. 
 
 “ i. The indicator for exhibiting the pressure of the steam in the generator, and of the 
 water in the boiler ; it may be connected with either by means of the valves attached to 
 the levers. 
 
 “ j. Valve to regulate the pressure of water. 
 
 “ v j 1. Valve to regulate the pressure of steam. 
 
 “ k. The steam pipe. 
 
 “l. The gun. 
 
 “ m. The discharging lever acting upon the valve isr. 
 
 “o. The discharging cock, by a simple adjustment in which balls are transferred from 
 the charging tube p to the gun barrel, singly or in a continuous shower. 
 
 Clever and effective as this steam gun undoubtedly was it did not 
 meet with the approval of our War Authorities, and it must now be con- 
 sidered a thing of the past. Had it been brought forward in these 
 later days, when the art of warfare depends so much upon the skill of 
 engineers, it might perhaps have met with a more cordial reception. 
 And it may be that in the future, for special services and fixed positions, 
 some such gun may become practicable and valuable. For the present 
 it is forgotten in the adoption of machine guns which are charged with 
 “ villanous saltpetre 5 ' in the shape of gunp jwder. 
 
 The well-known revolver was, perhaps, the first arm which called the at- 
 tention of modern artillerists to guns of this class. Even the revolver 
 is not new, lor in the armoury of the Tower of London is still shown a 
 rough description of revolver invented some hundreds of years back. 
 If I remember rightly it consists of eight barrels or chambers forged in 
 one piece, not unlike the first form of Colt’s revolver, which was intro- 
 
448 
 
 boy’s playbook of science. 
 
 duced about twenty-five years ago. The machine guns now in use bj 
 different nations are mostly revolvers on an enlarged scale. 
 
 The first gun of this kind which made any sensation was the mitrail- 
 leuse, adopted by the French armies just prior to the Franco-Prussian war. 
 Its manufacture and nature were kept very secret by the French Govern- 
 ment, and all kinds of exaggerated reports were spread as to its awfully 
 destructive nature. However, although in one or two actions it came into 
 prominent use, it did not save the French from German conquest, and, in 
 the sequel, most of the guns fell into the hands of the enemy. The 
 mitrailleuse has been tested by the English Government against an 
 American weapon known, after its inventor, as the Gatling gun, with the 
 result that the latter weapon has been adopted in our Service, both on land 
 and sea. Compared with the steam-gun already described, the Gatling 
 is far more destructive in its effects, and as it is mounted as an ordinary 
 piece of artillery, it can be readily moved from place to place. Moreover, 
 there is, of course, no fire to light, for there is no steam to trouble about. 
 
 The gun consists of a number of parallel barrels which revolve and 
 are placed upon a main shaft. A feed-case, containing cartridges, is 
 attached, and, by a clever mechanical contrivance, these cartridges drop 
 into their places and can be fired by turning a handle at the back of 
 the weapon. The gun can be made to discharge nearly 500 balls per 
 minute, and its range is something over one mile and a quarter. We 
 can easily imagine what a deadly leaden hail this must represent, and 
 what awful havoc it would make in the ranks of an enemy. Placed in 
 the crosstrees of a ship of war, it would effectually scour the decks of 
 any vessel within its range, as well as prevent any attempt at boarding 
 by small boats. But the entire aspect and conditions of naval warfare 
 have been completely altered since the days when brave Nelson trod 
 the decks of the Victory . The introduction of ironclads, with their 
 impregnable sides and hidden crew, in which everything is worked by 
 steam machinery, down to the loading of the guns, renders war upon 
 water a new art. All things considered, the Gatling gun will, perhaps, 
 prove of greater service on terra firma. It may be mentioned that the 
 weapon has recently been improved in many important details by 
 additions and modifications which increase its rapidity of action and 
 general efficiency. These improvements were lately brought before 
 the public and demonstrated by the inventor. 
 
 The conduction of heat through gases is also very slow when heat is 
 applied to the upper part of any stratum of air. Heat appears to be 
 diffused through air by the circulation and rising of the heated and 
 lighter strata, and the sinking of the colder currents which take their 
 places ; hence the danger of sitting in a room under an open skylight. 
 A current of cold air may descend upon the head of the individual, 
 whilst the warmer air takes some other opening to escape from. No 
 doubt the movement of heated volumes of air is subject to definite 
 laws, which apply themselves in every case, but are rather difficult to 
 grasp when the subject of ventilation is concerned. The philosophical 
 ventilator is often dreadfully teased by the inversion of all that he had 
 
CONDUCTION OF HEAT BY GASES. 
 
 449 
 
 planned, or the total failure of his apparatus. No specific mode of 
 ventilation can be found to suit all rooms and buildings ; they are like 
 the patients of a physician who cannot be cured by one medicine only, 
 but must have a treatment adapted properly to each case. If the fires’ 
 candles, gas, or oil-lamps, doors, windows, and chimneys, were always 
 under the control of the scientific ventilator, his task would be verv 
 simple, but it is well understood that a ventilating system whicfi 
 answers well if certain doors communicating witli lobbies are closed, 
 fails directly they are accidentally opened. The watchful care of the’ 
 ventilator must begin with the lowest area door, and in his calculations 
 lie must study the effect of every other door or window that may be 
 opened, so that if a scientific man undertakes to ventilate a house, he 
 must have a well-drawn plan hung up in the hall, and it must be 
 clearly understood by .the inmates that any interference with that plan 
 will prejudice the whole. 
 
 There are a few common principles which will guide in ventilation 
 and these are, first, the rise of hot and the fall of cold air; second, 
 that if an aperture is provided at the top of a room for the escape of 
 hot air, an equally large aperture must be left for the entry of cold air ; 
 third, the aperture for the escape of hot air must be adapted in size to 
 the number of persons likely to enter the room, and the number of gas 
 or other lights burning in it. During the daytime, moderate apertures 
 tor the exit and entrance of air may suffice, but these must be largely 
 increased at night, when the room is filled with people and lighted up. 
 Expanding and contracting openings are therefore desirable, and they 
 are to be regulated by rules stated on the plan of the ventilating system 
 (already alluded to as being hung up in the hall) of the house which 
 has submitted itself to a perfect system of ventilation, and no hall- 
 keeper, footman, or butler should be allowed to remain in his post 
 unless he undertakes to comprehend the system and work it properly by 
 the written rules. J J 
 
 <c /P r ‘ A r n o us Smit h> in a very able paper “ On the Air of Towns,” says— 
 
 . 0ne of the conditions of health, and a most important, if not the most 
 important of all, is to be found in the state of the atmosphere. As to 
 the effect on the inhabitants, the question becomes exceedingly com- 
 plicated ; but the Registrar-General’s returns are an unanswerable 
 reply as to the results of the lethal influences of the district. Eew 
 people seem clearly to picture to themselves the meaning of a decimal 
 plan m the per-centage of death, and few clearly see that there are 
 districts of England where the deaths at least in some years, and when 
 no recognised epidemic occurs, are three times greater than in others. 
 When we hear of the annual deaths in some districts being 34 per 
 cent., and in the whole of England 2 2, it is simply that 34 die instead' 
 oi 22, whilst even that is too slightly stated, as the whole of England 
 would show a lower death-rave if the towns were not used to swell it.” 
 
 This quotation is given here to remind our readers of the important 
 question of a supply of pure air as well as pure water and pure food ; 
 and it the agricultural labourer, with all his exposure to variable 
 
450 
 
 boy’s playbook of science. 
 
 weather, can take the first place in the scale of mortality, and outlive 
 the members of all other trades and professions, it is evident that the 
 importance of pure air is not overrated. 
 
 Every effort ought, therefore, to be made in large schools, hospitals, 
 and barracks, to enforce a rigid system of supply of fresh air, and a 
 sewage or removal of the impure ; and in the use of a certain test em- 
 ployed by Dr. Smith for the detection of organic matter in the air a 
 number of approximations were obtained, which clearly demonstrated 
 that 1 grain of organic matter was detected in 72,000 cubic inches of air 
 in a room, and the same quantity in 8000 cubic inches taken from a 
 crowded railway carriage. 
 
 To show the rising of heated air, a long glass tube, about three- 
 quarters of an inch in diameter, may be provided and held over the 
 flame of a spirit lamp at an angle of sixty degrees. As the tube warms, 
 the heated air rushes past the flame with great rapidity, and pulls it 
 out or elongates it so much, that the sharp point of the spirit-flame 
 
VENTILATION. 
 
 451 
 
 will frequently be seen at the end of a tube ten feel six inches ir. 
 length. The flame is, as it were, the sign-post that indicates the path 
 or direction of the air. (Pig. 420.) 
 
 Upon the like principle, heated air may be dragged down the short 
 arm of a syphon, provided the other arm is sufficiently long to impart a 
 strong directive tendency to the upward current, and this mode of 
 setting air in motion has been frequently proposed in numerous schemes 
 for ventilation. In order to prove the fact that an inverted syphon 
 will act in this manner, an iron pipe of three inches diameter and 
 six feet long may be bent round during the construction into the form 
 of a syphon, so that the short length is about one foot long, and the 
 long length the remaining four feet, allowing one foot for the bend. If 
 the interior of the long arm is first warmed by burning in it a little 
 spirits of wine from a piece of cotton or tow wetted with the latter 
 (which can be easily done by dropping in such a wetted piece into the 
 bend of tube, so that it is just under the opening of the long part of 
 the tube), the air is soon set in motion up the long pipe, and as it must 
 be supplied with fresh vo- 
 lumes of air to take the 
 place of that which rises, 
 and as the only entrance for 
 the fresh air can be down 
 the short arm of the sy- 
 phon, the circulation soon 
 commences, and it pro- 
 ceeds as long as the upper 
 arm is kept sufficiently 
 warm. If a flame is held 
 over the mouth of the 
 short arm, it is immedi- 
 ately dragged downward, 
 whilst, if held at the 
 mouth of the long pipe, 
 the motion of the air is 
 seen by the assistance of 
 the flame to be in the 
 contrary direction. (Fig. 
 
 421.) 
 
 This plan of ventilation 
 was proposed to be used 
 in rooms in connexion with 
 the chimney and chimney- 
 piece, and in order to give 
 it an ornamental appear- 
 ance, the chimney-piece was supplied with two ornamental hollow 
 columns, the ends of which were open at the mantelshelf, and the* 
 tubes or columns were continued under the hearthstone, proceeding 
 up the back of the grate and entering the chimney, in which there 
 would be a constant current of heated air, and it was expected that 
 
 G G 2 
 
 Fig. 421. a b. Inverted sheet iron syphon. At c is 
 seen the piece of tow moistened with alcohol, which, 
 being set on fire, warms the tube b. d. A lighted torch 
 of coloured spirit, the flame of which is dragged down 
 the tube at a by the descending current, and is impelled 
 upwards by the ascending current b. 
 
452 
 
 boy’s playbook of science. 
 
 ihe syphon arrangement would keep a current of air always in 
 motion, and thus help to ventilate the room. (Fig. 422.) This plan, 
 
 Fig 42 9 . a b. Chimney-piece supported on two hollow ornamental pillars corresponding 
 with the short arm of a syphon, c c c. The dotted line showing the pipes leading from 
 -each pillar under the hearth, and terminating in a long pipe passing into the chimney. 
 The arrows show the path of the air descending from the chimney-piece and ascending in 
 the chimney. 
 
 however, does not appear to have been adopted, and wisely so, because 
 half the time the syphon arrangement might invert itself, and vomit 
 smoky air out of the chimney into the room ; indeed it is surprising what 
 •odd and contradictory freaks are performed by currents of air. The 
 author remembers a case where two rooms on the same floor, the one 
 u dining-room and the other a drawing-room, were always exhibiting the 
 most absurd phenomena of smoke. If the fire in one room was lit, then 
 the other, in a few moments, began to smell exactly like the inside of a 
 .gas manufactory, and was, of course, more or less filled with smoke, 
 whilst the room in which the fire was actually burning remained quite 
 free from this annoyance. The smoke appeared to issue from the 
 wainscot or moulding which runs round at the bottom of the wall, and 
 was at first thought to be an escape from the chimney of the kitchen 
 beneath, the inside of which was duly examined and thoroughly stopped 
 with cement in every place likely to afford a channel to the smoke, and 
 
VENTILATION OF ROOMS. 
 
 453 
 
 the crevice whence the smoke issued was also filled in neatly with 
 cement. But it was all in vain; the smoke then made its way out from 
 another part of the cornice, and at last the rooms exhibited a beautiful 
 reciprocating action. If the drawing-room fire was lighted the dining- 
 room was full of smoke, and if the latter was lighted the former had the 
 agreeable visitation. At lagt the backs of the two grates were ex- 
 amined, and in each was discovered a hole about one inch in diameter ; 
 and it was also found that the spaces at the back of the stoves had not 
 been filled in properly, and, indeed, communicated with the hollow space 
 behind the cornice. When, therefore, the fire was lighted, and coals 
 heaped on just above the hole, the gas and smoke distilled through the 
 orifice and travelled on, where it found the most convenient exit ; and 
 the fact is sadly at variance ( apparently ) with theory, because it might 
 be considered that cold air would rush towards a fire, and that the 
 draught ought to have been from the cornice to the chimney instead of 
 vice versa. The fact seems to be that the coal in all grates is, in the act 
 of burning, distilling and giving off inflammable gas ; when the coal was, 
 therefore, heaped above the orifice, and was, possibly, caked hard at the- 
 top, the gas distilling from it escaped more easily from the little orifice 
 than elsewhere, and chance determined that the channel or delivery pipe 
 should be in the direction of the drawing-room when the fire was burn- 
 ing in the dining-room, and in the contrary direction when the fire was 
 lighted in the latter chamber. The nuisance was stopped by plugging 
 the holes at the back of the grate with clay, and putting a sheet of iron- 
 over the orifice. 
 
 Before Dr. Paraday was appointed as a scientific counsellor to assist 
 the deliberations of the Trinity Board in connexion with lighthouses, all 
 the lamps were burnt in the lanterns with the smallest ana most imper- 
 fect arrangement for carrying off the heated air and products of com- 
 bustion ; as a natural consequence, and particularly on cold nights, the 
 windows of the lantern of the lighthouse wv^re covered with ice derived 
 from the condensation of the water produced by the combustion of the 
 hydrogen of the oil, whilst the carbon generated such quantities of car- 
 bonic acid that the light-keepers were unable to stay in the lantern, and 
 if obliged to visit the latter (whilst looking to improving the light of any 
 single lamp that might be burning dimly), they were almost overpowered 
 with the excess of carbonic acid, and stated, in their evidence, that it pro- 
 duced headache and sickness, and a tendency to insensibility. Paraday 
 immediately established a system of ventilation ; and by attaching a 
 copper tube to the top of each lamp-chimney, and centering them all in 
 one large funnel passing to the top of the lighthouse, the whole of the- 
 water which previously condensed on the glass windows and impeded 
 the light, besides injuring the brass and copper fittings, was carried off, 
 as also the poisonous carbonic acid gas ; and thus, as Dr. Paraday ex- 
 pressed himself, a complete system of sewage was applied to the lamps 
 of the lighthouses. 
 
 If any one of the numerous stories of ships saved by the Eddystone 
 Lighthouse could demonstrate more than another the value of this beacon 
 
454 
 
 boy’s playbook of science. 
 
 in mid ocean, it must be the graphic account in the Times of the gallant 
 conduct of the British Admiral with his fleet whilst breasting the frightful 
 storm of October, 1859, and endeavouring to reach Plymouth Sound : — 
 “ It was on Saturday, the 22nd October, that the Kero , the Trafalgar , 
 the Algiers , and the Aboukir, accompanied by the Mersey , the Emerald , 
 and the Melpomene , put to sea from Queenstown. Up to the afternoon 
 of Monday the squadron met with no remarkable adventure, but about 
 that time, just after the crews had been exercised at gunnery practice, 
 heavy storms of hail and sleet began to set in. Still there was no imme- 
 diate indication of the tempest at hand, and at sunset topsails were 
 double-reefed and courses reefed for the night, with no particular cha- 
 racter about the wind, except that of extreme variability. As the morn- 
 ing broke on Tuesday — the day of the storm — the Land’s-end was 
 sighted, and the rain and the wind continued to increase. About nine a.m. 
 the advent of the gale was no longer doubtful; topgallantyards were 
 sent on deck and topgallantmasts struck, and the signal was given from 
 the flagship, ‘Porm two columns; form line of battle; Admiral will 
 endeavour to go to Plymouth.’ To Plymouth, accordingly, the course of 
 the fleet was shaped, but so terrifically had the wind increased that it 
 became very questionable whether the sternmost ships of the line could 
 possibly succeed in entering the Sound. Upon this the Admiral deter- 
 mined to wear the fleet together, stand off, and face the storm, a ma- 
 noeuvre which, under circumstances of great difficulty, was most gallantly 
 executed. The ships were close upon the Eddystone Lighthouse, round 
 which they ‘ darted like dolphins’ under the tremendous pressure of the 
 gale, the Trafalgar stopping in the midst of the storm to pick up a man 
 who had fallen overboard. The whole squadron now stood off the land, 
 the Mersey and Melpomene furling their sails, and the former vessel 
 steaming along ‘ like an ocean giant.’ Still the gale increased till about 
 three p.m., when there occurred that remarkable phenomenon by which 
 these rotatory tempests are characterized. The fleet had got into the 
 very centre of the storm, the * eye’ of the tornado, and, though the sea 
 towered up and broke in tremendous billows all around, the wind sud- 
 denly ceased and the sun shone. When, however, the signal had been 
 given and obeyed for setting sail again, the ships soon encountered the 
 gale once more — not, as before, from the S.E., but the N.W. — and in 
 greater force than ever. It was now a perfect hurricane ; and for three 
 hours the whole fury of the tempest was poured upon the squadron. 
 When it began, at length, to abate a little, the four line-of-battle ships 
 and one of the frigates were still in company, and all doing well. The 
 Mersey and the Emerald had steamed into Plymouth, but the five re- 
 maining vessels kept in open order throughout that terrible night, wore 
 in succession by night signal at about one a.m., made the land at day- 
 light, formed line of battle, came grandly up Channel under sail at the 
 rate of eleven knots an hour, steamed into Portland, and ‘ took up their 
 anchorage without the loss of a sail, a spar, or a ropeyarn.’ ” 
 
 After making the important improvement in the ventilation of light- 
 houses, many letters were addressed to the learned philosopher by 
 
The British fleet rounding the Eddystone Lighthouse during the great storm 
 of October, 1859. p . 454 , 
 

FARADAY’S LAMP. 
 
 * 455 
 
 numerous light-keepers, one of which in plain but striking language 
 related that “ the enemy (alluding to the water and carbonic acid) was 
 now driven out” 
 
 The ingenious invention alluded to was succeeded by another and 
 equally simple but philosophical arrangement, which Dr. Earaday pre- 
 sented to his brother, and it was duly patented. It consisted of an 
 arrangement for ventilating gas burners, and it must be obvious that a 
 necessity exists for such ventilation, because every cubic foot of coal 
 gas when burnt produces a little more than a cubic foot of carbonic 
 acid. A pound weight of ordinary coal gas contains about T 3 oths of its 
 weight of hydrogen, which when burnt produces two pounds and T 7 oths 
 of a pound of water. A pound of ordinary coal gas also contains about 
 -^ths of its weight of charcoal, which produces when burnt rather 
 more than two and a half pounds of carbonic acid gas — viz., 2*56. In 
 order to burn this quantity of gas nineteen cubic feet and y^ths of a 
 foot of atmospheric air, containing 4*26 cubic feet of oxygen, are 
 required. 
 
 It is not therefore sur- 
 prising that as common coal 
 gas is sometimes purified 
 carelessly, and contains a 
 minute trace of sulphuretted 
 hydrogen, with some bisul- 
 phide of carbon vapour, that 
 it should produce the most 
 prejudicial effects in badly 
 ventilated rooms, and espe- 
 cially in some of those 
 perched up glass boxes in 
 large places of business, 
 where clerks are obliged to 
 sit for many consecutive 
 hours, lighted by gas, and 
 breathing their own. breath 
 and the products of combus- 
 tion from the gas light, 
 thereby rendering them- 
 selves liable to diseases of 
 the lungs, and also to very 
 troublesome throat attacks, 
 when leaving their close 
 glass boxes, and passing into 
 the cold night air. The dan- 
 gerous product of the com- 
 bustion of ordinary coal gas 
 is sulphurous acid — viz., the 
 
 Fig. 423. a b. Gas pipe and argand burner ; the 
 air enters, as usual, up the centre of the argand. 
 c c. The first glass chimney open at the top. d d. 
 The second glass chimney closed at the top, with a 
 disc of double talc, and fitting over c c, and leaving 
 a space between the two glasses, down which the 
 air passes, and into the ventilating tube, e e. 
 h h. The ground-glass globe closed at the top, and 
 surrounding the whole.* 
 
 • Mr. Faraday, ofWardour-street, supplies this ventilating lamp. 
 
45C 
 
 boy’s playbook of science. 
 
 same gas as that generated when a sulphur match is burnt : and if it 
 will attack the bindings of books, and damage furniture, goods in shops, 
 curtains, &c., in consequence of the large quantity of water with which 
 it is accompanied, how much more is it not likely to injure the delicate 
 organism of the breathing apparatus of the lungs ? Dr. Faraday’s lamp 
 is therefore a great boon, but, like a great many other clever things, it 
 must be adapted to the currents of air and draught from the room ; and 
 means must be taken to prevent the draught becoming too powerful in 
 Faraday’s lamp, or else the illuminating power is destroyed by the 
 thorough combustion of the carbon of the coal gas, and the heat gene 
 rated is so intense that the glasses soon crack, and of course become 
 useless. The lamp will answer very well if (as has been already stated) 
 the draught in the ventilating pipe is not too great. 
 
 The system already explained and illustrated is likewise carried 
 out on a much larger scale in the ventilation of coal pits, where a shaft 
 is usually sunk into the ground for the admission of air, which, after 
 circulating through the intricate windings and mazes of the coal pit 
 workings, escapes at last from another shaft, at the bottom of which is 
 placed a powerful furnace, and this is kept burning night and day, so 
 
THE UPCAST AND DOWNCAST SHAFT. 
 
 457 
 
 that the movement of the air is maintained in one direction — viz., from 
 the outer air down the shaft called the downcast , thence to the galleries, 
 where the coal hewers are working, to the second shaft, near which 
 the furnace is placed, and up this latter the air travels ; the shaft, pit, 
 or funnel being very appropriately termed the upcast. 
 
 Should the furnace at the bottom of the upcast be neglected, the 
 ventilation may be just balanced, or set slightly towards the downcast ; 
 under these circumstances the carbonic acid from the fire will begin to 
 circulate in the galleries, and poison those who are not aware of its 
 presence and take the proper means to escape. Such accidents, amongst 
 the host of others that occur in a coal pit, have actually been recorded ; 
 and the firemen, whose duty it might be to attend to the proper burning 
 of the furnace, have had to pay the penalty of death for their own careless- 
 ness in falling asleep and neglecting to maintain the ventilation of the 
 mine in one direction. (Fig. 424.) 
 
 These details are amply sufficient to demonstrate the manner in which 
 heat is diffused through air, whilst the rarefication of the air by heat 
 suggests the cause of those frightful storms of wind that rush from 
 other and colder parts of the surface of the globe, to supply the void 
 produced by the cooling and contraction of the enormous volumes of 
 gaseous matter. 
 
 The Radiation of Heat. 
 
 When rays of heat are emitted from incandescent matter, they are not 
 necessarily visible, nay, they are generally invisible, and not accom- 
 panied with a manifestation of light, and pass with great velocity through 
 a void or vacuum, also through air and certain other bodies. From 
 what has been stated respecting the manner in which air, by continually 
 moving, and by convection, carries off heat, it might be thought that no 
 proof existed that invisible rays of heat are really thrown off from a 
 tail filled with boiling water. But this question is set at rest by the 
 fact, that such a ball will cool rapidly when suspended by a string inside 
 the receiver of an air pump from which the atmospheric air has been 
 removed, so that no conduction of the particles of air could possibly 
 remove the heat. 
 
 In the year 1786, Colonel Sir B. Thompson examined the relative 
 conducting powers of air and a Torricellian vacuum — the latter being 
 used because, as the experimenter stated, it was impossible to obtain a 
 perfect vacuum, on account of the moist vapour which exhaled from the 
 wet leather and the oil used in the machine, for at that time carefully 
 ground brass plates were not used in air-pumps, but plates only, with a 
 circular piece of wet leather upon them. In a paper which Colonel Sir B. 
 Thompson read before the Royal Society, he stated that “It appears that 
 the Torricellian vacuum, which affords so ready a passage to the electric 
 fiuid, so far from being a good conductor of heat, is a much worse one 
 than common air, which of itself is reckoned among the worst ; for when 
 the bulb of the thermometer was surrounded with air, and the instru- 
 ment was plunged into boiling water, the mercury rose from 18° to 27° 
 
45 S 
 
 boy’s playbook of science. 
 
 in forty-five seconds ; but in the former experiment, when it was sur- 
 rounded by a Torricellian vacuum, it required to remain in the boiling 
 water one minute thirty seconds to acquire that degree of heat. In the 
 vacuum it required five minutes to rise to 48° T %ths; but in air it rose 
 to that height in twd minutes forty seconds ; and the proportion of the 
 times in the other observation was nearly the same. 
 
 “ It appears, from other experiments, that the conducting power of air 
 to that of the Torricellian vacuum, under the circumstances described, 
 is as 1000 to 702 nearly, for the quantities of heat communicated being 
 equal, the intensity of the communication is as the times inversely. By 
 others it appears that the conducting power of air is to that of the 
 Torricellian vacuum as 1000 to 603.” 
 
 It is therefore very interesting to discover that the attention of 
 
 experimentalists was early 
 directed to the fact that heat 
 was independent of the air, 
 and passed either as waves 
 of heat or molecules of heat 
 through space. The velo- 
 city with which heat moves 
 through a vacuum is very 
 great, and in an experiment 
 performed by M. Pictet, no 
 perceptible interval took 
 place between the time at 
 • which caloric quitted a 
 heated body and its recep- 
 tion by a thermometer at a 
 distance of sixty-nine feet. 
 It appears also, from the 
 experiments of the same 
 philosopher, to be thrown 
 off or radiated in every di- 
 rection, and not to be di- 
 verted (as shown at p. 429) 
 by any strong current of air 
 passing it transversely. Sir 
 Humphrey Davy ignited the 
 charcoal points connected 
 with a battery in a vacuum, 
 taking care to place the 
 charcoal points at the top 
 of the jar, and a concave 
 mirror, with a delicate ther- 
 mometer in its focus, at the 
 Fig. 425. The air-pump and receiver, containing at bottom of the vessel placed 
 A the electric light in the focus of a concave mirror, nT1 air-THimn relate 
 
 and at b a delicate thermometer, also in the focus of a "P on ™ e , air P^PP P icUe ‘ 
 concave mirror. The effect of radiation was 
 
THE RADIATION OF HEAT. 
 
 459 
 
 ascertained first when the receiver was full of air, and next when it was 
 exhausted to x^th (i.e., 199 parts pumped out, leaving only one part 
 of air in the receiver). In the latter case, the effect of radiation was 
 found to be three times greater than in an atmosphere of the common 
 density. The greater rise of the thermometer in vacuo than in air is to 
 be ascribed to the conducting power of the latter ; for this conducting 
 power, by reducing the temperature of the heated body, has a constant 
 tendency to diminish the activity of radiation, which is always pro- 
 portional to the excess of the temperature of the heated body above that 
 of the surrounding medium. (Fig. 425.) 
 
 Count Bumford’s experiments with a Torricellian vacuum gives the 
 proportion of five in vacuo to three in air for the quantities of heat lost 
 by radiation, and by conduction or diffusion. It is not, perhaps, de- 
 parting very far from the truth, if it be stated that one half of the heat 
 lost by a heated body escapes by radiation, and that the rest is carried 
 off by the convective power of currents of air. 
 
 If the process of radiation was not constantly proceeding, it can easily 
 be imagined that the temperature of our globe would become so elevated 
 by the regular accession of heat from the sun’s rays, that the vegetation- 
 would be parched up and destroyed, and consequently all animals and 
 the human race must become extinct. The best time to notice the 
 radiation of heat from the earth is at night and after a hot summer’s 
 day. If the sky is clear, it will be noticed (with the help of a ther- 
 mometer,) that the ground is several degrees colder than the air a few 
 feet above it. (Fig. 426.) It is this reduced temperature that causes 
 
 Fig. 426. Negretti and Zambra’s terrestrial radiation thermometer. The bnlb of this 
 instrument is transparent, and the divisions engraved on its glass stem. In use it is placed 
 with its bulb fully exposed to the sky, resting on grass, with its stem supported (by .little 
 forks of wood, and protected from the wind. 
 
 the deposition of dew, and produces the earth-cloud which so nearly 
 resembles a sheet of water as to have been occasionally mistaken for an 
 inundation, the occurrence of the previous night. Mr. Luke Howard 
 has called this cloud, which is the lowest form of these draperies of the 
 sky, “ The Stratus,” or evening mist ; but when permanent, and increased 
 to a depth so as to rise above our heads, it is then called the morning 
 fog, so peculiarly agreeable in London when incorporated with the 
 black smoke, making a fine reddishr-yellow ochreous mist. By placing a 
 thermometer, standing at the ordinary temperature of the air, cased 
 
460 
 
 boy’s playbook op science. 
 
 with a good radiating material, such as filaments of cotton, in the focus 
 of a concave mirror, and by turning this arrangement towards a clear 
 sky in the evening, it will be noticed that the temperature falls several 
 degrees. Good radiators of heat are black and scratched surfaces, 
 filaments of cotton, grass, twigs, boughs, and certain leaves, especially 
 those with a rough surface. 
 
 Bad radiators of heat are bright and polished metallic surfaces, white 
 woollen cloth or flannel, bard and dense substances, such as a gravel 
 path and stone, or those leaves which have a polished surface, such as 
 the common laurel. It is the frozen dew ana mist which produce the 
 beautiful effect of hoar-frost and icicles on the trees and bushes, the 
 primary cause being the radiation of heat from the various objects on 
 the surface of the earth, as well as from the latter itself. When the 
 wind is high, dew does not deposit, as it is necessary that the air should 
 be calm, in order to receive the cooling impression of the cold earth, and 
 to deposit the moisture, which it holds in solution as invisible steam. 
 When the wind blows, it mixes all parts of the air together, and prevents 
 that difference of temperature which causes the deposit of dew. Hence 
 the evening mist will be more generally observed in the bosom of a 
 valley surrounded by hills and screened from the winds that may blow 
 from either quarter. The continual presence of moisture in the air is 
 well shown by the condensation of water on the outside of a glass of 
 cold spring water, or especially on the outside of a jug containing iced 
 water. The invisible steam is always ready to bathe the tender plants 
 with dew, which would otherwise perish and be burnt up during a hot 
 summer, if they did not radiate heat at night, and thus condense water 
 upon themselves. The presence of w r atery vapour in the air becomes 
 therefore a matter of great importance, and hence the construction of 
 hygrometers or measurers of the moisture in the air. 
 
 llegnault’s condenser hygrometer consists of a tube made of 
 silver, very thin, and perfectly polished ; the tube is larger at one 
 end than the other, the large part being 1*8 in depth by 8 TO in diameter. 
 This is fitted tightly to a brass stand, with a telescopic arrangement for 
 adjusting when making an observation. The tube has a small lateral 
 tubulure, to which is attached an India-rubber tube with ivory mouth- 
 piece ; this tubulure enters at right angles near the top, and traverses 
 it to the bottom of largest part. A delicate thermometer is inserted in 
 through a cork, or India-rubber washer, at the open end of the tube, 
 the bulb of which descends to the centre of its largest part. A ther- 
 mometer is attached for taking the temperature of the air ; also a bottle 
 for containing ether. 
 
 To use the condenser hygrometer, a sufficient quantity of sulphuric ether 
 is poured into the silver tube to cover the thermometer bulb. On allowing 
 air to pass bubble by bubble through the ether, by breathing in the 
 tube, an uniform temperature will be obtained ; if the ether continues 
 to be agitated by breathing briskly through the tube, a rapid reduction 
 of temperature will be the result. At the moment the ether is cooled 
 down to the dew-point temperature, the external surface of that portion 
 
HYGROSCOPES AND THE WEATHER. 
 
 461 
 
 of the silver tube containing the ether will become covered with a coating 
 of moisture, and the degree shown by the thermometer at that instant 
 will be the temperature of the dew-point. 
 
 The most simple form of the hygrometer was formerly a very favourite 
 indicator of the state of the weather, and usually consisted of the 
 figure of a monk with 
 his hood, which is at- 
 tached to a bit of cat- 
 gut; this covering of 
 paper, painted to re- 
 present the hood, falls 
 over the head on the 
 approach of damp 
 weather, and inclines 
 well back during the 
 period that the air is 
 dry or contains less 
 moisture ; and simple 
 as it is, this hygrometer, 
 in conjunction with the 
 reading of the baro- 
 meter, may assist Pa- 
 terfamilias in deciding 
 the fate of a pet bon- 
 net or velvet mantle, 
 which is or is not to 
 be worn on a doubtful 
 day. (Fig. 427.) 
 
 A decision on the 
 possible changes of the 
 weather requires con- 
 siderable experience, 
 and it has been said 
 that one of the most 
 
 celebiated marshals of C0V ers the head to dotted , 
 
 France owed hlS inva- various intermediate positions, being quite back and on the 
 shoulders in dry states of the air. A thermometer, d, is 
 usually attached. 
 
 The monk hygro scope, in which the hood, a b, 
 ’ ,ed line c in wet weather, .‘ind takes 
 
 riable success in mili- 
 tary combinations and 
 attacks to his attention to the signs of the weather, as indicated by 
 the state of the air during the phases of the moon. Inexperienced 
 persons (and by that we mean young persons) may, however, take a 
 certain position in the rank of “ weather prophets” by consulting the 
 veathercock, the barometer, and the hygrometer, before committing 
 themselves to an opinion, if asked to say what the weather will be. 
 
 The dry and wet bulb hygrometer (as represented in the next en- 
 graving) consists of two parallel thermometers, as nearly identical as 
 possible, mounted on,a wooden bracket, one marked dry, the other wet . 
 The bulb of the wet thermometer is covered with thin muslin, round the 
 
462 
 
 boy’s playbook of science. 
 
 neck of wliicli is twisted a conducting thread of lamp-wick, or common 
 darning-cotton; this passes into a vessel of water, placed at such a 
 distance as to allow a length of conducting thread of about three inches ; 
 the cup or glass is placed on one side, and a little beneath, so that the 
 water within may not affect the reading of the dry bulb thermometer. In 
 
 observing, the eye should be 
 placed on a level with the top 
 of the mercury in the tube, and 
 the observer should refrainfrom 
 breathing whilst taking an ob- 
 servation. The temperature of 
 the air and of evaporation is 
 given by the readings of the 
 two thermometers , from which 
 can be calculated the dew-point, 
 tables being furnished for that 
 purpose with the instrument. 
 (Fig. 428.) 
 
 The colour of the sky at par- 
 ticular times affords the most 
 excellent guidance to doubting 
 members of pic-nic or other 
 out-of-door parties. Not only 
 does a rosy sunset presage fine 
 weather, and a ruddy sunrise 
 bad weather, but there are 
 other tints which speak with 
 equal clearness and accuracy. 
 A bright yellow sky in the even- 
 ing indicates wind ; a pale yel- 
 low, wet ; a neutral grey colour 
 constitutes a favourable sign in 
 the evening, an unfavourable 
 one in the morning. The clouds, 
 again, are full of meaning in 
 themselves. If their forms are 
 soft, undefined, and feathery, 
 the weather will be fine; if. 
 their edges are hard, sharp, and 
 defined, it will be foul. Gene- 
 rally speaking, any deep, un- 
 usual hues betoken wind or 
 rain, while the more quiet and 
 delicate tints bespeak fine 
 weather. 
 
 nativesin the neighbourhood of Calcutta for the purpose of obtaining small 
 
THE RADIATION OF HEAT. 
 
 403 
 
 quantities of ice. In that climate, the thermometer during the coldest 
 nights does not indicate a lower temperature than about 40° Pahr. 
 The sky, however, is perfectly cloudless, and as heat radiates with great 
 rapidity from the surface of the ground, the Indian natives ingeniously 
 place very shallow earthenware pans on straw, which is a bad conductor 
 of heat, and hence insulates the pans from communication with the 
 parched earth. In a few hours, the water in the pans is covered with a 
 thin sheet of ice, and there can be no doubt of its production by an 
 absolute loss of heat by radiation, because the plan does not succeed on 
 a windy night, and succeeds best even w r hen the pans are sunk in 
 trenches dug in the earth. A windy night prevents that difference of 
 temperature between one portion of the surface of the earth and another, 
 which is so essential to a steady and uniform loss of heat, as it must be 
 evident that the continual mixture of warmer portions of air with that 
 which is colder would tend to prevent the desired lowness of temperature 
 oeing attained. 
 
 The manner in which heat is observed to be radiated has suggested 
 another theory to the fertile brain of philosophical observers, and it has 
 been supposed that the conduction of heat may be nothing more than a 
 radiation from one particle of matter to another, as through a bar of 
 copper, in which the particles, though packed closely together, are not 
 supposed to be in actual contact, so that it is possible to conceive each 
 separate atom of copper receiving and radiating its heat to the neigh- 
 bouring particle, and so on throughout the length and breadth of the 
 metal. By this theory the radiation of heat through a vacuum is brought 
 into close connexion with that of the radiation of heat through the air 
 and other solid and liquid bodies. 
 
 Some of the most interesting phenomena of heat are those discovered 
 by Leslie, who has proved in a very satisfactory manner that the rapidity 
 with which a body cools, depends (like the reflection of light) more on 
 the condition of the surface than on the nature of the material of which 
 the surface is composed. With a globular and bright tin vessel it was 
 observed that water of a certain heat contained in it, required 156 
 minutes to cool ; but when the latter vessel was covered with a thin 
 coating of lamp-black and size, the water fell to the same degree as that 
 noticed in the first experiment in the space of eighty-one minutes. 
 
 By very careful observations made with a differential air thermometer 
 Leslie determined that the power of radiating heat in various sub- 
 
 stances was as follows : — 
 
 Lamp-black 100 
 
 Writing paper 98 
 
 Sealing wax 95 
 
 Crown glass 90 
 
 Plumbago 75 
 
 Tarnished lead 45 
 
 Clean lead 19 
 
 Iron, polished lit 
 
 Tin plate, gold, silver, copper 
 
464 
 
 BOY’S playbook of science. 
 
 As in the reflection of light, it was noticed that a piece of charcoal 
 covered with gold leaf, partook of the nature of the precious metal so 
 far as its power of throwing off or scattering the rays of light was con- 
 cerned, so a piece of glass covered with gold-leaf appears to possess 
 the same power of radiating heat as that of any brilliant metal. 
 
 Radiant heat, like light, can be propagated through a great variety 
 of substances, but is stopped by the larger number ; and it can be re 
 fleeted, refracted, polarized, absorbed, or it may undergo a secondary 
 radiation. 
 
 The intensity of radiant heat follows the same law as that of light, 
 and decreases as the square of the distance from its source. The same 
 law that governs the reflection of light, also prevails with that of heat ; 
 and it may be found by experiment that the angle of incidence is equal 
 to the angle of reflection, so that the heat is disposed of in the same 
 manner as light when it falls upon bright polished planes, convex and 
 concave surfaces ; hence the use of bright tin meat screens and Dutch 
 ovens, and of all those simple pieces of culinary furniture which are em- 
 ployed in the kitchen for the purpose of arresting the cold currents of 
 air that set towards burning matter, as also to reflect the heat upon 
 whatever viands may be cooking before the fire. A bright silver teapot 
 retains its heat better than a dirty one, and the fact is determined very 
 readily by pouring boiling water into two teapots, the one being made of 
 bright tin and the other of black japanned tin. A thermometer inserted 
 into each vessel will soon show that the latter radiates, and therefore 
 loses its heat quicker than the former ; the relative radiating powers of 
 bright and blackened tin being as 15 to 100. Pipes for the conveyance 
 of hot water or steam should be kept bright, if possible, although this 
 trouble is avoided usually by packing them in bad conductors of heat, 
 whilst the polish of the cylinder of a steam-engine is of great impor- 
 tance as a means of economizing heat. 
 
 When the finger is approached within an inch or so of a red-hot ball, 
 the heat radiated from the latter is so intense that it cannot be held there 
 
THE RADIATION OF HEAT. 
 
 465 
 
 for more than a few seconds. If, however, the finger is coated with 
 gold leaf it may be kept near the iron ball for some considerable time, 
 because the radiant heat is reflected from the surface of the gold. If 
 the word heat is written upon a sheet of paper and the letters after- 
 wards gilt, the whole of the white surface is rapidly toasted and scorched 
 when held before a fire, whilst the surface of the paper under the gold 
 leaf remains perfectly white, which can be ascertained by turning the 
 paper round and observing the other side. A sheet of paper gilt inside 
 and turned round as a cone, being left open at both ends, may be em- 
 ployed as a reflecting surface ; and if a bit of phosphorus, placed on 
 paper, is held, say at two feet from a red-hot ball of about two inches 
 diameter, the radial heat from the latter has not sufficient intensity at 
 that distance to set it on fire quickly ; if, however, the cone of gilt paper 
 is used between the two, and the phosphorus brought into the focus of 
 the rays of radial heat, it very quickly takes fire. (Fig. 429.) 
 
 Dr. Bache has determined by experiments that the radiation of heat 
 from a body is not affected by colour, so that in winter all coloured clothes 
 are alike in that respect, and radiate heat without any appreciable dif- 
 ference. The power of absorbing heat, however, is greatly dependent on 
 colour ; and as a general rule, good radiators of heat (such as a black 
 cloth, or indeed any surface covered with lamp-black), are also excel- 
 lent absorbents of heat. Dr. Hooke and Dr. Franklin placed pieces of 
 cloth of similar texture and size on snow, allowing the sun’s rays to fall 
 equally upon them. The dark specimen always absorbed more heat 
 than the light ones, and the snow beneath them melted to a greater 
 extent than under the others ; and they both remarked that the effect 
 was nearly in proportion to the depth of the shade, as in the following 
 order : — After black, the maximum absorbent quality was possessed by* 
 first, blue; second, green; third, purple; fourth, red; fifth, yellow. 
 The minimum absorbent power was observed to belong to white. 
 
 When radiant heat is allowed to pass through glass, the latter sub- 
 stance is not found' to be transparent to heat rays as it is to those of 
 light, but a considerable proportion of heat is arrested and stopped- 
 consequently glass fire-screens are to be found in the mansions of the 
 wealthy, because they obstruct the heat but do not exclude the cheerful 
 light and blaze of the fireside. 
 
 w- 
 
 IT II 
 
4CG 
 
 boy’s playbook of science. 
 
 Fig. 130. Hancock’s steam omnibus, which ran on the common roads. 
 
 CHAPTER XXVIII. 
 
 THE STEAM-ENGINE. 
 
 It must be apparent to those who read popular works on science, that 
 they possess, at all events, one point of utility— viz., that they are 
 indicative of the various subjects that may be selected in science for 
 special, searching and exhaustive study. The subject of steam and the 
 steam engine is not one that could be thoroughly treated of in the 
 narrow space allowed in this volume, but enough may be said to _ give 
 some instruction and to impart common principles, whilst the minute 
 details are better examined and learnt in the works of Bourne, Rankine, 
 and other authors who devote themselves specially to the important 
 commercial question of steam. 
 
 The first truth to be comprehended is, that all matter contains within 
 its substance the power of creating heat— or as it may be expressed 
 more plainly, solids, fluids, and gases contain what is termed latent or 
 insensible heat, in contradistinction to the heat which is apparent when 
 we touch a vessel containing warm water or approach a cheerful fire ; 
 this latter is termed sensible heat, and has formed the subject of the 
 preceding chapters. 
 
 If a cold horse-shoe nail is applied to a thin dry slice of phosphorus 
 laid on a sheet of paper, no combustion of the phosphorus ensues, be- 
 cause the temperature of the iron is not sufficiently high to affect that 
 combustible substance ; but if the horse-shoe nail is vigorously hammered 
 on an anvil, the particles of the metal are brought closer together, and 
 if it is applied to the phosphorus, so much heat has been generated, 
 thrust or squeezed out by the hammering or condensation of the iron, 
 that it is now sufficiently warm to set fire to it. 
 
LATENT HEAT. 
 
 4G7 
 
 The reverse or antithesis to this experiment — viz., the production of 
 cold — would be shown if it were possible to expand a mass of metal 
 suddenly, and this can be effected by first melting together 
 
 207 parts by weight of lead. 
 
 118 „ „ tin. 
 
 284 „ „ bismuth. 
 
 When these metals are in the liquid state and perfectly mixed, they 
 are poured from a sufficient height into a pail of cold water, for the pur- 
 pose of granulating or dividing them into small fragments. 
 
 If the granulated compound metal is now mixed with 1017 parts by 
 weight of quicksilver, it becomes suddenly liquefied and expanded : 
 liquefaction is the reverse of solidification, and hence cold is produced from 
 the natural heat of the compound metals being rendered latent by the 
 change from the solid to the liquid state ; so that a small quantity of water 
 placed in a glass tube, ana surrounded with the metals whilst lique- 
 fying in the mercury, becomes rapidly converted into ice, the fall of 
 the temperature, as shown bv a thermometer, being from 60° Fahr. to 
 14°, which is 18° degrees below the freezing point of water. In the 
 former case, by hammering the iron the latent heat is made sensible ; 
 whilst in the latter case, by the liquefaction of the compound metal in 
 mercury, the sensible heat is rendered latent . The heat rendered latent 
 by melting different substances is not a constant quantity, but varies 
 with every special body employed, and the Drs. Irvine have proved 
 this fact by the following experiments : — 
 
 Ditto, reduced to the 
 
 Heat of fluidity. specific heat of water. 
 
 Sulphur .... 143*08° Falir 27*14. 
 
 Spermaceti . . . 145 „ .... — 
 
 Lead 163 „ .... 5*6. 
 
 Bees’-wax .... 175 „ .... — 
 
 Zinc 493 „ .... 48*3.. 
 
 Tin 500 „ .... 33* 
 
 Bismuth .... 550 „ ... 23*25. 
 
 Every one of these substances requires more heat to bring them into 
 the liquid condition than ice, for which 140° of heat are sufficient, or 
 are rendered latent during its conversion into water. 
 
 In coining at the Mint, the cold blank pieces of gold, silver, or 
 copper become hot directly they have sustained the violent and sudden 
 pressure of the coining press, and they must be heated again, or an- 
 nealed, to restore the equilibrium of the heat disturbed by the violent 
 blow, or else they remain hard and unfit to sustain the finishing process 
 of milling. 
 
 The condensation of water when it assumes a smaller bulk by union 
 with sulphuric acid, is easily proved by measuring a pint of water and 
 a pint of acid, and mixing them together, when a very great increase of 
 temperature may be perceived ; and by placing into the mixture a cold 
 copper wire that picviously could not ignite phosphorus, it becomes 
 
 H h 2 
 
468 
 
 boy’s playbook of science. 
 
 very hot, and when removed and wiped it will cause phosphorus to fire 
 directly it touches that substance. When the mixture of sulphuric acid 
 and water is measured after it has cooled, it has no longer a bulk of two 
 pints, but is found to have lost bulk equal to one or more ounces by 
 measure. The heat evolved by a mixture of four parts of strong sul- 
 phuric acid and one part water is shown by the thermometer to be 
 300° Fahr., and this mode of obtaining heat has been used bv aeronauts 
 for the purpose of obtaining artificial warmth without the danger of 
 setting fire to the gas in the balloon. 
 
 When alcohol and water are mixed a change of density occurs, and 
 heat is produced ; and if equal measures of alcohol of a specific gravity 
 of *825, and water, each at 50° Fahr., are mixed, a temperature ot 70 
 Fahr. is obtained; if the mixture is made in a glass vessel, as shown in 
 the annexed cut, the combination is very apparent. To Perform 
 experiment properly, water is poured into the lower tube and bulb, ana 
 alcohol into the top one ; when this is done, the stopper is inserted, and 
 the whole thoroughly shaken and mixed together ; the warmth which is 
 
LATENT HEAT. 
 
 4G9 
 
 thus obtained is apparent to the hand, whilst the con- 
 traction is shown after the mixture is cold, as it no 
 longer fills the two bulbs of the instrument. (Fig. 432.) 
 
 The latent heat of gases is easily shown by suddenly 
 condensing air in a small syringe or pump, of which the 
 piston contains a minute fragment of amadou (a species 
 of fungus, Polyporus igniarius ; this, according to Sim- 
 monds, after having been beaten with a mallet, and 
 dipped in a solution of saltpetre, forms the spunk or 
 German tinder of commerce ; it is also used as a styptic, 
 and made into razor strops), which takes fire, and before 
 the invention of vesta and other matches, tobacco-smokers 
 were in the habit of obtaining a light for their pipes 
 and cigars in this manner — viz., by the latent heat ob- 
 tained . from the contraction or compression of air. 
 
 Then, again, an instructive though opposite parallel is 
 afforded by suddenly expanding or rarefying air in a 
 glass receiver provided with a delicate thermometer. 
 
 By pumping out some of the air, a considerable diminu- 
 tion of the temperature occurs, and equal to several 
 degrees of the thermometer. Every child knows that 
 steam direct from the kettle will scald, but if it issues 
 from a’ high-pressure boiler, say at fifteen pounds on 
 the square inch, the hand may be held with impunity in 
 the escaping steam, as it merely feels gently warm, and 
 not scalding. This is due partly to the loss of heat 
 rendered latent by the expansion of the high-pressure 
 steam directly it passes into the air, and partly to the 
 currents of air. that are dragged into an escaping jet of steam, 
 tendency of the air to rush 
 into a jet of steam was 
 discovered by Faraday, and 
 explains those curious ex- 
 periments with a jet of 
 steam by which balls, empty 
 flasks, and globular vessels 
 are sustained and supported 
 either perpendicularly or 
 horizontally. 
 
 If steam at a pressure of 
 about sixty pounds per inch 
 is allowed to escape from 
 a proper jet, and a large 
 lighted circular torch com- 
 posed of tow dipped in tur- 
 pentine held over it, the 
 course of the external air is 433 - Jet discharging high-pressure steam 
 
 c u b. Lighted torch held round the escaping steam 
 Shown by the direction of the flames from the former all rush into lie latter. 
 
 Fig. 432. Glass 
 bulbs and tube to 
 show the contrac- 
 tion in bulk of a 
 mixture of alcohol 
 and water. 
 
 This 
 
470 
 
 boy’s playbook of science. 
 
 the flames, which are forcibly pulled and blown into the jet of steam 
 with a roaring noise, indicating the rapidity of the blast of air moving 
 to the steam jet. (Fig. 433.) 
 
 Egg-shells, empty flasks, india-rubber or light copper and brass balls, 
 are suspended in the most singular manner inside an escaping jet of high- 
 pressure steam ; and, before the explanation of Faraday, reams of paper 
 were used in the discussion of the possible theory to account for this 
 effect ; and what made the explanation still more difficult was the fact 
 that the jet of steam might be inclined at any angle between the hori- 
 zontal and perpendicular, and still held the ball, egg-shell, or other 
 spherical figure firmly in its vapoury grasp. (Fig. 434.) 
 
 I may here mention a curious exhibition which I witnessed at the 
 offices of the Westinghouse Brake Company at Westminster. Here there 
 is a full-sized model of the railway brake, which is kept charged with 
 air at the pressure of 85 lbs. on the square inch. At one side of the 
 apparatus is a tube furnished with a jet, which has a ball and socket 
 joint, so that it can be turned to different angles. A cock is fixed to 
 this jet, so that the air can be turned on or off. It seems that one day 
 the engineer in charge took a child’s indiarubber ball in his hand, in 
 order to see how far the escaping blast would project it. To his sur- 
 prise the ball remained suspended in mid-air. More than this, he found 
 that it would also remain suspended although the nozzle through which 
 the air was rushing was inclined almost to the horizontal, as in the case 
 of the egg-shells figured above. This led to further experiments, and 
 balls of all kinds of indiarubber and solid wood up to five inches in 
 diameter were used with a like result. At the time of my visit I had 
 the pleasure of watching the behaviour of these several globes, and the 
 effect was most curious and interesting. The hollow indiarubber balls 
 revolved so quickly that their forms became flattened, the shape in fact 
 of this revolving earth — an oblate spheroid. But perhaps the most 
 remarkable effect was produced when the engineer actually picked up 
 with the air jet a heavy wooden ball from an adjoining shelf. The 
 nozzle was next fitted with a jet pierced with four holes, one in the 
 centre, and the other three occupying the corners of a triangle round 
 
LATENT HEAT. 
 
 471 
 
 it. Four glass marbles were then placed one by one above these holes, 
 And they were presently dancing in mid-air, supported apparently on 
 nothing. 
 
 A large ball measuring more than a foot in diameter has lately been 
 placed in the large hall at the Polytechnic Institution. This is kept 
 suspended in mid-air by the action of a powerful dfir-blast, and the 
 effect of this ball gracefully dancing upon nothing is very curious. This 
 arrangement has been contrived by Mr. Pichler, a gentleman whose 
 name is well known in connection with the institution. To his ingenuity 
 is due the life-sized figure of Leotard, which has for so many years 
 delighted the juveniles by its performance on the trapeze. But Mr. 
 Pichler has lately produced a still more wonderful automaton in the 
 counterfeit presentment of the renowned Blondin. This marvellous 
 figure walks along a rope stretching from end to end of the large hall, 
 lifting each foot alternately in the most life-like manner. The figure 
 wheels before it a barrow, as the veritable Blondin himself did across 
 the yawning chasm of Niagara. It has no support whatever but that 
 furnished by the rope upon which it treads, and the means by which its 
 natural movements are governed remain an inexplicable mystery to all 
 beholders. I am sorry to think that the crowds which assembled to 
 see the real Blondin go through his perilous task are not more nu- 
 merously represented at the performances of his effigy. It seems hard 
 to think that the only attraction in the former case is the chance of 
 witnessing a fatal accident, which would of course be quite impossible 
 with Mr. Pichler’ s automaton. 
 
 In consequence of the great rush of air towards a jet of escaping high- 
 pressure steam, Mr. Goldsworthy Gurney has patented the application 
 of this principle in his ventilating steam jet, which he has already suc- 
 cessfully applied ; in one case especially, where a coal mine had been on 
 fire for several years, and the whole working of the coal-measures in the 
 pit was jeopardized by the spreading of the combustion to new workings ; 
 the fire was first extinguished by carbonic acid gas, pulled, as it were, 
 into the coal-mine by a jet of steam blowing into the downcast , but 
 placed in connexion with a furnace of burning coke ; and the circulation 
 of the carbonic acid, called choke-damp , through the pit workings, was 
 further assisted by a jet of high-pressure steam blowing upwards, and 
 placed over the mouth of the upcast shaft. 
 
 The experiment succeeded perfectly at the South Sauchie Colliery, 
 near Alloa, about seven miles from Stirling, where a fire had raged for 
 about thirty years over an area of twenty-six acres in the waste seam 
 of coal nine feet thick. 
 
 dilating the coalmine, Mr. Gurney’s 
 
 Colliery, and very economically, the 
 
 waste steam alone being used. Experiments have also been satisfac- 
 torily made with it for blowing a cupola for smelting iron, and with dry 
 steam — i.e., steam of a very high pressure — escaping through a warm 
 tube, the results were perfectly successful. 
 
 With this digression from the subject of latent heat derived from 
 
472 
 
 boy’s playbook of science. 
 
 the compression of air, we return again to the subject with another case 
 in point, furnished by the Fountain of Hiero, as it is called, at Schemnitz, 
 in Hungary, described by Professor Brande ; and it may be observed 
 that all the phenomena related would apply to the great pressure of the 
 water from the water-towers at the Crystal Palace, if fitted with a 
 similar air-vessel. 
 
 “ A part of the machinery for working these mines is a perpendicular 
 column of water 260 feet high (the Crystal Palace water-towers are 
 each 284 feet high), which presses upon a quantity of air enclosed in a 
 tight reservoir; the air is consequently condensed to an enormous 
 degree by this height of water, which is equal to between eight and 
 nine atmospheres ; and when a pipe communicating with this reservoir 
 of condensed air is suddenly opened, it rushes out with extreme velocity, 
 instantly expands, and in so doing it absorbs so much heat as to preci- 
 pitate the moisture it contains in a shower of snow, which may readily 
 be gathered on a hat held in the blast. The force of this is so great, 
 that the workman who holds the hat is obliged to lean his back against 
 the wall to retain it in its position/’ 
 
 The best examples of latent heat are furnished by ice, water, and 
 steam, and we are indebted chiefly to Dr. Black for the elegant and con- 
 clusive experiments demonstrating the important truths connected with 
 the latent heat of these three conditions of matter. When various solids 
 are heated, they frequently pass through certain intermediate conditions 
 of softness, terminating in perfect liquidity; but ice and many other 
 bodies change at once to the liquid state on the application of a suiii- 
 cient quantity of heat. The process of melting ice is very slow, because 
 every portion must absorb or render latent a certain quantity of heat 
 before it can take the liquid state — hence the difficulty of melting blocks 
 of ice when they are surrounded with non- conducting materials; and 
 this fact the author has proposed to take advantage of in keeping water 
 cool which is to be supplied to the ova of salmon whilst taking them to 
 stock the rivers of Australia. 
 
 In order to prove that heat is rendered latent by the liquefaction of 
 ice, it is only necessary to weigh a pound of finely-powdered ice and a 
 pound of water at 212° Fahr. ( boiling water), and mix them together ; 
 when the ice is all melted, the resulting temperature is only 52°, there- 
 fore the boiling water has lost 160° of temperature, of which 20° can be 
 accounted for, because the resulting temperature of the melted ice is 
 52°; but in the liquefaction of the pound of ice, 140° have disappeared 
 or become latent, or, as Dr. Black termed it, have become combined . 
 
 1 lb. of ice at 32° -f 20° = 52°, the resulting temperature. 
 
 1 lb. of water at 212° — 52° = 160° — 20 = 140°, rendered latent. 
 
 140° represents the result obtained from innumerable experiments made 
 by mixing equal parts of ice and boiling water, and it is this large quan- 
 tity of latent heat required by ice and snow that prevents their sudden 
 liquefaction, and the disastrous circumstances that would arise from the 
 floods that must otherwise always be produced. 
 
THE LATENT HEAT OF WATER. 
 
 473 
 
 To put the fact beyond all doubt, it is advisable to mix together equal 
 weights of water at 32° and boiling water at 212°, and the result is 
 found by the thermometer to be the mean between the two, because 
 half the extremes are always equal to the mean ; and if the two tempera- 
 tures are added together and divided by two, the result is a temperature 
 of 122°, as shown below: — 
 
 11b. of ice water at °32~{-llb. of water at 212 0 =244°-^2=122°. 
 
 From similar experiments Dr. Black deduced the important truth, 
 “ that in all cases of liquefaction a quantity of heat not indicated by , or 
 sensible to , the thermometer, is absorbed or disappears, and that this heat 
 is withdrawn from the surrounding bodies , leaving them comparatively 
 cold .” At p. 79 it is shown how the sudden solution or liquefaction of 
 certain sail s produces cold, and hence numerous freezing mixtures have 
 been devised. In olden times, when officials in authority did what they 
 pleased, without being troubled with disagreeable returns, and colonels 
 clothed their men, and were merchant tailors on the grand scale, gun 
 cartridges were not confined to practice on the enemy, but they did duty 
 frequently in the absence of ice as refrigerators of the officers’ wine, in 
 consequence of the gunpowder containing nitre or saltpetre ; as a mere 
 solution of this salt finely powdered will lower the temperature of water 
 from 50°Fah. to 35°; whilst a mixture of four ounces of carbonate of 
 soda and four ounces of nitrate of ammonia dissolved in four ounces of 
 water at 60°, will in three hours freeze ten ounces of water in a metallic 
 vessel immersed in the mixture during the liquefaction or solution of 
 the salts. 
 
 Fahrenheit imagined he had attained the lowest possible temperature 
 by mixing ice and salt together, and it is by this means that confectioners 
 usually freeze their ices, or ice puddings ; the materials are first incor- 
 porated, and being placed in metallic vessels or moulds, and surrounded 
 with ice and salt placed in alternate layers, and then well stirred with a 
 stick, they soon solidify into the forms which are so agreeable, and so 
 frequently presented at the tables of the opulent. The temperature 
 obtained is Fahrenheit’s zero — viz., thirty-two degrees below the freezing 
 point of water. According to the very wise police regulation observed 
 in London, all householders are required to sweep or remove the snow 
 from the pavement in front of their houses, and this is frequently done 
 with salt ; should an unfortunate shoeless beggar, tramp past whilst the 
 sudden liquefaction is in progress, the effect on the soles of his feet is 
 evidently very disagreeable, and the rapidity with which he retires 
 from the zero affords a thermometric illustration of the most lively 
 description. 
 
 Heat the Cause of Vapour . 
 
 Every liquid, when of the same degree of chemical purity, and under 
 equal circumstances of atmospheric pressure, has one peculiar point of 
 temperature at which it invariably boils. Thus, ether boils at 96° Fahr., 
 and if some of this highly inflammable liquid is placed carefully in a 
 
474 
 
 boy’s playbook of science. 
 
 flask, by pouring it in with a funnel, and flame applied within one inch 
 of the orifice, no vapour escapes that will take fire ; but if the flame oi 
 
 a spirit lamp is applied, the 
 ether soon boils, and if the 
 lighted taper is again 
 brought near the mouth of 
 the flask, the vapour takes 
 fire, and produces a flame 
 of about two feet in length. 
 This fire only continues as 
 long as the flame of the 
 spirit-lamp is retained at 
 the bottom of the flask, and 
 on removing it the vessel 
 rapidly cools. The length 
 of the flame is reduced, and 
 is gradually extinguished 
 for the want of that essence 
 of its vitality, as it were — 
 viz., heat. (Tig. 135.) If 
 a thermometer is introduced 
 into the flask, however rapid 
 may be the ebullition or 
 boiling of the ether, it is 
 found to be invariably at 
 
 96 ' ■ hi ^ I 
 
 Fig. 435. Heat the cause of vapour. 
 
 The heat carried off by evaporation is most elegantly displayed by 
 placing a little water in a watch glass, and surrounded by charcoal 
 saturated with sulphuric acid, in the vacuum of an air-pump. The rapid 
 evaporation and condensation of the water by its affinity for the sul- 
 phuric quickly produces ice ; and the pumps and other apparatus of 
 Knight and Co., Foster-lane, City, are greatly to be recommended for 
 this and other illustrations. 
 
 The illustration of the determination of the fixed and invariable 
 boiling point belonging to every liquid is further carried out by intro- 
 ducing some water into a second flask standing above a lighted spirit- 
 lamp, with a small thermometer, graduated, of course, properly to degrees 
 above the boiling point of water ; when the water boils, it will be found 
 to remain steadily at a temperature of 212°. And however rapidly the 
 water may be boiled, provided there is ample room for the steam to 
 escape, the heat indicated by the thermometer is like the law of the 
 Medes and Persians, which altereth not, and it remains standing at the 
 number 212°. The only exception (if it may be so termed) to this law 
 is brought about by the shape and nature of the containing vessel ; 
 under a mean pressure the boiling point of water in a metallic vessel is 
 generally 212°; in a glass vessel it may rise as high as 214° or 216°, but 
 if some metallic filings are dropped in, the escape of steam is increased, 
 and the temperature may then drop immediately to 212°. 
 
 When a thermometer is inserted in a flask containing water in a state 
 
THE BOILING POINT OF WATER. 
 
 475 
 
 of ebullition or boiling, so that the bu. 
 wholly surrounded with steam, it will 
 the latter is exactly the same as that 
 boils at 96°, the vapour will be 96°, 
 Steam has therefore exactly the same 
 temperature as the boiling water 
 that produces it. (Fig. 436.) 
 
 Whilst performing the last expe- 
 riment, it may be noticed that the 
 steam inside the neck of the flask is 
 invisible, and that it only becomes 
 apparent in that kind of intermediate 
 condition between the vaporous and 
 liquid state called vesicular vapour — 
 a state corresponding with the “earth 
 fog,” and called by Howard the 
 strains. When a flask containing 
 boiling water is placed under the 
 receiver of an air pump (as soon after 
 the ebullition has ceased as may be 
 possible), and the air pumped out, it 
 will be noticed that the water again 
 begins boiling as the vacuum is ob- 
 tained, showing that the boiling point 
 of the same fluid varies under dif- 
 ferent degrees of atmospheric pres- 
 sure, and according to the height of 
 
 the barometer. 
 
 
 Height of 
 
 Boiling point 
 
 barometer. 
 
 of water. 
 
 26 ... . 
 
 . 204-91 0 
 
 26*5 . . . 
 
 . 205-79 
 
 27 ... . 
 
 . 206-67 
 
 27*5 . . . 
 
 . 207-55 
 
 28 ... . 
 
 . 208-43 
 
 28-5 . . . 
 
 . 209*31 
 
 b does not touch the fluid, but is 
 >e found that the temperature oi 
 >f the former ; and if the liquid 
 if at 212°, the steam is 212°. 
 
 Fig. 436. Thermometer in the steam 
 escaping from boiling water. 
 
 Height of 
 
 Boiling point 
 
 barometer. 
 
 of water. 
 
 29 . . . 
 
 . . . 210-19° 
 
 29-5 . . 
 
 . . . 211-07 
 
 30 . . , 
 
 . . . 212 
 
 30-5 . , 
 
 . . . 212-88 
 
 31 . . , 
 
 . . . 213-76 
 
 Alcohol and ether confined under an exhausted receiver boil violently 
 at the ordinary temperature of the atmosphere, and in general liquids 
 boil with 124° less of heat than are required under a mean pressure of 
 the air; water, therefore, in a vacuum must boil at 88° and alcohol at 49°. 
 
 On ascending considerable heights, as to the tops of mountains, the 
 boiling point of water gradually falls in the scale of the thermometer. 
 Thus, on the summit of Mont Blanc water was found by Saussure to 
 boil at 187° Fahr. In Mr. Albert Smith’s delightful narrative of his 
 ascent of Mont Blanc, he mentions the violent commotion and escape of 
 the whole of the champagne in froth directly the bottle was opened at 
 the summit of this king of mountains. 
 
 Dr. Wollaston’s instrument for measuring the heights of mountains 
 
47G 
 
 boy’s playbook of science. 
 
 by the variations of the boiling point of water has long been known and 
 used for this purpose. 
 
 If a Florence flask is first fitted with a nice soft cork, and this latter re- 
 moved, and the former half filled with water, which is then boiled over a gas 
 or spirit flame, the same fact already mentioned and illustrated in the pre- 
 ceding table may be rendered apparent when the flask is corked and re- 
 moved from the heat. If it is now inverted, and cold water poured over it, 
 an ebullition immediately commences, because the cold water condenses 
 the steam in the space above the hot water in the flask, and producing 
 
 a vacuum, the water boils as 
 readily as it would do under 
 an exhausted receiver on an 
 air-pump plate. (Fig. 437.) 
 
 Water may be heated con- 
 siderably higher than 212°, if 
 it is enclosed in a strong 
 boiler, and shut off from 
 communication with the air ; 
 by this means steam of great 
 pressure is obtained. 
 
 Dr. Marcet has invented a 
 very instructive form of a 
 miniature boiler, supplied with 
 a thermometer and barometric 
 pressure gauge, which can be 
 purchased at any of the in- 
 strument makers, and is 
 figured and described in 
 nearly every work on che- 
 mistry. 
 
 The reason water boiled in 
 an open vessel does not rise 
 to a higher temperature than 
 212° is because all the excess of heat is carried off by the steam, and 
 is said to be rendered latent in the vapour. The fixation of caloric 
 in water by its conversion into steam may be shown by the following 
 experiment. Let a pound of water at 212° and eight pounds of iron 
 filings at 300° be suddenly mixed together. A large quantity of steam 
 is instantly generated, but the temperature of the water and escaping 
 steam are still only 212°; hence the steam must therefore contain all 
 the degrees of heat between 212° and 300 c , or eight times 88. When 
 the water is heated in the hydro-electric machine or other boiler, to 
 322*7°, it very quickly drops to 212° when the steam is allowed to blow 
 off ; yet if the latter is collected, it represents but a very small quantity 
 of water which constituted the steam, and it has carried off and ren- 
 dered latent the excess of heat in the boiler — viz., the difference be- 
 tween 212° and 322*7°, or 110*7° 
 
 If steam can carry off heat, of course it may be compelled, as it were, 
 
 Fig. 437. The paradoxical experiment of water 
 boiling by the application of cold water. 
 
THE LATENT HEAT OF STEAM. 
 
 477 
 
 to surrender it again ; and this important elementary truth is shown by 
 adapting a tube, bent at right angles, and a cork, to a flask containing 
 a few ounces of water, and when it boils, the steam issuing from the 
 end of the pipe may now be directed into and below the surface of some 
 water contained in a beaker glass ; in a very short time the water in the 
 latter will be raised to the boiling 
 point by the condensation of the 
 steam and the latent heat arising 
 from it. (Pig. 438.) The amount 
 of latent heat is enormous, when 
 it is remembered that water by 
 conversion into steam has its bulk 
 prodigiously enlarged — viz., 1698 
 times, so that a cubic inch of 
 water converted into steam of a 
 temperature of 21 2°, with the ba- 
 rometer at thirty inches, occupies 
 a space of one cubic foot ) and its 
 latent heat amounts, according to 
 Hall, to 950° ; Southeron, 945° ; 
 
 Dr. Ure, 967°. When we come 
 to the consideration of the steam- 
 engine, it will be noticed that the 
 question of the latent heat of 
 steam is one of the greatest im- 
 portance. 
 
 Fig 1 . 438. a. Flask for generating- steam. 
 b. Glass pipe bent at right angles to convey 
 the steam into the fluid containing some cold 
 water. 
 
 Temperature of Elasticity in inches Latent Heat. 
 
 Steam. of Mercury. 
 
 229° 40° 942° 
 
 270 80 942 
 
 295 120 950 
 
 The same weight of steam contains, whatever may be its density, the 
 same quantity of caloric, its latent heat being increased in proportion as 
 its sensible heat is diminished ; and the reverse. In consequence of the 
 enormous amount of latent heat contained in steam, it is advantageously 
 employed for the purpose of imparting warmth either for heating rooms 
 or drying goods in certain manufacturing processes. The wet rag-pulp 
 pressed and shaken into form on a wire-gauze frame or deckle , passes 
 gradually to cylinders containing steam, and is thoroughly dried before the 
 guillotine knife descends at the end of the paper machine, and cuts it into 
 lengths. In calico stiffening and glazing, also in calico printing, steam- 
 heated cylinders are of great value, because they impart heat without the 
 chance of setting the goods on fire. The elementary principles already de- 
 scribed with reference to heat, will prepare the youthful reader for the 
 application of the expansion of water into steam, as the most valuable 
 motive power ever employed to assist the labour of man. 
 
478 
 
 boy’s playbook of science. 
 
 Fiff 439. The first steam-boat, the Comet, built by Henry Ceil, in 1311, who brought 
 steam navigation into practice in Europe. 
 
 CHAPTER XXIX. 
 the steam-engine — continued . 
 
 « So shalt thou instant reach the realm assign’d 
 In wondrous ships, self -mov'd, instinct with mind. 
 ***** 
 
 Though clouds and darkness veil the encumbered sky 
 Fearless, through darkness and through clouds they lly, 
 
 Tho’ tempests rage, — tho’ rolls the swelling main, 
 
 The seas may roll, the tempests swell in vain ; 
 
 E’en the stern god that o’er the waves presides, 
 
 Safe as they pass, and safe repass the tides, 
 
 With fury burns ; while careless they convey, 
 
 Promiscuous, ev’ry guest to ev’ry bay.” 
 
 These lines, from Pope’s translation of the “Odyssey,” were very 
 aptiv quoted twenty-five years ago by Mr. M. A. Alderson, m his treatise 
 on the steam-engine, for which he received from Dr. Bnkbeck, the 
 
HERO'S-STEAM ENGINE. 
 
 479 
 
 originator of Mechanics’ Institutions, the prize of 207, being the gilt of 
 the London Mechanics’ Institution, and these lines seem to indicate 
 some sort of rude anticipation by the ancients of that free passage of 
 the ocean by the agency of steam which has rendered ships almost 
 independent of wind and weather. 
 
 Homer’s description, as above, of the Phoenician fleet of King Alcinous, 
 in the eighth book of the “ Odyssey,” is certainly an ancient record of 
 an idea, but nothing more. In a work written by Hero of Alexandria, 
 about a hundred years b.c., and entitled <f Spiritalia seu Pneumatica” a 
 number of contrivances are mentioned 
 for raising liquids and producing mo- 
 tion by means of air and steam, so 
 that the first steam-engine is usually 
 ascribed to Hero; and the annexed 
 cut displays the apparatus. (Fig. 
 
 440.) 
 
 It is a remarkable circumstance 
 that Sir Isaac Newton applied the 
 same principle in a little ball, mounted 
 on wheels, containing boiling water, 
 and. provided with a small orifice; 
 and in his description he says : “ And 
 if the ball be opened, the vapours will 
 rush out violently one way, and the 
 wheels and the ball at the same time 
 will be carried the contrary way.” 
 
 From the time of Hero, there does 
 not appear to be any record or men- 
 tion made of steam apparatus till the 
 year 1002, when, in a work called 
 “ Malmesbury’s History,” mention is 
 made of an organ in which the sounds 
 were produced by the escape of air 
 (query, steam) by means of heated 
 water. It is strange that, in these 
 days of steam application, the Cal- 
 liope, or steam organ, was not long 
 since an important feature at the Crystal Palace, Sydenham ; and it 
 only shows how the same ideas are reproduced as novelties in the ever- 
 recurring cycles of years. 
 
 On the revival of classical learning throughout Gothic Europe, the 
 work of Hero began to attract attention, and it was translated and printed 
 in black letter, and most likely first from the Arabic character, as in the 
 year 1543 the first fruits appeared in Spain, where Blasco de Garay, a 
 sea captain, propelled a ship of 200 tons burden, at the rate of three 
 miles per hour, before certain commissioners appointed by the Emperor 
 Charles the Fifth. Alas for inquisitorial Spain ! had she looked deeper 
 into the matter, and performed her auto-da- fees on the boilers of steam- 
 
 Fig.440. Hero’s steam-engine, a. The 
 boiler in which steam is produced, and 
 then passes through the hollow support b, 
 from which there is no outlet but through 
 the two apertures, c c. The reaction of 
 the air on the issuing steam produces a 
 rotatory motion in the jets, c c, attached 
 to a centre but hollow axle. 
 
480 
 
 BOY S PLAYBOOK OF SCIENCE. 
 
 engines instead of tlie bodies of poor human beings, what lasting glories 
 would have been her reward. The invention made its d6but in Spain, 
 the commissioners reported, the worthy inventor was rewarded, but the 
 mighty giant, invoked was put to sleep again for at least 150 years. 
 The steam giant was disturbed with dreams; one Mathias, in 1563, 
 gave him a nightmare; Solomon de Caus, in 1624, nearly woke him up ; 
 Giovanni Bianca, in 1629, did more ; and the Marquis of Worcester, in 
 the middle of the seventeenth century, as the evil genius of Spain, 
 carried off the giant bodily and made him the slave of England; at least, he 
 experimented, and wrote such wondrous tales of his new motive power, 
 that in 1653 we read of steam being fairly tethered to its work, and set 
 to draw water out of the Thames at Vauxhall ; and Cosmo de Medici., 
 a foreigner who inspected the apparatus in 1653, says, “It raises water 
 more than forty geometrical feet by the power of one man only, and in a 
 very short space of time will draw up full vessels of water through a 
 tube or channel not more than a span in width, on which account it is 
 considered to be of greater service to the public than the other machine 
 near Somerset House, which last one was driven by two horses ” 
 
 What would these worthy gentlemen think could they peep into the 
 present day, and find that every trade and manufacture depends upon 
 the power of steam to put in motion machines which seem possessed of 
 actual intelligence, so perfect is their work. And that, by the same 
 agency, huge ships cross the seas in every latitude. 
 
 The first really useful steam-engine was made, not by a plain Mr., 
 but again by a captain — namely, Captain Savery, who appears to have 
 been the first inventor who thoroughly understood and applied the 
 vacuum principle. (Fig. 441.) 
 
 a a. The furnaces which contain the boiler, b 1 and b 2. The two fireplaces, c. The 
 funnel or chimney, which is common to both furnaces. In these two furnaces are placed 
 two vessels of copper, which I (Savery) call boilers— the one large as at l, the other small 
 as d. d. The small boiler contained in the furnace, which is heated by the fire at b 2. 
 e. The pipe and cock to admit cold water into the small boiler to fill it. f. The screw that 
 covers a«>d confines the cock e to the top of the small boiler, g. A small gauge cock at 
 the top of a pipe, going within eight inches of the bottom of the small boiler, h. A large 
 pipe which goes the same depth into the small boiler, i. A clack or valve at the top of 
 the pipe n (opening upwards), k. A pipe going from the box above the said clack or 
 valve in the great boiler, and passing about one inch into it. l l. The great boiler con- 
 tained in the other furnace, which is heated by fire at b 1. m. The screw with the regu- 
 lator, which is moved by the handle z, and opens or shuts the apertures at which the 
 steam passes out of the great boiler at the steam-pipes o o. k. A small gauge cock at the 
 top of a pipe, which goes half way down into the great boiler, o 1, o 2. Steam pipes, one 
 end of each screwed to the regulator ; the other ends to the receivers p p, to convey the steam 
 from the great boiler into those receivers, p 1, p 2. Copper vessels called receivers, which 
 are to receive the water which is to be raised, q. Screw joints by which the branches of 
 the water-pipes are connected with the lower parts of the receivers, r 1, 2, 3, and 4. Valves 
 or clacks of brass in the water-pipes, two above the branches q and two below them ; they 
 allow the water to pass upwards through the pipes, but prevent its descent ; there are 
 screw-plugs to take out on occasions to get at the valves r. s. The forcing-pump which 
 conveys the water upwards to its place of delivery, when it is forced out from the receivers 
 by the impelled steam, t. The sucking-pipe, which conveys the water up from the bottom 
 of the pit to fill the receivers by suction, v. A square frame of wood, or a box, with holes 
 round its bottom in the water, to enclose the lower end of the sucking-pipe to keep away 
 dirt and obstructions, x is a cistern with a bung cock coming from the force-pipe, so as it 
 shall alwrays be kept filled with cold water, ty. A cock and pipe coming from the bottom 
 of the said cistern, with a spout to let the cold run down on the outside of either of the re- 
 ceivers, p p. z. The handle of the regulator to move it by, either open or shut, so as to let 
 the steam out of the great boiler into either of the receivers 
 
THE FIRST USEFUL STEAM-ENGINE. 
 
 481 
 
 Fig. 441. Savery’s engine. 
 I I 
 
482 
 
 boy’s playbook of science. 
 
 This is Saverv’s own description (taken from the “ Miner’s Friend,” 
 printed in 1702), of his water-engine, which differs from that suggested 
 by the Marquis of Worcester, in the fact that he made the pressure of the 
 air carry the water up the first stage. Savery’s patent was “ for raising 
 water and occasioning motion to all sorts of mill-work by the impellant 
 force of fire;” and the patent was granted in the reign of King 
 William the Third of glorious memory. 
 
 Thus Saverv overcame, as he remarks, the “oddest and almost 
 insuperable difficulties,” and introduced a steam apparatus or engine, a 
 good many of which were constructed, and employed for raising water. 
 The mechanical skill required to construct the boiler, the very heart (as 
 it were) of the iron engine, had not been acquired in the time of Captain 
 Savery, and hence the weakness of the boilers, and the danger of working 
 them. As the pressure required was very considerable to overcome the 
 resistance of a lofty column of water, these engines were gradually 
 relinquished for those of another clever mechanician — viz., for those of 
 Thomas Newcomen, an ironmonger of Dartmouth, who, about the year 
 1705, constructed and introduced the cylinder , from which the transition 
 was gradually made to the mode of condensing by a jet of cold water, 
 the use of self-acting valves, and the construction of self-acting 
 engines by Smeaton, Hornblower, and finally by the illustrious Watt, 
 whose portrait heads the first chapter on Heat in this book. 
 
 Newcomen was assisted in his work by one Cawley, a glazier ; and 
 their persevering labours were crowned with a successful result of the 
 most memorable importance in the history of the steam-engine. 
 
 In the engine by Savery, the operation of the steam was twofold — 
 namely, by the direct pressure from its elasticity, and by the indirect 
 consequence of its condensation, which affords a vacuum. This last 
 may be said to be the only principle used by Newcomen, who employed 
 a boiler for the generation of steam, and conveyed it by a pipe to the 
 bottom of a hollow cylinder, open at the top, but provided with a solid 
 piston, that moved up and down in it, and was rendered tight by a stuffing 
 of hemp, like the piston of a boy’s common squirt. It can readily be 
 understood, that if the jet of the latter was connected with a tight little 
 boiler, and steam blown into it, that the piston of the squirt would rise 
 to the top of the barrel in which it works, being thrust up by the 
 pressure or force of the steam ; but unless the steam was cut off, and 
 cold water applied to the interior of the barrel, the piston could not 
 descend again. As soon, therefore, as Newcomen had thrust up the 
 piston by the action of steam, he introduced a jet of cold water, sup- 
 plied from an elevated cistern beneath the piston, when the steam was 
 condensed into water, and a vacuum or void space obtained. The piston 
 being free to move either up or down, was now forced in the latter 
 direction by the pressure of the air, which is a constant force equal to 
 fifteen pounds on the square inch ; and thus the piston in Newcomen’s 
 engine was raised by heat — viz ., by steam, and thrust down by cold—- 
 i.e., by the condensation of the steam producing a vacuum. The void 
 obtained in this manner was very considerable, because one cubic foot of 
 
NEWCOMEN'S STEAM-ENGINE. 
 
 483 
 
 steam at 212° condenses into one cubic inch of water. The production 
 of a vacuum with the aid of steam is quickly effected by boiling some 
 water in a clean camphine can, and when the steam is issuing freely from 
 the mouth of the latter it is then corked, and cold water thrown over the 
 exterior. Directly the temperature is lowered, the steam inside the tin 
 vessel is condensed suddenly into water, and a void space being suddenly 
 obtained, the whole pressure of a column of air of a breadth equal to 
 the area of the vessel, and of a height of forty miles, is brought sud- 
 denly down like a sledge-hammer upon the sides of the tin vessel, and 
 as they are not sufficiently strong to offer a proper resistance, they are 
 crushed in like an egg-shell by the giant weight which falls upon them. 
 
 The barometer, or measurer of the weight of the air, consists of a glass 
 tube about thirty-three inches in length, hermetically sealed at one end, 
 and containing mercury that has been carefully boiled within it, and 
 being perfectly filled the tube is inserted in a cistern of clean mercury, 
 when it gravitates to a height equal to the pressure of the air, leaving 
 a space at the top called the torricellian vacuum. As the atmospheric 
 air decreases in density by admixture with invisible steam or vapour, any 
 given volume becomes specifically lighter : hence the column of mercury 
 falls to a height of about twenty-eight inches ; whilst if the aqueous 
 vapour diminishes, the weight of the air becomes greater, and the baro- 
 meter may rise to a height of about thirty-one inches. 
 
 Having thus secured a “reciprocating motion, 55 Newcomen applied it 
 to the working of a force-pump by the intervention of a great beam or 
 lever suspended on gudgeons (an iron pin on which a wheel or shaft of 
 a machine turns) at the middle, and suspended like the beam of a pair 
 of scales ; and, in . fact, he invented that method of supporting the 
 beam which is in use to the present day. Supposing we compare 
 Newcomen’s beam to a scale beam, he attached to the extremities 
 (instead of scale pans) a water pump and his steam cylinder — the latter 
 being at one end, and the former at the other. The beam played at 
 “ see-saw : 55 by the primary action of the steam on the bottom of the 
 piston in the cylinder it was pushed up at this end, and of course 
 suffered an equal fall at the other, to which the pump piston was 
 attached ; and when the motion was reversed by the condensation of the 
 steam, down went the piston again by the pressure of the air, whilst 
 that of the water pump was again raised, and being provided with 
 proper valves, the water was pumped slowly out of the mine, although 
 the steam power used was very moderate, and only just sufficient to 
 counterpoise the weight of the atmosphere. Newcomen made the end 
 attached to the water pump purposely heavier than the steam piston of 
 the other end of the beam, and by this means the work of the steam, 
 by its elasticity, was very moderate, whilst the actual lift of the water 
 from the mine was performed by the pressure of the air, equal (as 
 already stated) to fifteen pounds on every square inch of the surface of 
 the steam piston. This engine is called the atmospheric engine, and in 
 the next cut we have a picture taken from a photograph by the “ Watt 
 Club 55 of the actual model of the Newcomen engine in the Hunterian 
 
484 
 
 boy’s playbook of science. 
 
 Museum of the University of Glasgow : the dimensions being — length, 
 27 in.; breadth, 12 in.; height, 50Mn.; from which, ff iul765, James Watt, 
 
 Fig. 412. Model of the Newcomen engine, in which the furnace and boiler, the steam 
 cylinder, beam, water-pump, and elevated cistern of water, are apparent. 
 
 in seeking to repair this model , belonging to the Natural Philosophy Class 
 in the University of Glasgow, made the discovery of a separate condenser , 
 which has identified his name with that of the steam-engine.” (Fig. 442.) 
 
 In Newcomen’s engine, the opening and shutting of the cocks re- 
 quired the vigilant care of a man or boy, and it is stated on good 
 authority that a boy who preferred (like nearly all other boys) play to 
 work, contrived, by means of strings, a brick, and one or two catches on 
 the working beam, to make the engine self-acting. 
 
 This poor boy’s ingenious contrivance paved the way for the improved 
 
watt’s steam-engine. 
 
 485 
 
 methods of opening and shutting the valves, which were brought to a 
 
 g -eat state of perfection by Beighton, of Newcastle, about 1718. 
 
 etween that time and the year 1763, we find honourable mention made 
 of Smeaton in connexion with the steam-engine, but the name of the 
 great James Watt at this time began to be appreciated, and by a series 
 of wonderfully simple mechanisms, he at last perfected the machine 
 whose origin could be traced back not only to the time of Blasco de 
 Garay, in 1543, but even to the days of the ancient mechanicians, such 
 as Hero, who lived 130 b.c. 
 
 In 1763, James Watt was a maker of mathematical instruments in 
 Glasgow, and his attention was drawn to the subject of the steam- 
 engine by his undertaking to repair a working model of Newcomen’s 
 steam-engine, which was used by Professor Anderson, who then filled 
 the Chair of Natural Philosophy, and subsequently founded the Ander- 
 sonian Institution. The repairs required for this model induced Watt 
 to make another, and by watching its operation, he discovered that a 
 vast quantity of heat, and therefore fuel, was wasted in the constant and 
 successive heating and cooling of the steam cylinder. About two years 
 after, when Watt was twenty-nine years of age, he had made so many 
 experiments, that he was enabled to put into a mechanical shape his 
 original ideas, which are embodied in his patent of 17 69, as follows : — 
 
 “ My method of lessening the consumption of steam, and consequently 
 fuel, in fire-engines, consists of the following principles : 
 
 “ First : That vessel in which the powers of steam are to be employed 
 to work the engine, which is called the cylinder in common fire-engines, 
 and which I call the steam-vessel, must, during the whole time the 
 engine is at work, be kept as hot as the steam that enters it — first, by 
 enclosing it in a case of wood or any other materials that transmit heat 
 slowly ; secondly, by surrounding it with steam or other heated bodies ; 
 and thirdly, by suffering neither water nor any other substance colder 
 than steam to enter or touch it during that time. 
 
 “ Secondly : In engines that are to be worked wholly or partially by 
 condensation of steam, the steam is to be condensed in vessels distinct 
 from the steam-vessels or cylinders, although occasionally communi- 
 cating with them ; these vessels I call condensers ; and whilst the engines 
 are working, these condensers ought at least to be kept as cold as the 
 air in the neighbourhood of the engine, by application of water or other 
 cold bodies. 
 
 “ Thirdly: Whatever air or other elastic vapour is not condensed by 
 the cold of the condenser, and may impede the working of the engine, is 
 to be drawn out of the steam-vessels or condensers by means of pumps 
 wrought by the engines themselves, or otherwise. 
 
 " Fourthly : I intend in many cases to employ the expansive force of 
 steam to press on the pistons, or whatever may be used instead of 
 them, in the same manner as the pressure of the atmosphere is now 
 employed in common fire-engines. In cases where cold water cannot be 
 ha d in plenty, the engines may be wrought by this force of steam only, 
 by discharging the steam into the open air after it has done its office. 
 
 “ Lastly : Instead of using water to render the piston or other parts 
 
486 
 
 boy’s playbook of science. 
 
 of the engines air and steam-tight, I employ oils, wax, resinous bodies, 
 fat of animals, quicksilver, and other metals in their fluid state. 
 
 “And the said James Watt, by a memorandum added to the said 
 specification, declared that he did not intend that anything in the fourth 
 article should be understood to extend to any engine when the water to 
 be raised enters the steam-vessel itself, or any vessel having an open 
 communication with it.” 
 
 “About the time he obtained his patent, Watt commenced the con- 
 struction of his first real engine, the cylinder of which was eighteen 
 inches in diameter, and after many impediments in the details of the 
 work he succeeded in bringing it to considerable perfection. The bad 
 boring of the cylinder, and the difficulty of obtaining a substance that 
 would keep the piston tight without enormous friction, and at the same 
 time resist the action of steam, gave him the most trouble, and the em- 
 ployment of a piston rod moving through a stuffing-box was a new 
 feature in steam-engines at that time, and required great nicety of 
 workmanship to make it effectual. While Watt was contending with 
 these difficulties, Roebuck’s finances became disarranged, and in 1773 
 he disposed of his interest in the patent to Mr. Boulton, of Soho. 
 As, however, a considerable part of the term of fourteen years, for 
 which the patent was granted, had already passed away, and as several 
 years more would probably elapse before the improved engines could be 
 brought into operation, it was judged expedient to apply to Parliament 
 for a prolongation of the term, and an Act was passed in 1775 granting 
 an extension of twenty-five years from that date, in consideration of 
 the great merit of the invention.” (Bourne’s “ Treatise on the Steam- 
 engine.”) , 
 
 In Fig. 443 (p. 487) we give an illustration of a low-pressure con- 
 densing engine and boiler of eight-horse power, constructed on the prin- 
 ciple of Boulton and Watt, as the latter had fortunately united his skill, 
 learning, originality, and experience with Mr. Boulton, of Soho, near 
 Birmingham, whose metal manufactory was already the most celebrated 
 in England. 
 
 During the explanation of this eight horse-power engine, the oppor- 
 tunity may be taken to discuss occasionally the special improvements 
 effected by Watt. The steam-pipe a conveys the steam generated in 
 the boiler b to the slide-valve c, which is kept close to the surface, 
 against which it works by the pressure of the steam. 
 
 Here we notice some of the valuable improvements of Watt in the 
 admission of steam above as well as below the piston, by which he 
 increased the power of his engine, and no longer confined it to the force 
 of the atmospheric pressure. It is also necessary to remark the beauti- 
 fully simple mechanism of the slide-valve, by which steam is admitted 
 alternately above and below the piston. Want of space prevents us 
 tracing out the gradual improvements effected by Watt, and therefore 
 we take his invention as it stood in the year 1780, and refer our readers 
 to Bourne’s “ Treatise on the Steam-engine” for the full and minute 
 particulars of the improvements to that date. 
 
WATT S STEAM-ENGINE. 
 
 487 
 
 Fig. 443. An eiglit-horse power condensing steam-engine, after the principle of 
 Boulton and Watt, and explained in pages 426 to 432. 
 
 ’lie/ ’ 
 
488 
 
 BOY ? S playbook of science. 
 
 At that time it occurred 
 to Watt that the conden- 
 sation of the steam from 
 the cylinder after it had 
 done its work, might be 
 made more perfect if a 
 perpetual vacuum was 
 maintained beneath the 
 piston, while an alternate 
 steam-pressure and vacu- 
 um were produced above 
 it. (Eig. 444.) 
 
 Instead of obtaining a 
 specific advantage the 
 contrary occurred, and 
 W~att was obliged in this 
 case to return to the 
 ponderous Newcomen 
 counterweight to balance 
 the difference in the va- 
 cuum above and below 
 the piston, consequently 
 this form of the cylinder 
 and valves was abandoned. 
 The juvenile reader will 
 perceive in the above 
 drawing that the superior 
 arrangement of Watt’s 
 cylinder to that of New- 
 comen arises from the 
 steam operating above 
 and below the piston, 
 and that the piston 
 rod works air-tight in a 
 stuffing box at the top of 
 the cylinder. A most im- 
 portant improvement in 
 the employment of steam 
 as a motive power has 
 been discovered in the 
 mode of using it “ expan- 
 sively,” by which the steam, at a pressure say of sixty pounds on the 
 square inch, is admitted below the piston, and then cut off and allowed to 
 expand and drive up the latter without the expenditure of any more 
 fuel, and leaving, after lifting the piston to a height say of three feet, 
 an average or mean power of thirty pounds on the square inch. 
 
 Returning to the eight-horse condensing engine , d is the steain cylinder 
 surrounded by a case to prevent the steam cooling and to maintain in the 
 
 r 1 
 
 r 
 
 
 i 
 
 Fig. 44t. “ e e is the cylinder. j. The piston, a. The 
 steam-pipe. b. The regulating or throttle valve, e. The 
 eduction and equilibrium single valve, performing the 
 functions of both. c. The upper, and / the under, port- 
 holes, by which passages only the steam can enter and 
 pass away. d,j, g. The eduction-pipe by which the steam 
 passes from above the piston during every returning 
 stroke to the condenser, a perpetual exha ustion being m ain- 
 tained beneath it.”— From Bourne on the Steam-engine. 
 
watt’s parallel motion. 
 
 480 
 
 cylinder the same, or nearly the same, temperature as that of the steam 
 in the boiler, according to the condition of Art. I. of Watt’s Patent, 
 quoted at p. 485 of this 
 book. The same outer 
 case is apparent around the 
 cylinder in Pig. 444; e, the 
 piston, which, by stuffing 
 with hemp or other proper 
 material, fits the interior of 
 the cylinder in the most 
 accurate manner, and pre- 
 vents the escape of steam 
 by its sides : e is the piston 
 rod attached to the parallel 
 motion. This clockwork- 
 like piece of mechanism has 
 often been quoted as one of 
 the masterpieces of Watt, 
 and in its greatest perfection 
 is called the complete parallel 
 motion, and may be found 
 in all the best land beam 
 steam-engines. The object 
 of the parallel motion is to 
 cause the piston and pump 
 rods to move always in 
 straight lines, never deviat- 
 ing to either side. (Pig. 445.) 
 
 In the eight horse-power engine shown in page picture, e is also 
 attached to the piston e, which moves the beam f, and the other end 
 of this beam, by the connecting rod g> gives motion to the heavy fly wheel 
 G, by means of the crank h. 
 
 h is an eccentric circle on the axle of the fly wheel g, it gives motion 
 •to the slide valve, which admits the steam alternately above and below 
 the piston. The slide valve and its seat are contained within an oblong 
 box or case, large enough to permit the easy motion of the valve within 
 it, and usually forming an enlargement in the course of a pipe. 
 
 The valve rod by means of which the valve is opened and shut, 
 passes out through a stuffing box ; or, instead of such a rod, a valve 
 of moderate size often has a nut fixed to it, within which works 
 
 Fig. 415. a b is half the beam, a being the main 
 centre, b e. The main links connecting the piston- 
 rod r with the end of the beam, g d. The air-pump 
 links, from the centre of which the air-pump rod is 
 suspended, c d and e d produce the parallelism, 
 because c d is moveable only round the fixed centre 
 
 c, whilst ed is not only moveable round the centre 
 
 d, but the centre itself in the arc described by c d, 
 and by this action e d corrects the distorting in- 
 fluence of its own radius. The dotted lines and 
 letters above enable the observer to see the effect of 
 the movement of the beam on the parallel motion. 
 
 a screw on the end of an axle which passes out through a bush, and 
 has shoulders within and without to prevent it from moving lon- 
 gitudinally, and a square on the outer end on which the key fits that 
 is used in turning it. i is the throttle valve inside the steam pipe and 
 lever connected with a governor for regulating the admission of steam 
 into the cylinder. 
 
 Here, again, we pause in the description of our eight horse-power 
 engine to illustrate more particularly this admirable contrivance of 
 
490 
 
 boy’s playbook of science. 
 
 Watt, which remains to the present day without any material alteration 
 even in the best steam-engines. (Fig. 446.) 
 
 Fig. 446. a. The seat of the throttle valve, z. The valve itself turning on a spindle, 
 which passes through its centre, a is the steam pipe. to. The throttle valve lever on 
 which the rod h, proceeding from the governor, acts, d d. The spindle of the governor 
 revolving by a belt acting on the pulley a. e e. The balls hung on the ends of the arms, 
 which cross each other at e like a pair of scissors. When d d is set in motion, the balls fly 
 out by centrifugal motion, and in doing so draw down the collar into which the lever p 
 works by means of the links./ A When f is depressed, of course h rises, and the valve z is 
 partly closed, and the supply of steam reduced. 
 
 In the eight-horse engine already partly explained, Jc is the cylinder 
 of an air-pump to remove any air, and the water which condenses the 
 steam, from the condenser l. There is also the eduction pipe, which 
 conducts the steam from the cylinder to the condenser l. o is the 
 pump that supplies cold water to the cistern s, in which the condenser 
 and air-pump stand, p is a rod connected with the injection cock for 
 admitting a jet of water into the condenser from the cistern, and which 
 is continually flowing during the working of the engine, q q, cast-iron 
 columns, four of which support the principal parts of the engine. 
 
 We now come to the boiler of the steam-engine, which is of course 
 of almost equal importance with the engine itself ; and the one in our 
 page-picture is a good type of one of the favourite boilers used by 
 Messrs. Boulton and Watt, and is called the “Wagon boiler. 35 The 
 boiler is made of wrought-iron plates rivetted together, and properly 
 strengthened where necessary; and the steam-pipe a conveys the 
 steam to the engine. It may be remarked here that the cylindrical 
 
THE BOILER OF THE STEAM ENGINE. 
 
 491 
 
 boiler — consisting of two cylinders, one within the other, of which the 
 former contains the fire, whilst the furnace -draught circulates outside the 
 latter, and the space between the two cylinders being filled with water — 
 is the form of boiler which is most highly approved of, and is employed 
 in the famous economical steam-engines of the Cornish mines. 
 
 As the water evaporates in the form of steam, the boiler must be con- 
 tinually supplied with fresh water, which comes (as will be noticed by 
 inspecting the page picture) from the hot well s, by means of the hot 
 water pump r , attached to the beam r. The water is pumped to the top 
 of a column rising above but connected with the boiler. There is a 
 cylindrical float, inside the column of water, connected with the boiler, 
 suspended over a pulley by a chain passing to the damper of the furnace. 
 The damper and float balance each other, and when the water in the 
 boiler rises to too high a temperature, it causes the float to rise in the 
 column of water, which lowering the damper or shutter that stops the 
 draught of the chimney of the furnace T, diminishes the intensity of the 
 heat, and reduces the formation of steam. On the other hand, as the 
 temperature diminishes, the float descends and the damper rises, and 
 permitting more air to rush to the burning fuel in the fire, a greater 
 quantity of steam is generated. 
 
 There is likewise a stone float inside the boiler, for regulating the 
 supply of water by the feed pipe, or column of water, which latter must 
 always be sufficiently lofty to press with greater force than the steam 
 produced in the boiler, or else the power of the steam might, under cer- 
 tain circumstances, eject or blow out the water from the top of the 
 column. The stone is suspended by a brass wire which works through 
 a stuffing box, and is connected with a lever, to which is attached a 
 heavy counterpoise, so adjusted that when the stone is immersed to a cer- 
 tain depth in water (according to the principle of a solid body losing weight 
 in a fluid, explained in the article on specific gravity, page 48), it shall 
 exactly balance the latter, but when the water sinks in the boiler, and 
 the stone is no longer surrounded with water, it becomes heavier, and 
 sinking down opens a conical plug, ground so as to fit water-tight into 
 a hole in the bottom of the column of water or feed pipe, and directly 
 the plug opens, water rushes into the boiler; being cut off again as 
 the stone rises when immersed or surrounded with the proper height of 
 water. Unless our juvenile readers refer to the article on specific 
 gravity, they will not understand the otherwise seeming anomaly of a 
 stone float. 
 
 A large hole, called the man -hole, covered with an iron plate and 
 securely fastened with screws, is provided for the purpose of allowing 
 the engineer to enter the boiler, when cold, for the purpose of clearing 
 out the incrustation and dirt arising from the water. To prevent the 
 incrustation of lime and other earthy matters, it is sometimes usual, on 
 the principle “ that prevention is better than cure ,” to put a large log of 
 “ logwood 5 * inside the boiler, as it is found that the colouring matter 
 curiously prevents the earthy matter, so well known as the “fur” in 
 iron “ tea-kettles/’ sticking to the sides of the boiler. Sal ammoniac 
 
492 
 
 boy’s playbook of science. 
 
 and oilier salts also Lave the same property, but neither are mach used, 
 the mechanical labour of chipping out the boiler and stopping its work 
 for a day or so, being preferred to the prevention plan already 
 described. 
 
 There is also a valve opening inwards to prevent the consequences of 
 a sudden condensation in the boiler, and also a safety valve and lever 
 with weights opening outwards, and allowing the steam to escape when 
 it reaches a dangerous excess, and in order to look as it were at the 
 'state of the pressure inside the iron boiler, a proper steam gauge is pro- 
 vided, also two cocks — viz., a water and steam cock, to enable the en- 
 gineer to ascertain if the water is up to, and does not exceed, the 
 proper height, because when turned, supposing that all is going on pro- 
 perly, the former, No. 7, should eject water, the latter, No. 8, steam. 
 
 It is truly wonderful, considering the number of safeguards and 
 warnings provided, that accidents ever happen to boilers, but the 
 statistics of deaths and annual destruction of property show that science 
 is powerless, nay, absolutely dangerous, when handled by ignorant and 
 careless persons. The great fly-wheel, which is usually such an awe- 
 inspiring and marvellous exhibition of strength in an engine of any great 
 power, is employed for the purpose of storing up force, so that if any 
 parts of the engine work indifferently (they all work with resistance), it 
 shall equalize the wants of the whole, and by its inertia it will continue 
 to move until its motion is stopped by a resistance equal to its mo- 
 mentum. 
 
 In starting an engine, the engineer may sometimes be observed la- 
 bouring to move the “ fly-wheel/’ and when once he succeeds in getting 
 it to move, the resistance of the other parts of the machinery is soon 
 overcome. Mr. Alderson, in his prize essay, remarks that " it is in the 
 property which the steam-engine possesses of regulating itself, and pro- 
 viding for all its wants, that the great beauty of the invention consists. 
 It has been said that nothing made by the hand of man approaches so 
 near to animal life. Heat is the principle of its movement ; there is in 
 its tubes circulation, like that of the blood in the veins of animals, 
 having valves which open and shut in proper periods ; it feeds itself, 
 evacuates such portions of its food as are useless, and draws from its 
 own labours all that is necessary to its own subsistance. To this may 
 be added, that they are now regulated so as not to exceed the assigned 
 speed, and thus do animals in a state of nature. That the safety valves, 
 like the pores of perspiration, open to permit the escape of superfluous 
 heat in the form of steam. The steam gauge, as a pulse to the boiler, 
 indicates the heat and pressure of the steam within; and the motion of the 
 piston represents the action and the power of which it is capable. The 
 motion of the fluids in the boiler represents the expanding and collapsing 
 of the heart ; the fluid that goes to it by one channel is drawn off by 
 another, in part to be returned when condensed by the cold, similar to 
 the operation of veins and arteries. Animals require long and frequent 
 periods of relaxation from fatigue, and any great accumulation of their 
 power is not obtained without great expense and inconvenience. The 
 
THE LOCOMOTIVE STEAM-ENGINE. 
 
 493 
 
 wind is uncertain ; and water, the constancy of which is in few places 
 equal to the wants of the machinist, can seldom be obtained on the spot 
 where other circumstances require machines to be erected. To relieve 
 us from all these difficulties, the last century has given us the steam- 
 engine for a resource, the power of which may be increased to infini- 
 tude : it requires but little room ; it may be erected in all places, and 
 its mighty services are always at our command, whether in winter or 
 summer, by day or by night, on land or water ; it knows no intermission 
 but what our wishes dictate. 55 
 
 The high-pressure steam-engine appears to have been first brought 
 into general use by Trevethic and Vivian, although the primary notion 
 of such a modification of the Newcomen or water-engines did not ori- 
 ginate with them. As the name implies, the steam is brought to a 
 much higher temperature and pressure than is required in the con- 
 densing engines of Boulton and Watt. It consisted, in the first place, 
 of a cylinder open at the top, and provided with a piston. To save 
 heat the cylinder was fixed inside the boiler, and was provided with a 
 two-way cock worked by a crank, for the purpose of supplying and 
 cutting off the steam. The downward stroke was produced by the 
 atmosphere, and the steam having done its work, was simply blown away 
 and wasted in the air. 
 
 The engine was provided with a fly-wheel, to which the piston-rod 
 was at once attached, producing a continuous rotatory movement 
 without the assistance of the heavier parallel motion, or hot and cold 
 water pumps. 
 
 This form of engine was soon adopted for pumping work — such as 
 that of draining fens ; and in 1804 Mr. Bichard Trevethic used it for 
 propelling the first carriage on the Merthyr Tydvil rail or tram way, 
 and it was then speedily adopted in all the coal districts where the levels 
 were moderate. Stephenson the elder, succeeded by the late lamented 
 Bobert Stephenson, followed with inventions and improvements of the 
 locomotive steam-engine; and we are told in “Once a Week 55 that, 
 
 “ One of those best qualified to speak to the latter’s contributions to 
 the development of the locomotive engine, states that from about five 
 years from his return from America, Bobert Stephenson’s attention was 
 chiefly directed to its improvement. £ None but those who accompanied 
 him during the period in his incessant experiments can form an idea of 
 the amazing metamorphosis which the machine underwent in it. The 
 most elementary principles of the application of heat, of the mode of 
 calculating the strength of cylindrical and other boilers, of the strength 
 of rivetting and of staying flat portions of the boilers, were then far 
 from being understood, and each step in the improvement of the engine 
 had to be confirmed by the most careful experiments before the brilliant 
 results of the Bocket and Planet engines (the latter being the type of 
 the existing modern locomotive) could be arrived at. 5 
 
 “ Stephenson’s time was not, however, so fully taken up during the 
 above interval as to preclude attention to his other civil engineering 
 business, and he executed within it the Leicester and Swannington, 
 
494 
 
 boy’s playbook of science. 
 
 Whitby and Pickering, Canterbury and Whitstable, and Newton and 
 Warrington Hail ways ; while Jie also erected an extensive manufactory 
 for locomotives at Newton, in Lancashire, in partnership with the 
 Messrs. Tayleur. About the middle of the above period, also, the first 
 surveys and estimates for the London and Birmingham Hailway were 
 framed, leading eventually to the obtaining of the Act. Then followed 
 the execution of that line, and here Hobert Stephenson had an oppor- 
 tunity of showing his great talent for the management of works on a large 
 scale. This was the first railway of any magnitude executed under the 
 contract system ; perfect sets of plans and specifications (which have 
 since served as a type for nearly all the subsequent lines) were prepared 
 — no small matter for a series of works extending over 112 miles, 
 involving tunnels and other works of a then unprecedented magnitude. 
 
 “ Many other railways in England and abroad were executed by him 
 in rapid succession; the Midland, Blackwall, Northern and Eastern, 
 Norfolk, Chester and Holyhead, together with numerous branch lines, 
 were executed in this country by him ; and among railways abroad may 
 be enumerated as works either executed by him or recommended in his 
 capacity of a consulting engineer, the system of lines in Belgium, Italy, 
 Norway, and Egypt, and in Erance, Holland, Denmark, India, Canada, 
 and New Zealand. 
 
 “ Hobert Stephenson first saw the light in the village of Willington, 
 at a cottage which his father occupied after his marriage with Miss 
 Fanny Henderson — a marriage contracted on the strength of his first 
 appointment as “breaksman” to the engine employed for lifting the 
 ballast brought by the return collier ships to Newcastle. Here Hobert 
 was born on the 17th of November, 1803. As the cottage looked out 
 upon a tramway, the eyes of the child were naturally familiarized from 
 infancy with sights and scenes most nearly connected with his future 
 profession.” 
 
 In locomotive steam-engine boilers, the principal object is to generate 
 steam with the greatest rapidity ; hence the boiler consists of two parts 
 — viz., a square box containing the fire, and around which a thin stratum 
 of water circulates, whilst the draught for the fire rushes through a 
 number of copper tubes placed in the second or cylindrical part of the 
 boiler. By the use of these tubes an immense surface of water is 
 exposed to the action of the fire, and the steam is not only generated 
 with amazing rapidity, but is also maintained at a very high pressure. 
 
 Within the last few years “ superheated steam” has been favourably 
 mentioned, and employed economically for driving certain engines. 
 The principle consists in first generating steam, and then passing it 
 through coils of strong wrought-iron pipe, by which it acquires addi- 
 tional heat, and we have therefore combined in steam the ordinary 
 principle of evaporation of water with the heated-air principle of 
 Stirling, described at p. 427. We give a drawing of Scott’s patent 
 generator and superheated steam engine. (Fig. 447.) 
 
 The apparatus is used as follows : — A fire is made in the furnace, and 
 so soon as a pyrometer connected with that indicates about 800 degrees. 
 
SUPERHEATED STEAM. 
 
 495 
 
 a little water is pumped into the coils by hand, which is immediately 
 converted into steam. The donkey engine is then started, which 
 
 Pig. 447. Scott’s patent generator, or new versus old steam. 
 
 maintains the necessary feed of air and water. The generator produces 
 a copious supply of elastic mixed gaseous vapour, at a pressure of 
 250 pounds on the square inch ; and it is stated that this engine works 
 satisfactorily, and is started in the incredibly short time of from three 
 to five minutes, so that for marine engines in war vessels, expecting to 
 to be ordered out suddenly, no fuel need be burnt till the moment 
 required. 
 
 Experiments with superheated steam have already been tried most 
 successfully on board the Peninsular and Oriental Company’s ship the 
 Valetta , whereby it is stated that a saving of thirty per cent, in fuel 
 
496 
 
 boy’s playbook of science. 
 
 is obtained. The engine to which the superheated steam was adapted 
 was constructed by Penn and Sons, and the vessel attained a speed of 
 nearly sixteen knots per hour, and under the most adverse circum- 
 stances had an abundance of steam to spare. 
 
 “ A most important experimental improvement in steam machinery 
 was on Thursday last tried for the first time down the river, on board 
 the Peninsular and Oriental Company’s ship, the Vciletta . The actual 
 nature of the improvement may be described in a few words as con- 
 sisting of a simple apparatus for working marine engines by means of 
 superheated steam ; but it is not too much to say that in the success or 
 failure of this experiment are involved results so important as to affect 
 materially all ocean-going steamers, and, indeed, steam machinery of all 
 kinds. To be able to work machinery with superheated steam, means to 
 command increased power with a thirty per cent, reduction in the con- 
 sumption of fuel. A principle which can effect such important changes 
 in the universal application of steam has not remained undiscovered to 
 the present day. The want of superheated steam has long been felt, 
 and the enormous comparative advantages of working engines on such 
 a plan have long been known. A simple and effective working of the 
 principle, however, has been an engineering difficulty which various ex- 
 pedients — all, however, sufficiently successful to show the value of the 
 improvement — have failed to obviate entirely. This obstacle has now, 
 we believe, been effectually overcome by Mr. Penn, and the value of the 
 improvement so clearly demonstrated, that the general application of 
 the principle to steam machinery of every kind may now be regarded as 
 certain. 
 
 “The idea of working engines by superheated steam, and the immense 
 saving of fuel and increase of power it would effect, was, we believe, 
 first started many years ago by Mr. Howard, and subsequently by Dr. 
 Haycraft. The difficulties, however, in the way of its adoption at that 
 time, and the undue estimate of the importance of the principle, pre- 
 vented those gentlemen from realizing very great practical results. At 
 a later period the matter was again taken up by an American engineer — 
 Mr. Weatherliead — who, however, only superheated a portion of Jlie 
 steam and mixed it with common steam in its way to the cylinders. The 
 success which attended even this partial application of the process again 
 revived the idea, and encouraged other engineers to turn their attention 
 to the subject. The result of these renewed efforts is that several 
 methods of securing the great economy to be effected by superheating 
 the steam are now under trial, and there is no doubt that a most im- 
 portant step in the progress of steam, especially as applied to ocean 
 navigation, is now at last on tlie point of being successfully accom- 
 plished. 
 
 “ The value of the improvement on the score of economy in working 
 may be best illustrated by a single fact — namely, that the Peninsular 
 and Oriental Company’s bill for coal annually amounts to the enormous 
 sum of 700,000Z., and that by working their vessels with superheated 
 steam properly applied, it is become almost certain that, without any 
 
SUPEEHEATED STEAM. 
 
 m 
 
 detriment to the machinery, from 28 to 30 per cent, of this gigantic 
 outlay can be saved. As to the various proposed methods of super- 
 heating steam, it may be briefly explained, that the conditions required 
 to be fulfilled are perfect simplicity of arrangement with ready control 
 over the apparatus ; that it should be so placed as not to be liable to 
 accidental injury in the engine-room; and that the heat employed for 
 superheating the steam should be waste heat which has already done its 
 duty in the boilers and is passing away. 
 
 “ All these conditions have been most satisfactorily fulfilled by Mr. 
 Penn in the new engines on board the Valetta , which were tried down 
 the Thames for the first time on Thursday. The Valetta , as our readers 
 may remember, was for many years the mail-boat between Marseilles, 
 Malta, and Constantinople. While thus employed, she had Penn’s 
 engines of 400 horse-power, and to work these up to an average speed 
 of 15 miles an hour required a consumption of fuel of from 70 to 75 
 tons of coal per day. At no time was it less than from 45 to 55 tons. 
 These engines have now been removed to a vessel nearly double the 
 tonnage of the Valetta , and the latter fitted with engines by Mr. Penn 
 on the superheating principle. We may mention that, besides this 
 alteration, the Valetta has been considerably improved. A poop and 
 forecastle have been added, increased accommodation given to passengers, 
 and the whole vessel fitted up in the richest style. The saloon is one 
 of the simplest and handsomest things of the kind we have seen, suffi- 
 ciently lofty and capacious, and above all, admirably ventilated on the 
 system which is now being adopted on all sea-going steamers, and the 
 merit of devising which belongs to Mr. Robinson, of the Peninsular and 
 Oriental Company. 
 
 “ To return* however, to the engines. Mr. Penn, at the repeated 
 request of Mr. Allen, the Managing Director of the Peninsular and 
 Oriental Company, undertook to apply to them the principle of super- 
 heating, to which his attention had many years before been seriously 
 directed by Dr. Haycraft. His method of doing this is to place in the 
 smoke-box of the boiler, through which the hot air from the furnace 
 first passes, as large a number of small pipes as is consistent with 
 allowing a free draught from the furnaces. Through these all the steam 
 from the boilers passes in its way to the cylinders. By this plan an 
 immense heating surface in the pipes is secured, the steam is in a 
 subdivided form, so as to be readily acted on, and the waste heat from 
 the furnace is utilized at the point where its intensity is greatest, and 
 where the greatest conveniences exist for applying the apparatus. By 
 means of three ordinary stop-valves, the whole contrivance can be 
 shut in or off from the engines at pleasure. In ordinary engines steam 
 leaves the boilers at about 250°, but declines from this temperature in 
 its way to the engines to 230°, undergoing from condensation a still 
 greater and more serious diminution of heat in the cy finders. Prom 
 these causes, and also from the immense quantity of waste heat which 
 escapes through the smoke-box and up the funnels, there has always 
 been a theoretical loss of steam power amounting to forty per cent., as 
 
498 
 
 boy's playbook of science. 
 
 compared with the coal consumed. It is this loss of power and waste 
 of heat which the superheating process is intended to prevent, and 
 which will, of course, allow a reduction of from twenty-eight to thirty 
 per cent, on the fuel now consumed. By the superheating process the 
 steam is raised in passing along the pipes in the smoke-box (where the- 
 heat is about 650°) from a temperature of 250° to 350°, and so enters 
 the cylinders at 100° in excess of the temperature due to its pressure. 
 This extra heat is, of course, rapidly communicated to the metals, and 
 prevents the condensation in the cylinders or other parts of the engines, 
 which would otherwise, of course, take place. Singularly enough, a 
 smaller amount of cold water is required to condense the steam at this 
 high temperature of 350° than when at the ordinary heat of common 
 steam. 
 
 “ The trial trip of the Valetta on Thursday was most satisfactory, not 
 only as regards the engines, but still more so as to the application for 
 the superheating process. At the measured mile at the Lower Hope, 
 near the Nore, the result of repeated runs gave an average speed of 
 nearly 14 J knots per hour, thus realizing with engines of 260 horse- 
 power, and a small consumption of fuel, the same rate of speed as had 
 been gained with her previous engines of 400 horse-power, and a con- 
 sumption of seventy-five tons of coals per day. The superheating 
 apparatus evidently effected a most important saving in fuel, but until 
 an average of many days’ working can he obtained, it would be difficult 
 to estimate the exact amount economized. There seems, however, every 
 reason to believe that an average of fourteen knots an hour can be 
 obtained with a consumption of only from twenty-four to twenty-six 
 tons per diem. The thermometer during the trial indicated in the steam 
 pipes an addition to the ordinary temperature of 100°, which Mr. Penn 
 believes to be enough for all practical purposes of superheating. Even 
 when making from thirty-three to thirty-four revolutions per minute, 
 and driving the vessel against a strong head wind and tide, it was 
 impossible to consume all the steam generated, which was blowing off 
 from both boilers all the trip. The engines are remarkable for the 
 extraordinary beauty and simplicity of their proportions, qualities well 
 known in all engines from Penn and Sons, and which, combined with 
 the strength of the materials and perfection of the workmanship, make 
 this firm the foremost in the world for machinery of this description. 
 Both cylinders are oscillating, of sixty -two inches diameter, and with a 
 stroke of four feet six inches. The paddles are on the feathering 
 principle, and the boilers of Lamb and Co.’s patent. During the whole 
 course of the trials, and when going at one time nearly sixteen knots, 
 there was no perceptible vibration, even at the end of the saloon nearest 
 to the engines. When it is remembered that the superheating process 
 which can effect such important results is capable, as we have said, of 
 application to steam machinery of every kind, including even loco- 
 motives, it cannot be doubted that the trial of Thursday and its great 
 success is one of the most important events for the progress of steam 
 which we have had to chronicle for many years.” (The Times , April 23rd 
 1859. 
 
STEAM VESSELS. 
 
 499 
 
 Whilst speaking of the application of this somewhat novel condition 
 oi steam, it may be observed that many inventors, who have paid little 
 or no attention to first principles, have proposed to apply the vaponrs of 
 alcohol, ether, or turpentine, instead of that of water ; and they have 
 founded their notions on the idea that in consequence of the less latent 
 and sensible heat of alcohol, ether, and turpentine vapour, and of the 
 small quantity of fuel required to boil them, that they would compete 
 advantageously with steam. This view of the case, however, is soon 
 proved to be a very shortsighted one, because the amount of expansion 
 has been quite overlooked ; and if it was desirable, by way of com- 
 parison, to produce a cubic foot of steam, alcohol, ether, or turpentine, 
 the steam would stand first for cheapness, and would require the least 
 quantity of fuel to produce it, so that if the more expensive of com- 
 bustible liquids could be obtained for nothing, it would still be cheaper 
 to employ water. 
 
 Latent heat, or 
 equivalent for fuel, 
 
 A cubic foot of water yields 1700 cubic feet of steam . = 1000° 
 
 A cubic foot of alcohol produces 493 cubic feet=457°. 
 
 Then, by rule of proportion, 493 cubic inches : 457 
 
 :: 1700 : . . . . : . . . 1575° 
 
 A cubic foot of ether yields only 212 cubic feet of 
 vapours 312°, and 212 : 312° :: 1700 : . . . . . 2500° 
 
 A cubic foot of the oil of turpentine affords 192 cubic 
 feet of vapour ==183°, and 192 : 183 :: 1700 : . . . 1620° 
 
 It will therefore be seen that water, when converted into steam, 
 expands eight times as much as sulphuric ether, and nearly three times 
 and a half as much as alcohol. 
 
 The application of steam for the purpose of propelling vessels has 
 already been mentioned in connexion with the Spanish inventor, Blasco 
 de Garay, in the year 1543, The first patent in this kingdom granted 
 for that purpose was that of Mr. Jonathan Hull in 1773. In 1787, 
 Mr. Miller tried a number of important experiments in the propulsion 
 of vessels by steam-engines, and it would appear that Lord Cullen 
 advocated his ideas, and endeavoured to secure the co-operation of the 
 great firm of Boulton and Watt, who, occupied with their land engines, 
 could not pay attention to it ; and twenty years elapsed after the reply 
 of Watt to Lord Cullen’s application, before the real novelty appeared 
 of a first successful experiment with a steam-boat in “ the open sea/* 
 by Henry Bell, in 1811. A picture of this boat, called the Comet, which 
 was afterwards wrecked, is shown at p. 478. Henry Beil’s novelty was 
 success, and he is fairly entitled to the merit of first introducing steam 
 navigation into Europe. 
 
 In 1811, the public stared with mingled astonishment and satisfaction 
 at the realization of that which was called a fable. Only forty-seven 
 years afterwards another generation spontaneously exhibits the liveliest 
 interest in the gigantic private speculation of the Great Eastern. Henry 
 
 k k 2 
 
500 
 
 boy's playbook of science. 
 
 Bell’s vessel of 1811 was 40 feet keel, 10 feet 6 inches beam, and 
 25 tons burden ! The Great Eastern is 692 feet long, 83 feet wide s 
 60 feet deep, and 24,000 tons burden ! ! Although the use for which 
 she was designed — the conveyance of passengers across the broad 
 bosom of the Atlantic — has been abandoned on account of the working' 
 expenses being too heavy for competition with smaller ships, the Great 
 Eastern must ever remain a monument of scientific skill and enterprise. 
 It must be remembered too that she has been instrumental in bringing 
 two great countries within speaking distance of one another by means 
 of electric cables deposited at the bottom of the ocean. It is worthy of 
 notice that the first message transmitted to the New "World was this 
 
 “glory to god in the highest, on earth peace, 
 
 GOODWILL TOWARDS MEN.” 
 
501 
 
 INDEX. 
 
 Absorption of Light, 397 
 Action, Chemical, 209 
 Adhesion, 67 
 
 Aeronauts, Celebrated, 120 
 Affinity, Chemical, 83 
 Air of Towns, 449 
 Albumenized Paper, 148 
 Alphabet, 239 
 
 Alum, Crystallization of, 275 
 Amorphous Phosphorus, 180 
 Analysis, fcpectrum, 365 
 Ancient Illusions, 321 
 Angle of Incidence, 312 
 Aphengescope, 358 
 Archimedes, 331 
 Aristotle, 311 
 Astronomy, 19 
 Atlantic Cable, 500 
 
 Atmospheric Air, Composition of, 103 
 Atoms and Particles, 5 
 Attraction of Particles, 11 
 Aurora Borealis, 264 
 Automatic Blondin, 471 
 Azote, 102 
 
 Baily’s Beads, 27 
 Bakewell’s Telegraph, 243 
 Balard, 161 
 
 Balloon, Construction of, 112 
 Ballooning, History of, 112 
 Balmain’s Luminous Paint, 295 
 Bancalari, Father, 291 
 Bath, Preservative, 155 
 Bath, Silver, 145 
 Batteries, Electric, 207 
 „ Gas, 129 
 ,, Le Clanche, 235 
 
 „ Microphone, 259 
 
 „ Sand, 231 
 Beale’s Chorentoscope, 355 
 „ Rinker, 357 
 Becquerel, 296 
 Bell, Electric, 234 
 Bell’s Magnetic Telephone, 248 
 Benzoic Acid, 78 
 Bill Distributor, 118 
 Biunnial Lantern, 349 
 Bleaching, 139 
 Blondin, Automatic, 471 
 Boron, 163, 173 
 
 Box, Tinder, 293 
 Brick, Seeing through a, 315 
 Bromine, 132, 161 
 Browning’s Electric Lamp, 281 
 Brush, F. C. 278 
 Bude Light, 97 
 Bunsen and Kirchhoff, 365 
 Burning Diamond, 165 
 
 Cable, Atlantic, 500 
 Cailletet, M., 131. 
 
 Calliope, 479 
 Camera Obscura, 141 
 „ Photographic, 143 
 „ Tourists’, 153 
 Candle, Combustion of, 299 
 
 „ Flame and Magnetism, 292 
 „ Jablochkoff, 283 
 Cane Grotto, del, 169 
 Canton’s Phosphorus, 296 
 Capillary Attraction, 69, 360 
 Carbon, 163 
 
 „ Photographic Process, 149 
 Carbonic Acid, Liquification of, 131 
 Cardboard Lamp, Edison’s, 285 
 Cascade, Gassiott’s, 269 
 „ Illuminated 335 
 Cause of Vapour, 474 
 Cavendish Bottle, 123 
 Centre of Gravity, 32 
 Centre of Percussion, 44 
 Centrifugal Force, 17 
 „ Railway, 18 
 
 Centripetal Force, 25 
 Chadwick’s Gas Generator, 353 
 Chalk Cylinder, Edison’s, 255 
 Charcoal, 164 
 Chemical Action, 209 
 „ Affinity, 83 
 „ Experiments, 87 
 
 „ Symbols, 86 
 „ Tank, 360 
 Chemistry, 81 
 Chlorine, 132 
 
 „ Preparation of, 133 
 
 Chorentoscope, 355 
 Circuit, Microphone, 260 
 „ Telephone, 249 
 Clarke’s Magnetic Machine, 274 
 Cleaning Glass, 146 
 
502 
 
 INDEX. 
 
 Coalpits, Ventilation of, 456 
 Coating Gelatine Plates, 159 
 „ Plates, 146 
 Code, Signal, 340 
 Cohesion, 59 
 Coil Experiments, 265 
 „ Induction, 261 
 „ Medical, 271 
 Collodion, 143 
 
 ,, Emulsion, 154 
 Colours of thin-plates, 389 
 Colour Top, 378 
 Colouring Lantern Slides, 362 
 Combustion of Candle, 299 
 Steel, 297 
 
 Company, Edison Telephone, 257 
 
 Compass, Mariners’, 220 
 
 Compressed Gas, 352 
 
 Concave Mirror, 324 
 
 Concert, Telephonic, 304 
 
 Conducting Wires, 232 
 
 Conduction of Heat, 429 
 
 Conductors, Lightning, 234 
 
 Conic Section, 22 
 
 Convection of Heat, 443 
 
 Convex Mirror, 328 
 
 Cooke & Wheatstone’s Telegraph, 235 
 
 Copying Telegraph, 243 
 
 Cork Borer, 91 
 
 Corona, 29 
 
 Corpuscular Theory, 300 
 Cowper’s Telegraph, 244 
 Crystallization, 73 
 
 „ Instantaneous, 79 
 
 Current, Earth, 233 
 Curves of Force, 286 
 Cylinder, Edison’s Chalk, 255 
 „ Electric. Machine, 195 
 
 Daguerre, 142 
 Dance of Witches, 308 
 Dancing Figures, 197 
 Daniell’s Cell, 208 
 Dark Room, 147 
 Davy, Sir H., 186 
 Decomposition of Light, 363 
 „ of Water, 128 
 
 De la Rue’s Discharger, 217 
 Detector Lamp, Symons’ 437 
 Detonating Pane, 202 
 Developing Photographs, 145 
 Dia-Magnetic Bodies, 288 
 Dia-Magnetism, 286 
 Diamond, Burning, 165 
 Diffraction Apparatus, 393 
 Diffusion of Gases, 6 
 Discharger, De la Rue’s, 217 
 Discoveries, Spectroscope, 368 
 Dissolving Tap, 350 
 „ "Views, 349 
 Distorted Images, 320 
 Dobereiner Lamp, 127 
 Double Plate Machine, 196 
 „ Refraction, 399 
 Dry Photographic Processes, 152 
 Duboscq’s Fountain, 333 
 „ Polarizer, 404 
 Dynamite, 273 
 
 Earth, Specific Gravity of, 59 
 „ Current, 233 
 „ Plates, 233 
 Eclipses, 19, 26 
 Eel, Electrical, 189 
 Eddystone Lighthouse, 454 
 Edison’s Cardboard Lamp, 285 
 „ Phonograph, 251 
 „ Telephone, 254 
 
 „ Telephone Company, 257 
 
 Electrical Eel, 189 
 Electric Batteries, 207 
 „ Bell, 234 
 „ Candle, 283 
 „ Fuse, 216 
 „ Lamp, Browning’s, 281 
 
 „ „ Edison’s, 285 
 
 „ Lighting, 281 
 
 „ Machine, 195 
 
 „ Telegraph, 230 
 Electricity, Frictional, 185 
 „ Magneto, 274 
 
 „ Sources of, 187 
 
 „ Voltaic, 205 
 
 Electro-Gilding, 215 
 „ Magnet, 221 
 
 Magnetic Machines, 223 
 „ Magnetism, 218 
 Electrophorus, 200 
 Electroscope, 190 
 Electro- Silvering, 214 
 Electrotype, 212 
 Elements, 86 
 
 „ Transmutation of, 370 
 Ellipse, 23 
 
 Emulsion, Collodion, 154 
 „ Gelatine, 156 
 Engine, Magnetic, 223 
 „ Newcomen’s, 482 
 
 „ Savery’s, 481 
 „ Steam, 466 
 „ Stirling’s Hot-Air, 427 
 Etching on Glass, 163 
 Ether, Vapour of, 58 
 Exchange, Telephone, 256 
 Expansion of Gases, 425 
 „ Liquids, 419 
 
 „ Solids, 415 
 
 Experimental Gramme Machine, 277 
 Experiments with Coil, 265 
 Explosive Shells, 117 
 
 Fabricius, 141 
 Falls of Niagara, 280 
 Faraday, 186 
 
 Faraday’s Heavy Glass, 287 
 Father Bancalari, 291 
 Feather and Coin Experiment, 14 
 Ferrous-Oxalate Developer, 159 
 Fire Annihilator, 171 
 „ Balloons, 425 
 First Railway, 494 
 „ Steamboat, 478 
 Fixing Solution, 149 
 Flashing Signals, 338 
 Flash, Lightning, 203 
 Fluorine, 132, 162 
 Fog Horns, 340 
 
INDEX. 
 
 503 
 
 Fountain, Illuminated, 333 
 Fox Talbot, 143 
 Frame for Printing, 148 
 Franklin, 185 
 Fraunhofer’s Lines, 366 
 Freezing Apparatus, 79 
 Frictional Electricity, 185 
 Fuze, Electric, 216 
 
 Galvani, 205 
 Galvanometer, 188 
 
 „ Needle, 207 
 Gas Bottle, 352 
 „ Generator, 353 
 Gases, Diffusion of, 6 
 „ Expansion of, 425 
 „ Liquifaction of, 131 
 „ Specific Gravity of, 55 
 Gassiott, 264 
 Gassiott’s Cascade, 269 
 Gatling Gun, 448 
 Gelatine Plates, 157 
 „ Coating, 168 
 „ Process, Photographic, 156 
 Gilding, Electro, 215 
 Glass Cleaning, 146 
 „ Etching on, 163 
 Glowworm, 295 
 Gramme Machine, 277 
 Gravitation, 11 
 Gravity, Centre of, 32 
 „ Specific, 48 
 Gray’s Telephone, 247 
 Great Eastern, 217, 500 
 Gregorian Telescope, 329 
 Grotto Del Cane, 169 
 Grove Battery, 208 
 „ Gas Battery, 129 
 Gun, Gatling, 448 
 „ Steam, 444 
 Guy Fawkes, 298 
 
 Heat, Conduction of, 429 
 „ Convection of, 443 
 „ Latent 467 
 „ Radiation of, 457 
 „ Sources of, 413 
 Heavy Glass, 287 
 Heliograph, 338 
 Hercules, Temple of, 327 
 Hermes, 81 
 
 Hero’s Steam Engine, 479 
 Hiero, King, 51 
 High Pressure Steam, 493 
 Horn Silver, 141 
 Hot Air Engine, 427 
 Hughes, Professor, 257 
 
 „ Printing Telegraph, 243 
 Huyghens, 300 
 Hydrogen, Inhalation of, 110 
 „ Liquifaction of, 131 • 
 
 „ Phosphuretted, 182 
 „ Preparation of, 107 
 Hygrometer, 462 
 Hygroscopes, 461 
 
 Iceland Spar, 399 
 Illuminated Fountain, 333 
 
 Illusions, Ancient, 321 
 Images, Distorted, 320 
 Incandescent Platinum, 216 
 Incidence, Angle of, 312 
 Induction Coils, 261, 272 
 „ Magnetic, 222 
 Inertia, 9 
 Inpenetrability, 3 
 Insulating Stool, 192 
 Insulator, 232 
 Iodine, 132, 139 
 Iriscope, 394 
 
 Jablochkoff Candle, 283 
 James Watt, 412, 485 
 Jar, Spangled, 267 
 Joule, 229 
 
 Kaleidoscope, 336 
 
 Kaleidoscopic Colour Top, 378 
 
 Kalotrope, 374 
 
 Key, Morse, 242 
 
 King Hiero, 51 
 
 King’s Electric Lamp, 284 
 
 Konn, 284 
 
 Lamp, Davy’s Safety, 435 
 „ Dobereiner, 127 
 „ Edison’s Electric, 285 
 „ Submarine, 130 
 Lantern, Biunnial, 349 
 „ Experiments, 358 
 „ Magic, 346 
 „ Opaque, 357 
 
 „ Pipette, 361 
 
 „ Triple, 350 
 Latent Heat, 467 
 Lavoisier, 93 
 
 Leaning Tower of Pisa, 40 
 Leclanch6 Battery, 235, 
 
 Lenses, 344 
 Leyden Jar, 202, 266 
 Light, 294 
 
 „ Absorption of, 387 
 „ Bude, 97 
 
 „ Decomposition of, 363 
 „ Polarization of, 395 
 „ Propagation of, 13 
 „ Reflection of, 310 
 „ Refraction of, 341 
 „ Sources of, 295 
 „ Theory of, 300, 376 
 „ Velocity of, 304 
 „ Waves of, 391 
 Lighthouses, 453 
 Lighting by Electricity, 281 
 Lightning Conductors, 234 
 „ Flash, 203 
 Lime-jet for Lantern, 352 
 Limelight, 98, 124 
 Lines of Fraunhofer, 366 
 Liquids, Expansion of, 419 
 „ Specific Gravity of, 54 
 Liquifaction of Gases, 131 
 Loadstone, 219 
 Lontin, 278 
 
 Lord Rosse’s Telescope, 329 
 Loud-speaking Telephone, 254 
 
INDEX. 
 
 504 
 
 Lucifer Matches, 180 
 Luminous Paint, 295 
 
 „ Photograph, 296 
 „ Tube, 199 
 
 Machine, Electric, 195 
 „ Guns, 448 
 
 Magic Lantern, 346 
 „ Mirror, 316 
 Magnet, Electro, 221 
 
 „ Lantern Slide, 358 
 „ Natural, 219 
 „ Rotating, 224 
 Magnetic Curves, 286 
 „ Engine, 228 
 „ Induction, 222 
 
 „ Machines, 223 
 
 „ Spark, 189 
 Magnetising Steel, 220 
 Magnetism, 218 
 
 „ and Candle Flame, 292 
 „ on the Screen, 358 
 Magneto-electricity, 274 
 Mariners’ Compass, 220 
 Matches, Lucifer, 180 
 Medical Coil, 271 
 Metal, Fusible, 417 
 Metals, Specific Gravity of, 53 
 „ Tenacity of, 62 
 Microphone, 245, 257 
 
 „ Battery, 259 
 „ Circuit, 260 
 Microscope, 379 
 
 „ Oxy-hydrogen, 354 
 Mines, Ventilation of, 456 
 Mirror, Concave, 324 
 „ Convex, 328 
 „ Magic, 316 
 „ of Archimedes, 331 
 Mitrailleuse, 448 
 Model Telegraph, 237 
 Momentum, 32 
 Moon, Phases of, 25 
 Morse Key, 242 
 „ Sounder, 242 
 „ Telegraph, 241 
 
 Natural Magnet, 219 
 Needle, Galvanometer, 207 
 Negative and Positive, 143 
 Newcomen’s Engine, 482 
 Newton’s Rings, 388 
 Niagara Falls, 280 
 Niepce, 142 
 Nitrogen, 102 
 
 „ Liquifaction of, 131 
 „ Preparation of, 103 
 
 Oersted, 218 
 Olefiant Gas, 138 
 Omnibus, Steam, 466 
 Opaque Lantern, 357 
 Optical Instruments, 294 
 Optics, 294 
 Organ, Steam, 479 
 Oxalate of Potash, 159 
 Oxy-calcium Light, 98 
 Oxygen, Compressed, 352 
 
 Oxygen, Experiments with, 92 
 „ Preparation of, 88 
 
 „ Liquifaction of, 131 
 
 Oxy-hydrogen Blowpipe, 125 
 „ Microscope, 354 
 Ozone, 100 
 
 „ Experiment with, 102 
 
 Paint, Luminous, 295 
 Pane, Detonating, 202 
 Paper, Albumenized, 148 
 „ Transfer, 151 
 Paramagnetic Bodies, 288 
 Particles and Atoms, 5 
 Percussion, Centre of, 44 
 Perkins’ Steam Gun, 444 
 Phases of the Moon, 25 
 Phenakistiscope, 372 
 Phonautograph, 252 
 Phonograph, Edison’s, 245, 251 
 „ Section of, 253 
 
 Phosphorescence, 295 
 Phosphoroscope, 296 
 Phosphorus, 163, 178 
 
 „ Amorphous, 180 
 
 „ Canton’s, 296 
 Phosphuretted Hydrogen, 182 
 Photodrome, 375 
 Photographic Apparatus, 143 
 „ Camera, 143 
 
 „ Printing, 148 
 
 Photography, Art of, 141 
 Photometer, 306 
 
 „ Woodbury’s, 150 
 
 Physioscope, 357 
 Pictet, M., 131 
 Pipette for Lantern, 361 
 Pisa, Leaning Tower of, 40 
 Pixii’s Machine, 276 
 Plate Electric Machine, 195 
 Plates, Earth, 233 
 Platinum, Incandescent, 216 
 Platinotype Process, 151 
 Plucker, 290 
 Pneumatic Trough, 89 
 Polarization of Light, 395 
 Polarizer, Duboscq’s, 404 
 Potash, Oxalate of, 159 
 Potassium in Water, 8, 12 
 Power, Transmission of, 280 
 Preservative Bath, 155 
 Priestley, 92 
 
 Printing, Photographic, 148 
 Professor Edison, 251 
 „ Hughes 257 
 Pseudoscope, 385 
 Pyramids, 42 
 
 Radiant Light, 305 
 Radiation of Heat, 457 
 Railway, Centrifugal, 18 
 „ The First, 494 
 Rainbow, 364 
 Reade’s Iriscope, 394 
 Reflection of Light, 310 
 Refraction, Double, 399 
 „ of Light, 341 
 Reiss’ Transmitter, 246 
 
INDEX. 
 
 505 
 
 Reverser, 240 
 Rings, Newton’s, 3S8 
 Rinker, Beale’s, 357 
 Robert Stephenson, 493 
 Roger Bacon, 81 
 Rose’s Fusible Metal, 417 
 Rotating Magnet, 224 
 Ruhmkorff’s Coil, 2b 1 
 
 Safety Lamp, 127, 435 
 Sand Battery, 231 
 Savart’s Wheel, 246 
 Savery’s Engine, 481 
 Saxton’s Machine, 276 
 Sciopticon, 347 
 Section of Phonograph, 253 
 Seeing through a Brick, 315 
 Selenium, 163, 177 
 Shadow Dance, 309 
 Shell Signal, 119 
 Shunt, Telephono, 250 
 Siemens & Wheatstone, 276 
 Signal Code, 340 
 „ Lamp, 341 
 Signals, Flashing, 338 
 Silver Bath, 145 
 „ Horn, 141 
 Silicon, 163, 173 
 Silvering, Electro, 214 
 Single Voltaic Couple, 206 
 Sir Humphry Davy, 186 
 Slaughtering Cattle, 273 
 Slides, Woodbury, 348 
 Snow Crystals, 73 
 Soap Bubble Experiment, 58 
 Solids, Expansion of, 415 
 Sounder, Morse, 242 
 Sources of Electricity, 187 
 „ Heat, 413 
 
 „ Light, 295 
 
 Spangled Jar, 267 
 Spark, Magnetic, 189 
 Specific Gravity, 48 
 
 „ „ of Earth and Planets, 59 
 
 Spectra on Screen, 368 
 Spectroscope, 366 
 
 „ Star, 369 
 „ Discoveries, 368 
 Spectrum Analysis, 365 
 Star Spectroscope, 369 
 Steamboat, the First, 478 
 „ Engine, 466 
 „ „ Hero's, 479 
 
 „ Gun, 444 
 ,, Hammer, 67 
 „ High Pressure, 493 
 ,, Omnibus, 466’ • * 
 
 „ Organ, 479 
 „ Superheated, 496 
 Steel, Combustion of, 297 
 Stephenson, Robert, 493 
 Stereomonoscope, 383 
 Stereomoscope, 384 
 Stereoscope, 380 
 Stirling’s Engine, 427 
 Stool, Insulating, 192 
 Submarine Lamp, 130 
 Sulphur, 163, 174 
 
 Superheated Steam, 496 
 Symbols, Chemical, 86 
 Symons’ Detector Lamp, 437 
 
 Tank, Chemical, 360 
 Tap, Dissolving, 350 
 Telegraph, Bakewell’s, 243 
 
 „ Cooke & Wheatstone’s, 235 
 „ Copying, 243 
 
 „ Cowper’s, 244 
 
 „ Electric, 230 
 
 „ Model, 237 
 
 „ Morse, 241 
 
 „ Printing, 243 
 
 „ Writing, 244 
 
 Telephone, 245 
 
 „ Bell’s Magnetic, 248 
 „ Circuit, 249 
 
 ,, Concert, 304 
 
 „ Exchange, 256 
 
 „ Gray’s, 247 
 
 „ Loud-speaking, 254 
 
 ,, Shunt, 250 
 
 ,, Thread, 247 
 
 „ Tone, 247 
 
 „ Varley’s, 247 
 
 Telescope, 379 
 
 „ Gregorian, 329 
 
 „ Lord Rosse’s, 329 
 Temple of Hercules, 327 
 Tenacity of Metals, 62 
 Thaumatrope, 374 
 Theory of Light, 300, 376 
 { ^Hrmometer, 420 
 I Thin Plates, Colours of, 389 
 Thread Telephone, 247 
 Thundercloud, 204 
 Tides, 16 
 Tinder-box, 298 
 Tombola, 36 
 Tone Telephones, 247 
 Toning Solution, 149 
 Tourmaline, 401 
 Tourists’ Camera, 153 
 Towns, Air of, 449 
 Transfer Paper, 151 
 Transmission of Power, 280 
 Transmitter, Reiss’s, 246 
 Transmutation of Elements, 370 
 Triple Lantern, 350 
 Tubes, Vacuum, 272 
 
 Vacuum Tubes, 272 
 Vapour, Cause of, 474 
 Varley’s Telephone, 247 
 Velocity of Light, 304 
 Ventilation, 449 
 
 „ of Mines, 456, 471 
 Vibration, 302 
 Views, Dissolving, 349 
 Volta, 186, 206 
 Voltaic Couple, Single, 206 
 „ Electricity, 205 
 Voltameter, 210 
 
 Water, Decomposition of, 128 
 „ Hammer, 65 
 Washed Plate Process, 152 
 
506 
 
 INDEX. 
 
 Washing Emulsion, 158 
 Watt, James, 412, 485 
 Wave Motion, 10 
 Waves of Light, 301, 391 
 Weather Predictions, 461 
 Weighing Carbonic Acid, 168 
 Westinghouse Brake, 470 
 Wet Collodion Process, 144 
 Wheatstone & Siemens, 276 
 Wheatstone’s Telephonic Concert, 304 
 Wheel, Savarts’, 246 
 
 Whitworth’s Planes, 61 
 Will-o’-the-Wisp, 184 
 Wires, Conducting, 232 
 Witches Dance, 308 
 Wollaston, 365 
 
 Woodbury’s Lantern Slides, 348 
 „ Lime-Light Jet, 354 
 
 „ Photometer, 150 
 
 Writing Telegraph, 244 
 
 Zinc and Copper Battery, 188 
 
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