?ss \B73- ■ ■ ."■ , ..... ...... .mmmm '.■•...'."'.'■■' Ji'fi":':. - Illlp, .llSliil Cornell University Library QH 205.P55 1879 Practical hints on the selection and use 3 1924 003 074 329 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/cu31924003074329 SELECTION AND USE .,Oap. Eve-piece. f -DIAGRAM SHOWING THE DIFFERENT PARTS OF THE MICRO- SCOPE, AND THEIR NAMES, PRACTICAL HINTS ON THE SELECTION AND USE OF THE MICROSCOPE. INTENDED FOB BEGINNERS. By JOHN PHIN. Abridged from the Author's larger work, "HOW TO USE THE MICROSCOPE." SECOND EDITION. FULLY ILLUSTRATED. NEW YORK: THE INDUSTRIAL PUBLICATION COMPANY. 1892. Copyright secured, 1879, by John Phin. CONTENTS. Peeface. ......... v Intboduction. - is The Miceoscope. What it is ; What it Does ; Different Kinds of Microscopes ; Essen tlal Parts of the Microscope ; Names of the Different Parts, 13 Simple Micboscopes. Hand Magnifiers; Watch-Makers' Eye-Glasses ; Engravers' Glasses ; Coddington Lens ; Stanhope Lens ; Stands for Simple Microscopes; Baspail's Microscope: Excelsior Microscope; Twenty-five Cent Microscopes; Penny Microscopes; Craig Microscope, 23 Selection op a Miceoscope poe Pbactical Pubposes. Must be Adapted to Beauirements and Skill of User ; Microscopes for Botany ; For Physicians ; For Students ; Magnifying Power BeQuired ; The Stand ; The Stage ; Mirror ; Body ; Draw-Tube ; Adjustment for Focussing ; The Diaphragm ; Objectives ; Eye- Pieces, - 33 Accessoet Appabatus. Stage Forceps; Forceps Carrier; Object Holder; Plain Slides; Concave Slides ; Watch-Glasses ; Watch-Glass Holder ; Animal- cule Cage; Zoophyte Trough; Compressorium ; Gravity Com- pressorium ; Growing Slides ; Frog Plate ; Table, 47 Illumination op Opaque Objects. Diffused Light ; Bulls-Eye Condenser; Side Beflector; The Lieb- erkuhn, - 61 Illumination op Teanspaeent Objects. Direct and Eefleeted Light; Axial or Central Light; Oblique Light; The Spot Lens; The Parabolic Illuminator; Polarized Light, 63 How to Use the Miceoscope. General Hints; Simple Hand Magnifiers; Compound Micro- scopes ; Practical Notes on Illumination ; Monochromatic Light ; Care of the Microscope, - 66 contents. Collecting Objects. Where to Find Objects ; What to Look for ; How to Capture them ; Nets; Bottle-Holders ; Spoons; Collecting Walking Cano; Water Strainer; Wright's Collecting Bottle ; Aquaria for Micro- scopic Objects ; Dipping Tubes, 75 The Preparation and Examination of Objects. Cutting Thin Sections of Soft Substances ; Sections of Wood and Bone; Improved Section Cutter; Sections of Bock; Knives; Scissors; Needles; Dissecting Pans and Dishes; Dissecting Microscopes ; Separation of Deposits from Liquids ; Preparing whole Insects ; Feet, Eyes, Tongues, Wings, etc., of Insects ; Use of Chemical Tests ; Liquids for Moistening Objects ; Re- fractive Power of Liquids ; Iod-Seram ; Artificial Iod-Serum ; Covers for Keeping out Dust ; Errors in Microscopic Observa- tions, ... 85 Preservative Processes. General Principles ; Preservative Media— Canada Balsam, Solu- tion of Balsam, Colophony, Damar Medium, Glycerine, Glycer- ine Jelly, Hantzsch's Fluid, Glycerine and Gum, Deane's Gelatine, Alcohol, Thwaite's Fluid, Boale's Liquid, Goadby's Fluids, Pacini's Fluid, Castor Oil ; General Bules for Applying Preservative Fluids, - 96 Apparatus eoe Mounting Objects. Slides ; Covera; Cells ; The Turn-Table ; Cards for Making Cells ; Hot-Plate ; "Lamps ; Eetort Stand ; Centering Cards ; Mounting Needles; Cover Forceps; Slide Holder: Water Bath; Simple Form of Spring Clip, 104 Cements and Tarnishes. General Bules for Using ; Gold Size, Black Japan, Brunswick Black, Shellac, Bell's Cement, Sealing Wax Varnish, Colored Shellac. Damar Cement, Marine Glue, Liquid Glue, Dextrine, 116 Mounting Objects. Mounting Transparent Objects Dry; Mounting in Balsam; Mounting in Liquids ; Mounting of Whole Insects ; How to Get Bid of Air-Bubbles ; Mounting Opaque Objects ; Wooden Cells ; Pierce's Cell ; Prof. Smith's Plan ; Deep Cement Cell, - 119 Finishing the Slides. Covering with Paper ; Tarnishing for Preservation ; Labeling, 124 PREFACE. Ten years ago the term " cheap " when applied to micro- scopes meant worthless ; to-day it has a very different signifi- cation, for some of our best makers have devoted their atten- tion to the production of easily used instruments of very moderate cost. This has caused a demand for a simple and inexpensive book for beginners which would teach them how to use these microscopes effectively, and it is in the hope of supplying this demand that the present volume has been prepared. As the reader who makes a comparison will readily see, it is merely an abridgement of the author's larger work on the same subject. All matter relating to the use of complicated and expensive instruments has been omitted, and several parts have been rewritten with the view of making them more simple and complete. In the unabridged edition very full directions are given for examining objectives and for the employment of the differ- ent methods of illumination. These, although of the utmost importance to physicians and students, are not available by the class for whom this volume has been prepared. The omission of all description and figures of objects may, perhaps, require a word of explanation. This book is in- tended to teach the use of the microscope, not the revela- tions of the microscope. It is, therefore, a companion to every book on Botany, Zoology, Histology, Entomology, etc., but not a substitute for them. It tells how to cut a potato, and how to examine, preserve, and mount the thin section thus obtained, but for a description of the cells and of the starch which fills them, we must refer to some work on botany of which there are several of great excellence. INTRODUCTION. Thousands of microscopes throughout the country are at the pres- ent day lying idle, simply because their owners do not know how to use them. If properly employed they might be made to afford an incalculable amount of instruction and amusement; but, as it is, they are a drag upon the popularization of science, because they convey the idea that the microscope is a difficult instrument to use, and that it is not of much account after we have learned to use it. The owners of these microscopes have examined all the mounted objects at their command, the entire number of which probably does not exceed two or three dozen, and they have no information as to the best methods of preparing common objects for examination or pre- servation. Even the objects that they possess have never been ex- plained to them, and are merely pretty toys. The fly's eye is inter- esting because it looks like a piece of netting, aud the butterfly's wing is attractive because it is probably a little more brilliant than the most brilliant silk dress, but neither of these objects interests of itself and because of its beautiful structure. Moreover it often happens that an instrument which, when first purchased, was of very fair quality, has, through ignorance and carelessness, become so soiled and dimmed that it no longer serves the purpose intended. On more than one occasion have we seen a fine microscope leave the dealer's hands in excellent order, and re- turn in a week entirely unfit for use. Microscopes in this condition, instead of being a source of instruction and pleasure, are an eyesore and an occasion of annoyance. They continually serve as reminders of awkwardness and failure, of wasted time and ill-spent money. And yet with proper instruction and a due amount of care all this might have been avoided. It is also a fact to be regretted that heretofore the microscope has not been extensively employed in the arts, and in everyday life, simply because practical men have not been taught how to ase it, and consequently have been unable to avail themselves of the advan- tages which it offers; but if carefully and judiciously selected, and properly handled, it is capable of affording an amount and kind of assistance which cannot be safely neglected. It may be made to aid in the examination of raw materials, and of the finer kinds of work; it will enable us to measure spaces which would otherwise be inap- preciable, and this, in an age when even in ordinary machine shops the thousandth part of an inch is frequently an important quantity, renders it indispensable to the careful and skillful mechanic; on the x itfTisofotJdtfidtt. farm it will enable the agriculturist to examine closely and minutely the various noxious insects and forms of fungi and blight, and thus aid him in identifying them and applying the proper remedy; and in the examination of minute seeds, such as timothy, clover, etc., it will prove a very valuable assistant, enabling him to detect any in- feriority in the quality, or any impurity or adulteration. Frequently the agricultural seeds offered in market contain minute seeds of of- fensive weeds, many of which are so small that they are not easily dis- covered by the naked eye. Every farmer and mechanic knows the value of a good pair of eyes, and he also knows that an agent which doubles or trebles our power in any given direction at once confers upon us in that respect a superiority over our fellowB. Very few men are twice as strong as their comrades; still fewer have three times the strength of ordinary men, and it may be safely affirmed that no man possesses the power of ten ordinary men. But a microscope of very ordinary capacity at once multiplies our powers of sight by ten, twenty, or even a hun- dred timeB, while those of the better class enable us to see things with a keenness and clearness which, when compared with that af- forded by the naked eye, is as more than a thousand to one. Thereare four distinct and important directions in which a mi- croscope may be made to serve us: 1. It is capable of affording the most refined and elevating kind of pleasure by the exhibition of ob- jects of extreme beauty and interest. There are few more splendid sights than the gorgeous colors displayed by some objects when viewed by polarized light, and even the tints of certain minerals, and the brilliant scales of certain insects, when viewed as opaque objects, by means of a good condenser, surpass anything that is familiar to us in our ordinary experience. On the other hand the exquisite beauty of form which is characteristic of most of the ob- jects with which the microscopist concerns himself can be fully ap- preciated only by those who have seen them. As a source of inno- cent amusement and pleasure, therefore, the microscope has few or no equals; for it may be safely affirmed that a five-dollar instrument is capable of affording gratification of greater variety and intensity, and of longer continuance, than that yielded by anything else of the same cost. This arises chiefly from the fact that most other in- struments, when once exhibited, with their slides or fixtures, lose their freshness and interest, and become old. While for the micro- scope, a few fibres of wool from the carpet, a few grains of sand from the sea-shore, or a handful of wild flowers from the field, yield ob- jects of surpassing beauty. Everything in nature and in art may bo subjected to inspection by it, and will then disclose new beauties and fresh sources of knowledge. Under it the point of the finest cambric needle looks like a crow-bar, grooved and seamed with scratches; the eye of the fly is seen to consist of thousands of eyes; and the dust on the butterfly's wing appears to be what it really is, scales laid on with all the regularity of shingles or slates on a house ; while to prepare and examine these simple objects requires no great skill and no elaborate apparatus. 2. As a means of imparting instruction to the young, the micros- cope has now become indispensable. The changes which of late years have taken place in the views held by our ablest men in regard to the best education are too well known to need even mention. No education that does not include a knowledge of natural science is now regarded as complete, and there is a very wide range of the most essential and practical knowledge that can be reached only through the microscope. Thus, when we look at a leaf with the naked eye, we see but a green mass of matter, possessing a certain beautiful form, it is true, but disclosing none of those organs which render it more complicated and wonderful than anything ever pro- duced by our most skilful mechanics. Looked at by the micro- scope, however, this same leaf is found to be made up of innumer- able parts, each one of which is highly complex and beautiful; it is furnished with mouths for breathing, with cells for storing, digest- ing and assimilating nutriment, and with ribs for strengthening its structure; and all this, which is perfectly invisible to the unassisted vision, becomes distinct and obvious when we call to our aid a microscope of even moderate power. It is true that much of this may be taught by means of books, engravings and verbal descrip- tions, but every one knows that for distinctness and impressivenets the very best engravings fall far short of a view of the real object. 3. As an instrument of research, the microscope now occupies a position which is second to none. There is hardly any department of science in which ar student can hope to reach eminence without a familiarity with the microscope. Botany and Zoology have been developed almost wholly by its aid, and so necessary is it in the study of these sciences, that Schleiden, one of the most successful of investigators says of it: " He who expects to become a botanist or a zoologist without using the microscope, is, to say the least of him, as great a fool as he who wishes to study the heavens without a telescope." In chemistry its services have been very important, and in geology and mineralogy it has opened up new fields of research which almost promise to revolutionize these sciences. Medicine has XII INTRODUCTION. long acknowledged the microscope as one of its most efficient as- sistants, and in the practice of the best physicians it is regarded as an indispensable means of diagnosis in some diseases. 4. As an assistant in the arts. Its importance in this department is but just beginning to be recognized, and in a former paragraph we have endeavored to point out a few of the subjects to which il may be applied with good hopes of success. These important and obvious advantages are not difficult to secure, provided we avoid two mistakes which are very commonly made bj beginners. One of these consists in supposing that it is only bj means of very expensive and complicated instruments that anything of value can be accomplished in microscopy. Now while it is cer- tain that, in some departments of study, none but the very best microscopes are of any value at all, it is equally certain that a verj wide range of study and of practical work can be thoroughly culti- vated by means of apparatus of very moderate cost, and of great simplicity of construction. The great discoveries of Ehrenberg, which opened up entire new fields of research and of thought, were made with a microscope which at the present day would not com- mand $25. Indeed some of the French instruments that are sold for $15 will show a very large proportion of the objects that arc figured in his earlier works. Most of the great anatomical and botanical discoveries were made with simple microscopes of no great power, and it is not many years since one of the most successful workers in the field of botany gave it as his opinion that a power ot 300 diameters is capable of showing everything that is of impor- tance in this science. The other error is of precisely the opposite kind. It is not at all unusual to meet persons who seem to think that all that is necessary in order to become a microscopist is to buy a microscope and place objects under it! Such people always entertain an exaggerated idea of the power of the microscope as an instrument of research. 'For example, they think that in order to detect adulteration all that is necessary is to place a sample under the microscope, when all im- purities will at once stand out conspicuously! To their imagination every blood corpuscle is clearly marked with the name of the animal from which it was obtained! Truth lies between these extremes. No progress can be made without steady application and persistent labor, but any person of fair average ability and a moderate degree of perseverance can soon learn to follow the beaten track at least, if not to branch out into original research. ' THE SELECTION AND USE THE MICROSCOPE. What is a Microscope 1— The microscope is an instru- ment which enables us to see either very minute objects or very minute parts of large objects. It is a very popular idea that the name microscope is applicable only to complex instru- ments of considerable power; but this is clearly wrong. A ten cent magnifying glass has as good a right to the name micro- scope as has a complicated binocular instrument with all the latest improvements. By common consent, however, the small hand instruments, without stands, are generally called magni- fiers. An attempt has been made to introduce the foreign word loupe as an equivalent of magnifier. The word loupe is, how- ever, superfluous, and is used only by ostentatious pedants, and by foreigners who are ignorant of English. What tlie Microscope Does.— It is well known that the further off any object is, the legs it appears. A house at a distance appears less than a man who is close by, and the dis- tinctness with which an object is seen depends largely upon its apparent size. Thus, at a distance, a house not only appears very small, but the windows cannot be distinguished from the rest of the building. As we draw nearer it becomes apparently larger, and the different parts become more distinct. First the windows are seen clearly, then the individual panes of glass, then the bricks, and finally the grains of the material of which the bricks are made. When, however, we approach too closely we again find it impossible to see distinctly, as may easily be 14 SELECTION AND TOE proved by a very simple experiment. Place some fine print, such, for example, as the present page, at a distance of six feet from the eye, and gradually move closer to it. At six feet the letters will be indistinguishable; at two feet they will be quite distinct; at one foot still more distinct; at three inches they •will be quite blurred. There is, therefore, a limit to the degree of closeness with which we can approach any object for the purpose of examining it, and the object of a microscope is to enable us to get close to it, as it were, without blurring our view. If, without changing the distance of the eye from the paper (three inches) we introduce between the two a lens of one inch focus, and bring it into proper position, we will find that the indistinctness formerly complained of disappears, and the object is now not only seen clearly, but appears very much magnified. That objects appear large in proportion to their nearness to the eye may be thus shown: Take two slips of paper printed with type of the same size (two clippings from a newspaper answer well) and place one at a distance of ten inches from the eye and the other at a distance of five inches — the edge of the upper slip being placed so as to lie about the middle of the lower one. In this way we can readily compare the apparent sizes of the type on the two slips, and one will be found to appear just twice as large as the other, though, of course, we have the evidence of our senses to prove that they are precisely of the same size. Moreover, as the usual distance for distinct vision is about ten inches, in persons of middle age, it will be found that a lens which enables us to view any object clearly and distinctly from a distance of one inch, will enable us to see it just ten times larger and ten times more dis- tinctly than we could do when looking at it from a distance of ten inches. A consideration of these facts led the late Dr. Goring to propose the name engiscope as a substitute for the word microscope — the word engiscope signifying to see things at a very short distance. The facts which we have just detailed must, however, be re- garded as illustrations, rather than explanations of the action of the microscope. It is evident that the power of a lens to in- crease the distinctness with which any object is seen, depends not only upon the action of the lens upon the rays of light, but upon the influence which such modified light exerts upon the OP THE MICROSCOPE. 15 organs of vision. Now, the eye, considered merely as an optical instrument, is in reality a small camera obscura in which the cornea, crystalline lens, and other transparent portions, combine to throw upon the retina an image of external objects. That the transparent portions of the eye do in fact act as a lens, and throw a real image upon the retina or posterior portion of the eye, is easily shown by taking the fresh eye of an ox and grad- ually shaving off the coating at the back until it becomes transparent. If the eye, so prepared, be then held towards a window or any very bright object, a distinct but inverted image of the window or other object will be see on the coat of the eye. The action of the eye in this case is the same as that of a lens, and the general mode of action of lenses under such cir- cumstances may be easily illustrated by means of a common hand magnifier or even a spectacle glass. If the reader will hold before a window, at a distance of, say, six feet, a sheet of white paper, and will place a magnifisr in front of the paper, then by properly adjusting the distance between the magnifier and the paper, a picture of the window will be thrown on the latter. If the magnifier and paper be now removed to a dis- tance of twelve feet from the window, the picture of the latter will be only half as large as it was in the first place, and it will also be found that the distance of the lens from the paper will have to be readjusted and made less. That the eye possesses this power of adjustment we are all conscious, for we feel that if, when the eye is adjusted for the distinct vision of distant objects, we suddenly look at those which are near, the condition of the eye requires to be changed before a distinct view can be had, and to make this change requires an effort of which we are perfectly conscious. When a lens is held in front of a sheet of paper, so as to throw on the latter a distinct image of the objects in front of it, the distance between the paper and the lens is called the focal distance or focal length of the latter. This, as we have just seen, varies with the distance of the object which gives the image. In order, therefore, to secure a standard in this respect the object selected is always one whose distance is so great that it may be practically regarded as infinite. 16 SELECTION AND USE. When we examine an object, first at a distance, and then close at hand, -we see it through the medium of two different sets of rays, those in the latter case entering the eye in such a direction that the image thrown on the retina is larger than the image produced when the object is more distant. The lens acts, however, by bending the rays so that the same set, which, if allowed to pursue their natural direction would not produce a distinct image, are caused to enter the eye in such a direction that the image is large and clear. The manner in which the lens acts . to produce these effects is not difficult to understand. It is true that the ultimate causes which produce these phenomena are beyond our knowledge, but in this respect the ablest philos- opher has very little advantage over the veriest tyro. It may ' be difficult also for the general reader to follow the mathe- matical demonstrations of the action of lenses. There are, however, a few simple facts which are easily understood, or at least demonstrated and accepted as facts, and which, when clearly and firmly grasped by the mind, render the construction of the microscope comparatively easy of comprehension. There are two ways in which the subject may be studied. We may examine the facts experimentally, by using lenses and actual eyes in the way we have described, or we may fol- low the course of the rays as laid down in any good book on optics. A combination of both methods will of course give the clearest views on the subject, and we would therefore ad- vise the reader to provide himself with a few lenses of various degrees of curvature, and consequently of various magnifying powers, and test all the statements made in the text. He will thus acquire such a practical knowledge of the action of lenses as can be obtained in no ether way. For this purpose the cheapest lenses are good enough. One or two cheap magni- fiers and a few glasses from old spectacles will serve every pur- pose. The simplest methods of arranging such lenses will be found in a note on a subsequent page, and although very ac- curately made tools are required for the construction of ser- viceable optical instruments, it will be found that a very large number of simple but valuable experiments may be worked out with the aid of a few wooden rollers and a little paper and paste. OF THE MICROSCOPE. 17 While the magnifying power of lenses depends upon their focal length, this in turn depends upon the material of which the lens is made, and also upon the curvature given to its sur- faces. Lenses of precisely the same form, and made respect- ively of diamond, flint glass, crown glass and Canada balsam would possess different magnifying powers; the diamond mag- nifying most, the flint glass next, crown glass next, and Canada balsam least of all. On the other hand, of two lenses composed of the same material, that which has the sharpest curvature to its surfaces will magnify most. Now, on reflection, it will be evident to even the least mathematical mind that lenses which have very sharp or quick curves must of necessity be small. Suppose the curve which bounds the figure of a lens has a radius of half an inch, it is evident that the largest lens which could be made with this curve would be one inch in diameter, and then it would be a perfect sphere. Most lenses, however, resemble thin slices off the spheres, or in some cases two such slices joined together, so that the diameter of the lens is in general greatly less than the radius of the curves which form its surface. Therefore, we see that all lenses of high power are of necessity small, and when lenses are required of very high power they become so minute as to be handled only with great difficulty. Indeed, before the modern improvements in the microscope, many of the lenses used by scientific men were nothing more than little globules of glass, brought to a round form by fusion. We have made this lengthened explanation of a very simple matter because we have found amongst beginners in micro- scopy a very general idea that large lenses are the most power- ful. " Send me one of your largest and most powerful mag- nifiers," is an order with which every optician is familiar, and yet such an order contains a contradiction in terms. A lens cannot possibly be large and magnify greatly at the same time. The Different Kinds of Microscopes.— Microscopes are divided into two classes — simple and compound — the dif- ference between them being purely optical, and not mechanical; for a simple microscope may be very, complex and expensive, while, on the other hand, a microscope may be. compound and 18 SELECTION AND TTSE yet contain very few parts. Thus the little vertical French microscopes, 'which cost only $2,50, are compound, although very simple in construction, while a simple microscope, if bin- ocular, and provided with all desirable adjustments, might be a very complicated affair. The difference between simple and compound microscopes is this: in the simple microscope we look at the object directly, while in the compound microscope we look at a magnified image of the object. In the simple microscope, objects are always seen in their natural position, while in the compound microscope they are inverted, and right becomes left, and left becomes right. This makes it very diffi- cult for beginners to work upon objects under the compound microscope; and hence simple microscopes are almost always used for dissecting and botanizing. It is true that by adding more lenses, and making the instru- ment still more compound, we can again invert the image, and thus bring it back to its original and natural position, and almost all the very expensive microscopes are furnished with these extra lenses arranged in a piece of accessory apparatus technically known as an erector. The distinguishing feature of the compound microscope remains, however, the same. Certain forms of the microscope, in which concave lenses are substi- tuted for the usual convex form, also give erect images, but this does not affect the general truth of the statement just made. Simple microscopes frequently consist of more than one lens. Thus, in using the ordinary pocket magnifiers with two or three lenses, it is usual to employ all the lenses at once, look- ing at the object through two or three lenses at the same time when a high power is required. In this case, however, the two or three lenses are placed close together and act in the same way as a- single lens, with surfaces more -sharply curved than •those of any of the lenses forming the combination. 'Under such circumstances the image is not inverted, but if we now ■separate the lenses sufficiently, we will find that on again bring- ing the object into focus, the image is inverted and greatly .enlarged. Moreover, it will be found that the magnifying power may be greatly increased by increasing the distance be- tween the two lenges, and it wiUalsp be found that as the dis- OF THE MICROSCOPE. 19 tance of the two lenses from each other is increased, the dis- tance at which the combination is placed from the object must be made less and vice versa.* The early forms of the compound microscope consisted of little more than the two lenses we have just described, but the modern instrument, even in its simplest form, is a vastly more complicated arrangement. In the best forms, for the lcna next the eye there is substituted an eye-piece consisting of two lenses with a diaphragm between them, while the objective, or lens next the object, is composed of from four to ten different pieces of glass, forming two or more lenses, which are so arranged that each shall correct the defects of the others, and this optical combination is mounted on a stand which is sometimes a mar- vel of mechanical ingenuity. *The student who possesses a little mechanical genius and a desire to become experimentally acquainted with the properties of lenses and the construction of the microscope, would do well to procure a couple of cheap lenses, say one of half inch focus, and one of about two inches focus, and test by actual trial the statements made in the text. Such lenses may be con- veniently arranged in a tube formed of writing paper and gummed on the edges. All the most important properties and defects of lenses may be thus illustrated and studied. By means of a little extra care, two such lenses, ar- ranged as we have described, in tubes blackened on the inside, and mounted on a little wooden stand, the focus being adjusted by sliding the tube hold- ing the lenses within another tube, also of paper, will give not only a very fair view of such objects as the wing of a fly, the scales on a butterfly's wing, and even the barbs on the sting of a bee, but it will show the globules of blood quite distinctly, and we have even given a very interesting exhibi- tion of the circulation of the blood in the foot of a frog by means of a temporary arrangement of this kind, which we put together for the pur- pose of explaining to a little girl the construction of the microscope. We would not recommend any one to use such a microscope for purposes of work or study, because the fallacies to which it may give rise are too numerous and too serious. But any boy, or even girl, who will undertake the construction of such an instrument, cannot fail to obtain thereby an amount of information which the perusal of volumes would not give. As hints towards aiding our young friends, we may remark that our tubes were made of the best stiff paper, rolled up tight and pasted only along the outer edge. The lenses were secured in their places by being attached to the bottoms of pill-boxes, holes being punched through to admit the light. Pill-boxes with holes were also used for diaphragms to reduce the effects of aberration. A piece of mirror reflected the light, and the sides etc., of an old cigar box furnished material for the stand. Fifly cents covered all expenses. 20 SELECTION AND USE Essential Parts of the Microscope.— When a good lens is held steadily at a certain distance from an object which is properly illuminated, this distance depending upon the form and material of the lens, we are enabled to see the object clearly and distinctly. When, however, this distance is either in- creased or diminished, the object becomes blurred and indis- tinct. The point at which vision is most distinct is called the focus* of the lens, and when we are able to see it clearly the object is said to be in focus; when the distance is either in- creased or diminished, it is said to be out of focus. An object is said to be within the focus when the lens is too near it, and beyond the focus when the lens is too far away. The performance of any lens depends greatly upon the ac- curacy with which it is adjusted to the correct focal distance, and the steadiness with which it is held there. For all ordi- nary purposes, lenses which do not magnify more than ten diameters may be very conveniently held in the hand without any special means of support; but when the power ia much greater than this, or where, as in the compound instrument, the microscope is bulky and heavy, it becomes necessary to use some mechanical contrivance which will hold, the microscope steadily in its position in relation to the object, otherwise the view.becomes indistinct. Thus a good lens, magnifying from thirty to forty diameters, will very readily show the individual corpuscles or globules in the blood of the frog, provided it is arranged on a steady support and accurately adjusted for focus. If merely held in the hand the corpuscles will probably be in- visible. Hence the importance of providing efficient means for adjusting the focus and holding and illuminating the object, and the object of the stand is to furnish these means in a com- pact and convenient form. Every microscope, therefore, *It is scarcely necessary to Inform the reader that the focus described iu the text is not precisely the focus of the lens itself, But the focus of a compound lens of which the eye forms one element. Hence the focal dis- tance varies with different eyes, and so does the apparent size of objects. To short sighted people objects appear of larger size than they do to persons of ordinary eye-sight. In working with the compound microscope, we frequently find that different people require a different focal adjust- ment. OF THE MIOBOSOOPE. 21 whether simple or compound must possess: 1. Certain means for supporting the object and placing and maintaining it in proper position; 2. Means for illuminating the object, whether it be opaque or transparent; 3. Means for transmitting to the eye an enlarged image of the object. NAMES OF THE DIFFERENT PARTS. The different parts which are employed for securing these several ends, have been constructed of an almost endless variety of forms, according to the fancies of the different makers and the requirments of different microscopists. The following are the names of the essential parts of a compound microscope of ordinary construction. The names of the different parts of the simple microscope are the same as those of the compound microscope, but the latter has several parts which do not exist in the former. The Stand is the term properly applied to the entire frame used for supporting and illuminating the object and carrying the optical part, the latter consisting of the eye-piece and the objectives. Stands are frequently sold separately, or furnished with eye-pieces only — the purchaser making such a selection of objectives as may best suit his special needs. The Base or Foot is that part which supports the rest of the stand. The Body is the tube to which the eye-piece and objectives are attached. The Arm is that part which carries the body. A Collar n a short tube through which anoiher tube (the body or the draw-tube, for example) is made to slide. In many microscopes the body does not slide in a collar. The Stage is the plate upon which the object is placed for examination. The Eye-piece is the short brass tube, with its lenses, which is next the eye. The eye-piece contains an Eye- Glass, which is that next the eye; a Field- Glass, placed next the objective, and a Diaphragm, consisting of a brass plate with a hole through it, and so arranged as to cut off the outer rays of light. The 22 SELECTION AND USE tube in which these lenses are secured is in general movable, and the best microscopes are furnished with several eye-pieces of different powers. We may here remark that where a micro- scope is furnished with several eye-pieces, the shortest eye-piece gives the greatest magnifying power. The Object- Glass or Objective is the lens or lenses which is placed next the object. The term is frequently applied to the glass plate or slide upon which the object is placed, but this use of the word is entirely wrong, and tends to produce con- fusion. A Draw-tube is a secondary body which receives the eye-piece, and slides within the main body like the draw of a telescope. It enables us to increase the distance between the eye-piece and the objective, and thus to change the magnifying power, as explained in a previous paragraph. The objective is moved to or from the object by two methods, which are called respectively the coarse and fine adjustments. The Coarse Adjustment is used for bringing the objective ap- proximately but rapidly into focus. To effect this the body either slides through a tubular collar or is attached by means of dovetail slides to the arm, and in either case it is moved up and down either by a rack and pinion (or some substitute there- for) or directly by hand. The Fine Adjustment is employed for bringing the object exactly into focus. It usually consists of a fine s^rew. which moves either the entire body or the lower part of it. In some cheap stands, the fine adjustment is effected by moving the stage towards the objective. The Mirror reflects the light, and causes it to pass through the object and the body of the instrument. A Sub-stage is furnished with some instruments. It is used for holding and centering various means of illumination. Clips are springs attached to the stage for jthe purpose of holding in place the glass slide or plate carrying the object. The Object is that which is subjected to examination. It is usually mounted upon A Slide, or plate of glass, which is laid upon the stage. OF THE MICROSCOPE. 23 DIFFERENT FOEMS OF THE SIMPLE MICEOSOOPE. To describe the different forms in market, either of simple or of compound microscopes, -would require a large volume. "We shall therefore content ourselves 'with a description of certain typical models which afford variety enough for all practical purposes. Hand Magnifiers. — These are so generally useful and applicable that no person who attempts to work much with the microscope can possibly do without one. They are found in market in a great variety of forms, styles of mounting, and price, and are too well known to need minute description. Large lenses, magnifying two or three times, are mounted singly, and used chiefly for the examination of pictures, and as reading glasses; the smaller sizes of the same style serve for the examination of fine engravings. Very small lenses of con- siderable power, and simply mounted in a frame, are also sold by most opticians. They are known as "watch-charms," and magnify about fifteen diameters. We have also seen a very powerful magnifier mounted in a little ring attached to a pair of eye-glasses. For the purpose of the student and naturalist, a very excellent form is that which is shown as attached to the Excel- sior microscope. It consists of three lenses, mounted in frames, and enclosed in a case so as to be perfectly protected. Each lens has a different focal length, and the three, when combined, give a magnifying power of twenty-five to thirty diameters. Being very portable, and possessing a variety of powers, it is a favorite form of pocket microscope. Magnifiers composed of two or more lenses, are to be had of two very distinct kinds. The lenses may either be simply united in one frame, without any special adaptation to each other, or the instrument may consist of two or more achromatic lenses combined together in a fixed and accurately deter- mined relation. Examples of the former are found in the ordinary two and three lens magnifiers we have just described; the latter are not so common, since they are somewhat expen- 24 SELECTION AND USE sive when well made, but they give most excellent results. They are known as achromatic doublets and triplets, and several makers have become famous for the simple microscopes of this class made by them. The late K. B, Tolles, of Boston, came early into the field with lenses which soon became famous, and at present most of the prominent microscope makers, such as the Bausch & Lomb Optical Company, James W. Queen & Com- pany and others, make a specialty of lenses of this kind. The simple microscopes of Steinheil, of Munich, and Browning, of London, are also of notable excellence. Those made by Brown- ing are known under the name of Platyscopic lenses. Where two or more simple lenses are used together (without being combined so as to form a compound microscope) the power of the combination is always equal to the sum of the powers of the separate lenses. Thus if we have a lens of half an inch focus and one of one inch focus, one magnifyingten and the other twenty diameters, the resulting power is thirty and and not two hundred times. In the compound microscope, on the other hand, the' combination of an objective magnifying twenty diameters with an eyepiece magnifying ten diameters, gives a magnifying power of two hundred diameters. Two or more lenses, properly adapted to each other and used together, give results greatly superior to anything that can be ob- tained from a single lens, at least so far as clearness and accuracy of definition is concerned. But when used as a working or dis- secting microscope, they are open to the objection that the dis- tance at which they must be placed from the object is very small, and hence it is frequently inconvenient to use them for work- ing upon objects. Thus if we have a plano-convex lens of a quarter of an inch focus, and one of three quarters of an inch focus, and place them at a distance of a sixteenth of an inch from each other, we will have a very good magnifier which will enlarge objects about thirty-five to forty times, but we must place it at but a very short distance from the object. IE we separate the lenses a little, the definition will be improved, but the working distance, as it is called, will be diminished. Those •who have studied optics are quite familiar with these facts, but the ordinary reader does not always think of them, and yet they OF THE MICBOSOOPE. 25 are very important when we come to choose a microscope for working or dissecting purposes. Watch-Makers' Eye-Glasses.— These are well known, and may be obtained of almost any power within the useful range of a single lens. The eye-glass ordinarily used by watch- makers magnifies about eight times, but glasses magnifying twenty diameters are not uncommon. Glasses of the latter power are usually doublets, that is, they consist of two lenses, arranged together, one being of much longer focus than the other. If well-made they give excellent definition and a large field, and, when mounted on a stand, are very serviceable as dissecting microscopes*, especially in working upon coarse objects, and picking out shells, the larger foraminifera, etc. Their form enables us to support them by means of a small wire ring, arranged as in a retort stand, and the large bell- mouth of the frame prevents any light from entering the eye, except that which has passed through the lens. They are very cheap, and any intelligent boy can make a tolerable stand for one. The same stand will answer for several glasses of differ- ent powers. Engravers' Glasses.— These are mounted in frames, in the same manner as the watch-maker's eye-glass, but as they are larger, and are therefore not so readily held in the eye, after the fashion of the latter, they are always used with a stand of some kind. Those of the best quality are, in general, doublets, which give a large field of view, with very good definition, and they are altogether the best microscopes for examining bank bills, fine engravings and similar objects. *The term dissecting microscope is applied to all microscopes used for working upon objects under moderate magnifying powers. They are used not only for dissecting, properly so called, but for the study of botany, mineralogy, etc., as well as for numerous investigations in the arts. A good microscope of this kind is absolutely indispensable to those who hope to do more than merely look at objects prepared by others. In sub- sequent paragraphs we describe some of the best instruments of this kind. A complete dissecting microscope should be furnished with stand, mirror, etc., and if the student can afford it, there should be some good mechanical means of adjusting the focus. 26 SELECTIOSf AND ttSE The Coddington Lens.— Whenever a power greate* than twenty diameters is required for examining objects, a Cod- dington, if well made, will be found to be the best lens in use, always, of course, excepting the carefully corrected doublets and triplets previously mentioned. The price of the latter, however, is in general four to eight times that of a good Cod- . dhigton. It has this defect, however, that the working focus is very short, and therefore for a dissecting microscope a doublet is to be preferred. In using a Coddington lens, great care must be taken to secure good illumination of the object, and the shortness of the focus makes this difficult to those who have had no experience. The Stanhope Lens is similar in form to the Codding- ton, but is very different in construction. It consists of a cylinder or rod of glass, one end of which is rounded so as to form a lens, while the other end is either flat or slightly curved. The distance between the lens and the flat surface is exactly equal to the focal distance of the lens. Transparent objects, such as the scales of insects, animalcules in water, etc., are sim- ply placed on the flat surface of the glass cylinder, and when looked at through it, they appear greatly magnified. It is easily used, but can not well be employed as a working micro- scope. It is this kind of lens that is used in the construction of those watch charms in whieh a large picture is seen on look- ing through a very small hole. The picture is a photograph attached to the flat end of a small glass rod, the other end of the rod being formed into a lens of exactly the right focal length required to show the picture clearly and considerably magnified. Lenses and photographs of this kind are usually mounted as miniature opera-glasses. Stands for Simple Microscopes.— For ordinary pur- poses of examination, the magnifiers we have just described serve very well when merely held in the hand, but their per- formance is greatly improved when they are mounted on appro- priate stands, which not only enable us to adjust the focus with great accuracy, but which hold the lens steadily in relation to the object, and thus prevent any necessity for that constant ad- justment of the eye itself, 'which always occurs when a lcnstrem- Otf THE MIOEOSCOfB. 27 bles. Of the simple microscopes in use there are but two that re- quire attention — Easpail's and the Excelsior. For & description of the elaborate dissecting microscopes of the London micro- scope makers, as well as those of Nachet, and others, we must refer to the large works of Carpenter, Beale, Prey, etc. Raspail's Microscope.— In this instrument the magni- fying glasses are supported by an arm which projects horizon- tally from an upright column that screws into the top of a box, in which the entire instrument is packed when it is not in use. This column also supports a stage which may be moved up and down by rack work, and a mirror for reflecting the light up- wards through the object. This was the instrument so largely used by Easpail in his investigations into the structure of plants, and described by him in his works, and hence it has been called by his name. It resembles very closely the instrument called the Society of Arts Simple Microscope, which is manufactured by Mr. Field of Birmingham. Tlie Excelsior Microscope.— The accompanying en- graving gives a very clear view of this microscope, which is constructed as follows: To one end of the lid of a small wooden case or box, is at- tached one of the ends of the box; and when the lid is reversed and turned upside down, it may be slid into the groove which usually receives it, and then forms a stand for the lenses and glass stage, as is shown in engraving. The lenses and stage are supported by a steel rod, D, the lower end of which is hinged to the lid, so that it may be turned down and he in a groove provided for it. When raised into the position shown in the figure, it is held very securely in place by means of the button, E; and this button also serves to retain it in the groove when it is turned down. The glass stage, G, which is fitted into a frame of hard rubber, slides easily on the stem, D, so as to be readily adjustable for focus, while at the same time it may be firmly fixed, by means of a set-screw, at any desired height, and will then serve as a stage for dissecting purposes. The frame which holds the lenses fits on to the top of the stem. A mirror, H, is fitted into the case, and is readily adjustable by means of the button shown on the outside, so that light may 28 sEiiEcmoN and toe be reflected up through the stage when the objects to be ex- amined are transparent; and when they are to be viewed by re- flected light there is a dark ground of hard rubber (not shown in the engraving) which is also carried by the stem, D, and may be turned under the stage, so as to cut off all transmitted light. Dissecting needles (K and L), with neat handles, fit into appropriate grooves. When the lenses and stage are re- moved from the stem they are readily packed in the case; the THE EXCELSIOE MICROSCOPE. stem is then turned down and held in its groove by the button, E; the lid is drawn out of the groove, turned over, and re- placed so that the vertical piece (0) closes the open end of the box, and the whole thing is packed into a compass which readily admits of its being carried in the vest poaket. The lenses are well made, and being provided with a proper diaphragm, great clearness of definition is secured. Two styles OP THE MICROSCOPE. 29 of frame are sold, one containing two, and the other three lenses, the latter being altogether the cheapest, in proportion to the power furnished. The magnifying powers are about as follows: With the lens of longest focus, five diameters; with the lens of medium focus, eight diameters; with the lens of shortest focus, ten diameters. When the lenses of shortest and medium foci are combined the magnifying power is about eighteen diameters; all three lenses together give a power of twenty-five to thirty diameters. In using a combination of two or more lenses, the lens of shortest focus should always be placed nearest to the object. As a dissecting microscope for botanical, entomological, and physiological work, this instrument is very efficient and con- venient. The glass plate is fitted into the stage so as to form a cell capable of holding water, so that dissections may be carried on under that liquid, or aquatic animals may be kept alive and examined at leisure. The stage may also be turned, so that the flat side will be up when so desired, in which posi- tion it is most convenient for some purposes, such as dissec- tions and the teasing out of tissues by means of needles. The only serious defect in the Excelsior microscope is that it is not sufficiently steady for ordinary work, the case which forms the base or foot being, for portability's sake, made quite small. This difficulty is, however, easily remedied by screwing the case to a piece of pine board six inches long, four inches wide, and three-quarters of an inch thick. A single small screw, which does not deface the instrument, is sufficient, and when the microscope is to be carried in the pocket it is easily de- tached from its temporary stand. Its low price, $2.75, is a strong recommendation. A very serviceable stand for a simple microscope is easily ex- temporized as follows: Procure a good sound wine cork and bore two holes through it, the holes being at right angles to each other, and to the axis of the cork. The holes should be of the right size to slide easily, but firmly, on a wire about the sixteenth of an inch in diameter. One piece of such wire is stuck perpendicularly in a wooden foot, and serves as a stand upon which the cork slides up and down; another piece of wire has a ring at one end for holding the magnifier, while the 30 SELECTION AND USE other end is thrust through the second hole in the cork and is supported by it. Whenever a piece of apparatus is to be supported steadily, while at the same time it is necessary that it should be easily moved and adjusted, nothing serves so well as a fine cork sliding on a smooth wire. Twenty-five cent Microscopes.— Before leaving this subject it may be well to say a few words about those very cheap microscopes which have been so extensively advertised. We frequently see in the papers an advertisement in which some person offers to send for twenty-five cents a microscope which will show animalcules in water, globules of blood etc., etc., and the question naturally arises, Are these microscopes good for anything, or is the advertisement a swindle — the advertiser taking the money and sending nothing in return? As a general rule, those who send to such advertisers, receive in return, a plate of brass or lead, with a glass bead fastened in a hole in the centre. The glass bead is formed by fusion and is frequently ground flat and polished on the side by which it was attached to the thread or rod of glass from which it was made, forming in such cases a hemispherical lens. Such lenses are very easily made by any one. Take a strip of flint glass, such as a piece of flint glass tubing/ or a piece of glass rod, draw it out to a thread in the flame of a spirit lamp, fuse the end and allow it to gather into a drop. Give plenty of time and a good strong heat, so that the surface of the little globe may become well-fused and truly round. The best re- sults are always obtained by holding the thread perpendicularly, as when held horizontally the globule is apt to become dis- torted. Make one or two dozen of these, and in separating them from the glass rod leave about an eighth of an inch of the latter attached to .each globule, to serve as a handle, in the next step of the process, which consists in inserting them to about half their depth in a plate of cement, consisting of shellac thickened with very dry and finely powdered pumice- stone. To form such a wax plate, melt some shellac in a ladlo or large iron spoon, mix it carefully with as much powdered pumice-stone as can be conveniently stirred in, remove it from OF THE MICEOSCOPB. 31 the fire, Btir well until it begins to stiffen, and then pour it out on a flat metal plate — the surface of a smoothing iron answer- ing very well. The plate of cement should be from one-half to three-quarters of an inch thick, and the little globules are easily fastened into it by seizing them by the small handles left on them, holding them by a pair of forceps in a lamp flame until they are hot enough to melt the cement, and then pressing them in to about half their depth or a little more. When quite cold they will be very securely held. The little handles, or tails, are now nipped off with a pair of cutting pliers, and the glo- bules ground all at once on a fine grindstone, or still better on a metal plate charged with emery. When they have been re- duced nearly to the surface of the plate of cement, they should be ground with emery of the finest kind, and as soon as all coarse scratches have been removed they should be polished on a buff leather with crocus martis or putty powder. When finely polished they may be removed from the cement by means of a small chisel, and any cement that adheres may be dissolved off by means of alcohol. They are then mounted in thin plates of lead, brass, or, what is better still, vulcanite. Out of two dozen such globules, carefully made and well polished, three or four may be obtained that will give satisfactory definition, and it was with such lenses that the early microscopists made many of their discoveries. These men, however, took great pains in making and polishing them, and rejected hundreds as unfit for use. The objections t c» the microscopes of this kind, that are ordinarily sold, are that they are badly made, and that good and bad are sold together without any selection being exercised. But, even if well made, they are very difficult to use, and very unsatisfactory in their results, even in the hands of persons of great skill. The polish of a fused surface never equals that of a surface finely cut and polished, as every housekeeper that is familiar with common, and with cut glass, very well knows. The fused surface of these little globes is, therefore, always more or less, covered with striae or very minute ridges which interfere with their defining powers, and we have described thus minutely the process of their manufacture, rather for the purpose of giving our readers such information as will enable them to understand how they can be sold so cheaply, than in the hope that they will endeavor to make them for themselves, 32 SELECTION AUD USE Penny Microscopes.— A few years ago a man in London made a living by selling through the streets a microscope which would show the eels in paste and vinegar, and of which the price was only one penny, (equal to two cents.) These micro- scopes were thus made: In the bottom of a pill-box he punched a small hole and then blackened the inside of the box. In this hole was placed a drop of Canada balsam or damar varnish, which was allowed to dry. When hard, the balsam formed a very tolerable lens. A drop of water, balsam, or varnish, laid on the under side of a slip of clear glass will often enable us to extemporize a microscope capable of doing good service in the hands of a skillful observer. The outline of the drop should be perfectly round, and the glass plate should be held as level as possible. We have derived great assistance from such a lens, when better could not be had. The Craig Microscope.— This microscope at one time attained an unprecedented degree of popularity, not on account of its merits, but because of the extensive puffing and adver- tising which it received. It consists of a vertical frame, some- what like that of the cheap French microscopes, having a mirror, but no sliding tube, as there is no occasion for any. The slide which holds the object is slipped through a horizontal slit cut in the stand, and the lens with its frame is laid on it. The lens is a fused bead of glass set in a little frame, to the under side of which is attached a thin plate of glass, whose lower surface is exactly in the focus of the bead, so that when a drop of water or vinegar is placed on the glass plate, or such objects as insects' scales, wings, etc. , are laid on it, they are ex- actly in focus. Hence, this microscope is said to require no adjustment for focus. This is true when the objects to be ex- amined are actually in contact with the glass plate, but when we wish to examine objects that are covered with thin glass (as all valuable preparations should be) or objects having a percep- tible thickness, it is impossible to adjust it for focus, and hence it is impossible to examine such objects satisfactorily. OS THE MICROSCOPE. 33 ON THE SELECTION OF A MICROSCOPE FOE PRAC- TICAL PURPOSES. The object of all the information given in the preceding pages, is to enable the reader not only to understand and use the microscope, but to select one judiciously; and, therefore, in every section we have offered hints bearing in this direction. We now propose to give tbe reader such special instructions as are necessary in addition to those previously offered. In selecting a microscope, regard must be had, not only to the excellence of the instrument, but to its adaptability to the purpose for which it is intended, and to the person who is to use it. A complicated and expensive compound microscope, if placed in the hands of a person having little experience or skill, would evidently be worse than wasted, while to attempt to con- duct elaborate and delicate investigations by means of a cheap non-achromatic instrument, would simply be to throw away time, and wantonly incur the risk of serious errors. And yet no mis- take is more frequently made. A microscope is wanted; the purchaser is liberal with his means, and he is saddled with an ex- pensive instrument entirely unsuited to his requirements. Or, on the other hand, a physican or student of limited means re- quires an instrument, and being unable to afford the price of a really good one, he is induced to purchase a cheap affair, whose indications, when applied to the subjects for which he requires it, are entirely unreliable; whereas, he ought to be told that if he cannot afford a microscope with good objectives, he ought to leave microscopy in its applications to medicine and physio- logy alone. So, too, we often see compound microscopes sold to students of elementary botany, when a cheap dissecting mi- croscope is really what they need. It would be impossible to give anything like a list of special cases in which the different styles of microscopes prove most 34 SELECTION AND USE useful : the reader whose attention is called to this point will have little difficulty in deciding the question for himself. We merely give the general rule, that where dissections of plants and animals are to be carried on, a simple microscope should in general be chosen, while the compound microscope fur- nished with good objectives, is indispensible whenever high powers are required for the examination of objects. Having decided upon the kind of microscope that is needed, the next step is to determine the individual quality of the dif- ferent instruments that may be offered to us. To do this thoroughly, it will in every case be found a good plan to take up, point by point, all those elements that are necessary or desir- able in a microscope, and in this way subject the instrument to the most careful scrutiny. Unless a microscope is made specially to order, it will be difficult to find one that will com- bine all desirable features, but the plan we suggest certainly enables us to decide most readily and accurately as to the pres- ence or absence of those points which are desirable for our pur- poses. The following are the chief points that demand atten- tion: Magnifying Power.— We place this first, because usually the first question in regard to a microscope that is asked by be- ginners is, "What is its magnifying power? " Nowmagnifying power, although an important element, is after all but a secondary consideration. A microscope magnifying a thousand diame- ters could easily be made and sold at a profit for five dollars, and a few cents expended in paper and paste will at any time double, or even treble, the magnifying power of an ordinary compound instrument. The proper question is not how much does a microscope magnify, but how much will it show. A magnifying power of one hundred diameters, obtained by the use of first-class objectives, will enable us to see more of the true structure of an object than could be reached by a magni- fying power of five hundred, the lenses in the latter case being of inferior quality. But, although not the first consideration, rragnifying power is a feature of sufficient importance to deserve careful deliberation, and without a knowledge of the powers required, and the mode in which they are expressed, the begin- OP THE MICROSCOPE. 35 ner 'will often encounter difficulty. Both these points being es- sential, therefore, before discussing the magnifying powers best suited to different purposes, it may be well to say a word in regard to the mode in which magnifying power is always ex- pressed by scientific men. When we look at a small object through a microscope, and see it magnified to twice its length, it is evident that its breadth is also magnified twice, and consequently its surface, no matter what the shape may be, is magnified four times. It might also be said that as we only take cognizance of bodies having a sen- sible thickness, this thickness must be magnified twice, and therefore the object is magnified twice four, or eight times. The latter, however, is a view -which is never insisted upon, and even those who claim the most for their microscopes, never do more than express the magnifying power in surfaces. Scien- tific men are, however, agreed tliat to express a magnifying power in surfaces is to convey a wrong impression in regard to the assistance rendered by the instrument to the natural vision, for a careful study of the physiology of vision, teaches us that our power to appreciate and distinguish the features of any object depends upon the distances to which the characteris- tic points of that object are separated, and this can be meas- ured only by linear, and not by superficial units. There are other considerations which lead to the same conclusion, but for the beginner it is sufficient to know that all scientific mi- croscopists are agreed that when the magnifying power of a microscope is stated, it shall be stated in diameters, and not in areas. By common consent, then, ten times means ten diame- ters. And yet it is a very common thing for charlatans, and those who wish to deceive the public, to say that a microscope sold by them magnifies ten thousand times, or one hundred di- ameters, and as " ten thousand times " is much more readily appreciated by the popular mind tlian "one hundred diame- ters," the majority of those who read such statements suppose that they will be enabled to see ten thousand times more than they could see with the naked eye, which assuredly is not the case. In some instances these advertisers do not even state the diameters. We have now before us, clipped from a journal of deservedly good reputation, an advertisment which reads as 36 SELECTION AND TOE follows, omitting what printers call the " display " arrangement of the words : ' ' Microscopes constructed on scientific principles magnifying 10,000 times." The microscope in question, as we learned by personal examination, gives a magnifying power of about one hundred diameters. Carpenter speaking upon this point says: " The superficial magnifying power is of course es- timated by squaring the linear ; but this mode of statement is never adopted by scientific observers, although often em- ployed to excite popular admiration, or attract customers, by those whose interest is concerned in doing so. " We would, therefore, advise our readers to look with suspicion upon any concern advertising in this manner. Of course an advertisement claiming a magnifying power of "10,000 areas or 100 diame- ters " is unobjectionable, because both expressions are placed upon an equal footing. It must also be borne in mind that great though unintentional mistakes are often made by dealers in stating the power of the microscopes they offer for sale. Not long ago a friend told us that he had been offered a small microscope having a magnifying power of 500 diameters, for a moderate sum. We called to see it, taking the precaution to put a micrometer and a foot rule in our pocket. By actual measurement the highest magnifying power of this microscope was 45 diameters ! Another instance occurs in the catalogue of a well-known and honorable business house, who offer a very neat and well made instrument, whose magnifying power is claimed to be 350 diameters. Careful measurement of several instruments, however, gave an average power of less than 200 diameters! Indeed it will in general be found that the magni- fying power stated by dealers who do not devote their chief at- tention to microscopes, is greatly over estimated. So much, then, being clearly understood in each case, the question naturally arises, What should be the magnifying powers possessed by microscopes intended for certain specifiedpurposes? That a certain magnifying power is necessary, no matter what the quality of the lenses may be, is true beyond a doubt. Thus, for example, suppose we wish to see the lines on the Pleurosigma Angulation, which lines are about the one fif ty- thoas-indth of an inch apart; what magnifying power would be necessary? OF THE MICEOSCOPE. ' 37 With tlie best illumination, the average human eye can just clearly distinguish lines which are the two-hundredth of an inch apart. Some eyes, under favorable circumstances, can see lines placed as close together as 250 to the inch, but the aver- age is as we have stated.* To be visible even to the best eyes, therefore, the lines on the Angulatum, must be magnified so that thi y will present the same appearance as lines spaced so as to give at the very most, say, 200 to the inch. This requires a magnifying power of 250 diameters, and with less than this they cannot be seen, no matter how good the objective may be. And when Dr. Frey says that they can be seen with a power of 80 or 100 times, while "weaker objectives, magnifying 40 or 50 times, should show something of the lines," he makes a state- ment that we cannot accept. In order, therefore, that an object may be distinctly seen, it must be magnified to a certain extent, but the magnifying power absolutely necessary in any given case, will also depend upon whether the microscope is to be used for general purposes of investigation, or merely for the recognition of known forms. For the latter purpose a power of 100 may be sufficient, while for the former, on the same class of objects, a power of 500 would be the least that would be serviceable. The following are a few of the cases in which the power required can be stated approximately : For medical purposes (except for pocket instruments, intended merely to enable the observer to recognize known forms) a power of 400 is needed, and the objective should be of really excellent quality. Students of histology require a microscope with a wider range of power. Low powers are more useful to them than to the medical man, and if they push their researches in cer- tain directions, there is no limit to the magnifying power needed. *To test the statement in the text, place a glass micrometer, ruled 200 lines to the inch, on the stage of a microscope, and by means of the mirror throw a beam of light upon it, just as if for examination by trans- mitted light in the usual way. If we now look at the lines, not through the tube, but simply from one side, they will appear distinctly as well-de- fined lines. Try the same with a micrometer ruled 250 to the inch; some eyes will be able to distinguish the lines, but very many will fail to do so. 38 SELECTION AND USB A good two-third, one-fifth, .and one-tenth, giving magnifying powers of from 50 to 1000 diameters, will, in general, answer most requirements. It must be borne in mind, however, that beginners can hardly be expected to use a one-tenth inch objec- tive to great advantage, and, therefore, the purchase of this item may safely be deferred. For the study of botany, and the ordinary facts of vegetable physiology, a power of 300 is sufficient; but the very minute forms of vegetable life require a much higher power, and so do certain of the higher points in the physiology of plants. For the detection of adulteration, Hassal recommends the inch and the quarter-inch objectives, giving a magnifying power with No. 1 and No. 2 eye-pieces, of from 60 to 350 diameters. For ordinary purposes of instruction and amusement in the household, a microscope magnifying from 30 to 150 diameters will be found most satisfactory, and for these reasons: Saeh an instrument is easily managed; if well made it gives a power amply sufficient for all ordinary objects, and it need not be ex- pensive. Moreover, while it is an easy matter to prepare ob- jects so that they maybe seen satisfactorily under low and me- dium powers, it requires great skill and long practice to enable the student to prepare objects so that they may be examined with profit under a high power. And finally, under a high power, but a very small portion of any ordinary object can be seen at once, and consequently many of those things that are best suited for popular examination can only be seen piecemeal — a very unsatisfactory mode of proceeding. Thus, under a power of 750 diameters, a fly 's foot could not possibly be seen as a whole ; we might examine a single claw or pad at a time, but not the whole foot, and consequently would find great difficulty in ac- quiring an idea of what the general structure of the foot is. To give the reader clearer ideas upon this point, we have just measured the diameters of the fields seen under French and American objectives, with the following results: With a magni- fying power of 25 diameters, the field is about a quarter of an inch; with 50 diameters, it is one-eighth of an inch; with 100 diameters, one-sixteenth of an inch; with 500 diameters, one- eightieth of an inch; and with 1000 diameters, the one-hundred- and-fiftieth of an inch, a space which is ordinarily invisible OF THE MICROSCOFB.' 39 to the naked eye. Consequently, when these high powers are used, it becomes very difficult for beginners to place the object properly under the microscope, for, as will be readily seen, unless it is adjusted with a variation less than the one-hundred-and- fiftieth of an inch, it cannot be seen at all. The lowest powers that will show satisfactorily certain well- known objects, are about as follows: The scales, or so-called feathers on the wings of most butterflies can be very well seen with a power of 25 diameters; under the same power, the eye of a fly shows very distinctly the several smaller eyes, or ocelli, of which it is composed; the individual corpuscles or globules of the frog's blood can be distinguished with a power of about 35 diameters, human blood requiring 40 to 50; to show dis- tinctly the form, etc., of these same corpuscles requires a power of 200 and upwards. The same may be said of starch granules. Human hair and wool may be seen veiy satisfactorily under a power of 100 diameters, the former appearing like a cord, a quarter of an inch thick. In order to show the peculiar char- acteristics of these fibres, however, the lenses must be good. Cotton and flax can be readily distinguished under a power of 80 diameters. A question very frequently asked in regard to cheap micro- scopes is, Will they show the animalcules in water? And in almost all the advertisements of cheap microscopes, we are told that they will do this. Now, good well water does not contain animalcules that can be seen with ordinary microscopes. It is only in stagnant water that they are found, and many of them can be seen with the naked eye, without the use of any microscope whatever. O thers require the use of microscopes having powers a hundred fold greater than that of the best microscopes in ordinary use. It is evident, therefore, that such statements are worthless as affording any indication of the character of a microscope. A microscope magnifying fif- teen to twenty diameters will show objects that are perfectly invisible to the naked eye, and with fifty diameters, provided the definition is good, we can obtain a very interesting view of nany of the most beautiful objects described in the books, and sometimes called animalcules, such as the Volvox Olobator, the larger Vorticelli, etc., etc. 40 SELECTION AND USE The Stand.— This should be firm and substantial, with, the centre of gravity very low. Nothing detracts so much from the performance of an objective as tremor and vibration, and a large majority of the microscopes in market are very shaky, from the fact thai they a-e made tall and showy in order to command a higher price. It is 'well, therefore, to bear in mind that size is no criterion of the value of a microscope. Instrument makers very properly give the size of their instruments, and it generally happens that the largest instruments by the same maker bear the highest prices. Other things being equal, however, small, compact instruments are altogether to be preferred. Some years ago the rage was for large, showy microscopes, which made a fine appearance in the office of the physician, and the study of the naturalist. It was found, however, that in this case efficiency was sacrificed to show, and all our best makers are now cutting down the sizes of their instruments, and making them steady, substantial, durable and easily operated. There is, of course, a limit to the extent to which stands may be reduced in size without sacrificing their efficiency, and some makers seem to forget this. There are stands in market that are too small every way for anything but special classes of work. The bodies are too small to secure efficiency in the eye- pieces and objectives; the stage is too small to allow of the use of slides of proper size, and there is no room beneath the stage for the attachment of proper illuminating apparatus. All this is as inconvenient as the three-feet-high microscopes of the end of the last century. The weight of the stand is a subject concerning which many seem to differ in opinion. One writer goes so far as to say that no stand weighing less than fifteen pounds can be steady enough for the performance of good work. It will be found, however, that a judicious distribution of the material, and a proper con- struction of the different parts, will more effectually resist the usual sources of unsteadiness than any increase of absolute weight. Of course, if it is merely desired to make the micro- scope steady, in the sense that an inkstand is steady — that is, not liable to be tipped over — weight is everything. Bat the stands that are most difficult to tip over are not those that resist vibrations most perfectly. For the latter a tripod with a OF THE MIOKOSCOPE. 41 small area of support is best; for the former a stand with a flat base resting over its "whole surface on the table should be pre- ferred. It is obvious that the causes of unsteadiness are either vibra- tions transmitted from the floor, or movements caused by the hand in performing the necessary manipulations and adjust- ments. The first can never be stopped by weight, unless, indeed, we make the stand ss heavy that its weight will impart rigidity to the table and floor, and this would require a good deal more than fifteen pounds, or even twice that. For the cheeking of vibrations transmitted from the floor, no device is better than the stand or table described in a subsequent sec- tion. So far as movements transmitted by the hand are con- cerned, if a stand of three or four pounds will not resist them, the observer should set himself about learning delicacy of movement before he proceeds any further. All microscopes made in this country and in England are, now constructed so that the body may be inclined to any angle, thus giving the power of using the microscope in any position — vertical, inclined or horizontal. The importance of this is easily seen when we consider that on the one hand, when liquids are to be examined, it is sometimes necessary, or at least desira- ble to use the microscope in a vertical position, though this is a very tiresome and inconvenient position, and one that is not calculated to enable the observer to obtain the best possible re- sults; and on the other, it is equally necessary that the body of the microscope should be capable of assuming the horizon- tal position when the camera lucida is to be employed for making drawings, as will be hereafter explained. And yet Frey actually gives the preference to microscopes that do not incline, and which must always be used in a vertical position! This, of course, necessitates the complicated and expensive ar- rangement which he describes for adapting the camera lucida to the vertical instrument, a singular instance of prejudice against an obvious and successful improvement. The Stage.— In every case, a large, roomy stage is of the utmos'- importance. One great objection to most French in- 42 SELECTION AND TOE struments is that the stages are too small. It should also be firm and substantial, so that its position in regard to the other parts of the stand cannjt be varied by slight pressure. At the same time^ however, it must be borne in mind tliat no stage ever was made so firm that even a slight pressure would not affect it. If, therefore, therreader is determined not to rest content with anything short of & perfectly rigid stage, he will reject all the best microscopes in market. In most microscopes the object is held in place by spring clips, and these should not be too strong or they will be very inconvenient. They should also be so attached that they may be easily removed or turned out of the way. The Mirror. — In microscopes of modern construction, the mirror is made of glass, coated with pure silver, (ordinary mir- rors are coated with an amalgam of mercury and tin) and the best instruments are provided with two mirrors, one plane and the other concave. In both mirrors the surfaces of the glass should be accurately ground and polished. Blown glass will not answer. The plane mirror reflects the light just as it falls on it, while the concave one causes parallel rays (such as those from the sun) to converge and me< t at a point, and renders divergent rays (such as those from a lamp) either less divergent, parallel, or convergent, as the e.ise may be. The concave mirror should be large, but the plane mirror is as efficient when small as when large. Where but one mirror is provided, the concave is the one usually selected. In English and American microscopes of even the cheapest construction, the mirror is so arranged that it may be made to send a beam of light through the object very obliquely. This is absolutely necessary for some purposes, but not for the ex- amination of ordinary objects. The ability to use oblique light, as it is called, is, however, a great advantage. It not only enables us to resolve lined objects, but to secure important changes in the illumination of common objects. A very fair dark ground illumination may also be secured by placing the mirror in such an oblique position that none of the light can enter the object-glass directly. OV THE MICfiOSCoRE. 43 The Body. — The only point connected with the body of the microscope which requires consideration is its size, and this must of necessity vary so much according to the purposes to which the microscope is to be applied, that no rule can be laid down. Pocket microscopes are of necessity small; micro- scopes intended to give very great magnifying power must be large. A standard size is seven to eight inches in length. The diameter is not of very great importance in bodies of moder- ate length, but Beale says that in his long tubes, intended to produce great magnifying power, a diameter of two to two-and- a-half inches was found to be absolutely necessary. An inch and an eighth is a good size for ordinary instruments. Since a very long body is inconvenient when the microscope is used in a ver- tical position, the best instruments are furnished with a Draw Tube, whereby, the length of the body may be varied at pleasure. As explained in a former paragraph, (page 15,) when the distance between the eye-piece and the object- glass is increased, the magnifying power is increased also. The draw tube, therefore, gives us the means of varying and adjusting the magnifying power of the microscope, and this is sometimes of great use. Thus, suppose it were required to draw an object to a scale magnified exactly one hundred diame- ters; it might be impossible to procure an eye-piece and an objective that, with a fixed length of body, would give exactly this amplification, but when we are able to vary the magnify- ing power by changing the length of the body, it is easy to get at it exactly. This, however, is but one of many advantages afforded by the draw-tube. If the objective be good, and the eye-piece not very high, an easy and very satisfactory way to increase the magnifying power of the microscope is to lengthen the body by means of an additional tube. Dr. Beale, who has been a most successful worker with high magnifying powers, tells us that in practice he has found this plan si much more advantageous than the use of a deep eye-piece, that he never uses the latter. In some cases he has extended the length of the tube to two feet with good results. We have frequently adopted this method, and where brass tubing could not be had we have used smooth writing paper, and a. little paste with very good effect. 44 SBLEOSIOtf AND tJSE The inside of all draw-tubes and bodies should be well blackened. When bright or white the glare greatly injures the defining power. When draw-tubes are so arranged that they rub against the inside of the tube forming the body, they in- variably make the latter bright by friction. They should, therefore, always slide in a collar. It is always well to have the lower end'of the draw-tube furnished with the Society screw, as by this means it is sometimes possible to use objectives of greater working distance than could otherwise be employed. Adjustments for Focussing.— In the cheaper forms of the microscope the adjustment is made directly by hand, one tube sliding within another. In a better class of instruments the objective is brought nearly into position by sliding the body through an outer tube, and then the fiaal adjustment is made by means of a screw or other mechanical means. But in all the best microscopes, the coarse adjustment, as it is called, is made by means of a rack and pinion, while the fine adjust- ment is made in the manner just mentioned. Instead of a rack and pinion, a chain is sometimes employed, and the coarse adjustment is also made in some cases by screws of very wide pitch, and similar devices. Nothing, however, can equal a smoothly cut and well-fitted rack and pinion. It is sometimes alleged that the chain is more delicate, but this is not so. We have now in our possession a cheap, but well made microscope, the rack and pinion of which is so delicate, that with it we can focus an objective of an eighth of an inch focal distance with sufficient accuracy for all ordinary purposes. For ordinary purposes, especially the work of the physician and medical student, the coarse adjustment may be more easily dispensed with than the fine one, but at the same time it must be remembered that any mode of adjustment in which the body is liable to turn round, is incompatible with the use of many important pieces of apparatus. Thus, for example, any turn- ing of the body interferes with the use of the double nose- piece, the polariscope in its higher applications, Prof. Smith's opaque illuminator, etc. A rack and pinion, or its equivalent, should, therefore, always be chosen, especially as it does not add more than five or six dollars to the cost of the instrument. OF THE MICROSCOPE. 45 The Diaphragm —Nothing tends so much to obscure our view of the finer points of structure in any object as to have them "drowned" in a superabundance of light, conse- quently in order to regulate the amount of light which passes through the object, a diaphragm is employed. As ordinarily constructed, it is simply a metal plate placed below the stage, and pierced with holes of various sizes, which miy be brought exactly under the field of view, the smill holes allowing but a small amount of light to pass, while the large ones admit a full stream. OljjectiTes.— These are by far the most important part of the microscope, and unless they are carefully corrected it is impossible to obtain clear and accurate views with any except the very lowest powers. Consequently common or non-achrom- atic objectives are never employed in microscopes which mag- nify more than one hundred diameters. First-class achromatic objectives are quite expensive, single ones often costing more than the price of a very fair micro- scope, all complete. Most makers furnish what are known as students' objectives, which cost much less, and are capable of doing very good work. A still cheaper grade of objectives are those known as French triplets. Of these the half-inch and the quarter-inch are frequently very good. Objectives are rated either by numbers or by the focal dis- tance of the simple lens t > which they are equivalent. Thus an inch objective is one that magnifies ten diameters, the eye being ten inches from the object. This is without the eye- piece, and if the eye-piece magnifies ten times also, the magni- fying power of the microscope will be one hundred diameters. As regards the quality ol the objective to be chosen, the most obvious rule would be to select the best that is attainable. To this rule, however, an exception must be made. To use a first-class glass with results equal to its quality, requires more skill than most beginners possess, and therefore the second class objectives will, in their hands, actually do better work than their more expensive rivals. And for the comfort of those who cannot afford the more expensive instruments, we would remind them that it is astonishing how far patience, 46 SELECTION AND USE skill and experience will go to make up for a deficient instru- ment. Indeed, it is unfortunately true that some who possess the very best glasses, and have done the most to throw ridicule upon all work done with inferior lenses, have never made a single contribution of the slightest importance to any depart- ment of microscopical science. It is a well-known fact that the very expensive objectives, unless well arranged as to illumination and the adjustment for thickness of cover, are practically worthless. An important point f*r consideration will, of course, be, whether or not the glass is intended for original work, or merely for the study or examination of well known objects. The work of the physician and student is chiefly amongst well known objects, and may be very satisfactorily accomplished by means of good non-adjusting objectives, a great point in favor ' of such glasses being that work may be done with them more rapidly than with glasses that require greater care and skill. Eye-Pieces. — The magnifying power of every microscope depends upon three things: The focal length of the objective, the length of the body, and the eye-piece. The best micro- scopes are, therefore, furnished with several eye-pieces, whereby the magnifying power may be varied. There is, however, a limit to the extent to which this may be done. The image ob- tained by very powerful or deep eye-pieces, as they are called, is raraly satisfactory. The extent to which the definition of really good objectives is deteriorated by the use of eye-pieces of pocr quality is sometimes very great. The lenses composing the eye-piece should be free from air- bubbles, specks and strise, and the surfaces should be well pol- ished. On looking through the eye-piece at a strongly and evenly illuminated surface, the entire field of view — that is, the whole of the bright circle that is seen, should have the light evenly diffused over its surface, and the edges or border of this circle should be sharp and black. The different eye-pieces are generally denoted by letters — A, B, C, D, etc., A being the lowest, and B, C, D, etc., successively higher. Some makers use numbers — 1, 2, 3, 4, etc. These letters and numbers are, however, entirely arbitrary, in this point OV THK MIOBOSOOPE. 4.7 resembling the numbers assigned to objectives by continental makers. A great improvement upon this arbitrary and uncer- tain system would be to assign to each eye-piece its proper power expressed in inches. Thus, an eye-piece magnifying the same as a simple lens of two inches focus, should be called the two-inch eye-piece. And here let us call attention to the terms deep and shallow, as applied to eye-pieces. By all authors of repute, a deep eye-piece is one of great magnifying power, while a shallow eye-piece it. the reverse. See the Micrographic Dictionary, and the works of Car- penter, Beale, Lardner, Frey, etc. , etc. It is, therefore, singu- lar that Dr. Lankester, in his popular little work, ' ' Half -Hours with the Microscope, " should have committed the mistake of giving definitions exactly the opposite, upon the ground that eye-pieces of great magnifying power are always short, while low eye-pieces are always long. It is evident, however, that the terms are liable to give rise to confusion, and we pre- fer the words high and low — the meaning of which is so ob- vious as to require no explanation, as every body knows what high magnifying power is While clearness of definition and resolving power are the most important qualities of every good microscope, magnifying power is also of considerable consequence, as explained in a former section. Therefore, every good microscope should be provided with at least one eye-piece of considerable power. It often happens that with the objectives and eye-pieces at hand, the amplification, as it is called, or, in other words, the extent to which the object is magnified, is not sufficiently great to enable us to make out its structure, while the objective has not by any means reached the limit of its defining power. In this case a high power eye-piece, which costs comparatively little,. will greatly extend our power of successful examination. ACCESSORY APPARATUS. Every microscope should be accompanied with certain pieces of accessory apparatus, which are necessary for the convenient and thorough examination of objects, but which do not form part of the instrument itself. Some of these are intended for 48 SELECTION AND TO* the better illumination of the ob- ject, and will be described in the section on "Light;" others are used for the procuring and preparation of objects, and will be described in the section devoted to that subject. The following are employed chit fly for holding and presenting objects that have not been " mounted:" m^i Stage Forceps.— This little in- strument accompanies the oldest microscopes. It consists of a pair of very delicate forceps, such as those attached to the forceps-car- rier in Fig. 4, which close by the spring of the jaws, and hold any ob- ject that may be placed in their grasp. They are opened by pressing on the pins which are seen at the sides. They are in general fastened to the microscope by being stuck into a hole in the stage, and the object may not only be moved back- ward and forward, but it can be turned round. The better class of forceps carry a small brass tube (shown in Fig. 4) which is filled with cork, and which serves to re- ceive pins, etc. , for holding insects, and other objects. Foi ceps-Carrier. — However well made the forceps may be, it is almost impossible to slide, with suf- ficient delicacy, the rod through the tube that holds it. Consequently, it is exceedingly difficult to bring into the field of view, the exact part of the object, that we may wish to OF THE MICBOSCOPE. 4 tJSB The operation which, we have thus briefly described as appli- cable to the potato, is required for a great many other materials ; for whenever a substance is to be examined under any except the very lowest powers, it is absolutely necessary to obtain it in pieces as thin as possible, so that the light may readily pass through them, and it is in general requisite to increase their transparency either by immersing them in a fluid, or by some other means. In preparing objects for the microscope, our aim is in general to examine either the ultimate structure of the substance under investigation, or the arrangement of its different parts; and the processes which are most available for this purpose may be classed under three heads: 1, Mechanical, such as section-cutting, dissection and injection; 2, Chemical, such as the use of iodine for detecting starch; of alcohol for hardening certain structures; of coloring substances for stain- ing germinal matter, etc.; 3, Optical, such as the action whereby certain liquids change the transparency of some ob- jects. Of some of these processes, such as injection, staining and the extended use of chemical tests, elaborate .descriptions would be required in order to enable the student to carry them out with success, and we must refer him to the works of Beale and Prey, which are very complete on these points. Thin sections of any soft substance are easily made with a very sharp knife — a good razor being probably the best availa- ble instrument. For work in the higher departments of micro- scopy, and for the preparation of fine objects for sale, special instruments known as section-cutters are employed, but for the ordinary work of investigation, they are not absolutely neces- sary though very convenient. Using a good sharp razor, it is an easy matter to shave off any soft substance a wedge shaped piece*, the edge of which thins off to nothing, and which pre- sents in its different parts all varieties of thickness, so as to afford a perfect opportunity to study the object under examination. In this way, which is known as the " free-hand" method, suitable sections of most animal and vegetable substances may easily be prepared, and the student will be surprised at the dexterity which a little care and practice will confer. For cutting sections of very soft tissues a special knife, known as Valentin's knife, has been invented. It consists of two OB 1 THIS MICROSCOPE. 87 blades so arranged in one handle that their distance from each other may be easily regulated. When a cut is made with this double-bladed knife, a thin slice of the tissue passes between the blades, and constitutes the section. It is an instrument, however, which will hardly be used by beginners. Sections of substances of greater consistence, such as wood and soft bones, are most easily made in a regular section cutter. The patterns according to which these instruments are constructed are very various, but they all act on the principle of raising above the surface of a brass table, by means of a fine screw, the substance to be cut, and then passing a Very sharp razor or knife over the table so as to shave off the projecting part of the object. The table is usually of brass, ground and polished. This gives rise to two serious defects. The metal is too soft in the first place, so that it is impossible to press with sufficient force on the razor without cutting into the table, and secondly, when any soft metal has been ground on a grindstone or emery wheel, the surface becomes so impregnated with gritty matter, that it very rapidly destroys the edge of the cutting tool. We avoid these difficulties by fitting to our section cutter a stout plate of hardened steel, the surface of which has been highly polished by means of buff leather. Quekett describes a cut- ting machine in which the difficulties we have mentioned are obviated by fixing the knife in a frame so that it is raised above the table, and does not touch the metal. Its edge is thus pre- served from injury, and the blade itself cannot be affected by variations in the pressure exerted. Dr. Curtis, of this city, has adopted the same principle in his section cutter, the details of which are admirably carried out. In making sections of wood and similar substances, the speci- men is first well soaked in dilute alcohol, and is then fastened securely into the tube of the section cutter, either by wedges or by casting wax or paraffin around it. The process of raising it by means of the screw and passing the knife over it, is simple enough, and can easily be learned. With the ordinary cutting machine, success in making thin sections seems to depend upon the perfect sharpness of the cutting edge, the thorough moistening of the knife and section, and the rigidity of the blade. The latter point frequently fails OO SELECTION AND TJSE to receive the attention that it deserves. Where a thin, flexi- ble blade is used, a moderate change in the amount of pressure employed will make a great difference in the thickness of the section, even so far as to double it. When the blade is stiff, a change in the degree of pressure has but little effect. Soft substances must first be hardened either by immersion in alcohol or other means, and in general must be supported by being surrounded with melted wax or paraffin. Where the specimen is very slender (such as a hair) it must be carefully supported between firm and rigid clamps. Corks and similar yielding substances, which are' recommended in most books, never give a cross section accurately taken at right angles. The same is true of the plan so much recommended for obtaining sections of hair, viz. : to pass the razor over the face shortly after shaving. We get sections it is true, but they are all oblique. The best way to get true sections is to imbed the sub- stances in glue, gum, paraffin, wax or some such material. Sections of bone are prepared by sawing off a tbin slice in the first place, and cementing it to a slide by means of thick or old balsam; one side is then filed or ground flat, and polished on buff leather, after which the section is transferred to another slide so as to expose the other side, which is then filed down and polished as before. Great care must be taken so as to hit just the right thickness, and the operation of cementing to the slide must be performed expeditiously, so that the balsam may not saturate the section, and render it too transparent, as when , this occurs certain very important features become invisible. Very hard substances require special apparatus, and consid- erable still. Still it is astonishing what may be accomplished by means of good files, whetstones and grindstones in the way of preparing thin and transparent sections even of such sub- stances as rocks and stones. In order to acquire correct ideas in regard to the structure of objects, of which sections are examined, the student should fa- miliarize himself with the geometrical forms produced by cut- ting cylinders, cones, spheroids, etc., in various directions. Thus a cylindrical vessel, cut square across, shows a circle; when cut obliquely it shows an oval (ellipse) of greater or less length and when cut longitudinally it shows two lines which have no OP THE MICROSCOPE. 89 apparent connection -with each otber. The truth is, however, that we should never deduce the form of vessels from sections alone. In every case it is necessary to examine carefully dis- sected preparations as well as sections* The soft parts of animals and vegetables are frequently pre- pared for examination by careful dissection, that is to say the different parts are separated from each other, and freed from ex- traneous matter by means of knives, scissors, forceps, needles, camel hair pencils, etc. The knives used by the microscopist are similar to the scalpels ordinarily employed by anatomists, but smaller, and unless very finely tempered and well-sharpened, they are worthless. The knives sent out with low priced micrd- scopes are in general the veriest trash, and the same is true of the needles. There are three kinds of scissors which the microscop- ist will find useful — plain, straight scissors, elbow scissors, and curved scissors. They must be small, sharp and well made. But • the most useful, as well as the simplest instruments for dissecting are a pair of needles, or, rather, a needle and a very fine spatula. The needles used are those ordinarily employed by seamstresses; they should be fixed in a light wooden handle and carefully polished. The latter is a most important point, for it will be found that ordinary needles are too rough for deli- cate work, as may be easily seen by examining them under the microscope. For microscopical purposes needles are made both straight and curved — the latter being a very useful form. la order to bend a needle, it must first be heated in the flame of a candle, then bent by proper pliers, after which it must be carefully re-tempered. There is little danger of getting it too hard, provided it is not burned. After being hardened it must be carefully re-polished. The handles should be light and smooth. Ordinary penholders make good handles and cost but a trifle, but in case of need any piece of straight-grained, light wood will answer. Universal handles, handles with ferrules, handles wound with thread, etc,, look as if they were not com- mon articles, and are purchased by many, but no working mi- croscopist would give them table-room. All the so-called uni- versal handles in market are too clumsy and heavy. In using needles or knivera for dissection, they are generally used in pairs, that in the right hand being used for teasing or 90 SEfcECTIOtf AND TJSE Witting, while fhf one in the left hand is used for holding the object firmly in its place. For the latter purpose, however, -we prefer a very narrow spatula, curved and highly polished. Curved needles, with the curve placed flat, answer very well, however. For the removal of loose matter, and for arranging parts which have been dissected out, there is nothing more useful than good camel hair pencils. Indeed, they are indispensable, and with needles and pencils — two of the simplest and cheapest articles — it is possible to do almost everything. During the process of dissection the object must be supported upon a glass plate or a dissecting pan, according to its size. Some of the finest preparations have beeu.worked up on ordinary slides three inches long by one wide, and as it is almost always neces- sary to have the object covered with liquid, a single drop suf- fices in this case. But where larger objects are to be dissected, ordinary slides are not large enough, and besides there> is no provision made for holding a sufficient quantity of liquid. Various kinds of dissecting dishes or pans have therefore been devised. Those used by the author are exceedingly simple and cheap, and are shown in Fig. 33. We use three kinds, two with opaque bottoms, and one in which the bottom is transparent. The latter is used for objects which are transparent) and is precisely like the others, except that a portion Fig. 33. of the metal bottom is cut away and a piece of plate glass cemented over the aperture. Those used for opaque objects are simply oblong tin dishes, each two inches long, one and a quarter ■wide and half an inch deep. The bottom plate extends on each side, so as to form rests for the fingers, by which the pan may be kept steady. Into this pan is poured a mixture of erpu.l parts of resin and beeswax, softened if necessary with a little lard. It should be just so soft that a pin may be easily stuck into it, and this affords us the means of pinning out the different parts of a dissection as we progress. In one dish the wax is colored black with lampblack, and this forms a wonderfully effective back ground for most objects; the W8E iffi the OtheV OP THE MICEOSCOPB. 91 pan is white, chalk or sulphate of baryta being substituted for lampblack. The pan with a transparent bottom is of precisely the same size, except that the depth is but half as much — the extra depth in the other pan being filled with wax. A quarter of an inch is a sufficient depth of liquid for most objects, and when the sides of the pan are higher than necessary they inter- fere with the use of knives and needles. Dissections may also be carried on in watch-glasses, though they are not quite as convenient as pans with perfectly flat bottoms. The kind known as lunette glasses should be chosen, as they are flat in the centre. "When a watch-glass is used for this pur j pose, it is necessary to cement it into a hole cut in a thin piece of wood about four inches long, and of a width which is rather greater than the diameter of the glass. Most of this work is, of course, done under a simple micro- scope. The Excelsior, when screwed to a larger base, as de- scribed on page 29, answers very well. Larger and more ex- pensive dissecting microscopes are supplied by most opticians. In addition to these general methods, which are applicable to a great variety of subjects, there are a few special processes which must be adopted in particular cases. In some instances, as when the line of investigation is a new one, the microscop- ist must work out his own processes, but the following special cases will probably prove interesting to beginners. It frequently happens that the objects for which the micro- scopist is searching are found mixed with coarser materials, and in this case it will be found possible to effect a separation by the process known as elutriation or washing. Mix the mat- ter thoroughly with water in a tall jar and allow it to settle, la a short time — say one minute — the very coarse particles will have fallen to the bottom, and if the liquid be now poured off and allowed to settle, the finer portion will be found in the second vessel. By graduating the time and carrying the pro- cess out to its full extent, a wonderfully perfect separation may be effected. Diatomaceous earth may frequently be treated in this way to advantage. In some cases separation must be effected by burning, or the action of chemical agents. Guano and various organic matters yield interesting residues after everything soluble has been 92 SELECTION AUD USE washed away and everything combustible has been burnt either with fire or nitric acid. So too the siliceous cuticles of plants may be procured by destroying all the other parts by chemical means. The best way is to heat them in nitric acid, and add to the hot liquid a small quantity of powdered chlorate of pot- ash. The quantities used must be very small, and great care must be exercised. It is frequently necessary to separate a small quantity of deposit from a large amount of liquid, filtering being inadmis- sible. For this purpose use a conical glass or a large test tube, allow plenty of time for the deposit to settle, and give occa- sionally a slight stir, sq as to detach the particles from the sides of the vessel. Then pass a large dipping tube (one quar- ter of an inch in diameter) to the bottom, the upper end of the tube being closed with the finger. On withdrawing the finger the liquid and deposit rush in. Have ready a small ball of soft cement (resin and beeswax equal parts, softened with oil) and with it close the upper end of .the tube, which may now be withdrawn, carrying the liquid with it. Place the tube in a vertical position, with its lower end on a slide or in a watch- glass, and support it either by means of the ring of a small retort stand or by a simple wire having a ring (horizontal) at the upper end, and a small piece of board for a foot. Beale directs us to cork the tube, but this is difficult unless the tube is made specially for the purpose with a mouth like that of a test tube. Tubes made in this way are, however, the most con- venient, and a good velvet cork closes them perfectly. There is a class of insect preparations, which are quite inter- esting, though they are not as instructive as inferior prepara- tions made by the process of dissection. We refer to the whole insects found in most collections. They are prepared by soak- ing the insect in liquor potasses, which may be had from any druggist; this renders the internal organs soluble and the outer horny skeleton transparent. The viscera are then expelled by pressure with a camel hair pencil, the insect well washed in pure water, soaked first in alcohol, aud then in turpentine, and finally mounted iu balsam. The points requiring attention are these: Soaking just the right length of time in the potash, for if ihe insect remains too long in this liquid it will be destroyed; OF THE MICBOSCOPB. 93 allowing plenty of time for the alcohol to displace the •water, and for the turpentine to displace the alcohol; and manipula- ting the insect with great care, so as not to break any of the parts. The eyes of insects are prepared by macerating them in very weak potash, and, while still soft, pressing them between two slips of glass. If allowed to harden before being pressed they will split at the edges. The handsomest preparations of eyes are obtained by taking a thin slice from a large eye, such as that of a dragon fly, and treating it as directed. The feet of insects are in general easily prepared. Moderate soaking in potash, careful washing in water, thorough soaking in alcohol and turpentine, and careful management in properly displaying them on the slide, are the secrets of success. The student who wishes to make a careful study of these objects, however, should place them in glycerine, after soaking them in potash and thoroughly washing them. They should of course be deposited in a cell filled with liquid, and then covered with thin glass, and examined. The so-called tongues, etc., of in- sects require no potash, being sufficiently transparent without it, and after being soaked successively in alcohol and turpen- tine, they may be mounted in balsam. When wanted for exam- ination merely, immerse them in dilute glycerine, and if the student can succeed in mounting them in cells, in glycerine or some of the gelatinous media hereafter described, they will show their structure to far better advantage than in balsam. In determining the character of what is brought into view by the processes detailed, great aid will be derived from the use of chemical tests. Thus, in the case of the potato, previously described, most persons who had read anything at all upon such subjects, would recognize the starch granules. All starch granules, however, are not of the same form as those found in the potato; indeed, some would hardly be recognized at all, except by those having considerable experience. But if a little of the tincture of iodine be brought into contact with them, they at once be- come deeply blue. This subject is too extensive to be dis- cussed here, but those who desire to become proficient in the use of the microscope cannot safely neglect it. In most cases after an object has been carefully brought into proper mechanical condition, in one of the ways we have de- 94 SELECTION AND TTSE scribed, it is necessary to immerse it in some suitable medium, so as to render it clear and transparent. The action of such media may be very -well illustrated by the following experiment : Take a short piece of black human hair, place it on a slide, bring it into focus and examine it. It will appear as a dark cord with a light line running down the centre, and from this circumstance has arisen the erroneous popular idea in regard to the tubular structure of hair. Apply a drop of glycerine di- luted with an equal bulk of water, and again examine it. The appearance will have entirely changed, having become clearer and more definite, so that the structure of the hair is more easily made out. This effect depends upon the refracting power of the liquid used. The following liquids are usually employed for this purpose, their efficiency being in direct ratio to their index of refraction, which we append to each. Water, 1.336; glacial acetic acid, 1.38; alcohol, 1.372; vitreous humour, 1.340; sea-water, 1.343; equal parts of glycerine and water, 1.40; pure glycerine, 1.475; oil of turpentine, 1.478; Canada balsam, 1.532—1.549; bisulphide of carbon, 1.678; oil of annis, 1.811. Alcohol and water, and solutions of various salts in water are also very useful. When a pure article of glycerine is not avail- able, a solution of white sugar may be used with good results. Great care must be exercised lest the fluid that is added should change the form or structure of the object. Upon this subject the remarks of Frey are very judicious. Hesays: "Theory requires that each constituent of the body should be examined in a fluid medium which resembles in respect' to quality and quantity, the fluid which saturates the living tissue. Naturally this requirement cannot be completely fulfilled in practice; our aim should be to approach it as nearly as possible. Saliva, vitreous humour, amniotic liquor, serum and diluted albumen are generally recommended as suitable media for the investiga- tion of delicate changeable tissues, and, in certain cases, they accomplish their object in a satisfactory manner. But do not expect them to suffice for every case. Not unfrequently one and the same tissue of different species of animals reacts differ- ently with the same fluid medium, as may be seen with the blood corpuscles. M. Schultze has communicated to us an im- portant and readily proved observation of Landolt's, that ani- 03? THE MICBOSCOPE. 95 mal fluids may be preserved from decomposition for a long time by the addition of a small piece of camphor." Schultze recommends as a neutral fluid, suitable for most tissues, a liquid ■which he calls " Iod-serum." It consists of the amniotic fluid of the calf, to which has been added a concen- trated tincture of iodine or a strong solution of iodine in the proportion of sis drops to the ounce. The color of the solution is at first wine yellow, but after a few hours it becomes paler; this paleness afterwards increases, and the subsequent addition of a few drops of the iodine solution becomes necessary. As the amniotic fluid is not always attainable, a good substitute may be prepared by mixing 1 ounce white of egg, 9 ounces water, and 40 grains chloride of sodium, with the proper pro- portion of tincture of iodine. During the entire process of preparation, the greatest atten- tion must be paid to cleanliness. Particles of dust, which to the unassisted vision are invisible, become offensively prominent under the microscope. To exclude these, and to protect the objects, it is important that the latter should be kept carefully covered when not actually undergoing some operation. Small bell glasses are recommended for this purpose by Dr. Carpenter, and they answer admirably. We prefer, however, as being cheaper and less bulky, watch glasses to which a handle has been cemented as shown in Fig. 34. The handle may be a little knob, turned out of a piece of wood, or where this is not conveni- ent a small cork will answer. A little sealing Fig. 34. wax serves for a cement, the watch glass be- ing heated before the wax is applied. Flat plates of glass answer well to cover the dissecting pans previ- ously described. When a number of objects are to be protected for some time, we place them on a piece of plate glass eight inches square, cover each with a watch-glass cover, and protect the whole by means of a bell jar with ground edges. The latter fits closely to the plate glass and excludes everything, while the small covers protect the individual specimens when the large cover is raised for the purpose of getting at them. Singular mistakes have arisen from the fact that foreign 9G SELECTION AND USE bodies which have accidentally found their way into a prepara- tion have been mistaken for part of the specimen. The only way to avoid similar errors is to exclude all such intruders by means of proper covers, and to become familiar with them so that they may be instantly recognized when present. Dr. Beale gives the following list as those that are most apt to find their way into the preparations of the microscopist: Oil globules; milk; starch from the potato, wheat and rice; bread crumbs; feathers; worsted; fibres of flax, cotton and silt of different colors; human hair, cat's hair and hair from blankets; the scales of butterflies and moths, particularly those from the common clothes moth; fibres of wood, fragments of tea leaves, hairs from plants, vegetable cellular tissue and spiral vessels; particles of sand. The curious circumstances under which such bodies will find their way into a specimen was recently illustrated in the author's experience. In a liquid submitted for examination, and said to be pure, he found foreign matter. It proved to be brick dust, used to clean the tin funnel with which the vessel was filled, and which had been washed in by the passage of the fluid. The student can have no better exercise than to examine these intruders and familiarize himself with their ap- pearance. Preservative Processes.— The object of all preserva- tive processes is to prevent any change either in the structure or composition of the object. An object may be most perfectly prepared and beautifully mounted, but if it be not so treated as to preserve it from change, the labor thus expended is wasted, as regards the preservation of a permanent record. And yet how many objects there are that we would like to keep for future examination and comparison, or to show to friends. This department of the treatment of objects is, therefore, of great importance, and success in it can only be obtained through a thorough understanding of the principles involved. There are four methods in common use for the preservation of perishable animal and vegetable substances: 1, Constant ex- posure to temperature considerably below the freezing point of ffater; 2, the perfect exclusion of air; 3, reduction to a state of complete dryness; and 4, the employment of certain anti-septic OF THE MI0EOS0OPB. 97 compound. The third and fourth are the methods usually em- ployed in microscopy, but the same principles which render the second method so successful in the preservation of canned fruits and meats, deserve the attention of the microscopist. Drying, as a preservative process, can be applied to but few specimens, chiefly transparent insect preparations, and opaque objects. Blood and similar matters are also sometimes pre- served by drying. Such preparations are so easily dried that no special directions are needed. Warming them over a lamp, or preferably on a water-bath, before applying the thin glass cover (as directed in the section on mounting objects) is al- most always sufficient. Where the specimen is liable to be in- jured by heat it may be dried by placing it over sulphuric acid, and covering both acid and preparation with a bell jar having ground edges and resting on a perfectly flat plate of glass. The acid soon absorbs all the moisture and renders the object perfectly dry. Where a cell is used for an opaque object, and dryness is essential, great care must be taken to make the cell impervious to air, otherwise dampness will be sure to penetrate, and if the object be of animal or vegetable origin, fungi will be very apt to grow on it. We have found cells of cardboard peculiarly liable to this defect, and such cells should always be thoroughly saturated, and coated with varnish, such as gold size or Canada balsam. The great dependence of the microscopist, however, is in the employment of certain preservative media, of the most impor- tant of which, the following is a list: Canada Balsam:. — Of all the media employed for the mount- ing and preservation of objects, Canada balsam is undoubtedly the most generally useful, and it is probable that more objects are mounted in this material than in all the other media put together. As a preservative it is perfect, and its action in rendering many objects transparent and clear is often of great value. Frey tells us that "several sorts of Canada balsam occur in commerce. To be good it should be of thick consistence, nearly colorless, and thoroughly transparent. " One difficulty, however, is that much of the Canada balsam that is sold is factitious, being ,made of cheap resins dissolved in impure turpentine. Such 98 SELECTION AND USB ■balsam soon becomes cloudy, and is very apt to crack. Balsam that is too highly colored may be bleached by exposure to sun- light — a process applied by most opticians to the balsam used "by them for cementing the lenses of achromatic combinations. Balsam when new is quite fluid, too much so, indeed, for the mounting of most objects. On the other hand, old balsam is thick, and is apt to crack. Microscopists generally keep balsam in wide-mouthed bottles, and take out what is wanted by means of a glass rod. As the process of evaporation, which makes balsam thick and viscid, goes on more slowly in narrow-mouthed bottles, we prefer the latter, and transfer the balsam to the glass slide by means of a fine wire with a small loop at the end. The wire is passed through a cork, or preferably a wooden stopper, and descends to such a depth as to be just below the surface of the balsam. As the latter is used up, the wire is pushed down, and if cemented in its place by the balsam, a little heat soon frees it. The latter remark applies also to the wooden stopper, which is very apt to stick in the neck of the bottle. A very slight ex- posure to the flame of a spirit lamp is sufficient to loosen it. Solution of Balsam. — When the objects that are to be pre- served in balsam would be injured by the heat necessary to melt it, it is advisable to use a solution of balsam in ether or chloroform. The balsam used for making the solution should be old and thick. This solution is frequently sold with the label, " Balsam for use without heat." Colophony. — Thiersch recommends a solution of resin or colophony in absolute alcohol. The advantage which this ma- terial presents is that the preparation may be placed in it di- rectly from the absolute alcohol, without becoming cloudy, and without prejudice to the durability of the specimen. He advises the microscopist to prepare the colophony himself from Venice turpentine, which is done by dissolving it in an equal volume of ether, filtering it through paper, and evaporating, until, when cold, it breaks with a conchoidal fracture. The material that remains is then to be dissolved in absolute alco- hol until it is of a syrupy consistence. OF THE MICEOSCOPE. 99 Dajiae Medium. — Gum damar has been recently introduced amongst the materials used by microscopists, and •with some it has found great favor. Carpenter speaks highly of it. Dia- toms are said to show better in it than in balsam, and for delicate physiological preparations, especially transparent in- jections, it is very excellent. It is thus prepared: Half an ounce of gum damar is dissolved in one ounce of oil of turpen- tine, and half an ounce of gum mastic in two ounces of chloro- form. The solutions are filtered and mixed. Ordinary damar varnish, such as is used by painters, is some- times sold for microscopical purposes, but it ■ does not give satisfactory results. Preparations which have been preserved and mounted in balsam or damar are very durable, while those that are mounted in fluids are a source of continual annoyance and loss. Many microscopists, therefore, exclude from their cabinets all preparations mounted in liquid on the ground that sooner or later they will become worthless. And many of our best dealers refuse to have anything to do with them. Neverthe- less, as Prey well says, " the natural condition of the tissues is completely represented only when mounted in a moist condi- tion. This method permits of the most accurate recognition of delicate textural relations, pale cells and fibres, etc., and should not be omitted with any tissue in the production of histologi- cal collections." Glycebine. — At the head of the list of preservative media for moist preparations stands glycerine. "Its strong refrac- tive power, its property of combining with water, and of at- tracting the same from the atmosphere, render it an invalua- ble medium for mounting animal tissues containing water, It may be truly said, that what Canada balsam is to dry tissues, glycerine is to moist ones. " — (Frey.) Much of the glycerine in market is very impure, and although the impurities do not show themselves very strongly at first, they soon become mani- fest by the darkening of the liquid, (owing probably to the presence of lead), and the formation of a cloudy precipitate. Dr. Beale strongly recommends Price's glycerine, and we have found it very excellent. 100 SELECTION AND USE When employed as a preservative, glycerine is used either pure or diluted, according to circumstances. Equal parts of glycerine and water form a very excellent medium for most objects. It is alleged, however, that fungi are very apt to grow in glycerine and its solutions. We are inclined to believe that this may be avoided by adopting the precaution detailed at the end of this section. We have now before us specimens that were mounted in pure glycerine and water, eighteen years ago, and they are still quite perfect. If, however, there should be any danger in this direction, the addition of a little camphor will prevent the evil. Glycerine exerts a powerfully solvent action on many salts, particularly salts of lime, such as the car- bonate, and hence it is employed for preventing scale in the boilers of steam-engines. This property renders it dangerous to use it for the preservation of structures containing com- pounds of lime. Glycerine Jelly. — The original directions given by Law- rance are as follows: " Take any quantity of Nelson's gelatine, (any good gelatine will answer, however,) and let it soak for two or three hours in cold water; pour off the superfluous water, and heat the soaked gelatine until melted. To each fluid ounce of the gelatine add one drachm of alcohol, and mix well; then add a fluid drachm of the white of an egg. Mix well while the gelatine is fluid but cool. Now boil until the albumen coagulates, and the gelatine is quite clear. Filter through fine flannel, and to each fluid ounce of the clarified gelatine add six fluid drachms of Price's pure glycerine, and mix well. For the six fluid drachms of glycerine a mixture of two parts of glycerine to four of camphor water may be sub- stituted." Glycerine jelly is a very excellent medium, and is easily used. At ordinary temperatures it is quite solid, but when slightly heated it melts, and may be used like balsam, directions for mounting in which will be found in the next section. Objects - that are to be mounted in glycerine jelly should be soaked until thoroughly saturated with a mixture of 7 parts glycerine, C parts water, and 1 part alcohol. It is also well, after immers- ing them in the melted jelly, to place the slide for a short time OF THE MICEOSCOPE. 101 on a water bath heated to about 125° Fah. The jelly then pen- etrates every part of the preparation. When intended for use in very warm climates the proportion of the gelatine to the other ingredients should be increased. Hantzsch's Fluid. — Very beautiful preparations of delicate vegetable forin3 have been prepared with, this liquid, even the coloring matter being left unaltered. It consists of 3 parts of pure alcohol, 2 parts of distilled water and one part of glycer- ine. The object, placed in a cell, is covered with a drop of this liquid, and then set aside under a bell-glass. The alcohol and water soon evaporate, so that the glycerine alone is left, and another drop of the liquid is then to be added, and a second evaporation permitted; the process being repeated if necessary, until enough glycerine is left to fill the cell, which is then to be covered and closed in the usual manner. We have used this liquid with gratifying success. It is easily prepared, is not difficult to use, and it gives very excellent re- sults. Glycekine am> Gum. — Of this medium Carpenter says: " For many objects that would be injured by the small amount of heat required to melt Deane's gelatine or glycerine jelly, the gly- cerine and gum medium of Mr. Farrants will be fonnd very useful. This is made by dissolving 4 parts by weight of picked gum arabic in 4 parts of uold distilled water, and adding 2 parts of glycerine. The solution must be made without the aid of heat, the mixture being oooasionally stirred, but not shaken, whilst it is proceeding: afte^ it has been completed, the liquid should be strained (if not perfectly free from impurity) through fine cambric previously well washed out by a current of clear cold water; and it should be kvjpt in a bottle closed with a glass stopper or cap (not with coik), containing a small piece of camphor. The great advantage of this medium is that it can be used cold, and yet soon viscifibs without cracking; it is well suited to preserve delicate animal as well as vegetable tissues, and in most cases it increases their transparency. Deane's Gelatine. — Before the Introduction of glycerine jelly, Deane's gelatine was a favorite medium, and we still use 102 SELECTION AND USB it ■with success. Take gelatine, 1 ounce; honey, 5 ounces; ■water, 5 ounces; rectified spirit, J ounce; creosote, 6 drops. Soak the gelatine in -water until soft, and then add it to the honey, which has been previously raised to a boiling heat in another vessel. Then boil the mixture, and when it has cooled somewhat add the creosote mixed with the spirit. Lastly, fil- ter through fine flannel. When required for use, the bottle containing the mixture must be slightly warmed, and a drop placed on the preparation upon the glass slide, which should also be warmed a little. Next, the glass cover, after having been breathed upon, is to be laid on with the usual precau- tions. The edges may be covered with a coating of Bruns- wick black. Care must be taken that the surface of the drop does not become dry before the application of the glass cover; and the inclusion of air-bubbles must be carefully avoided. Alcohol. — Mixed with water in various proportions, alcohol forms one of our best preservative liquids, for both animal and vegetable substances. The chief objection to it is the difficulty with which it is retained in the cell. Thwaite's Fltiid. — Take water, 16 ounces; alcohol, 1 ounce; creosote, sufficient to saturate the spirit; chalk, as much as may be necessary. Mix the creosote and spirit, stir in the chalk with the aid of a pestle and mortar, and let the water be added gradually. Next add an equal quantity of water saturated with camphor. Allow the mixture to stand for a few days and filter. Used for preserving desmidiss, and also animal substances. Beale's Liquid. — Creosote, 3 drachms; wood naphtha, 6 ounces; distilled water, 64 ounces; chalk, as much as necessary. Mix the naphtha and creosote, then add as much prepared chalk as may be sufficient to form a thick, smooth paste; after- wards add, very gradually, a small quantity of the water, which must be well mixed with the other ingredients in a mortar. Add two or three small lumps of camphor, and allow the mix- ture to stand in a lightly covered vessel for a fortnight or three weeks with occasional stirring. The almost clear supernatant fluid may then be poured off and filtered if necessary. It should be kept in well-corked or stoppered bottles. OF THE MICBOSCOEE. 103 Goadby's Fluids. — Goadby used two distinct fluids, desig- nated by letters A and B, the difference being that alum -was a constituent of one and not of the other. Of both fluids there were several degrees of strength, which were designated by numbers. A fluid, as usually employed (A2), consisted of rock salt, 4 ounces; alum, 2 ounces; corrosive sublimate, 4 grains; boiling water, 2 quarts. To make the B fluid take rock salt, 8 ounces; corrosive sublimate, 2 grains; boiling water, 1 quart. Pacini's Fluid. — Take corrosive sublimate, 1 part; pure chloride of sodium (common salt), 2 parts; glycerine, 13 parts; distilled water, 113 parts. This mixture is allowed to stand for at least two months. After that time it is prepared for use by mixing one part of it with three parts of distilled water, and filtering it through filtering paper. This fluid is very strongly recommended by Frey. It is used for blood globules, nerves and ganglia, the retina, cancer cells, and especially delicate pro- teinous tissues. Castob Oiii. — This is used for preserving certain crystals. The best cold-drawn castor oil answers the purpose. There are a few general rules which we have found essential to the successful use of these media, but which are often neglected, the result being the ultimate destruction of the specimens. One of the most important points is the use of an abundance of the medium (we are now talking of preserving, not mounting) and the gradual saturation of the object with it. A piece of fresh muscle, simply mounted in a shallow cell with a drop or two of Goadby's fluid, will spoil in a very short time. The same object, properly treated, may be preserved indefin- itely. The proper course is to completely immerse the object in a considerable quantity of the liquid, and if necessary change the liquid several times until the substance to be pre- served has been thoroughly subjected to the action of the medium. For this purpose the quantity contained in ordinary cells is altogether too little; small cups, basins, large watch- glasses, etc., are needed. It must be remembered that the sub- stance acted upon generally absorbs certain constituents of the preserving fluid, and hence the latter is left either very weak 104 SELECTION AND USE or there is an unequal distribution of the constituents as re- gards the substance itself and the surrounding fluid. Moreover the fluids contained in many objects are displaced by the pre- serving medium, and tend to dilute the latter. In most cases, therefore, where the preserving medium is a liquid, the desired result is best attained by soaking the substance in the fluid for several days before mounting, changing the liquid two or three times, and finally mounting in fresh fluid of regular strength. We would lay great stress upon this point, having seen many fine preparations spoiled by pursuing a different course. The late Dr. Goadby, whose skill in this department was well known, always insisted upon this course, and during a some- what extended intercourse with him, and observation of his methods and processes, we became fully convinced of its im- portance. With many preservative liquids, it is well to begin with a diluted article, and gradually increase the strength at each change of fluid until the proper strength has been reached. This course is specially recommended with glycerine and saline solutions. Another point which demands attention is the entire exclu- sion of air, especially of oxygen. Now air adheres with great tenacity to most surfaces, such as those of glass or metal, and it dissolves to a considerable extent in all watery solutions. To get rid of it, the surface of the cell and cover should be either well warmed, and then allowed to cool just before being filled, or washed with alcohol (after which it may be dried). To ex- pel the air from the liquids, they should be boiled, and to pre- vent the absorbtion of a fresh dose of air, they should be kept well stoppered. But as air will find access to the liquids so as ultimately to saturate them, it is necessary to boil the fluids at frequent intervals, so as to get rid of this element. Without strict attention to these points it is almost impossible to pre- serve animal substances for any length of time in saline fluids. Mounting Objects.— For the purpose of conveniently exhibiting and comparing objects, and arranging them in cab- inets where they can be at all times accessible, it is necessary to mount them securely in such a manner that they may be easily OF THE MICROSCOPE. 105 handled. For purposes of mere examination and study, mounting is unnecessary, but when the objects are to be kept for future reference it is indispensable. It is true that where the specimens are large they might be kept in bottles in a pre- servative fluid, and taken out when wanted. This would be very inconvenient, however, and with very minute or delicate objects it would be almost impracticable. There are three modes in which objects are mounted: 1. Dry, the object being simply attached to the slide and suitably pro- tected. 2. In balsam, the object being immersed in Canada balsam, damar medium, copal varnish, or some similar mate- rial. 3. In fluid, the object being mounted in some of the pre- servative liquids previously described. Specimens may be mounted in any of these ways, so as to be viewed either as transparent or opaque objects, and the instruments and mate- rials required are neither numerous nor expensive. With those named in the following list almost any ordinary object may be neatly put up, though it is of course to be expected that occa- sions will frequently arise when special instruments and methods, which are not described by any author, will be needed. Experience alone can enable the microscopist to treat such cases successfully. Slides. — Most objects are mounted between two pieces of glass, one of which is called the slide and the other the cover. As it is convenient to have these slides all the same size, so that they may be easily arranged in cabinets, the Microscopical Society of London has adopted a slide three inches long by one inch wide as the standard size for use amongst their members, and this size has been generally adopted by microscopists throughout the world. All the best slides that are found in market are of this size, and the microscopist who fails to adopt it will be subject to great inconvenience when he desires to ex- change objects with others who are pursuing similar studies. Several other sizes are employed by the French, most of them being quite small (2 J by £ and 2J by f ), but as these small slides are the only ones that can be used with some French micro- scopes — -the stages of which are too small to take a slide 3 by 1 — they are usually kept in stock by dealers in microscopic appar- 106 SELECTION AND USE fitus. Small slides have this advantage, that they cost less, and take up less room in a cabinet. Large slides look best, and af- ford more room for descriptive labels, which is an important point. But since slides 3 by 1 have been adopted by common consent, the microscopist who mounts specimens, or who buys objects mounted on slides of a different size, commits a mis- take for which the advantages offered by the small slidas are but a slight compensation. The only exceptions to this rule are where the objects are too large to be mounted securely on a slide of standard size, or where a large number are to be pre- pared for the purpose of illustrating some special series of in- vestigations. It is to be presumed that such a series will never be broken up and separated, and as it will in all probability be assigned to its own cabinet, it is sometimes of advantage to have it upon slides of a size other than that in common use. As the objects composing such a series will probably be num- bered and catalogued, there is no necessity for extended de- scriptions on the labels, and therefore slides of half the usual size (1} by 1) will serve very well. The cabinet may thus be reduced in bulk by one-half. We have a special cabinet, illus- trative of textile fibres, mounted upon slides of small size, and find it quite convenient. The glass from which slides are cut should be free from air- bubbles, scratches and that wavy appearance which is due either to inequalities in the surface or to irregularities in the composition of the glass itself. Ordinary window glass is en- tirely unfit for the purpose. The most suitable kind is plate glass, the surface of which has been ground and polished, so as to be perfectly even and smooth. Glass of this kind is used for looking-glasses and by photographers, and when other material, could not be had, we have made very excellent slides out of broken looking-glasses and photographer's plates, though it is difficult to get the latter thin enough. Slides of good glass are, however, manufactured in quantity and sold at a reason- able price, so that under ordinary circumstances it will hardly pay the microscopist to cut out his own slides. Moreover the elides sold by the dealers have the edges neatly ground, an operation which the microscopist will find tedious and trouble- OF THE MICROSCOPE. 107 As procured from the manufacturers, the elides are always dirty, never having been washed after the process of grinding and polishing the edges. If this dirt were soft it would not matter so much, but it is in general hard and gritty — being in fact the grinding sand — and the consequence is that the surfaces of the slides are very apt to be scratched and injured. There is but one firm that exports slides to this country, and they are very careless in this respect. Out of a gross of slides it is often difficult to find two dozen that are not so scratched as to be worthless for the finest class of work. Having procured the slides, however, the first thing to do is to clean and assort them. They should be cleaned by being rinsed in water con- taining a little washing soda; the dirt being removed if neces- sary by the use of an old nail brush or tooth brush. Until this has been done they should not be wiped with cloth or leather, for by so doing the particles of sand are dragged along the surface, making a deep mark. They should then be washed in pure water, carefully wiped with a soft cloth, and assorted for thickness and quality. It is in general best to sort them into three classes — thick, medium and thin — the latter being used for test and other very delicate, objects. Elaborate instru- ments have been devised for measuring the thickness of the slides, so as to assort them accurately, but they are entirely un- necessary; the eye is a sufficiently accurate guide. To deter- mine their quality, they must be examined under the micro- scope, and as it is only the central portion that is of any con- sequence in this case, we place them on a brass plate, 3 by 1, with the edges slightly turned up, and having a hole five- eighths of an inch in diameter in the centre. That part which lies over the hole is the only part which it is necessary to ex- amine. Slides which contain air-bubbles, strise or scratches, are at once laid aside to be used either for opaque objects or those of a very coarse kind. Those that are perfect are care- fully stored away where they will not be subject to injury. Covers. — After being properly arranged on the slide with a suitable preservative medium, the objects must be covered with a small piece of thin glass. Glass intended specially for this purpose is made in England, and imported either in sheets or 108 SELECTION AND tISB cut into squares and circles of suitable sizes. Directions for cutting these covers would be out of place here. The beginner ■will always find it most economical to buy them ready cut. Of the two kinds — round and square — the former are, for all ordi- nary purposes, the most convenient, as covers of this shape are best suited to cells made with the turn-table, and they may also be finished more easily and neatly than the square ones. Covers should be carefully assorted for thickness, since the thickness of the cover exerts a material influence on the per- formance of all lenses except those of the lowest power or quality. Where objectives which do not adjust for thickness of cover are employed, the microscopist should find out the exact thickness to which they have been corrected by the maker, and use glass of this thickness in covering all objects that are to be examined by means of these lenses. The inexperienced student will be apt to find some difficulty in cleaning these covers. They are so fragile that it is difficult to rub them, so as to remove dirt, without breaking them. The best method is to soak them in a weak solution of potash, linse them off carefully several times with clean water, and after pouring the last water off, give them a final rinsing by taking them up in a pair of forceps and moving them about in a tum- bler of clean water. They should then be laid (singly, of course) on a wiping block and wiped. Wiping blocks are made by covering a flat block of wood with chamois leather or linen, drawn tightly so as to present a flat but somewhat soft surface. These blocks are generally made round and with handles, but we prefer them oblong (4 by lj inches) and without handles. One of them is laid on the table face up ■ upon this face the thin glass is laid and wiped with the other block. In this way the thinnest glass can be cleaned without risk of fracture. Cells — Tokn-Takle. — All objects that are mounted dry or in fluid should be placed in cells, as unless this is done it is dif- ficult to arrange the object properly or to secure the thin cover permanently. In the majority of cases these cells consist of little more than a ring of cement laid on the glass slide and allowed to harden, and their depth does not exceed the thick- ness of a sheet of paper. Such cells are in constant demand. OF THIS MIOEOSCOPE. 109 and are almost always made by the microscopist himself by means of a little instrument known as a turn-table or whirling table, of which there are several different forms in market. A cheap and efficient form is shown in Fig. 35. The table is sup- ported by a spindle upon which it turns, motion being com- municated by means of a milled ring. The slide is held in its place by two spring clips, and it is brought to the centre, by means of a guide or bar, c, with a square projection. This is carefully arranged, so that a slide 3 by 1 shall be accurately centered. Hence it follows that the rings and cells on all the slides put up by the owner may be instantly and accurately e_ Pig. 35.— TUBN-TABLE. centered by simply placing them on the table and bringing- them up to a firm bearing against the guide. This bar or guide may, however, be instantly removed when desired, and when this is done, any cell may be truly centered by the usual methods. This turn-table, therefore, enables us always to bring cells of our own make instantly to a perfectly accurate centre, while other cells can be centered at any iime with very little trouble. To most turn-tables there lies the objection that the devices for centering and holding the slide make one side heavier than the other, and consequently, as every mechanic knows, irregu- lar and eccentric motion is the result. On many otherwise Well-made instruments it is, from this cause, impossible to make a true cell, particularly if we attempt to work at a high speed. 110 SELECTION AND TTSE In the turn-table j ust described, this difficulty is obviated by a heavy-headed screw, of the precise weight necessary, which is screwed into the under surface of the plate, and gives a per- fect balance to the wheel. It then runs smoothly and truly. Those who once see a turn-table, will find no difficulty either in understanding the method of using it, or in putting this knowledge into practice. The slide, being held on the table either by springs or clutches, is made to revolvo rapidly, and a brush, charged with cement or varnish, is held against its sur- face so as to leave a ring. There is a slight knack about making good cells, which it requires a little practice to acquire. The brush must be held in the direction of a tangent to the ring — that is, it must not point to the centre of the circle, but must lie so that the ring, as it revolves, will draw the cement away from the brush. Practice alone can give expertness in doing this, and we would advise the beginner to work steadily for a few hours at making cells on pieces of common window glass, strips of which can be had for nothing from any glazier. The chief points to be attended to are the position of the brush and the consistence of the cement. If the latter be too fluid, it spreads and does not form a well-defined circle. If too thick it does not leave the brush as freely as is necessary. The method of preparing the cement will be explained under the proper head. Kg. 41. Where a turn-table is not at hand, very good cells may be made as follows: On a card draw the outlines of a slide with a series of circles in the centre, as shown in Fig. 41; lay the slide on the card so that the centre of the circles will be at the centre of the slide, and then paint a circle of cement on the Or THE MICROSCOPE. Ill slide by hand, the rings beneath serving as a guide. Very good cells may be thus made, but the process is of course more tedious than that with the turn-table, and does not give as neat results. A few precautions are necessary in order to insure the per- manent adhesion of the cells to the glass. In addition to pro- viding cement of good quality, we must see that the slide is dry and recently heated. It is difficult, with most cements, to use hot slides, as the cement is apt to flow; but the slide should have been recently heated, and after the cement has partially hardened, the cells should be baked by exposure to a temper- ature as high as they will stand. This is easily done by placing them on a board or plate, and leaving the latter for a short time in an oven. Where cells of greater depth are required, rings of various materials are cemented to the slide. For objects mounted dry, rings of leather or cardboard answer well, provided they are carefully varnished so as to be impervious to air and moisture. For liquids, rings of glass, tin, ebonite, etc., are used. Kings of rubber and gutta-percha have been suggested, but they do not answer, as they soon become rotten. Full directions for making and using deep cells may be found in the works of Quekett, Carpenter, Beale, Frey, etc. Hot-Plate. — This is simply a stout plate of brass or iron, which is supported over a lamp by suitable means. The com- mon plan is to insert four stout wires to serve as legs, but a better mode is to support the plate on the ring of a retort stand, as its distance from the lamp can thus be readily ad- j usted and the temperature regulated. The hot-plate serves to distribute the heat, and thus to prevent the slides from becom- ing suddenly and unequally heated. Moreover, by means of it several slides can be heated at once, and thus much time may be saved. It should be tolerably heavy. The one we use is of cast iron, six inches long and three inches wide. The upper surface has been ground so as to be tolerably smooth, When a hot-plate is not at hand, a good substitute may be found in a smooth brick, or, better still, a plate of soapstone. These may be heated in the fire and will retain their heat for a long time. 112 SELECTION AND USE Lamp. — Any lamp, or even candle, will answer, but we prefer a spirit lamp, the flame being free from smoke and easily man- aged. At night the kerosene lamp used for giving light will answer. Where gas is used, the Bunsen burner is a great con- venience. Whatever lamp or burner be used, it should be sur- rounded with a chimney or shade, so as to prevent the flicker- ing of the flame by currents of air. The best shade is a tin cylinder, with rows of holes at top and bottom for the admis- sion and exit of air. Retort Stand. — A suitable retort stand is a very simple affair, and is best made at home. Ours consists of a board of hard wood, 5 inches by 4, into which is screwed a rod fourteen inches long, and a quarter of an inch in diameter. The rings have no screws, but are simply pieces of wire, one end of which is twisted round the rod, while the other is formed into a ring of the required size. Kings formed in this way are easily moved on the upright rod, but no weight placed on them in the usual manner can cause them to slip down. Cards fob Centering the Objects. — Unless the objects are placed on the centres of the slides, the latter have a very awkward look. By drawing the outlines of a slide on a card, and marking out the centre, this difficulty is easily overcome. A card marked off in this way is shown in Fig. 42. It is well to have two cards, one black with a white centre, and the other white with a black centre, as some objects, when immersed in the medium in which they are to be mounted, OF THE MICROSCOPE. 113 show best against a dark ground, while others are most easily seen against a light one. Those wLo use the self-centering turn-tables may readily centre their slides by painting on them a ring of some water-color, which is easily washed off. The ring . is, of course, laid on the side opposite to that which receives the object. Mounting Needles. — These are similar to dissecting needles, but beiDg used in balsam, varnish and similar substances, they cannot be used for dissection, and should be kept by them- selves. They are most easily cleaned by being warmed over the lamp, and wiped with a piece of soft leather. When the balsam is burned on them, as recommended by some, it leaves a crust which is not easily removed. Covek Fobceps. — In placing the cover on the object, the ordinary forceps are very inconvenient. We have long used a pair of forceps bent as in Fig. 43, and with the points carefully adjusted. The mode of using the instrument will be obvious from the engraving. A very ingenious device intended to answer the same purpose has been invented by Dr. Fletcher. These forceps are self-closing, so that the thin glass cover is held without any effort. After the cover is in position on the slide, by pressing on the blades they open and allow it to slip out. If the cover should stick to^he forceps in the slightest de- gree, it may be pre- vented from moving when the forceps are removed by in- serting a common pin in the slit seen in Fig. 44. When using the forceps shown in Fig. 43, the same end may be attained by means of a wire fork (a hair-pin is as good as anything), which may be made to straddle the nose of the instrument. Kg. 43. Fig. 44. 114 SELECTION AND USE Slide Holder. — The hot slides cannot be comfortably held in the fingers, and therefore a pair of -wooden forceps become a necessity. Those usually sold are made by screwing together two thin slips of wood with a piece of brass or lead inserted be- tween them at one end. To admit the slide, the slips are forced apart by pressing on pins arranged as in the stage forceps. When placed on a table the metal counter-balances the slide, and keeps it from touching the surface on which it is laid — a very important point. The Eng- lish forceps, being all wood, fre- quently tip with a heavy slide. A common spring clothes-pin is frequently used, but when we come to lay the slide down, the clothes-pin holds it in an awk- ward manner. The end of the hot slide is sure to lie on the table, and if fluid balsam or other me- dium should be present, the fact that the slide is not level produces bad results. By cutting off about half an inch from one of the limbs of the forceps part of the pin, however, this difficulty is avoided. The slide may then be grasped in such a way that when the clothes-pin is placed on the table, the glass will be held in a perfectly level position. A glance at Fig. 45 will show what we mean. A great advantage of this form of holder is that it costs but a trifle, so that the micro- scopist can supply himself with an abundance of them, and thus several slides may be cooling, while work on others is going on. When very heavy slides are used, it may become necessary to screw a plate of sheet lead to the under side of the plpthes-pin, so as to prevent tipping. rut OF THE MICROSCOPE. 115 Water Bath. — A water bath is indispensable in those cases where a certain very moderate degree of heat is not to be ex- ceeded. Few persons fully appreciate the difficulty of regu- lating or even estimating the temperature of an object held over a naked flame, and mischief is often done before the operator is aware of it. A serviceable water bath is easily extemporized out of an old fruit can and a small beaker glass. This serves for exposing material and preparations to a temperature lower than that of boiling water. Where slides are to be so heated, the simplest contrivance is a flat tin box, with all tbe joints (cover and all, of course,) tightly soldered. A small tube, closed with a cork, serves to admit the water. Spring Clips. — One of the first of the needs which impress themselves upon tbe mind of the beginner, is the necessity for something to retain the thin cover in its place, until the ce- ment, which is intended to hold it permanently, dries. An end - less variety of spring clips have been invented for this purpose, but we have never seen anything that we liked better than the simple article shown in Fig. 46, and which we have used for Fig. 46. over fifteen years. It consists simply of a piece of brass wire bent as in the engraving. The slide being held in the left hand, the clip, held by the upper wire, is brought so that the projecting part of the ring is placed under the edge of the slide. The upper part is then lifted up so as to open the clip, which is then slid on to the slide until the vertical point is in the right position. When a broader surface than the point of the wire is needed, a piece of cork may be stuck on it, and if 116 SELECTION AND USE there should be need for greater pressure than that which the spring of the wire affords, this can be obtained by sliding a small brass ring on to the clip. Various other forms of spring clip have been invented, but none that we consider more simple, or that we like better than the above, which has this great merit, that any one can make it for himself out of materials that may be obtained at any hard- ware store. It must be borne in mind, however, that all clips constructed upon this plan are apt to cause a slight displace- ment of the object, from the fact that the movement of the point is not quite perpendicular. With delicate objects this is a matter of importance. The only remedy is to use the end pressure of a rod moving in fixed guides. CEMENTS AND VAENISHE8. A supply of carefully selected cements and varnishes is indis- pensable to the microscopist, and it is also well that he should understand the nature and properties of the materials used, otherwise he will be liable to make gross blunders. Thus, of the different articles in use, some are easily mixed with each other, while others separate as soon as left to themselves; some dry in one way and some in another. It would require a vol- ume to detail the properties of the different substances which enter into the composition of the cements used by the micro- scopist. We have space for only the following hints, which, however, we hope will prove useful. Cements become hard in three different ways — cooling, evap- oration and oxidation. Shellac, sealing wax, electrical cement, etc., when melted by heat, furnish examples of the first pro- cess. Shellac and sealing-wax dissolved in alcohol, and asphalt and damar dissolved in turpentine, dry by the second process — the solvents evaporating and leaving behind the material which they had dissolved. Drying oil in all its forms, such as gold size, paint, etc., becomes hard by oxidation — not, as is gener- ally supposed, by evaporation. In the case of varnishes which dry by the evaporation of some of their constituents, it is obvious that if a fresh layer Or THE MIOBOSOOPE. 117 be laid over an old one, the old layer will be softened, and if there should be any tendency to a vacuum in the cell, the softened cement will be unable to resist the outside pressure, and will creep in and spoil the object. So, too, with varnishes or cements formed chiefly of drying oil or gold size. If the different coats be laid on too thickly or too rapidly, the part that is beneath cannot easily harden, but will remain tor a very long time in a semi-liquid condition. We have just removed some brass rings from slides to which they were attached four months ago by means of gold size, and although the outer surface of the cement was hard and dry, the interior was quite liquid, freely soiling the fingers. Goia> Size. — The most extraordinary recipes have been given for the preparation of this cement, which is in reality nothing but good linseed oil rendered very drying by the usual methods. Gilders frequently make it into a semi-paint by adding coloring matter, thus forming a ground of a shade similar to the gold they use, and this seems to have misled some of our best writers. There is no ochre, litharge, or anything of the kind present in good gold size. It does not pay to pre- pare gold size in small quantities, and it may be obtained from any color dealer. The older it is the better, and it is well, therefore, to lay in a good stock, which must be kept carefully corked. The working supply should be kept in a small bottle. This is the favorite cell making material employed by Dr. Car- penter, and it is certainly the most reliable cement we have. It adheres firmly to glass, and if laid on in very thin successive layers, tolerably deep and very durable cells may be built up, but the process requires considerable time, otherwise the under layers will remain soft. It has this great advantage over asphalt, damar, and other cements composed of solid materials dissolved in some menstruum, that fresh coats have but very slight action on the old layers on which they may be laid. It mixes with turpentine, and consequently with most materials soluble in turpentine, but when once dry and hard, turpentine, alcohol, ether, etc., have little or no action on it. It does not mix with alcohol, and therefore cannot be mixed with the solution of shellac in alcohol in any of its forms. 118 SELECTION AND USE Black Japan. — When this can be procured oi good quality, it makes a very excellent cell. It adheres very firmly to the glass provided the latter be exposed to a moderate heat after the cement has become dry. Black Japan dries up and thick- ens when kept, but may be thinned with turpentine. Bbtjnswick Black. — This is simply a solution of asphaltum in turpentine. Occasionally it is rendered very black by the addition of a little lampblack. When good, it makes a very excellent cement. Its quality depends chiefly upon the char- acter of the asphaltum that is used in iis preparation. Now there are several varieties of asphaltum in market, the most common kind at the present day being that obtained from coal tar. This seems to be entirely unfit for the purpose. The proper kind is that which is found native in several parts of the world. The two kinds are easily distinguished by their odors. Shellac. — This well known substance, when dissolved in alcohol, forms a varnish or cement of great value to the micro- scopist, and is the proper one to be used when glycerine is em- ployed. Much of the shellac in market is artificially made from resin and wax, and makes a poor varnish. Heal shellac must be employed if failure would be avoided. Bell's Cement. — Carpenter states that this cement is merely shellac dissolved in alcohol. With us it has presented no ad- vantage over other cements. Sealing Wax Yaenish. — This is prepared by dissolving the best sealing wax in alcohol. It unfortunately happens that all the fancy colored sealing wax in market is of inferior quality. Very excellent red wax may be obtained, but we have never been able to obtain good blue, black, green or other colored wax. We therefore make varnish of these colors by dissolv- ing in alcohol the materials used for making the best red wax, substituting some other color, however, for the vermillion. Coloeed Shellac. — Bleached shellac, dissolved in alcohol, and colored with aniline blue, red, etc., makes a very fine trans- parent varnish. 01* THE MICitOSCOftB!. 119 Damae Cement. — This is a mixture of equal parts of damar varnish and gold size, mixed together. It should stand for some time before being used. It is said to be very excellent. It is very tough, and serves well as an outer coating over such brittle cements as shellac and sealing wax varnish. Marine Glue. — This is undoubtedly the strongest cement in use for joining pieces of glass or glass and metal together. E'rilful microscopists make- great use of it; beginners do not find it so easy to manage as some others. In using it, the simplest method is to cut it in small pieces, lay it on one of the surfaces that are to be joined, melt it by heat, and apply the other surface, making sure of perfect contact by rubbing the two pieces upon each other, if they will allow of it. Marine glue may be obtained from most dealers in microscopes. The cement known as liquid glue, is simply a solution of shellac in alcohol. For attaching labels, paper covers, etc., to tbe slides, nothing is better than good dextrine. After having mixed the dextrine with water to the proper consistence, add six drops of glycer- ine to the fluid ounce of dextrine. This will prevent the labels or covers from cracking off. Having provided himself with the necessary tools and mater- ials, the next step is to learn how to use and apply them, and this will probably be most easily taught by describing a few char- acteristic examples. And first of all, selecting the most easily mounted of all objects, we commence with the scales on the butterfly's wings. Having prepared a cell of proper size, and allowed it to dry, the first step is to select a cover to suit it, and give a final cleaning to both slide and cover. When every particle of dust has been removed, breathe gently on the slide, and press the wing lightly against it, and within the cell. A large number of scales will at once adhere to the slide, and the next step is to attach the cover. Place the slide on the hot- plate, (which must not be too hot, however,) and when it is thoroughly dry, and the cement somewhat soft, lay the cover on by means of the cover forceps. Press it into contact with the cement, and the operation is completed. It is not difficult to see when the cover and the cement are in perfect contact, 120 SELECTION AND USB and great care must be taken to close the cell all round in this •way. It is true, this point is not of so much consequence with the particular object under consideration, but with some ob- j ects it would be quite important. The scales are now mounted dry, and may be kept for any length of time; no dust can soil them, and they are not liable to be injured by contact with other bodies. It only remains to label and " finish " the slide as hereafter directed. Next to the above in simplicity is the mounting of such ob- j ects as the wings of insects in balsam. Suppose we wish to mount one of the smaller wings of a bee or wasp, so as to show the curious hooks with which it is armed: Place the warm slide on the centering card, drop a little balsam on the centre, and again warm the slide, so that any air that may be present may collect in fine bubbles which can be removed by means of a cold mounting needle. When the air-bubbles have been re- moved, seize the wing (previously well cleaned with a camel hair brush) with a pair of fine forceps, and lower the tip of it into the warm balsam. Then slowly lower the wing until it is en- tirely immersed. Drop, very little more balsam on it, warm the slide again (slightly this time), and remove air bubbles if there should be any. Then take a clean cover in the covOr for- ceps, make it quite warm, and place it over the object by allow- ing it to first touch one edge of the balsam, and then to grad- ually fall down so as to exclude all air bubbles. In the case of the bee's wing it does not answer to apply much pressure as this would tend to distort the hooks. Press the cover into place as much as it will bear and no more, lay the slide in a warm place for some time until the balsam hardens, and then clean and finish the slide. In mounting objects in balsam and fluids, the great difficulty to be encountered is the presence of air bubbles. Careful and j udicious management, however, readily enables us to avoid them. In the first place see that they are entirely removed from the balsam on the slide. This is much more easily done before immersing the object in the balsam then afterwards. Next see that the air is expelled from the object. In the case of the wing, this is effected by slowly immersing the object in the balsam. Lastly see that no air enters with the cover. To OP THE MI0EOS0OPE. 121 do this see that the cover is hot, and that it is lowered on the balsam slowly, and from one side. If in any case there should be a vacant space under the cover as at a Fig. 47, and it should be desired to fill it, do not apply the fresh balsam directly at a. To do so would certainly be to inclose a large air bubble. Drop the balsam at b, warm the slide, and the balsam will creep in by capillary attraction, and expel the air. Pig. 47. Let us now suppose that we have some small insect which we have prepared by soaking in potash, and which we desire to mount in balsam. Such a preparation if immersed directly in balsam, would be spoilt, since the balsam and watery solu- tion would not mix. Therefore, proceed as follows: Wash the insect in pure water, and drain off the water; wash with strong alcohol, drain off the alcohol, and soak for twenty-four hours in the strongest alcohol you can get. ' Pour off the alcohol and soak for twenty-four hours in turpentine. The object may now be immersed in balsam without difficulty. Air pumps and similar contrivances are generally recom- mended as the best means for removing air bubbles, but we never use fchem. If the object be dry, we soak it in alcohol until all the air has been expelled, then transfer to turpentine, and finally to balsam. This requires time, it is true but it does not occupy the time of the microscopist. The soaking process goes on without any attention from him, and while it involves far less labor, with us it has always given far better results, tnough we have used very fine air pumps, and followed the best published directions. Take the case of a dry shaving of wood, many of which are well worth mounting. It would be 122 SELECTION AND USE very laborious to get the air oxit of this by means of the air pump, while by soaking successively in alcohol and turpentine, it can be mounted with great ease. Let us now take the cise of an object mounted in fluid in a cell. Suppose it is the so-called tongue of a fly, which of course has been soaked for some time in the liquid in whit h it is to be finally mounted, viz., dilute glycerine. We make a cell of suita- ble thickness, ■which in this case may be made with shellac dissolved in alcohol. Several coats will be required, and as shellac alone does not adhere well to glass, we prefer to lay on first a coat of gold size or Japan, and when this is thoroughly dry, to lay the shellac on it. No difficulty will be found in making a cell of sufficient depth. The cell is now to be filled with the liquid, the object placed in it, and the whole carefully examined for air bubbles, which must be removed if they exist. The cover is now applied, all superfluous fluid removed by means of a camel hair pencil, which has been moistened and then squeezed dry, and finally the edge of the cover is to be coated with a thin layer of cement. After a day or so another layer of cement should be laid on, and this process repeated until at least three layers have been applied. We give no directions for the construction and use of very deep cells as this is work that will hardly be attempted by be- ginners. When opaque objects are to be mounted either in balsam, or in fluid, the process required is the same as that employed for transparent objects. Very many opaque objects are, however, mounted dry, and in this case all that is needed is to attach them to a slide, and see that they are properly protected. When thin they may be readily mounted in cement cells, and this is altogether the neatest and most secure plan where it can be used. Thicker objects require deeper cells, which may be made of card, ebonite or electrical cement. (3 parts resin, and 1 of wax, colored with ochre or any similar matter). Cells of card are made by first punching out a disc like a gun wad." and then punching a hole in this so as to leave a ring. The ring is to be cemented to the glass slide and carefully var- nished. Wooden slides with a cell bored in the centre, are reeom- OV THE MICBOSOOEE. 123 mended very highly, and seem to answer a very good purpose. The cells are not bored quite through the wooden slip, and as they are blackened on the inside, any small object that may be cemented to the bottom of them shows very well. For seeds, small shells, and similar objects, they answer admirably. Iu most cases it will be found unnecessary to cover the celte with thin glass. Several slides may be packed together face to face, and if held in firm contact by means of a rubber ring, dust will be entirely excluded. Or they may be arranged in the drawers of an ordinary cabinet, face down, the labels being placed on the backs. This will effectually exclude the dust. Some years ago we mounted a large number of specimens of minerals on leather discs, which were cemented to glass slides. These leather discs were three-quarters of an inch in diameter, and we had a lot of pill-box covers which exactly fitted them. These covers, when slipped on to the discs, protected the ob- jects perfectly, and the whole formed a very cheap, convenient and excellent mode of mounting. A very ingenious cell for opaque objects, the invention of Prof Pierce, of Provi- dence, R. I., is shown in Pig. 48. It consists of a metallic cell, having a broad flange like the rim of a hat, which is cemented to an ordinary Fig. 48. glass slide, as shown in section in the lower figure. To this cell is fitted a metal cap, which covers and protects the object. The object may be placed directly on the glass, or raised by means of a disc of any re- quired thickness, so as to be more easily illuminated. The slide, with cell uncovered and containing an object, is shown in the upper figure. Uncovered objects may in this way be very perfectly protected from dust and mechanical violence. Where it is desirable to cover objects with thin glass, the method devised by Prof. H. L. Smith will be found very excel- lent. He takes a circular disc of thin sheet wax, which is easily cut with a punch from the sheet wax ordinarily used for mak- ing flowers, and attaches it by means of heat to the centre of a 124 « SELECTION AND USE glass slide. A brass ring, of which the interior is the same size as the disc, is then attached to the slide, and the object is fixed to the wax by slightly moistening the surface of the latter by a minute drop of turpentine. When dry, a cover, which exactly fits into the bevel of the ring, is attached with a little cement, and the whole may then be finished off on the turn table. The appearance is very elegant, and the specimens are perfectly pre- served. A cell which we have found very durable, easily and quickly made, and very neat, is constructed as follows: Having pro- cured some good gold size and pure litharge, grind the latter to a very fine powder. Mix the litharge and gold size to the thickness of cream, and color either black or dark olive by adding lamp-black. With this paint, as it may be called, make as many cells as are wanted, and when made, dust finely pow- dered litharge over them until they ai - 9 covered a sixteenth of an inch deep; allow them to stand a few minutes, and then shake off all the loose litharge by means of a few smart taps. The surface of the cell will now be quite rough. Allow it to stand a few hours, and then press it against a plate of glass. If this be done carefully, a smooth, solid ring will be left on the slide. If the edges should not be as smooth as they ought to be, it is easy to trim them off on the turn-table by means of a small chisel. Such cells, after a few weeks, become very hard, and may be finished so as to be very neat. By introducing a few obvious and unimportant modifications, we have, in this way, made cells of some depth which held liquids quite well. Finishing the Slides.— After the objects have been mounted, the slides may be finished in one of two ways: they may be covered with paper, or they may be left without any covering, the labels being attached directly to the slide. In the latter case the edges of the slide must have been previously ground and polished, and, as a general rule the thin cover is circular and not square, and is finished with a neat coat of var- nish on the edge. This varnish serves to do something more than merely ornament the slide; it secures the cover in its place, and prevents the drying up of the medium used for mounting. Even in the case of Canada balsam it is of use, for OF THE MICROSCOPE. 125 if gold size be used as the varnish, it prevents the evaporation of the turpentine, and the ultimate drying and cracking of the balsam. Where glycerine jelly, glycerine, or glycerine and gum are used, it becomes indispensable. The process employed for finishing slides in this way is as follows: The objects having been mounted, the slides are laid away until the balsam, cement, etc., have been hardened, when all superfluous matters of this kind are easily removed with a small chisel made out of a brad-awl ground thin and sharp. A small chisel-pointed piece of hard wood, and a little water, will remove the last traces of balsam or varnish, and if necessary a final cleaning may be given with a rag moistened with alcohol. The slide is then placed on the turntable, and a neat rin& of varnish, either plain or colored, is run around the edge. The proper labeling of the slides is an important matter. Our system is as follows: As soon as the object is mounted, the slide is labeled on the under side with a very thin gummed label, and it is also numbered on the upper side with a writing diamond. Of this number a record is kept, so that even if the label should fall off or get soaked off, a new label may be pro- vided. As soon as the slide is finished, the regular label is attached, and the small label removed. As regards designs, etc., for labels, the variety is endless. Each microscopist will probably select the one that accords most nearly with his own taste. Established I87Q. STANDARD BOOKS PUBLISHED AND FOE SALE BY THE INDUSTRIAL PUBLICATION CO. 22 College Place, . . „ . New York. These boohs will be sent, postpaid,, to any address in any accessible part of the world, on receipt of price. — Full Descriptive Catalogues may be had free New Catalogues, with additions of new books, are issued from time to time, and will be sent to any address on request. — Address, INDUSTRIAL PUBLICATION CO., 82 College Place, New York. THE STEEL SQUARE AND ITS USES. Being a Description of the Square and Its Uses in Obtaining the Lengths and Bevels of all kinds of Rafters, Hips, Groins, Braces, Brackets, Purlins, Collar-Beams, and Jack-Rafters. — Also, its Application in Obtaining the Bevels and Cuts for Hoppers, Spring Moldings, Octagons, Stairs, Diminished Stiles, &c. — By Fred. T. Hodgson, author of "Practical Carpentry," " The Builders' Guide," &c. — Third Edition, Revised and Greatly Enlarged. — Illustrated by Nearly One Hundred Fine Engravings. — Cloth, gilt. . . $1 This is the only practical work on the steel square and its uses ever published. It is thorough, accurate, clear, and easily understood. Confounding terms and scientific phrases have been religiously avoided where possible ; and everything in the boot has been made so plain that a boy of twelve years of age, possessing ordinary intelligence, can understand it from end to end. This new edition, just issued, is illustrated by nearly one hundred handsome engravings, showing how the square may be used for solving nearly every problem in the whole art of carpentry. The carpenter who possesses this book need not waste time and material " cutting and trying." He can lay out his work to a hair's breadth, and "cut to the line." And, in these days, the workman who can not lay out his work accurately at the first attempt stands no show. The book is absolutely indispensable to every person who may have to use a carpenter's square. Joiners, cabinet-makers, bricklayers, stonecutters, plasterers, lumber-dealers, amateurs, and all who build a fence, tinker a gate, or make a chicken-coop will find something in this little volume that will help and aid them to do their work better and more intelligently than they could without a knowledge of its contents. Many difficult and troublesome mathematical problems can be solved by the use of this tool, and the methods of solving them are shown in this book. It describes how painting, plastering, and brickwork can be measured, and how many mechan- ical difficulties can be overcome with great ease. It explains how ellipses, parabolas, octagons, circles, and many other figures, may be described by the steel square. It is safe to say that this dollar book will easily enable any intelligent mechanic to save ten dollars in time and material during the first three months that he has it in use. CATALOaTJE OF INDUSTRIAL BOOKS. STEEL SQUARES AND THEIR USES. Being a Description of the "Various Steel Squares and Their Uses in Solving a large number of Mechanical Problems in Constructive Carpentry, Joinery, Sheet-metal Work, Cut-stone or Brick-work. Also, showing how many Geometrical and other Problems may be solved by the use of the Steel Square. — By Peed. T. Hodgson, author of "The Steel Square and Its Uses," "The Slide-Rule, and Its Uses," "Practical Carpentry," "The Builders' Guide," fee- Finely Illustrated.— Cloth $1 This forms Part II of " The Steel Square and Its Uses," and is not in any sens© . a substitute for the First Part, which still remains what it always has been — a neces- sity to every intelligent workman. Part II is an extension and enlargement of the First Part, giving new problems, new methods, and new wrinkles for shortening the labor and increasing the accuracy of the workman. It is illustrated in the same handsome manner which characterizes the First Part, to which it forms a companion volume. With these two volumes in his possession the workman has at command the entire practical mathematics of construction, and is prepared to lay out any piece of work more easily, quickly, and accurately than it can be done by any other method. PRACTICAL CARPENTRY. Being a Guide to the Correct Working and Laying-out of all kinds of Carpenters' and Joiners' Work, with the Solutions of the Various Problems in Hip-Boofs, Gothic Work, Centering, Splayed Work, Joints and Jointing, Hingeing, Dovetailing, Mitering, Timber- Splicing, Hopper-work, Skylights, Baking Moldings, Circular Work, &c. — To which is prefixed a thorough treatise on "Car- penters' Geometry." — By Feed. T. Hodgson, author of "The Steel Square and Its Uses," " The Slide-Rule, and How to Use It," "The Builders' Guide," &c. — Illustrated by over Three Hundred Engravings. — Cloth, gilt $1 This is the most thorough book of the kind ever published. It is thorough, practical, and reliable; and at the same time is written in a style so plain that any workman or apprentice can easily understand it. STAIR-BUILDING MADE EASY. Being a Full and Clear Description of the Art of Building the Bodies, Carriages, and Cases for all kinds of Stairs and Steps. — Together with Illustrations Showing the Manner of Laying Out Stairs, forming Treads and Risers, building Cylinders, preparing Strings; with Instructions for making Carriages for Common, Platform, Dog-legged, and Winding Stairs. — To which is added an Illustrated Glossary of Terms used in Stair-Building, and Designs for Newels, Balusters, Brackets, Stair-Moldings, and Sections of Hand-Rails.— By Fred. T. Hodgson, author of "The Steel Square and Its Uses," &c. — Illustrated by over One Hundred and Twenty Engravings, many of them full-page size. — Cloth, gilt. ... $1 This work takes hold at the very beginning of the subject, and carries the student along by easy stages until the entire subject of stairbuilding has been un- folded, so far as ordinary practice can ever require. This book, and the following one on Ha/nd-RoMvng, cover nearly the whole subject of Stair-Building. CATALOGUE OF INDUSTRIAL BOOKS. A NEW SYSTEM OF HAN D-RA1 LI NG. Or, How to Cut Hand-Railing for Circular and other Stairs, square from the Plank, without the aid of a Falling Mould. — By An Old feTAiRBtriLDER. — Edited and corrected by Feed. T. Hodgson, author of "Stair-building Made Easy," &c— Cloth, gilt. . . $1 The system is new, novel, economic, and easily learned. Rules, instructions, and working drawings for building rails for seven different kinds of stairs are given. THE BUILDERS' GUIDE, and Estimators' Price-Book. Being a Compilation of Current Prices of Lumber, Hardware, Glass, Plumbers' Supplies, Paints, Slates, Stones, Limes, Cements, Bricks, Tin, and other Building Materials. Also, Prices of Labor and Cost of Performing the Several Kinds of Work Required in Building; together with Prices of Doors, Frames, Sashes, Stairs, Moldings, Newels, and other Maehine-work. — To which is ap- pended a large number of Building Rules, Data, Tables, and Useful Memoranda, with a Glossary of Architectural and Building Terms. — By Fred. T. Hodgson, author of "The Steel Square and Its Uses," "The Slide-Rule, and How to Use It," "Practical Car- pentry," &c— Cloth $2 CARPENTERS' and JOINERS' POCKET COMPANION Containing Rules, Data, and Directions for Laying Out Work, and for Calculating and Estimating. — With Frontispiece showing the parts of an Architectural Column; also containing many other Illustrative Engravings. — Compiled by Thomas Moloney, Car- penter and Joiner. — Cloth 50 cents. This is a compact and handy little volume, containing the most useful rules and memoranda, practically tested by many years' experience in the shop, factory, and building. Also, a treatise on the framing-square. It is by a thoroughly practical man, and contains enough that is not easily found any where else to make it worth more than its price to every intelligent carpenter. EASY LESSONS IN ARCHITECTURE. Consisting of a Series of Questions and Answers explaining in Simple Language the Principles and Progress of Architecture from the Earliest Times. — By Thomas Mitchell. — Illustrated by nearly One Hundred and Fifty Engravings. — New Edition, with American additions. — Cloth 30 cents. Architecture is not only a profession and an art, but an important branch of every liberal education. No person can be said to be well educated who has not some knowledge of its general principles and of the characteristics of the different styles. The present w*k is probably the best architectural textbook for beginners ever published. The numerous illustrative engravings make the subject very simple, and prevent all misunderstanding. It tells all about the different styles, their pecu- liar features, their origin, and the principles that underlie their construction. HINTS AND AIDS TO BUILDERS. Gives hints and prices, tells how to measure, explains building terms, and, in short, contains a fund of information for all who are interested in building. — Paper 25 cents. CATALOGUE OF INDUSTRIAL BOOKS. BUCK'S COTTAGE AND OTHER DESIGNS. Buck's Designs in Architecture, showing a Variety of Designs, together with a large amount of Miscellaneous Matter, making it a very valuable book. — Forty designs for fifty cents. Just the book you want, if you are going to build a cheap and comfortable home. It shows a great variety of cheap and medium-priced cottages, besides giving a number of useful hints and suggestions on. the various questions liable to arise in building, such as selections of site, general arrangement of the plans, sanatary questions, &c. Cottages costing from $500 to $5, 000 are shown in considerable va- riety, and nearly every taste can be satisfied. The information, on site, general arrangement of plan, sanatary matters, &c, is worth a great deal more than the cost of the book. WATER-CLOSETS.— A Historical, Mechanical, and Sanatary Treatise. — By Glenn Brown, Architect; Associate American Institute of Architects. — Neatly bound in cloth, gilt title. . $1 This book contains over 250 engravings, drawn expressly for the work by the author. The drawings are so clear that the distinctive features of every device are easily seen at a glance, and the descriptions are particularly full and. thorough. Every known water-closet is fully described, and an account given of its qualities, advan- tages, and defects. The paramount importance of this department of the construc- tion of our houses renders all comment upon the value of such a work unnecessary. PLASTER: HOW TO MAKE AND HOW TO USE. Being a Complete Guide for the Plasterer in the Preparation and Application of all kinds of Plaster, Stucco, Portland Cement, Hydraulic Cements, Lime of Tiel, Rosendale and other Cements. With Useful and Practical Information on the Chemistry,Qualities, and Uses of the Various Kinds of Limes and Cements. — Together with Eules for Measuring, Computing, and Valuing Plaster and Stucco Work. — To which is appended an Illustrated Glossary of Terms used in Plastering, &c. — By Fred. T. Hodgson, author of "The Builders' Guide, and Estimators' Price-Book," "Practical Carpentry," &c. — Cloth, gilt • $] This work is illustrated with numerous engravings in the text, and three plates, giving some forty figures of ceilings, center-pieces, cornices, panels, and soffits. It is an invaluable book for plasterers, bricklayers, masons, builders, architects, and engineers. HANDSAWS: THEIR USE, CARE, AND ABUSE. How to Select and How to File Them. — Being a Complete Guide for Selecting, Using, and Filing all kinds of Handsaws, Backsaws, Compass and Keyhole Saws; Web, Hack, and Butchers' Saws; Showing the Shapes, Forms, Angles, Pitches, and Sizes of Saw- teeth suitable for all kinds of Saws, and for all kinds of Wood, Bone, Ivory, and Metal. ■ — Together with Hints and Suggestions on the Choice of Files, Saw-sets, Filing-clamps, and other matters pertaining to the Care and Management of all classes of Hand and other Small Saws. — By Fred. T. Hodgson, author of "The Steel Square and Its Uses," " The Slide-Rule, and How to Use It," "The Builders' Guide," "Practical Carpentry," &c— Illustrated by over Seventy-five Engravings. — Cloth, gilt $1 This work is intended more particularly for operative carpenters, joiners, cab- inet-makers, carriage-builders, and woodworkers generally, amateurs or professionals. CATALOGUE OF INDUSTRIAL BOOKS. THE PRACTICAL UPHOLSTERER. Giving Clear Directions for Skillfully Performing all kinds of Upholsterers' Work in Leather, Silk, Plush, Reps, Cottons, Vel- vets, and Carpetings. — Also, for Stuffing, Embossing, Welting, and Covering all kinds of Mattresses, &c. — Rules for Measuring Valances, Curtains, Tapestry, Window and Door Drapery, Curtain Rods, Persian Beds, Mantel Drapery, Lambrequins, Cushions, Floor-Cloths, Festoon Blinds and Curtain-Hangings, and all kinds of Upholstery. — Fully Illustrated with Engravings of Tools, Sketclies of Furniture, and numerous full-page Illustrations of Original Decorative Designs. — By A Practical Upholsterer. 12mo, cloth $1 This work contains a number of original designs in drapery and upholstery, ■with full explanatory text, and an immense number of working illustrations. It gives a description of tools, appliances, and materials. It tells how to upholster ■chairs, parlor furniture, bedroom furniture, &c. It contains rules for cutting bed- hangings, window-curtains, door-hangings, blinds, and for measuring and cutting ■carpets. It gives arithmetical calculations for cutting carpets, curtains, &c, mantle- board drapery, festoons, and, in short, everything pertaining to upholstery. There is nothing published in this country that is so thorough and complete in the instructions given for upholstering, as this book. It is invaluable alike to the ^practical workman and the amateur. CABINET-MAKING, UPHOLSTERING, FURNITURE. Hints and Practical Information for Cabinet-makers, Upholsterers, and Eumiture-men Generally. — Together with a Description of all kinds of Finishing, with Full Directions Therefor; Varnishes, 'Polishes, Stains for Wood, Dyes for Wood, Gilding and Silvering, Recipes for the Factory, Lacquers, Metals, Marbles, &c.j Pictures, Engravings, &c. — Cloth, gilt $1 This book contains an immense amount of the most useful information for those who are engaged in the manufacture, superintendence, or construction of furniture or woodwork of any kind. It is one of the cheapest and best books ever published, and contains over one thousand hints, suggestions, and methods; and ■descriptions of tools, appliances, and materials. All the recipes, rules, and directions have been carefully revised and corrected by practical men of great experience, so that they will be found thoroughly trustworthy. It contains many of the recipes recently sold at from $5 to $500. THE WORKSHOP COM PANION -Part I. A Collection of Useful and Eeliable Recipes, Rules, Processes, Methods, Wrinkles, and Practical Hints, for the Household and the Shop Paper, 35 cents. — Cloth, gilt title, 60 cents. This is a book of 164 closely printed pages, forming a dictionary of practical information for mechanics, amateurs, housekeepers, farmers, — everybody. It is not a mere collection of newspaper clippings, but a series of original treatises on various subjects, such as alloys, cements, inks, steel, signal-lights, polishing mate- rials, and the art of polishing wood, metals, &c; varnishing, gilding, silvering, bronz- ing, lacquering, and the working of brass, ivory, alabaster, iron, steel, glass, &c. CATALOGUE OF INDUSTRIAL BOOKS. THE WORKSHOP COMPANION -Part II. A Collection of Useful and Reliable Recipes, Rules, Processes, Methods, Wrinkles, and Practical Hints, for the Household and the Shop Paper, 35 cents. — Cloth, gilt title, 60 cents. This is an extension of the first part, and contains subjects which have not been discussed in the earlier volume. These two volumes contain an immense amount of practical instruction on matters in regard to which information is constantly desired by amateurs and practical men. THE PRACTICAL ASSISTANT, AND WORKSHOP COMPANION.— A Treasury of Useful Information relating to the Arts and Sciences of everyday life. — Containing Useful and Reliable Processes, Recipes, Wrinkles, Methods, Rules, Data, Tables ; and Hints for the Factory and the Household, the Shop and the Farm.— Edited by John Phin.— Cloth, $1 This is Parts I and II of " The Workshop Companion," described above, hand- somely bound together in cloth, with gilt title. THE AMATEURS' HANDBOOK OF PRACTICAL INFORMATION, for the Workshop and Laboratory. Second Edition. — Greatly Enlarged. — Neatly bound. . . 15 cents. This is a handy little book, containing just the information needed "by amateurs in the workshop and laboratory. Directions for making alloys, fusible metals, cements, glues, &c.; and for soldering, brazing, lacquering, bronzing, staining and polishing "wood, tempering tools, cutting and working glass, varnishing, silvering, gilding, preparing skins, &c. The new edition contains extended directions for preparing polishing powders, freezing mixtures, colored lights for tableaux, solu- tions for rendering ladies' dresses incombustible, &c. There has also been added a very large number of new and valuable recipes. The Workshop Companion, Part I, above described, contains all the matter that is to be found in "The Amateurs' Handbook." MECHANICAL DRAUGHTING. The Student's Illustrated Guide to Practical Draughting. — A series of Practical Instructions for Machinists, Mechanics, Apprentices, and Students at Engineering Establishments and Technical In- stitutes. — By T. P. Pemberton, Draughtsman and Mechanical Engineer. — illustrated by numerous engravings. — Cloth, gilt. $1 This is a simple but thorough book, by a draughtsman of twenty-five years' experience. It is intended for beginners and self-taught students, as well as for those who pursue the study under the direction of a teacher. DRAWING INSTRUMENTS. Being a Treatise on Draughting Instruments, with Rules for their Use and. Care; Explanations of Scales, Sectors, and Protractors. Together with Memoranda for Draughtsmen; Hints on "Purchasing Instruments, Paper, Ink, Pencils, &c. Also, a Price-list of all Mate- rials required by Draughtsmen. — Illustrated with twenty-four Explan- atory Illustrations. — By Fred. T. Hodgson. — Paper. ... 25 cents. CATALOGUE OF INDUSTRIAL BOOKS. THE SLIDE-RULE, AND HOW TO USE IT. Being a Compilation of Explanations, Rules, and Instructions, suitable for Mechanics and others interested in the Industrial Arts. — Compiled and arranged by Fred. T. Hodgson. — 25 cents. Rules are given for the measurement of all kinds of boards and planks, timber in the round or square, glaziers' work and painting, brickwork, paviors' work, tiling and slating, the measurement of vessels of various shapes, the wedge, inclined planes, wheels and axles, levers, the weighing and measurement of metals and afi solid bodies, cylinders, cones, globes, octagon rules and formulas, the measurement of circles, and a comparison of French and English measures, with much other informa- tion useful to builders, carpenters, bricklayers, glaziers, paviors, slaters, machinists, and other mechanics. Possessed of this little hook and a good slide-rule, mechanics might carry in their pockets some hundreds of times the power of calculation that they now have in their heads, and the use of the instrument is very easily acquired. THE ENGINEER'S SLIDE-RULE, and Its Applications. A Complete Investigation of the Principles upon which the Slide- Rule is constructed; together with the Method of its Application to all the Purposes of the Practical Mechanic. — By William Tonkes. — Paper , 25 cents. THE LIGHTNING CALCULATOR. Practical Mints on Lightnmg Calculating. — To which are added Rules, Tables, Data, Formulae, and Memoranda, for making rapidly those everyday calculations that are required in business, mechan- ics, and agriculture. — Paper 20 cents. A CENTURY OF INVENTIONS. An exact reprint of the famous "Century of Inventions" of the Marquis of Worcester (first published in 1663). — With an Intro- duction, Notes, and a Life of the Author. — With Portrait after a Painting by Van Dyke. — Edited by John Phin.— Cloth. . . . $1 This is one of the most extraordinary hoots ever published. The famous "Century of Inventions" is of more than mere historical interest. It contains nu- merous hints and suggestions of what might be accomplished, and will be found of great interest and value to every one interested in mechanics. Many persons claim that the Marquis of Worcester anticipated many of our most important modern inventions and discoveries. Great care has been taken to reproduce exactly (so far as modern type, &c, could do it) the edition published by the Marquis himself. It has been entirely out of print for many years. THE ELECTRICIAN'S POCKET COMPANION. Electrical Rules, Tables, Tests, and Formulae.— By Andrew Jameson, C.E., F.R.S.E.— Fully illustrated.— Cloth. ... 75 cents. This is the most compact and thorough work in the market for the practical electrician. It contains minute directions for all calculations, tests, &c, with clear engravings of the apparatus employed. The following list of contents will give an Idea of its scope: — , . Formulse of the Absolute Units,— Practical, Electrical, and Mechanical. Heat and Light Units. Electro-chemical Equivalents, Electrolysis, Heat and Energy of Combustion. Practical Methods of Electrical Measurements. Electric Conductors: Copper, &e. — Insulators: Guttapercha, &e. Submarine Cables.— Aerial Land-lines. Electric Lighting, and Transmission of Power. CATALOGUE OF INDUSTRIAL BOOKS. LECTURES IN A WORKSHOP.-By t. p. Pemmkton, formerly Associate Editor of The Technologist; author of "The Student's Illustrated Guide to Practical Draughting." — With an Appendix containing the famous papers by Whitworth "On Plane Metallic Surfaces of True Planes"; "On the Uniform System of Screw-Threads"; "Address to the Institution of Mechanical En- gineers, Glasgow"; "On Standard Decimal Measures of Length." Cloth, gilt $1 We have here a sprightly, fascinating hook, full of valuable hints, interesting anecdotes, and sharp sayings. It is not a compilation of dull sermons or dry math- ematics, but a live, readable book. The papers by Whitworth, now first made readily accessible to the American reader, form the basis of our modern systems of accurate work. THE NEW POCKET CYCLOPEDIA. A Compendium of General Knowledge, Useful and Interesting Facts, Valuable Statistics, and Practical Information. — 16mo., cloth 50 cents. This is a handy volume of 164 pages, printed in small but clear type on. very fine thin paper, so that the book may be .readily carried in the pocket or trunk. It con- tains all those facts and figures which are most commonly referred to in everyday life, great care being taken to secure accuracy and clearness. It is not a collection of "curio as information" made up from newspaper clippings, but a thoroughly arranged manual of the most useful general knowledge. HOW TO BECOME A GOOD MECHANIC. Intended as a Practical Gruide to Self-taught Men: Telling What to Study; What Books to Use; How to Begin; "What Difficulties will be met; How to Overcome Them. In a word, how to carry- on such a course of self-instruction as will enable the young mechanic to rise from the bench to something higher. — Paper, 35e. This is not a book of "goody-goody" advice, neither is it an advertisement of any special system, nor does it advocate any hobby. It gives plain practical advice in regard to acquiring that knowledge which alone can enable a youug man engaged in any profession or occupation connected with the industrial arts to attain a po- sition higher than that of a mere workman. CEMENTS, GLUE, AND PASTE. A Practical Treatise on the Preparation and Use of all kinds of Cements, Glue, and Paste. — B3' John Phin, author of "How to "■ Use the Microscope." — Paper 25 cents. Every mechanic and householder will find this volume of almost every-day use. ft contains nearly two hundred recipes for the preparation of cements for almost , ivery conceivable purpose. HINTS FOR PAINTERS, DECORATORS, AND PAPER-HANGERS. Being a Selection of Useful Rules, Data, Memoranda, Methods, and Suggestions for House, Ship, and Furniture Painting; Paper- • Hanging, Gilding, Color-Mixing, and other matters useful and instructive to painters and decorators. — Prepared with special reference to the wants of amateurs. — By An Old Hand. — Paper 25 cents. CATALOGUE OF INDUSTRIAL BOOKS. THE HARDWOOD FINISHER: With Rules and Directions for finishing in Natural Colors, and in Antique, Mahogany, Cherry, Birch, Walnut, Oak, Ash, Redwood, Sycamore, Pine, and all other Domestic Woods. Finishing, Filling, Staining, Varnishing, and Polishing. Also, Miscellaneous Rules for Dyeing, Gilding, and Bronzing.— Compiled and Edited by Feed. T. Hodgson, late Editor of The Builder and Woodworker, and of The Cabinetmaker and Upholsterer. — ]2mo, cloth. . . $1 In this country the art of using wood for almost every purpose has gone far fceyond anything that has ever been attempted by any other people. The modem houses of the Americans are finished "with a richness and beauty in the woodwork of which our fathers, not to speak of our grandfathers, had little idea. The car- penter, builder, or painter who does not fully understand the best methods of xinishiug the hard woods so as to preserve and increase their beauty is behind the times. The" object of this book is to aid him in acquiring the knowledge necessary to this end; and the author has certainly succeeded in producing an exhaustive treatise on the subject. THE ENGINEER'S HANDY-BOOK: Containing a series of Useful Calculations for Engineers, Tool- makers, Millwrights, Draughtsmen, Foremen in Engineering Es- tablishments, and for the better class of Mechanics and Artizans Generally. Also, Rules to determine the Proportion of Wheels for crew-cutting by a Lathe, &c. — From the fifth London edition, with American additions. — 32mo, cloth 50 cents. PLAIN DIRECTIONS FOR THE CONSTRUCTION AND ERECTION of LIGHTNING- RODS. — By John Phin, C.E., author of "Chemical History of the Six Days of Creation," "How to Use the Microscope," &c. Enlarged and fully illustrated. — Third edition. — 12mo, cloth, gilt title 75 cents. This is a well-known and standard work. It is simple and practical, intended to convey just such information as will enable every property-owner to decide whether or not his buildings are thoroughly protected. It is the only book on this subject published in this country that has not been written in the interest of some patent or some manufacturing concern. ' By following its directions any ordinarily skillful mechanic can put up a rod that will afford perfect protection, and that will not infringe on any patent. Every owner of a house or barn ought to procure a copy. TRADE "SECRETS" AND PRIVATE RECIPES. A Collection of Recipes, Processes, and Formulas that have been offered for sale at prices varying from 25 cents to $500. With Notes, Corrections, Additions, and Special Hints for Improve- ments. — Edited by John Phin, assisted by an experienced and skillful pharmacist.— Cloth, gilt title 60 cents. This work was prepared by the author for the purpose of collecting and pre- senting in a compact. form all those recipes and so-called "trade secrets" which have been so extensively advertised and offered for sale. It is by no means a claptrap book, though it exposes many claptraps. It contains a large amount of valuable information that can not be readily found elsewhere ; and it gives not only the formate, &c, for manufacturing an immense variety of articles, but important and trustworthy hints as to the best way of making money out of them. Even as a book of recipes it is worth more than its price to any one who is interested in the subject on which it treats. CATALOGUE OF INDUSTRIAL BOOKS. A PRACTICAL CUIDE' TO SUCCESS IN THE USE OF RECIPES, Formulae, &c, with Hints on Chemical and Mechanical Manipula- tion. — Intended- as a supplement to all books of recipes. — By John Phin. — 12mo, paper 25 cents. While it is an undoubted fact that many of the recipes published in the ordinary- collections are erroneous, either from original blunders on the part of the authors or from mistakes in copying, failure in the use of others frequently arises from defective information and vicious methods on the part of those who attempt to put them in practice. The object of the present book is to give such hints and cautions- as will enable the worker to secure success wheTe success is possible ; and where the products are intended for sale it gives special and valuable advice as to the best methods of putting them on the market. A MANUAL OF INSTRUCTION IN THE ART OF WOOD ENGRAVING- With a Description of the necessary Tools and Apparatus, and Concise Directions for their Use ; Explanations of the Terms used and the Methods employed for prodncing the various classes of Wood Engravings.— By S. E. Puller.— Fully illustrated with engravings by the author, separate sheets of engravings for trans- fer and practice being added. — New edition, neatly bound. 50 cts. A really thorough and practical work, written for those who want to learn the art without the aid of a teacher. A GUIDE TO COLLODIO ETCHING.-By Eev. Benjamin Hartley. — Illustrated by the author. — 12mo, cloth $1.00 This volume gives complete and minute instructions for one of the most delight- ful of amateur arts. It is fully illustrated by woodcuts of all the apparatus used (which is very simple and easily made), and also by actual photo-prints of the etchings themselves. THE PRACTICAL POCKET COMPANION. A Cyclopedia of the most useful Facts, Figures, and General Information required by everybody in everyday life. — Edited by John Phin, author of "How to Use the Microscope," "The Work- shop Companion," "Chemical History of the Six Days of Crea- tion," &c. — Numerous illustrations 10 cents. Contents. — Abbreviations in Common Use — Business Laws and Commercial Rules — Acceptances — Agencies — Bills of Exchange— Checqnes — Common Carriers — Corporations — Law of Finding — Indorsements — Innkeepers — Negotiable Instruments — Partnerships — Promissory Notes — Protests — Receipts — Concrete Walls for Houses — Copyrights — Rules for Correspondence — How to treat Accidents to the Eye — Fac- tors of Safety — Best Methods of Extinguishing Fires — Language of Flowers — Sig- nificance of Gems and Precious Stones— Periods of Gestation and Incubation — Legal Holidays — Homestead Law — Distinguishing Characteristics and Anxious Periods of Infectious Diseases— Prevention of Attacks of Insects — Knots, and How to Tie Them, with full page of illustrations— General Rules — Single Draw-knot — Galley- knot — Square-knot, or Reefin^-knot — Weaver's-knot, or Sheet-bend-knot — Half -hitch — Two Half -hitches — Clove-hitch — Timber-hitch — Bowline-knot — Fisherman's-knot — Whipping or Binding — Tying Parcels — Care of Leather— Lightning-rods, general rules for — Best Materials — Proper Size and Best Shapes of Rod — Painting— Points, or Air-Terminals — Ground Connections — Arrangement and Mode of Attaching the Rod to the House — Value of Moneys of Foreign Nations — Passports— Patents — Anti- dotes for Poisons — Postal Rules and Rates — Railroad and Steamboat Signals — Rules for Spelling and the Use of Capitals— Trade-marks— Weather Indications, &c. CATALOGUE OF INDUSTRIAL BOOKS. WHAT TO DO AND HOW TO DO IT IN CASE OF ACCIDENT.— A book for everybody.— Cloth, gilt. 50 cts. This is one of the most useful books ever published. It tells exactly what' to do in case of accidents, such as severe cuts, sprains, dislocations, broken bones, burns with fire, scalds, burns with corrosive chemicals, sunstroke, suffocation by foul air, hanging, drowning, frost-bite, fainting, stings, starvation, lightning, poisons, accidents from machinery and from the falling of scaffolding, gunshot wounds, &c. It ought to be in every house, for young and old are liable to accident, and the directions given in this book might be the means of saving many a valuable life. COMMON SENSE IN THE POULTRY-YARD. A Story of Failures and Successes, including a full account of 1,000 hens and what they did. With a complete description of the houses, coops, fences, runs, methods of feeding, breeding, market- ing, &c, and many new wrinkles and economical dodges. — By J. P. Haig. — "With numerous illustrations. — Cloth, gilt title. $1 This is a lively and entertaining work, which embodies the actual experience of many years in the keeping of poultry in large and small numbers. It is the most thoroughly practical work on poultry in the market, and contains an amount of solid information which, to even the keeper of a dozen fowls, will make it worth many times its cost. A DICTIONARY OF PRACTICAL BEE-KEEPING. With Notes and Practical Hints.— By John Phin, author of "How to Use the Microscope," &c. — Numerous illustrations. — Cloth, gilt 50 cents. This work discusses thoroughly nearly five hundred subjects. Gives in con- densed form an immense amount of valuable information under the different head- ings. Under the heads Bee, Comb, Glucose, Money, Race, Species, Sugar, "Wax, and others, it brings together a large number of important facts and figures now scat- tered through our bee literature and costly scientific works, and are not easily found when wanted. Here they can be referred to at once under the proper head. PLAIN DIRECTIONS FOR ACQUIRING THE ART OF SHOOTING ON THE WING. With Useful Hints concerning all that relates to Guns and Shoot- ing, particularly in regard to the art of loading so as to kill. To which has been added several valuable and hitherto secret recipes, of great practical importance to the sportsman. — By An Old Game- keeper.— 12mo, cloth 75 cents. This book contains a novel and most valuable feature found in no other work on this subject. This is a series of graduated lessons by which the self-taught young sportsman is enabled to advance step by step from such easy marks as a sheet of pa- per nailed on a fence to the most difficult trap-shooting and the sharpest snap-shots . THE PISTOL AS A WEAPON OF DEFENCE, In the House and on the Eoad.— 12mo, cloth. ... 50 cents. This work aims to instruct peaceable and law-abiding citizens in the best means of protecting themselves from tie attacks of the brutal and the lawless, and it is the only practical book puWished on this subject. Its contents are as follows :— The Pistol as a Weapon of Defence-The Carrying of Firearms-Different kinds of Pistols in Marked-How to Choose a Pistol— Ammunition different kinds : powder caps, bullets, copper cartridges, &c.-Best form of Bullet-How to Load-Best Charge for Pistols^-How to Kegulate the Charge-Care of the Pistol: how to clean it— How to Handle and Carry tie Pistol-How to Learn to Shoot— Practical Use of the Pistol— How to Protect Yourself and Disable your Antagonist. CATALOGUE OF INDUSTRIAL BOOKS. CHEMICAL HISTORY of the SIX DAYS of CREATION By John Phin, author of "How to Use the Microscope," &c. 12mo, cloth 75 cents. In this volume an attempt is made to trace the evolution of our globe from the primeval state of nebulous mist, "without form and void," and existing in "dark- ness," or with an entire absence of the manifestation of the physical forces, to the condition in which it was fitted to become the habitation of man. While the state- ments and conclusions are rigidly scientific, it gives some exceedingly novel views of a rather hackneyed subject. THE SUN: A Familiar Description of his Phenomena. By Eev. Thomas William Webb, M.A., F.R.A.S., author of "Celestial Objects for Common Telescopes." — With numerous illustrations. — 12mo, cloth 40 cents. This work gives, in a delightfully popular style, an account of the most recent discoveries in regard to the sun. It is freely illustrated. HOW TO USE THE MICROSCOPE. A Book of Practical Hints on the Selection and Use of the Microscope. Intended for beginners. — By John Phin, editor of. The American Journal of Microscopy. — Sixth edition. Greatly enlarged, with over eighty engravings in the text, and eight full- page engravings, printed on heavy tint paper. — 12mo, cloth; $1.25 This work has been received with such general favor that it has passed through five large editions in a few years. It gives a full account of the different kinds of microscopes; of the various accessories, and of the best methods of using them; of the best methods of collecting, preparing, and preserving objects, and preparing slides and cabinets. Many of the illustrations, devices, and methods used, are original with the author, although they have been freely copied and appropriated without credit by several other writers. A BOOK FOR BEGINNERS WITH THE MICROSCOPE. Being an abridgement of "How to Use the Microscope." — By John Phin. — Fully illustrated, and neatly and strongly bound in boards 30 cents. This book was prepared for the use of those who, having no knowledge of the use of the microscope, — or, indeed, of any scientific apparatus, — desire simple and practical instruction in the best methods of managing the instrument and preparing objects. THE MICROSCOPE.— By Andrew Ross.— Fully illustrated. 12mo, cloth, gilt title 75 cents. This is the celebrated article contributed by Andrew Ross to "The Penny Cyclo- pedia,' 1 and quoted so frequently by writers on the microscope. Carpenter and Hogg, in the latest editions of their works on the microscope, and Brooke, in his treatise on Natural Philosophy, all refer to this article as the best source for full and clear information in regard to the principles upon which the modern achromatic microscope is constructed. It should be in the library of every person to whom the microscope is more than a toy. It is written in sinfple language, free from abstruse technicalities. CATALOGUE OF INDUSTRIAL BOOKS. THE ANGULAR APERTURE OF MICROSCOPE OBJECTIVES. By Dr. George E.Blackham.— Eighteen full-page illustrations. Printed on extra fine paper. — 8vo, cloth $1.25 This is the elaborate paper on Angular Axjerture read by Dr. Blackham before the Microscopical Congress, held at Indianapolis. SECTION-CUTTING FOR THE MICROSCOPE. A Practical Guide to the Preparation and Mounting of Sections for the Microscope, special prominence being given to the subject of Animal Sections. — By Sylvester Marsh, M.D. — Reprinted from the London edition. — "With illustrations. — 12mo, cloth, gilt title 75 cents. This is undoubtedly the most thorough treatise extant upon section-cutting in all its details. The American edition has been greatly enlarged by valuable explanatory notes ; and also by extended directions, illustrated with engravings, for selecting and sharpening knives and razors. THE MARVELS OF POND LIFE. A Year's Microscopic Eecreations among the Polyps, Infusoria, Rotifers, Water-Bears, and Polyzoa.— By Henry J. Slack, F.G.S., P.R.M.S., &c. — Seven full-page plates, and numerous wood en- gravings in the text. — Second edition.— 12mo, cloth, gilt. . $1 DIATOMS— Practical Directions for Collecting, Pre- serving, Transporting, Preparing, and Mounting Diatoms. — By Prof. A. Mead Edwards, M.D., Prof. Christopher Johnston, M.D., Prof. Hamilton L. Smith, LL.D.— 12mo, cloth. 75 cents. This volume contains the most complete series of directions for collecting, preparing, and mounting diatoms, ever published. The directions given are the latest and best. BACTERIA: FORMS AND MODES OF GROWTH. A Series of Papers on the Exhibits at the Biological Laboratory of the Health Exhibition, under the charge of Watson Cheyne. Reprinted from the London Lancet— Illustrated with over thirty engravings, showing the forms and modes of growth of the various species, and the apparatus used in the different "cultures."— 12mo, paper 25 cents. TRICHIN/E SPIRALIS: How to Detect Them and How to Avoid Them.— A Popular Account of the Habits, Modes of Propagation, and Means of Dissemination of Pork- worms or Flesh-worms.— By John Phin, author of "How to Use the Microscope."— Fully illustrated.— Paper. ... 25 cents. CATALOGUE OF INDUSTRIAL BOOKS. HANDBOOK OF URINARY ANALYSIS, Chemical and Microscopical.— For the Use of Physicians, Medical Students, and Clinical Assistants.— By Frank M. Deems, M.D., Laboratory Instructor in the Medical Department of the Univer- sity of New York; Member of the New York County Medical Society; Member of the New York Microscopical Society, &c. — Second edition. — Greatly enlarged, and fully illustrated. — Cloth. $1 This manual presents a plan for the systematic examination of liquid urine, urinary deposits, and calculi. It is compiled with the intention of supplying a concise guide, which, from its small compass and tabulated arrangement, renders it admirably adapted for use, both as a bedside reference-book and a work-table companion. The author is well known as one who has had for several years a very extended experience as a teacher of this important branch of physical diagnosis, and he has compiled a manual which will serve to lessen the difficulties in the way of the beginner, and save valuable time to the practitioner. THE MICROSCOPIST'S ANNUAL FOR 1879 Contains a list of all the microscopical societies in the country, -with names of officers, days of meeting, &c.; alphabetical and classified lists of all the manufac- turers of microscopes and objectives, dissecting apparatus, microscopic objects, materials for microscopists, &c, in Europe and America; postal rates, rules and regulations, prepared expressly for microscopists. Weights and measures, with tables and rules for the conversion of different measures into each other ; eustoms duties and regulations in regard to instruments and books ; value of the moneys of all countries in United States dollars: value of the lines on Nobert's test-plates; table of Moller's probe-platte, with the number of lines to inch on the several diatoms, &c; focal value of the objectives of those makers who number their objectives (Hartnack, Naehet, &c); focal value of the eyepieces of different makers; magnifying power of eyepieces and objectives, &e. The whole forming an indis- pensable companion for every working microscopist. — Limp cloth, gilt. 25 cents. A BOOK ABOUT BOOKS; or, Practical Notes on the Selection, Use, and Care of Books. Intended as a popular guide for bookbuyers, students, and all lovers of good reading. — Cloth 40 cents. This is a readable, gossipy book, full of literary anecdotes, and containing also a great deal of practical information, useful to every one that owns or expects to own books. The directions for binding, repairing, preserving, and handling books, " should receive the careful attention of every one that desires to keep his books in good condition j but even if regarded as mere pleasant reading for a leisure hour, there are few more readable and interesting books than this, with its gossip, chat, and stories. It is illustrated with three full-page engravings, one being a reproduc- tion of the first wood engraving of which there is any record; the second is an exceedingly curious woodcut representing the birth of Eve; and the third is an engraving of one of the curious "hornbooks" of the seventeenth century. RHYMES OF SCIENCE: WISE AND OTHERWISE. By Oliver Wendell Holmes, Beet Hakte, Inooldsby, Prof. Forbes, Prof. J. W. MoQ. Rankine, Hon. R. W. Raymond, and others.— With illustrations. Cloth, gilt title 50 cents. THE YOUNC SCIENTIST.— This journal was devoted to amateur Science and Art, and was deservedly a favorite with young people. We have a few bound volumes for sale. Price 75 cents each. THE AMERICAN JOURNAL OF MICROSCOPY. A few bound volumes for sale. Price $1 each. CATALOGUE OF INDUSTRIAL BOOKS. REMINISCENCES OF SCOTTISH LIFE AND CHARACTER. By E. B. Ramsay, M.A., LL.D., F.R.S.E., late Dean of Edinburgh. Third edition, from the author's latest edition. — With portrait. 12mo, cloth $1.50 The Scotch have made such a deep mark in the literature, science, and mechan- ics of the world, that whatever illustrates their peculiar modes and habits of thought ■and action must be of intense interest to every thinking mind. The above book consists of a series of anecdotes and descriptions which are unequalled for racy wife and quiet humor, and as affording a deep insight into liumun nature. It is not a compilation of jokes by a hackney bookmaker, but a work of broad views and philosophical thought, by a man of learning and ability. It is intensely interesting to every thoiightf ul reader ; but the Scotchman who fails to read At misses one of the grandest treats afforded by any literature. in Pres?, A DICTIONARY OF RECENT WORDS PHYSICAL SCIENCE AND ELECTRICITY. Giving their Meanings; the Formula and Value of the Units; awd numerous Practical Notes and Hints. By John Phin, Author of ' ' Practical Treatise on the Construction and Erection of Lightning-Rods, " "The Chemical History of the Six Days of Creation," "How to Use the Micro- scope," &c. — 12mo, cloth. 75 cents. This is a handy book, intended to give, in the simplest language and with thor- ough accuracy, the meaning of the new terms which have been introduced into physical and electrical science, and which are not to be found in any dictionary except the very late and expensive ones. It is intended for the use of the self- taught man. A LIVE PRACTICAL JOURNAL FOR WORKERS. THE OPERATIVE BUILDER. Edited by Fred. T. Hodgson, Author of "The Steel Square and Its Uses," "Practical Carpentry," " Stairbuilding Made Easy," &c. This is a monthly journal devoted to the arts conneetad fith tfco building trade, and especially to woodworking. It will be published monthly. Price 50 cents per year. »** Send for free specimen copy. Address INDUSTRIAL PUBLICATION COMPANY, New Yoek. CATALOGUE OF INDUSTRIAL BOOKS. IN PREPARATION. THE UNIVERSAL CARPENTER AND JOINER. By Fred. T. Hodgson, author of "The Steel Square and Its Uses,'' "Practical Carpentry," " Stairbuilding Made Easy," "The Build- er's Guide, and Estimator's Price-Book," &c. To be handsomely illustrated, and published in four parts, as follows : PART I CARPENTER'S GEOMETRY. Part I will contain Carpenter's Geometry, presented in an easy form, ■with examples of its practical applications in Carpentry and Joinery, showing how to get and work difficult "cuts" and pitches. PART II THE ART AND SCIENCE OF CARPENTRY. Part II will be an introduction to the Art and Science of Carpentry proper, with working drawings of Roofs, Bridges, Bevel and Skew Work. PART III AMERICAN JOINERY. Part III will contain a practical treatise on American Joinery, . with descriptions and examples of some of the best work in existence. This Part will be full of excellent , material for the Joiner and Finisher. PART IV JOINERY AND CARPENTRY. Part IV will contain a large number of examples in mixed Joinery and Carpentry, Rules for Working, Methods of Working, Tables, Data for Estimating, Formula for laying out work, and Recipes useful to the Practical Workman. It will be the aim of the author to make the above work the most complete treatise on Carpentry and Joinery published to date. It will be issued in four Parts, each part consisting of not less than 100 large royal octavo pages, printed on fine paper, and strongly bound in stiff paper covers. The price will be one dollar per Part; and when complete the whole will form one volume, the price of which, handsomely bound in extra cloth, will be $5. The First Part will be ready about the first of August, 1892, and the remaining Parts at intervals of about three months. To those sending advance orders for two Parts, accompanied with the cash, we will send a binding-order, which will be accepted by us as payment in full for binding the complete work in neat cloth, with gilt title. ■'.'■■' ■'■'::■:■ '■'/:- ""'■