To) CORNELL UNIVERSITY LIBRARY BOUGHT WITH THE INCOME OF THE SAGE ENDOWMENT FUND GIVEN IN 1891 BY HENRY WILLIAMS SAGE Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924005025766 THE VISIBLE UNIVERSE BY THE SAME AUTHOR. Small 4to, price 5s. cloth (post free). STAR GROUPS: A STUDENT'S GUIDE TO THE CONSTELLATIONS. " A knowledge of the principal constellations visible in our latitudes may be easily acquired from the thirty maps and accompanying" text contained in this work." — Nature. "A very compact and handy guide to the constellations. The maps are exceedingly clear." — Athetueum. "An excellent 'Student's Guide/ To young astronomers Mr. Gore's work would be a valued gift."— Schoolmaster. "This unpretending work takes the right direction. There are in all thirty maps showing stars to the sixth magnitude— the usual naked-eye limit — and each is accompanied by a brief commentary*. . . . The simplicity of its aim enhances its usefulness. For the purpose of a preliminary survey of the 'midnight pomp' of the heavens, nothing could be better."— Saturday Review. London : Crosby Lockwood & Son, 7, Stationers' Hall Court, E.C. New and Cheaper Edition. Price 6s. (post free). THE SCENERY OF THE HEAVENS: A POPULAR ACCOUNT OF ASTRONOMICAL WONDERS. Illustrated by Photographs of Star Clusters and Nebula? from the original Photographs taken at the Paris Observatory, and by Dr. Isaac Roberts at Liverpool ; also Drawings from recent sketches. " Mr. Gore has already earned a high reputation, which will be more than sustained by the present volume."— Science Gossip. "Forms an excellent introduction to an elevating and engrossing study." — Morning Post. "An exceedingly gcod book, in which amateurs will find amine of wealth." — Literary World. " The text is excellent, and.will no doubt greatly interest the general reader. . . . The chapter on variable stars, as might be expected from Mr. Gore, is especially good."— Nature. London: R. Sutton & Co., n, Ludgate Hill, E.C. From the original photogra; Messier), ph by Isaac Roberts, D.Sc, F.R.S. Messier). s, D.Sc, F.R.S, THE VISIBLE UNIVERSE CHAPTERS ON THE ORIGIN AND CONSTRUCTION OF THE HEAVENS J. ELLABD GOBE, p.r.a.8. Member of the Royal Irish Academy ; Fellow of the Royal Geological Society of Ireland ; Associate Member of the Institution of Civil Engineers ; Honorary Member of the Liverpool Astronomical Society; Corresponding Member of the Astronomical and Physical Society of Toronto AUTHOR OF "THE SCENERY OF THE HEAVENS," " STAR GROUPS," ETC. SEitk 55&32> " A knowledge of tbe construction of the heavens has always been the ultimate object of my observations." Sir W. Hebschel. " Of Law there can be no less acknowledged than that her seat is in the bosom of God, her voice the harmony of the world : nil things in heaven and earth do her homage — the very leasb as feeling her care, and the greatest as not exempted from her power." Bichard Hooker. PREFACE rpHE object of the following pages is not to propound -*- any new hypothesis, hut simply to explain and discuss theories which have been supported by well-known astro- nomers and other men of science. Hypotheses which are merely paradoxes will of course not be considered. As these are generally advanced by persons possessing no scientific knowledge, and apparently incapable of grasping the simplest principles of mathematical astronomy, their views are, as a rule, unworthy of serious thought or refutation. The latest results respecting the distribution of stars and nebulas,, their relative motions, and the physical constitution of the heavenly bodies, will be given ; and it is hoped that the work will prove of interest to the general reader as well as to the student of astronomy. With reference to the origin of matter itself, the Visible Universe may possibly have been evolved from a spiritual Unseen extending throughout a past eternity, as the authors of The Unseen Universe maintain ; but in the following pages I only propose to deal with the construe- Vi PREFACE. tion of the Universe as we see it, and its probable develop- ment from pre-existent matter. There are, however, two points in which the Universe, as we know it, apparently comes into contact with the Unseen. These are the mys- terious force of gravitation and the lnminiferous ether. That gravity is an amazing mystery no thoughtful person will deny. Various theories have been advanced to explain the method of its action, but none of them are really satis- factory solutions of the problem. Various views of the constitution of the ether have also been propounded, and its very existence is disputed by some writers! The're may possibly be a close connection between the two mysteries, and should the time ever come when we shall thoroughly understand the constitution of this, at present, inconceivable fluid, such knowledge may not improbably lead us to a solution of the great mystery of gravitation. The first four chapters contain a popular account of the theories which have been advanced to explain the evolution of the Solar System and the origin of the Sun's heat. The fifth and sixth chapters give some account of the lumini- ferous ether and the supposed constitution of matter. The seventh chapter deals with celestial chemistry. The remaining chapters describe the construction of the sidereal heavens and the various theories respecting the constitution of the Universe which have been advanced by eminent astronomers. September, 1892. J- E. G. CONTENTS. -♦- CHAPTER I. PAGE THE NEBULAR HYPOTHESIS 1 CHAPTER II. pate's theory 25 CHAPTER III. STELLAR EVOLUTION 35 CHAPTER IV. THE FUEL OF THE SUN 49 CHAPTER V. THE LUMINIFEROUS ETHER 57 CHAPTER VI. THE CONSTITUTION OF MATTER 63 CHAPTER VII. CELESTIAL CHEMISTRY 71 ' CHAPTER VIII. THE METEORITIC HYPOTHESIS 81 vii Vlll CONTENTS. CHAPTER IX. THE MILKY WAY AND STAR DISTRIBUTION CHAPTER X. CLUSTERING STARS AND STAR STREAMS . PAGE . 123 164 • CHAPTER XI. STELLAR DISTANCES AND MOTIONS . . • • • .182 CHAPTER XII. OIANT AND MINIATURE SUNS .... . . 199 CHAPTER XIII. SOME EARLIER THEORIES OF THE UNIVERSE . . . .211 CHAPTER XIV. SIR WILLIAM HERSCHEL'S THEORIES ..... 236 CHAPTER XV. SIDEREAL ASTRONOMY FROM HERSCHEL TO STRUVE . . . 251 CHAPTER XVI. STRUVE'S THEORY . 256 CHAPTER XVII.' proctor's views 290 CHAPTER XVIII. INFINITE SPACE AND A LIMITED UNIVERSE . 309 appendix 324 LIST OP ILLUSTKATIONS. — •— — PAGE The Great Nebula in Andromeda .... Frontispiece Plate I. The Spiral Nebula in Canes Venatici . . 23 „ II. The Milky Way in Cygnus, as drawn by Heis . 128 ,, IIa. The Milky Way in Cygnus, after Boeddicker 128 „ in. The Milky Way in Aquila and Serpens (Heis) . 129 ,, IV. Stars Visible to the Naked Eye, N. Hemisphere . (Heis) 144 „ V. Stars Visible to the Naked Eye, S. Hemisphere (Behrmann) 150 „ VI. Distribution of Naked-eye Stars, N. Hemisphere 151 „ VII. Distribution op Naked-eye Stars, S. Hemisphere 153 „ VIH. Distribution of Stars to Seventh Magnitude, S. Hemisphere 154 „ IX. Photograph of Portion of Milky Way in Sagit- tarius . . . 161 „ X. Photograph of Portion of Milky Way in Sagit- tarius 163 „ XL. Photograph of Stars in Gemini . . . .171 „ XII. Photograph of Star Cluster, Messier 38 . . 176 „ XIII. Relative Distances of Stars of Different Mag- nitudes 188 ix b LIST OF ILLUSTRATIONS. PAGE . 194 Plate XIV. Positions op the "Solar Apex" „ XV. Section op Sie W. Heeschel's Stellae Disc . 240 Fig. 1. Rich and Poor Regions in Andromeda and Lacerta „ 2. Rich Region near the Southern Cross „ 3. Region Rich in Lucid Stars „ 4. Rich and Poor Regions in Hydra and Antlia „ 5. Rich Region in Centaurus and Lupus „ 6. Curious Group of Stars near 4 Vulpeculse . „ 7. The Star Group near 4 Vulpeculse „ 8. Stream of Bright Stars in Scorpio „ 9. Star Streams in Lyra and Cygnus „ 10. Group of Stars in Taurus, showing Streams as seen with an Opera-Glass 174 „ 11. Streams of Small Stars in Telescopium and Corona Australis 175 152 152 155 156 157 166 167 172 173 *u* My best thanks are due to the Earl op Rosse, Me. Baenaed of the Lick Observatory, Dr. Boeddickee, M. M. Heney of the Paris Observatory, and Br. Isaac Roberts, for their kind permission to reproduce some of the illustrations given. J. E. G THE VISIBLE UNIVEESE. CHAPTER I. THE NEBTJLAB HYPOTHESIS. 1 " This world was once a fluid haze of light, Till towards the centre set the starry tides, And eddied into suns, that wheeling cast The planets." Tennyson. 2 IN the year 1755 the famous German philosopher Im- manuel Kant advanced a theory respecting the origin of the universe in a work entitled Allgemeine Naturges- chichte und Theorie des Himmels. This work is divided into two parts. In the first part Kant considers the con- stitution of the stellar heavens and the Milky Way, and reproduces views previously propounded by Thomas Wright, of Durham, and published in 1750 (see Chapter XIII.) . In the second part he treats of the origin of the Solar System, and it is this portion of his work which has an especial bearing on the. subject of the present chapter. 1 For most of the details contained in the present chapter I am indebted to M. Wolf's interesting and valuable work Les Hypotkises Cosmogomqves (Paris, 1886). 2 Tlie Princess. 1 Missing Page KANT S HYPOTHESIS. 6 planets depend upon their distance from the Sun. The density of the original mass increased from its surface to its centre. The exterior planets would therefore be formed from lighter materials than the interior. But the greater the distance of a planet from the Sun, the larger would be the sphere from which it could draw in particles to increase its mass. The outer planets should therefore be larger than the interior. This is roughly but not rigidly true. The large planets, as a rule, lie on the exterior and the smaller on the interior of the planetary system. But Neptune and Uranus are each smaller than Saturn, and Saturn is smaller than Jupiter. Kant explains this fact • in the case of Saturn, Jupiter, and Mars x by the influence of each planet on the sphere of action of its neighbours. Thus the size of Mars was ruled by the preponderating influence of the giant Jupiter, which in a similar way influenced the mass of Saturn. Mercury's small mass he attributes to the vicinity of the Sun, and also to that of Venus. Supposing the Sun and planets to have been formed from the same materials, Kant concluded that the meau density of the planets should be the same as that of the Sun. Adopting the figures given by Buffon, he found the ratio of the density to be 64 to 65. Modern results show that this equality of. density is only approximately true. The near approach to identity is, however, interesting and suggestive, and Kant thought it formed a conclusive proof of the truth of his hypothesis. According to Kant's theory, the satellites were formed 1 Neptune and Uranus were, of course, not discovered till after Kant's time. 4 THE VISIBLE UNIVERSE. from the planets in the same way that the planets were produced from the primitive mass. They therefore re- volve round their primaries in the same direction that the planets revolve round the Sun. M. "Wolf, however, points out that from the rotation assigned by Kant to the solar nebula it would result that the particles farther from the Sun would have a smaller linear velocity than those that are nearer, and that consequently the rotation of a planet, and the revolution of its satellites, should be contrary to the observed direction of motion. M. Zollner also admits that this motion should be— according to Kant's sup- • position — retrograde instead of direct. It also follows from Kant's theory that the larger planets should alone have satellites. The moons of Mars are there- fore opposed to Kant's hypothesis. According to Kant's view, comets have had the same origin as the planets, and differ from them — astronomically speaking — only in the eccentricity and inclination of their orbits. They were formed, he thought, at a great distance from the Sun, in regions of feeble attraction and highly rarified matter. Their movements should be generally — like the planets — direct. He attempts to show, however, that they might possibly be retrograde in some cases, but seems to think that the few comets with retrograde motion known in his day were either exceptions to the general rule, or that the apparent motions were due to errors of observation. Kant devotes a chapter of his work to a consideration of the origin of Saturn's rings. He thinks that Saturn was originally a body analogous to the comets, and revolved in an orbit of high eccentricity. Approaching the vicinity of LAPLACE S HYPOTHESIS. 5 the Sun, it became highly heated and surrounded by a vast atmosphere similar to a comet's tail. Gradually the orbit became nearly circular, and the planet cooling down its atmosphere condensed into the system of rings we now see surrounding it. This formation of a ring from a planetary atmosphere was due, he thought, to the rotation of Saturn on its axis, and on this hypothesis Kant computes the planet's period of rotation (unknown in his time) at 6h. 23m. 53s., a result which differs rather widely from Professor Asaph Hall's observed period of lOh. 14m. 24s. He also showed how the flattening at the poles of Saturn's globe might be computed. Kant conjectured that the earth was originally surrounded by a ring, and that the deluge recorded in Genesis was due to the rupture of this ring and its downfall on the earth ! Kant's theory seems to have been unknown to Laplace. It has one point in common with Laplace's Nebular Hypo- thesis, namely, that it supposes the Solar System to have been evolved from a primitive nebulous mass ; and to Kant seems certainly due the credit of having first advanced this bold hypothesis. Kant's primitive mass, however, differs essentially from Laplace's nebula, both in its properties and the character of its motion, and Kant's views are often in direct opposition to those of his illustrious successor. Laplace's Nebular Hypothesis was originally propounded in the first edition of his work Exposition du Systeme du Monde, published in the year 1796. The theory was further advanced in the third edition of the same work, which appeared in 1808, and was completed, in subsequent editions, the sixth and last of which was published in 1836, D THE VISIBLE UNIVERSE. nine years after the author's death. Although presented by Laplace " avec la defiance que doit inspirer tout ce qui n'est point un resultat de l'observation ou du calcul," it should be remembered that the hypothesis was the result of long and careful consideration by one of the most brilliant mathematicians which the world has ever produced. The fundamental idea in Laplace's theory was that the Sun's atmosphere originally extended beyond the orbit of all the planets, and that it has gradually shrunk to its present limits, 1 abandoning at intervals masses of matter which afterwards consolidated into planets. Laplace seems to have adopted Sir W. Herschel's view of the formation of stars from planetary nebulas, or rather from a nebula with a condensed centre. This he considered to have been the original condition of the Sun, but he supposed that the formation of the planetary system did not commence until the condensation of the original nebula was far advanced and a true nucleus had been formed. Laplace's original nebula differed essentially from Kant's primitive mass. The latter was supposed to consist of separate particles revolving round a centre, according to the law of equal areas in equal times, whereas Laplace's nebula consisted of an elastic gas, the different layers of which rotated with the same angular velocity. This nebula extended to a point at which the centrifugal- force due to its motion of rotation was exactly balanced by gravity acting towards the centre. Its form was that of an ellipsoid, of which the ellipticity or flattening at the poles 1 Laplace's words are : " L' atmosphere du Soleil s'est primitiranent etendue au dela des orbes de toutes les planetes, et qu'elle s'est resserree succesivement jusqu'a ses limites actuelles." FORMATION OF RINGS. 7 could not exceed ^. Laplace does not assign any reason for the existence of rotation in his primitive nebula, and seems to have assumed that the rotation was a property with which it was originally endowed. 1 He supposes the planets to have been formed from rings detached by the force of the rotation, combined with the cooling and conse- quent shrinkage of the parent mass. These rings would continue to condense, and would eventually form a solid or liquid ring. But this would be an extremely rare case, and we have only one example of such a phenomenon in the Solar System, namely, the rings of Saturn, The rings would in most cases break up into separate masses of a spherical form, having a rotation on their axes in the same direction as that of their revolution round the central, nucleus. If one of these masses was of much greater size than the others, it would in the course of time gather together the smaller masses by the force of its attraction, thus forming a spherical gaseous mass revolving round the Sun or central nucleus. These masses condensing would form planets, and would in a similar way detach rings forming satellites revolving round their primary in the same direction that the planets revolve round the Sun. Laplace's hypothesis explains satisfactorily the following facts connected with the planetary system : (1) the ap- proximate coincidence of the planes of the planetary orbits with the plane of the Sun's equator ; (2) the small eccen- tricity of the orbits, which originally were probably circu- lar ; (3) the direction of revolution of the planets round the Sun and their rotation on their axes ; also the direc- 1 See Chapters on " Stellar Evolution " and " The Fuel of the Sun." 8 THE VISIBLE UNIVEBSE. tion of motion of the satellites round their primaries. These motions are all performed from right to left, or contrary to the motion of the hands of a clock. When Laplace's theory was published only four small planets were known between Jupiter and Saturn. Since that time over three hundred more have been discovered, and all these revolve round the Sun in the same direction as the larger planets. The probability against such an arrange- ment being merely the result of chance is very great indeed, and the facts have always been considered to be greatly in favour of Laplace's hypothesis. The discovery of the satellites of Uranus and Neptune — which have a retrograde motion — has however revealed two exceptions to the general rule. Laplace seems to have believed that the motion of the Uranian satellites was — like those of the other planets —direct. Neptune was discovered since his death. In both cases the motion is now known to be certainly retrograde. This retrograde motion is of course in direct opposition to Laplace's hypothesis, and to overcome the difficulty a ' theory to explain it has been advanced by M. Faye, 1 who thinks that Laplace's theory is untenable. This explana- tion -will be considered in the next chapter. Contrary to Kant's views, Laplace considered that comets were originally strangers to the planetary system. Comets of short period have usually direct motion and small inclinations, which agrees with Kant's theory, whereas parabolic comets, or comets with very long periods, agree better with Laplace's hypothesis. Mr. Monck points out that " retrograde comets of comparatively short period " (such as that connected with the November Leonid meteors) " would 1 See M. Faye's Stir VOrit/ine dn Monde (1885), p. 156. MODIFICATIONS OF LAPLACE'S HYPOTHESIS. 9 be inconsistent with Laplace's hypothesis unless they were . wanderers from space captured by some planet." Some modifications and additions have been proposed to Laplace's original hypothesis. Several objections have also been raised to it. I will consider the modifications first and the objections afterwards, as is done by M. C. Wolf in his interesting and valuable work Les Hypotheses Cosmogoniques (1886), to which I am indebted for most of the details given in the present chapter. The mechanical theory of the Sun's heat advanced in recent years by Helmholtz seems at first sight to lend support to the Nebular Hypothesis. 1 This theory, which is now very generally accepted by astronomers, supposes the solar heat to be due to the contraction of its mass caused by gravita- tion, and suggests that in former ages the Sun was of vastly larger size than it is at present, and possibly extended at one time beyond the orbit of Neptune. But on this theory the probable past duration of the Sun's heat can be computed, and this duration of solar activity does not meet the demands of geologists, 2 unless we admit that geological forces acted with much greater energy in former ages than they do at present. Professor Newcomb has suggested a modification in the supposed formation of the rings detached from the original nebula. He considers that in its original state the primi- tive nebula was of a form nearly spherical. As it con- tracted it would gradually assume the shape of a flattened spheroid, and afterwards that of a flat and thin disk. From this disk rings would separate, which would con- 1 See Chapter on " The Fuel of the Sun." 1 See Chapter on " Stellar Evolution." 10 THE VISIBLE UNIVERSE. solidate into planets, as Laplace supposed. 1 Professor Kirkwood, however, considers that the transformation of the original nebulous mass into a disk or close system of rings would " fail to account for the formation of the solar system as it actually exists." 2 He has also shown that the rings abandoned by the original nebulous mass might have been formed simultaneously and not at long intervals. On this view of the matter the larger planets— Jupiter, Saturn, Uranus, and Neptune — would take longer to cool down and would be less advanced in their life-history than the others; and this agrees well with the view — ably supported by the late Mr. Proctor— that these giant planets are still in a highly heated condition, and have not yet sufficiently cooled down to form the abode of living creatures. Let us now consider the principal objections which have been raised to the Nebular Hypothesis. I will take them in the order in which they are discussed by M. Wolf in the work already referred to. Some of these objections were anticipated and partially met by Laplace himself. 1 . It has been objected that the formation of such rings as Laplace supposes is impossible. " Supposing the original nebulous mass to have been homogeneous in structure and to remain so during its contraction, its period of rotation, at first excessively slow, would diminish, according to the. law of areas, as the square of the radius." 3 If when it extended to the orbit of Neptune it had a period of rotation equal to Neptune's period of revolution round the Sun, namely, 164-6 years, this period would be reduced to 67 1 Newcomb's Popular Astronomy, p. 498 (edition of 1878). 2 The Observatory, May 1880, p. 410. 3 Les Hypotheses Cosmogoniques, p. 35. OBJECTIONS TO THE NEBULAE HYPOTHESIS. 11 years when the nebula had shrunk to the orbit of Uranus, to 16*7 years at the orbit of Saturn, and to 4*94 years at the orbit of Jupiter. 1 This period would be reduced to only O0014 of a day for the radius of the Sun. These figures of course differ widely from the actual periods of revolution of the planets inside Neptune's orbit. The objection seems to have been anticipated by Laplace, for he supposed that at the centre of the original nebulous mass there existed — even in its earliest stage — a nucleus of comparatively considerable density, and that the friction between this central globe and the surrounding nebulous atmosphere, and the friction between the nebulous layers of this atmosphere, would check the increasing speed' of rotation as it contracted. Trowbridge considers that when the ring from which Neptune was afterwards formed was abandoned, probably more than one half the mass of the original nebula was within the earth's orbit, and that the greater portion of this half was even within the orbit of Mercury. It seems therefore inadmissible to assume that the nebulous mass remained homogeneous in density during its contraction, as this would not be consistent with Laplace's original hypothesis. But it has been further objected that after the Neptunian ring had been abandoned the nebula must have contracted " without further loss of matter " to the orbit of Uranus. How did this state of equilibrium exist for so long a period ? and what gave rise to the sudden rupture which then took place? Kirkwood points out that the equilibrium once disturbed could not be re-established, and that consequently small gaseous masses would be constantly abandoned which 1 The Observatory, May 1880, p. 411. 12 THE VISIBLE UNIVEKSE. would form small bodies and not large planets like Uranus, Saturn, and Jupiter. As Miss Clarke says, "Bach wisp of nebula, as it found itself unduly hurried, would have declared its independence, and set about revolving and con- densing on its own account. The result would have been a meteoric, not a planetary system." M. Roche, however, has shown by an ingenious and original investigation 1 that if we assume with Laplace that . the original nebula had a considerable central condensation, rings would be abandoned and planets formed at distances represented well by Bode's law. 2. It has been objected that, even admitting the forma- tion of such rings as Laplace supposes, the subsequent formation of large planets from these rings would be impossible. Laplace supposed that when a ring was aban- doned it would break up into fragments, and " if one of them was sufficiently powerful to unite successively by its attraction all the others about its centre, the ring of vapours would be changed into one sole spheroidal mass, circulating about the Sun, with a motion of rotation in the same direction with that of revolution." With reference to this point Professor Kirkwood says : " In regard to the mutual attraction here referred to, it may be remarked that two parts of the Neptunian ring on opposite sides of the Sun could produce no sensible pertur- bation of each other's motion. If, moreover, the fragments of any ring were distributed around the orbit with approxi- mate uniformity, their mutually disturbing effects would 1 Essai sur la Constitution du Si/stemr Solaire (Montpellicr, 1873). The details of M. Roche's investigation aTe difficult and not suitable for reproduction in these pages. OBJECTIONS TO THE NEBULAE HYPOTHESIS. 13 nearly destroy each other. That this state of things should have obtained in the case of some of the eight, principal planets is extremely probable. The theory, therefore, of planetary aggregation by the attraction between different parts of the rings, requires an indefinite antiquity of the' solar system. "Let us suppose, then, that the planet-forming process was due to the different velocities of the fragments into which a ring had been broken up. Take, for example, the ring which was transformed into Neptune. Let us assume that two fragments, A and B, differed in longitude by 180°, and that the mean distance of the centre of gravity of A from the Sun's centre exceeded that of B by 1000 miles. It is then easy to show that the corresponding difference of their angular velocities would not bring them together around the same nucleus in 150 millions of years. But even after all the fragments had thus been collected, other millions of years — assuming with Laplace that the united mass was still in the gaseous form — would be required for the process of condensation. The supposition we have made is not an extravagant one. In Laplace's cosmogony, therefore, hundreds of millions of years are involved in the separate history of a single planet. Is so great an implied age of the solar system admissible ? " * The objection is evidently a formidable one, but here again M. Eoche comes to the aid of the Nebular Hypo- thesis, and shows that the formation of planets from rings of nebulous matter would be possible under certain conditions. 2 1 Tlie Observatory, May 1880. 2 Mhnoires de I'Aeademie de Montpelier, 1849, 1850, 1851. 14 THE VISIBLE UNIVERSE. 3. The objection has been raised that the planets formed from Laplace's rings should have a movement of retrograde rotation on their axes. This objection has been especially insisted on by M. Faye, whose views on the subject will be considered in the next chapter. In a memoir on the conditions of stability in Saturn's rings, M. Hirn shows however that a planet formed from a ring would have a direct rotation, and M. Roche's investigations seem to lead to the same conclusion. M. "Wolf says : " Si je ne tromp'e, les remarques de M. Hirn et l'ingenieuse explication de la formation des anneaux que nous devons a M. Roche font disparaitre entierement l'objection de M. Faye." He further argues that even if we admit that the planetary nebula, formed from the condensation of a ring, had at first a retrograde rotation, this motion could not be sus- tained. For in the early period of its existence the in- cipient planet would be acted on by a powerful tidal action due to the attraction of the central mass, the result of which would be that the planet's rotation would be rendered direct. This result, he thinks, would be certainly true for the planets near the Sun, and would be doubtful only in the case of the external planets Uranus and Neptune, which have probably a retrograde rotation. It appears that this view of the matter was also presented by Laplace, who seems to have in this case, as in others, anticipated and dealt with most of the objections to his hypothesis. 4. Another objection which has been raised against the Nebular Hypothesis is that many of the satellites are at distances from their primary which are inconsistent with Laplace's theory. The Moon is a case in point.- Its distance from the earth is greater than the radius which m. roche's investigations. 15 the earth in its gaseous state would probably have had at the time of its formation from a nebulous" ring. The inner satellite of' Mars, Phobos, forms an exception in the opposite direction, its period of revolution being less than the planet's period of rotation on its axis. This point was briefly considered by Laplace with reference to the satellites of Jupiter. A more careful investigation of the subject was however necessary, and this has been undertaken by M. Boche. 1 He considers that the satellites were not formed during the early existence of the planetary nebula, and would not be formed until the nebula had — like the original solar nebula — considerably condensed at its centre, the mass being influenced in this case also by a strong tidal solar action. It follows from M. Roche's investigation that the planets, nearest to the Sun, being acted on by a stronger tide, would produce satellites more slowly and at a smaller distance from their primary than the others. The Moon, being an exception to this rule, must have been formed under peculiar conditions. As already stated, the Moon's comparatively great distance of 60 times the earth's radius is considered as an objection to Laplace's hypothesis. Calculation shows that when the gaseous mass, which afterwards consolidated and formed the earth, rotated in a period of 27 - 3 days (the Moon's period of revolution), the nebulous atmosphere would have extended only three-fourths of the distance which now separates the Moon from the earth. M. Roche, however, points out 2 that in considering the 1 Memoires de V Academic de Montpelier, vol. ix., 1877. Memoires de VAcademie de Montpelier, vol. ii., 1851, p. 399. 16 THE VISIBLE UNIVERSE. effect of tidal action on the nebulous mass we should — as in the case of oceanic tides — take into account, not the absolute attraction of the Sun, but the difference between the solar attraction exercised on a molecule of the atmo- sphere and that exerted on the centre of the earth. On this view of the matter he finds that the longer axis of the nebulous spheroid would, at the epoch referred to, be exactly 60 radii of the earth as it exists at present. This axis would, however, be always directed towards the Sun, the other axes at right angles to the major axis being shorter. M. Roche then concludes that the Moon had its origin, not in a ring, but in matter abandoned at the extremity of the longer axis at a time when the- nucleus had sufficiently consolidated. Researches by M. Simon agree with those of M. Roche. The formation of internal rings in the nebulous mass which afterwards formed the planet Mars would account, on this hypothesis, for the formation of Phobos, which seems to have been of rela- tively recent origin compared with the age of our Moon. With reference to the ring system of Saturn, M. Roche has shown that the rings have not consolidated into a satellite because that, within a distance of 2 - 44 radii of the planet, the attraction of the planet would produce on a nebulous satellite of the same density tides which would be inconsistent with a permanent form of equilibrium. The satellite would be shattered and fall in pieces on the sur- face of the planet. M. Hirn's conclusions agree with- those of M. Roche ; and the theory that Saturn's rings consist of a crowd of small satellites each revolving in its own orbit round the planet seems to be consistent with these views. Although the entire ring system lies within Roche's OBJECTIONS TO THE NEBULAE HYPOTHESIS. 17 limiting distance of 2-44 radii of the planet's globe, the jparticles composing it may be so small and of such rigidity as to resist the disruptive action of Saturn's attraction. That a nebulous ring might, under certain conditions, form a number of small planets instead of a single large one is evidently possible, for an example of such a result is visible in the system of small planets revolving round the Sun between the orbits of Mars and Jupiter. Kirkwood and Proctor have shown that the orbits of these minor planets are divided into zones separated by intervals ana- logous to the divisions in Saturn's ring system. These divisions in the "asteroid" system have been caused by the disturbing action of Jupiter, in the same way that the Cassini division in Saturn's rings is due to perturbations produced by the interior satellites. 5. Another objection to the Nebular Hypothesis is that the satellites of Uranus and Neptune revolve round these planets in a retrograde direction. The question of the rotation of these planets on their axis has not yet been decided by observation, but it seems highly probable from analogy that they rotate in the same direction that the satellites revolve round their primary. M. Faye considers this objection so important and so fatal to Laplace's theory that he has formulated a new theory of planetary evolution, which will be considered in the next chapter. It will therefore be interesting to examine the objection in detail, and inquire whether it is really so formidable as M. Faye supposes. Laplace himself was not ignorant of the fact that there was something exceptional in the motion of the satellites of Uranus (Neptune was not discovered till after Laplace's 18 THE VISIBLE UNIVERSE. death). But owing to the fact that the plane of the satellite orbits lies nearly at right angles to the plane of the planet's orbit, Laplace may have concluded — as M. Faye suggests x — that the motion of the satellites was really direct. However this may be, it seems probable that, according to the Nebular Hypothesis, the planets when first formed should have had their axes of rotation at right angles to the planes of their orbits, or the general plane of rotation of the original nebula. How, then, was the axis of Uranus brought so nearly into coincidence with the plane of the planet's orbit ? The answer to this question would involve the general one, namely, Why are the equators of all the planets more or less inclined to their orbit planes ? As far as is known the planet Jupiter is the only one 2 whose equator plane nearly coincides with the plane of its orbit, the angle between the two planes being about 3°. With reference to these inclinations Laplace says : " On conroit que les varietes sans nombre, qui ont du exister dans la temperature et la densite des diverses parties de ces grandes masses, ont produit les excentricites de leurs orbites, et les deviations de leurs mouvements du plan de cet equateur." With reference to the inclination of the planetary orbits to the general plane of the Solar System, M. Trowbridge points out that if we suppose a larger mass to be detached from one side of the equator of the original rotating spheroid than from the other side, a disturbance of 1 &ur I' Origine du Monde, p. 156. 2 If, however, Schiaparelli's observations of Mercury are correct, the axis of rotation lies nearly at right angles to the plane of the planet's orbit and Jupiter would not'be the only exception. PLANETARY INCLINATIONS. 19 equilibrium would result which would change slightly the direction of its axis of rotation, and that a change of this kind might have been produced when each ring was abandoned. Le Verrier and Tisserand have shown that the influence of perturbations between the planets would also tend to increase the inclination of their orbit planes. This influence would have a great effect in the case of a small mass acted on by other masses considerably larger. Of this we have examples in the case of Pallas and some of the other minor planets. The question of the inclination of the planetary equators to the planes of their orbits has been considered by M. Simon and Professor G. H. Darwin. The former has shown that if we suppose the earth to have been formed by the consolidation of a' series of rings, the inclination of these rings, acted on by the attraction of the Sun or central nucleus, would have increased in time. This might apply to the planets nearest the Sun, but at the great distance of Saturn and Uranus the disturbing action of the Sun would seem insufficient to produce the observed results. Professor Darwin has considered the question from a totally different standpoint. Supposing the planet to be in the state of a viscous spheroid which, according to Sir William Thomson, is subject to the same laws as a nebulous mass, he concludes that every increase in the equatorial protuberance would tend to increase the inclination of the equator to the plane of the planet's orbit. In the case of the earth he finds that the obliquity of the equator would have had nearly the same value as it has at present when the . earth, in its gaseous state, extended as far as the 20 THE VISIBLE UNIVERSE. Moon's orbit. In the case of the more distant planets he is obliged to invoke the aid of the satellites. M. Wolf, however, thinks that Professor Darwin's views are still beset with many difficulties. They do not satisfactorily explain why the Moon's orbit plane is inclined only 5° to the plane of the ecliptic, nor how it is that most of Saturn's satellites revolve in the plane of the planet's equator. Reviewing all the objections which have been raised against the Nebular Hypothesis, M. Wolf considers that most of them have been satisfactorily answered. He thinks that only two doubtful points remain, namely, (1) How the gaseons matter of the ring abandoned by the original nebulous ■ mass was consolidated into a planet of large size ; and (2) How the inclinations of the planetary equators and the orbits of the satellites on the planes of the planets' orbits have been produced. These difficulties are, however, not peculiar to Laplace's views, but are common to all theories which suppose the planetary system to have been evolved from a rotating nebulous mass. How the original nebulous mass acquired its motion of rotation Laplace did not attempt to explain. If we imagine the nebula to have been formed by the impact of two solid bodies, an oblique collision would give rise to the required rotation (see Chapter on " The Fuel of the Sun "). The late Mr. Jacob Ennis, however, concludes that the rotation was due to the action of gravitation alone. He says : — " My own discoveries have at length placed the nebular theory on a firm mathematical foundation. The chief of them are these : (1) That gravity must necessarily and unavoidably produce rotation as well as rotundity in all nebulas ; (2) That gravity may increase that rotation so rapidly as to afford a centrifugal equal to the centripetal force ; (3) That in nearly all nebulas forming solar and planetary 21 systems rotation must begin on the surface, and hence must be retarded by the unrotating or slowly rotating interior. This retarda- tion accounts for a vast number of most important stellar phenomena. Nothing in my calculations opposes the doctrine of equal are,as swept by the radius vector in equal times. If the nebulse forming our solar system and extending at first halfway to the nearest fixed star had originally a rotation velocity of only the one-third of a mile per hour, then its radius vector would have swept over an area equal to that of Mercury, whose orbital velocity is 110,000 miles per hour. To satisfy the law of equal areas described in equal times, Ennis finds that when the Sun was expanded to the orbit of Mercury the rotation velocity would be less than 56 miles per hour. At the earth's orbit it would be 22 miles per hour, and at the orbit of Neptune less than one mile per hour. But the Sun's present rotation velocity is about 4500 miles per hour. The velocity has therefore increased instead of diminished, as should have occurred according to some supporters of the Nebular Hypothesis. Ennis explains this increased velocity of rotation in the following way:— " In the course of contraction the radius vector of the nebulous Sun, instead of sweeping over equal areas in equal times, swept in fact over smaller and smaller areas at the distance of every succeeding planet. This would have stood as a valid objection to the nebular theory. But happily I discovered that nebular rotation must necessarily begin, in nearly all cases, not at the centre of the nebula, as all previous writers had supposed, but on the surface. This surface rotation must of necessity be retarded by friction on the unrotating interior ; hence the radius vector must sweep over smaller and smaller areas in proportion to the amount of retardation. But in a general sense the principle of equal areas in equal times holds true ; because what is lost in velocity by the particles on the exterior is gained by those of the interior. The sum of the areas swept by the radii vectores of all the particles must be a constant quantity ; but practically these areas cannot be computed, because we do not know the densities of the several strata of the 22 THE VISIBLE UNIVERSE. nebula, and hence we do not know the positions of the particles, or the length of their radii vectores. Nevertheless on Professor Loomis's plan, and what appears to be the plan of Comte, Nichol, and others, the principle of equal areas in equal times must be followed out with a single radius vector extending from the Sun's centre to his ^surface; and then the absurdity of their statements becomes manifest." Ennis thinks that gravity. is "the force which in the beginning put all the heavens and the earth in motion." He finds that "the velocity of a fall from infinite space 1 to the orbit of a planet is to the orbital velocity of a planet as 100 to 70 very nearly," and says :— " If the velocity of a fall from infinite space to any orbital velocity be as 100 to 70, then it may be objected that the force of gravity is too great to be the force which gave their velocities to the stars. To this it may be replied : (1) That no rotation of any nebula actually began off at infinite space : large contraction must .have taken place before rotation began ; (2) That rotation began generally on the exterior, and the velocity was retarded by friction on the interior. In the case of our solar system I have proved that this retardation between the orbits of Neptune and Uranus was one per cent, in a contraction of 250,000,000 miles in diameter of our nebulous Sun : so nearly does the actual velocity of Uranus agree with its velocity as due to the force of gravity." Ennis thinks that the " long-drawn-out arms " of the primitive nebulous clouds would as they fell " come down obliquely, and these oblique falls would lead to rotation." At first there would only be a rotation on the surface of the nebulous mass, but " The amount of rotation would be continually increasing, on account of the continual contraction of the nebulous globe. The contraction of the globe would increase the amount and velocity of rotation in this way : Every particle of a globe, as it went forward, went also downwards towards the centre by contraction. They would 1 This is known as the " parabolic velocity." Plate I. Photograph, of the Spiral Kehula 51 Messier (in Canes Venatici). R.A. 13h. 2Sm., Dec. K 47° 45'. By Isaac Roberts, D.Sc, F.R.S. Exposure of 4 hours on April 29, 1889. (From the original photograph.) EVIDENCE FROM PHOTOGEAPHS. 23 all, therefore, take the direction of an inclined plane, and go down all the while faster and faster, according to the law of descent down an inclined plane." With reference to the planetary velocities and the velocity of the Sun's rotation on its axis he says : — " All nebulae, solar and planetary, rotated with constantly increasing velocities. Hence each planet and satellite has a greater velocity than its next outer neighbour. But after the parting of the last equatorial ring, then the Sun and also the planets began to rotate with decreasing velocities. Therefore the equatorial velocity of the Sun is now less than the orbital velocities of the planets, and the equatorial velocities of the planets are less than the orbital velocities of the inner satellites. The cause of this is found to be the principle of retardation." The Nebular Theory was of course purely an hypothesis, and was not originally supported by any facts derived from direct observation. Recent photographs of spiral nebulas, 1 and especially of the great nebula in Andromeda, are considered by many to afford strong evidence in favour of the correctness of Laplace's hypothesis. In the Andromeda nebula we seem to see nebulous rings in actual process of formation (see Frontispiece), rings apparently in rotation round a strongly condensed central nucleus, and which, in the course of ages, will probably condense into planets revolving round a central sun. Judging from its great apparent size, and its probably vast distance from the earth, the system formed from this nebula will evidently be one of gigantic dimensions, 2 but probably the general principle of the process would be the same for smaller systems. Referring to these photographs Mr. Herbert Spencer says : " Practically demonstrated as this process now is, we may 1 See Plate I. 2 See Journal oft/ie British Astronomical Association, vol. i., p. 483. 24 THE VISIBLE UNIVERSE. say that the doctrine of a nebular genesis passes from the region of hypothesis into the region of established truth." The Nebular Hypothesis is supposed by some to be opposed to revealed religion. But this is not the case. On the contrary, it should tend to exalt our ideas of the Creator. As Herbert Spencer says, " Creation by manufacture is a much lower thing than creation by evolution. A man can put together a machine ; but he cannot make a machine develop itself. That our harmonious universe once existed potentially as formless diffused matter, and has slowly grown into its present organized state, is a far more astonishing fact than would have been its formation after the artificial method vulgarly supposed. Those who hold it legitimate to argue from phenomena to noumena, may rightly contend that the Nebular Hypothesis implies a First Cause as much transcending ' the mechanical God of Paley,' as this does the fetish of a savage." a 1 Westminster Review, July 1858. M. CHAPTER II. m. fate's theory. FAYE'S views on the Nebular Hypothesis are con- -• tained in a very interesting work Sur VOrigine du Monde, the second edition of which was published in Paris in the year 1885. He first considers the account of the Creation as given in the Book of Genesis. He then reviews, in a series of chapters, the ideas entertained by the ancient writers, Plato, Aristotle, Cicero, Lucretius, Virgil, and Ovid, — views of course very vague, and now possessing merely an historical interest. In the third part of the work he discusses the views of Descartes, Newton, Kant, and Laplace. The theories of Kant and Laplace have been considered in the first chapter of the present volume. In the fourth part he gives a summary of our present knowledge of the nebulae and clusters, double, binary, and variable stars, and the Milky Way, with reference to which he says : " On trouvera que la Voie lactde offre plus d'analogie avec nn vaste anneau en train de se decomposer en lambeaux qu'avec une couche plate et homogene d'6toiles et de nebuleuses." 1 With this view I fully concur, and hope in the pages of this volume to adduce strong evidence in. favour of the truth of M. Faye's opinion. He then 1 Snr VOrigine du Monde, Second EditioD, p. 214. 25 26 THE VISIBLE UNIVEESE. considers the question of the Sun's constitution, and the source of its light and heat, a subject which will be discussed in a subsequent chapter. 1 In the thirteenth chapter of his work M. Faye proceeds to propound his views on the evolution of the Solar System from materials originally scattered through space. He points out that we cannot endow a sun — as (he states) Laplace did — with an unlimited supply of heat, the heat expended by any sun and the heat it still possesses depending upon its mass and volume. This is, of course, true, but it should be remembered that the great principle of the Conservation of Energy has only been discovered in recent years and was unknown in Laplace's time. M. Faye estimates that the white and yellowish stars constitute about 95 per cent, of the stellar hosts. He considers that the red and variable stars are suns on the eve of extinction, but this is a conclusion which is far from being established with certainty. He points out that the motions of the primitive nebula from which suns and systems were formed are indicated by the Sun's motion in space, and that the rotation of the original mass survives in the revolution of the binary stars round the centre of gravity of their components. The chief difficulty experienced in imagining the exist- ence of a primitive nebulous mass lies in the fact that the diffusion of matter through space seems opposed to the law of universal gravitation, a force which tends to con- centrate all matter into one mass. Neither Kant nor Laplace attempted to explain how the primitive nebula originated, and to overcome this difficulty the late Dr. 1 See Chapter on " The Fuel of the Sun." FAYE S THEOET. 27 Croll proposed his Impact Theory of Stellar Evolution, which will be considered in the next chapter. But admitting the existence of a primitive nebula, we still find a difficulty in understanding how such diverse forms as single stars, double, triple, and multiple stars, solar systems and globular clusters, could all have been formed by a single process of condensation from similar masses of nebulous matter. M. Faye proceeds to consider each of these cases separately. First, with reference to isolated single stars. Imagine a spherical homogeneous mass, without internal motions of any kind. The component molecules would gravitate towards the centre. The mass would consolidate regularly, preserving its homogeneity, and would eventually form an incandescent motionless sphere, without planets, satellites, or rotation on an axis. M. Faye considers, and I think correctly, that the heavens do not contain many examples of this species of star. If,- on the contrary, the original mass had internal motions, the result would probably be that portions of the nebulous matter would fall towards the centre, not in straight lines, but in concentric ellipses, revolving in equal periods round a common centre of gravity. Thus M. Faye thinks a globular cluster would be formed. He considers, however, that the most general case would be that of a primitive nebulous mass, not homogeneous, and animated with vortices which, according to circumstances, due to the mass and distribution of portions of different densities, would cause the formation of two, three, or more globes, revolving round their common centre of gravity. Thus would be formed binary, triple, and multiple stars. 28 THE VISIBLE UNIVEKSE. He gives what he calls a complete table of binary stars, but recent calculations have now more than doubled the number of binary systems included in his list. As an example of a multiple star he mentions 8 Orionis — the so- called " trapezium " of telescopists — but recent measures by Mr. Burnham show that there is no relative motion in the components of this group, and it would seem very doubtful that they really form a physical system. 1 We have perhaps a few examples of quadruple systems, but of multiple systems (of more than four stars) I do not know of a single well-established case. M. Faye then proceeds to a consideration of the formation of the Solar System. He points out that if Jupiter and Saturn were still in a state of incandescence, the Sun seen from a Centauri would appear as a triple star. This is quite true ; for if these large planets had the same intrinsic brightness as the Sun, the Sun would be about a hundred times — or five stellar magnitudes — brighter than Jupiter ; and as the Sun would shine as a star of the second magni- tude (or slightly brighter) as seen from a Centauri, Jupiter would be visible as a star of about the seventh magnitude, and Saturn slightly fainter. But it is very certain that with their present brightness these planets would be utterly invisible from a Centauri, even with the Lick telescope. Seen from the stars, therefore, our Sun would appear as a single star, and as such it must be considered when com- paring it with its neighbouring suns in space. 1 Mr. Furnham says : " A comparison of these measures with those made by Struve, Hall, and others show beyond question that the six principal stars are absolutely fixed with reference to each other, so far as any chano-e is concerned which could be detected by observations covering more than half a century."— Ast. Nach., No. 2930. THE SOLAR AND STELLAR SYSTEMS. 29 The Solar System differs also from the binary stars in the eccentricities of the planetary orbits, which, with the excep- tion of Mercury and some of the minor planets, are -very small, while the majority of the binary systems have orbits of large eccentricity. Although this difference is not of especial importance from a mechanical point of view, still, as the circle is merely a particular form of the ellipse, we should not expect the planetary orbits to approach, in so many cases, so closely to the circular form. M. Faye therefore considers that among the initial conditions of the primitive nebula we must seek for a cause which has prevented the planetary orbits from becoming elliptical, and has preserved them through all their changes in a nearly circular form. 1 There is an essential difference between Faye's hypo- thesis and that of Laplace. Laplace supposed the primitive nebula to have had a considerable central condensation before the planet-forming rings began to be detached from the parent mass, the central nucleus afterwards condensing into the Sun, as we now see it. M. Faye's nebula, on the contrary, is supposed to have been homogeneous, without any central condensation. He describes it as "Amas chaotique homogene, a peu pres spherique, au sein duquel regnent de lents mouvements tourbillonnaires affectant une partie seulement de la masse." M. Faye thinks that the first result of a slow movement of rotation in the original spherical homogeneous mass would be the formation of concentric rings in the interior of the nebula, rings rotating in a single mass in the manner of a solid body round a centre at first void. 2 .These rings 1 Sur VOrigine du Monde, pp. 263, 264. 2 Ibid p. 266. 30 THE VISIBLE UNIVEESE. would then break up into separate portions, which would eventually consolidate into a single mass, as in Laplace's hypothesis. "The other particles having velocities either very great or very small would move in the same plane, describing ellipses concentric with the ring. If these ellipses -are very elongated, the materials which compose them approach closely to the centre, where they would produce a progressive condensation." l . . . " They would thus form a central mass, to which would be added all the materials of the primitive vortices which are not arranged, in regular rings." 2 The molecules near the exterior of the ring would have a greater linear velocity than those on the interior, and the resulting planet would therefore have a rotation in the same direction as that of the ring from which it was formed. This, he thinks, would have occurred in the case of the planets nearer the Sun, 3 and at a time when the central force acted according to a law directly proportional to the distance from the centre. These planets, he thinks, would be formed first and before the central body had taken a regular form. On his view of the matter the earth was formed before the Sun, and — contrary to Laplace's hypo- thesis — the interior planets are older than Uranus and Neptune, which M. Faye supposes to have been formed from rings detached after the Sun had consolidated, and when the central force acted according to the law at present operating in the Solar System, namely, inversely as the square of the distance. In these outer rings the velocity of the external parts, would be less than at the interior of 1 Sur V Origins du Monde, p. 265. 2 Tbid., p. 268. s Namely Jupiter and all the planets within its orbit. EVIDENCE FEOM GEOLOGY. 31 the ring, and the resulting planet would, therefore, have a retrograde motion of rotation, or opposite to that of its revolution round the Sun. The satellites of these planets would also have a retrograde motion round their primary, as is found to be the case with the satellites of Uranus and Neptune. In the case of Uranus he thinks that at the time of its formation the law of force was in a state of transition, and that the conflict between the two forces, namely, the force acting directly as the distance, and that acting inversely as the square of the distance, produced the high inclination of the planes of the Uranian satellites. 1 At the birth of Neptune the second law of force had become predominant, and hence the inclination of its satellite's orbit plane is not so great. In the fourteenth chapter of his work M. Faye derives some support to his theory from geological considerations. He points out the discordance which exists between the long periods demanded by geology and biology, and the period indicated for the duration of the earth's existence by Laplace's hypothesis. 2 To reconcile this discrepancy, be considers it necessary to assume that the earth was formed before the Sun, and that it was consolidated from materials scattered through a space very much larger than its present dimensions. In its earliest ages the internal heat would have been sufficient, he thinks, to keep the surface waters warm, and even to partly evaporate them. He finds evidence in favour of this view in the existence of a tropical vegetation from the equator to the poles up to 1 Sur V Origins du Monde, p. 276, footnote. 2 See Chapter on "Stellar Evolution." 32 THE VISIBLE UNIVERSE. the middle of the Secondary Period, a flora which must have flourished for millions of years. To explain this early heat, Dr. Blandet has suggested that during the Primary Period the Sua had an apparent diameter of 47°, and that about this time the planet Venus was formed from the Sun's atmosphere. To this M. Faye replies that, according to Laplace's hypothesis, the planets were formed from an excessively rare atmosphere of the central mass, and not from the Sun's photosphere, as Dr. Blandet's theory implies. He further points out that with an apparent solar diameter of 47°, the necessary high temperature at the poles would be enormously increased in other regions of the earth's surface, so that a uniform temperature could not have existed. On M. Faye's hypo- thesis the earth's internal heat would, he thinks, have been — at the period in question — sufficient to keep the whole of its surface at a uniform temperature without the aid of a central sun. This he shows by calculation to be possible if we suppose the earth's crust to have been much thinner at that period than it is at present. Owing to the absence of a sun, the light at this period would be feeble ; but he points out that the ferns which swarmed at that epoch flourish best in shade, and so do the insects which are found fossil in the rocks of these formations. 1 Let us now consider the objections which have been raised against M. Faye's hypothesis. 1. With reference to the rings formed in the original nebula, M. Wolf points out that M. Faye does not explain satisfactorily how these rings were produced, or how large planets were formed from these rings, so that in this 1 Sur VOrigine du Monde, p. 287. ROTATION OF THE PLANETS. 33 particular M. Faye's theory is not more satisfactory than Laplace's original hypothesis. It might still be argued that the rings would probably break up into a number of small planets (see Chapter I.). 2. It has been shown in the preceding chapter that even on Laplace's hypothesis the rotation of a planet would be at first retrograde, but would afterwards become direct, owing to the strong tides produced by the central nucleus on the incipient planet. It would appear, therefore, that in M. Faye's system the direction of rotation of the interior planets — at first direct — should have been reversed by the action of the Sun when it had consolidated. To this M. Faye would perhaps reply that these planets had so far consolidated before the Sun was formed that tidal action would be inoperative. M. Wolf further considers that M. Faye's division of the planets into two groups, one with a direct and the other with a retrograde motion of rotation, is contrary to a natural classification of the planets. He thinks that, from a con- sideration of their volumes, masses, and densities, the planets of the Solar System are clearly divided into two groups of four planets each, the groups being separated by the zone of minor planets. 1 There appears to be consider- able force in this objection. The so-called "terrestrial planets " seem to form a group quite distinct from the larger or "giant planets." M. Faye thinks that comets had their origin in the Solar System itself, but M. Wolf considers that the small number of known periodic comets is in favour of Laplace's theory that these bodies were drawn into the planetary 1 Les Hypotheses Cosmogonigues, p. 72. 3 34 THE VISIBLE UNIVERSE. system, from outer space, by the force of the Sun's attraction. M. Wolf finally concludes that, although many of the objections which have been advanced against Laplace's hypothesis may also, with equal force, be urged against that of M. Faye, still the theory of the latter astronomer explains more satisfactorily how the earth has had suffi- cient time to pass through the long periods indicated by geology. M. Faye's theory does not, however, admit of a longer period than twenty to thirty millions of years, while geologists and biologists demand at least a hundred millions for the duration of geological time. This conflict between astronomy and geology will be further considered in the next chapter. CHAPTER III. STELLAR EVOLUTION. AN interesting work on this subject was published by the late Dr. Croll a short time before his decease. 1 Adopting Laplace's Nebular Hypothesis of the origin of the Solar System, Dr. Croll takes a step farther back in time, and proceeds to consider the probable origin of the sup- posed nebulous mass from which the planetary system was originally evolved. This nebulous mass he supposes to have been formed by the collision of two dark bodies, moving directly towards each other in space with a high velocity. A large proportion of the energy of motion thus arrested would of course be instantly converted into heat, which would be sufficient to transform into the gaseous state — at least on their surface — the broken fragments of the colliding bodies. We have a familiar example of motion thus con- verted into heat in the case of a bullet striking an iron target, the heat caused by the concussion being sufficient to raise the temperature of the bullet to a considerable degree. In this case, however, the target, being of so much greater mass than the bullet, absorbs most of the developed heat, and being at rest the amount of heat generated in the 1 Stellar Evolution and its Relations to Geological Time, 1889. 35 36 THE VISIBLE UNIVEESE. bullet is not so great as if it met another bullet moving in the opposite direction. The first thing which strikes us in considering Dr. Croll's theory is the enormous velocity assumed — 476 miles a second ! The greatest velocity we know of among the stars having large proper motions is that of Arcturus, which, according to a somewhat doubtful parallax, is speed- ing through space with the amazing velocity of 368 m iles a second ! and fi Cassiopeia, for which a minute parallax indicates a motion of 315 miles per second. The small star 1830 Groombridge — aptly termed by Professor Newcomb "a runaway star" — is, if the small parallax 1 found for it can be relied upon — moving with a velocity of 20 mil es_a second. This is the velocity at right angles to the line of sight. The star may of course have also a velocity in the line of sight, which would increase the above velocity. Since, however, the apparent proper motion of 1830 Groombridge is the maximum known to astronomers, we must look on Dr. Croll's assumed velocity as somewhat excessive. The bodies coming into collision are assumed by Dr. Croll to be dark bodies, but of the existence of such dark bodies we have of course no positive evidence. He objects to the Nebular Hypothesis that it "begins in the middle of a process " ; but the assumption of two dark bodies coming into collision leaves unexplained the origin of these bodies, and not alone the origin of their existence, but the origin of their rapid motion still remains a mystery. Dr. Croll, however, says: "The changes that now occur arose out of preceding changes, and these preceding changes out of changes still prior, and so on indefinitely back into the 1 About one-tenth of a second of arc. COLLISION OP DAEK BODIES. 37 unknown past. This chain of causation — this succession of change, of consequent and antecedent — could not in this manner have extended back to infinity, or else the present stage of the universe's evolution ought to have been reached infinite ages ago. The evolution of things must therefore have had a beginning in time ; " 1 evidently admitting the possibility of a creation a nihilo. Assuming, however, the enormous velocity adopted by Dr. Croll, let us consider what the result of his hypothesis would be. He finds that for two bodies " each one-half of the mass of the Sun, moving directly towards ,'each other," the result of the collision would be the development of an amount of heat which would satisfactorily account for the " present rate of the Sun's radiation " for a period of 50 millions of years. He computes that the gas developed at the moment of collision " would have a temperature of about 300,000,000 degrees " of the Centigrade thermometer, "or more than 140,000 times " that of the voltaic arc ! The first result of the collision would be the shattering of both bodies into a number of fragments, which by their subsequent collisions inter se would be reduced to smaller fragments, and these again, by the same process, into smaller fragments still, which, being acted on by the enor- mous heat of the generated gas, would gradually become gaseous also, so that " in the course of time the whole would assume the gaseous condition, and we should then have a perfect nebula— intensely hot, but not very luminous," occupying a space equal in volume to that of our Solar System. "As the temperature diminished, the nebulous mass would begin to condense, and ultimately, according 1 Stellar Evolution, p. 110. 38 THE VISIBLE UNIVEESE. to the well-known nebular hypothesis, pass through all the different phases of rings, planets, and satellites, into our solar system as it now exists." To this hypothesis Dr. Croll gives the name of the "Impact Theory," to distinguish it from the Nebular Theory on the one hand, and from the meteoric and all other gravitation theories on the other. With reference to the fragments produced by the sup- posed collision, Dr. Croll considers that it would be "highly improbable, if not impossible, that the whole of the fragments projected outwards with such velocity should be converted into the gaseous condition." Many of the smaller fragments would pass away into outer space, thus forming meteorites, which on this theory must be looked upon as "the offspring of sidereal masses, and not their parents, as Mr. Lockyer concludes." Comets also he con- siders to have had a similar origin. He admits, however, that some meteorites may have come from other systems. A necessary assumption of Dr. Croll's theory is that the stars should be moving in all directions with various velocities " in perfectly straight lines, and not in definite orbits of any kind." He says : " So far as observation has yet determined all these conditions seem to be fulfilled." But are we justified in assuming that the stars are moving in straight lines ? It is certainly true that the observed proper motions are apparently in a straight line, except in a few cases, like Sirius and Procyon, in the motion of which irregularities exist, the cause of which has only been partially explained. But should we therefore assume that the motion is really rectilinear ? The small arc described in the comparatively limited number of years during which THE RUNAWAY STAR. 39 observations of this kind have been made, leaves it, I think, an open question whether the motion is really in a straight line, or whether the short line of motion hitherto observed is merely the small arc of a gigantic orbit described round some, as yet unknown, centre of attraction In considering the motion of 1830 Groombridge, Dr. Croll assumes with Professor Newcomb "that the number of stars belonging to the universe amounts to IOOjOOC^OOQ, 1 and that these have on the average five times the mass of the Sun, and are spread out in a layer across which light requires 30,000 years to pass " ; 2 and Professor Newcomb concludes that " either the bodies which compose our universe are vastly more massive and numerous than telescopic examination seems to indicate, or 1830 Groom- bridge is a runaway star, flying on a boundless course through infinite space with such a momentum that the attraction of all the bodies in the universe can never stop it." In speaking of " all the bodies of the universe," Professor Newcomb of course refers to the visible stars ; but as Dr. Croll assumes it possible " that space is occupied by dark bodies far more numerous and massive than the luminous one which the telescope reveals," the motion of 1830 Groombridge may be, partly at least, due to the force of gravitation. As, however, Professor Newcomb computes that the total attractive power of the visible stars should be increased no less than sixty-four times to account for 1 Professor Young also assumes 100,000,000 as the number of stars in the visible universe. 2 If light suffers any extinction in the ether— as Strove, supposed— then the distance of the faintest stars would be less and the light journey less. 40 THE VISIBLE UNIVEESE. the apparent velocity, it seems probable that a portion at least of the observed motion is due to initial velocity as the " Impact Theory " requires. As examples of stars with large "proper motions," Dr. Croll mentions 1830 Groombridge, 61 Cygni, e Indi, Lalande 21,258, Lalande 21,185, fi Cassiopeise, and Arcturus. To these may be added Lacaille 9352, a Southern star, which, with a proper motion of nearly 7 seconds of arc per annum, stands next in order to 1830 Groombridge ; Gould 32,416, which has an annual motion of about 6 seconds ; and the triple star 40(0 2 ) Eridani, of which the proper motion is 4'07 seconds. Other stars with considerable proper motions are : a Centauri, Lacaille 8760, Piazzi II. 123, Groombridge 34, Struve 2398, and ,8 Hydri. As Professor Asaph Hall says, " Although the parallax of the star introduces considerable uncertainty " into the computed velocities, " yet we already know enough to be sure that these velocities are very great. Some of them are comparable to that of a comet in close proximity to our Sun. But in most cases there is no visible object near the one in motion to which we can ascribe an attractive force, acting according to the Newtonian law, which would produce the velocity observed unless we assume enormous masses." 1 Dr. Croll lays stress on "the enormous space occupied by nebulae." Some of these are certainly of vast pro- portions. The large planetary nebula in Ursa Major, known as "The Owl Nebula," has an apparent diameter which, if placed at the distance of the nearest fixed star, would imply a real diameter of about 200 times the Sun's 1 Gould's Astronomical Journal, No. 177 (1888, August 8th). DENSITIES OF THE PLANETS. 41 distance from the earth ! As its distance is, however, possibly far greater than that of a Centauri, its dimensions may be even still larger ! Dr. Huggins finds the spectrum gaseous. It is possibly a solar system in its nebulous stage. Dr. Croll derives some evidence in favour of his hypo- thesis from the relative densities of the planets composing the Solar System, the interior planets being the heaviest and the exterior the lightest. This is, however, only roughly true in a general way, for although Mercury is the heaviest planet of the Solar System, the lightest is not Neptune, but Saturn. In speaking of the satellites Dr. Croll falls into a serious error. He says : "The satel- lites of Jupiter, for example, have a density one-fifth of that of the planet, or about one twenty-fifth of that of the earth, showing that when the planet was rotating as a nebulous mass the more dense elements were in the central parts and the less dense at the outer rim, where the satellites were being formed." As a matter of fact, how- ever, the density of Jupiter's first satellite (that nearest to the planet) is only a little less than that of Jupiter, that of Satellite IV. (the exterior one) is about equal to the density of the planet, while the densities of Satellites II. and III. are actually greater. This is a very different state of affairs to that supposed by Dr. Croll, the lightest being actually the nearest to the planet and the heaviest next in order. According to Professor Lockyer the temperature of the original solar nebula was as high as that of the Sun at present. Dr. Croll, however, considers that "in some of its stages the nebula had a very much higher temperature than that now possessed by the Sun." This seems very 42 THE VISIBLE UNIVEESB. probable, for the cooling process which is now going on in the Sun has in all probability been in action since the planets solidified, or possibly from an earlier date ; so that whatever temperature we may at present assign to the Sun, we must consider it to have been at a consider- ably higher temperature, say, twenty millions of years ago. As Dr. Croll points out, it is impossible that hydrogen or carbon could exist in the gaseous state in the cold of stellar space, unless possessed of considerable heat ; and we know from the evidence of the spectroscope that hydrogen does exist in some of the gaseous nebulae — notably in the great nebula in Orion. The feeble light emitted by these gaseous nebulae is well accounted for by the fact that incandescent hydrogen, although possessing intense heat, has very little luminosity. Dr. Croll, how- ever, ascribes the faint light of the nebulae as chiefly due to the enormous space occupied by these bodies, and computes that their density does not probably exceed toy 4V1F0) " that of hydrogen at ordinary temperature and pressure " (see Appendix, Note A). The quantity therefore of light would be very small, " resembling very much the electric light in a vacuum tube." Dr. Croll considers that the phenomenon of Temporary Stars, such as those of 1572, 1604, and 1876, is due to the collision of a star with one of the dark bodies, or with a swarm of meteorites. The continuance of visibility was, however, of varying duration in the recorded examples of these wonderful objects; those ofl572 and 1604 remain- ing bright for over a year, while the maximum brilliancy of those of 1866 and 1876 was only sustained for a few days or probably hours. His theory will also have to TEMPOEAEY STABS. 43 account for the remarkable fact noted by .Sir John Herschel, " that all stars of this kind on record, of which the places are distinctly indicated, have occurred, without exception, in or close upon the borders of the Milky Way, and that ODly within the following semicircle, the preceding having offered no examples of the kind." Since this was written, however, a notable exception to the rule occurred in the case of the temporary star of 1866, which so suddenly blazed out in Corona Borealis on the evening of May 12th of that year. But this star is itself an exception to the general rule, as it was not, correctly speaking, a new star, but an outburst of a small star previously known to astronomers. The temporary star of 1876, however, con- formed to Herschel's rule, as it appeared in the Milky Way, near p Cygni. 1 The fact of this star having appa- rently faded into a small planetary nebula seems in favour of Dr. CroU's hypothesis. Star clusters are explained by Dr. Croll on the supposi- tion that in some cases the fragments resulting from the collision would be so " widely distributed through space " as to "prevent a nebula condensing into a single mass." The separate fragments would ''gradually condense into separate stars, which would finally assume the conditions of a cluster." I presume that Dr. Croll refers more espe- cially to the " globular " clusters than to those in which the components are more widely scattered, and certainly a satisfactory theory of the origin of these wonderful " balls of stars " is a desideratum in sidereal astronomy. Sir William Thomson's conclusion that twelve millions 1 The " new star " in Auriga of 1892 also appeared in the Milky Way, hut in the preceding semicircle, contrary to Herschel's rule. 44 THE VISIBLE UNIVERSE. of years is the maximum period which can be allowed on the gravitation theory for the duration of the Sun's heat in past time, 1 and the apparent inadequacy of this period to meet the views of geologists as to the duration of life on the earth, also seems in favour of Dr. Croll's theory. It is objected, however, by Professor Kirkwood 2 that even if we admit that the Solar System originated in the col- lision, 800 millions of years ago, of two cold opaque bodies approaching each other in the same straight line with a velocity of 1700 miles per second, we must consider that only a portion of this period is represented by geo- logical time. For, after the collision, ages must have elapsed before the planets had separated from, the parent mass, and had sufficiently consolidated and cooled down to commence their geological history. When, however, the heated planet had cooled down to a temperature low enough to admit of the formation of an outer crust, its development into a life-bearing world would then be com- paratively rapid. For Sir William Thomson has shown 3 that the internal heat could have no appreciable effect upon the temperature of the earth's surface 10,000 years after the formation of a definite crust. This follows from the fact that the heat-conducting power of the igneous rocks is very small. An illustration of this may be observed in lava recently ejected from a volcano, which may be walked on without danger, while a few feet below its surface it still remains in the molten state. Trowbridge thinks that were the temperature of the Sun's surface " twice its present intensity the solar atmo- 1 Good Words, April 1887. 2 The Observatory, April 1878. 3 Philosophical Magazine, January 1863. GEOLOGICAL CONSIDEEATIONS. 45 sphere would be expanded beyond the earth's orbit." Under these conditions all forms of life would of course be impossible on the surface of our globe. If therefore Trowbridge's result be correct, it would follow that the shrinkage of the Sun's mass from the diameter of the earth's orbit to its present size must have taken millions of years. Professor Kirkwood is disposed to believe it more pro- bable " that in former ages the stratification of the earth's crUst proceeded more rapidly than at present." Geologists of the uniformitarian school do not seem willing to admit this hypothesis, and a short account of the evidence adduced by Dr. Croll as to the probable duration of geological time — a subject on which he was a well-known authority — may prove of interest to those of my readers who, like myself, take an interest in geological science. Dr. Croll considers that the attempt " to compress the geological history of our globe into the narrow space allotted by the physicist is hopeless, as well as injurious to geological science." He proceeds to obtain " an accurate measure of absolute geological time" by a consideration of the result of subaerial denudation, and the method he adopts to ascertain the amount of this denudation is by an estimate of the quantity of sediment annually carried down to the sea by the great river systems. From a number of rivers on which experiments in this direction have been made he selects the Mississippi, as draining a country " which may be regarded as in every way resembling the average condition of the earth's surface." and from experiments made by Messrs. Humphreys and Abbott on the amount of sediment annually carried down to the sea by this river he 46 THE VISIBLE UNIVERSE. arrives at the conclusion that one foot in 6000 years may " be safely taken as the average rate of denudation of the whole surface of the globe." As, however, the area of the earth's water surface is three times that of the land this amount would be equivalent to a layer of three inches thick spread over the whole globe. Assuming, then, that the average rate of denudation in past geological ages did not materially differ from what it is at present, and that the total quantity of stratified rock would, if uniformly spread over the whole globe, form a layer 1000 feet in thickness, we have a total period of 1000 multiplied by 6000, multiplied by 4, or 24 millions of years. This, however, represents only the time necessary to deposit the rocks which have been formed by denuda- tion from older rocks, and these again from rocks of still greater antiquity. Assuming that the existing stratified rocks have thus passed three times through denudation and deposition, we have a period of 72 million years. Dr. Haughton, calculating from the observed thickness of rocks down to the Miocene Tertiary, and assuming a period of 8616 years for each foot deposited on the ocean bed, finds for the age of the stratified rocks a period of 1,526,750,000 years ! Assuming the rate of denudation, however, at ten times greater in ancient times than at present, and adding one-third for the period since the Miocene Tertiary, he arrives at a final result of 200 millions of years ! Dr. Croll doubts the validity of Dr. Haughton's assumptions, especially the total thickness of rock he assumes, viz., 177,200 feet, or over 33 miles. Mr. A. Ii. Wallace, adopting Dr. Haughton's thickness, but assuming the sediment to be deposited along a belt of EVIDENCE FROM GEOLOGY. 47 thirty miles wide round the whole coast line of the globe, finds with an assumed denudation of one foot in 3000 years, a period of 28 million years. This, however, on Dr. Croll's assumption of re-formation and denudation repeated several times, would represent merely a fraction of the time required. Dr. Croll further shows, from the evidence of remarkable faults in various parts of the world, with downthrows varying from 3000 to 20,000 feet, the enormous amount of solid rock which must have been denuded off the surface of the earth during the progress of geological history. He estimates that three miles of rock have been removed since the beginning of the Old Red Sandstone. This would indicate a period of 45 millions of years. Assuming that the period before the Old Red Sandstone was equally long we have 90 millions of years as the " minimum duration of geological time." These enormous periods of time do not, however, seem to satisfy the demands of biologists and the supporters of the Darwinian theory. Judging "from the fact that almost the whole of the Tertiary period has been required to convert the ancestral Orohippus into the true horse," Professor Huxley believes- " that in order to have time for the much greater change of the ancestral ungulata into the two great odd-toed and even-toed divisions (of which change there is no trace even among the earliest Eocene mammals) we should require a larger portion, if not the whole of the Mesozoic or Secondary period," and still longer periods are demanded for the evolution of other animals, " so that on the lowest estimate we must place the origin of the mammalia very far back in Palaeozoic 48 THE VISIBLE UNIVERSE. times." Mr. Wallace speaks of possible periods of 200 and even 500 millions of years ! To account for the existence of the solar heat during these vast aeons of time it would he necessary to increase Dr. Croll's original assumption of a velocity of 476 miles per second very considerably ! Astronomers will not of course deny the mathematical accuracy of Dr. Croll's conclusions, but they consider such enormous velocities as improbable, and the collisions them- selves equally so. Without the aid of such collisions physicists will not admit that the Sun's life history can be extended backwards beyond a limited number of millions of years. The evidence afforded by geology seems to require a much longer period ; biologists and evolutionists demand still more, and hence has arisen a scientific conflict which at present — unless we accept Dr. Croll's theory — there seems no hope of bringing to a satisfactory conclusion. Further evidence in support of his theory is drawn by Dr. Croll from chemical considerations respecting the constitution of matter and the ether of space. These will be referred to in a subsequent chapter. CHAPTER IV. THE FUEL OF THE SUN. THE dazzling brilliancy of the Sun far exceeds all artificial sources of illumination. It has been shown experiment- ally that, compared with a standard candle placed at a distance of one metre from the eye, the Sun's light is equal in quantity to 1575 billions of billions of such candles ! (1575 followed by 24 cyphers). The intensity of the solar lights— or the amount of light per square inch of surface —is found to be 90,000 times greater than that of a candle^ and 150 times as bright as the lime light ! The blackest portion of a Sun spot exceeds the lime light in intensity, and even the electric arc when placed between the Sun's disc and the eye appears as a black spot ! l The question has often been asked, What is the fuel of the Sun ? What is the origin of the vast amount of heat and light which is constantly being radiated by our central luminary into surrounding space ? The question is a difficult one to answer if looked at in the light of actual combustion. The amount of fuel necessary to produce the observed effects is so enormous that it seems almost impossible to imagine where the fuel could come from. 1 Young's General Astronomy, pp. 212-li. 50 THE VISIBLE UNIVERSE. Sir William Thomson has calculated that the quantity of fuel required for each square yard of the solar surface would be no less than 13,500 pounds of coal per hour ! equivalent to the work of an engine of 63,000 horse-power. This enormous expenditure of fuel would be sufficient to melt a thickness of about 40 feet of ice per minute at the Sun's surface. Sir John Herschel says : " Supposing a cylinder of ice 45 miles in diameter to be continually darted into the San with the velocity of light, and that the water produced by its fusion were continually carried off, the heat now given off constantly by radiation would then be wholly expended in its liquefaction, on the one hand, so as to leave no radiant surplus ; while on the other the actual temperature at its surface would undergo no diminution." 1 He also says 2 the ordinary expenditure of heat by the Sun per minute would suffice to melt a cylinder of ice 184 feet in diameter and in length extending from that luminary to a Centauri ! As to the actual temperature of the Sun's surface very various estimates have been made by different computers. Secchi supposed it to be about 10,000,000 degrees of the Centigrade thermometer, and Sporer 37,000 degrees of the same scale, while M. Pouillet thinks that it lies between 1461 and 1761 degrees Centigrade. M. Becquerel, Pro- fessor Langley, and Sir William Thomson consider that the temperature of the solar photosphere cannot exceed 3000 degrees Centigrade. According to M. Sainte-Claire- Deville the temperature is somewhere about 2500 to 2800 degrees, and this agrees with subsequent experiments by 1 Outlines of Astronomy, Tenth Edition, p. 258. 2 Cape Observations, p. 446. THE FUEL OF THE SUN. 51 Bunsen and Debray. Sir Robert Ball says that " we shall probably be well within the truth if we state the effective temperature of the Sun to be about 18,000° Fahrenheit." * Secchi's estimate is probably very excessive and the smaller determinations nearer the truth. The actual heat of the Sun must, however, be very great. Professor Young says 2 : " When heat is concentrated by a burning glass, the temperature at the focus cannot rise above that of the source of heat, the effect of the lens being simply to move the object at the focus virtually towards the Sun ; so that if we neglect the loss of heat by transmission through the glass, the temperature at the focus should be the same as that of a point placed at such a distance from the Sun that the solar disc would seem just as large as the lens itself viewed from its own focus. The most powerful lens yet constructed thus virtually trans- ports an object at its focus to within aboutJaEa^unclied and fifty thousand miles of the Sun^s_^urfac^jj;ndjn_this focus the most refractory substances — platinum, fire-clay, the diamond itself — are either instantly melted or dissipated in vapour. There can be no doubt that if the Sun were to come as near us as the Moon, the solid earth would melt like wax." Messrs. Trowbridge and Hutchins consider that in the solar atmosphere where carbon is volatilised, the tempera- ture is about equal to that of the voltaic arc. It may be shown that were the Sun's mass composed of coal it. would all be consumed in about 6000 years. It has been suggested that the solar heat may be maintained by the fall of meteors on fits surface. A pound of coal 1 The Story of the Heavens, p. 495. ■ The Sim, p. 267. 52 THE VISIBLE UNIVERSE. falling on the Sun from an indefinite distance would develop by concussion 6000 times the heat that would be produced by its combustion. But the enormous quan- tity of meteors required for the purpose — about 3800 lb. per square foot per annum — renders this theory very im- probable. If the earth were to fall into the Sun, it would maintain its heat for a period of less than a hundred years. Jupiter falling into the Sun would supply its present expenditure for 32,000 years to come ; but, in view of the millions of years indicated by geological records, even this period must be considered as comparatively short. Another objection to this theory is that the quantity of matter required would, in the course of ages, add appre- ciably to the Sun's mass, and this increase of mass would derange the motions of the planetary system. The meteoric theory of the Sun's heat must therefore be abandoned. The theory now generally accepted by astronomers is that advanced by the eminent German physicist Hejmholtz, which ascribes the. heat of the Sun to the shrinkage of its mass caused by gravitation. It may be shown mathe- matically that this .shrinkage would undoubtedly produce the observed effect ; and as gravitati on mu st inevitably act on the component particles of the Sun's mass, it seems quite unnecessary to look further for a satisfactory theory. The amount of shrinkage required to account for the present solar radiation is so small that the diminution in the Sun's apparent diameter could not be detected by the most refined instruments of measurement. Sir William Thomson has shown that .this shrinkage would amount to only thirty-five metres 'on the radius per annum, or one ten-thousandth of its length in 2000 years, a quantity THE FUEL OF THE SUtf. 53 quite inappreciable. It would take over 10,000 years to reduce the Sun's diameter by one second of arc. According to Helmholtz's theory the Sun's heat was originally generated by the collision of two masses, as in Dr. Croll's theory, but differing from that theory in the supposition that the bodies approached each other under the effects of gravitation alone and not with any initial velocity. In some books it is " paradoxically stated " that the Sun is actually becoming hotter owing to condensation, but this is quite incorrect. As Sir William Thomson points out, " cooling and condensation go on together." In fact, as the Sun has been gradually losing heat for ages past, the amount of heat lost by radiation must be in .excess of that gained by shrinkage, and as this process is probably still in progress the Sun must be actually cooling down. Of course this cooling process is excessively slow, so slow, indeed, that one estimate makes the maximum loss not more than 1° Centigrade in seven years. According to Sir William Thomson, if the Sun's heat could be maintained by shrinkage until 20 million times the present annual expenditure is radiated away, the Sun's diameter would be reduced to one-half what it is at present, and its density would be increased to about 1 1*2, or about the specific gravity of lead. This would probably put a stop to all further shrinkage "through overcrowding of the molecules." Supposing the Sun to have been radiating out heat for the past 15 million years, the solar radius "must have been four times as great as at present." Sir William Thomson is not disposed to admit much more than 12 million years as the past duration of the Sun's history ; 54 THE VISIBLE UNIVERSE. but, as has been shown in the preceding chapter, this- period, immense as it is, will not satisfy the demands of geologists. To meet this difficulty Dr. Croll has advanced his "Impact Theory," which has been already considered. (Chapter III.) A necessary detail of Helmholtz's theory is that the Sun must be in a fluid state from its surface to its centre. Were this not so it would soon grow dark, " as the conduct- ing power of no known solid would suffice to maintain the incandescence." The idea of a sj)lidjiucleus enclosed in a fiery envelope must therefore be abandoned and consigned to the limbo of all such uncritical theories. Sir "William Thomson thus describes the action which would probably take place during the formation of the Sun according to the gravitation theory * : " Think of two solid globes each of the same mean density as the earth and of half the Sun's diameter, given at rest, or nearly at rest, at a -distance asunder equal to twice the earth's distance from the Sun. They will fall together and collide in exactly half a year. The collision will last for about half an hour, in the course of which they will be transformed into a violently agitated incandescent fluid mass flying outwards from the line of motion before the collision, and swelling to a bulk several times greater than the sum of the original bulks of the two globes. How far the fluid mass will fly out all round from the line of collision it is impossible to say. The motion is too complicated to be fully investigated by any known mathematical method. A mathematician with sufficient patience might, however, approximate to the truth. After a series of oscillations it will subside, 1 Good Words, April 1887. THE FUEL OF THE SUN. 55 probably in the course of 2 or 3 years, into the globular star of about the same dimensions, heat, and brightness as our present Sun, but differing from him in this, that it would have no rotation. " If, however, each had a transverse motion — in opposite directions — of 1-89 metre per second, the result would be a globe, like our Sun, rotating in 25 days. If the trans- verse velocity be anything more than 071 of a kilometre, they would escape collision, and would revolve in equal ellipses round the centre of inertia in a period of one year, just grazing one another's surfaces every time they came round to the nearest points of their orbits. If the initial transverse velocity be less than, but not much less than 071 of a kilometre per second, there will be a violent grazing collision and two bright suns, solid globes bathed in flaming fluid will come into existence in the course of a few hours, and will commence revolving round their common centre of inertia in long elliptic orbits in a period of little less than a year. Tidal interaction between them would diminish the eccentricity of their orbits, and, if continued long enough, would cause them to revolve in circular orbits round their centre of inertia with a distance between their surfaces equal to 6 - 44 diameters of each." The bearing of the latter portion- of Sir "William Thomson's remarks on the possible origin of binary stars will be obvious to the reader. The "violent grazing collisions " in a period of about a year seem also to suggest a possible explanation of the nature of some of the variable stars of which the periods of several do not differ much from 365 days. Indeed, this is the theory of variable stars advanced by Professor Lockyer in his " Meteoritic 56 THE VISIBLE UNIVERSE. Hypothesis," but in this theory the revolving masses are supposed to be swarms of meteorites and not solid bodies. The bright lines observed in some of the long-period variables when near a maximum of light indicate a great increase of heat, which may probably be due either to collisions of thousands of meteorites clashing together, or to solid bodies rendered incandescent by a "violent grazing collision." The discoveries which have been made respecting the chemical constitution of the Sun will be discussed .in a subsequent chapter. 1 1 See Chapter VII., " Celestial Chemistry." CHAPTER V. THE LUMINIFEROTJS ETHEK. rTIHE corpuscular, or emission, theory of light originally -L supported by eminent scientific men, even by Sir Isaac Newton himself, having been found incapable of explaining many optical phenomena, was abandoned, and the present generally accepted wave theory was substituted for it. This theory explains satisfactorily so many phenomena that, although possibly not a perfect theory, it has held its ground against numerous attacks which have been made on it from time to time. The theory that light is pro- pagated in waves evidently necessitates the hypothesis of a medium to transmit these waves through space. Some have suggested that this medium may perhaps consist of some kind of gaseous matter in a highly rarefied form ; but the great objection to this hypothesis is, that, however attenuated we may suppose such a gaseous medium to be, it would inevitably exercise a retarding influence on the motions of the planets round the Sun, which in the course of time could not fail to be detected by astronomical observations. We must therefore conclude that the lumini- ferous ether, as this hypothetical medium is called, cannot possibly consist of any form of matter with which we are familiar. 57 58 THE VISIBLE UNIVERSE. It may be asked, what, then, is the constitution of the ether ? This is a difficult question, and one which has not yet been satisfactorily answered. Sir John Herschel says : " Every phenomenon of light points strongly to the con- ception of a solid rather than a fluid constitution of the luminiferous ether, in_the_-&ejise../to none of its elementary molecules are to be supposed capable of interchanging places, or of bodily transfer to any measurable distance from their special and assigned localities in the universe." That the ether is not of the nature of solids, such as we know, is evident. It can therefore only be considered as a solid in the sense of the words which Sir John Herschel writes in italics in the above passage. As no terrestrial substance could possibly possess the property referred to without being an actual solid, it is clear that the ether cannot consist of matter in any form. In our ignorance of its real constitution we can only consider it as a perfect, or nearly perfect, fluid, possessing some of the properties of a solid. This may seem a rather paradoxical conception, but as all our experience of material substance is derived from matter in its various forms, we have no right to deny that a medium distinct from matter, and apparently possessing paradoxical properties, may exist in interstellar space. M. Hirn says that, " to explain a secular acceleration of 05" in the mean motion of the Moon, it would be sufficient if 1 kilogramme of gas were distributed over 975,000 cubic kilometres of space, a rarefaction one million times greater than that of a Crooke's vacuum of the millionth of an atmosphere. But the effect of the shock of the particles of this rarefied gas against a body like the Moon as it moved THE LUMINIFEEOUS ETHEE. 59 forward in its orbit would be to raise the gas to a tem- perature of 38,000° 0., and inconceivably attenuated as this interplanetary atmosphere would be the Moon would yet come into contact with 600 kilogrammes of it in each minute of time." 1 The effect of the earth's motion through such a gas would be that its atmosphere would be rapidly stripped off layer by layer. We may compare the elastic force of the ether, or its resistance to compression, with that of air by the following method, due to Sir John Herschel. The velocity of light is known to be about 186,400 miles per second. That of sound is about 1090 feet per second, but were there no heat given out by the compressing force of the sound-waves the velocity would be only 916 feet a second. As we cannot suppose any heat to be developed by compression in a perfect fluid like the ether, we must compare the smaller velocity of sound with the velocity of light. This makes the velocity of light about 1,074,525 times that of sound. Now from the theory of sound it follows that in media of different elasticities, but otherwise similarly constituted, these elasticities are to each other as the squares of the velocities of the waves which are propagated through them. It follows therefore that the elasticity of the ether exceeds that of air in the ratio of the square of 1,074,525 to 1, or about 1,154,600,000,000 times. This calculation is, however, based on the assumption that the ether and the air are similarly constituted. As, however, air is undoubtedly a form of matter and the ether is probably not, the two fluids cannot perhaps be properly compared. The above calculation will, however, show that 1 Nature, April 25th, 1889. 60 THE VISIBLE UNIVERSE. whatever the constitution of the ether may he its elastic force must be enormous. The fact that light has a finite and not an infinite velocity seems to imply that the ether is not an absolutely perfect fluid, and that it possesses some property which restricts the propagation of light to a limited, although enormous, velocity. Recent researches seem to show that electricity may be, like light and heat, merely "a mode of motion." If this be true, the question suggests itself, would the lumini- ferous ether also serve for the transmission of electricity, or is it necessary to imagine the existence of a separate electrical medium ? Now to fill the whole of interstellar space with different media, one for the propagation of light, another for the transmission of electricity, and perhaps a third for the conveyance of gravitative action, would be an hypothesis as improbable as it is certainly unphilosophical. Physicists have therefore sought for some evidence to show that the luminiferous ether may possibly act as a vehicle for electrical phenomena. Such evidence is fortunately forth- coming, and the results are very suggestive. Faraday found that when glass was subjected to the_ action of a powerful magnetic field it caused a rotation of the plane of polarisation of light, and a similar result was established for gases by the experiments of Kundt, Lippich, and Rontgen. An intimate relation between light and magnetism has been demonstrated by Dr. Kerr of Glasgow. Polishing the poles of an electro magnet, and examining with an analyser a beam of plane polarised light reflected from the polished surface, he found that when the pole is the positive one the plane of polarisation of the reflected beam is turned in the opposite direction to that of a beam THE LUMINIFE110DS ETHER. 61 reflected from the negative pole. Professor Fitzgerald has shown theoretically that Dr. Kerr's results are a necessary consequence of the reflection of light from a magnetic surface, so that observation and theory are here in perfect harmony. Dr. Kerr also finds that the property of elliptic polarisation is produced by a beam of light passed through a transparent insulator, like glass, when the insulator is under a powerful electrical strain. Some recent remarkable experiments made by Dr. Hertz have shown that an electric current may be reflected and refracted like a beam of light, and that the electro-magnetic and luminiferous disturbances are probably propagated in the same medium and with the' same velocity although with waves of different length. If the medium through which light is propagated be identical with that which conveys electrical action, we might expect that the velocity of transmission of each would be the same. This we find to be actually the case. Experiments show that the velocities in air are practically identical — each about 300 millions of metres, or 186,414 miles a second. For other media, through which light and electricity can both pass, we have for light the velocity inversely proportional to the refractive index of the medium (that of air being unity), and for electrical action the velocity proportional to the square root of the specific in- ductive capacity (also with reference to that of air). If therefore the velocities are the same, we should find the former quality equal to the latter (for waves of light of infinite period). Experiments do not, however, yield so close an agree- ment in this case, some media showing an identity of 62 THE VISIBLE UNIVEESE. the two values, wliile for others there is a discrepancy in the results, which, according to Clerk Maxwell, "is greater than can be accounted for by errors of observa- tion, and shows that our theories of the structure of bodies must be much improved before we can deduce the optical from the electrical properties." The observed dif- ference may, however, possibly be due to some modification in the density of the ether in the media experimented upon. Perhaps some time in the coming century science, with its advancing strides, may give to mankind some slight insight into the constitution of this incomprehensible fluid ; but at present we can only say with the Psalmist, " Such know- ledge is too wonderful and excellent for me : I cannot attain unto it " ; and to most of us this knowledge will never come till we find ourselves afloat at last on the " shoreless ocean of eternity." CHAPTEK VI. THE CONSTITUTION OF MATTEK. Tok ifibv Tveirkov oifieij iva> BvrjTocr aTriKakv^fe. 1 " Shall any gazer see with mortal eyes Or any searcher know by mortal mind ? Veil after veil will lilt — but there must be Veil upon veil behind." 2 Sir Edwin Arnold. THE question whether matter is continuous or homo- geneous in structure and i nfini tely divisible, or whether itjs composed of ultimate atoms of excessively small but defimte dimensions, is one which has exercised the minds of scientific men in all ages. The former theory was advanced by the ancient philosopher Anaxagoras, and was adopted in more recent times by Descartes, and it forms the foundation of Spinoza's philosophy. The latter hypo- thesis was proposed by Democritns and developed by Lucretius in ancient times, and it has been almost uni- versally adopted by modern physicists. The fact that all known bodies are more or less compressible has led to the conclusion that matter is really composed of ultimate indivisible atoms which, grouped together by " chemical 1 " My veil no mortal ever withdrew." An inscription in the temple of Athene Isis, at Sais on the Nile. 2 The Light of Asm, Book the Eighth. 63 64 THE VISIBLE UNIVERSE. affinity," form molecules, and that aggregations of myriads of these molecules constitute matter as we know it. Other properties of matter are also in favour of the atomic theory. Professor Clerk Maxwell says : " The theory that bodies apparently homogeneous and continuous are so in reality is in its extreme form a theory incapable of development. To explain the properties of any substance by this theory is impossible " ; * and it has been shown by Cauchy that, if matter were homogeneous and not molecular, there would be no dispersion of light through a glass prism. According to the molecular theory of matter, solid bodies are composed of an immense number of molecules all vibrating round a mean position. On the application of heat, which, as Professor Tyndall has shown, is merely " a mode of motion," the energy of the vibrating molecules is increased, and the solid gradually passes into the liquid state. A further rise of temperature increases the mole- cular motion to such an extent that the molecules separate from the others, and each follows its own path. The liquid then passes into the gaseous state, and the pressure of a gas against the surface of a vessel containing it — which is known to increase with the temperature if the volume is kept constant — is explained by the impact of the moving molecules on the bounding surfaces. i From a consideration of the motion of light in solids and liquids Cauchy found that the constituent atoms of matter 1 are so small that 400 m illions go to an inch. From j electrical experiments Sir "William Thomson calculated that the "ultimate particle" is about the TOO. millionth of an inch in diameter. From observations of gaseous pheno- 1 Encyclopedia Britannica, Ninth Edition, 1875, Article " Atom." THE SIZE OF ATOMS. 65 mena Clausius and Clerk Maxwell concluded that the size of the particle is the 500_millionth part of an inch. These different estimates are not very widely discordant, consider- ■ ing the extremely difficult character of the investigation. Taking a mean of the three results we may conclude that it would take 500 million atoms of ordinary matter placed in a line to measure an inch ! Sir William Thomson says : " Imagine a globe of water or glass as large as a football to be magnified up to the size of the earth, each constituent molecule being magnified in the same proportion. The magnified structure would be more coarse-grained than a heap of small shot, but probably less coarse-grained than a heap of footballs." * That the ultimate atoms of glass must be excessively small may be imagined from the fact " familiar to opticians, that fine rulings on glass whose distance apart is less than half of the wave length of light are readily resolv- able with optical distinctness by our modern microscopes, while the intimate texture of the glass is apparently as far removed from resolution as with the unarmed eye." Professor Tyndall says : " Thus does the eye of science pierce to what Newton called ' the most secret and noble works of Nature,' and make us at home amid the mysteries of a world lying in all probability vastly farther beyond the range of the microscope than the range of the microscope, at its maximum, lies beyond that of the unaided eye." The relative distance between two molecules of our atmosphere is probably about 50 times the diameter of a 1 Proceedings of the Royal Institution of Great Britain, Vol. X., Part II., p. 213. 5 66 THE VISIBLE UNIVEKSE. molecule. Lawn-tennis balls placed on a smooth surface at the angles of a series of equilateral triangles (touching each other), the sides of which are in length fifty times the diameter of a ball (about 10 feet), will represent these gaseous molecules ; and the length of the mean excursion of the vibrating molecules, a " free path " as it is called, would be about 3000 times the diameter of a ball, or 60 times the side of the equilateral triangle in the above illustration. With reference to the actual constitution of the ultimate particles of matter, Sir Isaac Newton supposed the atoms to be of a spherical shape and infinite hardness. Sap- porters of this hypothesis are still to be found, but Sir William Thomson says, " We are forbidden by the modern theory of the conservation of energy to assume anything short of perfect elasticity of the ultimate molecules of matter." That the atom is merely a centre of force, a mathematical point capable of displaying the forces of attraction and repulsion, was advocated by Boscovitch and Faraday ; but this seems a too purely metaphysical con- ception to satisfy the requirements of the physicist and mathematician. Probably the most philosophical theory hitherto pro- posed is that advanced by the eminent German physicist Helmholtz, who supposes the atom to be an excessively minute vortex-ring, originally formed by some rotational movement in the ether of space. Such rings would be indestructible, and they would possess the properties of perfectly elastic bodies. The hypothesis that the lumini- ferous ether is a perfect fluid — that is, homogeneous and not molecular in structure — differentiates it at once from THE " VOIITEX-RING THEOKY OF MATTEE. 67 ordinary matter which is supposed to consist of atoms of excessively small but definite dimensions. If we consider with Helmholtz that these atoms are vortex- rings produced by some Creative act in the ether, it will be seen at once that the two hypotheses are consistent with each other. According to Helmholtz's theory, when a vortex-ring is formed in a perfect fluid like the ether, it ceases to be ether, and becomes a particle of matter, which is indestructible as far as our experience goes. It can never be destroyed except by the same Creative power which first called it into being. Matter may, by the application of heat or cold or chemical action, be changed into apparently various forms — solid, liquid, or gaseous ; but it can never, by auy process with which we are acquainted, be annihilated, or resolved back into the ether from which it was originally evolved. Dr. Croll objects to the " vortex-ring " theory of matter that it violates the First Law of Motion. He argues that the so-called centrifugal force of the rotating atom necessi- tates the hypothesis of resistance from without to counter- balance it, but that the idea of resistance is inadmissible in a perfect fluid like the ether of space. He says : " If this fluid can offer no resistance to the passage of the atom as a whole, how then does it manage to offer such enormous resistance to the materials composing the atom, so as to continually deflect them from the straight path and com- pel them to move in a curve? The centrifugal force of these vortex-atoms must be enormous, for on it is assumed to depend the hardness or resistance of matter to pressure. Now the centripetal force which balances this centrifugal force must be equally enormous. If, then, this perfect 68 THE VISIBLE UNIVERSE. fluid outside the vortex-atom can exert this enormous force on the revolving material without being itself possessed of vortex-motion, there does not seem to be any necessity for vortex-motion in order to produce resistance. In short, how is the existence of the atom possible under the physical conditions assumed in the theory ? " x Here, however, there seems to be some misconception of the theory. Dr. Croll speaks of " the materials composing the atom," but, according to the vortex-ring theory, the ultimate atom is not composed of " materials " at all — if by "materials " matter is intended — -but simply of rotating portions of the ether (which is not matter), aggregations of numbers of such atoms constituting what we'know as matter. As to the ether offering no resistance to the passage of an atom through it, it must be remembered that resistance to motion in a fluid does not depend upon pressure, but upon friction, which by hypothesis does not exist in a perfect fluid. As, moreover, the vortex-atom has stood — ■ at least in the preliminary stages through which it has hitherto passed — the test of the powerful mathematical analysis applied to it by such giant intellects as Helmholtz and Thomson, it seems clear that Dr. Croll's objection, founded on the supposed " centrifugal force " in the vortex- atom, is more apparent than real. Professor Lodge says : " These whirling portions con- stitute what we call matter ; their motion gives them rigidity, and of them our bodies, and all other material bodies with which we are acquainted, are built up. One continuous substance filling all space, which can vibrate as light ; which can be sheared into positive and negative 1 Stellar Evolution, pp. 89, 90. ARE THE ELEMENTS ELEMENTARY ? 69 electricity, which in whirls constitutes matter, and which transmits by continuity, and not by impact, every action and reaction of which matter is capable,— this is the modern view of ether and its functions." x The Nebular Hypothesis assumes that the Solar System was evolved by condensation from a nebulous mass which originally extended beyond the orbit of Neptune. Its con- dition at that remote epoch of cosmical history is supposed to be represented by the gaseous nebulas, visible in the telescope. If this be so, if these masses of luminous gas represent solar systems in their initial stage, we are brought face to face with a great difficulty. The spectro- scope shows that these gaseous masses consist of simply hydrogen and another substance, which was for some time supposed to be nitrogen, but is now found not to be identical with that element. Indeed, in some cases the presence of a solitary bright line in the spectrum suggests that they are composed of a single element. Now the known elements of which terrestrial substances are composed exceed sixty in number, and of these more than a dozen have been identified by the spectroscope in the Sun. How then could all these have been produced out of a nebulous mass containing only one, two, or three elements ? No satisfactory reply to this question has ever been given. But the enigma would be solved could we assume that the known elements are really compound bodies and were originally evolved from one or more simple substances. Professor F. W. Clarke says : " It is plain that the nebular hypothesis would be doubled in importance, and ' Nature, February 1st, 1883, p. 330. 70 THE VISIBLE UNIVERSE. our views of the universe greatly expanded, if it could be shown that an evolution of complex from simple forms of matter accompanied the development of planets from the nebulas. Evolution could look for no grander triumph." Chemistry has not, however, succeeded in decomposing any of the known elements into simpler substances. Professor Lockyer's spectroscopic researches seem to show evidence in favour of the idea that some of the elements are actually dissociated in the intense heat of the solar photosphere, but his results have not been generally accepted by chemists and astronomers. At the meeting of the Vienna Academy of Sciences in December 1887 a paper was read by Professor Gruenwald, of Prague, in which he asserts his discovery of the com- pound nature of magnesium and carbon. I am not aware whether this supposed discovery has been confirmed or disproved. In the Astronomische Nachrichten, No. 2797, he also attempts to show that hydrogen is really a com- pound body composed of two elements, namely, " Coro- nium," which gives the 1474 K line of the solar corona, and " Helium," the unknown substance giving the line D 3 . This line D 3 is visible in the spectrum of the great nebula in Orion and some other nebulas. It has also been seen in the spectrum of the star P Cygni (" Nova" 1600), and in that of U Orionis, the so-called " Nova " of 1885. The hypothesis of the non-elementary character of the chemical elements seems to be looked upon with favour by some of our leading chemists and physicists, and possibly it may some day be discovered that they have all been evolved from one original simple substance, to which Mr. Crooks has given the provisional name of " Protyle." CHAPTER VII. CELESTIAL CHEMISTRY. SOON after the invention of the spectroscope and its application to the chemistry of terrestrial substances, an attempt was made to extend the investigation to the chemistry of the San and other celestial bodies. This attempt has met with complete success, and some account of the general results which have been arrived at in this field of scientific inquiry may prove of interest to the reader. When the Sun's light is examined with a spectroscope the resulting rainbow-tinted band of light is seen to be crossed transversely by a number of fine dark lines. These lines were first carefully observed by Fraunhofer in the year 1814, and are still known by the name of " Fraun- hofer's lines." Fraunhofer found that the dark line D in the yellow portion of the solar spectrum coincided exactly in position with the bright line D of the spectrum of sodium ; but it was not till 1859 that it was clearly demonstrated by Kirchhoff that the dark line D in the Sun's spectrum was due to the light of burning sodium shining through its own vapour. This remarkable and interesting discovery — the reversal of the bright spectrum lines of a chemical element due to absorption of light by the vapour of the same substance — laid the foundation of celestial chemistry, and 71 THE VISIBLE UNIVERSE. solved the problem of the chemical constitution of the heavenly bodies. The discovery thus made of sodium in the Sun was quickly followed by the detection of other chemical ele- ments in the solar spectrum. In the case of iron no less than 460 dark lines in the Sun's spectrum, corresponding exactly with 460 bright lines in the spectrum of incan- descent iron, have been observed and mapped by Kirchhoff and Angstrom ; and ThaMn has found 170 lines in the spectrum of the metal titanium coinciding with dark lines in the solar spectrum. The conclusion is therefore irre- sistible that the metals iron and titanium exist in the Sun's atmosphere. Kirchhoff says: "This coincidence must be produced by some cause ; and a cause can be assigned which affords a perfect explanation of the phenomenon. The observed phenomenon may be explained by the sup- position that the rays of light which form the solar spectrum have passed through the vapour of iron, and have suffered the absorption which the vapour of iron must exert." According to Professor Lockyer the following elements exist in the glowing envelope of our central luminary 1 : — Hydrogen. Zinc. Palladium. Sodium. Cobalt. Molybdenum. Calcium. A luminium. Indium. Magnesium. Copper. Lithium. Iron. Strontium. Rubidium. Manganese. Lead. Caesium. Titanium. Cadmium. Bismuth. Chromium. Cerium. Tin. Nickel. Uranium. Grlucinum. Barium. Potassium. Lanthanum. Vanadium. Yttrium or Erbium, 1 TJie Chemistry of the Sun, pp. 158 and 220. STELLAR SPECTEA. 73 Those printed in italics certainly exist in the Sun ; the others with more or less probability. To the above list Professor Rowland adds, from his own observations, silicon, carbon, scandium, zirconium, niobium, palladium, neodymium, germanium, rhodium, and silver ; but omits from his list uranium, indium, lithium, rubidium, cassium, and bismuth. He finds 2000 lines or more of iron in the solar spectrum, and 200 or more of carbon. The next step forward in celestial chemistry was made in the year 1862 and 1863 by Drs. Huggins and Miller, who attempted to determine the character of the spectra of some of the brighter stars. 1 This was a matter of no small difficulty, as the light of even the brightest star is so small that the necessary dispersion by the prism renders the dark lines of the stellar spectrum not only difficult to measure but even to see. The finest nights and a telescope of considerable light-grasping power are necessary in these delicate observations. Huggins and Miller were, however, successful in their efforts, and succeeded in observing the spectra of Sirius, Vega, Arcturus, Capella, Betelgeuse, Pollux, Castor, and some other stars. In the brighter stars they found the dark lines " as fine and as numerous as they are in the solar spectrum." All the spectra ob- served did not, however, agree with the Sun's spectrum, some of them differing in the detail of the dark lines visible. They found a marked difference in the spectra of the two stars Aldebaran (a Tauri) and Betelgeuse (a Ononis), the former of these stars giving a spectrum with 1 A few of the solar lines had been previously recognised by Fraunhofer and Donati in some of the brighter stars, but nothing very definite was published on the subject. /4 THE VISIBLE UNIVERSE. fine lines, very similar to that of the Sun, while the latter showed a spectrum with dark bands. 1 In the case of Sirius the lines of hydrogen appeared very broad and dark, indicating a different chemical constitution, or rather a different condition of the stellar photosphere. These results have been abundantly verified by subsequent observations, and the stars have been divided into types according to the character of their spectra. Secchi pro- posed four types of stellar spectra. The following is Vogel's classification, according to Lockyer 2 : — Class I. — Spectra in which the Metallic Lines are extremely Faint or entirely Invisible. The most refrangible parts, blue and violet, are very vivid. The stars are white. {a) Spectra in which the lines of hydrogen are very strong. (b) Spectra in which the lines of hydrogen are wanting. (c) Spectra in which the lines of hydrogen and D 3 are bright. Class II. — Spectra in which the Metallic Lines are Numerous and very Visible. The blue and violet are rela- tively weaker ; in the red part there are sometimes faint bands. The colour of the star is clear bluish-white to deep reddish-yellow. (a) Spectra with numerous metallic lines, especially in the yellow and green. The lines of hydrogen are generally strong, but never as strong as in the stars of Class I. In some stars they are invisible, and then faint bands are generally seen in the red formed by very close lines. 1 This difference in the spectra is the more remarkable as the two stars are very similar both in brightness and colour — at least to my eye. 2 27ie Meteoritic Hypothesis, p. 345. STELLAR SPECTRA. 75 (b) Spectra in which, besides dark lines and isolated bands, there are several bright lines. Class III. — Spectra in which, besides the Metallic Lines, there are numerous Dark Bands in all parts of the Spec- trum, and the Blue and Violet are remarkably Faint. The stars are orange or red. (a) The dark bands are fainter towards the red. (b) The bands are very wide, and the principal are fainter towards the violet. This subdivision of Secchi's Class III. is objected to by Lockyer and Pechiile, but this will be referred to further on. We will now consider each class separately. Class I. — The following bright stars show spectra of this type : Sirius, Vega, Begulus (a Leonis), Spica (a Virginia), Fomalhaut (a Piscis Australis), Castor, a Ophiuchi, a Coronae Borealis, /3, 7, h, e, £, and 97 Ursse Majoris, Algol (/3 Persei), and others. (a) This subdivision includes Sirius and Vega. The hydrogen lines in Sirius are remarkably strong and broad, and may be seen even with small optical means. I have seen them distinctly with a McClean's star spectroscope attached to a three-inch refractor. According to Lockyer's Meteoritic Hypothesis, stars in this sub-class are the hottest bodies in the universe. 1 It is worthy of notice that all the stars which have been found by the spectroscope to be close doubles, as Spica, f Ursss Majoris, and /3 Aurigas, belong to this class, and also the Algol variables, of which the spectra have been examined, viz., Algol, X Tauri, and U Monocerotis. (b) This subdivision includes the brighter stars in Orion, with the exception of a (Betelgeuse). 1 The Meteoritic Hypothesis, p. 374. 76 THE VISIBLE UNIVERSE. (c) Includes /3 Lyras, 7 Cassiopeiae, P (34) Lyrae, and some small stars. According to Lockyer's Meteoritic Hypo- thesis stars in this sub-class are increasing in temperature. 1 With reference to 34 Cygni, Lockyer says : " In addition to the hydrogen lines there is a bright line in P Cygni, the wave-length of which I have found to be about 447. This appears to be coincident with Lorenzoni's/of the chromo- sphere spectrum, and it is also seen in the spectrum of the nebula in Orion. In all three cases it is associated with the line D 3 ." 2 Glass II. — -The following bright stars show spectra of this type : Capella (a Aurigee), Arcturus (a Bootis), Aldebaran (a Tauri), Pollux (/3 Geminorum), a Cygni, a Hydras, 7 Leonis, a Serpentis, a Ursas Majoris, etc. (a) This subdivision includes stars with spectra similar to that of our Sun. The spectrum of Capella very closely resembles the solar spectrum ; but in others, as in Alde- baran and a Cygni, there are marked variations. (b) The variable star R Geminorum is an example of this sub-class. According to Lockyer stars in this sub-class are increasing in temperature. 3 Class III.— This class, which includes the banded or "columnar" spectra, 4 is divided into two sub-classes by Vogel, as above described. Secchi, however, restricted Class III. to stars of Vogel's sub-class (a), and placed the stars of sub-class (b) in another class, Class IV. Pechule and Lockyer defend Secchi's classification on the 1 The Meteoritic Hypottesis, p. 375. 2 Ibid., p. 409. s Ibid., p. 375. '' In addition to the " bands " characteristic oE this type of spectra photo- graphs reveal the presence of an underlying system of " lines " similar in general character to those of the solar spectrum. STELLAE SPECTEA. 77 ground that the spectra (a) and (b) are very dissimilar. Stellar spectra are known which are intermediate in character between Classes I. and II., and between II. and III., but no well-marked transition spectrum between Secchi's Classes III. and IV. has yet been observed. Ac- cording to Pechiile, " le IV. type representerait une phase bien distincte, la derniere peut-etre avant l'extinction total e." Vogel's sub-class (a) includes a Herculis, Betelgeuse (a Orionis), a Ceti, @ Pegasi, fi Cephei, % Cygni, U (" Nova ") Orionis, and numerous other stars, many of which are variable in light. In the spectra of Betelgeuse and /3 Pegasi the hydrogen lines are only obscurely visible. Vogel's sub-class (b) — equivalent to Secchi's Class IV. — includes 19 Piscium, U Hydrse, and others, some of which are also variable. This type is a comparatively rare one. It includes at present only 113 stars, accordiDg to Espin, down to magnitude 8 - 8. In the spectra of these stars the characteristic dark bands agree exactly in position with the bright bands of the hydrocarbon spectrum, such as are shown by burning alcohol. They have been called " carbon stars," and show no evidence of free hydrogen. Underlying the banded spectrum in both Classes III. and IV., another spectrum, with fine lines somewhat similar to the solar spectrum, has been observed. Lockyer thinks that " stars of Vogel's Class III. a are of a cometary character and a little more condensed than the bright-line stars." 1 According to his Meteoritic 1 Ihe Meteoritic Hypothesis, p. 361. Lockyer considers that these stars "cannot be masses of vapour like our Sun, bat they are unquestionably clouds of incandescent stones," p. 350. 78 THE VISIBLE UNIVERSE. Hypothesis, " stars of Class III. a are still increasing in temperature by the condensation due to gravity, while the red stars of Class III. b are at a nearly equal mean tempera- ture, but are cooling bodies." 1 Still greater difficulty is experienced in the observation of the spectra of those faint objects, 1 the nebulas. The extreme faintness of some of these is thus described by Dr. Huggins, who was the first to examine them with the spectroscope : " The light of some of those visible in a moderately large instrument has been estimated to vary from itbtt to -rshru °f the light of a single sperm candle consuming 158 grains of material per hour, viewed at a distance of a quarter of a mile ; that is, such a candle a quarter of a mile off is 20,000 times more brilliant than the nebula 1 ." Of 70 nebulas examined by Dr. Huggins about one-third showed a spectrum of one, two, three, or four lines, indicating a gaseous constitution. " The light of the nebulas and clusters become spread out by the prism into a spectrum which is apparently continuous." One of the bright lines visible in the nebular spectra has been shown to be certainly due to hydrogen. 3 In his first observations Dr. Huggins was disposed to attribute another of the nebular lines to nitrogen, but recent careful measures have shown him that the line does not really coincide with a line of nitrogen, but is distinct from it. Lockyer considers that one of the bright lines in the spectrum of the great nebula in Orion coincides with 1 The Meteoritic Hypothesis, p. 376. 2 It has been shown experimentally that when the light of glowing hydrogen is reduced to a certain point, only one line, the blue line F, remains visible. The G line and other lines of hydrogen have, however, also been photographed in the spectrum of the Orion nebula by Dr. Huggins. THE NEBULAE SPECTRUM. 79 the edge of a magnesium fluting. Dr. Huggins, however, finds that such is not the case, but that the nebular line falls " within the termination of the magnesia band," 1 or towards the blue end of the spectrum. Dr. Huggins has arrived at the same result with the planetary nebula 2 5 , (G. C. 4234), and his observations on this nebula have been confirmed by Mr. Keeler at the Lick Observatory. The great nebula in Andromeda, although somewhat similar in appearance to the nebula in Orion, shows a totally different spectrum. Instead of bright lines we have here a continuous spectrum, but with the red end deficient. Although this nebula has never been resolved into stars, the evidence of the spectroscope shows that it is not gaseous. Observations recently made by Dr. and Mrs. Huggins have shown that the red end of the spectrum, although very faint, is distinctly visible when carefully looked for. Mrs. Huggins says that if an oil lamp is placed " at such a distance and in such a manner that its spectrum is photometrically equivalent to the nebula spec- trum, observed simultaneously with it, it will be seen that the lamp spectrum is cut off, as is the nebular spectrum." 2 Lockyer thinks that this great nebula con- sists of swarms of meteors, and that it is in a more con- densed state than the nebula in Orion. The difference in the colours of stars may, in some cases at least, be due to a difference in their chemical constitu- tion. For instance, in the beautiful double star Albireo (/3 Cygni) it has been found that in the spectrum of the orange-coloured component there are very few dark lines 1 Proceedings of the Royal Society, Vol. XLVIII., p. 203. 2 The Observatory, December 1890. 80 THE VISIBLE U^TIVEESE. in the orarjge portion of the spectrum, most of the lines beiDg confined to the blue and red. In the blue star, on the contrary, there are a great number of dark lines in the red and yellow and comparatively few in the blue : hence the blue light predominates. In this case, then, the differ- ence of colour is due to a real difference in physical constitution, and not merely to an effect of contrast. Further particulars respecting stellar t spectra will be found in the chapter on the Meteoritic Hypothesis (Chapter VIII.). CHAPTER VIII. THE METEOKITIC HYPOTHESIS. AN elaborate and interesting volume, containing a state- ment of the grounds on -which he has. based his meteoritic theory of the universe, was published by Pro- fessor Lockyer towards the close of the year 1890. 1 la this work the able and ingenious author has worked out his hypothesis in great detail ; and a review of the principal facts and arguments advanced by Lockyer and also by his opponents may prove of interest both to those who accept and those who reject his views. Professor Lockyer commences his work with an account of the falls of meteoric stones recorded in history. The earliest of these dates back so far as 1478 B.C., but of course with some uncertainty. Falls are noted by Plutarch in 705 B.C., and by Livy in 654 b.c. Other falls are re- corded at the river iEgospotamus, 468 B.C., and at Pessi- nuntia in Phrygia, 264 B.C. In the Chinese annals of Ma-tuan'-lin, Biot has found a record of sixteen falls between the years 644 B.C. and a.d. 333. Iu the year a.d. 1492, November 16th, a stone weighing 1 The Meteoritic Hypothesis. A Statement of the Results of a Spectro- scopic Inquiry into the Origin of Cosmical Systems (Macmillan & Co., 1890). 81 6 82 THE VISIBLE UNIVERSE. 260 lb. fell near the town of Ensischeim in Alsace. This stone is still preserved in the Town Hall. In 1622 a stone fell in Devonshire, and in 1628 another in Berkshire. On December 13th, 1795, a stone weighing 56 lb. fell about ten yards from a labourer working near Wold Cottage, Thwing, Yorkshire. The fall was accom- panied by a loud explosion. On April 26th, 1803, a large number of stones fell near l'Aigle, in the department of Orne, France. On September 10th, 1813, several stones were seen to fall between the lands of Scagh and the village of Adare (in the neighbourhood of Patrick's Well), in the county of Limerick, Ireland. One of them weighed 17 lb. Another weighing about 74 lb. fell at the same time in the lands of Brasky, about three miles distant from the others. On April 20th, 1876, a piece of iron weighing 7| lb. fell at Bowton, near Wellington, Shropshire. It detonated like the discharge of heavy artillery, and penetrated the ground to a depth of eighteen inches. On March 14th, 1881, a stone "weighing 3 lb. 8£ oz. was seen to fall by four persons near Middleborough, York- shire. It was accompanied by a whizzing or rushing noise in the air, and made a hole in the ground 11 inches deep. The stone was warm when felt at the bottom of the hole a few minutes after its descent." 1 On May 10th, 1879, a meteor exploded at Esterville, Emmet county, Iowa (U.S.A.), and fragments weighing 170 and 500 lb. fell to the earth. The latter was " dug up .' TJie Scenery of the Heavens, p. 137. To make the list of meteoric falls in Great Britain more complete I have added some falls not mentioned by Lockyer, METEORIC STONES. 83 from a depth of 14 feet in stiff clay soil." A chemical examination of the smaller mass showed the metallic portion to consist of an alloy of iron, nickel, and tin. 1 In 1885, near Mazapil, in Mexico, the appearance of a large fire-ball was followed by a loud explosion, and the fall of a number of stones. "About 800 lb. of stones, nearly two hundred in number, have been picked up in a region seven miles by four, a little east of the end of the meteor's path." Professor Lockyer says : , " The largest meteorites of which mention is made are those of Otumpa (province of Tucuman, South America), an iron weighing 30 tons ; of Durango (Mexico), 19 tons ; and of Cranbourne (Aus- tralia), now in the British Museum, which weighs over 3 tons. The Nejed iron, the largest which has been seen to fall, weighs nearly 130 lb." 2 The general form of meteorites is fragmentary, indicating that they are the fractured portions of larger masses, burst asunder by the force of the explosion which generally accompanies these phenomena. In the case of the meteorite which fell at Butsura in 1861, pieces picked up at places three or four miles asunder could be actually fitted to- gether to form the original mass ! Meteorites are usually covered by a black crust, clearly due to the intense heat developed by the mass in rushing through the earth's atmosphere with " planetary velocity," a velocity which, according to Lockyer, is sufficient to raise the air to a temperature of from 4000° to 6000° C. 3 The 1 American Journal, July 1879. 2 The Meteoritie Hypothesis, p. 20. 3 Ibid., p. 16. 84 THE VISIBLE UNIVEESE. highest recorded velocity of flight through the air is about 45 miles per second, or about double the orbital velocity of the planet Venus. Meteorites are, however, only fused on their surface. Before they enter the earth's atmosphere they have, of course, the temperature of interstellar space. If the meteorite be large and its fall to the earth rapid, this original low temperature may be retained in its interior for some time after it reaches the earth. It is recorded that one of the large fragments of the Dhurmsala (India) meteorite which fell in 1860 "was found in moist earth half an hour or so after its fall coated with ice." x According to Lockyer the chemical elements most com- monly found in meteorites are as follows :— Hydrogen Calcium Iron Aluminium Nickel Carbon Magnesium Oxygen Manganese Sulphur Cobalt Silicon Copper Phosphorus, and "the following less frequently, or in smaller quan- tities " : — Lithium Chromium Sodium Tin Potassium Arsenic Strontium Antimony Titanium Chlorine Nitrogen. Of these only hydrogen, nitrogen, and carbon occur in an elementary condition." 2 1 Young's General Astronomy, Article 765. 2 The Meteoritie Hypothesis, p. 23. COMPOSITION OF METEORITES. 85 " The absolute absence of free quartz " from meteorites is remarkable, as this is one of the most widely diffused minerals known in terrestrial rocks. On the other hand, many of the meteoritic compounds are unknown on earth. For instance, we have compounds of sulphur and iron, sulphur and calcium, sulphur with calcium and titanium, and sulphur with iron and chromium, which are " new to our mineralogy." Various alloys of nickel and iron are also found. Among the compounds common to meteorites and terres- trial rocks may be mentioned magnetic pyrites, magnetite, chromite, olivine, augite, anorthite, labradorite, etc. Of these olivine is one of the most usual substances met with in the "stones." In the "irons," iron, nickel, and magnesium are the principal constituents. Magnesium is also found in the " stones." Meteorites also include a quantity of occluded hydrogen in the " irons," and carbonic acid in the " stones." x The gases obtained from the Lenarto meteorite were found to contain about 85^ per cent, of hydrogen. In the " irons," or " siderites," the amount of iron varies from 80 to 98 per cent, and the nickel from 6 to 10 per cent. Sometimes, however, the nickel is found in much larger quantities ; in one case amounting to' " 59 per cent., while the iron was only 37 per cent." 2 From the presence of a mineral peculiar to meteorites, known as Daubreelite, Dr. Lawrence Smith "inferred a 1 This view has, however, been called in question by Mallet. The Meteor- itic Hypothesis, p. 27. 2 Tlie Meteoritic Hypothesis, p. 27. 86 THE VISIBLE TJNIVEESE. common origin for two meteorites which fell four years apart." 1 In his investigations on the spectra of metals found in meteorites Professor Lockyer made experiments at varying temperatures represented by the heat of the Bunsen burner, Oxy-coal-gas flame, Electric arc, Spark with jar, the first being the lowest and the last the highest temperature. In the case of magnesium he finds that of three well- known lines in the green part of the spectrum, known as b u b^ and b i} only two, b x and b 2 , are seen in the flame spectrum, in which another line, " the remnant of a fluting, appears at wave-length 5210, so as to form a triplet." A line in the blue also appears, and the fluting at 500. In the spark spectrum the line at " 5210 practically disappears and is replaced by b i} the wide triplet thus giving way to a narrower one, b x and b % being common to both." " At the same time the line in the blue disappears and gives places to two new ones." 2 Lockyer finds that at the temperature of the Bunsen burner (as ordinarily used) the fluting at 500 " far eclipses the other parts of the spectrum in brilliancy." It is on the identity of this fluting (or rather its brightest edge) with the chief line in the spectrum of the nebulfe that the meteoritic hypothesis mainly depends. The question of this identity, which has been disputed by Lockyer's opponents, will be considered further on. Lockyer finds that " in meteorites in which the quantity 1 The Meteoritic Hypothesis, p. 28. - Ih'ul ., p. 39. SPECTRA OF METEORITES. 87 of iron is very considerable it is always the manganese that makes itself visible first, because its volatility is greater than that of iron." 1 The observations made with the oxy-cbal-gas flame " gave in all about ten or a dozen lines belonging to the metals magnesium, iron, sodium, lithium, and potassium, and two flirtings, one of manganese and one of iron." In the spectra of meteorites raised to the tempera- ture of the electric arc the number of visible lines became so numerous that Lockyer had recourse to photography in order to register them. He says : — "A photograph of the spectrum of the Oberukirchen meteorite, taken in this way, shows no less than 378 lines, of which 348 are due to iron. . . . Besides the iron lines the photograph also shows 16 lines of nickel, 3 of chromium, 1 of cobalt, 4 of manganese, 2 of titanium, and 4 unknown lines. It is also worth noting that this particular meteorite shows practically no sodium, although the nickel line, between the two D lines, is pretty bright." 2 The spectra of meteorites at the temperature of the "quantity spark" without Leyden jar show "in all about twenty lines belonging to the metals magnesium, sodium, iron, strontium, barium, calcium, chromium, zinc, bismuth, and nickel, and four lines of unknown origin." 3 At the temperature of the jar spark " a very great number of lines is visible." Lockyer, however, considers that, for the purpose of his inquiry, these high-temperature spectra are not of so much importance as those at low temperatures. Most of Lockyer's experiments were made on " undoubted meteorites," fragments of which were obtained from the British Museum. 1 The Meteoritic Hypotliesis, p. 53. ' Ibid., p. 55. 3 Ibid., p. 58. 88 THE VISIBLE UNIVERSE. Lockyer's general conclusions with reference to these experiments are : — (1) " That only the lowest temperature lines of Magnesium, Sodium, Iron, Chromium, MaDganese, Strontium, Calcium, Barium, Potassium, Lead, Bismuth, and Nickel are seen in the meteorites under the various conditions. They are not all visible in one meteorite or under one particular condition. (2) "That in the case of Magnesium the line most frequently seen is the remnant of the fluting at 500, while in a photograph the main ultra-violet line recorded is the one at 373, previously recorded under those conditions by Messrs. Liveing and Dewar. In the quantity spark other lines are seen, notably b lt b 2 , b 4 , and 521. The line at 500 was considerably brightened when the number of cells was reduced, thus showing it to be due to some molecule which can exist best at a low temperature. (3) " That in the case of Manganese the only line visible at the temperature of the Bunsen burner, 5395, is the only line seen in the meteorites, with the exception of one in the violet at 403. (4) " That the lines of iron seen in the meteorites are those which are brightest, when wire gauze is burned in the flame ; chief among these lines are 579, 5268, 4383, and 6024." Professor Lockyer then proceeds to show the identity of origin of luminous meteors and falling stars with meteorites. With reference to the light emitted by shooting stars, which are probably very small bodies, " Professor Herschel has calculated that a single grain moving at the rate of 30 miles a second represents a dynamical energy of 55,675 foot pounds." A large portion of this energy is of course converted into light and heat. The spectra of meteors and shooting stars show the sodium line, and the bright b line of magnesium, and, according to Konkoly, the lines of marsh gas. It appears from the observations of Professors Herschel, Newton, and Secchi that shooting stars first become visible at an average THE SPECTRUM OF THE AURORA. 89 height of 72 - 7 miles, and disappear at a height of 51-5 miles. 1 Discussing the observations of the aurora and its spec- trum, Lockyer attempts to prove that the phenomenon is due to meteoric dust in the " higher reaches " of the atmo- sphere. He identifies the characteristic line of the aurora — frequently the only line visible — with "the remnant of the brightest manganese fluting at 558." After considering the probable identity of other lines seen by different observers in the auroral spectrum he says : — " I think it will be granted that, after what has preceded, there is strong evidence of an intimate relation between the spectrum of the aurora and the spectra of meteorites, which leads to the conclusion that the upper reaches of the atmosphere contain particles of mag- nesium, manganese, iron, and carbon." 2 The objections which have been advanced against this conclusion will be considered further on. Lockyer shows that traces of meteoritic dust are visible in oceanic deposits dredged up by the Challenger Expedi- tion. In some very interesting chapters on meteors and meteoric showers, Lockyer discusses their relation to comets, a relation which has been chiefly established by the researches of Professors Herschel, Newton, and Schiaparelli. He says : " We must picture a comet as a loose, transparent, illuminated, free-moving swarm of small solid granules suspended in empty space," 3 and " that the head of a comet is merely the denser part of the swarm." " 1 The Meteoritic Hypotliesis, p. 67. 3 Ibid., p. Hi. 1 Ibid., p. 97. " Hid., p. 146. 90 THE VISIBLE UNIVERSE. Having described the appearances presented by comets at different distances from the Sun, Lockyer discusses the theories which have been advanced to account for the phenomenon of the tail. It appears that Kepler was the first to suggest that the tail was due to an impulsive force resident in the Sun, an hypothesis which was accepted by Newton, Euler, and Laplace. Olbers considered that the repulsion was due to electrical action, and this theory, adopted by Roche and Bredechin, seems to be now almost universally received. M. Roche determined mathematically " the surface on which the gravity of a small particle was nil in consequence of the solar and cometary attractions. This is called the limiting surface." 1 "The limiting surfaces which Roche's calculations require are so very like some of the surfaces actually observed in the head of a comet, where they can be best seen, that it is suggested that the movement of the particles takes place in the precise direction where they would flow according to M. Roche's mathematical investigations. 2 . . . M. Roche there- fore considers the existence of a repulsive force which counterbalances solar attraction established by his researches." 3 Bredechin divides the tails of comets into three distinct types. In the first type the tails are long and straight- like that of the great comet of 1861. In these he computes that the small particles composing the tail are shot out from the nucleus with a velocity of about 14,000 or 15,000 feet per second. In the second type the velocity is about 3000 feet a second. In this case the forces of attraction and repulsion are nearly balanced, and the tail is plumy 1 The Meteoritic Hypothesis, p. 160. 2 Ibid., p. 163. 3 Ibid., p. 164. THE SPECTKA OF COMETS. 91 and gently curved. In the third type the velocity of repul- sion falls to only 1000 feet per second. The tails are short and strongly curved, and the repulsive force is only about one-fifth of the Sun's attractive force. Bredechin thinks that tails of the first type are probably composed of hydrogen, those of the second of hydrocarbons, and those of the third type of the vapour of iron and heavier metals. Lockyer then proceeds to discuss the character of the spectra shown by comets at different distances from the Sun. He says : — "In the comets of 1866 and 1867 when they were observed away from the Sun, only one line was seen near wave-length at 500. . . . It is probable also that one of the bands mentioned by Konkoly in his observations on the Great Comet (6) 1882 (date of periastron passage 17th September) on the 1st November was this same line which lies at or near the position of the low temperature fluting of magnesium at 500. By that date the D line of sodium and the carbon flutings had passed their maximum intensity and had begun to fade out. The same line was also probably seen in Coggia's Comet by Vogel (III. 1874), who records a bright line at about 499, when the comet was yet a month from perihelion, and when, therefore, the appearance of the low temperature characteristic of the magnesium spectrum would be expected." 1 He finds also that comets at a distance from the Sun show lines corresponding to those of carbon at a low temperature. In comets at the mean distance from the Sun Lockyer finds evidence of hot carbon, magnesium, manganese, and lead. In the spectra of comets immediately preceding the perihelion passage he finds hot carbon, "the radiation of 1 TIte Meteoritic Hypothesis, pp. 171, 172 92 THE VISIBLE UNIVERSE. manganese replaced by absorption," lead absorption, and also " cool carbon absorption masking the radiation of hot carbon." In the spectra of comets close to the perihelion he finds evidence of the magnesium line b and the carbon lines near wave-length 426 — indicating a high temperature. He also finds "line absorption" in comet Wells and the great "September comet" of 1882. In the former there was evidence of the presence of iron, sodium, manganese, carbon, and magnesium, and in the latter the same elements with the addition of lead. With reference to Ooggia's comet of 1874, Lockyer says : "While ten minutes' exposure of a photographic plate gave no image of the comet, the faintest of the seven chief stars in the Great Bear gave an impression in two minutes." 1 Professor Lockyer thus sums up the sequence of the spectral changes in comets : — " The first visible stage in the spectrum of a comet is that in which a single line is visible ; relying on the position given by Dr. Huggins this may with great probability be attributed to the radiation of magnesium. The next is that in which this line is replaced wholly or partially by the spectrum of cool carbon. The line 521, also -seen in the spectrum of magnesium, is then added, and cool carbon is replaced by hot carbon. The radiation of manganese (558) and some- times of lead (546) follow. Absorption phenomena next appear ; manganese 558 and lead 546 being indicated by their masking effects upon the citron band of carbon. The absorption band of iron is also sometimes present at this stage, at which also the group of carbon flutings, which I have called carbon B, probably also makes its appear- ance. As the temperature increases still further, magnesium is . represented by b, and lines of iron appear ; this takes place when the comet is at or near perihelion. At this point the repellent action 1 The Meteoritic Hypothesis, p. 205. THE CONSTITUTION OF COMETS. 93 of the Sun upon the comet is most effective, and if the vapours are driven off in the line of sight with sufficient velocity, the bright lines will suffer displacement. A double set of phenomena will thus be presented : there will be radiation lines of one wave-length from the vapours thus driven off, and the absorption lines of a different wave- length from the vapours surrounding the meteorites in the head. " As the comet recedes from perihelion, these changes take place in inverse order. . . . " This complete sequence has never been observed in any single comet, but it has been continued in some comets where it has been left off in others." 1 ■ Comparing the spectra of comets and aurorse he finds them very similar, and thinks the view that the aurora spectrum "is produced by meteoric dust in our atmosphere is thus greatly strengthened." 2 Lockyer then proceeds to develop his theory that the light of comets is chiefly due to collisions between the component meteorites. With reference to the observed transparency of comets he says : " To enable the comet to reduce by one-tenth the light of a star seen through it, it would require to be 300 miles thick, supposing the stones to be 1 inch cube and 20 feet apart." Assuming the total mass of a comet to be j-^ that of the earth and its volume 250 times greater, he says that if we assume the stones to be ten inches cube, their average distauce apart would be about 1 7 feet. " By making the stones larger, and thus increasing the distances between them, the luminosity would be retained, while at the same time the swarm would be sufficiently transparent. It thus seems to suit the hypothesis better if we regard the separate stones to be greater than 10 inches cube." 3 The hypothesis 1 The Meteoritie Hypothesis, pp. 215, 216, 217. 2 Ibid., p. 225. 3 Ibid., p. 229. 94 THE VISIBLE UNIVERSE. referred to is that of Professor Tait ; but Lockyer says : " The mass of individual comets probably never exceeds ^^ of that of our globe. The meteorites composing them must therefore be very far apart, seeing that this small mass is distributed through spaces millions of miles in extent." x Part of a comet's light may, he thinks, be due to " external collisions." He says : — " But it is not unnatural to suppose that a meteoritic swarm moving through space and ploughing its way through a meteoritic plenum will encounter other meteorites, and from this cause the number of external collisions will depend, in the first place, upon its size. If the earth, some 8000 miles in diameter, encounters 400,000,000 daily, a comet as large as the Sun, as some of them are, will naturally encounter an enormous number." 2 The remarkable variations of brightness observed in the Pons-Brooks comet of 1883, and Sawerthal's comet of 1888, seem to favour this idea of collisions with external swarms. Lockyer thinks that the great increase of brilliancy of comets near perihelion may partly be due to collisions which take place " between the meteorites of the comet and those which occupy the outer cooler regions of the Sun," and he thinks that " collisions between individual meteorites would not retard the motion of a comet as a whole." With reference to the disputed question of the origin of comets, Lockyer favours the view that both shooting stars and comets did not originate within the Solar System, but are of cosmical origin — that is, that they have been drawn into our system from external space by the force of gravitation. Professor Kirkwood has shown that 1 The Meteoritic Hypothesis, p. 229. 2 Ibid., p. 232. METEOKIO SWAEMS. 95 cometary perihelia show a "tendency to crowd together about the direction of the Sun's journey in space." 1 Mr. Monck, however, doubts the correctness of this conclusion. It was shown by Leverrier that the Leonid swarm of meteors, which produces the great meteoric display every thirty-three years about November 14th, "possibly owed its existence as a member of our system to the attraction of Uranus." This probably took place about a.d. 126. Lockyer next discusses the probable existence of meteoric swarms in interstellar space. He gives an interesting historical notice of Sir William Herschel's observations of nebulas and the different classes into which these wonderful objects were divided by that great astronomer. Having referred to the observations of Sir John Herschel and Lord Eosse, and the spectroscopic discoveries of Dr. Huggins, he proceeds to discuss the spectra of the nebulas, and the probable identity of the bright lines observed with the lines of terrestrial elements. As is well known, the spectra of the true nebulas consist of a very faint continuous spectrum, crossed by one, two, three, or four bright lines. 2 One of these bright lines is certainly due to hydrogen. Another of these lines — that near wave-length 500 — is always considerably brighter than the others, and is known as " the chief nebular line." This line was at first supposed to coincide in position with one of the lines in the spectrum of nitrogen, but this is now known to be an error. It lies near the nitrogen line (or rather double line), but is quite 1 Tlie Meteoritio Hypothesis, p. 249. 2 In the spectrum of the "great nebula" in Orion other bright lines are visible. The complete hydrogen series of lines were photographed by Dr. Huggins in 1890. 96 THE VISIBLE UNIVERSE. distinct from it. It also lies near a line of lead, but is distinct from that line also. According to Lockyer it is identical with a line near 500, seen in the spectra of the comets of 1866, 1867, 1882, and in Coggia's comet of 1874, when these comets were at some distance from the Sun. With reference to the spectra of comets and nebulas he says : — " Other flutings and lines again are special to comets and others to nebulas. Thus there are practically no indications of hydrogen in comets, although the hydrogen lines are amongst the brightest in nebulae. Again the lines 447, 479, 495, 509, 554, and 5872 are seen in nebulse, but not in comets. On the other hand, the cool carbon flutings and the fluting at 568 are seen in comets, but not in nebulae. Most of these apparent discrepancies are explained by a consideration of the. differences in the conditions of comets and nebulas. It must be remembered that in the case of comets there is an action which repels the vapours produced by collisions, and the vapours first affected will, of course, be those which are less dense. Hydrogen will thus be repelled from the comets, whilst the denser vapours of magnesium and carbon remain. There is then a good reason why hydrogen lines should not be seen in cometary spectra. As there can be no such repulsion in the sparse swarms which constitute nebula?, hydrogen lines are seen in them." ' With reference to the actual position of the " chief nebular line " near wave-length 500, Lockyer maintains that it coincides exactly with the brightest edge of the magnesium fluting — that is, the least refrangible (on the red side) of the group of lines which constitute the fluting. This line was first identified by Dr. Huggins in 1864 with one of the lines of nitrogen. In 1874 observations seemed to show that it coincided with a line of lead. Later observations, however, proved that it does not coincide with either of 1 The Meteoritic Hypothesis, p. 291. THE NEBULAE LINE. . 97 these lines. Observations by Lockyer in 1887 with a spectroscope of small dispersion (one prism of 60°) seemed to show that it coincided with the edge of the magnesium fluting. The dispersion used was, however, clearly insuffi- cient to decide so delicate a point. Using a higher disper- sion, viz., a Steinheil spectroscope with three and four prisms, and a Cooke spectroscope of sixteen prisms attached to a 30-inch reflector, he again found the nebular line to be coincident with the edge of the magnesium fluting. To avoid some difficulties attending these experiments he then employed a siderostat, a 10-inch object glass, and a Steinheil spectroscope, and, observing the spectrum of the Orion nebula, he arrived at the following conclusion, with which his assistants agree : — " The observations have left no doubt in my mind as to the coinci- dence of the chief nebula line with the magnesium fluting, under such conditions that at the same time the coincidence of the F line of hydrogen with the third nebula line was demonstrated. Lieutenant Bacon and my assistants concur in this view." He then discusses the appearance of the nebular line, and the evidence in favour of its being a fluting and not a line. He thus describes the appearance of the magnesium fluting at 500 :— " The compound fluting of magnesium near \ 500 is very similar to that of carbon. It consists of a series of bright lines of gradually diminishing brightness and increasing distances apart towards the more refrangible end, and each has a fringe ' on the more refrangible side. The first maximum (the least refrangible) is brighter than the 1 " With higher dispersion the fringes break up into series of fine lines very close together." The Meteoritic Hypothesis, p. 313. 7 98 THE VISIBLE UNIVERSE. others, and the fringe close to it is brighter than the second maximum : hence when "the remnant of the magnesium fluting near 500" is referred to, the first maximum, with that portion of its fringe which is brighter than the second maximum, is meant." ' He then quotes the earlier observations of the nebular line, which show that it was seen nebulous at the edges by several observers, including Dr. Huggins. Lockyer's own observations of this line in the Orion nebula with the 30- inch reflector show that "whilst the F line is thickened equally on both sides, the chief line thickened only on the more refrangible side." 2 '. . . " In still more recent obser- vations with a siderostat the chief line was noted by Mr. Fowler and Lieutenant Bacon to have a decided fringe on the more refrangible side." Lockyer argues that " high dispersion is not so likely to show the fluted character of the chief line as low, for the more the fringe is dispersed the fainter it must become" ; and he finds that the spectrum of burning magnesium when its light is reduced by neutral tint-glass shows the fluting in question with an appearance very similar to that of the chief nebular line in the Orion nebula. Dr. Huggins' more recent observations of the nebular line will be given further on. From his spectroscopic results Lockyer concludes that " nebulas are really swarms of meteorites or meteoritic dust in the celestial spaces. The meteorites are sparse, and the collisions among them bring about a rise of temperature sufficient to render luminous some of their chief consti- tuents." 3 He considers that "the nebula in Andromeda is more condensed than that in Orion, for the reason that 1 The Meteoritic Hypothesis, p. 314. 2 Ibid., pp. 317, 318. s Ibid., p. 322. COLLISION SHELLS. 99 its spectrum resembles a comet when it is known to Tbe more condensed than at aphelion." * He thinks that the rapid increase of light observed in the novm or temporary- stars indicates that their sudden increase of brilliancy and subsequent rapid decrease is due to the incandescence of small masses of matter, a consideration which strengthens the view that these so-called " stars " consist of clouds of meteoric stones. With reference to the probable origin of the various forms observed in the nebulae, Lockyer supposes that " streams or sheets of nebulous material, invisible if undis- turbed, may encounter others, and in this way luminous patches of undefined shape may be produced by motions and crossings and interpenetrations, the brighter portions being due to a greater number of collisions per unit of volume." He explains the appearance presented by the planetary nebulas by supposing collisions to occur along the sphere of intersection of the meteorites moving in elliptic orbits round a common centre. In some cases these collisions would start the meteors in new orbits in the interior of the first shell, thus giving rise to a smaller collision shell and the appearance of a globular nebula with a bright central luminosity. If these inner orbits are very elongated, the intersection shell will become nearly a point, thus producing the appearance of a "nebulous star." He explains the appearance presented by those wonderful objects the " spiral nebulas " by supposing the original swarms composing the nebulas to be invaded from without " by other swarms which feel its attraction and have their paths deflected. ... If they enter in excess 1 Tlie Meteoritic Hypothesis, p. 325. 100 THE VISIBLE UNIVERSE. from any direction, we shall have the appearance of broken rings or spirals." 1 This seems to me a rather weak point in the theory, for these spiral nebulas certainly suggest a rotating mass, gradually breaking up into rings by the force of the rotation. Lockyer explains the appearance of those nebulas which resemble comets in shape by " either a very con- densed swarm moving at a very high velocity through a sheet of meteorites at rest, or the swarm at rest surrounded by a sheet all moving in the same direction." 2 He next proceeds to discuss the classification of the stars and their spectroscopic division into types. This classifi- cation will be found in the chapter on "Celestial Chemistry" in the present volume (Chapter VII.) . According to Lockyer's "new views" the stars of Vogel's Class III. a — which includes many variable stars — are not suns like ours, but closely resemble comets, and probably consist of swarms of meteorites, " clouds of incandescent stones." However this may be, he justly remarks " how a body constituted in any way like the Sun could change its magnitude from the thirteenth to the sixth every year or so, or change its hydrogen lines from bright to dark once a week, passes comprehension ; and the more closely a ' star ' resembles the Sun the less likely are such changes to happen." 3 Comparing the spectra of certain comets with those of stars showing bright lines, he concludes that these stars " are nothing more than swarms of meteorites a little more condensed than those which we know as nebulas." 4 1 The Meteoritie Hypothesis, p. 336. 3 Ibid., p. 353. 1 Ibid., p. 338. « Ibid., p. 356. OOSMIOAL GROUPS. 101 All these conclusions rest of course on the supposed coincidence of certain lines in the spectra of comets, nebulae, and stars with bright lines and flutings, a coincidence which has been disputed by other observers. Relying, however, on the accuracy of his experiments Lockyer proposes a "new grouping of cosmical bodies." He supposes some of these bodies to be increasing in temperature, while others — like our own Sun — are cooling. 1 He represents this hypothesis graphically by a temperature curve. On the rising branch of the curve he places at the lowest tempera- ture the nebulae and stars with bright lines, but without hydrogen. Above these come nebulae with hydrogen, and stars of Class II. b. Then stars of Class I. c, Class III. a, some of Class II. a, and at the summit of the curve stars of Class I. a, like a Lyree, representing the highest known temperature. On the descending or cooling branch of the curve he places the stars of Class II. a, which closely resemble our Sun, and stars of Class III. b. These he afterwards divides into groups, forming the following classification : — " Group I. — Radiation lines and flutings predominant. Absorption beginning in the last species. Group II. — Mixed radiation and absorption predominant. Group III. — Line absorption predominant with increasing tempern - ture. The various species will be marked by increasing simplicity of spectrum. Group IV. — Simplest line absorption predominant. Group V. — Line absorption predominant with decreasing tempera- ture. The various species will be marked by decreasing complexity of spectrum. 1 Lockyer's curve rests on this assumption, but it should be stated that ome astronomers doubt that the Sun is really cooling. 102 THE VISIBLE UNIVEESE. Gkoup VI. — Carbon absorption predominant. Group VII. — Extinction of luminosity." 1 Of these groups he places L, II., and III. on the rising branch of the temperature curve, IV. at the top, and V., VI., and VII. on the descending or cooling branch. He then proceeds to divide these groups into sub-groups and species, according to the character of the spectra shown by the various objects included in each group. He gives a detailed discussion of the bright-line spectra shown by the stars 7 Argus, Argelander-Oeltzen 17,681, Lalande 13,412, the Wolf-Rayet stars in Cygnus, and 7 Cassiopeia. The spectrum of 7 Argus, as observed by Copeland, Ellery, Lockyer himself, and Respighi, he considers " due to low-temperature sodium and iron, and to carbon flutings or a bright continuous spectrum." In A.-Oe. 17,681, the spectrum of which was observed by Pickering and Vogel, he finds hot carbon, manganese, and iron bright lines on a continuous spectrum. In Lalande 13,412, also observed by Pickering and Vogel, he finds " a continuous spectrum from the meteorites, and carbon bands, one of them appearing beyond the continuous spectrum in the blue as a bright band ; bright lines of hydrogen, manganese, and iron being superposed on both." In the 1st Wolf-Rayet star in Cygnus (DM + 35°, 4001), observed by Wolf, Rayet, and Vogel, he finds a faintly continuous spectrum with hot carbon, and "the strongest low-temperature lines of manganese, iron, and cadmium, with a strong manganese fluting, and the green sodhtm 1 The Meteoritie Hypothesis, pp. 381, 382. BRIGHT LINE STAES. 103 line appear on the continuous spectrum. There is no absorption of any kind." 1 In the 2nd star in Cygnus (DM + 35°, 4013), also observed by Wolf, Rayet, and Vogel, he finds a continuous spectrum with bright carbon, and bright lines of iron, manganese, sodium, and some as yet undetermined substance giving a line at 636, which, however, was observed " as a bright line in the Limerick meteorite at the temperature of the oxyhydrogen blowpipe." In the 3rd Wolf-Rayet star in Oygnus (DM + 36°, 3956) he finds a continuous spectrum with " the low-temperature manganese line, and the strongest manganese fluting ; the low-temperature iron line, the green sodium," and the 636 line of the Limerick meteorite. In 7 Cassiopeite — the spectrum of which has been observed by Secchi, Vogel, Huggins, Gothard, Konkoly, and Sherman — he finds evidence of a continuous spectrum with bright lines and bands of hot carbon, hydrogen, manganese, iron, magnesium, hydrocarbon, the line 636 of the Limerick meteorite, and a line at 463 of unknown origin, which was seen " bright in R Geminomm, but has up to the present not been detected in any experiment with meteorites." * From recent observations of these stars Dr. Huggins finds, however, that the bright lines attributed by Lockyer to carbon, do not coincide with the carbon bands. With reference to the sequence of temperature in the Cygnus stars, Lockyer concludes that "1st Oygnus is the coolest, 2nd Cygnus ranks next above it in temperature, and 3rd Cygnus is the hottest of the three." 1 „ ' The Meteorit'io Hypotlwsis, Chap. XXXV. 104 THE VISIBLE UNIVERSE. From photographs of the region in Cygnus containing the Wolf-Bayet stars, Professor Pickering discovered four other stars with bright lines in their spectra. Among these is the star P(34) Cygni — the so-called Nova of 1600. With reference to its spectrum Lockyer says : — " In addition to the hydrogen lines there is a bright line in P Cygni, the wave-length of which I have found to be about 447. This appears to be coincident with Lorenzoni's / of the chromosphere spectrum, and it is also seen in the spectrum of the Nebula in Orion. In all three cases it is associated with the line D 3 .' Lockyer then proceeds to discuss Duner's observations of the bands and flutings visible in stars of the third type. 2 He shows that the dark bands visible in the spectra of these stars may, in some cases at least, be partly due to contrast with adjoining bright flutings. He iden- tifies some of the bright spaces between the bands, seen by Duner, with the radiation flutings of carbon. These lie near Duner's bands 8, 9, 10, and 11. He also finds indications of absorption flutings and bands due to iron, manganese, lead, barium, magnesium, and chromium. He argues that the differences in the spectra observed in these stars may be mainly accounted for by differences in the amount of interspace in the meteoric swarms which con- stitute them. By the term " interspace " he denotes " the relative areas of space and meteorite in a section of the swarm at . right angles to the line of sight." With a reduction of the spacing he contends that " (1) the tem- perature must increase, (2) the carbon spectrum must first get more intense, and then diminish afterwards as the 1 The Meteoritio Hypothesis, Chap. XXXV. 1 Sur les Etoiles a Spectres de la Troisieme Classe (Stockholm, 1885). DUNER S OBSERVATIONS. 105 spaces, now smaller, are occupied by vapours of other substances, (3) the continuous spectrum of the meteorites must increase, (4) the spectrum must gradually get richer in absorption bands." 1 Discussing Duner's individual observations he finds that the extreme stages of spacing (or degrees of condensation of the meteorites) are indicated by (a) "the first stage, representing almost a cometic condition of the swarm before condensation has begun," 2 — among Duner's stars of this stage referred to by Lockyer there are many variable stars, — (b) " the last stage before all the bands fade away entirely." Among the stars of this stage referred to by Lockyer (p. 418) there are no known variable stars. In stars with discontinuous spectra, like a Herculis, R Hydras, and X Herculis, he considers that the meteorites "are wide apart, though not at their widest." In other cases the spectra are not discontinuous, "and the flutings, instead of being black, are pale." Here he thinks " the average distances between the meteorites have been reduced." 3 This stage includes the variable stars T Ursaa Majoris and B, Camelopardali. Proceeding to the consideration of his Group III. he discusses the spectral characteristics which differentiate Group II. from Group III. Defining Group II. as the "mixed fluting" group, he draws the line between the groups at the stage where carbon radiation ceases. He considers that a Ceti is " the most advanced Group II. star of which observations have at present been made." 4 1 TJie Meteoritic Hypothesis, p. 417. 2 Ibid., p. 418. 3 Ibid., p. 420. 4 Ibid., p. 435. The spectrum of a Orionis seems to be also a transition, spectrum. 106 THE VISIBLE UNIVERSE. In the spectra in Group II. he finds the following general sequence from the earlier to the later species: — " (1) The hydrogen lines are thin. D is thicker than 6. The iron fluting is faint. 499, E, 5327, 540, 568 and 579 are thin. 546 and 558 are fairly thick. " (2) The hydrogen lines are thicker. P, D, and b are equally thick. E, 5327, 540, 579, and 499 are much thicker, being nearly as strong as F. The iron fluting has gone. " (3) The hydrogen lines are very much thicker than the other lines. D and b are equally thick, E is nearly as strong as b, while the other lines are fainter. " (4) The hydrogen lines are very broad, while all the remaining lines are exceedingly faint." l The stars i Aurigse and a Tauri (Aldebaran) belong to the earlier species, and ft Persei (Algol) and a Aquilse (Altair) to the later species. The greater width of the hydrogen lines in the latter stars . indicate a higher tem- perature. Stars in Group IV., like a Lyras (Vega) and Sirius, in which the hydrogen lines are wider still, represent the point of maximum temperature among cosmical bodies. In Groups III. and V. the former is supposed to include bodies in which the temperature is increasing, and the latter — which includes our own Sun — bodies in which the temperature is decreasing. The criterion between these two classes — which have very similar spectra — is, accord- ing to Lockyer, found in the relative intensities of certain lines. There is a " double line about wave-length 540, which, with the two iron lines E (5268) and 5327, forms a trio." Now " the double " in Group V. is considerably weaker than E, whereas that in Group III. is very nearly 1 Tlie Mcteoritic Hyjwthesis, p. 441. STELLAR SPECTRA. 107 as strong as E. The appearance presented to the eye by the real trio in stars of Group III. is accordingly very different from that presented by the three lines in stars of Group V." 1 Again there is a line near wave-length 499, which in some stars is very strong, but is " only seen as a very faint line in Oapella, Arcturus, or the Sun, and is consequently an important criterion." x Two lines at 579 and 568 also seem to be special to Group III., at least they are much stronger in these stars than in those of the solar type. By these criteria it is now possible to divide the stars of Vogel's Class II. a into two groups. Group VI., which includes Vogel's III. b stars (Secchi's 4th type), is defined, according to Lockyer, " by enormous carbon absorption, which is the real origin of the inversion of the dark spaces first pointed out by Secchi, although he missed its significance." He thinks that " the blood-red stars are approaching the extinction of their light, chiefly by continuous absorption, strongest at the blue end." Group VII. includes dark bodies, which of course give ■ no spectrum, and are therefore invisible to us (at least, those which may exist in interstellar space) either with the tele- scope or spectroscope. Lockyer then proceeds to discuss the binary and multiple star systems. He considers that in most cases binary stars originally existed in the condition of double nebulte, although in some of them it is possible that the com- panion was added to the system in the same way that periodical comets have been occasionally added to our own. 1 Tlte Meteoritie Hypothesis, p. 143. 108 THE VISIBLE UNIVERSE. The colours of the objects included iu Lockyer's Groups are, as a general rule, as follows : — " Group I. — Blue, greenish-blue, white, or pale grey. Group II. — Yellowish-red. Group III. — Yellow to white. Group IV. — Bluish-white. Group V. — "White to yellow. Group VI. — Reddish-yellow to blood-red. Group VII. — Dark bodies." ' Lockyer thinks that the binary stars probably originated as follows : — 1. Magnitudes, colours, and spectra of the components identical. Both originated either " in the same nebulosity with two condensations, or in a double nebula." 2. Magnitudes nearly equal, but colours and spectra different. Possibly " the one with the most advanced spectrum has the smaller mass." 3. Magnitudes very unequal. Probably the fainter com- ponent has the smaller mass ; "and if it is proportionately in advance as indicated by the spectrum, or colour, we may regard both components as having had a common origin. If the smaller one be less advanced than the larger one, we have to regard it as a later addition to the system." " If the two stars are of equal mass, and revolve round their common centre of gravity, they have in all probability done so from the nebulous stage, and therefore they will have arrived at the same stage along the evolution road, and their colours and spectra will be identical." " If, however, the masses are very different, then the smaller mass will run through its changes at a much 1 The Meteoritic Hypothesis, p. 448. BINARY STARS. 109 greater rate than the larger one. In this way it is possible that the stars seen so frequently associated with globular nebulas may be explained ; while the nebula with a larger mass remains still in the nebulous condition, the smaller one may be advanced to any point, and may indeed even be totally invisible (Group VII.) while the parent nebula is still a nebula." 1 Lockyer then divides into classes the binary systems included in Chamber's edition of Smyth's Bedford Cata- logue. In Class I. he includes those " in which the magni- tudes and colours of the components are almost identical." Among these he includes 32 Orionis, magnitudes 5 and 7, f Ursas Majoris 4, 5|, e Ophiuchi 7, 9, £ Cephei 5 and 7 ; but it can hardly be said that the magnitudes of these are " identical." In Class II. he includes those of " equal magnitude and similar colours." In Class III. he groups those of " equal or nearly equal magnitudes, one star being Blue " ; but here again he includes stars like 49 Piscium, magnitudes 7, 10|, t Leonis 4, 7|, £ Bootis 3|, 6|, 70 Ophiuchi 4|, 7, 33 Pegasi 6|, 10/ which are certainly not of " nearly equal magnitude." Indeed, observers of double stars would speak of them as " rather unequal." In his Class IV. Lockyer includes doubles of " very unequal magnitudes, the smaller star being Blue." It seems doubtful, however, that all these stars with faint companions are really binary. Class V. includes pairs of "unequal magnitudes, the fainter star being Red." 1 The Meteoritic Hypothesis, p. 450. 2 A difference of 3£ magnitudes implies that the brighter component is 25 times brighter than the companion. 110 THE VISIBLE UNIVERSE. With reference to f Hercnlis, which he cannot place in any of the ahove classes, Lockyer thinks that possibly " we have here to deal with an added companion." Lockyer next proceeds to suggest, in accordance with his theory, a probable cause for the variability in light and colour observed in the variable stars. In an introductory chapter he gives an interesting historical account of the discovery of Mira Ceti, % Cygni, Algol, and ,3 Lyra3, and the theories which have been advanced to account for their variability. In the next chapter he develops his own theory, based on the meteoritic hypothesis of the constitu- tion of cosmical bodies. In the case of the regular variables he considers that the variation in light " is caused by the revolution of one swarm or body round another (or their common centre of gravity)." " In the case of the revolu- tion of one swarm round another, an elliptic orbit is assumed, and the increase of light at maximum is produced by collisions among the meteorites at periastron. In the case of the revolution of a swarm round a condensed body, the increase of light at maximum is produced by the tidal action set up in the secondary swarm." 1 In the case of irregular variability he considers the variation to be " caused, (a) by the revolution of more than one swarm or body round another (or their common centre of gravity) ; or (b~) by the interpenetration of meteoritic sheets or streams. In the case of the revolution of more than one swarm round another in elliptic orbits the irregular maxima are caused by difference of period and periastron conditions." This seems a very plausible hypothesis, but it is of 1 The Meteoritic Hypothesis, p. 475. MIRA CBTI AND ALGOL. Ill course open to grave objections on mechanical principles. In the case of great variation of light — six to eight magni- tudes — he supposes the orbit of the revolving swarm to be very elliptical. With less variation the orbit will be an ellipse of smaller eccentricity, and when the ellipse becomes nearly a circle " the smaller swarm will never be entirely out of the larger one, and at periastron the number of collisions will not be very greatly increased." He gives a light curve of Mira Ceti, but falls into an inaccuracy with reference to its magnitude at minimum. He says " it descends to the tenth, and so far as observa- tions with ordinary instruments go, it is invisible. . . . What happens to the light of the star below the tenth magnitude it is impossible to say." * Now Schmidt found the minimum magnitude to be 9*5, but Schonfeld states that he has never seen it fainter than the distant companion, or 9*1, and that it is usually somewhat brighter. 2 At the minimum of 1874 it was 8-6, according to Schonfeld. It thus appears that Mira is never so faint as 1 Oth magnitude. Lockyer accepts the eclipsing satellite theory of Algol, and indeed this hypothesis has been practically proved by recent spectroscopical observations. The light variation, however, does not amount to so much as two magnitudes, as shown in Lockyer's light curve (p. 486). Professor Pickering's photometric observations show that the total variation very little, if anything, exceeds one magnitude, and this is confirmed by my own eye estimations and those of other observers. Some observers, however, make the variation about 1*5 magnitude, but it is certainly not greater 1 The Meteoritic Hypothesis, p. 484. 2 See my first Catalogue of Known Variable Stars, pp. 167, 171. 112 THE VISIBLE UNIVERSE. than this. It may be stated here that Herr J. Plassmann, the well-known German astronomer, has recently announced his discovery of a secondary minimum in the light of Algol and X Tauri. This occurs about midway between two prin- cipal minima. The most probable explanation of a secondary minimum in an Algol star — if it exists — would seem to be that the satellite has some inherent light of its own which is cut off when it passes behind the disc of the primary star. No change occurs in the spectrum of Algol during the course of its light variation, but in the case of Ceraski's Algol star U Cephei a considerable change in the spectrum has been observed at minimum. Professor Pickering finds that in this latter case the eclipse must be a total one, and that consequently the satellite must have some inherent luminosity. From the change in the spectrum Lockyer concludes that " probably the companion has an absorbing action of some kind on the light of the central star passing through it or its surroundings." With reference to the variability of stars in Group VI. (Vogel's III. b) Lockyer thinks " the variation would seem to be due to swarms of meteorites moving round a dim or nearly dark body, the maximum light occurring at peri- astron, when the tidal action in the swarm is greatest ; in consequence of this dimness the addition of the light of what we, with our solar conditions, should term a large comet would make a great difference in the total radiation." * He then gives tables of variable stars arranged according to the character of their spectra, from which it appears that the greater number of variables are found among those stars of the third type in which the bands are " wide and strong." 1 The Mcteoritic Hypothesis, p. 488. VAEIABLE STAES. 113 He next tabulates the known variables, having spectra of the third type, according to length of period, the details respecting amount of variation and length of period being derived from my Revised Catalogue of Variable Stars, and the colours of the stars from Chandler and Duner. Chandler found that the longer the period of variation the redder the tint, but Lockyer finds that this relation between colour and period " is only a general one." According to Lockyer's hypothesis the bright- lines of hydrogen " might be expected to make their appearance at maximum, accompanying the greatly increased intensity of the carbon flutings." Bright lines of hydrogen have been observed by Espin in E Cygni and Mira Ceti in 1888, and in R Leonis, R Hydras, % Cygni, R Andromedaa, and S Cassiopeiae in 1889. These bright lines were also photo- graphed in the spectra of Mira by Pickering in 1886. 1 Lockyer finds that the carbon bands at 517 and 546 also brightened in the spectra of Mira near maximum in October 1888, and that " in variable stars of this class the proof is now complete that the increase of luminosity is accompanied by cometary conditions, and that it is due to the increased radiation of carbon." This "proof" of course rests on the supposed identity of the bands in the spectrum of Mira with those of carbon. Lockyer adds : — "These observations of Mira, and others which Mr. Fowler and myself have made on stars with Bunsen comparisons, entirely justify the conclusions drawn by Dr. Copelandfrom his work on U Orionis (when it was thought to be a Nova) that bright flutings of carbon were in question in that star, although that conclusion has been contested." 2 1 The Meteoritio Hypothesis, p. 505. 2 Ibid., p. 508. 8 114 THE VISIBLE UNIVERSE. In the case of /3 Lyrae, Lockyer supposes that two swarms revolve round a principal mass, or " condensing nebulas," of which the magnitude is 4-5. 1 One of these has a period of revolution of about 6 days, and the other of about 12 days. The former of these raises the light at periastron (by collisions) to magnitude &4:. 1 The latter only raises the light to S'9. 1 If we suppose the apastra of the two stars to occur simultaneously, there will be two minima, " but the maxima will be constant" Lockyer thinks " that practically there can be no per- manently dark bodies in space ; they must at one time or another be accompanied by comets, and they must therefore be variables." In the concluding chapter of his work he sums up the general conclusions arrived at. He says (p. 532) : — " 25. The relatively small number of bodies in Group VI. seems to suggest that in the part of space open to our inquiries, bodies of which the temperature is increasing are more numerous than those in which the temperature is being reduced. "26. In recorded time there has been no such thing as ' a world on fire,' or the collision of masses of matter as large as the earth, to say nothing of masses as large as the Sun ; but the indicated distri- bution of meteorites throughout space indicates that such collisions form an integral part of the economy of nature." The latter passage reminds us of Dr. Oroll's " Impact Theory " (see chapter on " Stellar Evolution "). In a paper read before the Eoyal Society in November 1888 by Professor G. H. Darwin, he examines mathe- matically the question whether the conception of fluid pressure, required by the nebular hypothesis, is applicable 1 I have corrected the magnitudes given by Lockyer, which are incorrect. METBOEIC SWAEMS. 115 to a swarm of meteorites. He finds that such a swarm may be compared to a gas, which is supposed to consist of an immense number of molecules separated by small but finite spaces. " According to the Kinetic theory of gases, fluid pressure is the average result of the impacts of molecules. If we imagine the molecules magnified until of the size of meteorites, their impacts will still, on a coarser scale, give a quasi-fluid pressure. He suggests then that the fluid pressure essential to the nebular hypo- thesis is in fact the resultant of countless impacts of meteorites." 1 This conclusion favours Lockyer's con- tention that space may be considered as " a meteoritic plenum." In the Kinetic theory of gases the molecules are supposed to be perfectly, or at least highly, elastic, and in the collision of two meteoric stones Professor Darwin considers that, as a portion of each is volatilised, the result will be like that of an explosive, and consequently there will be nearly perfect elasticity between the colliding meteorites. He finds that the analogy with the theory of gases will hold good for the swarm from which the Solar System is supposed to have been evolved, a swarm extending beyond the orbit of Neptune. He finds that the swarm, when widely diffused, will be subject to gaseous viscosity, and will first rotate as a solid body, but when more contracted "the central portion will revolve more rapidly than the outside." 1 Here closes, so to speak, the case for the plaintiff. Let us now consider the facts and arguments which have been brought forward by the opponents of Lockyer's 1 Monthly Notices, R.A.S., February 1889. 116 THE VISIBLE UNIVERSE. hypothesis, taking the various points in the order in which they are discussed in Lockyer's work on the subject. First, with reference to the magnesium fluting near 500, observed in the spectra of meteorites, Professors Liveing and Dewar find that this fluting does not represent a lower temperature than the triplet b, as Lockyer maintains. They also find " that it is a fluting of an oxide of mag- nesium, and is scarcely seen in the presence of hydrogen," l while undoubtedly hydrogen lines are seen in combination with the line near 500 in the nebular spectra. With reference to Lockyer's assumption of the identity of origin of luminous meteors and falling stars with meteoric stones, Mr. Monck contends that we have no certain proof that meteorites come to us from external space. Sir Robert Ball and Tschermak consider meteorites to be " of terrestrial origin, havingvbeen shot from terrestrial volcanoes in past ages, when volcanic action was more powerful than at present." 2 Mr. Monck does not agree with this view, and points out that those connected with comets cannot be of terrestrial origin. He admits, however, that some meteorites may be of terrestrial origin, and suggests that Mr. Lockyer's experiments may have been made with some of these terrestrial meteorites. With reference to the characteristic line of the auroral spectrum, which Lockyer identifies with the manganese fluting at 558, Dr. Huggins, in a paper read before the Boyal Society in 1889, gives the results of some observations of the spectrum of the aurora made in the year 1874, and comes to the conclusion that the wave-length of the auroral 1 Journal of the British Astronomical Association, No. 1, vol. i., p. 29. Journal of the Liverpool Astronomical Society, June 1888. THE AUKOEAL SPECTKTJM. 117 line is 5571 ± 0-5. After discussing the various measures of the line made by other observers, he says : — " It is certain, therefore, from Angstrom's first observation in 1867 alone, that the ausora line lies well on the more refrangible side of wave-length 5580." And again : — " After consideration, I think that I ought to point out that Mr. Lockyer's recent statement that ' The characteristic line of the aurora is the remnant of the brightest manganese fluting at 558 ' is clearly inadmissible, considering the evidence we have of the position of this line." ' Another objection to Lockyer's meteoritic theory of the aurora was communicated to the Royal Society towards the close of the year 1890 by Professors Liveing and Dewar. These physicists describe some experiments which they made with a view to decide the question "whether solid particles of sufficient minuteness would act like gaseous molecules in an electric discharge, and become luminous with their characteristic special radiation." This they find not to be the case. Dust formed by particles derived from magnesium, iron, manganese, cadmium, fused calcium chloride, metallic sodium, and fragments of the Dhurmsala meteorite was employed in the experiments, the dust being generated from a pair of electrodes formed from the materials mentioned. The experiments showed that the electric current drove the dust granules from its path and cleared them otT the electrodes. In no case could the lines characteristic of the materials composing the dust be 1 Proceedings of the Royal Society, Vol. XLV., pp. 434, 118 THE VISIBLE UNIVEESE. detected in the spectrum. From these experiments the authors think that " if the spectrum of the aurora be due, not to the ordinary constituents of our atmosphere, but to adventitious matter from planetary space, we conclude that such matter must be in, or must be brought into, the gaseous state, or at least have its properties entirely altered from those it possesses at ordinary temperatures, before it becomes luminous in the electric discharge." 1 With reference to the supposed connection between meteors, meteoric showers, and comets, the theory that comets originated within the Solar System was held by the famous Kant, and that they had their origin in external space by the equally famous Laplace. Professor H. A. Newton, who has carefully investigated the subject, although he favours the hypothesis of Laplace, arrived by calculation at results which, according to Mr. Monck, seem equally favourable to both hypotheses. Mr. Monck inclines to the opinion that some comets, at least, have originated " within the limits of the Solar System," and to this class he is disposed to assign " the four comets which have been con- nected with meteor showers." 2 Coming now to one of the crucial tests of the meteoritic hypothesis, namely, the supposed coincidence of the " chief nebular line " with the " remnant of the magnesium flut- ing " near wave-length 500, Dr. Huggins made a re-deter- mination of the exact position of the principal line in the Orion nebula in February 1890, and after a series of careful measurements he arrived at the result that the wave-length of the nebular line is about 5004 - 75, while that of " the 1 The Observatory, December 1890. 2 Journal of the Liverpool Astronomical Society, June 1S8S. THE CHIEF NEBULAE LINE. 119 termination" of the magnesium band is 5006-5. Dr. Hnggins also says "that a marked feature of this line (the nebular line) is its sharply denned character on the more refrangible side ; we were unable, under any of the conditions of observing, to detect even a suspicion of any softening of the more refrangible edge of the line, much less the faintest indication of a ' flare,' and certainly not the distinctive peculiarity of a 'fluting.' 1 From observa- tions of the hydrogen line in the same spectrum, Dr. Huggins finds that "the nebula has very little, if any, sensible motion in the line of sight." 2 The nebular line cannot therefore be displaced by any motion of the nebula. 2 These observations were confirmed by Mrs. Huggins and by Professor Liveing, using the same telescope and spectro- scope. Dr. Huggins therefore concludes, " (1) That the principal line is not coincident with, but Mis within, the termination of the magnesium-flame band. " (2) That in the nebula of Orion this line presents no appearance of being a ' fluting.' " He finds the same result in the spectrum of the nebula 2 5 (G. C. 4234). Dr. Huggins' result as to the sharp character of the line was confirmed by Professor Young and by Mr. Keeler at the Lick Observatory. Mr. Keeler observed " successively 1 Proceedings of the Royal Society, Vol. XLVIII. 2 It should be remembered, however, that as the Sun's motion in space is away from the Orion nebula, the spectrum should show — if the nebula be at rest — a motion of recession. The fact therefore of the hydrogen line showing no displacement would imply that the nebula has a motion in space in the same general direction as the Sun's motion, and with nearly the same velocity. More recently Mr. Keeler finds amotion of recession in the Orion nebula at the rate of 10'7 miles a second. 120 THE VISIBLE UNIVERSE. with one prism, a powerful compound prism, and then with a Rowland grating, 14,000 + lines to the inch." He says : " One thing that struck me particularly, and that there could be no doubt of, was the perfect sharpness and fineness of the nebular lines under the very considerable dispersion used. There is not the least doubt in my mind that they are all of gaseous origin — not remnants of flutings." 1 Subsequently Dr. Huggins' results with the nebula H 5 were also confirmed by Mr. Keeler. He says, in a letter to Dr. Huggins : " On comparing the brightest line with the magnesium fluting, both directly and by aid of the micrometer wire, the line was seen to be well within the limits of the fluting, and separated by a small but unmis- takable interval from the bright lower edge. . . . The edge of the fluting could not be brought into coincidence with the nebular line." Mr. Keeler subsequently examined the spectra of a number of planetary nebulas, and arrived at a similar result with respect to the position and character of the principal line, the mean wave-length deduced from ten nebulas being 5005-68, that of the magnesium fluting being 5006-36. The nebular line, however, showed a displacement, apparently due to the motion of the nebulas in the line of sight. "With reference to this shift in the position of the line, Mr. Maunder says : " The amount of the displacement is not so great as to make it altogether inconceivable that it is due to the relative motion of the nebulae and the Solar System. For all the ten nebulas are observed in that hemisphere towards which the Sun is travelling, and seven 1 Proceedings of the Royal Society, Vol. XL VIII. THE CHIEJT NEBULAE LINE. 121 of them are within 45° of the apex of the ' Sun's Way,' so that a correction must be applied which would tend to bring the nebular line nearer to the fluting ; how much nearer we cannot, in our ignorance of the speed of the Sun's motion in space, at present say, but the rate of 36 miles per second would suffice to make the accord a perfect one " ; * and in a paper in the first number of the Journal of the British Astronomical Association, Mr. Maunder adds : " Further, some allowance must be made for the difficulty of com- paring a line with a fluting ; we ought certainly not to measure from the centre of the nebular line to the extreme edge of the fluting. This will supply a small but further correction in the same direction. Keeler's observations so far, therefore, point distinctly to a close approximation of the nebular line to the position occupied by the maximum of the fluting, bat whether there is or is not an exact coincidence we cannot yet tell. . . . The conclusion is, then, that we do not know the position of the nebular line with sufficient accuracy to say positively that it does or does not accord with the magnesium fluting." 2 Here the matter rests at present (January 1892). One point is clear, however, that the dispersion used by Pro- fessor Lockyer was insufficient to decide the question, and further researches on the subject will be looked forward to with great interest. There seems to be another weak point in Professor Lockyer's theory, and that is that it affords no explanation ' The Observatory, November 1890. 2 Subsequent measures by Mr. Keeler give the true position of the " chief nebular line," when corrected for the earth's orbital motion and the Sun's motion, at 5005-93, thus showing that it does not coincide with the mag- nesium fluting {Journal B.A.A., Vol. I., No. 5, pp. 281, 282). 122 THE VISIBLE UNIVERSE. of how the planets and satellites of the Solar System were evolved. This has been pointed out by Mr. Monck. He says : " Will any advocate of the meteoritic theory give us an explanation of why all the planets and asteroids and the great majority of the satellites revolve in the same direction, why the orbits of the larger bodies of the system deviate so little from the circle, and why they are so nearly in the same plane ? Till this is done I think the nebular hypothesis has in this case the advantage." 1 A violent "grazing collision" between two dense meteoric swarms might, however, conceivably be supposed to produce a rotation in the swarm which would give rise to the observed planetary motions. "In the Gomptes Rendus of November 28th, 1S87, M. Stanislas Meunier objects to Mr. Lockyer's hypothesis that meteorites are made up of metals whose melting points are so different that the agglomeration cannot be supposed to have occurred at a high temperature." 2 Another objection raised by Mr. Monck is that it seems difficult to understand how the requisite number of colli- sions in a meteoric swarm could be produced and kept up, and "that meteor-clouds dense enough to produce the requisite amount of light by their collisions would also be dense enough to intercept a great part of it again on its way to the earth." 3 On the whole, therefore, we seem bound to conclude that the " weight of evidence " is against the truth of the " Meteoritic Hypothesis." 1 Journal of the Liverpool Astronomical Society, November 1890, p. 36. 2 The Observatory, January 1888. 3 Journal of the Liverpool Astronomical Society, June 1888, pp. 289, 290. CHAPTER IX. THE MILKY WAY AND STAR DISTRIBUTION. " Seen in the galaxy, that milky way, Which nightly, as a circling zone, thou seest Powdered with stars." Milton. THE nebulous band or zone of light known as the Milky Way, or Galaxy, is familiar to every one, and on a clear moonless night forms a conspicuous feature of the nocturnal heavens. It has attracted the attention of astro- nomers and philosophers from the earliest ages of antiquity, and various theories have been advanced to account for its appearance. One of the ancient writers — Oenopides — con- sidered it to be the original course of the Sun. Plutarch saw in it the marks of Phaeton's accident. 1 Anaxogoras thought it was the shadow of the earth, and Aristotle that it was due to atmospheric vapours ! Other equally absurd theories were entertained by the ancients, and Ovid says, in the first book of the Meta- morphoses : " When the sky is clear a path of very radiant 1 Phseton, son of Phoebus and Clymene, in ancient mythology, requested permission from his father to drive the chariot of the Sun, but after a few hours' driving, overcome by the heat, he dropped the reins. To prevent a general conflagration Jupiter struck him with lightning, and he dropped into the river Eridanus, now one of the constellations. 123 124 THE VISIBLE UNIVERSE. white colour may be seen in the empyrean. It is called the Milky Way, and along it the immortals repair to the august dwelling-place of the Lord of Thunder," a fable which is also referred to by Plato. The true theory, namely, that its light originates from myriads of small stars, was, however, advanced by Democritus,Manilius, and Pythagoras, and the invention of the telescope fully confirmed the correctness of this hypothesis. Before proceeding to inquire into the construction of the Milky Way, and the modern theories which have been advanced respecting its relation in space to the Sun and Solar System, it will be interesting to make an examination of its general appearance and structure as depicted by different observers. The representations of the Milky Way given in Proctor's and other popular atlases merely afford a general idea of its appearance, and show no details of the brightness, and faintness of its various parts — features which are very obvious when carefully observed. A mere passing glance might lead a casual observer to suppose that the Galaxy stretched as a band of nearly uniform brightness across the heavens. But good eyesight, careful attention, and a clear sky will soon disclose numerous details previously unsuspected, streams and rays of different brightness inter- sected by rifts of darkness, and interspersed with spots and channels of comparatively starless spaces. Heis, in his excellent Atlas Gcelestis Novus, gives an elaborate delineation of the Galaxy, as seen in northern latitudes. According to his drawing the general course of the Milky Way nearly coincides with a great circle of the celestial sphere, having its mean centre line inclined to THE GALACTIC POLES. 125 the Equator at an angle of about 65°, and intersecting that circle in about E. A. 7h. and 19h. The intersection at 19h. is that of the mean centre line of the main branch, which passes over a, S, and X Aquilee, and X and 8 Sagittarii. If, however, we assume the centre line to pass from 7 Cygni between the divided branches in Aquila and Ophiuchus, the intersection at this point with the Equator will be at about E. A. 18h. 40m. According to Sir John Herschel the position of the North Pole of the Milky Way is E. A. 12h. 47m., and North Declination 27°. Heis gives it E. A. 12h. 41 -2m., N. 27° (1880) ; Houzeau E. A. 12h. 49m., N. 27| ; and Gould E. A. 12h. 41m. 20s., N. 27° 21' (1875)— results in fairly close agreement. The South Pole is in about E. A. Oh. 47m., and Declination S. 27°. The near coincidence of the course of the Milky Way with a great circle of the star sphere implies of course that the Sun and Solar System are situated in or close to the general plane of the Galaxy. Heis divides the varying brightness of the different parts of the Milky Way into five magnitudes, the first magnitude corresponding to the luminous parts of the Galaxy between 7 and 7] Cygni ; near the variable star E Scuti ("Sobieski's Shield") ; and the bright spots near the bow of Sagittarius ; and the fourth and fifth magnitudes to the very faint nebulous light which he shows filling in the vacuities or " coal sacks " in Cygnus and Cepheus and bordering the Milky Way on both sides throughout nearly the whole of its course. This method of division into magnitudes is of course, to a great extent, an arbitrary one, and the lines of demar- cation between Heis' assumed magnitudes are not so sharply 126 THE VISIBLE UNI'VEBSE. defined in the sky as shown in his maps. There is also reason to think that Heis did not pay so much attention to the Milky Way as he did to his stellar magnitudes. 1 Still his drawing serves to give a fair representation of the general effect visible to a keen-sighted and careful observer, as Heis undoubtedly was. Following Heis' picture of the Galaxy in order of Eight Ascension, commencing at Cassiopeia's Chair, we find that the well-known square formed by /3, a, y, and k Cassiopeise is nearly filled in with nebulous light of about Heis' second order of brilliancy. This bright spot extends north of. 8 Cassiopeise up to e, where it merges into a long elongated spot of about the third magnitude, extending from Cephei to the borders of Camelopardus, and reaching with fainter light nearly to the Pole Star, where it joins an oval-shaped patch, of about fourth magnitude, covering the hind legs of the figure. From 8 and e Cassiopeise the brightness is of about the third and fourth magnitude, its width being reduced to a very narrow neck north of i Persei. This narrow isthmus of light lies at the south-western extremity of a large vacuity or " coal sack," which is bounded on the north by the oval-shaped spot above referred to, and its southern limit is roughly defined by the well-known curved stream of stars formed by 7, a, ty, 8, p, and X Persei. From near this stream a branch is thrown off from the Galaxy towards the south, enclosing near its southern extremity £ and Persei, the stars e and £ Persei lying on its eastern 1 An elaborate drawing of the Milky "Way has recently been made by Dr, Otto Boeddicker (of Lord Kosse's Observatory). This will be described further on. THE COUESK OF THE MILKY WAY. 127 boundary. From a and e Persei to a, e, £, and 77 Aurigaa the Milky Way is shown rather narrow and of nearly uniform brightness. South of this the stream widens out considerably, reach- ing a maximum width between 8 Geminorum and a Orionis. Here there are several spots slightly brighter than the rest, one especially of roughly circular form (about second order of brightness) enclosed by e, f, and 48 Geminorum, 1 one just north of 97 and fi Geminorum, and a vacuity (or spot with faint light) extending from i) Geminorum to the variable star S (15) Monocerotis. From the latter star the Milky "Way proceeds southerly with a somewhat increased and nearly uniform brightness across Monoceros and into the constellation Argo, where its brilliancy still further increases to 35° South Declination, at which point the stream passes below the boundary of Heis' maps. South of £ and it Argus, Heis shows a long narrow vacuity or " coal sack," and the northern portion of another a little to the east (both of these are shown by Proctor). The eastern border of the former " coal sack " is the brightest portion of the Galaxy in this vicinity as drawn by Heis. This forms a good illustration of a remarkable fea- ture of the Milky Way, viz., that bright streaks and dark vacuities are in several cases found close together, a feature which will have to be explained by any satisfactory theory of this wonderful zone. Let us now return to the point we started from in Cassiopeia, and trace the course of the Milky Way, as shown by Heis, in the opposite direction. From /3 Cassio- 1 Here Proctor shows 110 Milky Way light. 128 THE VISIBLE UNIVERSE. peiaa a narrow band of bright nebulosity extends towards the bead of Cepbens, and spreading out covers a large area, including a vacuity in wbicb 8, e, f, and X Cepbei are situated. This "coal sack" is rilled in witb very faint nebulous ligbt (about fifth order of brightness). Between this and a Cygni is another oval-shaped vacuity, the centre of which seems quite free from nebulosity [from which a narrow dark rift passes across the Milky Way between £ and p Cygni. This " rift," although very conspicuous to the eye, is, curious to say, entirely omitted by Heis, who shows in its place a very bright patch extending from p Cygni to o 1 and o 2 ]. From a Cephei a long vacuity stretches as far as m and e Cassiopeise. From a Cygni to Sagitta the Galaxy is very luminous, all the dark spaces shown in most star atlases being filled in, according to Heis, with faint nebulosity. The brightest part of this region is an elongated spot extending from 7 to /3 Cygni, the brightest part of all lying between 7 and 77 Cygni. In this spot Heis shows three gradations of brightness, bounded by a fainter region towards Lyra, and by a long vacuity (or very faint region) on the opposite side (see Plate II.). A fairly bright region, however, extends from v and an( ^ ^ Aquilaj. From this region a fainter exten- sion includes the brighter stars of the Dolphin's rhomb. The actual bifurcation of the two streams of the Milky Way (only partially separated in Cygnus) takes place between 7 and f Aquilee. Following the western or "broken branch," which is bright in the vicinity of e and £ Aquilaa, a patch of fainter • :".i •0 * " l ' • ■v • . • •»' • •\ ■? V • • s • i» .- 1 • otfVeoaJ *. 'i * u . . y ■ •a ■ ' f y. . . • • • ■ • 0'-! »" ■<> * •£ «• .« ? • Plate 11. The Milky Way in. Cygims . ^A& drmrrv byMeis. Plate 11^ The Milky Way in. Cygn.u.8, _AFber Boeddzcker- Stars to 8^ Truxjgiiihxdj&lhcmvHardinjg. THE COURSE OF THE MILKY WAY. 129 light occurs, then another brighter portion (but of varying brightness) extends to and includes the small group of stars formed by 67, 68, 70, 73, and 74 Ophiuchi, and seems to end in a point, the whole branch bearing a striking resemblance to a human leg and boot (sec Plate III.). It is, however, bounded on the west by very faint nebulosity, which extends from Lyra to about 41 Ophiuchi, and includes /3, , t, f, an( i § Sagittarii. The main branch here passes over y Sagittarii and below the limit of Heis' map. These bright spots in Sagittarius are shown by Heis of about the same brightness as the spot near rv cav eqpuo&SurfbuxiRrqjecticm/ ) Southern Hemisphere. MiLhy Way according ix> Gould*. y% y- / ..X; . . ' •♦ ' ■■>' ■A - \ X • ■ • A- . / ■ . .w- -\.-.\ tfo J~,~£.Go-rc,J)eZt. '~ Cygni. The Hyades also form a rich region ; but these may also — like the Pleiades — be considered as forming an open cluster. An extensive region of more than average richness covers Gemini, a portion of Taurus (including the Hyades), Orion, and the head and fore feet of Monoceros, and is connected with the rich southern region to be described further on. In addition to the poor spot in Cassiopeia referred to above may be mentioned that including the body and fore legs of Camelopardus and the ears of the Lynx. Imme- diately south of this is a pretty rich region, which includes 8 and £ Aurigse. Another poor region occurs in Pisces (between S and &> Piscium) ; another north of S Ursse Majoris (the faintest star of the " Plough ") and between that star and k Draconis ; one between Coma Berenices, £ Ursae, and 8 Leonis, and others less remarkable. It is worthy of remark here that the Northern Pole of the Milky Way lies close to Coma Berenices, which forms a rich region ; but this also may be considered as a loose cluster, like the Hyades. South of the Equator Heis' maps show the northern rich region above described, extending over Lepus and Canis Major, and Behrmann's maps carry it south over Columba and Argo to the Southern Cross. The existence of this rich 154 THE VISIBLE UNIVEKSE. southern region was strongly maintained by the late Mr. Proctor, 1 but has been doubted by some astronomers, and iistinctly denied by Mr. Henry Farquhar some years since. 2 A. mere glance, however, at Behrmann's maps is sufficient ;o show that such a rich region really exists, and a statisti- ;al enumeration confirms the judgment of the eye (see Plate VII.). It will not do to argue, as Mr. Farquhar does, that the ipparent richness found by Proctor is due to the fact that ' those who observed this part of the heavens included more md fainter stars in their sixth magnitude than did northern )bservers." This argument would apply to the whole of ;he southern sky, but I find that the region referred to is ■ich in lucid stars — not by comparison with the Northern Hemisphere, but with reference to the other portions of Behrmann's maps. This seems decisive as to the existence )f the rich region iu question. This region nearly coincides with the course of the VTilky Way from Canis Major to the Southern Cross, and ncludes within its boundaries a very rich spot about nidway between 77 Argus (the famous variable star) and Han opus (a Argus). This spot includes e, 1, and % Carinas average richness about 0-57). Most of the stars are, lowever, small. A still richer region, but of smaller area, ies between e Canis Majoris and /3, 8 Columbaa. The richest spot, however, in the Southern Hemisphere »f any considerable size, and containing bright stars, is hat situated immediately south preceding the Southern 3ross, and including o, 17, £> 6 Crucis, and a, /3, e, £ Muscse see Fig. 2). It lies on the Milky Way, and its close 1 Essays on Astronomy, p. 312. 2 Observatory, December 1879. Plate Vlll. Distribution of Stars to 7# Magnitude, Southern Hemisphere ( Urxtnornetrixv^irc/entmay) sat SOUTHERN RICH REGIONS. 155 proximity to the barren " coal sack " — in which Behrmann shows only two small lucid stars — is very remarkable and suggestive. It has an average of 06 to the square degree, or three stars to five square degrees. There are some other rich regions in the Southern Hemisphere, unconnected with the Milky Way, of which the most remarkable is a spot just north of 8, e, f Hydri, Fig. 3. — Region rich in lucid stars. From Behrmann' s Atlas. on the borders of Hydrus and Horologium (see Fig. 3). This is especially rich, as shown by Behrmann, but the stars are mostly small — several of them, indeed, below the sixth magnitude, according to the Uranometria Argentina. A tolerably rich, but very elongated region extends from near p Argus (about 25° S. Decl.) up to a and 8 Antlia) (see Fig. 4) ; but the stars are mostly small, and probably 156 THE VISIBLE UNIVERSE. would not, to average eyes, convey an impression of rich- ness. Immediately south of this is a very poor region, in which over an area of about a hundred square degrees Behrmann does not show a single star ! — another example Fig. 4.— Eich and poor regions in Hydra and Antlia. From Behrmann. of rich and poor regions in close proximity. Another isolated region, above the average richness, includes 77, J, /** v > $> X Centauri, and a, ft, 7, 8, e, t, fi, v, ir, etc., Lupi (see Fig. 5). This region lies near the borders of the Milky Way extension in Norma. Another very poor region lies between a, yjr, and a 158 THE VISIBLE UNIVERSE. Oapricorni on the one side, and ieure du systeme. Pour decider cette question, il faudra examiner la region du p61e avec deux telescopes, dont l'un aurait la penetration a peu pres egale a celle du telescope de Herschel, et l'autre une penetration plus grande. Si le nombre des etoiles visibles est le meme, dans les deux instruments, la limite est trouvee dans cette direction." The correctness of this opinion is shown by M. Celoria's observation already referred to, and the ques- tion will doubtless be finally decided by photography. By a further analysis Struve computes for an hour of R. A. of his zone (+ 15° to — 15°) " le nombre d'Stoiles que cette portion de la voute presenterait, si elle etait remplie dans sa totality, par des etoiles condensees comme au milieu de la voie lactee," and finds the following results : — 1,095,920 stars of magnitude 1 to HerschePs faintest. 4983 „ „ 1 to 9 of Bessel. 1422 „ „ 1 to 8 „ 279 „ „ 1 to 7 RELATIVE DISTANCES OF STARS. 273 " The cube roots of these numbers express the relation between the radii of the four spheres," and give : — Radius of sphere which contains the stars. For Herschel's stars . 1-0000 . 9-1684 „ 9 mag', of Bessel . 0-16567 . 1-5189 „ 8 „ „ . 0-10907 . 1-0000 „ 7 „ „ 0-06338 . 0-5811 Comparing these numbers with the corresponding densities from, formulae which he gives, and discussing the number of stars of the different classes in the whole 1 of the Northern Hemisphere, as shown in Argelander's Urano- metria, Struve computes a table of relative distances of stars of different magnitudes (see Appendix, Note P). From these results he draws the following conclusions : — ■ 1. The faintest stars visible to the naked eye, according to Argelander, are placed at a distance of 8'8726 times the mean distance of stars of the first magnitude. [With the now generally accepted light ratio of 2-512 the light of a first-magnitude star would be a hundred times the light of a sixth magnitude, and hence the distance of a sixth- magnitude star would be ten times the distance of a first magnitude, supposing both stars to be of equal size and brightness.] 2. The faintest stars of ninth magnitude observed in Bessel's zones are at a distance of 37-73 times the distance of stars of first magnitude, or 4-25 times that of stars of sixth magnitude. 3. The faintest stars seen in Herschel's sweeps with the 1 The number of stars .1 to 6 magnitude in the selected zone being inadequate for the purpose, 18 274 THE VISIBLE UNIVERSE. 20- feet telescope are at a distance of 227-8 times the distance of stars of first magnitude, or 25-67 times that of sixth- magnitude stars. "With reference to the supposed position of the Sun— a little outside the principal Galactic plane— Struve finds for its distance from that plane a final value of 0-21 of the mean distance of stars of the first magnitude, and says : " Mais comment expliquer a present la deviation de la voie lactee, de la forme du grand cercle ? Voici ce que je pense. La couche la plus condensed des dtoiles ne forme point un plan parfait, mais plutdt un plan brise' ; on bien, elle se trouve dans deux plans, incline's l'un sur l'autre d'environ 10°, et dont l'intersection est placde a pen pre's dans le plan de l'equateur celeste, le Soleil se trouvant a une petite distance de cette ligne d'intersection, vers le point 13h. de l'equateur." 1 Struve then proceeds to discuss the bearing of his own researches on the hypothesis of the extinction of light in the ether of space. This idea of light extinction seems to have been first suggested by M. L. de Cheseaux in an article published at Geneva in the year 1744. In this work Cheseaux attempts to determine the distance of stars of the first magnitude by a comparison between their light and that of the planet Mars, observed in various parts of its orbit. By this method he found a distance of 20,000 times 2 the Sun's distance from the earth, and the mean apparent diameter of a first-magnitude star equal toy^th of a second. ■ [Modern observations show that Cheseaux's distance is much too small, but his apparent stellar diameter is perhaps 1 Andes d'Astrmiomie Stellaire, p. 82. 2 Corresponding to a parallax of about 10 seconds of arc. OLBEES' VIEWS. 275 not far from the truth.] Olbers, from a comparison of Mars and Aldebaran, found for the latter a distance of 344,643 times the Sun's distance from the earth, and from comparisons of- Saturn and Procyon a distance for Procyon of 378,972 times the Sun's distance. [These distances, although much nearer the truth than Cheseaux's result, are still too small, as shown by more precise modern ob- servations.] For stars of the sixth magnitude Olbers found, by comparison with the planet Uranus, a distance nearly ten times . greater than stars of the first magnitude, 1 an estimate which agrees with that derived from the now generally accepted light ratio of 2"5-12. In a paper published by Olbers in Bode's Jahrbuch for 1823 2 he refers to an error of Halley, who denied that an infinite number of stars would produce a sky as brilliant as the Sun. Olbers maintains that such would be the case, and in order the reconcile the appearance of the sky with the hypothesis of a stellar universe of infinite extent, he thinks it is necessary to admit an extinction' of light in stellar space. He says : " Let us congratulate ourselves that nature has arranged the thing otherwise, and that each point of the celestial vault does not • send solar light upon the earth. Without considering the insupportable brightness and exorbitant heat which would reign (for the Almighty Creator would have . protected the earth and its organised beings against the action of this heat, even if it were 90,000 times greater than we experience at 1 From photometric experiments Sir W. Herschel deduced a distance for stars of sixth magnitude twelve times greater than that of stars of first magnitude. 2 Veber die Durehtichtiglieit des Weltraitns von E. Dr. Oilers, dated 7th March, 1823. 276 THE VISIBLE UNIVERSE. present), I only wish to mention the astronomy, imperfect to the last degree, which would be within the range of the inhabitants of the earth. We should know nothing of the starry sky, we could with difficulty discover our Sun by its spots, and with difficulty distinguish the Moon and the planets by their darker discs on the dazzling ground of the sky. Is it necessary then to abandon the idea of an infinity of systems of fixed stars because the celestial vault does not shine with the brightness of the Sun ? Is it necessary to restrict these worlds to an insignificant portion of infinite space ? By no means." l Sir W. Herschel estimated the " space penetrating power " of the telescope used in his gauges at 61"18 — that is, that with the aid of this telescope he could see stars at 61*18 times the distance of the faintest stars visible to the naked eye. This estimate was based on the assumption that the diameter of the eye pupil was 02 inch. As, however, a telescope gives a sharper image of a star than that produced by the unassisted vision, Struve thinks that a comparison between the two cannot be strictly made. To remedy this defect he substituted for the eye a small telescope of 0-211 inch aperture, magnifying about three times. This little instrument, he considers, gives the same quantity of light and produces an image which is independent of the nature of the observer's eye, whether short-sighted or long-sighted. Using this " module " telescope Struve found by numerous experiments that he could see in all directions of the sky nearly double the number of stars shown in Argelander's maps, or more exactly, 183 stars to Argelander's 100. 1 This quotation from Olbers' paper I have translated from the French of M. Struve. THE EXTINCTION OF LIGHT IN SPACE. 277 He finds, then, for the sphere which contains all the stars visible with the module, a. radius equal to 10-852 times the mean distance of stars of the first magnitude. 1 Herschel found this radius equal to 12, a close agree- ment. He also found for the range of Herschel's telescope 74*83 times the distance of sixth-magnitude stars, and 74-83 x 8-8726 = 663-94 times the mean distance of stars of the first magnitude. Now Struve's examination of Herschel's gauges gave for his faintest stars a distance equal to 25-672 times the mean distance of stars of the sixth magnitude, or a little more than one-third of the range due to its optical power. How is this difference to be explained ? Struve says : " Je ne vois point d'autre explication que celle d'admettre, que rintensite" de la lumiere de'croit en plus grande proportion que la raison inverse des Carre's des distances ; ce qui vent dire qu'il existe une perte de lumiere, une extinction, dans le passage de la lumiere par l'espace celeste." 2 Struve shows that, with a space-penetrating power of 74-83, the number of stars visible in Herschel's gauges should be 3021 instead of 122. He says: "Peut-etre, dira-t-on, y a-t-il une diminution de densite" dans le plan principal, vers les limites de la voie lactee. 3 Mais que savons-nous de ces limites ? La voie lact6e nous est absolu- ment insondable. Quelle est done la probabilit6 que le Soleil se trouve pres du centre d'un disque, dont l'6tendue nous est entierement inconnue. Souvenons nous enfin, que 1 See " Table of Relative Distances," Appendix, Note P. 2 Mudes d'Agtronomie Stelltdre, p. 86. 3 This is the most probable explanation. 278 THE VISIBLE UNIVEESE. l'examen des etoiles herscheliennes a conduit a la m&me loi moyenne du decroissement de densite" dans le sens per- pendiculaire an plan principal, qui a lieu dans le voisinage du Soleil, jusqu'a la distance des 6toiles de 8-eme et 9-eme grandeur. Par toutes ces considerations, j'ose avancer que nous avons d6couvert un fait, dans lequel l'extinction de la lumiere des 6toiles s'est manifested presque indubitaple- ment." 1 He then proceeds to determine the numerical value of this hypothetical extinction of light. Taking as unity the distance of stars of the sixth magnitude, and supposing that the light in passing over this unit of distance is reduced in intensity — by the absorption — from unity to a certain fraction, he computes from the theoretical range of Herschel's telescope, 74"83, and the actual range, 25-672 (deduced from an examination of Herschel's gauges), the value of this fraction. This he finds to be 0-92, and hence the loss of light is 0-08, or eight per cent, of the original intensity. From 'the Table of Eelative Distances (see Appendix, Note P) we have the distance of sixth-magnitude stars = 8-8726 times that of stars of first magnitude. From this he computes the loss of light for stars of first magni- tude, and finds it 0-009349, or t£ t of the original intensity. Calculating a table for stars at different distances, he finds that the effect of the extinction of light, which for stars of first magnitude is only one per cent., and eight per cent, for stars of the sixth magnitude, increases to thirty per cent, for Bessel's ninth-magnitude stars, and to eighty-eight per cent, for the faintest stars visible in Herschel's gauging telescope. Beyond this distance the 1 Etudes d'Astronomie Stellaire, p. 87. THE EXTINCTION OF LIGHT. 279 diminution of light becomes very rapid, and for a distance equal to 1470-8 times the distance of stars of first magni- tude the light would be reduced to 1U0 f 00U of its original intensity ! This diminution of light would-, of course reduce the range of telescopes very considerably. For Herschel's 40- feet telescope the theoretical range of 2300 units would be diminished to 368-5, or, in other words, the faintest stars visible in that telescope would be distant only 368| times the distance of stars of the first magnitude, instead of 2300 times that distance, if extinction of light did not lexist. For Lord Rosse's telescope of six feet, aperture the distance would be 422 units instead of the theoretical range of 3450. The distance of star clusters and nebulee, as computed by Sir W. Herschel, would, for the same reason, be con- siderably reduced. For example, the cluster 75 Messier, which he placed at a distance of 734 times the distance of stars of first magnitude, would, by the effect of extinction, be diminished to 228 times that distance. Considering the distribution of the stars as nearly uniform and proportional to the space, and assuming as before an infinite extension of the Milky Way in the direction of its principal plane, Struve investigates the proportion which stars of different classes contribute to the apparent brightness of the Galaxy. He computes a table, from which he draws the following conclusions : — "1. Admitting the extinction of light, the brightness of the Milky Way — supposed limitless in extent — is no longer necessarily infinite. Its brightness is now reduced to 3-3 times the brightness which would be produced by all stars 280 • THE VISIBLE UNIVERSE. of 1 to 9 magnitude of Bessel which are situated in that direction, or the 12 J times that of the stars visible to the naked eye (in the same direction). " 2. The stars which lie beyond the range of Herschel's 20-feet telescope do not contribute more than twelve per cent, to the total brightness of the Milky Way. " 3. Subtracting the amount of light due to the lucid stars (1 to 6 magnitude of Argelander) we obtain 0-92007, which expresses the light of the background of the sky for the middle of the Milky Way." Comparing the brightness of the Milky Way Zone with that of the celestial vault in the direction of the Galactic poles, he finds : — " 4. The total brightness of the sky in the direction of the Poles is only twenty-two per cent, of that in the middle of the Milky Way. " 5. The ratio between the brightness produced by stars of different classes in the two directions, viz., that of the Milky Way and that of its Poles, increases gradually as the stars become fainter. " 6. Subtracting the light of the lucid stars, we have the illumination in the direction of the Pole" (0-15170) "not even a sixth of the light of the Milky Way " (0-92007). The number 25-672, found by Struve for the space- penetrating power of Herschel's gauging telescope, depends on the assumption that the Milky Way is of infinite extension in the direction of its principal plane. As I have shown, however, this assumption is not warranted by Sir W. Herschel's observations. The difference between the space-penetrating power of his telescope as estimated by Herschel and the result computed by Struve may be THE CONSTITUTION OP THE MILKY WAY. 281 equally well explained if we suppose the stars composing the Milky Way to " thin out " near the limiting range of Herschel's telescope. The optical power of his instrument might have enabled him to reach stars at a distance of 74*83 times that of a star of the sixth magnitude — if the stars were there ; but if the stellar aggregation has sensibly diminished in density at this distance, the number of stars visible in his instrument would not be proportionately increased. 1 That the Milky Way is not infinitely extended in the direction of its plane seems clearly shown by Sir John Herschel's observations in the Southern Hemisphere. Some of these have been already quoted in the chapter on "The Milky Way and Star Distribution." In his Outlines of Astronomy (pp. 578, 579, 580, Tenth Edition) he says : — "When examined with powerful telescopes, the constitution of this wonderful zone is found to be no less various than its aspect to the eye is irregular. In some regions the stars of which it is wholly composed are scattered with remarkable uniformity over immense tracts, while in others the irregularity of their distribution is quite as striking, exhibiting a rapid succession of closely clustering rich patches separated by comparatively poor intervals, and indeed in some instances by spaces absolutely dark and completely void of any star, even of the smallest telescopic magnitude [the italics are Herschel's]. . . . In some, for instance, extremely minute stars, though never altogether wanting, occur in numbers so moderate as to lead us irresistibly to the 1 At a distance of 74'83 a sixth-magnitude star would be reduced in brightness about 9-37 magnitudes ("light ratio" = 2-512) or to magnitude 15'37. Herschel's original estimate of 61-18 would make his faintest stars 14-93 magnitude, which is perhaps nearer the truth. A distance of 25-672 would imply a magnitude of 13-04, which is about the minimmn msibile of a 6-inch refractor — according to Pogson's formula. This is of course on the assumption of no extinction of light. 282 THE VISIBLE UNIVERSE. conclusion that in these regions we see fairly through the starry stratum, since it is impossible otherwise (supposing their light not intercepted) that the numbers of the smaller magnitudes should not go on continually increasing ad infinitum. In such cases, moreover, the ground of the heavens, as seen between the stars, is for the most part perfectly dark, which again would not be the case, if innumerable multitudes of stars too minute to be individually discernible existed beyond. In other regions we are presented with the phasnomenon of an almost uniform degree of brightness of the individual stars, accom- panied with a very even distribution of them over the ground of the heavens, both the larger and smaller magnitudes being strikingly deficient. In such cases it is equally impossible not to perceive that we are looking through a sheet of stars nearly of a size, and of no great thickness compared with the distance which separates them from us. Were it otherwise we should be driven to suppose the more distant stars uniformly the larger, so as to compensate by their greater intrinsic brightness for their greater distance, a supposition contrary to all probability. In others again, and that not unf requently, we are presented with a double phenomenon of the same kind, viz., a tissue as it were of large stars spread over another of very small ones, the intermediate magnitudes being wanting. The conclusion here seems equally evident that in such cases we look through two sidereal sheets separated by a starless interval." " Throughout by far the larger portion of the extent of the Milky Way in both hemispheres, the general blackness of the ground of the heavens on which the stars are projected, and the absence of that innumerable multitude and excessive crowding of the smallest visible magnitudes, and of glare produced by the aggregate light of multitudes too small to affect the eye singly, which the contrary supposition would appear to necessitate, must, ' we think, be considered unequivocal indications that its dimensions in directions where these conditions obtain, are not only not infinite, but that the space-penetrating power of our telescopes suffices fairly to pierce through and beyond it." He then refers to Struve's speculations on the extinction of light, and says : — "The objection alluded to, if applicable to any, is equally so to every part of the Galaxy. We are not at liberty to argue that at one part of its circumference, our view is limited by this sort of cosmical THE CONSTITUTION OF THE MILKY WAY. 283 veil which extinguishes the smaller magnitudes, outs off the nebulous light of distant masses, and closes our view in impenetrable darkness ; while at another we are compelled by the clearest evidence telescopes can afford to believe that star-strown vistas lie open, exhausting their powers and stretching out beyond their utmost reach, as is proved by that very phaenomenon which the existence of such a veil would render impossible, viz. , infinite increase of number and diminution of magni- tude, terminating in complete irresolvable nebulosity. Such is, in effect, the spectacle afforded by a very large portion of the Milky Way in that interesting region near its point of bifurcation in Scorpio where, through the hollows and deep recesses of its complicated structure, we behold what has all the appearance of a wide and indefinitely prolonged area strewed over with discontinuous masses and clouds of stars which the telescope at length refuses to analyse. Whatever other conclusions we .may draw, this must anyhow be regarded as the direction of the greatest linear extension of the ground plan of the "Galaxy. And it would appear to follow, also, as a not less obvious consequence, that in those regions where that zone is clearly resolved into stars well separated and seen projected on a black ground, and where by consequence it is certain if the foregoing views be correct that we look out beyond them into space, the smallest visible stars appear as such, not by reason of excessive distance, but of a real inferiority of size and brightness." [The italics are Herschel's.] From these remarks it seems perfectly clear that Struve's conclusions are quite irreconcilable with Sir John Herschel's observations. 1 But apart from Struve's hypothesis of an infinite exten- sion of the Milky Way in the line of sight, his assumption of stellar condensation in planes parallel to the principal Galactic plane — a sort of stellar atmosphere — seems highly improbable. A sidereal system forming a disc of limited thickness, but of infinite (or rather indeterminate) diameter, 1 It should be stated, however, that Sir John Herschel's observations were not published till after the publication of Struve's memoir, and were there- fore, of course, unknown to the great Kussian astronomer. 284 THE VISIBLE UNIVEKSE. although very improbable, is at least conceivable ; but that this disc should increase in stellar density from its surface to its central plane, and then diminish in density again towards the opposite surface, seems too artificial an arrange- ment to represent a real law of nature. With reference to the extinction of light supposed by Struve, Professor Grant says, in his History of Physical Astronomy : " If such an hypothesis were true, we might reasonally presume that, in consequence of the light being everywhere extinguished at the same distance, the Milky Way would present a uniform aspect throughout its course. As, however, observations of the actual aspect of the Milky Way do not accord with this conclusion, the hypothesis from which it is deduced is manifestly inadmissible." In a memoir recently published on the apparent dis- tribution of the stars visible to the naked eye, 1 Professor Schiaparelli discusses the question of the probable extinction of light in interstellar space. From a consideration of the numbers of stars of different magnitudes down to the fifth magnitude contained in the Harvard Photometry, he finds a value for the "constant of extinction" equal to O9l90. With this co-efficient he computes a table of the extinction of light for stars down to the sixteenth magnitude — extend- ing the Harvard scale by means of the light ratio 2-5119, 2 adopted by Pickering. From this it appears that the distance of stars of the fifth magnitude, which, on the assumption of no extinction, would be — with the assumed light ratio — 6-31 times the distance of stars of the first 1 Sulla Distrilmzione Apparente delle Stelle visibili ad Occltio Nudo, Pubilicanoni del Reale Osservatorio di Brera in Milano,~S. XXXIV., 1889. 2 This is the light ratio now generally accepted by astronomers. SCHIAPARELU's VIEWS ON LIGHT EXTINCTION. 285 magnitude, is reduced by extinction to 5-269 times that distance. For stars of the sixth magnitude the distance is reduced from 10 to 7-576, and for stars of the sixteenth magnitude from 1000 to 65-548. He concludes therefore that for the naked-eye stars it is not of much importance whether we accept or reject the hypothesis of extinction. (His words are : " Per le stelle lucide adunque non e di molta importanza l'adottare l'ipotesi dell' estinzione piuttosto che il respingerla.") The extinction, however, for stars below the sixth magnitude would increase very rapidly, the light of tenth-magnitude stars being reduced from unity to the fraction 0-1324, and that of the sixteenth magnitude to the small fraction 0-0039, or more correctly to ^^ of its original amount. From, these values it appears that with- out extinction stars at sixteenth-magnitude distance would shine as tenth magnitude. Taking the number of stars down to the fifth magnitude contained in Argelander's Durchmusterung at 1024, and • assuming that the stars contained in that catalogue include all those to tenth magnitude, of which the distance is re- duced from ,63-096 to 23-948, on the above scale, Schiaparelli finds that — considering the volumes of the sphere contain- ing these stars — :the number of tenth-magnitude stars visible in the whole heavens should be 120,180. But from the numbers in the Durchmusterung it appears that the actual number visible would be over 600,000 for the whole star sphere, or nearly five times the number required on the hypothesis of extinction. If then we accept the theory of extinction, he considers it necessary to assume that we are. situated in a spherical cavity relatively free from stars, the stars increasing in number with increase of distance, 286 THE. VISIBLE UNIVEKSE. and for magnitudes below the tenth with very great rapidity. Hence it appears that the fundamental assumption of a uniform distribution of stars disappears from the brighter orders of stars, and to preserve it for the fainter orders the hypothesis of light extinction has been proposed. Schiaparelli concludes that such an hypothesis is not only unnecessary, but that it is ineffectual to produce the effect for which it was introduced, 1 and he considers that so rapid an extinction of light must be regarded as improbable. He thinks, however, that there is nothing for or against the supposition of a very small and very slow extinction of light, for instance, the tinrfch f the light at unit of distance ' proposed by Struve, or the ^-^th suggested by Olbers. That celestial space is not everywhere equally transparent he thinks very possible, and he compares the vibrations producing light to those of sound, which are propagated through the air, but are annihilated when they reach the limits of the atmosphere. Zollner objected to the theory of extinction that the light absorbed would be converted into heat, but Schiaparelli replies that we cannot consider the ether as acting like a gas, or any other form of matter ; and he points out that could we consider the ether as a gas, however . rariried, the supposed extinction would produce an absorption in the 1 His words are : " Cioe che noi ci troviamo in una specie di cayita sferica relativemente rara di stelle, dal oui centro esse si vadano addensando sempre piu col crescere delle distanze, e per ordini superiori al decimo anche con una grandissima rapidita. Cosi scompare dagli ordini superiori la costante frequenza delle stelle, per conservare la quale negli ordini inferiori 1' ipotesi dell' estinzione era stata invocata. Non solo dunque tale ipotesi non e necessaria al problema, come sopra si e detto, ma essa e impotente a raggiungere 1' intento, per il quale era stata introdotta." SCHIAPAEBLLI'S VIEWS ON LIGHT EXTINCTION. 287 light of the stars when observed with the spectroscope, and the greater the distance of the star the greater would be the absorption. No such absorption has yet been observed. Schiaparelli is disposed to believe that if any extinction of light really occurs, it is probably due to fine particles of matter scattered through interstellar space. He refers to the supposed constitution of comets' tails, of falling stars, and meteorites in support of this hypothesis.- [Here we are reminded of Lockyer's " meteoritic plenum."] He then investigates the question of the quantity of matter which would be necessary to produce the required extinction. He assumes with Gylden the mean parallax of stars of the first magnitude as 0-"083, which corresponds to a distance of 369 x 10 12 kilometres, and that for this distance the loss of light is -g^th, as supposed by Olbers. Taking the extinction as proportional to the distance (which we may do for short distances) we have the loss for each kilometre equal to unity divided by 259,200 x 10 12 . Then supposing a cylindrical space extending from the observer to the star, of which the cross section is one square kilo- metre, it would be .necessary that each cubic kilometre should contain as much matter as would suffice for the extinction of light on a transverse area expressed by one square kilometre, divided by 259,200 x 10 12 , or one square millimetre divided by 259,200, which if. collected would form an opaque spherical corpuscle of about a microm radius, or more exactly 1-H)38. Supposing this obscuring matter to be all divided into these small spheres, the quantity of such matter scattered through a volume' equal to that of the terrestrial globe, if collected into one mass, 288 THE VISIBLE UNIVERSE. would form a ball only 10-65 millimetres radius (or about 0-42 inch). In a sphere described with a diameter equal to the major axis of the earth's orbit, the collected matter would form a ball with a radius of 247 metres (or about 810 feet). For a sphere having a diameter equal to the mean distance of stars of the first magnitude, the collected corpuscles would form a globe of 307,000 kilometres radius, or nearly 48 times the mean radius of the earth. Schiaparelli con- siders that in these results there is nothing opposed to received ideas respecting the density of comets' tails, or the number of falling stars and meteorites supposed to exist in the Solar System. If we suppose the mass of the obscuring corpuscles greater, say globes of one millimetre radius, it would be necessary to admit in the same space a quantity of matter a thousand times greater, and even this supposition would not lead to inadmissible results. But in this case the matter scattered through space would begin to surpass in volume that of the stars themselves. 1 In conclusion Schiaparelli considers that there is nothing impossible in the idea of matter scattered through space in sufficient quantity to produce an appreciable extinc- tion of stellar light, and especially in the case of very distant stars. In this way he thinks we may explain the apparent blackness of the sky on which the stars are spread, 1 Schiaparelli's words are : " Cosi assumendo piccoli globi de 1 millimetre) di raggio, bisognerebbe ammettere nel medesimo spazio una quantita di materia opaco di un volume totale mille volte piu grande : e tale supposi- zione non condurebbe ancora a risultati inammisibili. In tale caso per6 la materia diffusa a questa modo per lo spazio cominoierebbe a supera in volume quella raocolta mi corps lucenti, che ohiamiamo stelle." THE EXTINCTION OF LIGHT IN SPACE. 289 without having recourse to the hypothesis of a limited number of stars, or to any conjectures as to the constitution of the luminiferous ether. A similar suggestion has been advanced by Mr. Monck to explain the limited number of the visible stars. I have already stated in the present chapter the evidence which seems opposed to the hypothesis of any extinction of light whatever in interstellar space, at least as far as our largest telescopes can reach. Beyond that distance, how- ever, the extinction of light may perhaps become appre- ciable, and may very possibly account for the fact that the number of the visible stars is finite. 19 CHAPTEE XVII. pkoctok's views. IN his very interesting work The Universe and the Coming Transits (1874), the late Mr. Proctor gave a summary of the views advanced by Kepler, Huygens, Wright, Kant, Lambert, and Michell. These have been already discussed in Chapter XIII. With reference to these theories Proctor says : " I do not hesitate to say that Wright, Kant, Lambert, and Michell did more to advance men's ideas respecting the constitution of the sidereal universe than all the astronomers who lived before the time of Sir W. Herschel" (p. 176). As the long quotation I have given from Wright's rare work will show, he was undoubtedly the originator of the " disc " theory of the Milky Way. This hypothesis, popularly attributed to Sir W. Herschel, was abandoned by that great astronomer himself in his later writings, as Strave has clearly demonstrated, and as Proctor has ably maintained in recent years. Struve's researches on the subject have been discussed in the pre- ceding chapter. In the present chapter I propose to give * some account of Proctor's objections to the " disc " theory, and of his own views on the construction of the sidereal heavens. 290 EXTERNAL GALAXIES. 291 Proctor thinks that Sir W. HerschePs elaborate series of papers (which are scattered through 37 volumes of the Philosophical Transactions of the Eoyal Society, 1780 to 1818) are worthy, of more careful study than they usually receive, a study which will clearly show that the " disc " theory of the Milky Way, definitely propounded by Herschel in 1785, was distinctly abandoned by him in 1811. The account given by Arago of Sir W. Herschel's theories has unfortunately been accepted by many English writers on astronomy ; but according to both Struve and Proctor this account is quite untrustworthy, and entirely misinterprets Herschel's views on the subject. The popular idea that Herschel considered all nebula as external galaxies is quite erroneous. Even in 1785 he looked on the nebulae as probably belonging to two distinct groups ; some possibly forming portions of the Milky Way, while others he considered as probably external galaxies. At this period he seems to have held the opinion that all nebulae had a stellar constitution. The spectroscope had not then been invented, and he attributed his failure to resolve some of these objects into stars to deficiency of optical power in his telescope. His opinion was in 1789 still unchanged, when he compared the different forms of nebulae to plants in the successive stages of their growth and subsequent decay. In the paper of 1802 he clearly shows his changed views on the construction of the Milky Way. He says : " The milky appearances deserve the name of clustering collec- tions, as they are certainly much brighter about the middle, and fainter near their undefined borders. ... We may indeed partly ascribe the increase both of brightness and 292 THE VISIBLE UNIVEKSE. compression to a greater depth of the space which contains the stars ; but this will equally tend to show their clustering condition; for, since the increase of brightness is gradual, the space containing the clusters in stars must tend to a spherical form if the gradual increase of brightness is to be explained by the situation of the stars." The recognition of this clustering tendency in the faint stars producing the Milky Way light is of course in direct opposition to the " disc " theory, which rests on the funda- mental assumption of a generally uniform stellar distri- bution. Again in the paper of 1814 he says : " This tendency of clustering seems chiefly to be visible in places extremely rich in stars. In order, therefore, to investigate the existence of a clustering power, we may expect its effects to be most visible in and near the Milky Way " ; and with reference to the irregular clustering portions : " Those which are in and very near the Milky Way may be looked upon as so many portions of the great mass drawn together by the action of a clustering power, of which they tend to prove the existence." These remarks show clearly enough the altered aspect of Herschel's views, and we may well ask with Struve, " pour- quoi les astronomes ont-ils maintenu generalement l'ancien systeme sur la voie lactee, enonc^ en 1785, quoiqu'il eut £te entierement abandonnS par l'auteur lui-m6me." 1 It seems high time therefore that this " disc " theory should be omitted from our text-books of astronomy, as it most certainly does not represent the more mature views of the great English astronomer. 1 Mtudes d'Astronomie Stellaire, p. 49. hekschel's latbe views. 293 It appears from Herschel's subsequent papers — published in 1817 and 1818 — that he did not formulate any very- definite theory to replace the one he had abandoned. Proctor, however, maintains that the principle enunciated in these papers — viz., " that the telescopic powers necessary to reveal and to resolve star groups, or particular star orders within groups, afford an indication of the distance at which these groups or orders lie " * — is unsound. In support of this opinion Proctor refers to observations of Sir W. Herschel of limited regions of the heavens in which he found -the brighter stars easily visible with low powers, while the faintest were individually invisible with his largest telescopes. On Herschel's principle this would imply that these star groups were of a cylindrical or conical shape, with their axes pointing directly towards the earth — an utterly improbable arrangement, and forming an hypothesis which, Proctor justly says, is " altogether untenable." By the application of this new but clearly erroneous principle, Herschel obtained results on which Struve subse- quently founded his hypothesis of an infinite extension of the Milky Way in the direction of its principal plane. Herschel said that " when he could not resolve the Milky Way it was because it is unfathomable." This Struve translates : " Si nos jauges cessent de r£soudre la voie lact^e en 6toiles, ce n'est point parce que la nature en est douteuse, mais parce qu'elle est insondable (fathomless)." 2 Accord- ing to Proctor the use of the French word " si " for the English "when" changes the whole meaning of the 1 These are Proctor's words, not Herschel's. 2 jkudes d'Astronomie Stellaire, p. 34. 294 THE VISIBLE UNIVEESE. sentence. However this may be, it seems evident that HerscheFs principle of the irresolvahility of star clusters, being a test of distance, would have led to the conclusion upon which Struve based his hypothesis of the extinction of light. Proctor says : " Where Hmschzi thought he was penetrating to the extreme limits of the sidereal system, he was in reality only analysing more and more searchingly an aggregation in tvhich many orders of stars were mixed up. What he failed to do was not (as he supposed) to sound the Galaxy, but to recognise as separate stars the minutest orders of orbs included within such aggregations." 1 All observations of star clusters and stellar aggregations seem to show the correctness of this conclusion. Proctor then proceeds to examine the evidence afforded by Sir John HerscheFs observations in the Southern Hemi- sphere. He justly remarks that the " Coal Sack " near the Southern Cross, and indeed the general aspect of the Galaxy in this region, indicates " that the Milky "Way, in this neighbourhood at any rate, is really what it appears to be, a belt or zone of stars separated from us by an appar- ently starless interval." With this opinion I fully concur. It certainly seems utterly improbable that the nearly circular blank space, known as "the Coal Sack," should represent a tunnel through a disc, of which the thickness is comparatively small, while its diameter, on Struve's hypo- thesis, stretches out almost to infinity. A straight tunnel- shaped opening of infinite length, or nearly so, with its axis pointing directly towards the earth, would form an extra- ordinary phenomenon, even in a solitary instance ; yet there 1 Tlie Universe and the Coming Transits, p. 217. The italics are Proctor's. SIE JOHN heesohbl's VIEWS. 295 are several 1 somewhat similar cases to be found in the Milky Way. That all these should represent tunnels radiating from a common centre is quite beyond the bounds of probability, and indeed such an hypothesis seems un- worthy of serious consideration. Sir John Herschel seemed inclined to consider the Galaxy as probably forming " a flat ring," although it does not appear that he definitely adopted this theory. His con- clusion that we cannot "without obvious improbability refuse to admit that the long lateral offsets which at so many places quit the main stream and run out to great distances, are either planes seen edgeways, or the con- vexities of curved surfaces viewed tangentially rather than cylindrical or columnar excrescences bristling up obliquely from the general level," 2 is objected to by Proctor, who thinks that " the obvious improbability seems to lie alto- gether the other way." A glance at Dr. Boeddicker's drawing of the Milky "Way will, I think, convince most people that Proctor's view is the correct one, and indeed it seems evident that the pro- bability of a number of planes or curved surfaces being so placed as to be seen edgeways is quite as small as the chance of a number of tunnel-shaped openings in a com- paratively thin disc being all directed to the centre of the disc. Sir John Herschel considered that "the tendency to aggregation of the brighter stars on the Milky Way is quite imperceptible among stars of a higher magnitude than the eighth, and except on the very verge of the Milky 1 And many small telescopic ones. 2 Outlines of Astronomy, Tenth Edition, p. 574. 296 THE VISIBLE UNIVEKSE. Way itself, stars of the eighth magnitude can hardly be said to participate in the general law of increase." " For the ninth and tenth the increase, though unequivo- cably indicated over a zone extending at least 30° on either side of the Milky Way, is by no means striking. It is with the eleventh magnitude that it first becomes conspicuous, though still of small amount when compared with that which prevails among the mass of stars of magnitudes inferior to the eleventh, which constitute sixteen-seven- . teenths of the totality of stars within 30° of either side of the Galactic circle." l From this he concludes " that the larger stars are really nearer to us (taken en masse, and without denying indi- vidual exceptions) than the smaller ones. Were this not the case, were there really among the infinite multitude of stars, constituting the remoter portions of the Galaxy, numerous individuals of extravagant size and brightness, as compared with the generality of those around them, so as to overcome the effect of distance and appear to us as large stars, the probability of their occurrence in any given region would increase with the total apparent density in that region, and would result in a preponderance of considerable stars in the Milky Way, beyond what the heavens really present, over its whole circumference." 2 In opposition to the view expressed in the opening sentence of the above quotation, Sir John Herschel says in his Outlines of Astronomy (p. 568, Tenth Edition) : " If we take in the whole amount visible to the naked eye, we shall perceive a great increase of number as we approach the borders of the Milky Way." The discrepancy between 1 Cape Observations, p. 383. 2 Hid., p. 383. AGGREGATION OF STAKS ON THE MILKY WAY. 297 these two statements Herschel explained, in a letter to Proctor, by saying that the passage in the Outlines refers " rather to a vague naked-eye impression than to the statistical resnlt of actual enumeration." 1 From an examination . of the stars down to 'Only the sixth magnitude Proctor found a well-marked tendency to crowding on the Milky Way. But in this investigation he omitted the " coal sacks " and vacuities, which Heis and Gould show to be rilled in with faint nebulous light, and the delineation of the Galaxy used in his inquiry was not very accurate. He found that " the whole of the Galaxy covers between one-tenth and one-eleventh of the heavens " ; but the draw- ings of Boeddicker, Gould, and Heis show a considerably greater extension. Houzeau's drawing of the Milky Way, however, covers, according to Plassmann, about one-tenth of the star sphere. But his drawing is very deficient in detail. In the chapter on the Milky Way I have shown that for the naked-eye stars north of the Equator, shown by Heis, the number of stars on the Milky Way is slightly in excess of that due to its area. This remark also applies to Houzeau's drawing of the Milky Way in both hemispheres. 2 A similar result was found by Major Markwick for Dr. Gould's stars to the seventh magnitude, south of the Equator (The Scenery of the Heavens, p. 265). Possibly a careful investigation of Dr. Boeddicker's drawing might show a still more marked tendency to aggregation of the lucid stars on the Milky Way ; but the computation would be a matter of no small difficulty, owing to the complicated ramifications of the Galaxy as delineated 1 The Universe and the Coming Transits, p. 194. 2 The Observatory, April 1890. 298 THE VISIBLE UNIVF.HSB. by Boeddicker. From an examination of the stars in Behrmann's Atlas I have, however, been able to verify Proctor's " rich southern region " extending from Canis Major to the Southern Cross. All the stars contained in Argelander's Durchmusterung (9 \ or 10th magnitude, equal to Herschel's 11th) were plotted by Proctor on a single chart (equal surface pro- jection). In this remarkable chart the cour-se of the Milky Way is clearly defined by a well-marked increase of stellar density. Proctor says : "In the very regions where the Herschelian gauges showed the minutest telescopic stars to be most crowded, my chart of 324,198 stars shows the stars of the higher orders (down to the eleventh magnitude) to be so crowded that by their mere aggregation within the mass they show the Milky Way with all their streams and clusterings. ... It is utterly impossible that excessively remote stars could seem to be clustered exactly where relatively near stars were richly spread. This might happen, no doubt, in a single instance ; but that it could be repeated over and over again, so as to account for all the complicated features seen in my chart of 324,198 stars, I maintain to be utterly incredible." 1 This argument seems quite unanswerable, and should, I think, serve to completely upset the original " disc " theory of the Milky Way, which, like many other errors, has per- sistently held its ground in astronomical text-books. The results derived from Proctor's chart are, however, in good agreement with the views expressed by Sir W. Herschel in his later writings, and it certainly does seem strange that the opinions held by Herschel, when, as Proctor says, " his 1 The Universe and the Coming Transits, p. 200. AGGREGATION OF STARS ON THE MILKY WAT. 299 labours- were but beginning, should be adopted by future astronomers in preference to those which were the fruits of his ripened experience." 1 Proctor also points out that if we consider the Milky Way as consisting of stars comparable in size and brilliancy with the brighter stars which stud our midnight sky, we must conclude that it lies at a vastly greater distance from our system than the lucid stars, and for this reason we should not expect to find any coincidence between the course of the Galactic streams and the configuration of the brighter stars which are optically projected on the. Milky Way. Several remarkable coincidences of the kind are, however, noted by Proctor, for instance, in Cygnus and in Scorpio ; and numerous examples of the apparent connection of star streams with rays and streams of Milky Way light may be traced in Dr. Boeddicker's drawing (see Plate IV.), which was executed from naked-eye observations only. Examined with a binocular I find that a similar relation exists in many places between the convolutions of the Galaxy and the small stars below the limit of naked-eye vision. I quote the following from my observing book : " 1889 Oct. 26, North of a Cygni, and near £ and v Cygni, the nebulous light of the Milky Way, as seen with binocular, seems to cling round and follow streams of small stars in a very remarkable way ; numerous small " coal sacks " and rifts are visible, in which comparatively few stars are to be seen with the binocular." This observation has been fully confirmed by photographs of this region obtained by Dr. Max Wolf in 1891. In some cases noted by Sir J. Herschel.at the Cape of 1 The Universe and the Coming Transits, p. 106. 300 THE VISIBLE UNIVERSE. Good Hope he found a sharply defined offshoot from the Milky Way with a tolerably bright star situated at the extremity of the projection. It seems impossible to escape from the conviction that a physical connection exists between these nebulous rays and the star streams with which they apparently coincide. That so many coincidences should be due to mere accident seems wholly improbable, and obvipusly leads to the con- clusion that the faint stars forming the nebulous light are, in reality, mixed up with the brighter stars, and do not lie at an immense distance behind them. Proctor also calls attention to the apparent coincidence Of streams in the irregular nebulae with streams of small stars visible in the same telescopic field of view. The evident connection between the nebulous light of the great Orion nebula and the stars visible in its vicinity — as shown by the spectroscope — clearly implies that stars and nebulous matter may co-exist in the same regions of space. The great majority of star clusters are found along the course of the Milky Way, while the irresolvable nebulas seem to aggregate towards the poles of that zone. The strongest evidence, however, in favour of the associa- tion between stars, star . clusters, and nebulae Proctor finds in the " Magellanic Clouds " in the Southern Hemisphere. ■In the larger of these " clouds " in particular we see stars of the seventh, eighth; ninth, and tenth magnitudes appar- ently mixed up with fainter stars and "clusters of all degrees of resolvability," in a space which, judging from its probably globular form, must be of small dimensions in comparison with its distance from the Solar System. It seems possible to imagine that one such object might THE MAGELLANIC CLOUDS. 301 be the result of foreshortening in a figure of cylindrical or conical shape, with its axis pointing towards the earth ; but, as Sir John Herschel remarks, " such an adjustment, impro- bable enough in one case, must be rejected as too much for fair argument in two. It must, therefore, be taken as a- demonstrated fact, that stars of the seventh or eighth magni- tude and irresolvable nebulae may co-exist within limits of distance not differing in proportion more than as 9 to 10." * This argument may, I think, be extended to the Pleiades, where, in a space of apparently spheroidal form, photo- graphy shows us stars of all magnitudes, from the third to the seventeenth magnitudes, mixed up with irresolvable nebulosity, which seems to cling round the brighter com- ponents. Dr. Boeddicker's drawing shows that this remarkable cluster is connected with the main stream of the Galaxy by a faint nebulous branch. Proctor was of opinion that the two Magellanic Clouds may possibly form . external galaxies. He says (Know- ledge, March 1886) : " We have in the Magellanic Clouds every one of the features which our Galaxy would present if seen from a distance. There are stars of the seventh magnitude which we may regard as being suns like Sirius, Vega, Altair, and other stars of the giant order, removed to many times the distance of the leading orbs of our Galaxy. Then there are fainter stars of all orders down to those so faint that they cannot be separately discerned with the most powerful telescopes we have, and appear only as milky nebulosity. There are star clouds of all orders; and, lastly, there are vast regions of gaseous matter, akin to the great Fish-mouth nebula in Orion, and the great 1 Outlines of Astronomy , Tenth Edition, p. 657. 302 THE VISIBLE UNIVERSE. key-hole nebula in the constellation Argo. If the nubecula are not external galaxies resembling our own, they present at any rate all the appearances which such galaxies would present from a very distant standpoint." With reference to the question of the resolvability of the star groups as a test of distance, Proctor points out that if a star group — the components of which are equal in magnitude, and individually visible to the naked eye — be supposed to pass away rapidly into space, each separate star would become fainter and fainter, and the distances separating them smaller and smaller, as the group receded from the eye. Now, if the " distances between them became too small to be distinguished while the stars themselves remained visible, clearly there would result a nebulosity of appearance." " But suppose that, on the contrary, the stars of the group became invisible when the group was at such a distance that the intervals separating star from star would not be indistinguishable (if only the stars were brighter). Then clearly the group would vanish with increasing distance without ever becoming nebulous. Clearly also, if a tele- scope were employed to bring the retreating group into view, the same conclusions would hold good. A group which would become nebulous to the naked eye before vanishing would become so when examined under a tele- scope, let the telescope's power be what it might ; while a group which would vanish without becoming nebulous to the naked eye would not become nebulous before vanish- ing under telescopic vision, whatever the telescopic power employed" 1 From this reasoning-r-which seems to be 1 Essays on, Astronomy, pp. 340, 341. STAB GROUPS. 303 sound — it is obvious that the resolvability of a star group, ia which the components are of equal brightness and equally- distributed, depends more on the constitution of the cluster than on its distance from the earth. A similar consideration is applicable to clusters containing stars of different classes of brightness. " Supposing a group of this kind to be passing away into space — as in the former case — the question whether it would become nebulous at any stage or stages of its progress would depend on the question whether or not the orders of stars about to disappear individually were congregated so closely that the eye could not distinguish the distances separating them." 1 Proctor considers that the correctness of the above reasoning is shown by Sir John Herschel's observations of the Magellanic Clouds. In the case of the smaller "cloud" (or nubecula minor) Herschel found the middle of the cloud clearly resolved into stars, while its edges remained irresolvable' with his 1 8^-inch reflector. He says : " The edge of the smaller cloud comes on as a mere nebula. . . . We are now in the cloud. The field begins to be full of a faint light, perfectly irresolvable. ... I should consider about this place to be the body of the cloud which is here fairly resolved into excessively minute stars, which, how- ever, are certainly seen with the left eye. . . . The borders fade away quite insensibly, and are less or not at all resolved. . . . This seems to be the body of the cloud. It is a fine rich large cluster of very small stars 12 ... 18 magnitude which fills more than many fields, and is broken into many 1 In the above considerations the question of the supposed extinction of light by the ether is of, course set aside. 304 THE VISIBLE UNIVERSE. knots, groups and straggling branches, but the whole (that is, the whole of the clustering part) is clearly resolved. . . . The lower part of the sweep (i.e., at 162° N.P.D.) contains a good deal of loose light, and is evidently the border of the Nubecula Minor ; but there are not many stars, and the light is perfectly irresolvable and not congregated into knots or distinct nebulae." 1 Now it is evident that, had the Nubecula Minor a great linear extension into space, the central portions would be more difficult to resolve into stars than the borders of the cloud. The above observations show that the exact opposite is the case, and obviously negatives the assumption of any great extension of the cluster in the line of sight. It would therefore seem to be clearly 'proved that the irre- solvability of a star cluster is no proof of enormous dis- tance, and that the stars visible to the naked eye in the Milky "Way and elsewhere are not necessarily at a greater distance from us than the small stars composing the Galaxy. Proctor finds that the nebulas, when charted, seem to run into streams or branches apparently connected with streams of stars, and he considers that this fact indicates a real and not merely an accidental association, leading us to the conclusion that the stars and nebulas form portions of one and the same sidereal system. .Charting .the stellar "proper motions" Proctor discovered that in many parts of the heavens the stars are apparently travelling together in systems. For instance, he found that the five stars of " The Plough," /3, 7, 8, e, and £ Ursas Majoris, are all moving in nearly the same direction through 1 Cape Observations, pp. 145, 146. STAR STREAMS. 305 space 1 — at least, apparently — and he predicted that if the motion in the line of sight conld be determined by the spectroscope, all would be found to . be moving either towards or away from the earth. This prediction was verified two years later by Dr. Huggins, who found that not only were the spectra of all five stars similar in character, but that all were receding from our system at the rate of about 20 miles a second. Other examples of apparently drifting star systems are found in Gemini and Taurus, especially in the Pleiades. The systematic star drift here referred to is of course distinct from that due to the Sun's motion in space. This is obvious in the case of the five stars in " The Plough," where the motion is nearly towards the "apex" of the solar motion instead of away from it. Proctor calls attention to the numerous instances of " star streams " and " star sprays " which may be traced in various parts of the heavens, both among the stars visible to the naked eye and also among the fainter stars shown in the charts of Argelander and Chacornac. It seems improbable that all these stellar reticulations should be due to accidental arrangement, and the apparent coinci- dence of many of them with streams and rays of Milky Way light adds weight, I think, to the hypothesis that they have a real and not merely an imaginary existence. Examples of this " stream "-forming tendency have been referred to in Chapter X. 1 Two small stars, Alcor and another, near f also participate in tLis motion. Dr. Auwers' subsequent determinations have, however, shown that in three of Proctor's stars, j3, 7, and S, the " proper motion " is small and doubtful. 20 306 THE VISIBLE TJNIVEKSE. Considering Sir W. Herschel's later views of the con- struction of the Galaxy, and Sir John Herschel's suggestion that its form might be that of a flat ring seen edgeways, Proctor was led to propose a new theory of the Milky Way, which represents it as forming a sort of spiral stream in space. The well-known " gap in Argo " he imagines as due to an opening between two of the spiral branches, and thinks that this gap could not possibly be explained either on the " cloven disc " or " flat ring " theory. Dr. Gould, however, in the charts of the Uranometria Argentina, shows this gap as filled in with faint nebulous light. The " Goal Sack " near the Southern Cross Proctor explains by a loop in the spiral, and the great brilliancy of the Galaxy in this region by the comparative proximity of one of the spiral branches to our system. But, on this hypothesis, one side of the vacuity should be somewhat brighter than the other, one portion of the spiral branch being nearer to the eye. Sir John Herschel's drawing of the Milky Way, made at the Cape of Good Hope, shows a general uniformity of brightness in the nebulous light surrounding the " Coal Sack," and in Dr. Gould's delinea- tion no well-marked inequality of brightness is perceptible in the bounding nebulosity. Proctor, however, points out that the difference of brilliancy would be slight. The whole aspect of the Milky Way in this vicinity suggests, I think, that the " Coal Sack " is a real, and not merely an apparent, opening through the Galactic Zone. Proctor applies to these circular openings reasoning similar to that applied by Sir John Herschel to the Magellanic Clouds, and concludes that, " if they are really openings at all, they are openings through a system which is not very proctor's spiral. 307 much deeper — measured in the direction of the line of sight — than the greatest width of the aperture itself." * With this opinion .1, fully concur, but not with the theory that the " Coal Sack " is formed by a loop in a stellar stream. Sir John Herschel's gauges at the Cape of Good Hope show that the " Coal Sack " — although apparently blank to the naked eye — is by no means devoid of telescopic stars. This is confirmed by Dr. Gould, who (in the charts of the Lranometria Argentina) shows this remarkable vacuity as filled in with faint nebulosity. 2 We cannot therefore consider it as a perfect opening ; but this does not detract from the argument in favour of its being a perforation through a comparatively thin stratum of stars. Proctor attributes the fading away of the " broken branch" in Ophiuchus (near 70 Ophiuchi) to increase of distance in the spiral stream in that direction ; but the appearance of this branch, as drawn by Boeddicker and Heis, tends, I think, to negative this hypothesis. In Heis' drawing the branch is shown rather brighter at its extremity (near 70 Ophiuchi) than at the point where it leaves the main Galactic stream. Boeddicker's representation of the Milky Way in this region is in fairly close agreement with Heis' delineation, but agrees rather better with its general appearance, as I see it. The description of the Milky Way as drawn by Dr. Gould (see Chapter IX.) shows, I think, that the supposed division of the Galaxy into two streams, from Aquila to the Southern Cross, is more apparent than real, and that the intricate convolutions of the Milky Way 1 The Universe and the- Coming Transits, p. 332. The italics are Proctor's. 2 Photographs recently taken in the Southern Hemisphere also confirm this. 308 THE VISIBLE UNIVBKSE. in this vicinity cannot well be represented by the hypothesis of a simple bifurcation. Proctor snms np his general conclusions in the following words : " The sidereal system is altogether more compli- cated, altogether more varied in structure, than has hitherto been supposed. Within one and the same region co-exist stars of many orders of real magnitude, the greatest being thousands of times larger than the least. All the nebulae hitherto discovered, whether gaseous or stellar, irregular, planetary, ring formed, or elliptic, exist within the limits of the sidereal system. They all form part and parcel of that wonderful system whose nearer and brighter parts constitute the glories of our nocturnal heavens." CHAPTER XVIII. INFINITE SPACE AND A LIMITED UNIVERSE. One Wonderful, enough for Man to know ! One Infinite, enough for Man to range I One Firmament, enough for Man to read I Young. IT is impossible for our minds to imagine space as limited by any conceivable boundary. With every mental effort to impose upon it any imaginable limits we feel ourselves irresistibly impelled to " break through the barriers of the heavens," and carry our thoughts beyond the boundary which we have vainly attempted to assign. "We are there- fore compelled to consider that space is infinite and bound- less. On the other hand, any attempt to grasp mentally this endless extension, this ever-widening infinitude, we find to be equally futile, and we are finally forced to confess that both limited and infinite space are alike unthinkable by the utmost efforts of the human intellect. What then is the construction of the visible universe ? the starry heavens as we see them? Some unreasoning people suppose that the number of the visible stars is infinite, or nearly so, but this is quite a mistake. The number visible in our largest telescopes, although of course 309 310 THE VISIBLE UNIVERSE. considerable, is only comparatively large, and compared with an infinite number must be considered as merely a drop in the ocean. The number visible to the naked eye, even with very good eyesight, is not only comparatively but absolutely small,. not much exceeding 7000 for the whole heavens ; and perhaps double this number would exhaust those which can be seen by persons gifted with exceptionally keen vision. Those who do not possess the power of effec- tive enumeration estimate the number visible to the naked eye as considerably greater than is really the case. This is partly due to the irregular distribution of the lucid stars over the celestial vault, and partly to the effect which the aspect of the starry sky produces on the imagination ; the fact of the stars increasing in number as they diminish in brightness inducing us to suspect the presence of points of light which we do not actually see. An attempt to count those seen with certainty in any selected portion of the sky will, however, convince any intelligent person that the number visible to ordinary eyesight, instead of being large, is really very small, and that the idea of a countless multitude is simply a popular fallacy based on an optical illusion. As I have elsewhere shown, 1 it may be proved mathe- matically that, supposing the number of stars infinite and equally distributed through infinite space, if there is no extinction of light in the ether, the whole heavens should shine with the brightness of the Sun. Such is clearly not the case. On the clearest nights the amount of light afforded by the stars is, on the contrary, very small, and the comparative blackness of the background on which they 1 The Scenery of the Heavens, p. 274. UNITE NUMBER OF THE VISIBLE STAKS. 311 are scattered is sufficiently obvious. 1 The number of the visible stars cannot therefore be infinite. If we assume with Struve that the light of very distant stars suffers total extinction in the ether of space — an assumption, however, • which I have elsewhere shown to be improbable — it follows that at a certain distance the light of all the stars beyond must be cut off, and that the most powerful telescopes which can ever be constructed by man will fail to pierce through the " cosmical veil " which shrouds the most distant stars from our view. It follows, therefore, that whether an extinction of light does or does not take place, the number of the visible stars must necessarily be limited. ■ An indication of this approaching limitation to telescopic vision is afforded by the fact that M. Celoria, using a small telescope, of power barely sufficient to show stars to the eleventh magnitude, found that he could see almost exactly the same number of stars near the Northern Pole of the Milky Way. as were visible in Sir William HerschePs large reflector ! indicating that — here at least — no increase of optical power will materially augment the number of stars visible in that direction. In fact, the smaller telescope seems here sufficient to pierce through the stellar stratum into the void beyond ; a result which affords further evidence against the hypothesis of an extinction of light in the ether. For Herschel's gauging telescope certainly revealed far fainter stars than those of the eleventh magni- tude in other portions of the heavens. It should therefore 1 According to Miss Clerke {System of the Stars, p. 7) the total light of all stars to 9J magnitude is about ^th of full moonlight. M. G. l'Hermite found for the total amount of starlight ^th of moonlight, but this estimate is evidently much too high. 312 THE VISIBLE UNIVERSE. have shown fainter stars at the Galactic Pole also, if such stars existed in that region of space. Their absence seems certain proof that very faint stars do not exist in that direction, and that here, at least, our sidereal universe is limited in extent. An examination by Miss Clerke of Professor Pickering's catalogue of stars surrounding the North Pole shows that " the small stars are overwhelmingly too few for the space they must occupy if of average brightness; and they are too few in a constantly increasing ratio." 1 Here again a " thinning out " of the stellar stratum seems clearly indi- cated, and suggests that a limit will ere long be reached, beyond which our most powerful telescopes will fail to reveal any further stars. (See Appendix, Note Q.) In my Planetary and Stellar Studies (p. 234) I have estimated the probable number of the visible stars at 70 millions. To show that this estimate is not largely in error I may mention that Professor Newcomb estimates the number of stars at 100 millions, and Professor Young also gives 100 millions as the probable number visible in • the great Lick telescope. M. Faye, in his VOrigine du Monde, 2 computes the number visible to the sixteenth magnitude at 31 millions. Admiral Smyth says {Celestial Cycle, vol. i., p. 270) : " We may now safely declare that nearly one hundred millions of suns are within telescopic reach "; and in a note he mentions that M. Cbambre in 1653, arguing with the astrologers of that day, ridiculed them for limiting the number of stars to 1028 (about the number recorded in the ancient catalogues), and "declared that the eight 1 Natm-e, August 9th, 1888. 2 Second Edition, p. 180. LIMITED NUMBER OF THE VISIBLE STABS. 313 spheres, properly packed, would stow away no fewer than 71,209,600." The reference to "the eight spheres" is of course absurd, but I merely quote Chambre's opinion to show that even his theory of the universe — such as it was — did not require an infinite number of stars. It will be seen, therefore, that the total number of stars visible, even in t>ur largest telescopes, is comparatively small. Indeed, compared with an infinite number it may be almost considered as a Vanishing quantity. In a ten- acre field of ripe oats the number of grains of corn 1 pro- bably exceeds the number of the visible stars ; and we should have to multiply the number of the stellar hosts by at least 10 to obtain the number of human beings now living on our comparatively tiny world ! The question naturally suggests itself, How is this limited number of stars to be explained? If space be really infinite — as we seem bound to suppose — it would be reasonable to expect that the number of stars would be • practically infinite also. But, as I have just shown, the number of the visible stars is certainly finite, and unless we admit an extinction of light in interstellar space the total number of stars in the universe must be finite also. The diagram representing the so-called " disc theory " of Sir William Herschel, which figures in so many astro- nomical text-books, clearly shows that its illustrious author considered that the vast cluster which forms — on this theory — our visible universe is limited in dimensions : in fact, " an islet in the boundless void." 1 There are 43,560 square feet in an acre. Taking 10 ears of corn to the square foot, and 30 grains in each ear — probably a moderate estimate — we have the number of grains on 10 acres equal to 130,680,000. 314 THE VISIBLE UNIVEKSE. Strave's modification of the " disc theory," namely, a disc of a certain thickness, but of infinite — or at least indetermi- nate — diameter, seems a very improbable hypothesis. Even on this theory our sidereal system is supposed to be limited in the direction of its thickness. If Struve's theory were to be accepted, we should also be obliged to accept his hypothesis of the extinction of light ; for otherwise the Milky Way should be much brighter than it is.. "With an infinite extension the Galaxy would of course shine with the brightness of the Sun. The com- paratively feeble gleam of the Milky Way on even the clearest nights should, I think, be sufficient to convince the thoughtful observer that its light is not due to a vastly extended stratum of stars. Even Sir John Herschel's reflecting telescope of 18£ inches aperture (now far sur- passed in space-penetrating powers by our modern instru- ments) sufficed in some places in the southern heavens to show the component stars of the Milky Way on a black background devoid of any nebulous light. With reference to one of his Galactic sweeps he says, " The northern end of the zone, though pretty rich in stars, is yet quite free from brightness of ground. It is as black as a coal," clearly showing that his optical power could — here at least — pene- trate fairly through the stellar stratum into the starless void beyond. Photographs of portions of the Milky Way in the Northern Hemisphere, taken at the Paris Observatory, show the fainter stars as points of light, on a perfectly black ground devoid of all nebulosity. More powerful telescopes will probably disclose the existence of many fainter stars, ' but all the evidence we have at present points to the con- THE CONSTRUCTION OF THE MILKY WAY. 315 elusion that the utmost limit of telescopic vision will very soon be reached, and that the most powerful telescopes which man can construct will ultimately show that the stars, even in the richest portions of the Galactic Zone, are strictly limited in number. The general aspect of the Milky Way seems, I think, sufficient to negative the "disc theory." The numerous convolutions, streamers, rifts, and " coal sacks " depicted in the drawings of Boeddicker and Gould can. hardly be explained by the honey-combed structure of a stellar disc, and one finds it difficult to resist the conclusion that the apparent streams of nebulous light, which are seen branch- ing out in all directions from the Galactic Zone, are really streams of stars in space, and that the apparent openings known as " coal sacks " are in reality perforations through a stellar stratum of comparative thinness, and not cosmical tunnels of immense length pointing directly towards the earth. But even if we knew the exact constitution of the great sidereal cluster of which our Sun forms a member, , this would not help us to answer, the question, How is it that, if space is infinite, the number of visible stars is finite ? A consideration of our own Solar System and its spatial surroundings may, however, assist us in framing some pro- bable hypothesis. We know that the dimensions of Jupiter's system of satellites are small in comparison with the dimen- sions of the Solar System, and that the diameter of the Solar System, measured across the orbit of the outermost planet Neptune, is small compared with the distance which separates us from the nearest fixed star. Roughly speak- ing the distance of a Centauri is 9000 times the distance 316 THE VISIBLE UNTVEBSE. of Neptune from the Sun. Hence if we represent the orbit of Neptune by a circle one foot in diameter, the void space surrounding the Solar System will be represented by a circle of 9000 feet, or nearly If miles across. Here we have a vast sphere, about 50 billions of miles in diameter, quite devoid of matter as far as we know, "and containing nothing except perhaps a few comets and meteoric swarms. Now, we may infer from analogy that the stars are pro- bably suns forming the centres of planetary systems similar to our own. The immense distance of the stars from the earth would of course render such planets as ours invisible even in our largest telescopes. Even if the " giant planet " Jupiter were revolving round a Centauri at the same dis- tance from that star that it is from our Sun, it would be utterly invisible to us even in the great Lick telescope. In certain rare cases, however, we seem to see planets of a much larger size revolving round some of the stars. I refer of course to those binary or revolving double stars in which a bright star is accompanied by a companion very much fainter than itself. Among these may be mentioned Sirius, 8 Cygni, 85 Pegasi, and 99 Herculis. The com- panion of Sirius is about 11 magnitudes fainter than its brilliant primary. This implies that Sirius is about 25,000 times brighter than its small attendant. If both are of the same intrinsic brightness, the ratio of their diameters would be 158 to 1, and the mass of Sirius nearly 4 million times the mass of the companion. Now the latest determination of the distance of Sirius, combined with my elements of the orbit, makes the mass of Sirius about three times the mass of the Sun. MASSES OF THE BINAKY STABS. 317 As the evidence of the spectroscope indicates that Sirius is a hotter star than our Sun, and therefore presumably brighter, surface for surface, we may not perhaps be very far wrong in assuming its diameter at 2,000,000 miles. This would make the diameter of the companion about 12,600 miles, or not very much larger than the earth. This computation is of course based on the assumption that it is a miniature sun and intrinsically as bright as Sirius . itself, perhaps a not very probable hypothesis. Indeed, the re- searches of Auwers on the irregularities in the proper motion of Sirius leads him to the conclusion that the mass of the small star is about half that of Sirius itself. This would make its mass about equal to that of the Sun, and would imply that it is nearly a dark body. "We may therefore consider it as a giant planet revolving round Sirius at a distance comparable with that of Uranus from the Sun. In the case of 8 Cygni (magnitudes 3 and 8) we have a difference of five magnitudes between the components, indicating that the primary is 100 times brighter than the companion. As, however, we know nothing definitely of the distance of 8 Cygni from the earth, it is impossible to com- pute the absolute dimensions of the components. The ratio of the diameters would, however, be — if of the same brilliancy — as 10 to 1, or about the same proportion which exists in the case of the Sun and Jupiter, and we may perhaps consider the companion as a giant planet in the sunlike stage of its existence. We .have the same relative brightness in the components of 85 Pegasi (magnitudes 6 and 11). An orbit recently computed for this binary by Mr. Schaeberle, combined with 318 THE VISIBLE UNIVERSE.' a small parallax found by Briinnow, gives a combined mass of about 11 times the mass of the Sun. As the diameters of the components would be about 10 to 1 — if of the same intrinsic brightness — their volumes would be in the ratio of 1000 (10 3 ) to 1. This would imply that the mass of the companion is about troth of the mass of our Sun, and its diameter (if of the same density) about 186,000 miles —possibly another giant planet in the sun-like stage. From the above considerations we may, I think, conclude that some, at least, of the stars are centres of planetary systems, and form with our Sun members of one great stellar system, separated from each other by distances vastly greater than the dimensions of each system. With reference to the clusters and nebulse the distance of these objects has' not yet been ascertained ; but from the fact that stars, clusters, and nebulas are mixed up in the greater Magellanic cloud in a space which is apparently of a globular form, we may conclude that clusters, nebulas, and small stars may co-exist in the same region of space, and that consequently the nebulas are not farther from the earth than the faint stars seen in the same direction. In the cosmological speculations propounded by Lambert about the middle of the eighteenth century that "philo- sophical geometer " considered each star with its planetary train as forming a system of the " first order." He sup- posed the Sun and all the visible stars — except those belonging to the Milky Way- — to form a great spherical cluster of stars in space. This he terms a system of the " second order." He then supposes a great number of these systems of the second order to be ranged on behind PEOBABLB CONSTITUTION OF THE 0NIVEBSB. 319 the other in the Galactic plane, thus forming, by their united light, the phenomenon of the Milky Way. This constitutes a system of the " third order," of a form not spherical but shaped like a disc, of which the diameter is vastly greater than the thickness, an arrangement some- what similar to Struve's Galaxy. Lambert supposes that the universe contains a great number of Milky Ways, which, combined, form a system of the " fourth order " ; and so on to systems of a higher order still. He did not consider the Milky Way as infinite in extent in the direction of its principal plane, and he estimates the distance of its remotest stars at about 150,000 times the distance of Sirius. He seems, however, to have overlooked the fact that stars at this vast distance would not be visible in the largest telescopes which could possibly be con- structed. His view of the construction of the Milky Way is not, I think, supported by the general aspect of the Galactic Zone, an aspect which seems to suggest that it really forms one system, and not a great number of systems ranged one behind the other in space. The modification of Lambert's hypothesis, which I have elsewhere supported (a similar view has also been advanced by Proctor 1 ), is as follows : — Suppose each sun with its attendant family of planets to form a system of the first order, as in Lambert's theory. All the visible stars, clusters, and nebulas, the Milky Way included, are then assumed to form a system of the second order. Here, however, our positive knowledge ends. Our most powerful telescopes cannot penetrate beyond our own 1 A similar hypothesis was also proposed by Sir John Hersohel. See Knowledge for January 1886, p. 83. 320 THE VISIBLE UNIYEESE. system of the second order. But we can extend the analogy, and imagine other external systems of the second order to exist in space, which, combined with our visible universe, forms a system of the third order, and so on to higher orders still. ' J Assuming the distance of the faintest stars visible in our largest telescopes at 2300 times the distance of a Oentauri (corresponding to the distance of a star of about the seven- teenth magnitude), we have the diameter of our sidereal system — the visible universe — 4600 times the distance of the nearest fixed star. Now the distance of a Centauri from the Sun is about 4500 times the diameter of Neptune's orbit. Hence, if we assume that the distance of the nearest external universe bears the same ratio to the diameter of our sidereal system that the distance between a Centauri and the Sun bears to the diameter of the Solar System, we have the following proportion : — Diameter of Solar System : Distance between Solar Systems :: Diameter of sidereal universe : Distance between universes, or 1 : 4500 : : 4600 x 4500 .: Distance of nearest external universe, from which we have ' Distance of nearest- external universe = 93,150,000,000 times the diameter of the Solar System, which multiplied by 5,584,000,000 = 520,149,600,000,000,000,000 miles, a distance which light, with its amazing velocity of 186,300 miles per second, would take nearly 90,000,000 years to traverse ! EXTERNAL UNIVERSES. 321 At this vast distance, an external universe, if of the same diameter as our own, would subtend, if seen at all, an angle of less than one minute of arc, and would therefore appear only as a small and faint nebula. It may perhaps be objected to the above calculation that our sidereal system may possibly extend much farther than 2300 times the distance of a Centauri ; but if so, the dis- tance of the nearest external universe will be proportionately increased and my argument thereby strengthened. The above hypothesis affords an obvious explanation of the fact that the visible stars and nebulse are limited in number. They all form part and parcel of one vast sidereal cluster — our visible universe — which is separated from all external galaxies by a vast starless void, in the same way that the Solar System is separated by empty space from the surrounding star sphere. The invisibility of the external universes may be explained on one or other of three assumptions. 1. The distance of even the nearest external universe is so. great that its light has not yet reached the earth. In view, however, of the vast epochs of time indicated by geological history this supposition is perhaps improbable. 2. Beyond the bounds of our visible universe a " thinning out" of the luminiferous ether may occur, ending in an absolute vacuum which would of course arrest the passage of all light from outer space. 3. In the vast space which separates our sidereal system from its nearest neighbour an extinction of light may possibly take place in the ether which would thus act as a "cosmical veil," and for ever hide from our view all external galaxies. 21 322 THE VISIBLE UNIVERSE. It was argued by Struve that such an extinction does really take place, even within the limits of our sidereal system ; but all the available evidence tends to show, I think, that there is no appreciable extinction of light, at least as far as our largest telescopes can penetrate into space. The case may, however, be 'far otherwise when external systems are concerned. The light of even the nearest of them, enfeebled by a distance of 20 million times that of a Centauri, might well be extinguished alto- gether by the absorption of light in such a vast thickness of a fluid medium, perhaps not absolutely perfect. I find that a Centauri placed at such a distance would — even if there were no absorption — be reduced to a star of about the thirty-sixth magnitude, which by Pogson's formula would require theoretically a telescope of over 24,000 feet in diameter even to glimpse ! We are not, however, precluded by this hypothesis from supposing that numerous similar systems exist in external space, and although we must consider the number of visible stars as strictly finite, the number of stars and systems really existing, but invisible to us, may be practically infinite. Could we speed our flight through space on angel wiDgs beyond the confines of our limited universe, to a distance so great that the interval which separates us from the remotest fixed star visible in our largest telescopes might be considered as merely a step on our celestial journey, what further creations might not then be revealed to our wondering vision ! Systems of a higher order might there be unfolded to our view compared with which the whole of our visible heavens might appear like a grain of sand on the ocean shore, systems perhaps stretching out INFINITE SPACE. 323 to infinity before us, and reaching at last the glorious " mansions " of the Almighty, the Throne of the Eternal ! But here, dear reader, " I touch a theme too great for me to handle, but which will assuredly be handled by the loftiest minds when you and I, like streaks of morning cloud, shall have melted into the infinite azure of the past." APPENDIX. Note A. The total mass of the Solar System may be taken as follows (earth's mass = 1) : — Sun = 332,262 Jupiter ... rr 317 Saturn ... = 95 Neptune z= 174 Uranus = 14-6 Earth ■ .. = 1-0 Venus ... = 0-8 Mars = 0-11 Mercury = 0-06 Satellites = 0-20 Minor Planets ... = 0-25 Total 332,708-42 Hence volume of globe equal in mass to the whole, and of the same specific gravity as the earth, would be — 7912 x ^332,708-42 = 548,244 miles. Now, when the primeval nebulous mass extended as far as the orbit of Neptune, its diameter was — 2,792,000,000 x 2 = 5,584,000,000 miles. Hence the density would be reduced in the ratio — 548,244 \ 3 1 / 548,244 \ 3 _ \5,584,000,000/ ' 1; ,584,000,000/ of the earth's present density. 056,607,300,000 325 326 APPENDIX. Assuming the earth's specific gravity at 5 '6 7, we have- Density of nebula = 1,056,607,300,000 186,350,493,827 Now, as water is about 773 times heavier than air, and air 14-44 times the weight of an equal volume of hydrogen gas, we have water = 773 X 14-44 = 11,162 times the density of hydrogen at ordinary temperature and pressure. Hence Density of nebula = il " " 186,350,493,827 16,695,081 of hydrogen, a result in close agreement with that found by Dr. Oroll. Note B. With a " light ratio " of 2-512, L = magnitude visible "by fits," with 1-inch aperture 9-2 Pogson, I = limiting magnitude for any given aperture, Pogson's formula is — Z = L + 5 log aperture =9-2 + 5 log aperture. From this formula we have the following : — Aperture in inches. 3 4 10 12 13 14 16 18f (Herschel) 20 23 (Princeton Observatory) Minimum visibile. 11-58 magnitude. . 12-2 . 1309 13-7 . 14-2 . 14-59 . 14-77 . 14-9 . 15-2 15-5 15-7 16-0 APPENDIX. 327 Aperture in inches. Minimum visibile. 24 ... ... ... ... 16-1 magnitude. 26 (Washington Observatory) 16 "2 „ 30 (Poulkowa „ ) 16-58 36 (Lick „ ) 16-98 „ 60 (Mr. Common's Reflector) 18-09 „ 72 (LordRosse's „ ) 1848 „ Sir J. Herschel estimates that for metallic mirrors ratio of aperture of refractor to reflector with equal light is as 5 to 7. Hence 185-inch mirror = 13-03-inch refractor, and min. visibile would be about 14 - 77 mag. For Lord Rosse's telescope we have 72 x 5 — = 51 -inch refractor and min. visibile — J. 7*7 mag. For silver on glass mirrors the ratio is about 8 to 9, and therefore 60 x 8 for Mr. Common's 5-feet reflector 53 - 33-inch refractor, and min. visibile = 17-8 mag. From this it appears that a star of 20 mag. would be far beyond the reach of any existing telescope. Note C. Points of Maximum Brightness of the Milky Way (Houzeau) Nos. B. A. = a. Decl. = «. Mag. Position. h. m. Deg. 1 • 1 2 + 61-0 5-6 To the north of. /3 Cassiopeia. 2 2 12 + 56-6 5-6 Nebula of Perseus. 3 3 4 + 62-4 6-7 Between 2 Camelopardi and 5 Persei. 4 4 41 + 40-8 6 Between f Aurigse and e Persei. 5 6 + 230 5-6 A ^ of H to ■q Geminorum. 6 6 50 - 2-8 5-6 To the north of s Monocerotis. 7 7 12 -25-2 6 A \ of { NaTis to 8 Canis Majoris. 8 7 58 -47-4 6 A $ of 7 to B Navis. 9 10 39 -59-2 5-6 Middle of Nos. 4448 and 4449 of Laoaille. 10 12 40 - 53-2 6 To the N.N.B. of /3 Crucis. 11 16 4 - 54-3 5 k Normse. 12 16 40 -46-6 5-6 Between rj Scorpii and e Normse. 13 16 47 -40-8 5-6 To the N.N.B. of £ Scorpii. 14 16 52 _ 32-6 6 Near p Cygni. • 15 17 30 - 17-4 6-7 To the south of £ Serpentis. 328 APPENDIX. Points of Maximum Brightness of the Milky Way (Houzeau) — continued. Nos. E. A = a. Decl. = «. Mag. Position. ' h. m. Deg. 16 17 35 - 225 6 Near D Ophiuchi. 17 17 46 -34-7 4 Nebula 7 Messier. 18 18 - 28-5 5 Round 716 Mayer. 19 18 8 - 18-7 4-5 To the north of /* Sagittarii. 20 18 21 + 4-8 6 Near r Ophiuchi. 21 18 23 - 14-4 5 Near s Olypei. 22 18 24 - 18-9 5-6 Between 728 and 729 Mayer. 23 18 41 - 7-0 4-5 Between I and n Aquilse. 24 18 48 + 11-6 6 Near 18 Aquilse. 25 18 56 - 1-2 6 Between 8 Serpentis and X Aquilae. 26 19 32 • + 11-8 5-6 Near % Aquilse. 27 19 43 + 29-1 5-6 To the E.N.E. of /3 Cygni. 28 20 3 + 36-0 5-6 Between i 1 and b 2 Cygni. 29 20 40 + 31-0 6 Near k Cygni. 30 20 57 + 35-2 6 Between X and u Cygni. 31 21 2 + 45-5 5 Between % and/ 2 Cygni. 32 21 25 + 47-5 5-6 Between -w x and g Cygni. 33 22 15 + 51-0 6 Near c Lacertae. Note D. Sir John Herschel gives the following results of the gauges in the Northern and Southern Hemispheres (Outlines of Astro- nomy, para. 795, 796, Tenth Edition). Northern Hemisphere. Zones of Galactic North Polar Distance. Deg. Deg. Average Number of Stars per Field of 15'. to 15 ' 4-32 15 „ 30 - 5-42 30 „ 45 8-21 45 „ 60 ... 13-61 60 „ 75 ... 24-09 75 „ 90 ... 53-43 APPENDIX. 329 Southern Hemisphere. Zones of Galactic South Average Number of Stars per Field of 15'. 6-05 6-62 9-08 13-49 26-29 59-06 Note E. Distribution of the Naked-eye Stars with reference to the Milky Way, according to Houzeau. Folar Distance. Deg. Deg to 15 15 30 30 45 45 60 60 75 75 90 Magnitudes. Total. Density. l 2 3 4 5 6 Northern Cap . 1 4 8 42 86 141 0-113 3rd Zone, North 3 6 18 42 74 295 438 0-122 2nd „ „ . 1 4 21 70 148 439 683 0-124 4 7 34 114 190 625 974 0-145 Middle . 7 11 46 108 243 730 1145 0-160 1st Zone, South . 3 11 34 111 257 619 1035 0-154 2nd „ „ . 7 28 65 141 465 706 0-129 3rd „ „ . 2 2 13 65 81 281 444 0-124 Southern Cap . 2 2 12 37 . 100 153 0-123 Total . 20 51 200 595 1213 3640 5719 0-139 Note P, The area of each division in square degrees may be determined as follows : — Set S = declination of northern limit of zone, and o 1 = „ southern ,, Then area of zone = 360 x 57-296 (sin 8 — sin S 1 ). „ „ = 20626-5 x (sin 8 - sin S 1 ). The area thus found must of course be divided by 36, to obtain the area of each division of 10° X 10°. 330 APPENDIX. Note G. Number of Stars given in different Catalogues, excluding Variable Stars, Nebula, and Clusters. Magnitudes. Northern Hemispl ere. Southern Hemisphere. Heis. Harvard Photometry. Oxford. Uranometria Argentina. Behrmann. Brighter than l'l . 4 } «{ 5 5 1-1 to 2-0 (both inclusive) 24 13 14 2-1 „ 3-0 „ 55 71 44 66 3-1 „ 4-0 ., 175 229 138 167 4-1 „ 5-0 „ 461 741 421 323 5-0 „ 55 „ „ 845 5-1 „ 6-0 „ „ Total to 6-0 „ „ 1640 1287 1247 2359 1913 1908 1822 2306 6-1 to 7-0 „ „ 4872 (to 6th mag. 6-7 mag. (Heis) . 1544 between -20° and -90°). 6-1 to 6i (U.A.) . 1395 6-m. stars (Argelander and others) measured below 6-0 . 491 Stars seen by Heis 0° to -20°. 1040 N.B. — The results given above for the Harvard Photometry are due to Mr. Monck. Summary of above results. Total number of stars seen by Heis in Northern Hemisphere, to 6-7 magnitude — = 2359 + 1544 = 3903. Total number of stars in Uranometria Argentina, in Southern Hemisphere, to 6 - 5 magnitude — = 1822 + 1395 = 3217. Total number of stars to 6-0 magnitude in both Hemispheres, Heis and Gould — = 2359 + 1822 = 4181. Total number of stars seen with the naked eye by Heis and Behrmann in both Hemispheres — = 2359 + 1544 + 1040 + 2306 = 7249. APPENDIX. 331 Note H. Distances of Stars of Different Magnitudes. Light ratio 2-5119. (On the assumption that 'there is no extinction of light in space.) Magnitude. Distance. 1-00 1-000 2-00 1-585 3-00 2-512 4-00 3-981 5-00 6-310 6-00 10-000 7-00 15-485 8-00 25-119 9-00 39-811 10-00 . 63-096 11-00 . 100-000 12-00 . 158-489 13-00 . 251-189 14-00 . 398-107 15-00 .. 630-957 16-00 . 1000-000 . Note I. Stars with Annual Proper Motion of more than 2". Star. Mag. E.A., 1890. Declination, 1S90. Motion per Annum. Remarks. b. m. s. deg. mm.' sec Groombridge 1830 65 11 46 38 + 38 30-5 7-0 Place from Green- wich, Ten-year Cat., 1880. Lacaille 9352 ■ 7-2 22 58 46 -36 29-2 6-9 Cordoba 32416 . 8-2 23 59 -38 16 6-1 61 Cygni . 5-1 21 1 58 + 38 12-5 5-2 Double. Lalande 21185 . 7-3 10 57 19 + 36 42-4 4-7 Place from Green- wich, Ten-year Cat, 1880. e Indi . 5-2 21 54 6 -57 14-3 4-6 332 APPENDIX. Stars with Annual Proper Motion of more than 2" (continued). Star. Mag. R.A., 1890. Declination, 1890. Motion per Annum Remarks. h. m. s. deg. min. sec. Lalande 21258 . .8-6 11 + 44 5-5 4-4 Place from Green- wich, Ten-year Cat., 1880. 40 Eridani . 4-4 4 10 13 - 7 49-2 4-1 Triple. H Cassiopiese 5-2 1 57 + 54 22-8 3-7 o Centauri . .-, 7-0-5 14 32 8 -60 22-7 3-7 Double. /A.-Oe. 14318 \ A.-Oe. 14320 9'2 15 4 -15 56 j 36 9-0 15 4 -15 51 Lacaille 8760 7-6 21 10 53 -39 17-2 3-4 e Eridani 4-4 3 15 30 -43 29-5 30 A.-Oe. 11677 9-0 11 14 21 + 66 26-5 30 Place from Green- wich, Ten-year Cat., 1880. Groombridge 34 . 7-9 12 6 + 43 23-9 2-8 Double. Piazzi II. 123 6'3 2 30 3 + 6 21-1 2-4 Place from Green- wich, Ten-year Cat., 1880. Lalande 25372 . 8-0 13 40 10 + 15 29-3 2-3 Do. a Bootis 0-2 14 10 39 + 19 45-6 2-3 Do. Struve 2398 . 8'B 18 41 33 + 59 27-7 2-3 Double. /3 Hydri 30 19 49 -77 52 . 2-2 Lalande 7443 8-5 3 55 52 + 35 0-4 2-2 Place from Green- wich, Ten-year Cat., 1880. "Weisse V. 592 9-5 5 26 - 3 40 2-2 Bradley 3077 5-9 23 7 59 + 56 33-7 2-1 Place from Green- wich, Ten-year Cat., 1880. f Tucanse .4-1 14 20 -65 31-3 2-0 Lalande 15290 . 8-3 7 46 31 + 30 56-6 2-0 Place from Green- wich, Ten-year Cat., 1880. Piazzi XIV. 212 . 5-9 14 51 2 -20 55-0 20 Do. APPENDIX. 333 Note J. "/I.V.O Parallax and Velocity, of Stars with Large Proper Motions. Star. Mag. Proper Motion. Parallax. Velocity. Miles per • Second. Light Journey. Years. See. Sec. Groombridge 1830 6-5 7-0 0-089, 231 36-6 Lacaille 9352 7-2 6-9' 0-285 71-2 11-4 61 Cygni . 5-1 5-2 0-45 34-0 7-2 e Indi . 5-2 4-6 0-20 67-7 16-3 Lalande 21258 8-6 4-4 ■ 0-262 494 12-4 40 Eridani . 4.4 4-07 0-166 72-1 19-6 p. Cassiopeia^ 5 -2 3-7 0-036 302-5 90-5 A.-Oe. 11677 9-0 3-0 0-10 88-3 32-6 n Eridani 4-4 3-0 0-14 630 23-3 a Bootis 0-2 2-3 0-018 376 181 f Tucanas . . . 4-1 2-0 0-06 98-1 54-3 85 Pegasi 5-8 1-22 0-054 66-5 60-3 6 TJrssB Majoris 3-2 1-1. 0-046 70-3 70-8 Note K. If A = wave length of ray when the observer arid star are relatively at rest, X 1 = wave length affected by relative motion, V = velocity of light (= 186,400 miles per second), v = velocity of approach, Then V •Y + v .-. A - A 1 = V A- A v + V or, A - V recession- X A 1 = V \ ' v whence For a motion of (A - Ai) A 1 V 334 APPENDIX. •. tf-X = A. * V - v' and V (X 1 - X) . v = £ — ■ Mr. Keeler of the Lick Observatory has observed and measured a displacement of the chief nebular line in several planetary nebulae. In the nebula N.G.C. 6790 he found a displacement of + 1-03 of a tenth-metre, indicating a motion of recession from the earth. Now, taking the wave-length, X, of the chief nebular line at 5006-71, we have X 1 = 5006-71 + 1-03 = 5007-74. Hence 186,400 x 1-03 5007-74 38-3 miles per second. Note L. The problem of determining the relation between the mean distance (taken as unity) of two neighbouring stars, and the radius r of the sphere, which contains N stars uniformly dis- tributed, has been treated by Lambert, Sir W. Herschel, and Schubert. As, however, the question has been treated from a different point of view by each computer, the results do not agree very well. According to Struve 1 all solutions should fulfil the fundamental condition that the number of stars contained in the interior of a sphere be proportional to the volume of the sphere. This is evident. " According to this condition we should have f 7r r 3 : N = s, and s would be the unit of space by which the volume increases for each additional star, or the modulus of volume for each star." To find from s the mean distance between two neighbouring stars, Struve supposes the geometric form of the module to be a tetrahedron, the length of the edge of this pyramid (=1) determining the mean distance required. The volume of such a pyramid being s = JL. v^y, we have — t£ = *^ 1 Etudes d'Astronomie Stellaire, Note 41. APPENDIX. 335 16 ttj-3 = N" -/2, and 16 7T N 35-573' Now, if in the field of a telescope of which the apparent radius = X, expressed in seconds of arc, the number of visible stars = n, we have for the number of stars N visible on the whole celestial vault, supposing a regular distribution, and r = A 3 / nV2 _ 2468 . 5 s/ni N = sin A. 2 Note M. Enumeration of Stars in Harding's Atlas to 8th mag. Inclusive. Hour. 0° to +15°. No. of Stars. 0° to -15°. No. of Stars. Total. Remarks. 0— 1 143 169 312 1— 2 120 155 275 2— 3 136 151 287 3— 4 124 187 311 4— 5 226 233 459 Hyades near N limit of zone. 5— 6 246 267 513 Orion. 6— 7 329 272 601 Milky Way. 7— 8 273 244 517 8— 9 254 230 484 9—10 210 235 445 10—11 232 232 464 ■ 11—12 223 173 396 12—13 218 186 404 Nebular region, North. 13—14 • 179 192 371 14—15 231 189 420 • 15—16 209 180 389 16—17 231 196 427 17—18 306 213 519 18—19 340 271 611 Milky Way. 19^20 . 323 243 566 j» » 20—21 289 278 567 21—22 211 213 424 22—23 189 192 381 23—24 153 177 330 Total . 5395 5078 ■ 10,473 Etudes (V 'Astronomie Stellaire, Note 41. 336 APPENDIX. Note N. The papers referred to in the text are as follows : — 1786. Catalogue of One Thousand New Nebulae and Clusters of Stars. 1789. Catalogue of a Second Thousand of New Nebulae, etc. 1791. On Nebulous Stars properly so called. 1794. On the Nature and Construction of the Sun and Exed Stars. 1796. Method of "observing the Changes that happen to the Fixed Stars, etc. 1799. On the Power of penetrating into Space by Telescopes. 1802. Catalogue of 500 New Nebulae, etc. 1806. On the Quantity and Velocity of the Solar Motion. 1811. Astronomical Observations relating to the Construction of the Heavens. 1814. Astronomical Observations relating to the Sidereal Part of the Hea.vens, and its Connection, with the Nebulous Part. 1817. Observations and Experiments on the Local Arrangement of the Celestial Bodies in Space, and to determine the extent of the Milky Way. 1818. Observations and Experiments for ascertaining the Dis- tances of Clusters of Stars, and investigating the Power of our Telescopes. APPENDIX. 337 Note O. Herschel computes the penetrating power p of a telescope in the following way : 1 — If S denotes the sum of the rays of light which the instrument conveys to the eye, and s the sum of the rays gathered by the eye pupil, then p = \/ -. If A is the s clear aperture of the mirror or object glass, and a that of the pupil of the eye = - 2 inch, and /t a co-efficient which denotes the relation between the quantity of light which falls on the object glass and that which issues from the eye piece, we have - = u. —g , whence p = — •/«.. In the Newtonian reflector with a small mirror of which the minor axis = b, the formula becomes p = vV A*-l Herschel determined /a by direct experiments on the loss of light by reflection, and by passage through lenses. In this way he found the following penetrating powers for his different telescopes : — - 1. No. 4 2. No. 8 3. Small Sweeper of 2 ft. 4. Telescope of 7 ft. 5. Large Sweeper of 5-2 ft. 6. Telescope of 10 ft. ... 7. Small Telescope of 20 ft. 8. Large Telescope of 20 ft. Aperture in inches. 0-75 1-17 4-2 6-3 9-2 12-0 18-8 3 - 56 Ordinary telescope. 4 - 50 Achromatic „ 12-84^ Newtonian reflectors with small mirror. 9. Large Telescope of 25 ft. 24-0 10. Large Telescope of 40 ft. 48-0 20-25 28-57 28-67 38-99 ( 75-08] 95-85 191-69J Telescopes with the " front view." No. 4 was the instrument with which Herschel discovered Etudes d' ' Astronomic Stellaire, Note 59. 22 338 APPENDIX. Uranus and made two catalogues of doubles. It was of high optical excellence. No. 8 was the principal instrument used by Herschel in his gauges. First used with a small mirror, afterwards improved by the " front view " construction. No. 10 was the great telescope constructed in 1789, and with which Herschel discovered the two minor satellites of Saturn, Mimas and Enceladus. In his researches on the penetrating power of telescopes Herschel does not take into account the magnifying power used, but says that if the telescope is to act with its full power, the A power should be greater than — . For the gauging telescope A A = 18-8, and a = 0-2, and therefore — = 94 is the smallest magnifier which should be employed with that telescope. The power used by Herschel in the sweeps and gauges was 157. 1 Note P. Table of Relative Distances (Struve'). Apparent Magnitude. Distance of Interior Limit. Mean Distance. Distance of Exterior Limit. 1 Argelander . 1-0000 1-2638 2 1-2638 1-8031 2-1408 3 2-1408 2-7639 3-1961 4 3-1961 3-9057 4-4374 5 4-4374 5-4545 62093 6 6-2093 7-7258 8-8726 6 Bessel . 8-2160 7 „ . 8-2'i'60 14-4365 8 „ . 14-4365 24-8445 9 „ . 24-8445 37-7364 Herschel's faintest 227-782 Etudes d'Astronomie Stellaire. Note 59. APPENDIX. 339 Note Q. The following table shows the number of stars to any given magnitude which should tJieoreticalfo/ be visible, according to Dr. Gould's formula — % n = 1-0051 x (3-9120)». Magnitude. No. of Stars. Magnitud a. .No. of Stars. To 1-0 inclusive 3-93 To 10-0 inol usive 843,718 » 20 „ 15-74 „ 11-0 3,283,876 „ 3-0 „ 6017 „ 12-0 12,911,448 »■ i-o „ 235-4 „ 13-0 50,511,900 „ 5-0 „ 920-9 „ 14-0 197,602,545 „ 6-0 „ 3,602-5 „ 15-0 773,021,071 „ 7-0 „ 14,093 „ 16-0 3,024,057,632 „ 8-0 55,131 „ 17-0 11,830,114,720 ,. 90 „■ 215,674 From this it appears that if the stars were uniformly scattered through space, and light suffered no extinction, bhe number of stars visible in the Lick telescope would be about 11,000 millions, or over 266,000 stars to each square degree ! Another way of looking at the question is as follows : — As- suming that the smallest star visible in the Lick telescope is of the 17th mag., we have, with a light ratio of 2 - 512, — Light of star of 6th mag. = (2512) 11 X light of 17th-mag. stars, Star of 6th mag. = 25,120 X light of 17th mag. If, therefore, of the same size and brightness, the distance of a 17th-mag. star will be \/25,120 X distance of 6th-mag. star. Hence, volume of space at distance of 17th-mag. star will be — (25,120) * X volume of sphere containing all stars to the 6th mag., or, 3,981,100 times the volume of sphere containing 6th mag. 340 APPENDIX. Now, supposing an equal distribution of stars, and the total number in both hemispheres to 6th mag. inclusive, as 4000 in round numbers (see Note G), we should have the total number of stars visible in the Lick telescope — 3,981,100 x' 4000 = 15,924,400,000. The "light ratio" derived from Gould's formula is 2'4827. This partly accounts for the discrepancy between the result computed above and that given in the preceding table. INDEX. ABBOTT, 45 iEgospotamus, 81 Albireo (J3 Cygni) 79, 80 Alcyone, 165, 207, 208, 253 Aldebaran, 73, 76, 106, 165, 190, 196 Algol, 75, 106, 110, 111, 112 Altair, 106, 129, 169, 196 Anaxagoras, 63 Angstrom, 72 Antares, 218 "Apex, Solar," 193, 194, 197, 252 Aroturus, 36, 73, 76, 107, 186, 187, 190, 196, 201, 218 Aristotle, 26 Argo," "Gap in, 131 Argus a (Canopus), 200, 206 „ y, 102 Atoms, size of, 64, 65, 66 Auriga o (Capella), 73, 76 „ ft 75 „ i, 106 Aurora spectrum, 116, 117 Auwers, 185, 305, 317 BACKHOUSE, 180 Bacon, Lieut., 97, 98 Ball, Sir Bobert S., 51, 116, 185 Barnard, 161, 179 Bechuanaland, 130 Becquerel, 50 "Beehive" in Cancer, 166 Behrmann, 149, 150, 153, 154-158 Belopolsky, 185 Betelgeuse, 73, 77, 180, 186, 206 Binary Stars, 28, 29, 55, 56, 107, 108, 109, 209, 253 Biot, 81 Blandet, Dr., 32 Bode's Law, 12 Boeddicker, Dr., 143-146, 160, 168, 180, 271, 295, 297-299, 301, 307, 315 Bond, 202 Bootes o, 36, 73, 76, 107, 186, 187, 190, 196, 201 Brasky meteorite, 82 Bredechin, 90, 189 " Broken Branch " of Milky Way, 307 BufEon, 3 Bunsen, 51 Burnham, 28 Butsura Meteorite, 83 CAMBLOPARDALI, B, 105 Canis Majoris a (Sirius), 73, 75, 106, 183, 185, 190, 199-201, 207, 208 Canis Minoris a (Prooyon), 185, 196 Canopus, 200, 206 Capella, 73, 76, 107, 196, 201, 204, 218 Cape Observations, 131, 134, 135, 136 Cassiopeia o, 185 7. 102 7i, 185, 191 ix, 36, 40 Cassiopeia's Chair, 152, 164 341 342 INDEX. Castor, 73, 75 Cauchy, 64 Celestial Chemistry, Chap. VII. Celoria, 265, 272, 311 Centauri a, 40, 163, 190, 202, 203, 316, 320, 321 Centauri w, 178 Cephei g , 109 Chemical Elements in Sun, 72, 73 „ „ meteorites, 84 Cheseaux, 274, 275 Cicero, 25 Clarke, Prof. F. W., 69 Clausius, 65 Clerke, Miss, 12, 190, 198, 311, 312 Clusters in Milky Way, 249 Star, 43, 248, 249 Cluster, solar, 159, 160 « Coal' Sacks " in Milky Way, 125, 126, 127, 132, 294, 299, 306 Collision shells, 99 Colours, star, 108 Coma Berenices, 166 Comte, 22 Conservation of Energy, 26 Copeland, Dr., 113 Corona Borealis, 164, 173 „ Australis, 173, 175 Corvus, 164 Cosmieal Groups, 101 Cranbourne meteorite, 83 Croll, Dr., Chap. III. and 67, 68 Cross, Southern, 132, 161, 164 Crucis, k, cluster, 170 Cygni, o and 7, 162, 163 " 61, 40, 163, 185, 187, 200 „ E, 113 „ X, 113 Cygnus stars, 102 DARWIN, PROF. G. H., 19, 20, 114, 115 Darwinian Theory, 47 Daubreelite, 85 Debray, 51 Democritus, 63, 124 De Morgan, 215, 216 Denudation, 45, 46 Descartes, 25 Dewar, 88, 117 Dhurmsala meteorite, 84, 117 " Disc theory " of Milky Way, Chaps. XIV., XV. Distance of nebulje, 189 Distance of stars, Chap. XL, App. Note H Distribution of stars, 146-160, App. Note E " Dolphin's Rhomb," 164 Draper Catalogue, 162 Duner, 104, 105 Dunkin, 194 Dunlop, 253 Durango meteorite, 83 Durham, Wright of, 214-227 ELEMENTS in the Sun, 72, 73 Elkin, Dr., 184, 185, 186, 200, 201, 206 Energy, Conservation of, 26 Ennis, Jacob, 20, 21, 22, 23 Ensischeim meteorite, 82 Eridani, 40, 48, 185 Eridanus, " River," 123, 172, 173 Espin, 113, 167, 168 Esterville meteorite, 82 Ether of space, Chap. V. Evolution, Stellar, Chap. III. External Galaxies, 244, 291, 301, 320- 322 Extinction of Light, 275-289 FARADAY, 60 Parquhar, 154 Faye, 14, 17, Chap. II., 312 Fitzgerald, Prof., 61 "Fixed" stars, 189 •Flamsteed, 220 INDEX. 343 Fomalhaut, 218 Fowler, 98, 113 Fraunhofer, 71 GALAXIES, external, 244, 291, 301, 320-322 Galaxy, or Milky Way, Chap. IX., etc. " Gap in Argo," 131 Gaseous nebulas, 244 " Ganges," star, 146, 239, 240, 253, 254, 264, 266, 267-271, App. Note D Geminorum 77, 169, 171 E, 103 Geological considerations, 45, 46, 47 Giant Suns, Chap. XII. Gill, Dr., 184, 185, 203, 205 Globular Clusters, 27 Gothard, 103 Gould 32,416, 40, 139-143, 152, 158- 160, 234, 263 Gould, Dr., 138-142, 152, 158-160, 263, 297, 306, 307, 315 Grant, Prof., 284 Groombridge 34, 40, 185 1830, 36, 39, 40, 190 Groups, Lockyer's, 101, 106, 107, 108 Gruenwald, Prof., 70 Gylden, 185, 187, 287 HALL, PROF., 5, 40, 185 Halley, 275 Harding, 243, App. Note M Harvard Photometry, 151 Haughton, Prof., 46 Heat of Sun, 50, 51 Heis, 124-131, 149-153, 150, 168, 297 Helmholtz, 9, 52, 66, 67 Herculis, o, 77, 105 „ V, 185 „ X, 105 99, 316 Herschel, Sir John, 50, 58, 59, 125, 131-136, 139, 142, 146, 150, 158, 160, 177, 178, 206 234, 237, 281-283, Chap. XVII. Herschel, Sir W., 6, 146, 148, 177, 183, 193, Chaps. XIV., XV., 276-280, Chap. XVII. Hertz, 61 Hevelius, 220 Hipparchus, 220 Hirn, 14, 58 Holden, 178, 179 Houzeau, 136-139, 147-149, 263, 297 Huggins, Dr., 41, 73, 78, 79, 92, 95, 103, 195, 305 Huggins, Mrs., 79 Humphreys, 45 Hutchins, 51 Huxley, Prof., 47 Huygens, 214 Hyades, 153, 160 Hydras E, 105 Hydri /3, 40 Hydrogen in nebulas, 78 „ Sun, 72 Hypothesis, Nebular, Chaps. I., II. „ of external galaxies, 244, 291, 301, 320, 322 IGNEOUS rocks, 44 Impact Theory, 38 Indi e, 40 Infinity of space, 309, 322, 323 JUPITER, 3, 12, 28, 52 „ satellites of, 41 KANT, 1-5, 25, 226-229, 248 Keeler, 79, 119, 120, 121 Kepler, 183, 212-214 Kerr, Dr., 60 Kinetic theory of gases, 115 Kirchhoff, 72 Kirkwood, Prof., 11, 12, 17, 44, 45, 94 Konkoly, 88, 91, 103 Kundt, 60 344 INDEX. LACAILLE 8760, 40 „ 9352, 40 L'Aigle, 82 Lalande 21,185, 40 21,258, 40 Lambert, 229-232, 318, 319 Langley, Prof., 50 Laplace, Chap. I., 25, 26, 29, 32, 33, 34, 248 Lava, 44 • Lenarto meteorite, 85 Le Verrier, 19 , Light of Sun, 49 Limerick meteorite, 103 Line, chief nebular, 118, 119 Lines in spectrum, 71 Lippich, 60 Liveing, 88, 117, 119 Livy, 81 Lockyer, Prof., 41, 74-78, Chap. VIII. Lodge, Prof., 68 Lorenzoni, 76 Lucretius, 25, 63 Lyrse a (Vega), 73, 75 ,-. A 76, 110 MAGELLANIC Clouds, 160, 161, 209, 253, 300, 301, 303, 304 Manilius, 124 Markwick, Col., 130, 297 Mass of the Solar System, App. Note A Matter, constitution of, Chap. VI. Ma-tuan-lin, 81 Maxwell, Clerk, 64, 65 Maunder, 120, 121 McClean, 75 Mercury, 3 Merope, 165 Mesozoic Period, 47 Meteoritic Hypothesis, Chap. VIII. Michell, Rev. John, 183, 233-235 Middleborough meteorite, 82 Milky Way, Chaps. IX., XIII. Miller, Dr., 73 Miniature suns, Chap. XII., 207 Miocene, 46 Mira Ceti, 110, 111, 113 Mississippi river, 45 Monck, 116, 118, 122, 162. 163, 289 Monocerotis 12, 168, 177 Moon, 14, 15, 16 Motion in line of sight, 195, 196, App. NoteK Motion, Sun's, in space, 192-194, 197 Motions, proper, 189-192 Mazapil meteorite, 83 NEAREST fixed star, 184 Nebulse, light of, 78 Nebuhe, size of, 40, 41 Nebular Hypothesis, Chaps. I., II., pp. 69, 70 Nejed meteorite, 83 Neptune, 3 Newcomb, 9, 312 Newton, Sir Isaac, 25, 66 Prof., 88, 89 Nichol, 22 North Pole of Milky Way, 125, 139 Nubecula Major, 138, 161 „ . Minor, 138, 161 Number of stars in Catalogues, App. Note a Number of visible stars, 310-314 OBERUKIRCHEN meteorite, 87 Oenopides, 123 Olbers, 275, 286, 287 Old Red Sandstone, 47 Ophiuchi f! and y, 169 70, 179, 185 Orion, "Belt "of, 143, 145 „ Great nebula in, 118, 119, 244 „ " Sword " of, 143, 145 „ U, 70, 113 Orionis a (Betelgense), 73, 77, 180, 186, 196 Orionis e, 196 INDEX. 345 Ononis, 32, 109 Orne, 82 Orohippus, 47 Otumpa meteorite, 83 Ovid, 25, 123 " Owl" nebula, 40 PARALLAX, 184-189, App. Note J Pechtile, 76, 77 Pegasi, 33, 109 Perseus, "festoon" in, 166, 172 Persei x, 168 Pessinuntia, 81 Phobos, satellite of Mars, 16 Pickering, Prof., 104, 111, 113, 162, 165, 195, 247, 284, 312 Piscium 49, 109 Planets round stars, 316-318 " Plassmann, 138, 150, 263, 264, 297 Plato, 25, 124 " Pleiad, Lost," 165 Pleiades, 152, 159, 160, 195, 207, 208, 220 Pleione, 165 "Plough," 164, 304, 305 Plutarch, 123 Pole Star, 196 . Pollux, 73, 76, 168, 196, 205 Pons-Brook comet, 94 Pouillet, 50 Prasepe, or the " Beehive," 166 Primary Period, 32 Pritchard, 185, 186, 205 Proctor, 10, 17, 146, 148, 151, 154, 172, 180, 192, 198, Chap. XVII. Procyon, 185, 196 "Proper motions" of stars, 189-192, App. Note I Pythagoras, 124 "DANCKEN, 194, 197 -EV Bayet, 102, 103 Red Stars, 104, 105 Regions, poor, 156-158, 169 Regions rich in stars, 152-155, 169 Regulus, 75, 196, 218 Rich spots, 152-155 Rigel, 196, 205, 218 Roberts, Dr. Isaac, 168, 171 Roche, 12, 13, 14, 15, 16, 90 RJJntgen, 60 Rosse, Lord, 95 Rowland, Prof., 73 Rowton meteorite, 82 " Runaway star," 39, 194, 195 Russell, 161, 170 SAGITTARIUS, Photographs in, Plates IX., X. Sainte-Claire Deviile, 50 Sandstone, Old Red, 47 Satellites, 17 Satwday Review, 143, 144 Saturn, 3, 213, 275 „ rotation of, 5 Saturn's rings, 5, 7, 17 Sawerthal's comet, 94 Scagh, 82 Schiaparelli, 89, 284-288 Scorpio, 30, 164, 170, 172 Scutum, 129 Secchi, 50, 88, 107 Secondary Period, 47 Serpentis 7, 191 Sherman, 103 Shrinkage of Sun, 52, 53 " Sickle " in Leo, 164 Simon, 19 Sirian-type stars, 74 Sirius, 73, 75, 106; 183, 185, 190, 199- 201, 207, 208, 218, 233, 316, 317, 319 " Sobieski's Shield," 125, 131 " Solar apex," 193, 194, 197 " Solar cluster," 159, 160 Solar System, 29 Southern Cross, 132, 161, 164 Spectra, stellar, 74-77 „ of stars in Milky Way, 247 23 346 INDEX. Spectrum, nebular, 78 „ solar, 71, 72 Spencer, Herbert, 23, 24 Spica, 75, 196 Spinoza, 63 Spiral nebulse, 99, 100 SpOser, 50 " Star Belt," 158, 159 Stars, binary, 28, 29,1 55, 1 565107-109, 209, 253 Stars, binary, triple^and multiple, 27 „ red, 26 „ temporary, 42 „ variable, 26, 110, 111 „ white, 26 „ yellow, 26 Star streams, Chap. X., 305 Stellar evolution, Chap. III. „ spectra, 74-77, 162, 163 Streams, star, Chap. X. Strove, 187, 193, Chaps. XV., XVI. „ L., 191, 194 „ 2398, 40 Sun, central, 198 „ heat of, 50, 51 „ light of, 49 „ shrinkage of, 52, 53 Sutton, 160 rpAIT, PROF., 94 Taungs, 130 Tauri o (Aldebaran), 73, 76, 106 Temporary stars, 42, 43 Tertiary Period, 47 Thalen, 72 Thomson, Sir William,' 19, 44, 50, 52, 53, 54, 55, 64, 65, 66 Tisserand, Dr., 19 Trowbridge, 11, 44, 45, 51 Thwing meteorite, 82 1 Now Lord Kelvin. Tycho Brahe, 182, 220 Tyndall, Prof., 65 TTRANOMETRIA Argentina, 139, U 143, 151, 152, 158, 159 Uranometria, Nova Oxonienm, 151 Uranus, 3, 17, 19, 31 Ursae Majoris, a, 76 ft 164, 186 „ . „ 7,164,186 e, 164, 186, 192 f, 75, 109, 164, 192 6, 191 T, 105 Ursse Minoris, ft 144 VARIABLE Stars, 26, 110, 111 Vega, 73, 75, 106, 186, 187, 196, 204, 205, 218 Velocity of stars, App. Note J Venus, 32 Virgil, 25 Vogel, 74, 76, 77, 102, 103, 107, 196 Volcano, 44 Vortex-ring structure .of Milky Way, 162 Vortex-ring theory of atoms, 66, 67 Vulpeculse, 5, 166-168 WAGNER, 185 Wallace, 46 Way, Milky, Chap.iIX., etc. Wellington, 82 Wells' comet, 92 Wolf, 4, 20, 33, 34, 162, 163, 299 Wolf-Rayet stars, 102 Wright, Thomas, 1, 214-226 ~\7"OUNG, Prof., 51, 119, 312 ^OLLNER, 4, ! Printed by Hazell, Watson, & Viney, Ld., London and Aylesbury. 7, Stationers' Hall Court, London, E.C. March, 18.91. 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It is Steam. S SAFE D USE 0F STEAM. Containing Rules for Unprofessional Seam-users. By an Engineer. Sixth Edition. Sewed, 6d. by then • rarity.'"-^""^ Mx/tamc^ ''"^ "*"* ^ *""*" b °'' er explo5 '° ns would become sensation Office Booh for Mechanical Engineers. THE MECHANICAL ENGINEER'S REFERENCE BOOK, for n?!; 6 o B ? ller Constr "<:t'on- In Two Parts. Part I. General Engineering liata. Part II. Boiler Construction. With 48 Plates and numerous Illus- trations. By Nelson Foley, M.I.N. A. Folio, half-bound. Price £5 $s. Coal and Speed Tables. pearly ready. A POCKET BOOK OF COAL AND SPEED TABLES, for Engineers and Steam-users. By Nelson Foley, Author of " Boiler Construction." Pocket- "T Z h e ' 3 *' h - ; v - leather - for mnT, ™ ^'fs are designed to meet the requirements of every-day use ; they are of sufficient scope .1 S. P ractl <-ai purposes, and may be commended to engineers and users of steam."— Iron. Wmiil'Tf' u l merits the attention of the practical engineer. Mr. Foley has compiled a r*Z..~ j tables, the information contained in which is frequently required by engineers, coal consumers, and users of steam."— Iron and Coal Trades Review. Fire Engineering. FIRES, FIRE-ENGINES, AND FIRE-BRIGADES. With a History of Fire-Engines, their Construction, Use, and Management ; Remarks on Fire- Proof Buildings, and the Preservation of Life from Fire ; Statistics of the Fire Appliances in English Towns ; Foreign Fire Systems ; Hints on Fire- Brigades, &c. &c. By Charles F. T. Young, C.E. With numerous Illustrations, 544 pp., demy 8vo, £1 4r. cloth. To such of our readers as are interested in the subject of fires and fire apparatus, we can most Heartily commend this book. It is really the only English wurk we now have upon the subject." — Engineering. ' It displays much evidence of careful research, and Mr. Young has put his facts neatly together, "is acquaintance with the practical details of the construction of steam fire engines, old and new, and the conditions with which it is necessary they should comply, is accurate and full." — Engineer. Estimating for Engineering Work, &c. ENGINEERING ESTIMATES, COSTS AND ACCOUNTS: A Guide to Commercial Engineering. With numerous Examples of Estimates and Costs of Millwright Work,' Miscellaneous Productions, Steam Engines and Steam Boilers ; and a Section on the Preparation of Costs Accounts. By A General Manager. Demy 8vo, 12s. cloth. {Just published. "This is an excellent and very useful book, covering subject-matter in constant requisition in every factory and workshop The book is invaluable, not only to the young engineer, but also to the estimate department of every works."— Builder. " This book bears on every page evidence that it has been prepared by an engineer accustomed to the work, and is no mere compilation, but contains a mass of valuable information of a kind useful even to experienced engineers." — Practical Engineer. " We accord the work unqualified praise. The information is given in a plain, straightforward manner, and bears throughout evidence of the intimate practical acquaintance of the author with every phrase of commercial engineering."— Mechanical World. 6 CROSBY LOCKWOOD & SON'S CATALOGUE. THE POPULAR WORKS OF MICHAEL REYNOLDS ("The Engine Driver's Friend"). Locomotive-Engine Driving. LOCOMOTIVE-ENGINE DRIVING: A Practical Manual for En- gineers in charge of Locomotive Engines. By Michael Reynolds, Member of the Society of Engineers, formerly Locomotive Inspector, L B. and S. C. R. Eighth Edition. Including a Key to the Locomotive En gin e. With Illustrations and Portrait of Author. Crown 8vo, 4s. 6d. cloth. " Mr. Reynolds has supplied a want, and has supplied it well. We can confidently recommend the book not only to the practical driver, but to everyone who takes an interest in the performance of loco- motive engines. 1 ' — The Engineer. "Mr. Reynolds has opened a new chapter in the literature of the day. . This admirable practical treatise, of the practical utility of which we have to speak in terms of warm commendation." — Atheneeum. " Evidently the work of one who knows his subject thoroughly." — Railway Service Gazette. " Were the cautions and rules given in the book to become part of the every-day working of our engine-drivers, we might have fewer distressing accidents to deplore." — Scotsman. Stationary Engine Driving. STATIONARY ENGINE DRIVING: A Practical Manual for En- gineers in Charge of Stationary Engines. By Michael Reynolds. Fourth Edition, Enlarged. With Plates and Woodcuts. Crown 8vo, 4s. 6d. cloth. "The author is thoroughly acquainted with his subjects, and his advice on the various points treated is clear and practical He has produced a manual which is an exceedingly useful one for the ■class for whom it is specially intended." — Engineering. " Our author leaves no- stone unturned. He is determined that his readers shall not only know something about the stationary engine, but all about it." — Engineer. " An engineman who has mastered the contents of Mr. Reynolds's book will require but little actua experience with boilers and engines before he can be trusted to look after them." — English Mechanic. The Engineer, Fireman, and Engine-Boy. THE MODEL LOCOMOTIVE ENGINEER, FIREMAN, AND ENGINE-BO Y. Comprising a Historical Notice of the Pioneer Locomotive Engines and their Inventors. By Michael Reynolds. With numerous Illustrations, and a fine Portrait of George Stephenson. Crown Svo, \s. 6d. cloth. " From the technical knowledge of the author, it will appeal to the railway man of to-day more forcibly than anything written by Dr. Smiles The volume contains information of a technical kind, and facts that every driver should be familiar with."— English Mechanic. "We should be glad to see this book in the possession of everyone in the kingdom who has ever laid, or is to lay, hands on a locomotive engine.'* — Iron. Continuous Railway Brakes. CONTINUOUS RAILWAY BRAKES: A Practical Treatise on the , several Systems in Use in the United Kingdom ; their Construction and Perform- ance. With copious Illustrations and numerous Tables. By Michael Reynolds. Large crown 8vo, gs. cloth. I' A popular explanation of the different brakes. It will be of great assistance in forming: public opinion, and will be studied with benefit by those who take an interest in the brake." — English Mechanic. " Written with sufficient technical detail to enable the principal and relative connection of the various parts of each particular brake to be readily grasped." — Mechanical World. Engine-Driving Life. ENGINE-DRIVING LIFE : Stirring Adventures and Incidents in the Lives, of Locomotive Engine- Drivers. By Michael Reynolds. Second Edition, with additional Chapters. Crown 8vo, zs. cloth. *' From first to last perfectly fascinating. Wilkie Collins's most thrilling conceptions are thrown into the shade by true incidents, endless in their variety, related in every page." — North British Mail. ''Anyone who wishes to get a real insight into railway life cannot do better than read * Engine- Driving Life* for himself, and if he once takes it up he will find that the author's enthusiasm and real love of the engine-driving profession will carry him on till he has read every page." — Saturday Review. Pocket Companion for Enginemen. THE ENGINEMAN'S POCKET COMPANION and Practical Educator for Enginemen, Boiler Attendants, and Mechanics. By Michael Rey- nolds. With Forty-five Illustrations and numerous Diagrams. Second Edition, Revised. Royal i8mo, y. 6d. strongly bound for pocket wear. " This admirable work is well suited to accomplish its object, being the honest workmanship- of a competent engineer." — Glasgow Herald. "A most meritorious work, giving in a succinct and practical form all the information an engine- minder desirous of mastering the .-.qientifiq principles of his datty calling would, require/' — The Milter. "A boon to thohe who are striving to become efficient mechanics.','— Daily Chronicle. CIVIL ENGINEERING, SURVEYING, &C French-English Glossary for Engineer's, &g. A POCKET GLOSSARY OF TECHNICAL TERMS: ENGLISH- FRENCH, FRENCH-ENGLISH; with Tables suitable for the Architectural, Engineering, Manufacturing and Nautical Professions. By John James Fletcher, . Engineer and Surveyor ; 200 pp. Waistcoat-pocket size, is. 6d. limp leather. " It ought certainly to be in the waistcoat-pocket of every professional man.'' — Iron. " It is a very great advantage for readers and correspondents in France and England'^ to hive so large a number of the words relating to engineering and manufacturers collected in a liliputian volume. The little book will be useful both to students and travellers."— Architect. The glossary of terms is very complete, and many of the Tables are new and well arranged. We cordially commend the book."— Mechanical World. Portable Engines. THE PORTABLE ENGINE; ITS CONSTRUCTION AND MANAGEMENT: A Practical Manual for Owners and Users of Steam Engines generally. By William Dyson Wansbrough. With 90 Illustrations. Crown 8vo, jr. 6d. cloth. "This is a work of value to those who use steam machinery. . . . Should be read by every one who has a steam engine, on a farm or elsewhere." — Mark Lane Express. " We cordially commend this work to buyers and owners of steam engines, and to those who have to do with their construction or use."— Timber Trades Journal. "Such a general knowledge of the steam-engine as Mr. Wansbrough furnishes to the reader should The acquired by all intelligent owners and others who use the steam engine." — Building News. " An excellent text-book of this useful form of engine, which describes with all necessary minuteness the details of the various devices. ... The ' Hints to Purchasers ' contain a good deal of common- sense and practical wisdom."— English Mechanic. CIVIL ENGINEERING, SURVEYING, etc. MR. HUMBER'S IMPORTANT ENGINEERING BOOKS. The Water-Supply of Cities and Towns. A COMPREHENSIVE TREATISE ON THE WATER-SUPPLY OF CITIES AND TOWNS. By William Humber, A-M. Inst. C.E., and M. Inst. M.E., Author of "Cast and Wrought Iron Bridge Construction," &c. &c. Illustrated with 50 Double Plates, 1 Single Plate, Coloured Frontispiece, and up- wards of 250 Woodcuts, and 'containing 400 pages of Text. Imp. 4to, £6 bs. elegantly and substantially half-bound in morocco. List of Contents. Machinery.-XII. Conduits.— XIII. Distribution of Water.— XIV. Meters, Service Pipes, and House Fittings.— XV. The Law and Economy of Water Works.— XVI. Constant and Intermittent Supply. — XVII. DescriptionofPlates.— Appendices, giving Tables of Rates of Supply, Velocities, &c. &c, I. Historical Sketch of some of the means that nave been adopted for the Supply of Water to Cities and Towns.— II. Water and the Foreign Matter usually associated with it.— III. Rainfall and Evaporation.— IV. Springs and the water- bearing formations of various districts. — V. Mea- surement and Estimation of the Flow of Water.— VI. On, the Selection of the Source of Supply. — VII. Wells.— VIII. Reservoirs.— IX. The Puri- fication of Water.— X. Pumps.— XI. Pumping together with Specifications of several Works illus- trated, among which will be found : Aberdeen, Bideford, Canterbury, Dundee, Halifax, Lambeth, Rotherham, Dublin, and others. The most systematic and valuable work upon water supply hitherto produced in English or in any other language. ... Mr. Humber's work is characterised almost throughout by an exhaustiveness much more distinctive of French and German than of English technical treatises. —Jingz rteer " We can congratulate Mr. Humber on having been able to give so large an_arnount of information on a subject so important as the water supply of cities and towns. The plates, fifty in ""^"if" ™° s '£ drawings of executed works, and alone would have commanded the attention of every engineer whose practice may lie in this branch of the profession." — Builder. Cast and Wrought Iron Bridge Construction. A COMPLETE AND PRACTICAL TREATISE ON CAST AND WROUGHT IRON BRIDGE CONSTRUCTION, including Iron Foundations. In Three Parts-Theoretical, Practical, and Descriptive. By William Humber, A-M. Inst. C.E., and M. Inst. M.E. Third Edition, revised and much unproved with us Double Plates (20 of which now first appear in this edition), and numerous Additions to the Text. In 2 vols., imp. 4 to, £6 16s. 6d. half-bound m morocco. " A very valuable contribution to the standard literature of civil engineering . I "^° n J°4Tf those p'ans, and I sections/large scale details are given, which very much enhance the instructive worm ot tflose illustrations."— Civil E?tgineer and A rchitecfs Journal. „,■.-„► Virion erected durine '" Mr. Humber's statefy volumes, lately issued-in which the most W rte "' b "fe s ,,^ c 'J? r %™f the last five years, under thedirection. of the late Mr. Brunei, Sir W. Cnbitt, Mr. Haw] taha- »,Mr.rj %., Mr. Fowler. Mr. Hemans, and others among our most eminent engineers, are orawn and spcahed .11 great detail." — Engineer. CROSBY LOCKWOOD & SON'S CATALOGUE. MR. HUMBER'S GREAT WORK ON MODERN ENGINEERING. Complete in Four Volumes, imperial 4to, price £12 I2J., half-morocco. Each volume sold separately as follows : — A RECORD OF THE PROGRESS OF MODERN ENGINEERING. First Series. Comprising Civil, Mechanical, Marine, Hydraulic, Railway, Bridge, and other Engineering Works, &c. By William Humber, A-M. Inst. C.E., &c. Imp. 4to, with 36 Double Plates, drawn to a large scale, Photographic Portrait of John Hawkshaw, C.E., F.R.S., &c, and copious descriptive Letterpress, Specifications, &c, £3 3-f. half-morocco. List of the Plates and Diagrams. Victoria Station and Roof, L. B. & S. C. R. (8 plates) ; Southport Pier (2 plates) ; Victoria Station and Roof, L. C. & D. and G. W. R. (6 plates) ; Roof of Cremorne Music Hall ; Hridge over G. N. Railway ; Roof of Station, Dutch Rhenish Rail (2 plates) ; Bridge over the Thames, West London Extension Railway (5 plates); Armour Plates : Suspension Bridge, Thames (♦ plates) ; The Allen Engine ; Suspension Bridge, Avon (3 plates) ; Underground Railway (3 plates). ' Handsomely lithographed and printed. It will find favour with many who desire to preserve in a permanent form copies of the plans and •specifications prepared for the guidance of the contractors for many important engineering works."— Engineer. HUMBER'S RECORD OF MODERN ENGINEERING. Second Series. Imp. 4to, with 36 Double Plates, Photographic Portrait of Robert Stephenson, C.E., M.P., F.R.S., &c, and copious descriptive Letterpress, Speci- fications, &c.,^3 3s. half-morocco. List of the Plates and Diagrams. Birkenhead Docks, Low Water Basin (15 plates); Ebbw Viaduct, Merthyr, Tredegar, and Aber- Charing Cross Station Roof, C. C. Railway (3 gavenny Railway ; College Wood Viaduct, Corn- plates) ; Digswell Viaduct, Great Northern Rail-. wall Railway ; Dublin Winter Palace Roof (3 way ; Robbery Wood Viaduct, Great Northern plates) ; Bridge over the Thames, L. C. ana D. Railway ; Iron PermanentWay ; Clydach Viaduct, Railway (6 plates) ; Albert Harbour, Greenock Merthyr, Tredegar, and Abergavenny Railway ; (4 plates). " Mr. Humber has done the profession good and true service, by the fine collection of examples he has here brought before the profession and the public."— Practical Mechanic's journal. NUMBER'S RECORD OF MODERN ENGINEERING. Third Series. Imp. 4to, with 40 Double Plates, Photographic Portrait of J. R. M'Clean, late Pres. Inst. C.E., and copious descriptive Letterpress, Specifications, &c.,£33-r* half-morocco. List of the Plates and Diagrams. (2 plates) ; Outfall Sewer, Reservoir and Outlet (4 plates); Outfall Sewer, Filth Hoist; Sections of Sewers (North and South Sides). Th a m hs Emb an k m ent. — Section of Ri verWall ; Main Drainage, Metropolis.— North Side. — Map showing Interception of Sewers; Middle Level Sewer (2 plates) ; Outfall Sewer, Bridge over River Lea (3 plates) ; Outfall Sewer, Bridge over Marsh Lane, North Woolwich Railway, and Bow and Barking Railway Junction; Outfall Sewer, Bridge over Bow and Barking Railway (3 plates) ; Outfall Sewer, Bridge over East London Waterworks' Feeder (z plates) ; Outfall Sewer, Reservoir (2 plates) ; Outfall Sewer, Tumbling Bay and Outlei ; Outfall Sewer, Penstocks. South Side. — Outfall Sewer, Bermondsey Branch Steamboat Pier, Westminster (2 plates) ; Landing Stairs between Charing Cross and Waterloo- Bridges ; York Gate (a plates) ; Overflow and Outlet at Savoy Street Sewer (3 plates) ; Steam- boat Pier, Waterloo Bridge (3 plates) ; Junction of Sewers, Plans and Sections ; Gullies, Plans, and Sections ; Rolling Stock ; Granite and Iron Forts. ^ "The drawings have a constantly increasing value, and whoever desires to possess clear representa- tions of the two great works carried out by our Metropolitan Board will obtain Mr. Humber "s volume.*'— Engineer. HUMBER'S RECORD OF MODERN ENGINEERING. Fourth Series. Imp. 4to, with 36 Double Plates, Photographic Portrait of John Fowler, late Pres. Inst. C.E., and copious descriptive Letterpress, Specifications, &c, £3 3-r. half-morocco. List of the Plates and Diagrams. Abbey Mills Pumping Station, Main Drainage, Metropolis (4 plates) ; Barrow Docks {5 plates) ; ManCruis Viaduct, Santiago and Valparaiso Rail- way (2 plates) ; Adam's Locomotive, St. Helen's Canal Railway (2 plates) ; Cannon Street Station Roof, Charing Cross Railway (3 plates); Road Bridge over the River Moka (2 .plates) ; Telegra- phic Apparatus for Mesopotamia; Viaduct over the River Wye, Midland Railway (3 plates); St. Germans Viaduct, Cornwall Railway (2 plates) : Wrought-Iron Cylinder for Diving Bell ; Millwall Docks (6 plates); Milroy's Patent Excavator; Metropolitan District Railway (6 plates); Har- bours, Ports, and Breakwaters (3 plates). "We gladly welcome another year's issue' of this valuable publication from the able pen of Mr. Hum- ber. The accuracy and general excellence of this work - are well known, while its usefulness' in giving the measurements and details of some of the latest examples of engineering, as carried out by the most eminent men in the profession, cannot be too highly prized." — Artizan. CIVIL ENGINEERING, SURVEYING, &>c. MR. HUMBER'S ENGINEERING BOOKS— continued. Strains, Calculation of. A HANDY BOOK FOR THE CALCULATION OF STRAINS IN GIRDERS AND SIMILAR STRUCTURES, AND THEIR STRENG'I 11. Consisting of Formulas and Corresponding Diagrams, with numerous details for Practical Application, &c. By William Humber, A-M. Inst. C.E., &c. Fourth Edition. Crown 8vo, with nearly 100 Woodcuts and 3 Plates, "]s. 6d. cloth. "The formulae are neatly expressed, and the diagrams good." — Atheneeum. "Weheartily commend this really handy book to our engineer and architect readers." — English Mechanic. Barlow's Strength of Materials, enlarged by Humber. A TREATISE ON THE STRENGTH OF MATERIALS ; with Rules for Application in Architecture, the Construction of Suspension Bridges, Railways, &c. By Peter Barlow, F.R.S. A New Edition, revised by hi* Sons, P. W. Barlow, F.R.S., and W. H. Barlow, F.R S.; to which are added, Experiments by Hodgkinson, Fairbairn, and Kirkaldy ; and Formulae for Calculating Girders, &c. Arranged and Edited by Wm. Humeer, A-M. Inst. C.E. Demy 8vo, 400 pp., with 19 large Plates and numerous Woodcuts, \%s. cloth. " Valuable alike to the student, tyro, and the experienced practitioner, it will always rank in future: as it has hitherto done, as the standard treatise on that particular subject."— Engineer. '* There is no greater authority than Barlow." — Building News. "As a scientific work of the first class, it deserves a foremost place on the bookshelves of every civil engineer and practical mechanic."— English Mechanic. Trigonometrical Surveying. AN OUTLINE OF THE METHOD OF CONDUCTING A TRIGO- NOMETRICAL SURVEY, for the Formation of Geographical and Topographical Maps and Plans, Military Reconnaissance, Levelling, &c, with Useful Problems, Formulae, and Tables. By Lieut. -General Frome, R.E. Fourth Edition, Revised and partly Re-written by Major-General Sir Charles Warren, G.C.M.G., K.Ji. With 19 Plates and 115 Woodcuts, royal 8vo, 16s. cloth. "The simple fact that a fourth edition has been called for is the best testimony to its merits. No words of praise from us can strengthen the position so well and so steadily maintained by ttus wonc. Sir Charles Warren has revised the entire work, and made such additions as were necessary to bring every portion of the contents up to the present date." — Broad Arrow. Field Fortification. A TREATISE ON FIELD FORTIFICATION, THE ATTACK ■ OF FORTRESSES, MILITARY MINING, AND RECONNOITRING. By Colonel I. S. Macaulay, late Professor of Fortification in the R.M.A., Wool- wich. Sixth Edition, crown 8vo, cloth, with separate Atlas of 12 nates, 12s. Oblique Bridges. TrnT TK A PRACTICAL AND THEORETICAL ESSAY ON OBLIQUE BRIDGES. With 13 large Plates. By the late George Watson Buck, M- 1 -^- Third Edition, revised by his Son, J. H. Watson Buck, M. I.C.E.; «*.*'**! addition of Description to Diagrams for Facilitating the Construction of Oblique Bridges, by W. H. Barlow, M.I.C.E. Royal 8vo, iar. cloth. , . " The standard text-book for all engineers regarding skew arches is Mr. Buck's treatise, and it would be impossible to consult a better."— Engineer. , i,,c^iwetHl thesubiect "Mr. Buck's treatise is recognised as a standard text-book, and his treatment has "^J™?^ ™ of many of the intricacies supposed to belong to it. As a guide to the engineer and architect, on confessedly difficult subject, Mr. Buck's work is unsurpassed, —building aews. Water Storage, Conveyance and Utilisation. WATER ENGINEERING: A Practical Treatise on the Measurement, Storage, Conveyance and Utilisation of Water for the Supply of Towns , for Milt Power, and for other Purposes. By Charles Slagg Water and Drainage Engineer, A.M. Inst.C.E., Author of "Sanitary Work in ^\ Sm ^"l? waS ' an<1 in Villages," &c. With numerous Illustrations. Crown 8vo, Is. 6d. cloth. " As a small practical treatise on the water supply of towns, and on some applications of water- power, the work is in many respects excellent."— Enj ineenng. eminent "The author has collated the results deduced from '"« W!" m '°i! mDsm ied by very clear authorities, and has presented them in a compact and P ractica . f °™'^ m t p r |";|d very carefully ■ad detailed explanations The application of water as a motive power is treated very caret y ■^-"SSSS" whf des&s to begin the study of hydraulics with a consideration of the practica. applications of the science there is no better guide."— Architect. CROSBY LOCKWOOD cV SON' 'S CATALOGUE. Statics, Graphic and Analytic. GRAPHIC AND ANALYTIC STATICS, in their Practical Applica- tion to tlie Treatment of Stresses in Roofs, Solid Girders, Lattice, Bowstring, and Suspension Bridges, Braced Iron Arches and Piers, and other Frameworks. By R. Hudson Graham, C.E. Containing Diagrams and Plates to Scale. With numerous Examples, many taken from existing Structures. Specially arranged for Class-work in Colleges and Universities. Second Edition, Revised and En- larged. 8vo, i6j. cloth. " Mr. Graham's book will find a place wherever graphic and analytic statics are used or studied."— Engineer. . " The work is excellent from a practical point of view, and has evidently been prepared with much care. The directions for working are ample, and are illustrated by an abundance of well-selected examples. It is an excellent text-book for'the practical draughtsman." — Atlienaum, Student's Text-Book on Surueying. PRACTICAL SURVEYING: A Text-Book for Students preparing for Examinations or for Survey-work in the Colonies. By George W. Usill, A. M.I. C.E. , Author of "The Statistics of the Water Supply of Great Britain." With 4 Lithographic Plates and' "upwards of 330] Illustrations. Second Edition, Revised. Crown 8vo, 7s. 6d. cloth. [Just published. " The best forms of instruments are described as to their construction, uses and modes of employment, and there are innumerable hints on work and equipment such as the author, in,his experience as surveyor, draughtsman and teacher, has found necessary, and which the student in his inexperience will find most serviceable." — Engineer. ... " The latest treatise in the English language on surveying, and we have no hesitation in saying that the student will find it a better guide than any of its predecessors. . . . Deserves to be recog- nised as the first book which should be put in the hands of a pupil of Civil Engineering, and every gentleman of education who sets out for the Colonies would find it well to have a copy. 1 ' — A rchitect. " A very useful, practical handbook on field practice. Clear, accurate and not too condensed."— Journal of Education. Suruey Practice. AID TO SUR VE Y PR A CTICE : for Reference in Surveying, Levelling, and Setting-out ; and in Route Surveys of Travellers by Land and Sea. With Tables, Illustrations, and Records. By Lowis D'A. Jackson, A.M.I.C.E., Author of "Hydraulic Manual," "Modern Metrology," &c. Second Edition, Enlarged. Large crown 8vo, \2s. 6d. cloth. "Mr. Jackson has produced a valuable vade-mecum for the surveyor. We can recommend this book as containing an admirable supplement to the teaching of the accomplished surveyor." — Athenmtm. *'As_a text-book we should advise all surveyors to place it in their libraries, and study well the matured instructions afforded in its pages." — Colliery Guardian. '~Xhe author brings to,his work a fortunate union of theory and practical experience which, aided by a clear and lucid style of writing, renders the book a very useful one." — Builder. Surveying, Land and Marine. LAND AND MARINE SURVEYING, in Reference to the Prepara- tion of Plans for Roads and Railways ; Canals, Rivers, Towns' Water Supplies ; Docks and Harbours. With Description and Use of Surveying Instruments. By W. Davis Haskoll, C.E., Author of "Bridge and Viaduct Construction," &c. Second Edition, Revised, with Additions. Large crown 8vo, 9^. cloth. _" This book must prove of great value to the student. We have no hesitation in recommending it, feeling assured that it will more than repay a careful study." — Mechanical World. " A most useful and well arranged book for the aid of a student. We can strongly recommendit as a carefully-written and valuable text-book. It enjoys a well-deserved repute among surveyors."— Builder. " This volume cannot fail to prove of the utmost practical utility. It may be safely recommended to all students who aspire to become clean and expert surveyors.!' — Mining Journal. Tunnelling. PRACTICAL TUNNELLING. Explaining in detail the Setting-out of the works, Shaft-sinking and Heading-driving, Ranging the Lines and Levelling under Ground, Sub-Excavating, Timbering, and the Construction of the Brickwork of Tunnels, with the amount of Labour required for, and the Cost of, the various portions of the work. By Frederick W. Simms, F.G.S., M. Inst. C.E. Third Edition, Revised and Extended by D. Kinnear Clark, M.Inst. C.E. Imp. 8vo, with 21 Folding Plates and numerous Wood Engravings, 30^. cloth. " The estimation in which Mr. Simms' s' book on tunnelling has been field for over thirty years cannot be more truly expressed than in the words of;the late Professor Rankine : — 'The best source of informa- tion on the subject of tunnels is Mr. F. W. Simms's work on Practical Tunnelling. "'^-Architect. " It has been regarded from the first as a text book of the subject . . . Mr. Clark has added immensely to the value of the book." — Engineer. CIVIL ENGINEERING, SURVEYING, frc. Levelling. A TREATISE ON THE PRINCIPLES AND PRACTICE OF LE FELLING, Showing its Application to purposes of Railway and Civil Engineer- ing in the Construction of Roads ; with Mr. Telford's Rules for the same. By Frederick W. Simms, F.G.S., M. Inst. C.E. Seventh Edition, withthe addition of Law's Practical Examples for Setting-out Railway Curves, and Trautwine's Field Practice of Laying-out Circular Curves. With 7 Plates and numerous Woodcuts, 8vo, 8s. 6d. cloth. %* Trautwine on Curves may be had separate, 5-r. "The text-hook oh levelling in most of our engineering schools and colleges."— Engineer. "The publishers have rendered a substantial service to the profession, especially to the younger members, by bringing out the present edition of Mr. Simms's useful work." — Engineering. Heat, Expansion by. EXPANSION OF STRUCTURES BY HEAT. By John Keily, C.E., late of the Indian Public Works and Victorian Railway Departments. Crown 8ro, y. 6d. cloth. Summary of Contents. Section VI.— Mechanical Force of Heat. Section VII.— Work of Expansion and Con- traction. Section I.— Formulas and Data. Section II.— Metal Bars. Section III.— Simple Frames. Section IV. — Complex Frames and Plates. .Section V. — Thermal Conductivity. Section VIII.— Suspension Bridges. Section IX.— Masonry Structures. "The aim the author has set before him, viz., to show the effects of heat upon metallic ana other structures, is a laudable one, for this is a branch of physics upon which the engineer or architect can find but little reliable and comprehensive data in books.'' — Builder. ' "Whoever is concerned to know the effect of changes of temperature on such structures as suspen- sion bridges and the like could not do better than consult Mr. Keily's valuable and handy exposition ot the geometrical principles involved in these changes." — Scotsman. Practical Mathematics. MATHEMATICS FOR PRACTICAL MEN: Being a Common-place Book of Pure and Mixed Mathematics. Designed chiefly for the Use of Civil Engineers, Architects and Surveyors. By Olinthus Gregory, LL.D., F.R.A.S., Enlarged by Henry Law, C.E. Fourth Ed., carefully revised by J. R. Young, formerly Professor of Mathematics, Belfast College. With 13 Plates, 8vo, £1 is. cloth. "The engineer or architect will here find ready to his hand rules for solving nearly every mathematical difficulty that may arise in his practice. The rules are in all cases explained by means of examples, m which every step of the process is clearly worked out." — -Builder. _ ' ._ . "One of the most serviceable books for practical mechanics. . . . It is an instructive book tor tne student, and a Text-book for him who, having once mastered the subjects it treats of, needs occasionally to refresh his memory upon them," — Building News. Hydraulic Tables. HYDRAULIC TABLES, CO-EFFICIENTS, and FORMULM fpr Finding the Discharge of Water from Orifices, Notches, Weirs, Pipes, and Kivers. With, New Formulae, Tables, and General Information on Ram-fall, Catctiment- . Basins, Drainage, Sewerage, Water Supply for Towns and Mill Power By JOHN Neville, Civil Engineer, M.R.I.A. Third Edition, carefully revised, with con- siderable Additions. Numerous Illustrations. Crown 8vo, 14*. cloth. "Alike valuable to students and engineers in practice; its study will prevent. ***»»•?»=?« . avoidable failures, and assist them to select the readiest means of successfully carrying out any given work connected withhydraulie engineering. "— Mining Journal. ■ „_ L "It is, of all English books on the subject, the one nearest to completeness ... . *ron me good arrangement of the matter, the clear explanations and abundance °f /or^ulav he ' S£& » calculated tables, and, above all, the thorough acquaintance w.th .both theory and construction, which is displayed from first to last, the book will be found to be an acquisition. —Arcluteci. Hydraulics. HYDRA ULIC MANUAL. Consisting of Working Tables and Explana- tory Text. Intended as a Guide in Hydraulic Calculations and Field Operations ' By Lowis D'A. Jackson, Author of "Aid to Survey Practice, Modern Metrology," &c. Fourth Edition. Enlarged. Large crown 8vo, 1 6.r. cloth. " The author has had a wide experience in hydraulic engineering and has been a ""^server of the facts which have come under his notice, and from the great mass of. ma ' e " a ' at ? , ^ e ^ n e t.s pro- instructed a manual which may be accepted as a trustworthy guide to *£ b ™ c a h J^?J^£ latest - fession. We can heartily recommend this volume to all who desire to be acquainted witn lire development of this important subject."— Engineering. „ _ , • „ « " The standard work in this department of mechanics. _— Scotsman. , d d it tuorou(r h • " The most useful fe«ur= of this work .is . its. ^^^^^m^T^^^o. 'adoption of recent experiments ; ibe text is 111 fact in greau part a snort accuuui ui s 'experiments." — Nature. CROSBY LOCKWOOD & SON'S CATALOGUE. Drainage. ON THE DRAINAGE OF LANDS, TOWNS AND BUILDINGS. By G. D. Dempsey, C. E., Author of "The Practical Railway Engineer," &c. Revised, with large Additions on Recent Practice in Drainage Engineering, by D. Kinnear Clark, M.Inst. C.E., Author of "Tramways: their Construc- tion and Working," " A Manual of Rules, Tables, and Data for Mechanical Engineers," &c. Second Edition, Corrected. Fcap. 8vo, Ss. cloth. [Just published. "The new matter added to Mr. Dempsey's excellent work is characterised by the comprehensive grasp and accuracy of detail for which the name of Mr. D. K. Clark is a sufficient voucher." — Atheneeum. . ... , ■ *' As a work on recent practice in drainage engineering, the book is to be commended to all who are making that branch of engineering science their special study."— Iron. " A comprehensive manual on drainage engineering, and a useful introduction to the student. — Building News. Tramways and their Working. TRAMWAYS: Their CONSTRUCTION and WORKING. Embracing a Comprehensive History of the System ; with an exhaustive Analysis of the Various Modes of Traction, including Horse Power, Steam, Heated Water, and Compressed Air ; a Description of the Varieties of Rolling Stock ; and ample Details of Cost and Working Expenses ; the Progress recently made in Tramway Construction, &e. &c. By D. Kinnear Clark, M.Inst. C.E. With over 200 Wood Engravings, and 13 Folding Plates. Two Vols. Large crown 8vo, yos. cloth. " All interested in tramways must refer to it, as all railway engineers have turned to the author's work ' Railway Machinery.' " — Engineer. "An exhaustive and practical work on tramways, in which the history of this kind of locomotion, and a description and cost of the various modes of laying tramways, are to be found."—; Building News. " The best form of rails, the best mode of construction, and the best mechanical appliances, are so fairly indicated in the work under review that any engineer about to construct a tramway will be enabled at once to obtain the practical information which will be of most service to him." — Athen&um. Oblique Arches. A PRACTICAL TREATISE ON THE CONSTRUCTION OF OBLIQUE ARCHES. By John Hart. Third Edition, with Plates. Imperial 8vo, 8s. cloth. Curves, Tables for Setting-out. TABLES OF TANGENTIAL ANGLES AND MULTIPLES FOR SETTING-OUT CURVES from 5 to 200 Radius. By Alexander Beazei.ev, M.Inst. C.E. Third Edition. Printed on 48 Cards, and sold in a cloth box, waistcoat-pocket size, 3^. 6d. " Each table is printed on a small card, which, being placed on the theodolite, leaves the hands free to manipulate the instrument- — no small advantage as regards the rapidity of work." — Engineer. " Very handy : a man may know that all his day's work must fall on two of these cards, which he puts into his own card-case, and leaves the rest behind." — Aihenaum. Earthwork. EARTHWORK TABLES. Showing the Contents in Cubic Yards of Embankments, Cuttings, &c. , of Heights or Depths up to an average of 80 feet. By Joseph Broadbent, C.E., and Francis Campin, C.E. Crown Svo, 5j. cloth. ** The way in which accuracy is attained, by a simple division of each cross section into three elements, two in which are constant and one variable, is ingenious." — Atheneeum. Tunnel Shafts. THE CONSTRUCTION OF LARGE TUNNEL SHAFTS. A Practi- cal and Theoretical Essay. By J. H. Watson Buck, M. Inst. C.E., Resident Engineer, London and North- Western Railway. Illustrated with Folding Plates, royal 8vo, 12s. cloth. " Many of the methods given are of extreme practical value to the mason, and the observations on the form of arch, the rules for ordering the stone, and the construction of the templates, will be found of considerable use. We commend the book to the engineering profession." — Building News. " Will be regarded by civil engineers as of the utmost value, and calculated to save much time and obviate many mistakes." — Colliery Guardian. Girders, Strength of. GRAPHIC TABLE FOR FACILITATING THE COMPUTATION OF THE WEIGHTS OF WROUGHT IRON AND STEEL GIRDERS, &>c, for Parliamentary and other Estimates. By J. H. Watson Buck, M. Inst. C.E. On a Sheet, is. (id. CIVIL ENGINEERING, SURVEYING, &c. 13 River Engineering. RIVER BARS: The Causes of their Formation, and their Treatment by "Induced Tidal Scour;" with a Description of the Successful Reduction by this Method of the Bar at Dublin. By I. J. Mann, Assist. Eng. to the Dublin Port and Docks Board. Royal 8vo, Js. id. cloth. " We recommend all interested in harbour works— and, indeed, those concerned in the improvements of rivers generally-to read Mr. Mann s interesting work on the treatment of river bars. "-Engineer. Trusses. TRUSSES OF WOOD AND IRON. Practical Applications of Science in Determining the Stresses, Breaking Weights, Safe Loads, Scantlings, and Details of Construction. With Complete Working Drawings. By William Griffiths Surveyor, Assistant Master, Tranmere School of Science and Art. Oblone 8vo! 4*. 6d. cloth. s ' "This handy little book enters so minutely into every detail connected with the construction of roof trusses, that no student need be ignorant of these matters."— Practical Engineer. Railway Working. SAFE RAILWAY WORKING. A Treatise on Railway Accidents : Their Cause and Prevention ; with a Description of Modern Appliances and Systems. By Clement E. Stretton, C. E.,Vice-Presidentand Consulting Engineer, Amalga- mated Society of Railway Servants. With Illustrations and Coloured Plates. ^Second Edition, Enlarged. Crown 8vo, 3*. 6d. cloth. [Just published. "A book for the engineer, the directors, the managers ; and, in short, all who wish for information on railway matters will find a perfect encyclopaedia in ' Safe Railway Working.' "—Railway Review. We commend the remarks on railway signalling to all railway managers, especially where a uniform code and practice is advocated."— Herepath's Railway Journal. . , "V au thor may be congratulated on having collected, in a very convenient form, much valuable lnlormahon on the principal questions affecting the safe working of railways."— Rail-way Engineer. field-Booh for Engineers. THE ENGINEER'S, MINING SURVEYOR' S,and CONTRACTOR'S FIELD-BOOK. Consisting of a Series of Tables, with Rules, Explanations of Systems, and use of Theodolite for Traverse Surveying and Plotting the Work with minute accuracy by means of Straight Edge and Set Square only ; Levelling with the Theodolite, Casting-out and Reducing Levels to Datum, and Plotting Sections in the ordinary manner ; Setting-out Curves with the Theodolite by Tangential Angles and Multiples with Right and Left-hand Readings of the Instrument ; Setting- out Curves without Theodolite on the System of Tangential Angles by Sets of Tan- gents and Offsets; and Earthwork Tables to 80 feet deep, calculated for every 6 inches in depth. . By W. Davis Haskoll, C.E. With numerous Woodcuts. Fourth Edition, Enlarged. Crown 8vo, \2s. cloth. !T ne book is very handy ; the separate tables of sines and tangents to every minute will make it ■useful for many other purposes, the genuine traverse tables existing all the same." — AtkeneEum. " Ey e ry person engaged in engineering field operations will estimate the importance of such a work and the amount of valuable time which will be saved by reference to a set of reliable tables prepared ■with the accuracy and fulness of those given in this volume." — Railway News. Earthwork, Measurement of. A MANUAL ON EARTHWORK. By Alex. J. S. Graham, C.E. With numerous Diagrams. Second Edition. i8mo, 2s. 6d. cloth. "A great amount of practical information very admirably arranged, arid available for rough estimates, -as well as for the more exact calculations required in the engineer's and contractor's offices." — Artizan. Strains in Ironwork. ■ THE, STRAINS ON STRUCTURES OF IRONWORK; with Prac- tical Remarks on Iron Construction. By F. W. Sheilds, M. Inst. C.E. Second Edition, with 5 Plates. Royal 8vo, $s. cloth. " The student cannot find a better little book on this subject." — Engineer. Cast Iron and other Metals, Strength of. A PRACTICAL ESSAY ON THE STRENGTH OF CAST IRON AND OTHER METALS. By Thomas Tredgold, C.E. Fifth Edition, in- cluding Hodgkinson's Experimental Researches. 8vo, \2s. cloth. 14 CROSBY LOCKWOOD cV SON'S, CATALOGUE. ARCHITECTURE, BUILDING, etc. Construction. THE SCIENCE OF BUILDING. ■ An Elementary Treatise on the Principles of Construction. By E. Wyndham Tarn, M.A., Architect. Third Edition, Revised and Enlarged, with 59 Engravings. Fcap. 8vo, 4s. cloth. {Just published. "A very valuable book, which we strongly recommend to all students." — Builder. "No architectural student should be without this hand-book of constructional knowledge." — Architect. Villa. Architecture. A HANDY BOOK OF VILLA ARCHITECTURE : Being a Series of Designs for Villa Residences in various Styles. With Outline Specifications and Estimates. By C. Wickes, Architect, Author of "The Spires and Towers of England," &c. 61 Plates, 4to, £1 I is. dd. half-morocco, gilt edges. "The whole of the designs bear evidence of their being the work of an artistic architect, and they will prove very valuable and suggestive." — Building News. Text-Booh for Architects. THE ARCHITECT'S GUIDE: Being a Text-book of Useful Infor- mation for Architects, Engineers, Surveyors, Contractors, Clerks of Works, &c, &c. By Frederick Rogers, Architect, Author of "Specifications for Practical Architecture," &c. Second Edition, Revised and Enlarged. With numerous Illus- trations. Crown 8vo, 6s. cloth. "Asa text-book of useful information for architects, engineers, surveyors, &c, it would be hard to find a handier or more complete little volume." — Standard. " A young architect could hardly have a better guide-book." — Tim&er Trades yournal. Taylor and Gresy's Rome. THE ARCHITECTURAL ANTIQUITIES OF ROME. By the late G. L. Taylor, Esq., F.R.I.B.A., and Edward Cresy, Esq. New Edition, thoroughly revised by the Rev. Alexander Taylor, M.A. (son of the late G. L. Taylor, Esq.), Fellow of Queen's College, Oxford, and Chaplain of Gray's Inn. Large folio, with 130 Plates, half-bound, £3 3s. N.B. — This is the only book which gives on a large scale, and with the precision of architectural measurement, the principal Monuments of Ancient Rome in plan, eleva- tion, and detail. "Taylor and Cresy's work has from its first publication been ranked among those professional books which cannot be bettered. . . . It would be difficult to find examples of drawings, even among those of the most painstaking students of Gothic, more thoroughly worked out than are the one hundred and thirty plates in this volume." — Architect. Architectural Drawing. PRACTICAL RULES ON DRAWING, for the Operative Builder and Young Student in Architecture. By George Pyne. With 14 Plates, 4to, 7-r. td. boards. Sir William Chambers's Treatise on Ciuil Architecture. THE DECORATIVE PART OF CIVIL ARCHITECTURE. Bv Sir William Chambers, F.R.S. With Portrait, Illustrations, Notes, and an Examination of Grecian Architecture, by Joseph Gwilt, F.S.A. Re- , vised and Edited by W. H. Leeds, with a Memoir of the Author. 66 Plates, 4to, 2 1 s. cloth. House Building and Repairing. THE HOUSE-OWNER'S' ESTIMATOR; or, What will it Cost to With numerous Illustrations. Fourth Edition, Revised. Crown 8vo, 3s. td. cloth'. " In two years it will repay its cost a hundred times over."— Field. " A very handy book"— English Mechanic. Cottages and Villas. COUNTRY AND SUBURBAN COTTAGES AND VILLAS: How to Plan and Build Them. Containing 33 Plates, with Introduction, General Explanations, and Description of each Plate. By James W. Bogue, Architect, Author of "Domestic Architecture," &c. 4to, 16s. dd. cloth. \Jtist published. ARCHITECTURE, BUILDING, &t. 15 The New Builder's Price Book, 1891. LOCKWOOD'S BUILDER'S PRICE BOOK FOR 1891. A Com- prehensive Handbook of the Latest Prices and Data for Builders, Architects, Engineers and Contractors. Re-constructed, Re-written and Greatly Enlarged. By Francis T. W. Miller. 640 closely-printed pages, crown 8vo, 4*. cloth. [Jtist published. " This book is a very useful one, and should find a place in every English office connected with the building and engineering professions." — Industries. ''This Price Book has been set up in new type Advantage has been taken of the trans- formation to add much additional information, and the volume is now an excellent book of refer- ence. "---^rc/K/ccr. " In its new and revised form this Price Book is what a work of this kind should be — compre- hensive, reliable, well arranged, legible and well bound.'' — British Architect. " A work of established reputation." — A thenceum. "This very useful handbook is well written, exceedingly clear in its explanations and great care has evidently been taken to ensure accuracy." — Morning Advertiser. Designing, Measuring, and Valuing. THE STUDENT'S GUIDE to the PRACTICE of MEASURING ana VALUING ARTIFICERS ' WORKS. Containing Directions for taking Dimen- sions, Abstracting the same, and bringing the Quantities into Bill, with Tables of Constants for Valuation of Labour, and for the Calculation of Areas and Solidities. Originally edited by Edward Dobson, Architect. With Additions on Mensura- tion and Construction, and a New Chapter on Dilapidations, Repairs, and Con- tracts, by E. Wyndham Tarn, M.A. Sixth Edition, including a Complete Form, of a Bill of Quantities. With 8 Plates and 63 Woodcuts. Crown 8vo, 7-r. 6d. cloth. " Well fulfils the promise of its title-page, and we can thoroughly recommend ■ it to the class for whose use it has been compiled. Mr. Tarn's additions and revisions have much increased the useful- ness of the work, and have especially augmented its value to students." — Engineering. m " This edition will be found the most complete treatise on the principles of measuring and valuing.- artificers' work that has yet been published." — Building News. Pocket Estimator and Technical Guide. THE POCKET TECHNICAL GUIDE, MEASURER, AND ESTI- MATOR FOR BUILDERS AND SURVEYORS. Containing Technical' Directions for Measuring Work in all the Building Trades, Complete Specifications- for Houses, Roads, and Drains, and an Easy Method of Estimating the parts of a. Building collectively. By A. C. Beaton, Author of "Quantities and Measure- ments." Fifth Edition. With 53 Woodcuts, waistcoat-pocket size, is. 6d. gilt edges- " No builder, architect, surveyor, or valuer should be without his ' Beaton.' " — Building News. " Contains an extraordinary amount of information in daily requisition in measuring and estimating.. Its presence in the pocket will save valuable time and trouble." — Building World. Donaldson on Specifications. THE HANDBOOK OF SPECIFICA TIONSj or, Practical Guide to the Architect, Engineer, Surveyor, and Builder, in drawing up Specifications and Contracts for Works and Constructions. Illustrated by Precedents of Buildings- actually executed by eminent Architects and Engineers. By Professor T. L. Donaldson, P.R.I. B. A., &c. New Edition, in one large vol., 8vo, with upwards- of 1,000 pages of Text, and 33 Plates, £1 us. 6d. cloth. " In this work forty-four specifications of executed works are given, including the specifications for parts of the new Houses of Parliament, by Sir Charles Barry, and for the new Royal Exchange, by Mr. Tite, M.P. The latter, in particular, is a very complete and remarkable document. It embodies, t a great extent, as Mr. Donaldson mentions, ' the bill of quantities, with the description of the works. ... It is valuable as a record, and more valuable still as a book of precedents. . . . Suffice it to say that Donaldson's * Handbook of Specifications' must be bought by all architects. —Builder. Bartholomew and Rogers' Specifications. SPECIFICATIONS FOR PRACTICAL ARCHITECTURE. A Guide to the Architect, Engineer, Surveyor, and Builder. With an Essay on the Structure and Science of Modern Buildings. Upon the Basis of the Work by Alfred Bartholomew, thoroughly Revised, Corrected, and greatly added to by Frederick Rogers, Architect. Second Edition, Revised, with Additions. With numerous "■■''■ Illustrations, medium 8vo, 1 5-f. cloth. ,,',,.' "The collection of specifications prepared by Mr. Rogers on the basis of Bartholomew s work is too well known to need n any recommendafipn from us. It is one of the books with wh.ch every, young archi- tect mus7be equipped ; for time has shown that the specifications cannot be setas.de through any defect in them."— Architect. 16 CROSBY LOCKWOOD & SON'S CATALOGUE. Building ; Civil and Ecclesiastical. A BOOK ON BUILDING, Civil and Ecclesiastical, including Church Restoration ; with the Theory of Domes and the Great Pyramid, &c. By Sir Edmund Beckett, Bart., LL.D., F.R.A.S., Author of "Clocks and Watches, and Bells," &c. Second Edition, Enlarged. Fcap. 8vo, $s. cloth. " A book which is always amusing and nearly always instructive. The style throughout is in the highest degree condensed and epigrammatic." — Times. Ventilation of Buildings. VENTILA TION. A Text Book to the Practice of the Art of Ventilating Buildings. With a Chapter upon Air Testing. By W. P. Buchan, R.P., Sanitary and Ventilating Engineer, Author of "Plumbing," &c. With 170 Illustrations. l2mo, 4.5. cloth boards. [Just published. The Art of Plumbing. PLUMBING. A Text Book to the Practice of the Art or Craft of the Plumber, with Supplementary Chapters on House Drainage, embodying the latest Improvements. By William Paton Buchan, R.P., Sanitary Engineer and Practical Plumber. Fifth Edition, Enlarged to 370 pages, and 380 Illustrations, 1 2 mo, 4;. cloth boards. "A text book which may be safely put in the hands of every young plumber, and which will also be found useful by architects and medical professors. '' — Builder. " A valuable text book, and the only treatise which can be regarded as a really reliable manual of the plumber's art." — Building News. Geometry for the Architect, Engineer, &c. PRACTICAL GEOMETRY, for the Architect, Engineer, and Mechanic. Giving Rules for the Delineation and Application of various Geometrical Lines, Figures, and Curves. By E. W. Tarn, M.A., Architect, Author of " The Science of Building," &c. Second Edition. With 172 Illustrations, demy 8vo, gs. cloth. *' No book with the same objects in view has ever been published in which the clearness of the rules laid down and the illustrative diagrams have been so satisfactory." — Scotsman. The Science of Geometry. THE GEOMETRY OF COMPASSES '; or, Problems Resolved by the mere Description of Circles, and the use of Coloured Diagrams and' Symbols. Bv Oliver Byrne. Coloured Plates. Crown 8vo, 3^. 6d. cloth. "The treatise is a good one, and remarkable— like all Mr. Byrne's contributions to the science ot geometry — for the lucid character of its teaching." — Building News. DECORATIVE ARTS, etc. ■Woods and Marbles, Imitation of. SGHOOL OF PAINTING FOR THE IMITATION OF WOODS AND MARBLES, as taught and practised by A. R. Van der Burg and P. Van der Burg, Directors of the Rotterdam Painting Institution. Royal folio, *8£ by I2j in., Illustrated with 24 full-size Coloured Plates; also 12 plain Plates, comprising 154 Figures. Second and cheaper Edition. Price j£i lis. td. List of Plates. a. Various Tools required for Wood Painting — 2, 3- Walnut ; Preliminary Stages of Graining and Finished Specimen — 4. Tools used for Marble Fainting and Method of Manipulation— 5, 6. St. liemi Marble; Earlier Operations and Finished Specimen — 7. Methods of Sketching [different Grains, Knots, &c— 8, 9. Ash: Preliminary Stages and Finished Specimen— 10. Methods of Sketching Marble Grains— 11,12. Breche Marble ; Prelimin- ary Stages of Working and Finished Specimen— 13. Maple; Methods of Producing the different Grains — 14, 15. Bird's-eye Maple; Preliminary Stages and Finished Specimen— 16. Methods of Sketching the different species of White Marble 17, 18. White Marble; Preliminary Stages of Pro- cess and Finished Specimen — 19. Mahogany ; Specimens_ of various Grains and Methods of Manipulation — 20, 2r. Mahogany ; Earlier Stages andFinished Specimen — 22, 23, 24. Sienna Marble ; Varieties of Grain, Preliminary Stages and Finished Specimen — 25, 26, 27. Juniper Wood ; Methods of producing Grain, &c— Preliminary Stages and Finished Specimen — 28, 29, 30. Vert de Met Marble ; Varieties of Grain and Methods of Work- ing, Unfinished and Finished Specimens — 31, 32, 33. Oak ; Varieties of Grain, Tools employed and Methods of Manipulation, Preliminary Stages and Finished Specimen— 34, 35, 36. Waulsort Marble ; Varieties of Grain, Unfinished and Finished Specimens. 'Those who desire to attain skill in the art of painting woods and marbles will find advantaee in consulting this book. . Some of the Working Men's Clubs should give their young men the opportunity to study it."— Builder. s " A comprehensive guide to the art. The explanations of the processes, the manipulation and manase- ment of the colours, and the beautifully executed plates will not be the least valuable to the student who aims at making his work a faithful transcript of nature."— Building News. DECORATIVE ARTS, &>c, i; House Decoration. ELEMENTARY DECORATION: A Guide to the Simpler Forms ot Everyday Art, as applied to the Interior and Exterior Decoration of Dwelling Houses, &c. By James W. Facey, Jun. With 68 Cuts. l2mo, zs. cloth limp. PRACTICAL HOUSE DECORATION : A Guide to the Art of Orna- mental Fainting, the Arrangement of Colours in Apartments, and the principles of Decorative Design. With some Remarks upon the Nature and Properties of Pig- ments. By James William Facey, Author of "Elementary Decoration," &c. With numerous Illustrations. l2mo, 2s. 6d. cloth limp. N.B. — The above Two Works together in One Vol., strongly half-bound, frice $s. Colour. A GRAMMAR OF COLOURING. Applied to Decorative Painting and the Arts. By George Field. New Edition, Revised, Enlarged, and adapted to the use of the Ornamental Painter and Designer, by Ellis A. Davidson. With New Coloured Diagrams and Engravings. i2mo, 3s. 6d. cloth boards. " The book is a most useful mum/ of the properties of pigments." — Builder. House-Painting, Graining, etc. HOUSE-PAINTING, GRAINING, MARBLING&* SIGN WRITING, A Practical Manual of. By Ellis A. Davidson. Fifth Edition. With Coloured Plates and Wood Engravings. i2mo, 6s. cloth boards. " A mass of information, of use to the amateur and of value to the practical man."— English Mechanic. " Simply invaluable to the youngster entering upon this particular calling, and highly serviceable to Ihe mm who is practising it."— Furniture Gazette. Decorators, Receipts for. THE DECORATOR'S ASSISTANT: A Modern Guide to Decora- tive Artists and Amateurs, Painters, Writers, Gilders, &c. Containing upwards of 600 Receipts, Rules and Instructions ; with a variety of Information for General Work connected with every Class of Interior and Exterior Decorations, &c, Fourth Edition, Revised. 152 pp., crown 8vo, is. in wrapper. " Full of receipts of value to decorators, painters, gilders, &c. The book contains the gist of larger treatises on colourand technical processes. It would be difficult to meet with a work so full of varied information on the painter's art." — Building News. . „ We recommend the work to all who, whether for pleasure or profit, require aguide to decoration. —Plumber and Decorator. * Moyr Smith on Interior Decoration. ORNAMENTAL INTERIORS, ANCIENT AND MODERN By J. Moyr Smith. Super-royal 8vo, with Thirty-Two Full-Page Plates and numerous smaller Illustrations, handsomely bound in cloth, gilt top, price iSs. "The book is well illustrated and handsomely got up, and contains some true criticism and a good many good examples of decorative treatment."— The Builder. «:„,„!„,. .v-i. ™ J,*™ "This is the most elaborate and beautiful work on the artistic decoration of »»«*>« «£* "* h ave seen. . . . The scrolls, panels, and other designs from the author's own pen are very^eauuful and chaste ; but he takes care that the designs of other men shall figure even more than his own. -Liver- toolAWwn^ ^ ^ ^ k tetest . n elaborate domestic ornament this handsome volume will be •welcome."— Graphic. British and Foreign Marbles. MARBLE DECORATION and the Terminology of British and Foreign- Marbles. A Handbook for Students. By George H. Blagrove . Airthw : of "Shoring and its Application," &c With 28 Illustrations. Cr 8vo, y. W-ctoUi. "This most useful and much wanted handbook should be in the hands of every architect and ^""u'lrfnlSeKfnual for students, and interesting to artistic readers generally."-**^ £C " " A carefully and usefully written treatise ; the work is essentially practical."-S«*i»»». Marble Working, etc. , J . ... . MARBLE AND MARBLE WORKERS: A Handbook .lot "Architects, Artists, Masons and Students. By Arthur Lee, Author of A Visit to Carrara, " The Working of Marble," &c. Small crown 8vo, is. cloth. n SON'S CATALOGUE. DELAMOTTE'S WORKS ON ILLUMINATION AND ALPHABETS. A PRIMER OF THE ART OF ILLUMINATION, for the Use of Beginners: with a Rudimentary Treatise on the Art, Practical Directions for its exercise, andExamples taken from Illuminated MSS., printed in Gold and Colours. By F. Delamotte. New and Cheaper Edition. Small 4to, 6s. ornamental boards. " The examples of ancient MSS. recommended to the student, which, with much good sense, the author chooses from collections accessible to all, are selected with judgment and knowledge, as well as taste." — Athenaum. ORNAMENTAL ALPHABETS, Ancient and Medieval, from the Eighth Century, with Numerals ; including Gothic, Church-Text, large and small, Germau, Italian, Arabesque, Initials for Illumination, Monograms, Crosses, &c. &c, for the use of Architectural and Engineering Draughtsmen, Missal Painters, Masons, Decorative Painters, Lithographers, Engravers, Carvers, &c. &c. Collected and Engraved by F. Delamotte, and printed in Colours. New and Cheaper Edition. Royal 8vo, oblong, 2s. 6d. ornamental boards. ■ ' For those who insert enamelled sentences round gilded chalices, who hlazoh shop legends over shop- doors, who letter church walls with pithy sentences from the Decalogue, this book will be useful." — Atlienceum. EXAMPLES OF MODERN ALPHABETS, Plain and Ornamental, including German, Old English, Saxon, Italic, Perspective, Greek, Hebrew, Court Hand, Engrossing, Tuscan, Riband, Gothic, Rustic, and Arabesque ; with several Original Designs, and an Analysis of the Roman and Old English Alphabets, large and small, and Numerals, for the use of Draughtsmen, Surveyors, Masons, Decora- tive Painters, Lithographers, Engravers, Carvers, &c. Collected and Engraved by F. Delamotte, and printed in Colours. New and Cheaper Edition. Royal 8vo, oblong, 2s. 6ii. ornamental boards. " There is comprised in it every possibleshape into which the letters of the alphabet and numerals can be formed, and the talent which has been expended in the conception of the various plain and ornamental letters is wonderful." — Standard. MEDIAEVAL ALPHABETS AND INITIALS FOR ILLUMI- NATORS. By F. G. Delamotte. Containing 21 Plates and Illuminated Title, printed in Gold and Colours. With an Introduction by J. Willis Brooks. Fourth and Cheaper Edition. Small 4*0, 41. ornamental boards. "A volume in which the letters of the alphabet, come forth glorified in gilding and all the colours of the prism interwoven and intertwined and intermingled." — Sun. THE EMBROIDERER'S BOOK OF DESIGN. Containing Initials, Emblems, Cyphers, Monograms, Ornamental Borders, Ecclesiastical Devices, Mediaeval and Modern Alphabets, and National Emblems. Collected by F. Dela- motte, and printed in Colours. Oblong royal 8vo, is. 6et. ornamental wrapper. " The book will be of great assistance to ladies and young children who are endowed with the art of plying the needle in this most ornamental and useful pretty work." — East Anglian Times. Wood Caruing. INSTRUCTIONS IN WOOD-CARVING, for Amateurs j with Hints on Design. By A Lady. With Ten Plates. New and Cheaper' Edition. Crown 8vO, 2j. in emblematic wrapper. "The handicraft of the wood-carver, so well as a book can impart it, maybe learnt from 'A Lady's' publication." — Athenaum. 3 " The directions given are plain and easily understood."— English Mechanic. Glass Painting. GLASS STAINING AND THE ART OF PAINTING ON GLASS. From the German of Dr. Gessert and Emanuel Otto Fromberg. With an Appendix on The Art op Enamelling. i2mo, 2s. 6d. cloth limp. Letter Painting. THE ART OF LETTER PAINTING MADE EASY. By Tames Greig Badenoch. With 12 full-page Engravings of Examples, is.6d. cloth limp. "The system is a simple one, but quite original, and well worth the careful attention of letter painters. It can be easily mastered and remembered." — Building News. CARPENTRY, TIMBER, &c. j 9 CARPENTRY, TIMBER, etc. Tredgotd's Carpentry, Revised and Enlarged by Tarn. THE ELEMENTARY PRINCIPLES OF CARPENTRY : A Treatise on the Pressure and Equilibrium of Timber Framing, the Resistance of Timber, and the Construction of Floors, Arches, Bridges, Roofs, Uniting Iron and Stone with Timber, &c. To which is added an Essay on the Nature and Properties of Timber, &c:, with Descriptions of the kinds of Wood used in Building ; also numerous Tables of the Scantlings of Timber for different purposes, the, Specific Gravities of Materials, &c. By THOMAS Tredgold, C.E. With an Appendix of Specimens of Various Roofs of Iron and Stone, Illustrated. Seventh Edition, thoroughly Revised and considerably Enlarged by E. Wyndham Tarn, M.A., Author of " The Science of Building," &c. With 61 Plates, Portrait of the Author, and several Woodcuts. In One large Vol., 4to, price 25^. cloth. "Ought to be in every architect's and every builder's library."— Builder. _, A work whose monumental excellence mast commend it wherever skilful carpentry is concerned. lot author s pmiciples are rather confirmed than impaired by time. The additional plates are of great intrinsic value."— Building News. Woodworking Machinery. WOOD WORKING MA CHINE R Y: lis Rise, Progress and Construction. With Hints on the Management of Saw Mills and the Economical Conversion of Timber. Illustrated with Examples of Recent Designs by leading English, French, and American Engineers. ByM. Powis Bale, A.M. Inst. C.E., M.I.M.E. Large crown 8vo, I2j. 6d. cloth. , .'."'■. " ale is evidently an expert on the subject, and he has collected so much information that his ' „IJ "-sufficient for builders and others engaged in the conversion of timber." — Architect. ,, T J e most comprehensive compendium of wood-working machinery we have seen. The author is a . IHorpiiEh master of his subject."— Building News. ■ . ihe appearance of this book at the present time will, we should think, give a considerable impe- tus to the onward march of the machinist engaged in the designing and manufacture of wood-working machines. It should be in the office of every wood-working factory.'' — English Mechanic. Saw Mills. SAW MILLS: Their Arrangement and Management, and the Economical Conversion of Timber. (A Companion Volume to "Woodworking Machinery.") , By M. Powis Bale. With numerous Illustrations. Crown 8vo, ior. 6d. cloth. ' "The administration of a large sawing establishment is discussed, and the subject examined from a financial standpoint Hence the size, shape, order, and disposition of saw-mills and the like are gone into in detail, and the course of the timber is traced from its reception to its delivery in its converted state. ■ f?m not desire a more complete or practical treatise."— Builder. .' 'We highly recommend Mr. Bale's work to the attention and perusal of all those who are engaged in d v? of wood conversion, or who are about building or remodelling saw-mills on improved principles. — wilding News. Carpentering. THE CARPENTER'S NEW GUIDE,- or, Book of Lines for Carpen- ters ; comprising all the Elementary Principles essential for acquiring a knowledge of Carpentry. Founded on the late Peter Nicholson's standard work. A New Edition, Revised by Arthur Ashfitel, F.S.A. Together with Practical Rules on Drawing, by George Pyne. With 74 Plates, 4to, £1 is. cloth. Handrailing and Stairbuilding. A PRACTICAL TREATISE ON HANDRAILING : Showing New and Simple Methods for Finding the Pitch of the Plank, Drawing the Moulds, Bevelling, Jointing-up, and Squaring" the Wreath. By George Coixings. Second Edition, Revised and Enllrged, to which is added A Treatise on Stair- building. With Plates and Diagrams. l2mo, is. 6d. cloth limp. \Just pubtistiea. " Will be found of practical utility in the execution of this difficult branch of joinery.' '-fg^fer. "Almost every difficult phase oi this somewhat intricate branch of joinery is elucidated by the aia of plates and explanatory letterpress." — Furniture Gazette* Circular Work CIRCULAR WORK IN CARPENTRY AND JOINERY: A Practical Treatise on Circular Work of Single and Double Curvature. By George Collings, Author of "A Practical Treatise on Handrailing. Illustrated with numerous Diagrams. Second Edition, izmo, is. 6d. cloth limp. , - . "An excellent example of what a book of this kind should be. Cheap In price, clear in definition and practical in the examples selected."— Builder. 20 CROSBY L0CKW00D &• SON'S CATALOGUE. Timber Merchant's Companion. THE TIMBER MERCHANT'S AND BUILDER'S COMPANION. Containing New and Copious Tables of the Reduced Weight and Measurement of Deals and Battens, of all sizes, from One to a Thousand Pieces, and the relative Price that each size bears per Lineal Foot to any given Price per Petersburgh Stan- dard Hundred ; the Price per Cube Foot of Square Timber to any given Price per Load of 50 Feet ; the proportionate Value of Deals and Battens by the Standard, to Square Timber by the Load of 50 Feet ; the readiest mode of ascertaining the Price of Scantling per Lineal Foot of any size, to any given Figure per Cube Foot, &c. &c. By William Dowsing. Fourth Edition, Revised and Corrected. Cr. 8vo, y. cloth. " Everything is as concise and clear as it can possibly be made. There can be no doubt that every timber merchant and builder ought to possess it. 1 '— Hull Advertiser. "We are glad to see a fourth edition of these admirable tables, which for correctness and simplicity of arrangement leave nothing to be desired." — Timber Trades' Journal. *' An exceedingly well-arranged, clear, and concise manual of tables for the use of all who buy or sell timber." — Journal of Forestry. Practical Timber Merchant. THE PRACTICAL TIMBER MERCHANT: Being a Guide for the use of Building Contractors, Surveyors, Builders, &c, comprising useful Tables for all purposes connected with the Timber Trade, Marks of Wood, Essay on the Strength of Timber, Remarks on the Growth of Timber, &c. By W. Richardson. Fcap. 8vo, y. 6d. cloth. ' * This handy manual contains much valuable information for the use of timber merchants, builders, foresters, and all others connected with the growth, sale, and manufacture of timber." — Journal of "Forestry. Timber Freight Book. THE TIMBER MERCHANT'S, SAW MILLER'S, AND IM- PORTER'S FREIGHT BOOK AND ASSISTANT. Comprising Rules, Tables, and Memoranda relating to the Timber Trade. By William Richardson, Timber Broker ; together with a Chapter on Speeds of Saw Mill Machinery, by M. Powis Bale, M.I.M.E., &c. i2mo, y. 6d. cloth boards. " A very useful manual of rules, tables, and memoranda, relating to the timber trade. We recom- mend it as a compendium of calculation to all timber measurers and merchants, and as supplying a real want in the trade." — Buildittg News. Packing-Case Makers, Tables for. PACKING-CASE TABLES j showing the number of Superficial Feet in Boxes or Packing-Cases, from six inches square and upwards. By W. Richard- son, Timber Broker. Second Edition. Oblong 4to, 3-f. 6d. cloth. " Invaluable labour-saving tables." — Ironmonger. " Will save much labour and calculation." — Grocer. Superficial Measurement. THE TRADESMAN'S GUIDE TO SUPERFICIAL MEASURE- MENT. Tables calculated from I to 200 inches in length, by I to 108 inches in breadth. For the use of Architects, Surveyors, Engineers, Timber Merchants, Builders, &c. By James Hawkings. Third Edition. Fcap., 3*. 6d. cloth. "Auseful collection of tables to facilitate rapid calculation of surfaces. The exact area of any surface of which the limits have been ascertained can be instantly determined. The book will be found of the greatest utility to all engaged in building operations." — Scotsman. " These tables will be found of great assistance to all who require to make calculations in superficial measurement." — English Mechanic. Forestry. THE ELEMENTS OF FORESTRY. Designed to afford Information concerning the Planting and Care of Forest Trees for Ornament or Profit, with suggestions upon the Creation and Care of Woodlands. By F. B. Hough. Large crown 8vo, ioj. cloth. Timber Importer's Guide. THE TIMBER IMPORTER'S, TIMBER MERCHANT'S, AND BUILDER'S STANDARD GUIDE. By Richard E. Grandy. Compris- ing : — An Analysis of Deal Standards, Home and Foreign, with Comparative Values and Tabular Arrangements for fixing Nett Landed Cost on Baltic and North American Deals, including all intermediate Expenses, Freight, Insurance, &c. &c. ; together with copious Information for the Retailer and Builder. Third Edition, Revised. i2mo, 2s. cloth limp. " Everything it pretends to be : built up gradually, it leads one from a forest to a treenail, and throws in, ?.s a makeweight, a host of material concerning bricks, columns, cisterns. &c." — English Mechanic. MARINE ENGINEERING, NA VIGA TION, &>c. 21 MARINE ENGINEERING, NAVIGATION, etc. Chain Cables. CHAIN CABLES AND CHAINS. Comprising Sizes and Curves of Links, Studs, &c, Iron for Cables and Chains, Chain Cable and Chain Making, Forming and Welding Links, Strength of Cables and Chains, Certificates for Cables, Marking Cables, Prices of Chain Cables and Chains, Historical Notes, Acts of Parliament, Statutory Tests, Charges for Testing, List of Manufacturers of Cables, &c, &c. By Thomas W.Traill, F.E.R.N., M.Inst.C.E., Engineer- Surveyor-in-Chief, Board of Trade, Inspector of Chain Cable and Anchor Proving Establishments, and General Superintendent, Lloyd's Committee on Proving Establishments. With numerous Tables, Illustrations, and Lithographic Drawings. Folio, £2 2s. cloth, bevelled boards. " It contains a vast amount of valuable information. Nothing seems to be wanting to make it a com- plete and standard work of reference on the subject. " — Nautical Magazine. Marine Engineering. MARINE ENGINES AND STEAM VESSELS (A Treatise on). By Robert Murray, C.E. Eighth Edition, thoroughly Revised, with considerable Additions by the Author and by George Carlisle, C.E., Senior Surveyor to the Board of Trade at Liverpool. i2mo, 5-r. cloth boards. "Well adapted to give the young steamship engineer or marine engine and boiler maker a general introduction into his practical work. — Mechanical World. "We feel sure that this thoroughly revised edition will continue to be as popular in the future as it has been in the past, as, for its size, it contains more useful information than auy similar . treatise. 1 '— Industries. " As a compendious and useful guide to engineers of our mercantile and royal naval services, we should say it cannot be surpassed." — Building News. "The information given is both sound and sensible, and well qualified to direct young sea-going hands on the straight road to the extra chief 's certificate. . . . Most useful to surveyors, inspectors, draughtsmen, and all young engineers who take an interest in their profession." — Glasgow Herald. " An indispensable manual for the student of marine engineering."— Liverpool Mercury. Pochet-Book for Naual Architects and Shipbuilders. THE NA VAL ARCHITECT'S AND SHIPBUILDER'S POCKET- BOOK of Formula, Rules, and Tables, and MARINE ENGINEER 'S AND SURVEYOR'S Handy Book of Reference. By Clement Mackrow, Member of the Institution of Naval Architects, Naval Draughtsman. Fourth Edition, Revised. With numerous Diagrams, &c. Fcap., \2s.6d., strongly bound in leather. "Should be used by all who are engaged in the construction or design of vessels. . . . Will be found to contain the most useful tables and formula? required by shipbuilders, carefully collected from the best authorities, and put together in a popular and simple form." — Engineer. "The professional shipbuilder has now, in a convenient and accessible form, reliable data for solving many of the numerous problems that present themselves in the course of his work." — Iren. "There is scarcely a subject on which a naval architect or shipbuilder can require to refresh his memory which will not be found within the covers of Mr. Mackrow's book. "—English Mechanic. Pochet-Booh for Marine Engineers. A POCKET-BOOK OF USEFUL TABLES AND FORMULA FOR MARINE ENGINEERS. By Frank Proctor, A.I.N. A. Third Edition. Royal 32mo, leather, gilt edges, with strap, 4s. "We recommend it to our readers as going far to supply a long-felt want."— Naval Science. " A most useful companion to all marine engineers." — United Service Gazette. Introduction to Marine Engineering. ELEMENTARY ENGINEERING: A Manual for Young Marine Engineers and Apprentices. In the Form of Questions and Answers on Metals, Alloys, Strength of Materials, Construction and Management of Marine Engines and Boilers, Geometry, &c. &c. With an Appendix of Useful Tables. By John Sherren Brewer, Government Marine Surveyor, Hongkong. Small crown 8vo, 2s. cloth. "Contains much valuable information for the class for whom it is intended, especially in the chapters on the management of boilers and engines."— Nautical Magazine. " A useful introduction to the more elaborate text books. '—Scotsman. t „„„i.j„ M , "To a student who has the requisite desire and resolve to attain a thorough knowledge, Mr. Brewer offers decidedly useful help." — Athenaum. Navigation. PRACTICAL NAVIGATION. Consisting of The Sailor's Sea-Book, by Tames Greenwood and W. H. Rosser; together with the requisite Mathe- matical and Nautical Tables for the Working of the Problems, by Henry Law, C E. and Professor J. R. Young. Illustrated. l2mo, Is. strongly half-bouud. CROSBY LOCKWOOD &• SON'S CATALOGUE. MINING AND METALLURGY. Metalliferous Mining in the United Kingdom. BRITISH MINING : A Treatise on the History, Discovery, Practical Development, and Future Prospects of Metalliferous Mines in the United Kingdom. By Robert Hunt, F.R.S., Keeper of Mining Records; Editor of "Ure's Dic- tionary of Arts, Manufactures, and Mines," &c. Upwards of 950 pp., with 230 Illustrations. Second Edition, Revised. Super-royal 8vo, £2 2s. cloth. "One of the most valuable Works of reference of modern times. Mr. Hunt, as Keeper of Mining Records of the United Kingdom, has had opportunities for such a task not enjoyed by anyone else, and has evidently made the most of them. . . . The language and style adopted are good, and the treat- ment of the various subjects laborious, conscientious, and scientific." — Engineering;. " The book is, in fact, a treasure-house of statistical information on mining subjects, and we know of no other work embodying so great a mass of matter of this kind. Were this the only merit of Mr. Hunt's volume it would be sufficient to render it indispensable in the library of everyone interested in the development of the 'mining and metallurgical industries of this country." — Atkenmum. " A mass of information not elsewhere available, and of the greatest value to those who may be in- terested in our great mineral industries.-' — Engineer. " A sound, business-like collection of interesting facts The amount of information Mr. Hunt has brought together is enormous. . . . The volume appears likely to convey more instruction upon the subject than any work hitherto published." — Mining Journal. Colliery Management. THE COLLIERY MANAGER'S HANDBOOK; A Comprehensive Treatise on the Laying-out and Working of Collieries, Designed as a Book of Reference for Colliery Managers, and for the Use of Coal-Mining Students pre- paring for First-class Certificates. By Caleb Pamkly, Mining Engineer and ■Surveyor ; Member of the North of England Institute of Mining and Mechanical Engineers ; and Member of the South Wales Institute of Mining Engineers. With nearly 500 Plans, Diagrams, and other Illustrations. Medium 8vo, about 600 pages. Price £1 $s. strongly bound. [Just ready. ' exceedingly creditable manner, and has produced a book Sl-iW. SerV ' Ce Studen ' s ' and those who are Poetically engaged in mining operations° ? - in^Z a ^T^^Zturl taT ° nheMmaS(ValaS '° m!n!nS enSi0=erS ' 3nd ° f c «« d «"bl e MINING AND METALLURGY. 23 Explosives. A HANDBOOK ON MODERN EXPLOSIVES. Being a Practical Treatise on the Manufacture and Application of Dynamite, Gun-Cotton, Nitro- Glycerine and other Explosive Compounds. Including the Manufacture of Collodion-Cotton. By M. Eissler, Mining Engineer and Metallurgical Chemist, Author of "The Metallurgy of Gold," ''The Metallurgy of Silver," &c. With about 100 Illustrations. Crown 8 vo, 10s. 6d. cloth. [Just published. " Useful not only to the miner, but also to officers of both services to whom blasting and the use of explosives generally may at any time become a necessary auxiliary." — Nature. "A veritable mine of information on the subject of explosives employed for military, mining and blastingpurposes," — Army and Navy Gazette. "The book is clearly written. Taken as a whole we consider it an excellent little book and one that should be found of great service to miners and others who are engaged in work requiring the use of explosives."— Athenaum. Gold, Metallurgy of. THE METALLURGY OF GOLD ; A Practical Treatise on the Metallurgical Treatment of Gold-bearing Ores. Including the'Processes of Concen- tration and Chlorination, and the Assaying, Melting and Refining of Gold. By M. Eissler, Mining Engineer and Metallurgical Chemist, formerly Assistant Assayer of the U.S. Mint, San Francisco. Third Edition, Revised and greatly Enlarged. With 187 Illustrations. Crown 8vo, 12s. (id. cloth. [Just published. "This book thoroughly deserves its title of a 'Practical Treatise.' The whole process of gold milling, from the breaking of the quartz to the assay of the bullion, is described in clear and oraeny narrative and with much, but not too much, fulness of detail."— Saturday Review.. "The work is a storehouse of information and valuable data, and we strongly recommena it 10 all professional men engaged in the gold-mining industry."— Mining Journal. Silver, Metallurgy of. THE METALLURGY OF SILVER: A Practical Treatise on the Amalgamation, Roasting, and Lixiviation of Silver Ores. Including the Assaying, Melting and Refining of Silver Bullion. By M. Eissler, Author of ' The Metal- lurgy of Gold." With 124 Illustrations. Crown 8vo, 10s. 6d. cloth. . "A practical treatise, and a technical work which we are convinced will supply a long felt wint amongst practical men, and at the same time be of value to students and others indirectly connected with the industries."— Mining Journal. „. _ ,. .■"•■; " From first to last the book is thoroughly sound and reliable."— Colhery Guardian. "For chemists, practical miners, assayers and investors alike, we do not know of any worK on the subject so handy and yet so comprehensive." — Glasgow Herald. Silver-Lead, Metallurgy of. THE METALLURGY OF ARGENTIFEROUS LEAD ORES: A Practical Treatise on the Smelting of Silver-Lead Ores and the Refining of Lead Bullion. Illustrated with Plans and Sections of Smelting^Furnaces and riant in Europe and America. By M. Eissler, Author of " The Metallurgy of Gold, " The Metallurgy of Silver," &c. Crown 8vo. [In the press. Metalliferous Minerals and Mining. „.,„ TREATISE ON METALLIFEROUS MINERALS AND MININU. By D. C. Davies, F.G.S., Mining Engineer, &c, Author of " A Treatise on Slate and Slate Quarrying." Illustrated with numerous Wood Engravings. Fourth Edition, carefully Revised. Crown 8vo, 12s. 6d. cloth. "Neither the practical miner nor the general reader, interested in mines, can have a better book for his companion and his guide." — Mining Journal. , . . ,.,„„», »• Mini-n? World. " We are doing our "readers aservictin calling their attention to t h '" a ! u ^ le J^. -^^f^ " A hook that will not only be useful to the geologist, the practical miner, and the metallurgist , out aIS °" 2i!S^"t^^.£^Su m ^^ the world this book has a real value, and it supplies an actual want." — AthentBUm. Earthy Minerals and Mining. , rT .,^. D ,, T c Ann A TREATISE ON EARTHY AND OTHER MINERALS, AND • ^/Sf Bfic^AVlE^ls. Uniform with ', ^^P^^g Volume to, the same Author's << Metalliferous Minerals and Mining. Witti 7& Wood Engravings. Second Edition. Crown 8vo, \2s. 6d. clotn. " We do not remember to have met with any English work on mining matters that contains the same manuals which have recently appeared."-.^"* Quarterly Review. 24 CROSBY LOCKWOOD <5- SON'S CATALOGUE. Mineral Surveying and Valuing. THE MINERAL SURVEYOR AND VALUER'S COMPLETE GUIDE, comprising a Treatise on Improved Mining Surveying and the Valuation of Mining Properties, with New Traverse Tables. By Wm. Lintern, Mining and Civil Engineer. Third Edition, with an Appendix on "Magnetic and Angular Surveying," with Records of the Peculiarities of Needle Disturbances. With Four Plates of Diagrams, Plans, &c. i2mo, 4-r. cloth. [Just published. " Mr. Lintern's book forms a valuable and thoroughly trustworthy guide." — Iron and Coal Trades* Review. " This new edition must be of the highest value to colliery surveyors, proprietors and managers."' Colliery Guardian. Asbestos and its Uses. ASBESTOS : Its Properties, Occurrence and Lses. With some Account of the Mines of Italy and Canada. By Robert H. Jones. With Eight Collotype Plates and other Illustrations. Crown 8vo, 12s. 6d. cloth. \Jusl published. " An interesting an invaluable work." — Colliery Guardian. " We counsel our readers to get this exceedingly interesting work for themselves ; they will find in it much that is suggestive, and a great deal that is of immediate and practical usefulness." — Builder. "A valuable addition to the architect's and engineer's library." — Building News. Underground Pumping Machinery. MINE DRAIN A GE : Being a Complete and Practical Treatise on Direct- Acting Underground Steam Pumping Machinery, with a Description of a large number of the best known Engines, their General Utility and the Special Sphere of . their Action, the Mode of their Application, and their merits compared with other forms of Pumping Machinery. By Stephen Michell. 8vo, 15J. cloth. " Will be highly esteemed by colliery owners and lessees, mining engineers, and students generally who require to be acquainted with the best means of securing the drainage of mines. It is a most valu- able work, and stands almost alone in the literature of steam pumping machinery." — Colliery Guardian. " Much valuable information is given, so that the book is thoroughly worthy of an extensive circu- lation amongst practical men and purchasers of machinery." — Mining Journal. Mining Tools. A MANUAL OF MINING TOOLS. For the Use of Mine Managers, Agents, Students, &c. By William Morgans, Lecturer on Practical Mining at the Bristol School of Mines. i2mo, 2s. 6d. cloth limp. ATLAS OF ENGRAVINGS to Illustrate the above, containing 235 Illustrations of Mining Tools, drawn to scale. 4to, 4*. 6d. cloth. " Students in the science of mining, and overmen, captains, managers, and viewers may gain practical knowledge and useful hints by the study of Mr. Morgans' manual." — Colliery Guardian. *' A valuable work, whichwill tend materially to improve our mining literature." — Mining Journal. Coal Mining. COAL AND COAL MINING: A Rudimentary Treatise on. By the late Sir Warington W. Smyth, M.A., F.R.S., &c, Chief Inspector of the Mines of the Crown. Seventh Edition, Revised and Enlarged. With numerous Illus- trations, l2mo, 4s. cloth boards. [Just published. " As an outline is given of every known coal-field in this and other countries, as well as of the principal methods of working, the book will doubtless interest a very large number of readers." — Mining Journal. Subterraneous Surueying. SUBTERRANEOUS SURVEYING, Elementary and Practical Treatise on; with and without the Magnetic Needle. By Thomas Fenwick, Surveyor of Mines, and Thomas Baker, C.E. Illustrated. i2mo, 3*. cloth boards. Granite Quarrying. GRANITES AND OUR GRANITE INDUSTRIES. By George F. Harris, F.G.S., Membre de la Societe Beige de Geologie, Lecturer on Economic Geology at the Birkbeck Institution, &c. With Illustrations. Crown 8vo, 2s. 6d. cloth. " A clearly and well-written manual for persons engaged or interested in the granite industry. ' — Scotsman. " An interesting work, which will be deservedly esteemed.'' — Colliery Guardian. " An exceedingly interesting and valuable monograph on a subject which has hitherto received unaccountably little attention in the shape of systematic literary treatment." — Scottish Leader. ELECTRICITY, ELECTRICAL ENGINEERING, &c. 25 ELECTRICITY, ELECTRICAL ENGINEERING, ETC. Electrical Engineering. THE ELECTRICAL ENGINEERS POCKET-BOOK OF MODERN- RULES, EORMULAl, TABLES AND DATA, By H. R. Kempe, M. Inst. K.E., A.M. Inst. C.E., Technical Officer Postal Telegraphs, Author of " A Hand- book of Electrical Testing," &c. With numerous Illustrations, royal 32mo, oblong, 5*. leather. [Just published. " There is very little in the shape of formulae or data which the electrician is likely to want in a hurry which cannot be found in its pages."— Practical Engineer. "A very useful book of reference for daily use in practical electrical engineering and its various applications to the industries of the present day."— Iron. " It is the best book of its kind."— Electrical Engineer. " Well arranged and compact. The Electrical Engineer's Pocket-Book is a good one."— Elec- trician. " "Strongly recommended to those engaged in the various electrical industries."— Electrical Review. Electric Lighting. ELECTRIC LIGHT FITTING: A Handbook for Working Electrical Engineers, embodying Practical Notes on Installation Management. By John W. Urquhart, Electrician, Author of " Electric Light, " &c. With numerous Illustrations, crown 8vo, 5*. cloth. [Just published. jj" Thi i ToIume deals witn "hat may be termed the mechanics of electric lighting, and is addressed to men who are already engaged in the work, or are training for it. The work traverses ?- 5r i_ e .,.!?' ground, and may be read as a sequel to the same author's useful work on ' Electric Light.'"— Electrician. . . ""^}? ' s f attempt to state in the simplest language the precautions which should be adopted in installing the electric light, and to give information for the guidance of those who have to run the plant when installed. The book is well worth the perusal of the workman, for whom it is written." — i.lectnca.1 Review. " We have read this book with a good deal of pleasure. We believe that the book will be of use to practical workmen, who will not be alarmed by finding mathematical formulas which they are ""able to understand."— Electrical Plant. Eminently practical and useful Ought to be in the hands of everyone in charge of an. .?i? hght P' 1 " 1 '-"— Electrical Engineer. Altogether Mr. Urquhart has succeeded in producing a really capital book, which we have no hesitation in recommending to the notice of working electricians and electrical engineers."— Electric Light ELECTRIC LIGHT: Its Production andUse. Embodying Plain Directions for the Treatment of Dynamo-Electric Machines, Batteries, Accumulators, and Electiic Lamps. By J. W. Urquhart, C.E., Author of "Electric Light Fitting," " Electroplating," &c. Fourth Edition, carefully Revised, with Large Additions and 145 Illustrations. Crown 8vo, 7s. 6d. cloth. [Just published. "The book is by far the best that we have yet met with on the subject."— Athenamn. ' It is the only work at present available, which gives in language intelligible for the most part to the ordinary reader, a general but concise history of the means which have been adopted up to the present time in producing the electric light." — Metropolitan. m . " The book contains a general account of the means adopted in producing the electric light, not only as obtained from Voltaic or galvanic batteries, but treats at length of the dynamo-electric machine in several of its forms."— Colliery Guardian. Construction of Dynamos. DYNAMO CONSTRUCTION: A Practical Handbook for the Use of Engineer Constructors and Electricians in Charge. With Examples of leading English, American and Continental Dynamos and Motors. By J. W. Urquhart, Author of "Electric Light," " Electric Light Fitting," &c. Crown 8vo. [Inthepress. Text-Booh of Electricity. THE STUDENT'S TEXTBOOK OF ELECTRICITY. By Henry M. Noad, Ph.D., F.R.S., F.C.S. New Edition, carefully Revised. With an Introduction and Additional Chapters, by W. H. Preece, M.I.C.E., Vice-President of the Society of Telegraph Engineers, &c. With 470 Illustrations. Crown 8vo, 12s. 6d. cloth. " The original plan of this book has been carefully adhered to so as to make it a reflex of the existing state of electrical science, adapted for students. . . . Discovery seems to have progressed with marvellous strides ; nevertheless it has now apparently ceased, and practical applications have commenced their Career; and it is to give a faithful account of these that this fresh edition of Dr. Noad s valuable text- book is launched forth."— Extract from Introduction by W. H. Preece, Esq. "We can recommend Dr. Noad's book for clear style, great range of subject, a good index, and a plethora of woodcuts. Such collections as the present are indispensable. —A thenaum. " An admirable text-book for every student— beginner or advanced— of electricity. —Engineering. 26 CROSBY LOCKWOOD &> SON'S CATALOGUE. Electrie Lighting. THE ELEMENTARY PRINCIPLES OF ELECTRIC-LIGHTING. By Alan A. Campbell Swinton, Associate I.E.E. Second Edition, Enlarged and Revised. With Sixteen Illustrations. Crown 8vo, is. 6d. cloth. "Anyone who desires a short and thoroughly clear exposition of the elementary principles of electric-lighting cannot do better than read this little work."— Bradford Observer. Electricity. A MANUAL OF ELECTRICITY; including Galvanism, Magnetism, Dia- Magnetism, Electro-Dynamics, Magno- Electricity, and the Electric Telegraph.. By Henry M. Noad, Ph.D., F.R.S., F.C.S. Fourth Edition. With 500 Woodcuts. 8vo, £1 4s. cloth. " It is worthy of a place in the library of every public institution."— Mining Journal. Dynamo Construction. HOW TO MAKE A DYNAMO: A Practical Treatise for Amateurs. Containing numerous Illustrations and Detailed Instructions for Constructing a Small Dynamo, to Produce the Electric Light. By Alfred Crofts. Third Edition, Revised and Enlarged. Crown 8vo, 2s. cloth. [Just published. " The instructions given in this unpretentious little book are sufficiently clear ana explicit to enable any amateur mechanic possessed of average skill and the usual tools to be found in an amateur's workshop, to build a practical dynamo machine." — Electrician. NAT URAL SCIENCE , etc. Pneumatics and Acoustics. PNEUMATICS : Including Acoustics and The Phenomena of Wind Currents, for the Use of Beginners. By Charles Tomlinson, F.R.S., F.C.S., &c. Fourth Edition Enlarged. With Numerous Illustrations. l2mo, is. 6d. cloth. " Beginners in the study of this important application of science could not have a better manual." — Scotsman. " A valuable and suitable text-book for students of Acoustics and the Phenomena of Wind Currents." Schoolmaster. Conchology. A MANUAL OF THE MOLLUSCA: Being a Treatise on Recent and Fossil Shells. By S. P. Woodward, A.L.S., F.G.S., late Assistant Palaeontologist in the British Museum. With an Appendix on Recent and Fossil Conchological Discoveries by Ralph Tate, A.L.S., F.G.S. Illustrated by A. N. Waterhouse and Joseph Wilson Lowry. With 23 Plates and upwards of 300 Woodcuts. Reprint of Fourth Edition, 1880. Crown 8vo, Is. 6d. cloth " A most valuable storehouse of conchological and geological information." — Science Gossip. Geology. RUDIMENTARY TREATISE ON GEOLOGY, PHYSICAL AND HISTORICAL. Consisting of " Physical Geology," which sets forth the Leading Principles of the Science ; and " Historical Geology," which treats of the Mineral and Organic Conditions of the Earth at each successive epoch, especial reference being made to the British Series of Rocks. By Ralph Tate, A.L.S., F.G.S., &c. &c. With 250 Illustrations. l2mo, $s. cloth boards. " The fulness of the matter has elevated the book into a manual. Its information is exhaustive and well arranged.' 1 — School Board Chronicle. Geology and Genesis. THE TWIN RECORDS OF CREATION; or, Geology and Genesis, their Perfect Harmony and Wonderful Concord. By George W. Victor le Vaux. Numerous Illustrations. Fcap. 8vo, $s. cloth. "A valuable contribution to the evidences of Revelation, and disposes very conclusively of the argu- ments of those who would set God's Works against God's Word. No real difficulty is shirked, and no sophistry is left unexposed." — 7 'he Rock. "The remarkable peculiarity of this author is that he combines an unbounded admiration of science with an unbounded admiration of the Written record. The two impulses are balanced to a nicety ; and the consequence is that difficulties which to minds less evenly poised would be serious find immediate solutions of the happiest kinds." — London Review. Astronomy. ASTRONOMY. By the late Rev. Robert Main, M.A., F.R.S., formerly Radcliffe Observer at Oxford. Third Edition, Revised and Corrected to the present Time, by William Thynne Lynn, B.A., F.R.A.S., formerly of the Royal Observatory, Greenwich. i2mo, 2s. cloth limp. "A sound and simple treatise, very carelully edited, and a capital book for beginners." — Knowledge. ' ' Accurately brought down to ihe requirements of the present time by Mr.Lynn."— Educational Times'. NATURAL SCIENCE, &-c. 27 DR. LARDNER'S COURSE OF NATURAL PHILOSOPHY. THE HANDBOOK OF MECHANICS. Enlarged and almost re- written by Benjamin Loewy, F.R.A.S. With 378 Illustrations. Post 8vo, 6s. cloth. "The perspicuity of the original has been retained, and chapters which had become obsolete have been replaced 1 by others of more modern character. The explanations throughout are studiously popular, and care has been taken to show the application of the various branches of physics to the industrial arts, and to the practical business of life." — Mining Journal. " Mr. Loewy has carefully revised the book, and brought it up to modern requirements."— Nature. " Natural philosophy has had few exponents more able or better skilled in the art of popularising the subject than Dr. Lardner : and Mr. Loewy is doing good service in fitting this treatise, and the others of the series, for use at the present time."— Scotsman. THE HANDBOOK OF HYDROSTATICS AND PNEUMATICS. New Edition, Revised and Enlarged by Benjamin Loewy, F.R.A.S. With 236 Illustrations. Post 8vo, 5*. cloth. "For those 'who desire to attain an accurate knowledge of physical science without the profound methods of mathematical investigation,' this work is not merely intended, but well adapted."— Chemical ."The volume before us has been carefully edited, augmented to nearly twice the bulk of the former edition, and all the most recent matter has been added. . . . It is a valuable text-book."— Nature. Eu "l^&M^k!^? * paSS exanlmat ' ons wil1 find it, we think, specially suited to their requirements."— THE HANDBOOK OF HEAT. Edited and almost entirely re-written by Benjamin Loewy, F. R. A. S. , &c. 117 Illustrations. Post 8vo, 6s. cloth. , . . *", e style is always clear and precise, and conveys instruction without leaving any cloudiness or lurking doubts behind."— Engineering. j A m ?i St ° x ' laus . t ' ve took on the subject on which it treats, and is so arranged that it can be under- stood by all who desire to attain an accurate knowledge of physical science. . . . Mr. Loewy has included all the latest discoveries in the varied laws and effects of heat."— Standard. 'A complete and handy text-book for the use of students and general readers."— English Mechanic. THE HANDBOOK OF OPTICS. By Dionysius Lardner, D.C.L., formerly Professor of Natural Philosophy and Astronomy in University College, London. New Edition. Edited by T. Olver Harding, B. A. Lond., of University College, London. With 298 Illustrations. Small 8vo, 448 pages, $s. cloth. "Written by one of the ablest English scientific writers, beautifully and elaborately illustrated." rr-Mechamc's Magazine. THE HANDBOOK OF ELECTRICITY, MAGNETISM, AND ACOUSTICS. By Dr. Lardner. Ninth Thousand. Edited by Geo. Carey Foster, B.A., F.CS. With 400 Illustrations. Small 8vo, 5*. cloth. . The book could not have been entrusted to anyone better calculated to preserve the terse and lucid style of Lardner, while correcting his errors and bringing up his work to the present state of scientific knowledge."— Popular Science Review. THE HANDBOOK OF ASTRONOMY. Forming a Companion to the "Handbook of Natural Philosophy." By Dionysids Lardner, D.C.L., formerly Professor of Natural Philosophy and Astronomy in University College, London. Fourth Edition. Revised and Edited by Edwin Dunkin, F.R.A.S., Royal Observatory, Greenwich. With 38 Plates and upwards of 100 Woodcuts. In One Vol., small 8vo, 550 pages, gs. 6d. cloth. " Probably no other book contains the same amount of information in so compendious and well- arranged a form— certainly none at the price at which this is offered to the public."— A theniEum. " We can do no other than pronounce this work a most valuable manual of astronomy, and we strongly recommend it to all who wish to acquire a general— but at the same time correct— acquaintance with this sublime science." — Quarterly Journal of Science. " One of the most deservedly popular books on the subject . . . We would recommend not only the student of the elementary principles of the science, but him who aims at mastering the higher and mathematical branches of astronomy, riot to be without this work beside him."— Practical Magazine. Dr. Lardner's Electric Telegraph. THE ELECTRIC TELEGRAPH. By Dr. Lardner. Revised and Re-written by E. B. Bright, F.R.A.S. 140 Illustrations. Small 8vo, 2s. 6d. cloth. " One of the most readable books extant on the Electric Telegraph."— English Mecltanic. 28 CROSBY LOCKWOOD &• SON'S CATALOGUE. DR. LARDNER'S MUSEUM Oh SCIENCE AND ART. THE MUSEUM OF SCIENCE AND ART. Edited by Dionysius Lardner, D.C.L., formerly Professor of Natural Philosophy and Astronomy in University College, London. With upwards of 1,200 Engravings on Wood. In 6 double volumes, £1 is., in a new and elegant cloth binding; or handsomely bound in half morocco, 3U. 6d. %* Opinions of the Press. " This series, besides affording popular but sound instruction on scientific subjects, with which the humblest man in the country ought to be acquainted, also undertakes that teaching of ' Common Things-' which every well wisher of his kind is anxious to promote. Many thousand copies of this serviceable publication bave been printed, in the belief and hope that the desire for instruction and improvement widely prevails ; and we have no fear that such enlightened faith will meet with disappointment." — Times. " A cheap and interesting publication, alike informing and attractive. The papers combine subjects of importance and great scientific knowledge, considerable inductive powers, and a popular style of treatment. " — Spectator. " The ' Museum of Science and Art ' is the most valuable contribution that has ever been made to- the scientific instruction of every class of society." — Sir David Brewster, in the North British Review. " Whether we consider the liberality and beauty of the illustrations, the charm of the writing, or the durable interest of the matter, we must express our belief that there is hardly to be found among the new books one rhat would be welcomed by people of so many ages and classes as a valuable present." — Examiner. *** Separate books formed from the above, suitable for Workmen's Libraries, Science Classes, &°c. Common Things Explained. Containing Air, Earth, Fire, Water, Time, Man, the Eye, Locomotion, Colour, Clocks and Watches, &c. 233 Illustrations, cloth- gilt, 5*. The Microscope. Containing Optical Images, Magnifying Glasses, Origin and Description of the Microscope, Microscopic Objects, the Solar Microscope, Micro- scopic Drawing and Engraving, &c. 147 Illustrations, cloth gilt, 2s. Popular Geology. Containing Earthquakes and Volcanoes, the Crust of the- Earth, &c. 201 Illustrations, cloth gilt, zs. 6d. Popular Physics. Containing Magnitude and Minuteness, the Atmosphere, Meteoric Stones, Popular Fallacies, Weather Prognostics, the Thermometer, the Barometer, Sound, &c. 85 Illustrations, cloth gilt, zs. 6d. Steam and its Uses. Including the Steam Engine, the Locomotive, and Steam Navigation. 89 Illustrations, cloth gilt, 2s. Popular Astronomy. Containing How to observe the Heavens. The Earth, Sun, Moon, Planets. Light, Comets, Eclipses, Astronomical Influences, &c. 182 Illus- trations, 4s. 6d. The Bee and White Ants : Their Manners and Habits. With Illustrations of Animal Instinct and Intelligence. 135 Illustrations, cloth gilt, zs. The Electric Telegraph Popularized. To render intelligible to all who can Read, irrespective of any previous Scientific Acquirements, the various forms of Telegraphy in Actual Operation. 100 Illustrations, cloth gilt, is. 6d. Dr. Lardner'8 School Handbooks. NATURAL PHILOSOPHY FOR SCHOOLS. By Dr. Lardner. 328 Illustrations. Sixth Edition. One Vol., 3-r. 6d. cloth. " A very convenient class-book for junior students in private schools. It is intended to convey, in clear and precise terms, general notions of all the principal divisions of Physical Science." — British Quarterly Review. ANIMAL PHYSIOLOG Y FOR SCHOOLS. By Dr. Lardner. With 190 Illustrations. Second Edition. One Vol., 3s. 6d. cloth. " Clearly written, well arranged, and excellently illustrated." — Gardener's Chronicle. COUNTING-HOUSE WORK', TABLES, CALCULATORS, &>c. 29 COUNTING-HOUSE WORK, TABLES, CALCULATORS, etc. Accounts for Manufacturers. FACTORY ACCOUNTS : Their Principles and Practice. A Hand-book for Accountants and Manufacturers, with Appendices on the Nomenclature of Machine Details ; the Income Tax Acts ; the Rating of Factories ; Fire and Boiler Insurance ; the Factory and Workshop Acts, &c, including also a Glossary of Terms and a large number of Specimen Rulings. By Emile Garcke and J. M. Fells. Third Edition. Demy 8vo, 250 Pages. Price 6s. strongly bound. "A very interestmg description of the requirements of Factory Accounts. ■ . . The principle of assimilating the Factory Accounts to the general commercial books is one which we thoroughly agree with."— Accountants* Journal. " Characterised by extreme thoroughness. There are few owners of factories who would not derive great benefit from the perusal of this most admirable work." — Local Government Chronicle. Foreign Commercial Correspondence. THE FOREIGN COMMERCIAL CORRESPONDENT : Being Aids to Commercial Correspondence in Five Languages, English, French, German, Italian, and Spanish. By Conrad E. Baker. Second Edition, Revised. Crown SVo, y. 6d. cloth. "Whoever wishes to correspond in all the languages mentioned by Mr. Baker cannot do better than study this work, the materials of which are excellent and conveniently arranged. Iney ■consist not of entire specimen letters, but— what are far more useful— short passages, sentences, or phrases expressing the same general idea in various forms."— A thcnaum. "A careful examination has convinced us that it is unusually complete, well arranged ana reliable. The book is a thoroughly good one." — Schoolmaster. intuitive Calculations. THE COMPENDIOUS CALCULA TOR ; or, Easy and Concise Methods of Performing the various Arithmetical Operations required in Commercial and Business Transactions, together with Useful Tables. By Daniel O 'Gorman. Corrected and extended by J. R. Young, formerly Professor of Mathematics at Belfast College. Twenty-seventh Edition, carefully Revised by C. Norris. Fcap. 8vo, 2s. 6d. cloth limp ; or, 3*. 6d. strongly half bound in leather. "It would be difficult to exaggerate the usefulness of a book like this to everyone engaged in com- merce or manufacturing industry. It is crammed full of rules and formula? for shortening and employing " C "Suppliersfedal & 2d rapid methods for all kinds of calculations. Of great utility to persons ■engaged in any kind of commercial transactions." — Scotsman. Modern Metrical Units and Systems. MODERN METROLOGY: A Manual of the Metrical Units and Systems of the present Century. With an Appendix containing a proposed English System. By Lowis D'A. j/ckson, A.M. Inst. C.E., Author of "Aid to Survey Practice," &c. Large crown 8vo, \2s. 6d. cloth. "The author has brought together much valuable and interesting information . . . Wea^j hut recommend the work tl the consideration of aU interested in the practical reform of our weights and m ™' eThSve tables of equivalent weights and measures of all sorts andl for ckwd««»£>^ . of the effects of the various systems that have been proposed or adopted, Mr. Jackson s treatise is without a rival." — Academy. The Metric System and the British Standards. A SERIES OF METRIC TABLES, in which the British Standard Measures and Weights are compared with those of the Metric ff^XiZld" Use on the Continent. By C. H. DoWLlNG, C.E 8vo 10, Strongly bound. ■' Their accuracy has been certified by Professor Airy, the AstJ°nomer-Ro y±^g*£- tem " Mr. Dowling's Tables are well put together as a ready reckoner for the conversion ot one system into the other."— Athenoium. iron and Metal Trades' Calculator. , r „,»rr„*T v THF TRDN AND METAL TRADES' COMPANION: For ex- p^oTtfousff SfrtainW thffalue of any Good, bought or sold by Weight, from „. Sefcwfto Il27p"cwt., and from one Earthing per pound to one shilling per pound. Each W Tabk ^Xfro^one pound to ,00 tons , to wia«^^-l«« Decimals, Square and Cube Root, Mensuration of Superficies and bol.a^ &c also Tables of Weights of Materials, and other Useful Memoranda. .By Ihomas ^Although specially adapted to the iron and ^^S^Zf^?^ °" M * ""* ■other business in which merchandise is bought and sold by weight. Kaimay » ys. 6d. cloth. [Just published. " The work will prove very useful, not merely to the technological student, but to tne practical soap- boiler who wishes to understand the theory of his art." — Cliemical News. ■ "Realty an excellent example of a technical manual, entering as it does, thoroughly and exhaustively, both into the theory and practice of soap manufacture. The book is well and honestly done, and de- serves the considerable circulation with which it will doubtless meet." — Knowledge. " Mr. Watt's book is a thoroughly practical treatise on an art which has almost no literature in our language. We congratulate the author on the success of his endeavour to fill a void in English technical literature."— Nature. Paper Making. THE ART OF PAPER MAKING: A Practical Handbook of the Manufacture of Paper from Rags, Esparto, Straw and other Fibrous Materials, Including the Manufacture of Pulp from Wood Fibre, with a Description of the Machinery and Appliances used. To which are added Details of Processes for Recovering Soda from Waste Liquors. By Alexander Watt, Author of " The Art of Soap-Making," "The Art of Leather Manufacture," &c. With Illustra- tions. Crown 8vo, ys. 6d. cloth. [just published. "This book is succinct, lucid, thoroughly practical, and includes everything of interest to the modern paper-maker. The book, besides being all the student of paper-making will require in his. apprenticeship, will be found of interest to the paper-maker himself. , It is the latest, most practical and most complete work on the paper-making art before the British public."— Paper Record. . " It may be regarded as the standard work on the subject. The book is full of valuable informa- tion. The 'Art of Paper-making,' is in every respect amodel of a text-book, either for a technical class, or for the private student." — Paper and, Printing Trades Journal. 'Admirably adapted for general as well as.ordinary technical reference, and as a handbook for students in technical education may be warmly commended."— The Paper Maker's Monthly Journal. Leather Manufacture. THE ART OF LEATHER MANUFACTURE: Being a Practical Handbook, in which the Operations of Tanning, Currying, and Leather Dressing are fully Described, and the Principles of Tanning Explained, and many Recent Processes Introduced; as also Methods for the Estimation of Tannin, and a Description of the Arts of Glue Boiling, Gut Dressing, &c. By Alexander Watt, Author of "Soap-Making," " Electro-Metallurgy," &c. With numerous Illustrations. Second Edition. Crown 8vo, gs. cloth. " A sound, comprehensive treatise on tanning and its accessories. The book is an eminently valuable production, which redounds to the credit of both author and publishers!"— Chemical Review. "This volume is technical without being tedious, comprehensive and complete without being prosy, and it bears on every page the impress of a master hand. We have never come across a better trade treatise, nor one that so thoroughly supplied an absolute want."— Shoe and Leather Trades Chronicle. Boot and Shoe Making. THE ART OF BOOT AND SHOE-MAKING: A Practical Hand- book, including Measurement, Last-Fitting, Cutting-Out, Closing and Making, with a Description of the most approved Machinery Employed. By John B. Leno, late Editor of St. Crispin, and The Boot and Shoe-Maker. With numerous Illustrations. Third Edition. i2mo, 2s. cloth limp. ... " This excellent treatise is by far the best work ever written on the subject. A new work embracing all modern improvements was much wanted. This want is now satisfied. The chapter on clicking, which shows how waste may be prevented, will save fifty times the price of the book. —Scottish Leather Dentistry. . „ MECHANICAL DENTISTRY: A Practical Treatise on the Construc- tion of the various kinds of Artificial Dentures. Comprising also Useful Formula:, : Tables, and Receipts for Gold Plate, Clasps, Solders, &c. &c By Charles Hunter. Third Edition, Revised. With upwards of ioo Wood Engravings. Crown 8vo, %s. 6d. cloth. " The work is very practical."— Monthly Review of Dental Surgery. . , ., _ rof « s ; or , "We can strongly recommend Mr. Hunter's treatise to all students P«P»™g f°' _ the P">te*™ of dentistry, as well as to every mechanical dentist."— Dublin Journal of Medical Science. Wood Engraving. , , , .. . ,, WOOD ENGRAVING : A Practical and Easy Introduction to the Study of the Art. By William Norman Brown. Second Edition. With numerous Illustrations. i2mo, \s. 6d. cloth limp. _ j.„,„„j ,h» firsf "The book is clear and complete., and will be useful to anyone wanting to understand the test elements of the beautiful art of wood engraving."— Graphic. j 2 CROSBY LOCKWOOD <3r> SON'S CATALOGUE. HANDYBOOKS FOR HANDICRAFTS. By PAUL N. HASLUCK. Metal Turning. THE METAL TURNER'S HANDYBOOK. A Practical Manual for Workers at the Foot-Lathe : Embracing information on the Tools, Appliances and Processes employed in Metal Turning. By Paul N. Hasluck, Author of "Lathe- Work." With upwards of One Hundred Illustrations. Second Edition, Revised. Crown 8vo, 2s. cloth. " Clearly and concisely written, excellent in every -my."— Mechanical World. Wood Turning. THE WOOD TURNER'S HANDYBOOK. A Practical Manual fit- Workers at tlie Lathe : Embracing Information on the Tools, Appliances and Processes Employed in Wood Turning. By Paul N. Hasluck. With upwards of One Hundred Illustrations. Crown 8vo, 2s. cloth. " We recommend the book to young turners and amateurs. A multitude of workmen have hitherto *ought in vain for a manual of this special industry." — Mechanical World. WOOD AND METAL TURNING. By P. N. Hasluck (being the Two preceding Vols, bound together). 300 pp., with upwards of 200 Illustrations, crown 8vo, y. 6d. cloth. Watch Repairing. THE WATCH JOBBER'S HANDYBOOK. A Practical Manual on Cleaning, Repairing and Adjusting. Embracing Information on the Tools, Materials, Appliances and Processes Employed in Watchwork. By Paul N. Hasluck. With upwards of One Hundred Illustrations. Crown 8vo, 2s. cloth. " All young persons connected with the trade should acquire and study this excellent, and at the ■same time, inexpensive work. 1 ' — Clerkenwell Chronicle: Clock Repairing. THE CLOCK JOBBER'S HANDYBOOK ; A Practical Manual on Cleaning, Repairing and Adjusting. Embracing Information on the Tools, Materials, Appliances and Processes Employed in Clockwork. By Paul N. Hasluck. With upwards of ico Illustrations. Cr. 8vo, 2r. cloth. ■" Of inestimable service to those commencing the trade."— Coventry Standard. WATCH AND CLOCK JOBBING, By P. N. Hasluck (being the Two preceding Vols, bound together). 320 pp., with upwards of 200 Illustrations, crown 8vo. 3s. 6d. cloth. Pattern Making. THE PATTERN MAKER'S HANDYBOOK. A Practical Manual, embracing Information on the Tools, Materials and Appliances employed in Con- structing Patterns for Founders. By Paul N. Hasluck. With One Hundred Illustrations. Crown 8vo, 2s. cloth. " This handy volume contains sound information of considerable value to students and artificers." — ^Hardware Trade Journal. Mechanical Manipulation. THE MECHANIC'S WORKSHOP HANDYBOOK. A Practical Manual on Mechanical Mani filiation. Embracing Information on various Handicraft Processes, with Useful Notes and Miscellaneous Memoranda. By Paul N. Hasluck. Crown 8vo, 2s. cloth. " It is a book which should be found in every workshop, as it is one which'will be continually .referred to for a very great amount of standard information." — Saturday Review. Model Engineering. THE MODEL ENGINEER'S HANDYBOOK: A Practical Manual on Model Steam Engines. Embracing Information on the Tools, Materials and Processes Employed in their Construction. By Paul N. Hasluck. With upwards of 100 Illustrations. Crown 8vo, 2s. cloth. " By carefully going through the work, amateurs may pick up an excellent notion oi the con- struction of full-sized steam engines." — Telegraphic Journal. ^Cabinet Making. THE CABINET WORKER'S HANDYBOOK; A Practical Manual -embracing Information on the Tools, Materials, Appliances and Processes em- ployed in Cabinet Work. By Paul N. Hasluck, Author of " Lathe Work," • &c. With upwards of 100 Illustrations. Crown 8vo, 2s. cloth. [Just published. '" Thoroughly practical throughout. The amateur worker in wood wil find it most useful."— Glasgow Herald. INDUSTRIAL AND USEFUL ARTS. 33 Electrolysis of Gold, Siluer, Copper, &o. ELECTRO-DEPOSITION : A Practical Treatise on the Electrolysis of Gold, Silver, Copper, Nickel, and other Metals and Alloys.' With descriptions of Voltaic Batteries, Magneto and Dynamo-Electric Machines, Thermopiles, and of the Materials and Processes used in every Department of the Art, and several Chapters on Electro-Metallurgy. By Alexander Watt, Author of " Electro-Metallurgy," &c. With numerous Illustrations. Third Edition, Revised and Corrected. Crown 8vo, 9^. , cloth. " Eminently a book for the practical worker in electro-deposition. It contains practical descriptions of methods, processes and materials, as actually pursued and used in the workshop.' 1 — Engineer, Electro-Metallurgy. ELECTRO-METALLURGY; Practically Treated. By Alexander Watt, Author of "Electro-Deposition," &c. Ninth Edition, Enlarged and Revised, with Additional Illustrations, and including the most recent Processes. i2mo, 4j. cloth boards. " From this book both amateur and artisan may learn everything necessary for the successful pro- secution of electroplating." — Iron. Electroplating. ELECTROPLATING: A Practical Handbook on the Deposition of Copper, Silver, Nickel, Gold, Aluminium, Brass, Platinum, &c. &c. ; with Descriptions of the Chemicals, Materials, Batteries and Dynamo Machines used in the Art. By J. W. Urquhart, C.E., Author of " Electric Light, " &c. Second Edition, Revised, with Additions. Numerous Illustrations. Crown 8vo, 5^. cloth. " An excellent practical manual." — Engineering. "An excellent work, giving the newest information." — Horological Journal. Electrotyping. ELECTROTYPING : The Reproduction and Multiplication of Printing ,. Surfaces and Works of Art by the Electro-deposition of Metals. By J. W. Urquhart, C.E. Crown 8vo, 5-r. cloth. " The book is thoroughly practical ; the reader is, therefore, conducted through the leading laws of electricity, then through the metals used by electrotypers, the apparatus, and the depositing processes, up to the final preparation of the work."— Art Journal. Goldsmiths' Work. THE GOLDSMITH'S HANDBOOK. By George E. Gee, Jeweller, &c. Third Edition, considerably enlarged. l2mo, 3-r. 6a?. cloth boards. "Agood, sound educator, and will be generally accepted as an authority."— Horological Journal. Silversmiths' Work. THE SILVERSMITH'S HANDBOOK. By GEORGE E. Gee, Jeweller, &c. Second Edition, Revised, with numerous Illusts. l2mo, 3*- 6d. cloth boards. "The chief merit of the work is its practical character. . . The-workers m the trade will speedily discover its merits when they sit down to study it." — English Rfechamc. ** The above two works together, strongly half-bound, price Is. Bread and Biscuit Baking. THE BREAD AND BISCUIT BAKER 'S AND SUGAR-BOILER 'S ASSISTANT. Including a large variety of Modern Recipes. With Remarks on the Art of Bread-making. By Robert Wells, Practical Baker. Second Edition, with Additional Recipes. Crown 8vo, 2s. cloth. [Just published. " A large number of wrinkles for the ordinary cook, as well as the baker. -Saturday Review. , ■THE. n pASTRYCOOK AND CONFECTIONER'S GUIDE. For Hotels, Restaurants, and' the Trade in general, adapted also for Family Use. By Robert Wells, Author of ' ' The Bread and Biscuit Baker s and Sugar Boiler s Assistant." Crown 8vo, 2s. cloth. u t t>"^lS "We cannot speak too highly of this really excellent work In these days of keen competition our readers cannot do better than purchase this book."— Baker s Times. Ornamental Confectionery. „ ., , *, , r ORNAMENTAL CONIECTIONERY : A Guide for Bakers, Con- fectioners and Pastrycooks ; including a Variety of Modern Recipes, and Remarks on Decorative and Coloured Work. With 129 Original Designs. By Robert Wells, Practical Baker, Author of "The Bread and Biscuit Baker s and Sugar-Boiler's Assistant, " &c. Crown 8vo, cloth gilt, 5*. [Just published. " A valuable work, practical, and should be in the hands of every ba ^« a °^?£ e S^fV,K s B ■ illustrative designs are alone worth treble the amount charged for the whole work. -Bakers I imis. 34 CROSBY LOCKWOOO <5r> SON'S CATALOGUE. Laundry Work. LAUNDRY MANAGEMENT. A Handbook for Use in Private and Public Laundries. Including Descriptive Accounts of Modern Machinery and Appliances for Laundry Work. By the Editor of "The Laundry Journal." With numerous Illustrations. Crown 8vo, 2s. 6d. cloth. " This book should certainly occupy an honoured place on the shelves of all housekeepers who wish to keep themselves au courant of the newest appliances and methods." — The Queen. Horology. A TREATISE ON MODERN HOROLOGY, in Theory and Practice. Translated from the French of Claudius Saunier, ex-Director of the School of Horology at Macon, by Julien Tripplin, F.R.A.S., Besancon Watch Manu- facturer, and Edward Rigg, M.A., Assayer in the Royal Mint. With Seventy- Eight Woodcuts and Twenty- Two Coloured Copper Plates. Second Edition. Super-royal 8vo, £z-2s. cloth, £2 10s. half-calf. " There'is no horological work in the English language at all to be compared to this production of M. Saunier's for clearness and completeness. It is alike good as a guide for the student and as a reference for the experienced horologist and skilled workman." — Horological Journal. " The latest, the most complete, and the most reliable of those literary productions to which con- tinental watchmakers are indebted for the mechanical superiority over their English brethren — in fact, the Book of Books, is M. Saunier's ' Treatise.* " — Watchmaker, Jeweller, and Silversmith. Watchmaking. THE WATCHMAKER'S HANDBOOK. Intended as a Workshop Companion for those engaged in Watchmaking and the Allied Mechanical Arts. Translated from the French of Claudius Saunier, and considerably enlarged by Julien Tripplin, F.R.A.S., Vice-President of the Horological Institute, and Edward Rigg, M.A., Assayer in the Royal Mint. With Numerous Woodcuts and Fourteen Copper Plates. Second Edition, Revised. With Appendix. Crown 8vo, gs. cloth. "Each part is truly a treatise in itself. The arrangement is good and the language is clear and concise.. It is an admirable guide for the young watchmaker." — Engineering. " It is impossible to speak too highly of its excellence. It fulfils every requirement in a handbook intended for the use of a workman. Should be found in every workshop." — Watck andClockmaker. " This book contains an immense number of practical details bearing on the daily occupation of a watchmaker." — Watchmaker and Metalworker (Chicago). CHEMICAL MANUFACTURES AND COMMERCE. The Alkali Trade, Manufacture of Sulphuric Acid, &c. A MANUAL OF. THE ALKALI TRADE, including the Manufacture of Sulphuric Acid, Sulphate of Soda, and Bleaching Powder. By John Lomas, Alkali Manufacturer, Newcastle-upon-Tyne and London. With 232 Illustrations and Working Drawings, and containing 390 pages of Text. Second Edition, with Additions. Super-royal 8vo, £1 ioj-. cloth. "This book is written by amanufacturer for manufacturers. The working details of the most ap- proved forms of apparatus are given, and these are accompanied by no less than 232 wood engravings, all of which may be used for the purposes of construction. Every step in the manufacture is very fully described in this manual, and each improvement explained." — Atheneeum. _ " We find not merely a sound and luminous explanation of the chemical principles of the trade, but a notice of numerous matters which have a most important bearing on the successful conduct of alkali works but which are generally overlooked by even experienced technological authors." — Chemical Review. The Blowpipe. THE BLOWPIPE IN CHEMISTRY, MINERALOGY, AND GEOLOGY. Containing all known Methods of Anhydrous Analysis, many Work- ing Examples, and Instructions for Making Apparatus. By Lieut. -Colonel W. A. Ross, R.A., F.G.S. With 120 Illustrations. Second Edition, Revised and En- larged. Crown 8vo, $s. cloth. "The student who goes conscientiously through the course of experimentation here laid down will gain a better insight into inorganic chemistry and mineralogy than if he had ' got up ' any of the best text-books of the day, and passed any number of examinations in their contents." — Chemical News. Commercial Chemical Analysis. THE COMMERCIAL HANDBOOK OF CHEMICAL ANALYSIS, or, Practical Instructions for the determination of the Intrinsic or Commercial Value of Substances used in Manufactures, in Trades, and in the Arts. By A. Normandy, Editor of Rose's "Treatise on Chemical Analysis." New Edition, to a great extent re- written by Henry M. Noad, Ph.D., F.R.S. With numerous Illus- trations. Crown 8vo, 12s. 6d. cloth. "We strongly recommend this book to our readers as a guide, alike indispensable to the housewife as to the pharmaceutical practitioner." — Medical Times. " Essential to the analysts appointed under the new Act. The most recent results are given, and the work is well edited and carefully written." — Nature. AGRICULTURE, FARMING, GARDENING, &°c. 35 Brewing. A HANDBOOK FOR YOUNG BREWERS. By Herbert Edwards Wright, B. A. An entirely New Edition, much Enlarged. [In the press. Analysis and Valuation of Fuels. FUELS: SOLID, LIQUID AND GASEOUS, Their Analysis and Valuation. For the Use of Chemists and Engineers. By H. J. Phillips, F.C.S., Analytical and Consulting Chemist to the Great Eastern Railway. Crown 8vo, 3^. 6d. cloth. [Just published. " Ought to have its place in the laboratory ot every metallurgical establishment, and wherever fuel is used on a large scale." — Chemical News. " Mr. Phillips' new book cannot fail to be of wide interest, especially at the present time."— Railway News. Dye-Wares and Colours. THE MANUAL OF COLOURS AND DYE-WARES : Their Pro- perties, Applications, Valuation, Impurities, and Sophistications. For the use of Dyers, Printers, Drysalters, Brokers, &c. By J. W. Slater. Second Edition, Revised and greatly Enlarged, crown 8vo, Js. 6d. cloth. "A complete encyclopaedia of the materia ii?ictoria. The information given respecting each article is full and precise, and the methods of determining the value of articles such as these, so liable to sophis- tication, are given with clearness, and are practical as well as valuable." — Chemist and Druggist. "There is no other work which covers precisely the same ground. To students preparing for examinations in dyeing and printing it will prove exceedingly useful." — Chemical News. Pigments. THE ARTISTS' MANUAL OF PIGMENTS. Showing their Com- position, Conditions of Permanency, Non-Permanency, and Adulterations ; Effects in Combination with Each Other and with Vehicles ; and the most Reliable Tests of Purity. Together with the Science and Arts Department's Examination Ques- tions on Painting. By H. C. Standage. Second Edition, crown 8vo, 2s. 6d. cloth. "This work is indeed multum-in~parvo, and we can, with good conscience, recommend it to all who come in contact with pigments, whether as makers, dealers, or users." — Chemicai Review. Gauging. Tables and Rules for Revenue Officers, Brewers, &o. A POCKET BOOK OF MENSURATION AND GAUGING: Containing Tables, Rules and Memoranda for Revenue Officers, Brewers, Spirit Merchants, &c. By J. B. Mant (Inland Revenue). Second Edition, Revised. Oblong l8mo, e,s. leather, with elastic band. \_Just published. " This handy and useful book is adapted to the requirements of the Inland Revenue Department, and will be a favourite book of reference. The range of subjects is comprehensive, and the arrangement simple and clear."— Civilian. " Should be in the hands of every practical brewer."— Brewers' Journal. AGRICULTURE, FARMING, GARDENING, etc. Youatt and Burn's Complete Grazier. THE COMPLETE GRAZIER, AND FARMER'S AND CATTLE- BREEDER 'S ASSISTANT. A Compendium of Husbandry ; especially in the departments connected with the Breeding, Rearing,' Feeding, and General Manage- ment of Stock ; the Management of the Dairy, &c With Directions for the Culture and Management of Grass Land, of Grain and Root Crops, the Arrangement of Farm Offices, the use of Implements and Machines and on Dra mng IrT gat on, Warping, &c ; and the Application and Relative Value of I Manures ByW illiam Youatt; Esq., V.S., and Robert Scott Burn. A New Edition partly Re- Writtten'andVeatly Enlarged by W. FreaM, B.Sc. Lond., LL. D One .large ,8vo Volume, nearly 1,000 pages. <- r * Agricultural Facts and Figures. „„, Bt .. with elastic band, f- d Farm Stud ents that we have "The most complete and comprehensive Note-bookfoj ^Farmers ™ ^ it t0 aU conn ected with seen It literally teems with information and we can cordially recanuueuu agriculture."— North British Agriculturist. CROSBY LOCKWOOD c> SON'S CATALOGUE. Flour Manufacture, Milling, etc. FLOUR MANUFACTURE : A Treatise on Milling Science and Prac- tice. By Friedrich Kick, Imperial Regierungsrath, Professor of Mechanical Technology in the Imperial German Polytechnic Institute, Prague. Translated from the Second Enlarged and Revised Edition with Supplement. By H. H. P. Powi.es, Assoc. Memb. Institution of Civil Engineers. Nearly 400 pp. Illustrated with 28 Folding Plates, and 167 Woodcuts. Roy. 8vo, 25.J. cloth. " This valuable work is, and will remain, the standard authority on the science of milling. . The miller who has read and digested this work will have laid the foundation, so to speak, of a successful career ; he will have acquired a number of general principles which he can proceed to apply. In this handsome volume we at last have the accepted text-book of modem milling in good, sound English, which has little, if any, trace of the German idiom." — The Miller. " The appearance of this celebrated work in English is very opportune, and British millers will, we are sure, not be slow in availing themselves of its pages." — Millers' Gazette. Small Farming. SYSTEMATIC SMALL FARMING; or, The Lessons of my Farm. Being an Introduction to Modern Farm Practice for Small Farmers in the Culture of Crops ; The Feeding of Cattle ; The Management of the Dairy, Poultry and Pigs ; The Keeping of Farm Work Records ; The Ensilage System, Construction of Silos, and other Farm Buildings ; The Improvement of Neglected Farms, &c. By Robert Scott Burn, Author" of "Outlines of Landed Estates' Management," and "Outlines of Farm Management," and Editor of " The Complete Grazier." With numerous Illustrations, crown 8vo, 6s. cloth. "This is the completest book of its class we have seen, and one which every amateur farmer will read with pleasure, and accept as a guide." — Field. " The volume contains a vast amount of useful information. No branch of farming is left untouched, from the labour to be done to the results achieved. It may be safely recommended to all who think they will be in paradise when they buy or rent a three-acre farm." — Glasgow Herald. Modern Farming. OUTLINES OF MODERN FARMING. By R. Scott BURN. Soils, Manures, and Crops — Farming and Farming Economy — Cattle, Sheep, and Horses — Management of Dairy, Pigs, and Poultry— Utilization of Town-Sewage, Irrigation, etc. Sixth Edition. In one vol., 1,250 pp., half-bound, profusely Illustrated, I2J. " The aim of the author has been to make his work at once comprehensive and trustworthy, and in this aim he has succeeded to a degreewhich entitles him to much credit." — Morning- Advertiser. " No farmer should be without this book.*' — Banbury Guardian. Agricultural Engineering. FARM ENGINEERING, The Complete Text-Book of. Comprising Draining and Embanking ; Irrigation and Water Supply ; Farm Roads, Fences and Gates; Farm Buildings, their Arrangement and Construction, with Plans and Estimates ; Barn Implements and Machines ; Field Implements and Machines ; Agricultural Surveying, Levelling, &c. By Professor John Scott, Editor of the " Farmers' Gazette," late Professor of Agriculture and Rural Economy at the Royal Agricultural College, Cirencester, &c. &c. In one vol., 1,150 pages, half-bound, with over 600 Illustrations, \is. *' Written with great care, as well as with knowledge and ability. The author has done his work well ; we have found him a very trustworthy guide wherever we have tested his statements. The volume will be of great value to agricultural students."- -Mark Lane Express. " For a young agriculturist we know of no handy volume likely to be more usefully studied." — Bell's Weekly Messenger. English Agriculture. THE FIELDS OF GREAT BRITAIN: A Text-Book of Agriculture. Adapted to the Syllabus of the Science and Art Department. For Elementary and Advanced Students. By Hugh Clements (Board of Trade). Second Edition, Revised, with Additions. i8mo, is. 6d. cloth. [Just published. " A most comprehensive volume, giving a mass of information." — Agricultural Economist. "It is a long time since we have seen a book which has pleased us more, or which contains 1 such a vast and useful fund of knowledge " — Educational Times. Tables for Farmers, &c. TABLES, MEMORANDA. AND CALCULATED RESULTS for Farmers, Graziers, Agricultural Students, Surveyors, Land Agents, Auctioneers, etc. With a New System of Farm Book-keeping. Selected and Arranged by Sidney Francis. Second Edition, Revised. 272 pp., waistcoat-pocket size, limp leather, Is. 6d. [Just published. " Weighing less than 1 oz., and occupying no more space than a match box, it contains a mass of facts and calculations which has never before, in such handy form, been obtainable. Every opera- tion on the farm is dealt with. The work may be taken as thoroughly accurate, the whole of the tables having been revised by Dr. Fream. We cordially recommend it. 1 ' — Bell's Weeklv Messenger. " A marvellous little book. . . . The agriculturist who possesses himself of it will not be disappointed with his investment." — The Farm. AGRI CULTURE, FARMING, GARDENING, &>c. 37 Farm and Estate Book-keeping. l £5f^ P l NG F0R - FARM ^RS AND ESTATE OWNERS. oIfZ XTnf^L^^f' in Three PI ^, a System adapted for all Classes Revised rM, 2 &"? W ° l ° DM , AN ' Chartered Accountant/ Second Edition, "The vofumeka in?i. 3 « H * ? l0th b ° afdS ' ° T > 2S ' 6d ' cloth lim P- [Just published. "Winw„ J r p tal st f dy of a most "nportant subject."— Agricultural Gazette i^ u ^^lh^&S.^^^ h 5lS^ ,,n,,, » wh,,e fu " and accurate ' beingtoa its cost a n 7rd|f»-j^S^ a S. andSUrVeyor WU1 find Mn W °° dn > aa 's "«!■. more than repay Farm Account Book. GOODMAN'S YEARLY FARM ACCOUNT BOOK. Giving a Iffin CC ° UDt ^ Diar y> and showing the Income and Expenditure Pmfir ,„S t Pa * rtment 0f 9 r °P s ' Live Stock ' Dair y. &c - &c - With Valuation, n^Hiv^f tt A S C °, U 5 t ' and Balance Sheet at the end of the Ye ar, and an Ap- Fno A f 0miS " ^ Uled and Headed for Entering a Complete Record of the Farm- ing Operations. By Johnson M. Woodman, Chartered Accountant, Author ot Book-keeping for Farmers." Folio, 7s. 6d. half-bound, contains every requisite form for keeping farm accounts readily and accurately."— Agriculture Early Fruits, Flowers and Vegetables. THE FORCING-GARDEN ; or, How to Grow Early Fruits, Flowers, and vegetawes. With Plans and Estimates for Building Glasshouses, Pits and Frames, i-ontauung also Original Plans for Double Glazing, a New Method of Growing the gooseberry under Glass, &c. &c, and on Ventilation, Protecting Vine Borders, &c. With Illustrations. By Samuel Wood. Crown 8vo, 3s. 6d. cloth, meat carf °IZa ?r .' and falrly fil J s a P lace that was in some de g ree vacant. The book is written with "Mr' W % ? v" 1 ? a8reat deal of valu at>'= teaching. "-Gardeners' Magazine. Fniir. m«™. S j?? ls . a . n on g>naI and exhaustive answer to the question, ' How to Grow Early ru.ts, * lowers and Vegetables f ' "—Land and Water. V Good Gardening. v PL d IN GUIDE TO GOOD GARDENING; or, How to Grow Vegetables, Fruits, and Flowers. With Practical Notes on Soils, Manures, Seeds, Wanting, Laying-out of Gardens and Grounds, &c. By S. Wood. Fourth Edition, with considerable Additions, &c, and numerous Illustrations. Cr. 8vo, y. 6d. cloth. _-, . TerT S ood book, and one to be highly recommended as a practical guide. The practical direc- * son's catalogue. WEALE^ R UDIMENTA RY SCIENTIFIC SERIES. * # * The volumes of this Series are freely Illustrated with Wood- m y cuts, or otherwise, where requisite. Throughout the following List it must ter 5 « Vmert be understood that the books are bound in limp cloth, unless otherwise stated; but the volumes marked with a J may also be had strongly bound in cloth boards for 6d. extra. N.B.^In ordering from this List it is recommended, as a means oj facilitating business and obviating error, to quote the numbers affixed to the volumes, as well as the titles and prices. CIVIL ENGINEERING, etc. 3 i. WELLS AND WELL-SINKING. By John Geo. Swindell, A.R.I. B.A., and G. R. Burnell, C.E. Revised Edition. With a New Appendix on the Qualities of Water. Illustrated . . .2/0 " Solid practical information, written in a concise and lucid style. The work can be recommended as a text-book for all surveyors, architects, &c." — Iron and Coal Trades Review. 3S . THE BLASTING AND QUARRYING OF STONE, for Building and other Purposes. With Remarks on the Blowing up of Bridges. By Gen. Sir J. Burgoyne, K.C.B. 1/6 43 . TUBULAR AND OTHER IRON GIRDER BRIDGES, describing the Britannia and Conway Tubular Bridges. With a Sketch of Iron. Bridges, &c. By G. Drysdale Dempsey, C.E. Fourth Edition . 2/0 44 . FOUNDATIONS AND CONCRETE WORKS. With Prac- tical Remarks on Footings, Planking, Sand, Concrete, B&on, Pile-driving, Caissons, and Cofferdams. By E. Dobson, M.R.I. B.A. Sixth Edition . .1/6 60. LAND AND ENGINEERING SURVEYING. For Students'and Practical Use. By T. Baker, C.E. Fourteenth Edition, revised and corrected by J. R. Young, formerly Professor of Mathematics, Belfast College. Illustrated with Plates and Diagrams 2/0J 8o«. EMBANKING LANDS FROM THE SEA. With Example.-, and Particulars of actual Embankments, &c. By John Wiggins, F.G.S. . 2/0 81. WATER WORKS, for the Supply of Cities and Towns. With a Description of the Principal Geological Formations of England as influencing Supplies of Water ; and Details of Engines and Pumping Machinery for raising Water. By Samuel Hughes, F.G.S., C.E. Enlarged Edition . . 4/0J " Every one who is debating: how his village, town, or city shall be plentifully supplied with puie water should read this book." — Newcastle Coitrant. II7 . SUBTERRANEOUS SURVEYING. By Thomas Fen- wick. Also the Method of Conducting Subterraneous Surveys without the use of the Magnetic Needle, and other modern Improvements. ByT. BAKER, C.E. 2/6| , l8 . CIVIL ENGINEERING IN NORTH, AMERICA, A Sketch of. By David Stevenson, F.R.S.E., &c. Plates and Diagrams. . 3/0 l67 . A TREATISE ON THE APPLICATION OF IRON TO THE CONSTRUCTION OF BRIDGES, ROOFS, AND OTHER WORKS. By Francis Campin, C.E. Fourth Edition . . . . a.'fij "For numbers of young engineers the book is just the cheap, handy, first guide they want." — Middiesborough Weekly News. " Remarkably accurate and well written." — Artizan. m . ROADS AND STREETS {THE CONSTRUCTION OF), in Two Parts : I. The Art of Constructing Common Roads, by H. Law, C.E., Revised by D. Kinnear Clark, C.E.; II. Recent Practice: Including Pavements of Stone, Wood, and Asphalte. By D. K. Clark, C.E. 4/6J "A book which every borough surveyor and engineer must possess, and which will be of considerable service to architects, builders, and property owners generally. ''"Building News. 203 . SANITARY WORK IN THE SMALLER TOWNS AND IN VILLAGES. By Charles Slagg, Assoc. M. Inst. C.E. Second Edition, enlarged 3/0 J " This is a very useful book There is a great deal of work required to be done in the smaller towns and villages, and this little volume wi)l help those who are willing to.do it. 1 ' — Builder. IS" The 1 indicates that these vols, may be had strongly ~bound at 6d. extra. WE ALE'S 'RUDIMENTARY SERIES. 43 Civil Engineering, etc., continued. 2i2. THE CONSTRUCTION OF GAS WORKS, and the Manu- facture and Distribution of Coal Gas. By S. HUGHES, C.E. Re-written by William Richards, C.E. Seventh Edition, with important Additions . 5/6J "Will be of infiniteiservice alike 10 manufacturers, distributors, and consumers.'* — Foreman Engineer. 2 13 . PIONEER ENGINEERING: A Treatise on the Engineering Operations connected with the Settlement of Waste Lands in New Cbuhtfies. By Edward Dobsqn, A.I. C.E. With numerous Plates. Second Edition . 4/6J " Mr. Dobson is familiar with the difficulties which have to be overcome in this class of work, and ' much of his advice will be valuable to young engineers proceeding to our colonies. "—Engineering. 216. MATERIALS AND CONSTRUCTION: A Theoretical and Practical Treatise on the Strains, Designing, and Erection of Works of Construction. By Francis Campin, C.E. Second Edition, carefully revised. ?/oJ " No better exposition of the practical application of the principles of construction has yet been published to our knowledge in such a cheap comprehensive form." — Building News. 219. CIVIL ENGINEERING. By Henry Law, M. Inst. C.E. Including a Treatise on Hydraulic Engineering by G. R. Burnell, M.I.C.E. Seventh Edition, revised, with Large Additions on Recent Practice by D. Kinnear Clark, M. Inst. C.E. 6s. 6d., cloth boards . 7/6 An admirable volume, which we warmly recommend to young engineers." — Builder. S 6o. IRON BRIDGES OF MODERATE SPAN: Their Con- struction and Erection. By Hamilton Weldon Pendred, late Inspector of Ironwork to the Salford Corporation. With 40 Illustrations .... 2/0 " Students and engineers should obtain this book for constant and practical use."*-Colliery Guardian. 268. THE DRAINAGE OF LANDS, TOWNS, AND BUILD- INGS. By G. D. Dempisey, C.E. Revised, with large Additions on Recent Practice in Drainage Engineering, by D. Kinnear Clark, M.I.C.E. Second Edition, corrected [jfust published. 4/6J MECHANICAL ENGINEERING, etc. 33. CRANES, the Construction of, and other Machinery for Raising Heavy Bodies for the Erection of Buildings, &c. By Joseph Glynn, F.R.S. 1/6 34. THE STEAM ENGINE. By Dr. Lardnjlr. Illustrated . 1/6 59. STEAM BOILERS: Their Construction and Management. By R. Armstrong, C.E. Illustrated J /6 " A mass ot information suitable ior beginners." — Design and Work. 62. THE POWER OF WATER, as applied to drive Flour Mills, and to give motion to Turbines and other Hydrostatic Engines. By Joseph Glynn, F.R.S., &c. New Edition, Illustrated . . . . • • V° 98. PRACTICAL MECHANISM, and Machine Tools. By T. ■ .Baker.C.E. WithRemarksonToolsandMachinery.byJ.NASMYTH.C.E. 2/6 139 THE STEAM ENGINE, a Treatise on the Mathematical Theory of, with Rules and Examples for Practical Men. By T. Baker, C.E. 1/6 "Teems with scientific information in reference to the steam-engine.-.0«tf* and IVor/i. 164. MODERN WORKSHOP PRACTICE, as applied to Marine, Land, and Locomotive Engines, Floating Docks, Dredging Machines, Bridges, Ship-building, &c. By T. G. Winton. Fourth Edition, Illustrated . . 3/6* "Whethe for the apprentice determined to master his profession, or far teg2£&£$£££* himself to' a higher position, this clearly written and practical treatise will be a great help. Scotsman. 16; IRON AND HEAT, exhibiting the Principles concerned in the Construction of Iron Beams, Pillars, and Girders, By J. Armour, C.E. . a/6 "A very useful and thoroughly practical little volume."-Jl/:«»«- Journal. m THE WORKMAN'S MANUAL OF ENGINEERING DRA WING By lOHN MAXTON, Instructor in Engineering Drawing. Ro^al Naval College, J Greeriwich. 'Sixth Edition 300 Plates and Diagrams . 3 /°I "A copy of it should be kep! for reference in every drawing &ce."-En gI necr,»g. & The% indicates that these vols, may be had strongly bound at6d. extra. A\ CROSBY LOCKWOOD &> SON'S CATALOGUE. Mechanical Engineering, etc., continued. tgo. STEAM AND THE STEAM ENGINE, Stationary and Port- able, An Elementary Treatise on. Being an Extension of the Elementary Treatise on the Steam Engine of Mr. John Sewell. By D. K. Clark, C.E. Third Edition 3/6£ " Every essential part of the subject is treated of competently, and in a popular style."— Iron. 2oo. FUEL, ITS COMBUSTION AND ECONOMY. Con- sisting of an Abridgment of " A Treatise on the Combustion of Coal and the Prevention of Smoke." By C. W. Williams, A. I. C.E. With extensive Additions by D. Kinnear Clakk, M. Inst. C.E. Third Edition, corrected 3/6J " Students should buy the book and read it, as one of the most complete and satisfactory treatises ud the combustion and economy of fuel to be had." — Engineer. 202. LOCOMOTIVE ENGINES, A Rudimentary Treatise on. By G. D. Dempsey, C.E. With large Additions treating of the Modern Locomotive, by D. K. Clark, M. Inst. C.E. With numerous Illustrations . 3/0J " A model of what an elementary technical book should be." — Academy. an. THE BOILERMAKER'S ASSISTANT in Drawing, Tern- plating, and Calculating Boiler Work, &c. By J. Courtney, Practical Boiler- maker. Edited by D. K. Clark, C.E. Third Edition, revised '. . . z'o " With very great care we have gone through the ' Boilermaker's Assistant,' and have to say that has our unqualified approval. Scarcely a point has been omitted."— Foreman Engineer. 2 i 7 . SEWING MACHINERY: Its Construction, History, &c. With full Technical Directions for Adjusting, &c. By J. W. Urquhart, C.E. 2/oJ " A full description of the principles and construction of the leading machines, and minute instruc- tions as to their management." — Scotsman, 223 MECHANICAL ENGINEERING. Comprising Metallurgy, Moulding, Casting, Forging, Tools, Workshop Machinery, Mechanical Manipula- tion, Manufacture of the Steam Engine, &c. By Francis Campin, C.E. . 2/6J "A sound and serviceable text-book, quite up to date." — Building News. 236. DETAILS OF MACHINERY. Comprising Instructions for the Execution of various Woiks in Iron in the Fitting-Shop, Foundry, and Boiler- Yard. By Francis Campin, C.E. ...... '. 3/0} "A sound and practical handbook for all engaged in the engineering trades."— Building World. 237 . THE SMITHY AND FORGE, including the Farrier's Art and Coach Smithing. By W. J. E. Crane. Second Edition, revised . . 2/6} "The first modern English book on the subject. Great pains have been bestowed by the auibor upon the book ; shoeing smiths will find it both useful and interesting." — Builder. 238. THE SHEET-METAL WORKER'S G UIDE : A Practical Handbook for Tinsmiths, Coppersmiths, Zincworkers, &c, with 46 Diagrams and Working Patterns. By W. J. E. Crane . Second Edition, revised. . t/6 " The author has acquitted himself with considerable tact in choosing his examples, and with no less ability in treating them." — Plumber. 2 5I STEAM AND MACHINERY MANAGEMENT: A Guide to the Arrangement and Economical Management of Machinery, with Hints on Construction and Selection. By M. PowiS BALE, M.Inst.M.E. 2/6J "Of high practical value." — Colliery Guardian. '• Gives the results of wide experience."- — Lloyd's Newspaper. 254 . THE BOILER-MAKER'S READY RECKONER, with Examples of Practical Geometry and Templating for the Use of Platers, Smiths, and Riveters. By John Courtney. Edited by D. K. Clark, M.I.C.E. Second Edition, revised, with Additions ........ 4/0 *„* The above, strongly half-bound, price 5s. " A most useful work. No workman orapprentice should be without it." — Iron Trade Circular. 255. LOCOMOTIVE ENGINE-DRIVING. A Practical Manual. for Engineers in charge of Locomotive Engines. By Michael Reynolds, M.S.E. Eighth Edition. 3s. 6d. limp ; cloth boards 4/6 "We can confidently recommend the book, not only to the practical driver, but to everyone who takes an interest in the performance of locomotive engines. — The Engineer. 256. ST A TIONAR Y ENGINE-DRIVING. A Practical Manual for Engineers in charge of Stationary Engines. By Michael Reynolds, M.S.E. Third Edition. 3J. td. limp ; cloth boards 4/6 " The author is thoroughly acquainted with his subjects, and has produced a manual which is an ■exceedingly useful one for the class for whom it is specially intended." — Engineering. IS" The % indicates that these vols, may be had strongly bound at 6d. extra. WE ALE'S RUDIMENTARY SERIES. 45 MINING, METALLURGY, etc. 4 , MINERALOGY, Rudiments of. By A. Ramsay, F.G.S. Third Edition, revised and enlarged. Woodcuts and Plates . . . .36* " The author throughout has displayed an intimate knowledge of his. subject, and great facility in imparting that knowledge to others. The book is of great utility." — Mining Journal. uj. SUBTERRANEOUS SURVEYING, with and without the Magnetic Needle. By T. Fenwick and T.Baker, C.E. Illustrated . . 2/6J ,33. METALLURGY OF COPPER: An Introduction to the Methods of Seeking, Mining, and Assaying Copper. By R. H. Lamborn. 2/6I IJS . ELECTRO-METALLURGY, Practically Treated. By Alex- ander Watt. Ninth Edition, enlarged and revised. With Additional Illustrations, and including the most Recent Processes . [Just published. 3/6J " From this book both amateur and artisan may learn everything necessary."— Iron. Ifa . MINING TOOLS, Manual of. By William Morgans, Lecturer on Practical Mining at the Bristol School of Mines .... 2/6 ^.MINING TOOLS, ATLAS of Engravings to Illustrate the above, containing 23s Illustrations of Mining Tools, drawn to Scale. 4to. . 4/0 " Students, Overmen, Captains, Managers, and Viewers may gain practical knowledge and useful hints by the study of Mr. Morgans' Manual." — Colliery Guardian. ,,6. METALLURGY OF IRON. Containing History of Iron Manufacture, Methods of Assay, and Analyses of Iron Ores, Processes of Manu- facture of Iron and Steel, &c. By H. Bauerman, F.G.S., A.R.S.M. With numerous Illustrations. Sixth Edition, revised and enlarged . . . . 5/0J " Carefully written, it has the merit of brevity and conciseness, as to less important points ; while a material matters are very fully and thoroughly entered into." — Standard. ,jo. COAL AND COAL MLNLNG, A Rudimentary Treatise on. By the late Sir Warington W.Smyth, M. A., F.R.S., &c, Chief Inspector of the Mines of the Crown. Sixth Edition, revised and enlarged . . . 3 '6 J " Every portion of the volume appears to have been prepared with much care, and as an outline is given of every known coal-field in this and other countries, as well as of the two principal methods of working, the book will doubtless interest a very large number of readers." — Mining Journal. , 95 . TEE MINERAL SURVEYOR AND VALUER'S COM- PLETE GUIDE.' Comprising a Treatise on Improved Mining Surveying and the Valuation of Mining Properties, with New Traverse Tables. By W. Lintern, Mining and Civil Engineer. Third Edition, with an Appendix on Magnetic and Angular Surveying, with Records of the Peculiarities of Needle Disturbances. With Four Plates of Diagrams, Plans, &c. . ... 3/6J * l Contains much valuable information, and is thoroughly trustworthy " — Iron&> Coal Trades Review. aH . SLATE AND SLATE Q UARR YING, Scientific, Practical, and Commercial. By D. C. Da vies. F.G.S. , Mining Engineer, &c. With numerous Illustrations and Folding Plates. Third Edition .... 3/0J "One of the best and best-balanced treatises on a special subject that we have met with." — Engineer. ^ A FIRST BOOK OF MINING AND QUARRYING, with the Sciences connected therewith, for Primary Schools and Self Instruction. By 1. H. Collins, F.G.S., Lecturer to the Miners' Association of Cornwall and Devon. Second Edition, with additions . .1/6 " For those concerned in schools in the mining districts, this work is the very thing that should be in ate hands of their schoolmasters."— Iron. ARCHITECTURE, BUILDING, etc. it. ARCHITECTURE— ORDERS— The Orders and their .Esthetic Principles. By W. H. Leeds. Illustrated 1/6 17. ARCHITECTURE— STYLES— -The History and Descrip- tion of the Styles of Architecture of Various Countries, from the Earliest to tiie Present Period. By T. Talbot Bury, F.R.I. B.A., &c. Illustrated , .2/0 V-Orders and Styles of Architecture, in One Vol., y. 6d. 18. ARCHITECTURE— DESIGN— The Principles of Design in Architecture, as deducible from Nature and exemplified in the Works of th. i 9I . PLUMBING : A Text-Book to the Practice of the Art or Craft of «he Plumber, With Chapters upon House Drainage and Ventilation. By Wm. Paton Buchan, R. P.,Sanitary Engineer. Fifth Edition, revised and enlarged, with 380 Illustrations . . . . . . ... 3I6Z "A text-book which may be safely put into the hands of every young plumber, and which will also* be found useful by architects and medical professors." — Builder. W THE TIMBER IMPORTER'S, TIMBER MERCHANT'S, AND BUILDER'S STANDARD GUIDE. By R. E. Grandy . .2/0 " Everything it pretends to be: built up gradually, it leads one irom- a forest to a treenail, and throws, in, as a makeweight, a host of material concerning bricks, columns, cisterns, &c." — English Mechanic. 206. A BOOK ON BUILDING, Civil and Ecclesiastical. By Sir Edmund Beckett, Bart., LL.D., Q.C., F.R.A.S., Author of "Clocks and Watches and Bells," &c. Second Edition, enlarged . . . . 4/6+ "A book which is always amusing and nearly always instructive."— 7¥«*W« 5*- 230. A PRACTICAL TREATISE ON HANDRAILING ; . Showing New and Simple Methods By Geo. Collings. Second Edition, Revised, including a TREATISE ON STAIRBUILDING. With Plates . 2/6" " Will be found of practical utility in the execution of this difficult branch of joinery. —Builder. 247. BUILDING ESTATES: A Treatise on the Development, Sale, Purchase, and Management of Building Land. By F. Maitland. Second Edition, revised •. , ■ ■ .. ' *'- h . '.'This book should undoubtedly be added to the library of every professional man dealing witn building land."— Z.a«*r' Agent's 'Record. 248. PORTLAND CEMENT FOR USERS. By Henry Faija, A.M. Inst. C.E. Third Edition, Corrected . . • ■ .; • -?'° " Supplies in a small compass all that is necessary to be known by users of cement. -Building* eivs 252. BRICKWORK : A Practical Treatise, embodying the General and Higher Principles of Bricklaying, Cuttingand Setting ; with the Applica- tion of Geometry to Roof Tiling, &o. By F. Walker . . • ..■■ lla " Contains all that a young tradesman or student needs to learn from books. —Building aews. aS9 . GAS FITTING: A Practical Handbook. By John Black. With 121 Illustrations..' . . . . •,.•■' r I ' r „„ ' _,- ' = »™ire &c* "Contain, all the requisite information for the successful fitttng 0™°°**/° 'Jjg^™? It is written in a simple practical style, and we heartily recommend it. '-Plumber and JJecaraJ : or. 253. THE TIMBER MERCHANTS, SA W MILLER 'ZAND 5 IMPORTER'S FREIGHT BOOK AND ASSISTANT. By WILLIAM Richardson, with additions by M. Powis Bale, M.I.M.li., .«=■ ■ • ■ a "* "A eouipendiutalof citail4UonS!wBih>suppliesa real want-in the trade. —Building news. 13- The % indicates that these, vols, may be had stronely bound at 6d. extra. 48 CROSBY LOCKWOOD 6* SON'S CATALOGUE. Architecture, Building, etc., continued. 23. [THE PRACTICAL BRICK AND TILE BOOK. Com- i*9- ■ prising: Brick and Tile Making, by E. Dobson, A.I.C.E.; Practical 252. Bricklaying, by A. Hammond ; Brickwork, by F. Walker. 550 pp. * with 270 Illustrations, strongly half-bound 6/0 25 s. CIRCULAR WORK IN CARPENTR Y AND JOINER Y. A Practical, Treatise on Circular Work of Single and Double Curvature. By George Collings. Second Edition 2/6 " Cheap in price, clear in definition, and practical in the examples selected." — Builder. 261. SHORING, and Its Application : A Handbook for the Use of Students. By George H. Blagrove. With 31 Illustrations . . .1/6 " We recommend this valuable treatise to all students." — Building News. 265. THE ART OF PRACTICAL BRICK CUTTING AND SETTING. By Adam Hammond. With go Engravings. [Just published. 1/6 1 The author has treated the subject from a workman's point of view ; the methods are thoroughly practical, and such as can be understood by the working brick-cutter.' ' — Building Nev s. *7- THE SCIENCE OR BUILDING: An Elementary Trea- tise on the Principles of Construction. Adapted to the Requirements of Architectural Students.- By E. Wyndham Tarn, M.A. Lond. Third Edition, revised and enlarged [Just published. 3/i J 2?I . VENTILATION: A Text Book to the Practice of the Art of Ventilating Buildings, with a Supplementary Chapter upon Air Testing. By William Paton Buchan, R. P., Sanitary and Ventilating Engineer, Author of " Plumbing," &c. With 170. Illustrations . [Just published. 3/6! SHIPBUILDING, NAVIGATION, etc. 5 ,. NAVAL ARCHITECTURE: An Exposition of the Elemen- tary Principles. By James Peake, H.M. Dockyard, Portsmouth . . 3/6J S3 . SHIPS FOR OCEAN AND RIVER SER VICE, Elementary and Practical Principles of the Construction of. By HakonA. Sommerfeldt. 1/6 S3 *\ AN ATLAS OF ENGRAVINGS to Illustrate the above. Twelve large folding Plates. Royal 4to, cloth 7/6 54. MASTING, MAST-MAKING, AND RIGGING OF SHIPS. Also Tables of Spars, Rigging, Blocks ; Chain, Wire, and Hemp Ropes, &c, relative to every class of vessels. By Robert Kipping, N.A. 2/0 s4 ». IRON SHIP-BUILDING. With Practical Examples and Details. By John Grantham. Fifth Edition 4/0 ss . THE SAILOR'S SEA BOOK: A Rudimentary Treatise on Navigation. By James Greenwood, B.A. With numerous Woodcuts and Coloured Plates. New and enlarged Edition. By W. H. Rosser . 2/6J *' Is perhaps the best and simplest epitome of navigation ever compiled. — Field. 55 PRACTICAL NAVIGATION. Consisting of The Sailor's 6i Sea-Book, by James Greenwood and W. H. Rosser ; together with 204. Mathematical and Nautical Tables for the Working of the Problems, by Henry Law, C.E., and Prof. J. R. Young. Half-bound in leather . . 7/ n . •11 v. ^ vas t amount of information is contained in this volume, and we fancy in a very short time that it will be seen in the library of almost every ship or yacht afloat." — Hunt's Yachting Magazine. so. MARINE ENGINES AND STEAM. VESSELS. By R. Murray, C.E. Eighth Edition, thoroughly Revised, with Additions by the Author and by George Carlisle, C.E 4/6J An indispensable manual for the student of marine engineering." — Liverpool Mercury. 8-jis. THE FORMS OF SHIPS AND BOATS. By W. Bland. Seventh Edition, revised, with numerous Illustrations and Models . . .1/6 99. NAVIGATION AND NAUTICAL ASTRONOMY, in Theory and Practice. By Prof. J. R. Young. New Edition. Illustrated . 2/6 " A very complete, thorough, and useful manual for the young navigator." — Observatory; ,06. SHIPS' ANCHORS, a Treatise on. By George Cotsell. r /6 149 . SAILS AND SAIL-MAKING, With Draughting, and the Centre ot Effort of the Sails. Also, Weights and Sizes of Ropes ; Masting, Rigging, and Sails of Steam Vessels, &c. By Robert Kipping, N.A. . 2/6J , 5 5. THE ENGINEER'S GUIDE TO THE ROYAL AND MERCANTILE NA VIES. By a Practical Engineer. Revised by P. F.M'Carthy, late of the Ordnance Survey Office, Southampton ■ .3/0 S3" The J indicates that these vols, may be had strongly bound at 6d. extra. WE ALE'S RUDIMENTARY SERIES. 49 AGRICULTURE, GARDENING, etc. 61*. A COMPLETE HEADY RECKONER FOR THE Ad- measurement OF LAND, &>c. By A. Arman. Third Edition, revised and extended by C. NOKRIS, Surveyor, Valuer, &c 2/0 . " A very useful bbok to all who have land to measure." — Mark Lane Express. "Should be in the hands of all persons having any connection with land." — Irisk Farm. 131. MILLER'S, CORN MERCHANT'S, AND FARMER'S READY RECKONER. Second Edition, revised, with a Price List of Modern Flour Mill Machinery, by W. S. Hutton, C.E 2/0 "Will prove an indispensable vade mecum. Nothing has been spared to make the book complete arid perfectly adapted to its special purpose.* — Miller. no. SOILS, MANURES, AND CROPS. (Vol. I. Outlines of Modern Farming.) By R. Scott Burn. Woodcuts 2/0 14 t. FARMING AND FARMING ECONOMY, Historical and Practical. (Vol. II. Outlines of Modern Farming.) By R. Scott Burn. 3/0 " Eminently calculated to enlighten the agricultural communitv on the varied subjects of which it treats ; hence it should find a place in every farmer's library." — City Press. 142. STOCK; CATTLE, SHEEP, AND HORSES. (Vol. III. Outlines of Modern Farming.) By R. Scott Burn. Woodcuts. . 2/6 " The author's grasp of his subject is thorough, and his grouping of facts effective. . . . We com- mend this excellent treatise.*'— Weekly Dispatch. 145. DAIRY, PIGS, AND POULTRY. (Vol. IV. Outlines of Modern Farming.) By R. Scott Burn. Woodcuts . . . . 2/0 "We can testify to the clearness and intelligibility of the matter, which has, been compiled from the best authorities." — London Review. ^.UTILIZATION OF SEWAGE, IRRIGATION, AND RECLAMATION OF WASTE LAND. (Vol. V. Outlines op Modern Farming.) By R. Scott Burn. Woodcuts a/ 6 " A work containing valuable information, which will recommend itself to all interested in modern arming." — Fiela. 140. OUTLINES OF MODERN FARMING. By R. Scott , 4 a . Burn, Author of "Landed Estates Management," "Farm Management,'" , 45 . and Editor of "The Complete Grazier." Consisting of the above Five 146. ) Volumes in One, 1,250 pp., profusely Illustrated, half-bound . . . . 12/0 "The aim of the author has been to make his work at once comprehensive and trustworthy, and in this aim he has succeeded to a degree which entitles him to much credit." — Morning Advertiser. "Should find a place in every farmer's library." — City Press. " No farmer should be without it." — Banbury Guardian. i 7J . FRUIT TREES, The Scientific and Profitable Culture of. From the French of M. Du Breuil. Fourth Edition, carefully Revised by George Glenn y. With 187 Woodcuts • • • • 3/°T " The book teaches how to prune and train fruit trees to perfection."— Field. 198. SHEEP: The History, Structure, Economy, and Diseases of. By W. C. Spooner, M.R.V.C., &c. Fifth Edition, with fine Engravings, including Specimens of New and Improved Breeds. 366 pp 3/ 6 + " The book is decidedly the best of the kind in our language."— Scotsman. , 0I KITCHEN GARDENING MADE EASY. Showing the best means of Cultivate every known Vegetable and Herb &c with . direc- tions for management all th; year round. By Geo. M. F. Glenn*. Illustrated 1/6J This book will be found trustworthy and usetuV-NortA British Agriculturist. *,, OUTLINES OF FARM MANAGEMENT. Treating of the General Work of the Farm ; Stock ; Contract Work ; Labour, &c. By R. Scott Burn, Author of " Outlines of Modern Farming, &c. . . . 2/6+ » The book is eminently practical, and may be studied with ■ adva'tage £y ^beginners in agriculture, while it contains hints which will be useful to old and successful farmers. -Scotsman. i OUTLINES OF LANDED ESTATES MANAGEMENT: 3 - Trying of The Varieties of Lands, Methods of Farming *« Sgung- gut of .. Aco =^^ M«- Tlie : indicates that these vols', may be had strongly bound at 6d. extra. 5 o CROSBY LOCK-WOOD & SON'S CATALOGUE. Agriculture, Gardening, etc., continued. 209 . THE TREE PLANTER AND PLANT PROPAGATOR • With numerous Illustrations of Grafting, Layering, Budding, Implements, Houses, Pits, &c. By S. Wood, Author of" Good Gardening," &e. . . 2/0 " Sound in its teaching and very comprehensive in its aim. It is a good book." — Gardeners 'Magazine, "The instructions are thoroughly practical and correct." — North British Agriculturist. 210 . THE TREE PRUNE R : Being a Practical Manual on the Pruning of Fruit Trees, including also their Training and Renovation, al?o treating of the Pruning of Shrubs, Climbers and Flowering Plants. With numerous Illustrations. By Samuel Wood, Author of " Good Gardening," &c. 1/6 " A useful book, written by one who has had great experience.'! — Mark Lane Express. *' We recommend this treatise very highly."— North British. Agriculturist. *«* Nos. 209 6* 210 in One Vol., handsomely half-bound, entitled "THE" TREE' Planter, Propagator and Pruner." By Samuel Wood. Price 3s. 6d. 2l8 . THE HAY AND STRAW MEASURER: New Tables for the Use of Auctioneers, Valuers, Farmers, Hay and Straw Dealers, &c, forming a complete Calculator and Ready Reckoner. By John Steele . 2 /o " A most useful handbook. It should be in every professional office where agricultural valuations are * conducted." — Land Agent's Record. 222. SUBURBAN FARMING. : A Treatise on the Laying-out and Cultivation of Farms, adapted to the Produce of Milk, Butter and Cheese, Eggs, Poultry, and Pigs. By the late Prof. John Donaldson. With Additions, illustrating Modern Practice, by R. ScorT Born. With numerous Illustrations 3/6^ ' ' An admirable treatise on all matters connected with dairy farms." — Live Stock yournal. 231 . THE ART OF GRAFTING AND BUDDING. By Charles Baltet. With Illustrations , 2/6J " The one standard work on this subject." — Scotsman. 232 . COTTAGE GARDENING; or, Flowers, Fruits, and Vege- tables for Small Gardens. By E. Hobday . . . ./ . . .1/6 " Definite instructions as to the cultivation of small gardens." — Scotsman. *' Contains much useful information at a small charge." — Glasgow Herald, 233 . GARDEN RECEIPTS. Edited by Charles W. Quin. i/6 " A singularly complete collection of the principal receipts needed by gardeners."— Farmer. "A useful and handy book, containing a good deal of valuable information." — Athen&um. 234 . MARKET AND KITCHEN GARDENING. By C. W. Shaw, late Editor of "Gawtening Illustrated" 3/°* "The most valuable compendium of kitchen and market-garden work published." — Former. *' A most comprehensive *«fttime on market and kitchen-gardening." — Mark Lane Express. 239 . DRAINING AND EMBANKING. A Practical Treatise. By John Scott, late Professor of Agriculture and Rural Economy at the Royal Agricultural College, Cirencester. With 68 Illustrations.. . . . 1/6 '* A valuable handbook to, the engineer, as well as to the surveyor." — Land. " This volume should be perused by all interested in this important branch of estate improvement." —Land Agent's Record, 240 . IRRIGATION AND WATER SUPPLY: A Practical Trea- tise on Water Meadows, Sewage Irrigation, Warping, &c. ; on the Construc- tion of Wells, Ponds and Reservoirs, &C By Prof. J. SCOTT. With 34 Illusts. 1/6 " A valuable and indispensable book for the estate manager and owner." — Forestry. "Well worth the study of all farmers and landed proprietors.'.'— Building- News. 24!. FARM ROADS, FENCES, AND GATES: A Practical Treatise on the Roads, Tramways, and Waterways of the Farm ; the Prin- ciples of Enclosures ; and the different kinds of Fences, Gates, and Stiles. By Professor John Scott. With 75 Illustrations 1/6 "Mr. Scott's treatise will be welcomed as a concisely compiled handbook." — Building News. "A useful practical work, which should be in the hands of every farmer.'* — Farpier. 242 . FARM BUILDINGS. A Practical Treatise on the Buildings necessary for various kinds of Farms, their Arrangement and Construction, with Plans and Estimates. By Prof. John Scott.- With 105 Illustrations . 2/0 " Vo one who is called upon to design farm-buildings can afford to be without this work."— Builder. "This book ought to be in the hands of every landowner and agent." — Kelso Chronicle. 243 . BARN IMPLEMENTS AND MACHINES. Treating of : the Application of Power to the Operations of Agriculture; and of tie various Machines used in the, Threshingrbarn, in the Stockyard, Dairy, &c. By Professor John Scott. With 123 Illustrations . . . . . .2/0 *f~ The \ indicates thajt these vols, may be had strongly bound at id. extra. WEALE'S RUDIMENTARY SERIES. ■ 51 Agriculture, Gardening, etc., continued. 544 . FIELD IMPLEMENTS AMD MACHINES: With Prin- ciples and Details of Construction and Points of Excellence, their Manage- ment,*^. By prof. John Scott. With 138 Illustrations .... 2/0 245. AGRICULTURAL SURVEYING: A Treatise on Land Surveying, Levelling, and Setting-out ; with Directions for Valuing and Re- porting on Farms and Estates. By Prof. J. SCOTT. With 62 Illustrations 1/6 239-) FARM ENGINEERING- By Professor John Scott. Com- tQ r prising the aboveSeven Volumes inOne, 1,150 pages', and over 600 Illustrations. 24S) Half-bound . . . . . . 12/0 "A copy of this work should be treasured up in every library where the owner thereof is in any way connected with \m&."-Farm and Home. 250. MEAT PRODUCTION : A Manual for Producers, Distribu- tors, and Consumers of Butchers' Meat By John Ew art. . . . 2/6 " A compact and handv volumeon the meat question." — Meat and Provision Trades' Review. 2 65. BOOK-KEEPING FOR FARMERS AND ESTATE OWNERS. A Practical Treatise, presenting, in Three Plans, a System adapted forall classes of Farms. By J. M. Woodman, Chartered Accountant. Second Edition, revised 2/6 *«* The above in cloth boards, strongly bound, 3s. 6d. "Will be found of great assistance by those who intend to commence, a system of book-keeping, tie author's examples being clear end explicit, and his explanations full and accurate." — Livestock Jouinj.1. MATHEMATICS, ARITHMETIC, etc. 32. MATHEMATICAL INSTRUMENTS, a Treatise on ; Their Construction. Adjustment, Testing, and Use concisely Explained. By J. F. Heather, M.A., of the Royal Military Academy. Woolwich. Fourteenth Edition, Revised, with-Additions, by A. T. Walmisley, M.I.C.E., Fellpw, of the Surveyors' Institution.- Original Edition, in 1 vol., Illustrated . . . 2/0 4. *,* In ordering the above, be careful to say " Original Edition" or give the number in the Series (32^ to distinguish it from the Enlarged Editionin 3 vols. ( Nos. 16&V9-70 J. 7 6. DESCRIPTIVE GEOMETRY, an Elementary Treatise on; with a Theory of Shadows and of Perspective, extracted from the French of G. Monge. To which is added a Description of the Principles and Practice of Isometrical Projection. By j. F. Heather, M. A. With 14 Plates . 2/0 178. PRACTICAL PLANE GEOMETRY.- giving the Simplest Modes of Constructing Figures contained in one Plane and Geometrical Con- struction of the Ground. By J. F. Heather, M.A. With 215 Woodcuts .2/0 "The author is well-known as an experienced professor, and the volume contains as complete 3 collection of problems as is likely to be required in ordinary practice. "— A rchitect. 83. COMMERCIAL BOOK-KEEPING. With Commercial Phrases and Forms in English, French, Italian, and German. By James Haddon, M.A., formerly Mathematical Master, King's College School . 1/0 84. ARITHMETIC, a Rudimentary Treatise on : with full Expla- nations of its Theoretical Principles, and numerous Examples for Practice. For the Use of Schools and for Self- Instruction; By J. &- Yootig, late Professor of Mathematics in Belfast College. Eterenfh "Edition . . .1/0 8 4 v? KEY "TO THE ABOVE. By J. R. Young . . .1/6 85 EQUATIONAL ARITHMETIC, applied to Questions of Interest, Annuities, Life Assurance, and General 'Commerce ; with vanous ■ Tables by which all Calculations may be greatly facilitated. By W. Hipsley. 2/0 86. ALGEBRA, the' Elements of. By James Haddon, M.A., . formerly MathematicalMaster of King's College School. With Appendix, containing Miscellaneous Investigations, and a collection of Problems . 2/0 86* A KEY AND COMPANION TO THE ABOVE. An • extensive repository of Solved Examples and Problems In . Illus tration^ of: he various Expedients necessary in Algebraical Operations, By J. R. \ oung sb EUCLID TkE Elements' of: with many Additional Proposi- &' fens andExpianatory Notes; to which is prefixed an Introductory Essay on 89. Logic. By Hfe'fnrY Law, C.E. . . • • • * * Said also separately, viz.:— ,/<; 88 Eucob, The First Three BoOfcS; 1 By HENRY LAW, C.E. . . . , . .. 1/0 8 9 l Euclid. Books 4, .5. ^ ii^jg-^J^jj^^L^CE^ — ' - ~^ tsr Thi\ indicates that theSe'vols. may be had strongly bound al,6d. extra: 52 CROSBY LOCK WOOD &> SON'S CATALOGUE. Mathematics, Arithmetic, etc., continued. 9 o. ANALYTICAL GEOMETRY AND CONIC SEC- TIO NS, a Rudimentary Treatise on. By Tames Hann. A New Edition, re-written and enlarged by Professor J. R.YOUNG 2/oJ "The author's style is exceedingly clear and simple, and the book is well adapted for the beginner and those who may be obliged to have recourse to sell'-tuition." — Engineer. 9 i. PLANE TRIGONOMETRY, .the Elements of. By James Hann, formerly Mathematical Master of King's College, London . .1/6 02 . SPHERICAL TRIGONOMETRY, the Elements of. By James Hann. Revised by Chakles H. Dowling, C.E 1/0 *»* Or with " The Elements of Plane Trigonometry," in One Volume, zs. 6d. 93. MENSURATION AND MEASURING, for Students and Practical Use. With the Mensuration and Levelling of Land for the purposes of Modern Engineering. By T. Baker, C.E. 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Heather, M.A. Illustrated . . . 1/6 "An excellent treatise." — British Journal 0/ Photography. I7 o. SURVEYING &• ASTRONOMICAL INSTRUMENTS. Including — I. Instruments used for Determining the Geometrical Features of a portion of Ground. II. Instruments employed in Astronomical Observa- tions. By J. F. Heather, M.A. Illustrated . . . . . .1/6 *' A good, sensible, useful book." — School Board Chronicle. *»* The above three volumes form an enlargement of the Author's original work, , 1 ' Mathematical Instruments " : price is. (See No. 32 in the Series. J \ MA THEM A TICAL INSTR UMENTS: Their Construction, 1S8. 1 Adjustment, Testing and Use. Comprising Drawing, Measuring, Optical, '69. j- Surveying 1 , and Astronomical Instruments. By J. F. Heather, MsA. 17°' Enlarged Edition, for the most part entirely re-written. The .Three Parts / as above, in One thick Volume 4/6J " An exhaustive treatise, belonging to the well-known Weale's Series. Mr. Heather's experience well qualifies him for the task he has so ably fulfilled." — Engineering- and Building Times. IS 8. THE SLIDE RULE, AND HOW TO USE IT. Con- taining full, easy, and simple Instructions to perform all Business Calculations with unexampled rapidity and accuracy. By Charles Hoare, C.E. With a Slide Rule, in tuck of cover. Filth Edition 2/6J I9 6. THEORY OF COMPOUND INTEREST AND ANNUI- TIES ; with Tables of Logarithms for the more Difficult Computations of Interest, Discount, Annuities, &c, in all their Applications and Uses for Mer- cantile and State Purposes. By Fedor Thoman, of the Soctet6 Credit Mobilier, Paris. Third Edition, carefully revised and corrected . . . '4/0J •' A very powerful work, and the author has a very remarkable command of his subject." — Professor A de Morgan. " We recommend it to the notice.of actuaries and accountants." — AthenaHtm.'" * H ," IS" The X indicates that these vols, may be had strcngfy bound a! 64. extra. tVEAZE'S RUDIMENTARY SERIES. 53 Mathematics,, Arithmetic, etc., continued. m . THE COMPENDIOUS CALCULATOR (Intuitive Calcu- lations); or, Easy and Concise Methods of Performing the various Arith- metical Operations required in Commercial and Business Transactions ; together With Useful Tables, &c. By Daniel O'Gorman. Twenty-seventh Edition, carefully revised by C. Norris . * 2/6 V The above strongly half-bound, price 3s. 6d. " It would be difficult to exaggerate the usefulness of this book to everyone engaged in commerce or manufacturing industry. It is crammed.full with rules and formulas for shortening and employing calculations in money, weights and measures, &c. of every sort and description." — Knowledge. 204. 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" Much may be learned, even by those who fancy they do not require to be taught, from the careful perusal of this unpretending but comprehensive treatise." — Art Journal. lS 6. A GRAMMAR OF COLOURING. Applied to Decorative Painting and the Arts. By George Field. New Edition, revised and enlarged by Ellis A. Davidson. With Coloured Plates . , . . 3/0J '.'The book is a most useful resume" of the properties of pigments."~ i -Builder. " One of the most useful of students' books." — Architect. 24 6. A DICTIONARY OF PAINTERS, AND HANDBOOK FOR PICTURE AMATEURS ; being a Guide for Visitors to Public, and Private Picture Galleries, and for Art-Students, including Glossary of Terms, Sketch of Principal Schools of Painting, &c. By Philippr;Dary"l, B.A. . 2/6J • v "Considering its small, compass, really admirable. We Cordially recommend the book."— Builder. »»• The J indicates that that vols., may be had strongly bound at 6d. extra. WEALE'S RUDIMENTARY SERIES. 55 INDUSTRIAL AND USEFUL ARTS. 23. BRICKS AND TILES. Rudimentary Treatise on the Manufacture of; containing an Outline of the Principles of Brickmaking. By E. Dobson, M.R.I. B.A. Additions by C ToMLlNSON, F.R.S. Illust. 3/ot " The best handbook on the subject. We can safely recommend it as a good investment." — Builaer. 67. CLOCKS AND WATCHES, AND BELLS, a Rudimentary Treatise on. By Sir Edmund Beckett, Bart* Q.C Seventh Edition. .4/6 *,* The above handsomely bound, cloth boards, S-f. 6d. "The best work on the subject probably extant. The treatise, on bells is undoubtedly the best in the language."— Engineering. "The only modern treatise on clock-making." — Horalogical Journal. 8 3 *». CONSTRUCTION OF DOOR LOCKS. From the Papers of A. C. Hobbs. Edited by Charles Tomlinson, F.R.S. With a Note upon Iron Safes by Robert Mallet. Illustrated 2/6 162. THE BRASp FOUNDER'S MANUAL: Instructions for Modelling, Pattern Making, Moulding, Turning, &c. By W. Graham. . "2/0 J aos. THE ART OF LETTER FAINTING MADE EASY. 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PRACTICAL ORGAN BUILDING. By W. E. Dickson, M.A., Precentor of Ely Cathedral. Second Edition, Revised, with Additions. 2/6J "The amateur builder will find in this book all that is necessary to enable him personally to con- struct a perfect organ with his owri hands." — Academy. " The best work on the subject that has yet appeared in book form."— English Mechanic. 262. THE ART OF BOOT AND SHOEMAKING, including " Measurement, Last-fitting, Cutting-out, Closing and Making ; with a Descrip- tion of the most Approved Machinery employed. By John Bedford Leno, late Editor of" St. Crispin "and "The Boot and Shoemaker." Withnumerous Illustrations. Third Edition . . ... •-;.,■•,.• , 2 /°+ "This excellent treatise is by far the best work ever written on the subject. The chapter on clicking, which shows how waste may be prevented, will save fifty times the price of the book.' —Scottish Leather ■ Trader. 2 6 3 MECHANICAL DENTISTR Y: A Practical Treatise on the Construction of the Various Kinds of Artificial Dentures,' comprising also Useful Formulae, Tables and Receipts for Gold Plate, Clasps, holders, &c. Bv Charles Hunter. . Third Edition, revised, with additions . . . 3/0T "We can strongly recommend Mr. Hunter's treatise to aU students preparing for the profession of dentisty, as well as to every mechanical dentist."-Z>««z« Journal of Medical Science. 270 WOOD ENGRA VING: A Practical and Easy Introduction " -"to the Study of the Art. ' By W. N. Brow n ■ . ■ [Just published. 1/6. »r TheX indicates, that these, vak,„ max it. had- strongly bxamd. at 6d.. extra. 56 WE ALE'S RUDIMENTARY SERIES, MISCELLANEOUS VOLUMES. 3 6. A DICTIONARY OF TERMS used in ARCHITECTURE, BUILDING, ENGINEERING, MINING, METALLURGY, ARCHAE- OLOGY, the FINE ARTS, &c. By. John .Weale. Sixth Edition. Edited by .Robt. Hunt, F.R.S., Keeper of Mining Records, Editor of *' Ure's Dictionary." Numerous Illustrations . 5/0 %* The above, strongly bound in cloth boards, price 6s. 41 The best small technological dictionary in the language.*' — Architect. "The absolute accuracy of a work of this character can only be judged of after extensive consultation and from our examination it appears very correct and very complete." — Mining Journal. "There is no need now to speak of the excellence of this work ; it received the approval of the com- munity long ago. Edited now by Mr. Robert Hunt, and published in a cheap, handy form, it will the utmost service as a book of reference scarcely to be exceeded in value." — Scotsman. 50. THE LAW OF CONTRACTS FOR WORKS AND SERVICES. By David Gibbons. 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A Manual of Home and Personal Hygiene. By the Rev. JamesTBaird, B.A 1/0 " The author gives sound instructions for the preservation of health." —A thenamm. " It is wonderfully reliable, it is written with excellent taste, and there is instruction crowded into every page." — English Mechanic. I5 o. LOGIC, Pure and Applied. By S. H. Emmens. Third Edition T /6 " This admirable work should be a text-book not only for schools, students and philosophers, for all Uterateurs and men of science, but for those concerned in the practical affairs of life, &c." — The News. i S3 . SELECTION'S FROM LOCKE'S ESSAYS ON THE HUMAN UNDERSTANDING. With Notes by S. H. Emmens . . 2/0 I54 . GENERAL HINTS TO EMIGRANTS. Containing No- tices of the various Fields for Emigration. With Hints on Preparation for Emigrating! Outfits, &c, Useful Recipes, Map of the World, &c. . . 2/0 , S7 . THE EMIGRANT'S GUIDE TO NATAL. By Robert James Mann, F.R.A.S., F.M.S. Second Edition, revised. Map . .2/0 193 . HANDBOOK OF FIELD FORTIFICATION. By Major W. W. Knollys, F.R.G.S. With 163 Woodcuts . . . . . 3/0J "A well-timed and able contribution to our military literature. . . . The author supplies, in a clear business style, all the information likely to be practically useful." — Chambers of Commerce Chronicle. 194 . THE HOUSE MANAGER: Being a Guide to Housekeep- ng, Practical Cookery, Pickling, and Preserving, Household Work, Dairy Management, the Table and Dessert, Cellarage of Wines, Home-brewing and Wine-making, the Boudoir and Dressing-room, Travelling, Stable Economy, Gardening Operations, &c. By An Old Housekeeper .... 3/6! "We find here directions to be discovered in no other book, tending to save expense to the pocket, as well as labour to the head."— John Bull. " Quite an Encyclopaedia of domestic matters. We have been greatly pleased with the neatness and lucidity of the explanatory details." — Court Circular. I94 . \ HOUSE BOQK{TM). Comprising: I. The House Manager. 112. l By an Old Housekeeper. II. Domestic Medicine. By Ralph Gooding, & f M.D. III. Management op Health. By James Baird. In One Vol., 112*. J strongly half-bound 6/0 XS" The X indicates that these vols, may be had strongly hound at 6d. extra. OGDEN, SMALB AND CO, LIMITED, PRINTERS, GREAT SAFFRON HILL, E.C. Cornell University Library QB 801. G66 The visible universe; chapters on the ori 1 , ' , 'T924' I 00 , 5 II '025 766