PRACTICAL HINTS THE SELECTION AND USE MICROSCOPE. INTENDED FOR BEGINNERS. BY JOHN PILIN, EDITOR OF "THE AMERICAN JOURNAL OP MICROSCOPY." FOURTH EDITION. THOROUGHLY REVISED AND GREATLY ENLARGED. Illustrated with Six Plates and Numerous Figures in the Text. PRICE ONE DOLLAR. NEW YORK: THE INDUSTRIAL PUBLICATION COMPANY. 1881. COPYRIGHT SKCmiKl). TO ittrs. cg . ttHnton, OF HAVANA, N. Y ., IN MEMORY OF MANY PLEASANT HOURS SPENT OVER THE MICROSCOPE WITH DEAR ONES WHO "HAVE GONE BEFORE," THIS LITTLE BOOK IS DEDICATED, BY HER SINCERE FRIEND, THE AUTHOR. CONTENTS. DLDICATION. -.......-iii PREFACE. _-...___ yii INTRODUCTION. - - - - - - - - > xl THE MICROSCOPE. What it Is ; What it Does ; Different Kinds of Microscopes ; Prin- ciples of its Construction, and Glossary of Terms; Essential Parts of the Microscope ; Names of the Different Parts, - 15 SIMPLE MICROSCOPES. Hand Magnifiers, with One, Two, and Three Lenses ; Doublets ; Power of Two or More Lenses When Used Together; Watch Makers' Eye-Glasses Single Lenses and Doublets ; Engravers' Glasses; Linen Provers; Stanhope Lens; Stanhope Collecting Microscope ; Coddington Lens , Achromatic Doublets and Trip- lets; Twenty-five Cent Microscopes Their Construction, and How to Make Them ; Penny Microscopes, to Show Eels in Paste and Vinegar ; Craig Microscope ; Novelty, Globe, etc., - 28 DISSECTING MICEOSCOPES. Essentials of a Good Dissecting Microscope ; Cheap Stands for Simple Microscopes, Excelsior Microscope; Raspail's Micro- scope, Compact Dissecting Microscope;* Binocular Dissecting Microscope, - - - - - - '/. " '- - 40 COMPOUND MICROSCOPES. Cheap Foreign Stands; French Vertical Microscopes; Conversion of Vertical Microscope into Collecting Microscope; the Boss Model; The Jackson Model; The Continental Model; The New American Model Cheap American Stands ; The Binocular Mi- croscope ; The Binocular Eye-Piece ; The Inverted Microscope ; Lithological Microscopes ; The Aquarium Microscope ; Micro- scopes for Special Purposes ; "Class" Microscopes, - 46 OBJECTIVES. Defects of Common Lenses; Spherical Aberration; Chromatic Aberration , Use of Diaphragms ; Corrected Objectives ; Defining Power , Achromatism , Aberration of Form ; Flatness of Field ; Angular Aperture ; Penetrating Power ; Working Distance ; Im- mersion and "Homogeneous " Lenses ; Lens Systems ; Duplex Fronts , French Triplets ; Focal Length of the Numbers used to Designate Objectives by Nachet, Hartnack and Gundlach; - 61 Jy CONTENTS. TESTING OBJECTIVES. General Rules; Accepted Standards-Diatoms, Ruled Lines, Arti- ficial Star; Podura; Nobert's Lines; Hollers Probe Platte; Table of Diatoms on Holler's Probe Platte, with the Number of Lines to the Inch on the Several Diatoms ; Hethods of Testing for Flat- ness of Field, Penetration, etc., - - - . - 84 SELECTION OF A MICBOSCOPE FOK PRACTICAL PURPOSES. Hust be Adapted to Reauirements and Skill of User; Hlcroscopes for Botany ; For Physicians ; For Students ; Magnifying Power Required ; The Stand ; The Stage ; Mechanical Stages ; Revolving Stage ; Stages for Special Purposes ; Diatom Stage, Safety Stage, etc.; Sub-Stage; Mirror; Body; Draw-Tube; Adjustments for Focussing; The Diaphragm; Objectives; High versus Low Angles; Eye-Pieces. - - -, - - '-' - M ACCEBSOBI APPARATUS. Stage Forceps; Forceps Carrier; Object Holder ; Plain Slides; Concave Slides ; Watch-Glasses ; Watch -Glass Holder', Animal- cule Cage ; Large Zoophyte Trough Small Zoophyte Trough ; Walmsley's Zoophyte Trough; The Weber Slide; The Cell- Trough ; The Compressorium > Gravity Compressoriuni ; Grow- ing Slides; Frog Plate; Table; Double Nose-piece, - - 12; ILLUMINATION SOUBCES OF LIGHT. Sun-Light; Artificial Light Candles, Gas, Lamps, Magnesium. Oxyhydrogen Light ; Parallel, Convergent and Divergent Rays, 143 ILLUMINATION OF OPAQUE OBJECTS. Diffused Light; Bulls-Eye Condenser; Side Reflector: The Lieber- kuhn; The Parabolic Reflector ; Objectives with Tapered Fronts; Smith's Vertical Illuminator ; Tolles' Vertical Illuminator. - 147 ILLUMINATION OF TRANSPARENT OBJECTS. Direct and Reflected Light; Axial or Central Light; Oblique Light : The Achromatic Condenser ; The Webster Condenser, and How to Use it; Wenham's Reflex Illuminator, and How to Use it; The Wenham Prism ; The Hemispherical Illuminator; The " Half Button " ; The Woodward Illuminator; Tolles' Illumina- ting Traverse Lens ; The Spot Lens ; The Parabolic Illumina- tor; Polarized Light, - - - .... 150 How TO USE THE MICROSCOPE. General Rules ; Simple Hand Magnifiers : Compound Microscopes ; Practical Notes on Illumination; White Cloud Illumination; Monochromatic Light ; Blue Cell ; Opaque Objects ; Hints to Be- ginners. --. 164 How TO USE OBJECTIVES OF LARGE APERTURE. Illuminnttion; Collar-Corrosion for Cover-Glass, - - - m CAKE OF THE MICBOSCOPE. Should be Kept Covered ; Care of Objectives ; Precautions to be Used when Corrosive Vapors and Liquids are Employed; To Protect the Objectives from Vapors which Corrode Glass ; Clean- ing the Objectives ; Cleaning the Brass Work, - - 175 COLLECTING OBJECTS. Where to Find Objects ; What to Look for; How to Capture Them ; Nets; Bottle-Holders ; Spoons; Collecting Walking Cane; Water Strainer ; Wright's Collecting Bottle ; Aquaria for Microscopic Objects; Dipping Tubes, - 177 THE PBEPABATION AND EXAMINATION OF OBJECTS. Cutting Thin Sections of Soft Substances ; Valentine's Knife ; Sec- tions of Wood and Bone ; Improved Section Cutter ; Sections of Eock ; 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 ; Refractive Powers of Different Liquids; lod-Serum; Artificial lod-Serum ; Covers for Keeping out Dust ; Errors in Microscopic Observations, - - - - - - - -187 PBESEEVATIVE PKOCESSES. General Principles ; Preservative Media Canada Balsam, Solution of Balsam, Colophony, Damar Medium, Glycerine, Glycerine Jelly, Hantzsch's Fluid, Glycerine and Gum, Deane's Gelatine, Alcohol, Thwaite's Fluid, Beale's Liquid, Goadby's Fluids, Pa- cini's Fluid, Castor Oil; General Rules for Applying Preservative Fluids, - ---.---.-198 APPABATUS FOB MOUNTING OBJECTS. Slides; Covers; Cells; Turn-TablesPlain, Matthew's, Kinne's, Cox's; Cards for Making Cells; Hot-Plate; Lamps; Betort Stand; Centering Cards; Mounting Needles; Cover Forceps; Slide Holder; Water Bath ; Simple Form of Spring Clip, - 206 CEMENTS AND VABNISHES. 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, 221 MOUNTING OBJECTS. Mounting Transparent Objects Dry ; Mounting in Balsam ; Mount- ing in Liquids ; Mounting of Whole Insects ; How to Get Bid of Air-Bubbles ; Mounting Opaque Objects ; Wooden Cells ; Leather Discs ; Pierce's Cell ; Prof. Smith's Wax Cell ; Deep Cement Cell, 224 FINISHING THE SLIDES. Covering with Paper; Varnishing for Preservation; Labeling; The Maltwood Finder, 229 PREFACE TO THIRD EDITION. This might with propriety be called the fourth edition the main idea of the work having been embodied in a pamphlet under the same title, published in 1873. but long since forgotten. The successive editions have reached their present form by accretion, rather than by develop- ment; like Topsey, the book has "growed," rather than been ' brought up. and just as that young lady exhibited numerous traits which were inconsistent with a proper training, so this book shows patch-work and inequalities which do not add either to its value or its attractiveness. Of all this the author is fully conscious, and if he could possibly havn secured the necessary leisure he would gladly have rewritten the entire volume. But pressing, or rather imperative calls upon his time, have prevented this, and he has, therefore, been compelled to feel satisfied with such general revision, and additions as were necessary to bring the work up to the present state of our knowledge. The book is still intended for beginners and has changed nothing of its elementary character. It is true that we have inserted a few pages relating to the higher class of objectives, and the accessories used with them, but those who do not possess such apparatus can easily skip these passages. That it is suited to the purpose for which it was intended, we have evidence, not only in the extended sale which it has secured, but in the fact that it has been adopted as an auxiliary text-book ha several of our schools and colleges. New York, January, 1881. PREFACE TO SECOND EDITION. The fact that an unusually large edition of this work has been sold in a comparatively short period, is, to the author, evidence that such a work was needed, and that the present volume has, to a certain extent, supplied the want. In the present edition, therefore, he has endeavored to introduce several important improvements, while at the same time the elementary character of the work remains unaltered. With a few very slight and unimportant exceptions, the entire matter of the former edition has been incorporated in the present, and in addition several important subjects, particularly the chapter on objectives, have been greatly enlarged. Viii PREFACE. Many important points still remain untouched, but it is believed that in its present form most beginners will find in it all the information that they may require upon general topics. As the want of all illustrations of the stands of different makers, and of many accessories, has been urged as an objection to the first edition, and as we have not deemed it advisable to fully supply this omission in the present issue, a word of explanation may not be out of place. One great object in view in the preparation of this book was the furnishing of a cheap manual for those who cannot afford the more expensive books of Carpenter, Beale, Frey, etc. To have given anything like a fair rep- resentation of the products of the different makers of this country and of Europe, would have nearly doubled the size and price of the volume. But if the reader will examine the engravings of stands, etc., in the books just mentioned, ho will find that, even in the best of them, these illustrations are mere reproductions of the figures found in the descrip- tive lists of the various dealers. As new editions of these lists are being constantly issued, and as they may in most cases be obtained without cost from those that publish them, we have thought it best to refer our readers to these catalogues for information in regard to the construction of the instruments of different makers. For the addresses of the promi- nent microscope makers of this country and Europe we refer our readers to ''The Microscopist's Annual." In this, as in the previous edition, we have omitted all descriptions of objects, believing that the proper aim of a book on the microscope should not be to teach the general principles of botany, zoology or histology, but simply the best methods of using the microscope in the pursuit of these studies. The proper books in which to find a descrip- tion of objects, are those which treat of that department of science which takes cognizance of (he special subject under consideration. The present volume is intended merely as a guide to the best general methods of using the microscope. It has been a source of great satisfaction to the author to be assured by those whom he deems good authority, that this little book has done much to foster the use of the microscope in this country, and he hopes that the present improved edition will tend to still further increase the deep interest which is already felt in an instrument which has done more than any other to extend our knowledge of organic nature. Xeic York. August, 1877. PREFACE. The Microscope and its applications in the Arts, and in general science, having deservedly occupied a prominent place in the pages of THE TECH- NOLOGIST, on INDUSTRIAL MONTHLY, a very large number of enquiries in regard to the best methods of using and applying this useful instrument have been directed to us. It would have been easy to answer these en- quiries by a reference to some one of the many treatises that have been published on this subject, but as most of these works are expensive, and as many of our correspondents desire an answer in a more concise and simple shape, we have endeavored to give, in cheap and compact form, the information that is most usually demanded. It is an unfortunate fact that while the microscope is daily growing in favor with those who know anything of its achievements, the operations of certain parties, too well known to the public, have brought a certain degree of suspicion upon all attempts to popularize this most valuable instrument. Microscopes, varying in price from twenty-five cents to two dollars and a half have been offered for sale, and the claim made for them that they are capable of showing clearly the structure of the more min- ute tissues, and that they may be used to advantage by physicians and naturalists. To the young student whose means are limited, and to the country practitioner, whose ability to supply himself with needed books and instruments often falls far short of his desires, the offer of a service- able microscope for a couple of dollars is a great temptation, and when the instrument in question is endorsed by a long list of clergymen, law- yers, and even editors, this temptation becomes irresistible. And if the purchaser should happen to' be unfamih'ar with really good microscopes, and unable to discriminate between a clear and accurately defined view of any object and one that is distorted and incorrect, he may be led to use it, and so fall into the most serious mistakes. That this, unfortunately, does happen too often must be well known to all who are familiar with the subject, and it is within our own knowledge that the most worthless cari- X PREFACE. cature of a microscope has been purchased and used under such circum- stances. We indulge a faint hope that the information conveyed in the following pages will enable the inexperienced reader to avoid these mistakes, and to assign a proper value to the certificates of clergymen and editors who vouch for the excellence of articles concerning whose properties and uses they are profoundly ignorant. These two classes we single out for repro- bation, because in this respect, at least they seem to be sinners above all other men. As stated in the title page, it is intended for beginners, and not for beginners in the use of the microscope only, but for those who have had little or no experience in the use of instruments of any kind. Hence the directions that are given are of the very simplest kind, and all theoretical explanations have been avoided, for the reason that any person that is desirous of studying the optical principles upon which the microscope is constructed will find in the ordinary text books on natural philosophy all the information he may want. Our object has been solely to impart such information as will enable the reader to make a beginning in the practice of microscopy, hoping that the start thus given will lead him to proceed with his studies, and ultimately acquire that knowledge, skill and dexter- ity which will enable him to avail himself of the extraordinary powers and advantages which the use of this instrument confers, both in scientific pursuits and in everyday life. Above all things, therefore, we have en- deavored to be accurate in our statements and judicious in our directions, and the reader is assured that no processes or methods are given which we ourselves have not frequently and successfully put in practice. JOHN PHIN. Yark, January. 1875. 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 nettiug, and 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 use 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, readers it indispensable to the careful and skillful mechanic; on the Xii INTBODTJCTIOK. 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 aud 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 fellows. 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 times, 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. There are 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- j ects 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 be INTKODUCTION. TJiJ 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 impressiveness 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 a 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 XIV IHTBODUCTIOS. long acknowledged the microscope as one of ite 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 it 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 by ' beginners. One of these consists in supposing that it is only by 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 very 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 are 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 of 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 7 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 the Microscope Does. It is well known that the further off any object is, the less 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 16 SELECTION AND TT8E 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 OF THE MICBOSCOPE. 17 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 seen 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 magnifier 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. 18 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 other 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. 19 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 woiild 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 2() SELECTION AND USE 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 lenses, and it will also be found that as the die- OF THE MICBOSCOPE. 21 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 lens 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 tho 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. Fifty cents covered all expenses. 22 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 is 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. But if the lens be merely held in the hand, without any firm support, it will be impossible for the observer to see the corpuscles. Another important point is the illumination of the object. Unless the object be properly illuminated it cannot be dis- * It is scarcely necessary to inform the reader that the focus described in the text is not precisely the focus of the lens itself, but the focus of a compound lens of -which the eye forms OHO element. Hence the focal distance varies with different eyes, and so does the apparent size of ob- jects. To short-sighted people objects appear of larger size than they do to persons of ordinary eye-sight. In working with the compound micro- scope we frequently find that different people require a different focal adjustment. OF THE MICROSCOPE. 23 tinctly seen, and consequently all microscopes, except the simplest forms of hand magnifiers, are provided with means for throwing the light upon the object, and for regulating the amount which shall either fall upon it or pass through it. Hence the importance of providing efficient means for ad- justing the focus and holding and illuminating the object, and the purpose which the stand is intended to fulfil, is to furnish these means in a compact and convenient form. Every micro- scope, therefore, of a grade above a hand magnifier, whether it be simple or compound, must possess : 1. Suitable means for supporting the object, and placing and maintaining it in proper position. 2. Means for illuminating the object, either by throwing the light upon it when it is opaque, or transmitting the light through it when it is transparent. 3. Means for transmitting to the eye an enlarged image of the object. The different parts which are employed for securing these several ends, have been constructed of an almost endless va- riety of forms, according to the fancies of the different makers and the requirements of different microscopists. As it is im- portant that the student should familiarize himself with the names of these different parts, we give a definition of them, and in order that there may be no opportunity for mistake or misapprehension, we have also engraved an outline of one of the ordinary forms of the microscope, and on this we have marked the names of the different parts. NAMES OF THE DIFFERENT PARTS. The following are the names of the essential parts of a com- pound 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 name properly applied to the entire frame used for supporting and illuminating the object, and for carry- ing and adjusting the optical part, the latter consisting of the SELECTION A>*D I'SE Fig. 1. DIAGRAM SHOWING THE DIFFERENT PARTS OF THE MICRO- SCOPE, AND THEIR NAM1 .>. OF THE MICROSCOPE. ZD eye- piece and the objective. Stands are frequently sold separ- ately, or furnished with eye-pieces only the purchaser making such a selection of objectives and other accessories, 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. 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. A Cottar is a short tube through which either the body, the draw-tube, or the eye-piece slides. The Arm is that part which carries the body. The Stage is the plate upon which, the object is placed for examination. Clips are springs attached to the stage for the purpose of holding in place the glass slide or plate carrying the object. A Sub-stage is furnished with some instruments. It is used for holding and centering various means of illumination. No sub-stage is shown in the diagram, Fig. 1. The sub-stage, with its centering arrangements, is shown very clearly in the Ross model, Plate I. Sub-stage Ring. Instead of being provided with a sub-stage, many cheap microscopes are furnished with w r hat is known as u sub-stage ring or tube. This serves to receive the polarizer, paraboloid, etc. The Object-Glass or Objective is the lens or lenses which are placed next the object. The term Object-glass is sometimes 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 confusion. The Society Screw is a screw of a certain standard size for con- necting the objective to the body. In microscopes furnished with a screw of the Society's standard, the objectives of any American or English maker may be used. The makers on the continent of Europe have now very generally adopted the So- ciety Screw. In this country the Society Screw has been uni- versally adopted, but as it has been found too small for low- power objectives of wide angle, another screw, named the 26 SEIiECTION AND USE Broad Gauge, is sometimes used in addition to the Society Screw. In all microscopes, means are provided for moving the objec- tive to and from the object, so as to bring the latter into focus, as it is called. According as the device used for this purpose acts coarsely but rapidly, or slowly but delicately, it is called a course or a fine adjustment. The best microscopes are provided with both kinds, so that the object is first brought approxi- mately, but rapidly, into focus by one, and then adjusted more slowly, but with great accuracy, by the other. The Coarse Adjustment has several forms. In Fig. 1 it consists of a rack and pinion. In some cases it is a chain movement ; very often it is effected by merely sliding the body up and down through a tubular collar by hand, as in Fig. 12. The Fine Adjustment usually consists of a fine screw, some- times called, improperly, a micrometer screw, which moves either the entire body or the 'lower part of it, called the nose-piece. In some cheap stands, the fine adjustment is effected by moving the stage towards the objective. The Nose-piece is a short tube, which fits into the lower end of the body, and carries the Society screw at its lower end. Sometimes it is made to slide out and in. and thus forms -part of the fine adjustment. In the instrument figured in the dia- gram, it is immovable. The term nose-piece is also applied to certain accessories which enable us to attach different pieces of apparatus to the microscope, as, for example, two or more ob- jectives at one time, the analyzer of the polariscope, etc. A Diaphragm is usually a thin plate of metal pierced with a hole, the size of which regulates the diameter of the pencil of rays that pass through. There is a diaphragm in the eye-piece which contracts the field of view, and cuts off those rays which tend to confuse the images, and all good microscopes have a dia- phragm attached to the stage, whereby the amount of -light passing through the object to the objective may be regulated. Instead of a thin plate of metal, an arrangement known as the "Iris diaphragm" is used in the microscope shown in the diagram. The Eye-piece or Ocular 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 & Diaphragm, consisting of a brass plate with a hole through it, and so arranged as to cut off the outer rays of light. The tube in which these lenses are secured is in almost nil cases removable, and the best microscopes are furnished Of THE MICROSCOPE. 27 with several eye-pieces of different powers, which may be changed at pleasure. We may here remark that where a mi- croscope is furnished with several eye-pieces, the shortest eye- piece gives the greatest magnifying power. The Cap is a cover which fits over the top of the eye-piece. It is pierced with a hole, to allow the rays Avhich pass through the instrument to reach the eye. This cap is sometimes covered with a second cap, which has no hole, but which is intended to exclude dust from the eye-lens, and which is removed when the instrument is in use. The Mirror reflects the light, and causes it either to fall upon the object or to pass through it, so as to render it visible. The Mirror-bar is a bar attached to the stand and carrying the mirror. It is usually made to turn on a pivot, and in the microscope shown in Fig. 1, it consists of two parts sliding tipon each other, so that it may be shortened or lengthened, as circumstances require. Accessories are those parts of the microscope Avhich are used only for special purposes, such as the paraboloid, the camera lucida, stage forceps, etc. 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. All these parts will be fully described in a siibsequent part of this volume, and their utility and importance explained. It is greatly to be desired that the young microscopist should familiarize himself with the terms employed, so that he may always use them accurately. Anything that he may say or write will then be clearly understood by all who have given careful attention to the subject. So important does the author deem this matter, that he has in an advanced state of prepara- tion an extended glossary or dictionary of microscopical terms. SELECTION AND USE SIMPLE MICROSCOPES. The simple microscope is an indispensable assistant to those who use the compound instrument, as well as to those who rely upon it alone for the examination of flowers, seeds, minerals, textile fabrics, etc. We shall therefore devote some space to a consideration of its various forms, though even then we shall be unable to do more than describe certain typical models which, however, afford variety enough for all practical pur- poses. | Hand Magnifiers. These are so generally useful and applicable that they are used by all who wish a cheap and yet efficient aid to natural vision. 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 considerable 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 sludent and naturalist, a very ex- cellent form is that shown in Fig. 2. It consists of a lens of suitable magnifying power set in a frame, which folds into a case, just as the blade of a pocket knife folds into its handle, thus allowing the instrument to be carried in the pocket with- out liability to injury. Similar magnifiers are made with two, three, and even four separate lenses, as shown in Fig. 3. The lenses are usually of different powers a 2 inch, 1 inch, and 1 inch, forming a very "useful combination. Each lens may be used separately, or two may be used together, or all three may 0V THE MICROSCOPE. be used at once, a considerable range of magnifying power being thus secured. Fig. 2. HAND MAGNIFIER SIMPLE LENS. The magnifiers shown in Figures 2 and 3 are furnished with what are called diaphragms that is to say, each one has a thin plate of some opaque material, having a hole of suitable size through its centre. This plate is placed over the lens when Fig. 3. HAND MAGNIFIER THREE LENSES. but one lens is used, and between the lenses when two or more are employed. It serves to cut off the marginal rays which do not give a clear image, and in this way it greatly improves the definition of the object. Two or more lenses, properly adapted to each other, and used together, give results greatly superior to anything that can be 30 SEiiEenoN AND USE obtained from a single lens, at least so far as clearness and accuracy of definition is concerned. But when used as a work- ing or dissecting microscope, they are open to the objection that the distance at which they must be placed from the object is very small, and hence it is frequently inconvenient to use them for working 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 six- teenth "of an inch from each other, we will have a very good magnifier which will enlarge objects about fifty times, but we must place it at but a very short distance from the object. If 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 are very important Avhen we come to choose a mi- croscope for working or dissecting purposes. 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 magnifying ten and the other twenty diameters, the resulting power is thirty and not two hundred times. In the compound microscope, on the other hand, the combination of an objective magnifying twenty diameters with an eye-piece magnifying ten diameters, gives a magnifying power of two hundred diameters. Watch-Makers' Eye-GIasses.- These are well known, and may be obtained of almost any power within the useful range of a singe lens. They are called "eye-glasses " because when in use they are held by the muscles around the orbif of the eye, and consequently require no extraneous support Fig. 4 shows the bell-mouthed form of the frame, which enables us to secure this result. The eye-glass ordinarily used by watch-makers magnifies about eight times, but glasses magnify- ing 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 OF THE MICBOSCOPE. 31 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 different powers. Fig. 4. WATCH-MAKERS' GLASS. The eye-glass shown in Figure 4 is a doublet, the front lens of which is set in a separate piece, shown in Figure 5. When the latter is removed, the remaining part forms a very service- able low-power glass ; when both are used together, the com- bination forms an excellent high-power magnifier. This form is one made by the Bausch & Loinb Optical Co. l.ngravers 9 Glasses. These are mounted in frames, similar to that of the watch-makers' 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, con- sisting of two plano-convex lenses, and as they give a large field of view, with very good definition, they are altogether the 32 SELECTION AND USE best microscopes for examining bank bills, fine engravings, and similar objects. The general form is shown in Fig. 6. Fig. 6. ENGRAVERS' GLASS. Linen Provers. These are a very old form of the simple microscope, and being iu very general use, they are manufac- tured in large quantities, while as it is necessary that they should be of good quality they afford an opportunity ot getting a good magnifier at a moderate price. The general . form is shown in Fig. 7, in which the instru- ment appears as in use. The upper plate carries the lens, and the length of the upright is such that when the base is placed upon any flat surface, that surface will be in focus. The base is pierced with a hole one quarter of an inch square, and when placed on a piece of cloth the lens enables us to count the number of threads which oc- Fig. 7.-UNEN PROVER. cu l^ that s P ace - Tllis indicates the fineness of the fabric. The Stanhope Lens 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 OF THE MCBOSCOPE. 33 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, animalcule in water, etc., are simply 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 microscope. It is this kind of lens that is used in the construction of those watch charms in which a large picture is seen on looking 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. The Stanhope lens seems to be a favorite in France, where it is manufactured very extensively, and sold under the name of the Stanhoscope. One advantage claimed for it is that no adjust- ment for focus is required, the flat surface of the lens being c Fig. 8. STANHOPE COLLECTING LENS. exactly in the focus of the curved surface. This feature, while presenting some slight advantages, has also the great disad- vantage that objects covered with thin glass cannot be ex- amined by such lenses, and neither can objects having a sensible thickness. The feature which we have just mentioned is imitated in some cases by placing a piece of thin glass in front of a small lens, and at such a distance that the outer sur- face of the thin glass will be exactly in focus, as is hereafter described when speaking of the Craig microscope. There is one purpose, however, to which this form of lens is applied with good effect, and that is to the construction of a " collecting lens " as it is called that is, a lens for examining drops of water when searching for diatoms, alge, animalcule, etc. Fig. 8 shows a lens of this kind made by Jas. W. Queen & Co., of Philadelphia. The lens is set in a brass frame, pro- 34 vided -with a handle, and after a drop of water has been placed on the flat surface of the lens, the cap, c, is screwed on, and the object examined by simply holding the instrument up to the light. A very excellent collector's microscope will also be found de- scribed amongst the compound instruments. The Coddington Lens. This lens was devised by Sir David Brewster, but having been made by a London optician for Mr. Coddington, it was called by his name, which has stuck to it ever since. It consists of a cylinder of glass, the two ends of which have been ground so as to form portions of the surface of the same sphere. A deep groove is cut around the cylinder, midway between the ends, and a diaphragm is thus formed between the two lenses. In Figure 9 is shown a very neat and convenient method of mounting the Coddington. This form of lens gives very sharp definition, so that when- ever a power greater than twenty diameters is required for examining objects, a Coddington, if well made, will be found to be the best lens in use, always, of course, excepting the carefully corected doublets and triplets hereafter described. The price of the latter, however, is in general four to eight times that of a good Coddington. But it has this defect, that the working Fig. 9. COUDINGTON LENS. focus is veiy 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. Those who desire to acquaint themselves with the structure and peculiarities of the most important simple microscopes, will find this subject very fully and very clearly treated in the article contributed by Andrew Ross to the "Penny Cyclopaedia," published by the Society for the Diffusion of Useful Knowl- edge. This article has been republished in book form. OF THE MICROSCOPE. 35 Achromatic Doublets and Triplets. 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 in- strument may consist of two or more achromatic lenses com- bined together in a fixed and accurately determined 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 expensive when well made. They are known as achromatic doublets and triplets, and one' maker in this country, Mr. Tolles, of Boston, has long been noted for the excellence of the simple achromatic microscopes of this class made by him. The advantages possessed by lenses of this kind are the larger field of view which they give, thus enabling us to obtain a clear view of objects of considerable size ; and the wonderfully in- creased sharpness of definition which they afford, owing to their wide angular aperture. They are usually mounted in the same style as the Coddington (Fig. 9), but are readily distinguished from the latter by the absence of any diaphragm. The lenses of which these magnifiers are composed are so constructed and combined that the field is perfectly flat and well defined in all its parts, so that a diaphragm is not necessary. Mere common lenses, put together so as to resemble these achromatic doublets, and without a diaphragm, would give such a misty view of ob- jects that they would be at once condemned. With the exception of the low and medium-power achromatic objectives used with the compound microscope, these doublets and triplets, when well made, are altogether the most satisfac- tory simple microscopes in use, and several firms now make a specialty of their manufacture. Amongst others we may name the Bausch & Lomb Optical Company, Messrs. E. & J. Beck, Browning, whose magnifiers of this kind are known as Platy- scopic lenses, and Steinheil, of Munich. To some it may appear that Ave have devoted more space to the simple microscope than its importance demands. Our excuse is that simple microscopes, of the different kinds we have just described, are not in such general use as they ought to be. This, however, seems to be the case even in France, the 36 SELECTION AND USE country of Raspail, who was the great advocate of the simple microscope, for Chevalier, in his work, says : "It is a matter of regret, from a scientific point of view, that the simple micro- scope is not more extensively used in France than it is, because in minute dissections it is capable of rendering immense service." 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 ladle or large iron spoon, mix it carefully with as much powdered pumice stone as can be conveniently stirred in, remove it from. OF THE MICKOSCOPE. 37 the fire, stir well until it begins to stiffen, and then pour it out <5 S' 2 P 3- - 5- PSifS 05 B D B IIP gs-m i " 5 t?J?S= g 3 I 1 I = Si ? iiii" B : ^^: : g: : g. : : : : : 2 : : g : : : S: : : t: : S: : : : g otnof*. S" o -1 t Vl 13 94 SELECTION AND USE that the test used is itself flat. Common glass slides are not flat, and as they are used for the cheaper kinds of micro- photographs, this fact may give rise to errors if we are not care- ful in our selections. The best slides are cut from glass plate which has been ground and polished so that the sides are per- fect planes, and it is this kind only that should be used. Care should also be taken to see that the object lies flat on the slide, and is not distorted by the cover. We have seen an objective condemned because it did not show all the diatoms in the field of view in focus at once, when the fact was that the diatoms were attached to the cover which was slightly wavy as covers often are. When it is suspected that the fault is not in the objec- tive, but in the slide or cover, the object should be carefully passed across the field of view, and the changes in focus noticed. This will iu general tell where the defect lies, for if the part that is apparently foggy should move as the object moves, it shows that the object itself is not flat. It has been recom- mended by high authority to test objectives for flatness of field by strewing some fine powder on a slide and seeing whether all the grains are in focus at once. For obvious reasons this is a very unreliable method. Penetration in low powers is perhaps most readily deter- mined by the examination of opaque objects of considerable thickness. The round pollen grains of the hollyhock, and the rounded forms of the polycystina are excellent tests for objec- tives of an inch or inch and a half. Lower powers ought to show coarser objects in all their dimensions, while for those of medium power the coarser cellular tissue of plants answers very well. It is more difficult to indicate a good test for penetra- tion in the higher powers, in which, by the way, we have often seen want of penetration mistaken for want of flatness of field. This arose simply from the fact that scarcely any object is absolutely flat, and hence, as explained under another head, the curvature of the object is sometimes taken as an indica- tion of a defect in the objective. Want of good working distance makes itself obvious during the examination of any object suited to the objective. OP THE MICBOSCOPE. 95 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 the con- struction of 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 the reader such special in- structions in regard to the choice of an instrument as are necessary in addition to those previously offered. Those who will examine the catalogues of the various makers of microscopes, will find the instruments divided into first, second, third, fourth, etc., classes, the microscopes in each succeeding class in this descending scale being smaller and less complete than those in the one preceding it. The first-class microscopes of almost all our prominent makers are large, beautifully-made instruments. They are provided with me- chanical movements in every part, whereby the utmost delicacy and precision in making an adjustment, and in recording it, may be obtained, and as a natural consequence, such instru- ments are quite expensive. Indeed, it will often be found that the hanging and adjustment of the mirrors alone, of these fine stands, cost as much as an entire microscope of the lower grades. Second-class stands are usually smaller than those of the first class, but they are frequently very complete as regards their adjustments and arrangements. Microscopes of the third and fourth class are usually much simpler in their construction, as well as less in size. In addition to these different classes, most manufacturers offer models adapted to special purposes, so that in setting out to procure a microscope, the beginner is very apt to be bewildered unless he has the guidance of some judicious friend. Of course those who are mere dealers always urge the purchase of the most complete and expensive microscope which the funds of the purchaser will enable him to procure, whereas SELECTION AND USE a comparatively cheap microscope would frequently answer liis purpose far better. The reader will of course bear in mind that by " dealer " we do not refer to experienced opticians, such as are most of our microscope makers. From these men the student will be pretty sure to get sound advice and efficient assistance. But, as is well known, every dealer in spectacles sets himself up as an optician, and professes to be competent to give advice in regard to the purchase of a microscope ; and the microscope which these men always advise the purchaser to procure is the one that will afford them the largest commissions. It is unnecessary to say that this is not always the instrument that will afford the greatest amount of satisfaction to the be- ginner in microscopy. 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 mistake is more frequently made. A microscope is wanted ; the purchaser is liberal with his means, and he is saddled with an expensive instrument entirely unsuited to his requirements. Or, on the other hand, a physician or student of limited means requires 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 which is at least pro- vided with good objectives, and the necessary facilities for using them, he ought to leave microscopy in its applications to medi- cine and physiology alone. We feel it the more necessary to be emphatic on this point, from the fact that cases involving such errors have so often come under our own observation. Thus we have seen cheap French instruments, with poor triplets, in the hands of physicians, and used in cases where the safety of the patient depended upon a correct diagnosis ! OP THE MICROSCOPE, 97 The first point to be decided, is the kind of microscope that should be procured that is to say, whether a simple or a com- pound microscope is wanted. If the student is desirous of working on objects^ under the microscope making dissections of flowers, etc. a simple microscope, of any of the kinds de- scribed in a previous chapter, will suit his purpose best. It should be arranged on a stand, and this he can either do him- self, or he can procure one of the many dissecting microscopes which he will find described in the catalogues of the manufac- turers. For such purposes a simple microscope is indispensa- ble, though when we come to examine the results of our work, (dissections, etc.) a good compound microscope is equally necessary. Attempts have been made to combine these two forms of the microscope in one instrument, and with considerable success, so far as increasing our power to examine our work as it pro- gresses is concerned. This is accomplished by so arranging the simple microscope that a compound body with its eye- piece may be slipped on or off, as required. And by using a single concave lens as an eye-piece, we can secure considerable magnifying power and great working distance, while at the same time the object is seen erect and not inverted, as when the ordinary compound body is used. This form is called the "Brucke Loupe" and is too little known in this country. But no such makeshift can take the place of a good compound microscope, although it may form a useful and convenient ad- dition to the student's outfit. The selection of a compound microscope will frequently be determined, not only by the wants, but by the means of the purchaser. To those who are obliged to put up with a cheap microscope, the only advice that we can give is to get the best they can for the money, and as newer and better microscopes are constantly coming into market, the best thing the student can do is to procure the latest catalogues of the different dealers, and examine and compare what they have to offer. There is no microscope in market to-day that will not probably be excelled by something better in less than twelve months from this time. To those whose means enable them to procure whatever they 98 SELECTION AND USE may require, a word of caution is also necessary. If your studies require the employment of the very best instrumental appliances, by all means procure either a first-class stand by some well-known maker, or a microscope ^ made to suit your special requirements. But at the same time do not fail to pro- vide yourself with one of what may be called the third-class in- struments ; that is, a microscope of moderate size, and destitute of those complicated arrangements which are the glory of all first-class stands. With such a microscope you will be able to do twice, yes thrice as much work as with the large heavy stands. The physician or working naturalist that procures a very expensive stand for every-day use, makes a great mistake. It is very well to have such a stand for special occasions, but for " ordinary work " the small stand is to be preferred. And this leads us to enquire what is or ought to be meant by " ordinary work ?" The expression is not an uncommon one, but it is one to which objection has been made on account of alleged indefiniteness. If we exclude from consideration the employment of the micro- scope for purposes of amusement or of elementary instruction, almost all microscopic work may be divided into two classes, which may very properly be called, respectively, ordinary work and purposes of research. Ordinary work in this sense consisls chiefly in searching for known forms, and does not demand anything like the instrumental perfection which is required for work which at all approaches the nature of original research. And by original research, we do not mean that research which is carried on for the purpose of making important scientific dis- coveries, but simply that which has for its end the examination of the structure and characteristics of objects which are un- known to the individual observer. In support of this view, it would be easy to cite numerous instances. Thus every one knows, that for the examination of different kinds of starch, and the investigation of their peculiar- ities, very good microscopes and high powers ought to be used. But Hassal, in his work on adulteration, tells us that a quarter- inch objective, of ordinary quality, and used on a common stand, is sufficient to discriminate between the different starches when they are mixed together, OP THE MICBOSCOKE. 99 The study of the diatoms, in so far as their structure is con- cerned, confessedly requires microscopes and objectives of the very highest class. And yet we have been told by a gentleman, whose name deservedly stands very high in connection with the study of these interesting objects, that for the determination of species, and for most other points which he has studied, he has used a good non-adjusting quarter, on a simple stand, and that it is but seldom that he has recourse to better objectives, of which, however, he has a full series by the most eminent makers. By the term " ordinary work," then, we may very properly designate all such examinations as lead us over ground that is well known, while no work that involves the examination of unfamiliar structures or the investigation of unknown processes, can be so called. But of all the work that is done with the mi- croscope, four-fifths (including the work of the physician) is " ordinary work." To those, therefore, who have abundant means at their command, we would by all means recommend the pur- chase of two microscopes always, of course, getting the cheap one first. If, during the course of their " apprenticeship," this cheap instrument should get injured, the loss will not be very great, and by the time the student has learned to use the cheap insti'ument, he will have acquired intelligent views as to his special needs in the matter of a more complete one, and will not be dependent upon the advice of any one. To those who cannot afford two microscopes, we would strongly recommend as a stand, one of the New American Models, previously described. If we except a few special de- partments, such as goniometry, etc. , these stands are equal to all demands, and will do justice to any objectives or accessories, while at the same time they are sufficiently compact and handy to allow of the convenient and rapid accomplishment of all kinds of simple work. To those who cannot afford one of these stands, the only advice we can offer is to get the best they can for the amount of money they have to spend. It would be impossible to give anything like a list of special cases in which the different styles of microscopes prove most ^0Q SELECTION AND TJSE useful t the reader whose attention is called to tins poiiifc 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? " Now magnifying 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, magnifying 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- CO? THE MICKOSCOFE. 101 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 iwice, 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 that 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 than "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 102 SELECTION AND TTSE 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 specified purposes? 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 Angulatum, which lines are about the one fifty- thousandth of an inch apart; whaj; magnifying power would be necessary? OF THE MICROSCOPE. 103 "With the 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 they 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. 104 SELECTION AND USE 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: Such 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 MICROSCOPE. 105 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 car *><} 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 very 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. Others 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 many of the most beautiful objects described in the books, and sometimes called animalcules, such as the Volvox Globator, the larger Vbrticelli, etc., etc. 106 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 that they are 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. But the stands that are most difficult to tip over are not those that resist vibrations most perfectly. For the latter a tripod with a OS 1 THE MICROSCOPE. 10? 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 so 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 checking 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 utmost importance. One great objection to most French in- 108 SELECTION AND USE 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 cannot be varied by slight pressure.* The most important points connected with the stage are the means provided for holding and moving the object, and the facilities afforded for attaching accessory apparatus. In the most complete stands, the object is held between sliding clips, which form a sort of clamp that is capable of being moved in two directions, at right angles to each other, by mechanical means, which generally consist of a screw for one direction and a rack and pinion for the other. This form, which is known as the mechanical stage, enables even a com- paratively unskilled person to bring any part of the object into the desired position in the field of view, and this with the utmost precision. These mechanical stages may be said to be characteristic of the higher classes of English microscopes, and as they are expensive, they are not generally used. Neither are they absolutely necessary for ordinary work with low or medium powers, for with any objective lower than one-twelfth of an inch focus, the object can be moved by hand quite as readily as by the screws, and we hold it to be a well established rule in all manipulations connected with scientific work, that whenever any operation can be performed satisfactorily by means of the hands alone, all special contrivances should be dispensed with. For low and moderate powers, therefore, we prefer the plain stage, on which the object is moved by means of the hands alone. But when very high powers are used, and especially when delicate micrometrical or goniometrical meas- urements are to be made, a well-made mechanical stage becomes a necessity. For while it is easy enough to bring an object very near to a given point by means of the fingers alone, it is almost impossible to sejcure perfect accuracy. In the effort to attain this the mechanical stage is a great assistance, and therefore when Frey utters a wholesale condemnation of the *At the same time, however, it must be borne in mind that no stage ever was made so firm that even a slight pressure would not affect it. If, therefore, the reader is determined not to rest content with anything Bhoit of & perfectly rigid stage, he will reject all the best microscopes in market. OP THE MICROSCOPE. 109 English microscopes, and asserts that they are unpleasantly loaded with what he is pleased to call "screws and unessential appurtenances," it seems to us that he commits a great error. These costly and complex instruments are intended for the highest class of work, and the most powerful objectives; per- fection of the work to be done, and not simplicity in the means by which it is to be done, is the end sought, and this can be attained only by the complex means employed. We have never found any of the so-called lever stages that fulfilled the requirements of the highest class of work, and, therefore, if a mechanical stage is to be chosen at all, the best form should be procured. A microscope fitted with a good mechanical stage leaves nothing to be desired, but when other forms are used, it is evi- dent that the chief points to be attained are these: 1. The object should be held steadily, but at the same time perfect freedom of motion should be allowed. 2. It should be possi- ble to remove instantly from the surface of the stage, every- thing in the shape of clips and holders, so that a clear field should be left for the adjustment of very large slides, plates, etc., or for the rotation of the object in relation to the light. 3. Even the simplest forms of the stage should be so constructed that it may be possible to pass every part of the object under the field of view, and this, without any risk of omitting even the smallest portion. This point is of special importance to physicians and naturalists. Thus, it not unfrequently happens that it is desirable to know whether or not certain forms are present in a given drop of liquid; unless we can subject every part of that drop to microscopical examination, we cannot be sure that the forms we are looking for are absent. There is always a risk of omitting some portion of the slide, and conse- quently doubt must always hang over the exhaustiveness of all our examinations. The only certain means of avoiding all risk USE and watch the different appearances which are produced by a change in the mode of illumination. Swinging the mirror to one side, so as to send the light through the object in an oblique direction, or, where the mirror cannot be turned to one side, merely turning it on the trunnions which support it, will often produce most important effects. From what has previously been said in regard to the neces- sity for clear and brilliant sources of illumination, the young microscopist may, perhaps, be led to suppose that the field of view cannot be too brilliantly illuminated. Such, however, is far from being the case. "With ordinary powers (those below 500 diameters) it is almost always necessary to moderate the light, even of a flat- wicked lamp, and still more that of a students' lamp. The finer details of an object cannot possibly be made out if the illumination be too strong; they are " drowned out," and the whole object becomes what artists and engravers call flat. The light may be regulated by the dia- phragm which has been previously described. Where the mi- croscope is not furnished with a diaphragm, increasing the dis- tance of the lamp from the instrument is the best mode of lessening the intensity of the light. Very bright light is exceedingly trying to the eyes, and therefore the student will find it advantageous to use lights of moderate intensity, and to increase their efficiency in every possible way. This may be done to a very great extent by judicious management chiefly by excluding from the eye all unnecessary light. In a room very brilliantly lighted with a number of powerful argand burners, it would be impossible to secure the proper illumination of a microscopic object by means of a candle, for the eye, accustomed to the bright light, would fail to be impressed by the weaker one. Extinguish the bright lights, give the eye a short time for rest, and the candle will answer very well. The principle thus illustrated finds a practical application in the use of pasteboard shades surround- ing the eye-piece, and excluding from the eye all light except that which passes through the microscope. Such a shade is easily made and adapted to any microscope, and is of great service. We have also in our own practice carried out the same principle by means of extra diaphragms to our eye- OP THE MICROSCOPE. Iby pieces, thus cutting off all the light which passes through the microscope, except that which actually serves to illuminate the object. It will also be found of great importance to secure perfect purity in the special illumination employed. Thus, if we are examining an object by transmitted light, it always detracts from the clearness and beauty of the image if light is reflected from its surface. It is, therefore, of advantage to shade the object by means of a small tin, brass or pasteboard shade, at- tached to the stage so as to prevent any light from the lamp from falling on the object. A difficulty which frequently occurs to young microscopists consists in the almost impossibility of securing a field of view equally illuminated in all parts. Assuming that the mirror is in proper position, and that there is nothing to shade any part, it will in general be found that the difficulty arises from the fact that the mirror throws images of the lamp, etc., upon the object. Sometimes this is very distinctly seen; the shape of the flame can be clearly distinguished, and the metal portions of the lamp appear as dark shades. The cause is that the lamp is at the exact distance at which the mirror forms an image of it on the upper surface of the slide, just as a lens, held in front of a white wall, will throw an inverted image of a lamp or candle on the wall, provided the relative distances of the wall, lens and candle are properly adjusted. The remedy is very simple; move the lamp either towards the microscope or away from it, as may be most convenient. As previously stated, the character of the illumination af- forded by a mirror, and by a white surface placed at a short distance from the object, are appreciably different. A very pleasant method of illuminating transparent objects consists in the use of a plate of plaster of paris. Its whiteness is probably as pure as-that of any other substance, and it is easily procured. The plate we use was cast in the cover of an old tin box, half an inch deep and three inches in diameter. A flat surface was secured by casting it upon a board. If cast on glass or metal, the surface is glazed and shiny, which is bad. Instead of plas- ter, fine white paper or cardboard may be used. Such surfaces must not be glazed, and they should be kept scrupulously clean. 170 SELECTION AND TJSB The light is also sometimes modified by passing it through ground or colored glass blue being a special favorite. Such light-modifiers, as they are called, produce a pleasant and equable illumination, which is a great relief to the eyes, but, except for the resolution of finely lined objects, we have not found them otherwise of any special advantage. When it is desired to obtain the greatest resolving power that a lens is capable of affording, the blue cell, as it is called, is probably the most efficient accessory. This is simply a glass tank, somewhat like a zoophyte trough, filled with a solution of oxide of copper in liquor ammonise. The solution is prepared by adding liquor ammoniae to a saturated solution of sulphate of cop- per, until the precipitate which is first formed is re-dis- solved. The intensity of the blue may be regulated, either by diluting the solution, or by varying the thickness of the layer of liquid. When it is desired to examine anything by light reflected from it, instead of light transmitted through it, the object should be placed before a dead-black surface, such as the dark part of the diaphragm, or a blackened card, and at such a distance from it that the surface of the background is not in focus. Then, place the condensing lens in relation to the lamp, so that a bright spot of light will fall on the object, and on bringing it into focus it will be clearly seen. Low powers only can be satisfactorily used for the examination of opaque objects by beginners. The beginner should commence with the simplest mounted objects, and afterwards, when a little skill in the manipulation of the instrument has been acquired, he should proceed to the examination of such simple unmounted objects as are easily prepared. The latter course will prove altogether the most valuable and instructive, for he who confines himself to the ex- amination of mounted objects only can never hope to become a microscopist. After a time, when a little skill has been acquired in the preparation of objects, the student may proceed to preserve and mount them. Most young people try to -mount before they have learned to prepare objects, and the conse- quence is that they soon find themselves in possession of a large collection of very poor slides. OP THE 3UICKOSCOPE. 171 On the Use of Objectives of JLarge Apertures. When the first edition of this book was issued, wide-angled ob- jectives were far from common. The "Battle of the Object- Glasses " was at its height, and objectives capable of resolving the Ampliipleura peUucida, or Nobert's nineteenth band, by sim- ple lamplight, were comparatively scarce. During the interven- ing years the opticians have been hard at work, and have turned out objectives of a high class to such an extent that almost every microscopical society numbers amongst its members those who have glasses of high balsam apertures. It is an unfortu- nate fact, however, that thus far the text-books are entirely in- nocent of any directions for using these glasses. We have now before us a treatise of over 400 pages, which left the author's hands as late as the middle of 1880, and which does not contain a single direction for the use of the cover correction ! As a justification of such omission, it has been alleged that objec- tives of large aperture require no more care and skill than others. From this position we most emphatically dissent, and if evidence were wanting we could cite the case of a prominent officer of one of our microscopical societies, and one who claims to be an expert in the use of the microscope, who thought it a great feat to show No. 18 of the Probe Platte with a J objective, which undoubtedly was capable of resolving No. 20 handsomely if properly handled ! The forthcoming work of Prof. J. Ed- wards Smith will probably be the first text-book that will have treated this department thoroughly, and students are anxiously looking forward to its appearance. Instruction in the proper methods of handling first-class objectives is best obtained from a living teacher. It will be found one of the most difficult things to learn from a book. One reason for this is that until he has become expert, or has seen the objects in the hands of some one who is expert, the student does not know what appearance to look for. The con- sequence is, that he is all the time working in -the dark. But after he has seen the Ampliipleura or the Saxonica well shown by some one who knows how to handle a good objective, he has a standard of excellence to go by, and it will be very strange if, after a few trials, he does not surpass the work of his teacher. Then, as soon as he has learned to bring out what he knows to 172 SELECTION AND TTSE be the best results on difficult diatoms, lie knows when his lenses are doing good work in his hands, and, so far as his in- strument is concerned, he feels confident that he can apply it to any class of objects and get views that are trustworthy. To get the best results from modern objectives of wide angle of aperture, there are two things that must be carefully at- tended to the illumination of the object, and the adjustment of the correction for the thickness of cover-glass. Of delicacy in focussing, which, by the way, is a most important point, it is unnecessary to speak. As regards illumination, the three great points that must be secured are purity, intensity, and suitability. By purity we mean that the light must be wholly of a certain degree of obliquity, for these wide-angle lenses gather in so many rays, that a diffused light, which does not affect low-angled objec- tives, greatly injures the working qualities of those of high angle. Thus, for example, if we are working by central light, it is necessary to shut out all the direct rays from the lamp, which would enter at every sort of angle, and produce con- fusion. A narrow pencil, produced by sending a beam of parallel rays of intense light through a small hole placed some distance below the stage, will give central illumination, which will give very different results from that obtained by a dull, diffused light, such as may be obtained from the flat side of the wick of a lamp, failing on a large mirror and reflected upward. When oblique illumination is used, great care should be taken to prevent rays of different degrees of obliquity from falling on the object. A large, concave mirror fills a large portion of the arc through which it swings, and its upper and lower edges reflect rays which fall upon the object with very different degrees of obliquity. Where very oblique rays are used, but a small proportion of them enter the glass slide, unless they are " guided " through by some such contrivance as the Beflex Illuminator, Tolles' Traverse Lens, etc. Bays of less obliquity enter much more freely, and although less in quantity than the others in the first place, they drown them out. In the exclusion of these rays consists in a great degree the value of many of the "illuminators" in common use, and the same effect may be secured to a considerable extent by OF THE MICKOSCO- 173 means of a simple screen. This fact lias been made very ap- parent by Prof. J. E. Smith, who, by the use of a simple "oblique diaphragm," as it is called, has secured results which were previously supposed to demand much more complicated and expensive arrangements. This oblique diaphragm, or screen, consists of a plate of very thin metal secured to the under surface of the stage. The stage then forms the upper surface of a >, and the metal plate the lower one. The angle may be adjusted at will by simply bending the plate, and it is evident that all rays from below will be entirely excluded. A piece of the thin iron known as ferrotype ptate is the cheap- est and best material for this purpose. Its surface should be dead black. The same result is obtained by the use of a conical dia- phragm fitted to the sub-stage. When such objects as difficult tests are viewed by oblique light, it will be found that there is a certain angle of illumina- tion at which the objective will generally perform best, and this must be found by careful experiment. The higher the angle of aperture of the objective, the greater may be the angle at which the object is illuminated, but it will be found that many objectives fail to work up to the full angle claimed for them by their makers. Such are the general principles to which the student must pay attention in regard to the matter of illumination, but in ad- dition there are numerous minor details, a knowledge and appre- ciation of which can only be acquired by practice. The finer objectives are so sensitive to the slightest changes, that the least movement of the mirror or lamp influences the result in a very marked degree. The other important point to be attended to is the cover- correction. This will be found to demand great patience and attention. The older authorities give fixed rules for regulating the cover-adjustment, but as it unfortunately happens that this adjustment varies not only with the thickness of the cover. glass, but with the depth to which the object is sunk in the mounting medium (and this is not always the same), and the angle of illumination, it will 1% seen that each object requires special attention in regard to these points. In addition to this, 174 SELECTION AND USE it will be found that each objective has its own special charac- teristics, which must be carefully studied by the owner if he would command success. The difficulty of giving any rules which will enable the student to put the "finer touches" on this kind of work, is well set forth by Dr. Blackham in a recent article,* from which we quote as follows : "It will probably be expected that something should be said here in reference to the adjustment of the objective for dif- ferent cover-glasses, etc., by means of the screw collar, but on this point, unfortunately, but little can be said, though, of course, it is a most important one, and the better the objective, and the wider its angle, the more important is accurate adjust- ment. Every wide-angled immersion objective that is worth having, is a separate work of art, and, as such, has an individ- uality with which the worker must become acquainted, and which he must learn to turn to his advantage. " None of these lenses which I have seen are perfectly achro- matic, and each has a special wave length at which it does its best. In Tolles', and Bausch & Lomb's, and I believe in Spencer's lenses, this is between the blue and the green, but the exact shade differs with different lenses, and must be found by experiment. My plan is to adjust roughly by means of the tint of the field, then to bring an object into the field (if we are at work on the Probe Platte, one of the easier diatoms, say Pleurosigma angulatum], and focus on it and arrange the illu- mination as accurately as possible, and then with the finger and thumb of the left hand, turn the correction collar of the objec- tive backwards and forwards, keeping the object in focus all the time by means of the forefinger of the right hand on the milled head of the fine adjustment, until the best effect is ob- tained. An occasional slight change in the position of the mir- ror is often needed. "In all these manipulations, deliberation and care are needed, and the patience of the beginner will often be sorely taxed, but let him remember that nothing worth having, can be gotten without trouble." * 'American Journal of Microscopy for February, 1880. OF THE MICROSCOPE. 175 Care of the Microscope. A microscope, when not in use, should always be kept well covered, either in its case or under a suitable cover. There is no more convenient mode of keeping a microscope than to stand it upon a cloth mat, and cover it with a glass shade. It is thus kept free from dust and vapors, and is always ready for use; but when it is kept in its case, and especially if it has to be screwed together, interesting, valuable, or even important objects, will often fail to be ex- amined, simply because too much time and labor are necessary to prepare for the operation. A good microscope should be so carefully protected, that it shall rarely require to be cleaned or dusted, as this wears off the lacquer, and exposes the metal, which, when thus uncov- ered, soon begins to tarnish. When dusting or cleaning becomes absolutely necessary, chamois leather, or a very fine old linen or silk handkerchief is most suitable. Never use coarse cloths, or those that have been lying about exposed to dust and dirt. The lenses should be kept in their boxes when not in use, and when they are attached to the microscope, great care should be taken to keep them from coming into contact with liquids. In order to prevent the latter accident as far as pos- sible, never examine liquids unless when they are covered with thin glass. In the pursuit of micro- chemical studies, the microscopist has frequently to deal with liquids that corrode metals, and even glass. In well-appointed laboratories inverted microscopes are used in such cases, but with ordinary instru- ments, special means must be employed. The object should be laid on a large piece of thin plate glass, and the brass work of the objective should be coated with oil. The rest of the metal work may be protected with oiled silk or thin india-rubber. When liquids which corrode glass are used, the front of the objective should be protected by means of a very thin leaf of the best mica, which may be attached either by glycerine or balsam. These, however, are exceptional precautions. In ordinary work it is sufficient to see that the lenses and metal work are kept free from stains and finger marks. Never touch with the fingers the surface of any lenses, either eye-pieces or objectives, as this will be certain to soil them. Use soft camel-hair brushes to remove particles of dust, etc. Where 176 SELECTION AND USE dirt adheres more strongly, use fine linen slightly moistened -with alcohol, and wipe dry with very fine chamois leather. Remem- ber, that alcohol, if used profusely, will attack the lacquer of the brass- work, and even dissolve the cement which holds the lenses together. When objectives are smeared with balsam, the best cleansing agent is said to be kerosene oil. The piece of leather used for wiping lenses should be free from dust, and is best kept in a small box by itself, and used for nothing else. It must be remembered that the glass of -which objectives are made is easily scratched, being soft when compared with parti- cles of sand and grit; consequently, when frequently wiped it soon loses that exquisite polish upon which its excellence of performance so much depends. What, then, are we to think of the directions given by the author of a popular work on the microscope, in which we are told to use a piece of leather, slightly impregnated with brick dust ! ! No better method of destroying an objective could possibly be devised. Therefore, see that in wiping, the slightest possible pressure is used, lest any particle of grit should make a scratch. The exposed parts of all microscopes, as well as the objectives and their cases, are lacquered, to protect them from being soiled by handling, but the interior of the boxes which hold the object-glasses are rarely so protected, and the black coating of the interior of bodies, draw-tubes, etc. , is frequently not very firmly attached. Therefore, never touch them with the fingers. After taking an objective out of its box, either screw on the cover of the box, or place the latter with its open end down, Do not stand it mouth up, so that it may catch all the dust. When exhibiting the microscope to others, great care is neces- sary to keep meddlesome fingers from soiling the glasses. Some people are never content when merely allowed to look at things: they insist upon handling them, and feeling them. To the young microscopist, we would say that if any of y our friends in- sist upon handling your objectives, eye-pieces, etc., put up the inatrument and pack it away. A microscope carefully used is as good after fifty years as when first made, but we have seen an instrument suffer more injury in half an hour at the hands of a thoughtless and dirty person, than it would have BUS tained in twenty years in the hands of a careful microscopist. V OF THE MICROSCOPE. 177 COLLECTING OBJECTS. Those who are engaged in special studies and researches re- quire no directions for collecting objects; but to those who use the microscope for purposes of general instruction or amuse- ment, a few hints may not be out of place. Almost every text- book on botany, physiology, mineralogy a.nd kindred subjects, will not only indicate a long list of objects, but will give di- rections for procuring them. Plants yield a very large variety of interesting subjects. Thus the cuticles of the leaves and flowers; cellular tissue as shown by dissections, and by cross and longitudinal sections; hairs, pollen, seeds, etc., all deserve careful microscopical examination. Insects furnish an almost unlimited field, and their wings, feet, eyes, mouth, scales, spira- cles, hairs, etc., are all worthy of careful preparation and exam- ination. It is, however, amongst the more minute forms of animal and vegetable life, as found in pools and running streams, that the most interesting objects are to be found, and the number and var- iety of these is so great that several large volumes would be re- quired to describe them. Even the ponderous works of Ehren- berg and Pritchard do not begin to exhaust the subject, and, therefore, it will be obvious, that even if we were to devote the whole of the present volume to this department, we could but skim the surface. Thus far we have had to depend chiefly upon foreign works for descriptions of these organisms, but it is fortunate that while the higher classes of plants and animals which inhabit Europe, and are described in European works, are entirely different from their congeners on this continent, the same does not hold true in regard to the lower forms. We have found localities which teemed with the Volvox Globator and various species of Closterium, Staurastrum, Pediastrum, etc. Hydras are to be found in great abundance, and so nearly. like the described European species that the beginner will find it difficult to detect the difference. We have repeatedly found the Sleplianoceras, Melicerta and other beautiful microscopic objects, and as for the more common ones, such as the VorticeUi, or 178 SELECTION AND TTSE wheel animalcules and Enlomostraca, or water fleas, they are to be found in every pool. Every young microscopist that is desirous of pursuing his studies in this direction, is met at the outset by two difficulties; the first is to obtain the objects, the second is to find out what they are after he has got them. The first is by no means a dif- ficult task, but the second will often puzzle more experienced students than those whom we expect to be readers of this book. We know of but two ways to accomplish it; one is the laborious plan of searching for them in the " Micrographic Diction- ary," or the books of Carpenter or Pritchard; the other is to obtain the desired information from some well-informed friend. The objects which are of most interest to the microscopisfc are not difficult to obtain, if we know where to look for them, but they are not to be found everywhere. Many stagnant pools will be found to yield but a scanty supply, while others, which, perhaps, to the uninitiated present a less promising appearance, will yield a rich harvest. Beginners are very apt to entertain the popular notion, that every drop of water teems with animal- cules, and that when placed under the microscope, it will appear to be literally filled with living things. This idea is fostered by popular writers who describe a drop of water as a globe filled with life, and by lecturers who exhibit pictures and enlarged im- ages of what they call "a drop of water," but which is in reality a considerable quantity of that liquid which has been artificially supplied with inhabitants. Clear well water is almost free from microscopic organisms, and the same is true of the water from clear brooks, which flow swiftly over a pebbly bottom. Ordin- ary rain water, as found in cisterns having free communication with the air, usually contains large numbers of the larvae of gnats and mosquitoes, and when exposed to the light it is almost always rich in wheel animalcules, and some of the lower forms of vegetable life. The water supplied to our cities is in gen- eral very rich in microscopic vegetables. Thus in the Croton water, which is comparatively pure, we have found a large number of very beautiful species, amongst them the exquisite Monachinus. The best way to secure a supply of the animal and vegetable inhabitants of city water, is to pass a considera- OF THE MICROSCOPE. 179 ble quantity of it through a filter, the surface of which will then furnish a large amount of valuable matter. But it is not in such fields that the microscopist will find his best hunting grounds. Along the edges of quiet pools of clear water is the best place for the finer vegetable forms, such as the Volvox Qlobator, Closterium, etc. If the water is much con- taminated with dead animal matter or with sewage, nothing will be found but the coarser organisms and animalcules, such as Paramecium. The same is true of small pools found in woods, or very much shaded with trees, and filled with dead leaves. Such places are, however, the favorite haunts of the larvae of insects, and also of frogs and Tritons. The size of the pools is not of much consequence. We remember on one occasion to have found by the roadside in Centre County, Pennsylvania, a little pool which was almost filled with the larvse of Tritons. The gills, which were beautifully developed, would have formed a splendid object under the microscope, but when we returned next day, for the purpose of securing some, the water had dried up, and the larvae were all gone. The little pools formed in boggy ground by the footsteps of cattle will often be found to contain large quantities of one or two species of desmids or diatoms. It will not do to look for these objects in similar pools formed in ordinary soft land, and temporarily filled with rain water. The ground must be na- turally and constantly wet, so that the pools are always kept filled by the infiltration of water from the surrounding soil. Such pools, however small, usually contain a large number of specimens, and it is in such places that one is most likely to find a supply of one variety unmixed with any others. While many of the most interesting objects will be found swimming freely about in the water, others of great beauty are always attached to floating weeds, sticks, etc. We have gen- erally been most successful in discovering specimens of this kind when we have placed the gathering in a large glass jar, and allowed it to stand quiet for some time. The water will then settle, and the objects of which the microscopist is in search will have time to expand, when they may be seen in a form resembling light mould, or down, attached to the surfaces of the solid matters. 180 SELECTION AND TJSE The surface of the mud at the bottom of ponds of clear waier, is frequently very rich in microscopic vegetable organisms. These minute plants seem to seek the light, and to rise through the mud which would otherwise cover them, so that by care- fully scraping the surface of the bottom, we are enabled to procure them in large numbers. It must, of course, be borne in mind, that while some species are found in fresh water, others are marine, that is, they live only in sea- water. The best locations for finding marine forms are: 1, the pools of c'ear water, found in salt marshes; 2, the surface of the mud at the bottoms of harbors and quiet coves; 3, the waters of the ocean itself, as well as that of^the bays and coves connected with it. The apparatus required for capturing these various objects, is neither bulky nor expensive. For larvse and the larger ani- malcules, the most useful implement is a small net. Ours con- sists of a ring of brass wire (iron wire would rust and destroy the net) about six inches in diameter, soldered to a tin tube or ferrule, which fits tightly on the end of a walking cane. To the ring is attached a bag of any light, gauzy material, which possesses the two qualities of letting water out rapidly, and keeping small objects in. With this net it is easy to capture anything from a small fish or a frog to the very smallest larva, and it is very portable, since an ordinary walking cane forms a sort of universal handle for this and other implements. Next to the net, we find the most useful articles to be bottles. They should be of clear glass, so that any object contained in them may be readily examined by means of a pocket lens. For this reason we prefer what are called homoeopathic phials of large size (half ounce and quarter ounce), and we generally carry a dozen or two when out on a tramp. A fair sample of the contents of a small pool is easily obtained by gently lowering the phial, mouth downwards, under the water, and bringing it cautiously to the place which is supposed to be richest in specimens. The phial is then turned mouth upward, the air rushes out and the objects are carried into the bottle by the force of the inrushing current of water. For small, shallow pools, the phial is most conveniently held in the hand, but when the water is deep a handle is required, and for this we use the holder shown, in. OF THE MICROSCOPE. 181 Fig. 55, which is made to fit on the end of the walking stick. It consists of a ferrule having a semi-cylindrical piece soldered at gHm ip^g^ right angles to it. The ferrule fits the cane, I and the bottle is fastened to the cross piece * by means of a rubber ring the method of arranging the latter being easily understood )U| from the engraving. A dozen or more bottles i [ of proper size may be taken along, and they Fig. 55. are so eas ity attached to the holder that there is no necessity for transferring a "dip" to another bottle. The contents are most easily carried in the bottle in which they were first obtained. When the water is too deep for a walking cane, a fishing rod or any long pole may be used, and where these prove too short, as in harbors, etc., a bottle may be lowered and raised properly by means of strings. For this purpose the bottle must be heavily loaded with lead round the neck, and two strings must be attached to it, one fastened to the neck and the other to the bottom. It is by the latter that the bottle must be lowered, but it must be raised by the other. If properly managed it will descend mouth downwards, but the tension of the string attached to the neck will invert it, and when raised by this string it will bring up its contents very perfectly. For scraping the surface of the mud at the bottom of shallow pools, we use the spoon shown in Fig. 56. It is simply a ring of tin five inches in diameter and one inch deep. The lower edge is " wired " as the tinsmiths call it, and there is a ferrule soldered to the side so that it may be fixed to the same cane that is used for the net. Over the Fig. 56. bottom is stretched a piece of some thin fabric, such as thin muslin, gauze or tarletan, which is held in place by a rubber band that slips over the wire ring on the lower edge It is best to make one side of the ring somewhat flat, so as to adapt it better to the flat surface of the mud. When the pieces of cloth get soiled, they are easily replaced, and, indeed, in some cases it is not a bad plan to carry the mud home in the Wet cloths, a dozen or more of which, with their contents, may 182 SELECTION AND USE Fig. 57. be easily packed in a tin box of small size. One of the boxes used by school children for lunch boxes answers very well, but any tin box with a lid or cover will answer. As it is im- portant that a record should be kept of the locality from which the dip was taken, we carry a few slips of parchment paper, one of which is pinned to each cloth, after the necessary memoranda have been written upon it with a hard pencil. On returning home, the contents of each cloth may be transferred to a separate bottle. This plan saves the carrying of nu- merous bottles, and the water required to fill them. An exceedingly coveni- ent traveling companion for those who are fond of collecting, is shown in the accompanying engraving, Fig. 57. The main part forms a very convenient walking cane of ordinary appearance. Like many fishing rods, however, it is hollow, and contains a sec- ond rod by which it may be extended to twice its length. This enables the user to reach the bottom of any ordinary pond, and to reach as far as is necessary from OF THE MICEOSCOPE. 183 the shore. Accompanying the cane, A, are the hooked knife, B, and the ring and bottle, C. These are made with a double screw, so that they may be attached either to the end of the cane itself, or to the inner rod, and in this way we can have either a short and stout handle, or a longer and more slender one, as circumstances may require. The bottle is made so as to screw into the brass ring, and the same screw enables us to fit a wooden cap on it, which thus encloses the contents tightly. The hook is made of fine steel, and has a sharp cutting edge, as seen in the engraving, so that it is easy to cut off a piece of weed, drag it out of the water and secure it. Those who carry such a cane do not attract attention by any unusual parapher- nalia, and at the same time they are at all times ready to secure any valuable material that may present itself. Sev- eral bottles may be carried in the pocket, and screwed into the ring as required. The collector who desires to make a thorough examina- tion of the microscopic flora and fauna of any pool or stream, must not rest content with infinitesimal quantities of material. It is not neces- sary, however, to lug home a gallon of water for the sake of the objects contained in it, , and so fully have microscop- ists been impressed with this idea, that the devices which have been prepared for strain- ing out the valuable portions are almost endless. The best and simplest that we have J3-/S i- f Fig. 58. WATEK-STBAIMBa, seen is a modification of an 184 SELECTION AND tJSE arrangement, designed, we believe, by Mr. Highley, and figured in Beale's work on the microscope. It consists, as shown in the engraving (see Fig. 58), of a bag or net of some light material, to the bottom of which is attached, by means of twine, or a strong rubber ring, a wide-mouthed bottle. Any quantity of water may be poured into the bag, and all the objects which it contains will roll down the sides of the bag and fall into the bottle, while the fluid escapes through the sides. Delicate objects are consequently not exposed to pressure, rubbing, or any other violence, as they would be in an ordinary filter or bag, and the whole affair is so simple that any one can make it. A slight modification of this arrangement will be found ad- mirably adapted to the microscopic examination of the water supplied to cities. The bag may be attached to any faucet, aud and all the water that is used in the household may be caused to pass through it. In this case, if the bag be made of some tolerably stout material, it may be firmly tied to the faucet, and then all the water that is consumed will be very thor- oughly purified. Another very excellent device is the bottle invented by Mr. Wright, of which a modified form is shown in Fig. 59. The mouth of the bottle is closed by means of a coik in which two funnels are inserted. One of these funnels is placed in the bot- tle, mouth down; the other projects above the cork, as shown in the engraving. The mouth of the funnel that is in the bottle is covered with muslin or flannel, held in place by a rubber band, which is prevented by a wire ring from slipping along the con- ical surface of the funnel. When water is poured into the other funnel, it passes into the bottle until the latter is full, and then it flows out of the first funnel, and is carried off by means of a short piece of rubber tubing. Meanwhile, all solid parti- cles are held back by the filter, and as the latter is horizontal and with the filtering Fig. 59. OF THE MICKOSCOPE. Ig5 surface downwards, most objects of interest fall away from it, and may be found in the water. A single bottle of this descrip- tion is sufficient, as the cork is easily removed, so that the water may be poured into other bottles. As ordinarily made and sold, Wright's collecting bottle is an expensive piece of apparatus, costing four or five dollars, but as shown in the engraving it may be made for a few cents by any tinsmith. Where it is desirable to keep the specimens thus obtained so that they may be examined, and their life-history studied, bottles and jars of almost any kind may be used, but those which we have found most convenient are what are known as "quin- ine " bottles, and may be had at most druggists. For ordinary objects they are just about the right size, and as they are made of tolerably clear glass it is easy to examine the objects through the sides of the bottle. A dozen or two of these little aquaria occupy very little space, and are easily handled. Great care must in general be taken to exclude from the vessels contain- ing the finer organisms, such predatory animalcules as devour them. Water fleas, the larvee of insects, etc. , will soon make away with the finer specimens. On this account great diffi- culty is found in keeping the Volvo.v Qlobalor, since it is greedily devoured by various rotifers, and these are exceedingly difficult to exclude. We have succeeded best in this case by partially filling a bottle with well-filtered water taken from the same pool as the specimens, and transferring the objects to it singly so as to avoid transferring their enemies too. For this purpose the dipping tube should be used. Some authors caution us against mixing the inhabitants of different pools, on the ground that being strangers to each other they will fight. This is more fanciful than accurate, though it has a basis of truth. It is not the circumstance that they are strangers that causes the diffi- culty, but the fact that the one is the natural prey of the other. The same thing occurs between inhabitants of the same pool. It must be remembered, however, that very slight changes in the conditions in which they are placed will often cause the de- struction of these objects. Thus, we have seen some very fine gatherings totally destroyed by being removed from soft, boggy water to clear, hard well water. Therefore, in transferring either animals or vegetables to an aquariun, it is well to supply 18(> SELECTION AND USE them with the same water, mud, etc., in which they were origi- nally found. It will sometimes, however, be- well to filter the water so as to remove all such inhabitants as are apt to eat up the others. Water, may be filtered through paper, or where fil- tering paper is inaccessible, the neck of a funnel may be loosely plugged with cotton. Even this does not quite free it from noxious eggs or germs, and we have sometimes boiled it in the flask in which the objects were to be kept. The mouth of the flask was then plugged with loose cotton, and when the water was cold, the objects we wished to preserve were introduced. "When floating freely in these diminutive aquaria, many ob- jects are as difficult to find and capture as would be a small fish in a large pond. The microscopist, therefore, requires special means for capturing them, and placing them on a slide. For this purpose nothing serves so well as what are known as dip- ping or fishing tubes. These are simply glass tubes of different diameters (from one tenth to. one quarter of an inch), and of any convenient length. They are used by closing the upper end with the finger, bringing the lower end near the object (un- der the water), and then removing the fingers from the uppei end. The water, in seeking to find its own level in the tube rushes in with great force and carries the object with it. By again placing the finger on the upper end of the tube, the latter may be lifted from the bottle, and the water with it, and by a little dexterous management it is easy to cause the object to flow out on a slide without allowing too much water to go with it. These tubes are made straight, curved, and with one end drawn to a point, but for most purposes the straight tube answers best as it is most easily kept clean. We prefer to grind the ends rather than to make them smooth by fusion, as the latter pro- cess generally contracts the opening, and renders the tube dif- ficult to clean. The best plan, however, is to heat the upper end strongly before the blowpipe, and turn the edge outward like the mouth of a test-tube. It is then easily closed, and the tube is very strong. The lower end should be ground. OF THE MICROSCOPE. 187 PREPABATION, PKESEBVATION AND MOUNTING OF OBJECTS. These three operations are so frequently applied as a single process to objects, that many writers have failed to make a suf- ficient distinction between them. By keeping the proper dis- tinction clearly in mind, however, the student will not only save much valuable time, but he will secure vastly better re- sults. Except by those who are more anxious to increase the number of objects in their cabinet than the amount of know- ledge which they possess, a very large proportion of the ob- jects examined will never be preserved or mounted at all. This however, should not prevent the utmost care being given to the process of preparing them for thorough examination. On the other hand it often happens that objects which have been carefully prepared and mounted, spoil because they have not been subjected to a proper preserving process. Hence the importance of treating these operations separately and fully. Tlie Preparation and Examination of Olbjects. It is a common but very erroneous idea that the only thing that is necessary in order to examine any object under the mi- croscope, is simply to place it on the stage, and get it into focus. With the exception of mounted objects, a very few transparent objects such as the wings of insects and some things that are viewed by reflected light, every substance re- quires to undergo careful preparation before it can be fit for profitable examination. A good example of the necessity for such preparation is seen in the common potato, a piece of which when simply placed on the stage of the microscope, and brought into focus, appears as a glistening rnass, and reveals nothing of its true structure. If we now cni from this lump, by means of a very sharp knife, an exceedingly thin slice, place it on a plate of glass, moisten it with a little spirit and water, or better still, glycerine and water, and place over it a thin glass cover, it will disclose to us a most wonderful and beautiful structure. The entire mass will be seen to be composed of cells, these cells be- ing filled with granules of starch of various sizes. 188 .SELECTION AND USE 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 ol 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 Frey, 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 OF THE 1IICBOSCOPE. 189 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 in jury, 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 ]90 SELECTION AITO USE 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 thin 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 skill. Still it is astonishing what may be accomplished by means of good files, Avhetstones 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 :vn oval (ellipse) of greater or less length, and when cut longitudinally it shows two lines which have no OF THE MICKOSCOPE. 191 Apparent connection with each other. 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 micro- 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 carved 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. In order to bend a needle, it must first be heated jn the flame of a caudle, 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 knives for dissection, they are generally used in pairs, that in the right hand being used for teasing or 192 SELECTION AND USE cutting, while the 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 parj;s 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 been 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. 60. 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. 60. 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 equal 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 wax in the other OF THE MICROSCOPE. 193 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- 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 42, 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. In a short time say t>ne 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 alter everything soluble has been 194 SKLECTION AND USE washed away and every tiling 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, so 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 potassse, 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, and then in turpentine, and finally mounted in 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 M1CKOSCOPE. 195 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- 196 fcEI/EOTTOtf AND TTSE scribed, it is necessary to immerse it in some suitable medium, so as to render it clear and transparent. The action of sucb 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, 1.5321.549; 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; GUI 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- OP THE MICROSCOPE 197 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 " lod-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 six 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. 61. 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. 61 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 198 SELECTION ANI> DSli 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 silk 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 water; 2, the perfect exclusion of air; 3, reduction to a state of complete dryness; and 4, the employment of certain anti-septic OP THE MICBOSCOPE. 199 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 200 SELECTION AND tfSii 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. OS 1 THE MICKOSCOPE. 201 DAMAK MEDIUM. Gum dainar 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 Frey 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." GLYCEKINE. 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. 202 SELECTION AND USE When employed as a preservative, glycerine is used either 1 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. GLYCEKINE JELLY. The original directions given by Law- ranee 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, 6 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 Otf THE MICKOSCOPE. 20 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 forms 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 AND 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 found very useful. This is made by dissolving 4 parts by weight of picked gum arabic in 4 parts of cold distilled water, and adding 2 parts of glycerine. The solution must be made without the aid of heat, the mixture being occasionally stirred, but not shaken, whilst it is proceeding: after 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 kept in a bottle closed with a glass stopper or cap (not with cork), containing a small piece of camphor. The great advantage of this medium is that it can be used cold, and yet soon viscifies 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 204 SELECTION AND USE it -with success. Take gelatine, 1 ounce; honey, 5 ounces; water, 5 ounces; rectified spirit, \ 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 Laving 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 FLUID. 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 desmidise, 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. OS' THE MICKOSCOPE. . 205 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 qu irts. To make the B fluid take rock salt, 8 ounces; corrosive sublimate, 2 grains; boiling water, 1 quart. P ACINI'S FITTED. 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. CASTOR OIL. 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 206 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 OP THE MICROSCOPE. 207 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 (2j by i and 2f by ), 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- 208 SELECTION AND tJSE atus. 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 slides 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 110 necessity for extended de- scriptions on the labels, and therefore slides of half the usual size (H 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 slides sold by the dealers have the edges neatly ground, an operation which the microscopist will find tedious and trouble- OP THE MICBOSCOPE. 209 As procured from the manufacturers, the slides are always uirty, 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, striae 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. COVEBS. 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 210 SELECTION AND T7SE cut into squares and circles of suitable sizes. Directions tot 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, rinse 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 l 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 TURN-TABLE. 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, OP THE MICROSCOPE. 211 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. 62. 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 Fig. 62. TUBS-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 time 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. 212 SEUBCTION AND USE In the turn-table just described, provision is made to obviate this difficulty. A heavy-headed screw, of the precise weight necessary, is screwed into the under surface of the table, and gives a perfect balance to the wheel. It then runs smoothly and truly. Numerous attempts have been made to produce a self-center- ing table, i. e., one in which the slides would be truly centered without requiring care and skill on the part of the operator. One of the earliest forms was that of Dr. Matthews, the centering part of which is shown in Fig. 63. Upon the surface of the table he arranges two triangular plates of brass, which rotate upon pins placed at equal distances on each side of the centre, and as the plates are of the same size, when- Fig. 63. MATTHEW'S THEN-TABLE, ever their inner faces are par- allel, these faces must be equi- distant from the centre. Hence, when a slide with parallel sides is placed between them, and the plates turned so as to press upon the sides of the slide, the slide will be truly cen- tered so far as its width is concerned. It is centered for length by a stationary pin, against which the end is always brought. Slides of irregular size are therefore centered only one way. There are at present, however, before the public, two tables which centre slides accurately in both directions. One was in- vented by C. Mason Kinne, of San Francisco, who describes it as follows: "As will be seen from the engravings, Figs. 64 and 65, which are reduced one-half, Kie slide will be grasped autom- atically, upon removing the finger from the lever, the spiral spring causing the clutches to instantly clasp the slide, and retain it in a central position. One corner of either end of the slide projects sufficiently for the purpose of taking hold with one hand, while the other ia pressing the lever, and can be fixed or removed without pushing along a circular disc to its edge. The slots are made to allow movement enough, so that OF THE MICROSCOPE. 213 Fig. 64. KINNE'S TURN-TABLE. (Upper side.) Fig. 65. KINNE'S TURN-TABLE. (Under side.) the clutches can grasp any piece of glass from l to 3 inches in diag- onal length, and the table is made of brass about a quarter of an inch thick, which gives weight sufficient to se- cure stability of move- ment. The whole rests on a small spindle 4 or 5 inches long, screwed into the centre of the brass stud, which is the fulcrum of the lever, and can be removed at pleasure to pack away. The pointed lower end of the spindle is stepped into a counter-sunk metal rest, and with a collar placed at a suitable distance above to allow of free movement of the hand, I find that a steady motion can be obtained with the thumb and finger, of any re- quired velocity, and is under greater control than with any milled-head device. " Mr. Kinne suggests a very simple method of constructing a home-made table on this plan: " The spindle can be fitted into any appliance, primitive or expensive, at the option of the worker, and I find that an old cigar -box, with a portion of one end removed, is just as useful as anything else, though if made for sale, a cheap varnished box could be furnished, and in which the table and spindle could be packed when desired. If fitted up with the cast iron stand, the whole might present a neater appearance, but the additional expense would not add to its utility." Slides which have been imperfectly centered on other tables, are recentered for varnishing by the use of two rectangular tri- angles and a little wedge. The inventor uses the corners of a broken slide and a piece of match. 214 SELECTION AND USE The other self-centering turn-table was invented by Mr. C. F. Cox, of New York, and is shown in Fig. 66. The slide is Fig. 66. COX THEN- TABLE. grasped by two angle-pieces, which are simultaneously moved to and from the centre by means of a right and left hand screw. When it is desired to re-varnish slides which have not been accurately centered in the first place, a pair of spring clips, attached to a stout bar, are fastened on. This can be effected in an instant. The arrangement is shown in Fig. 67, Fig. 67. COX TURN-TABLE. There is also a very ingenious device for placing a row of small cells along the middle of a slide. This consists of two equal right-angled triangles, the square corners of which fit into OF THE mCKOSCOPE. 215 the clutches, thus allowing the long sides to lie parallel to each other, and at equal distances from the centre. A slide may thus be grasped between them, and pushed along longitudin- ally, as may be desired. 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 revolve 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. Fig. 68. 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. 68; 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 216 SELECTION AND USE slide by nand, 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 a*d- justed 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. OP THE MICftOSCOPE. 217 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. .. 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 FOK 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. 69. Fig. fi9. 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, 218 SELECTION AND USE show best against a dark ground, while others are most easily seen against a light one. Those who 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 being 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 t be balsam is burned on them, as recommended by some, it leaves a crust which is not easily removed. COVER FORCEPS. 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. 70, 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 the forceps in the slightest de- gree, it may be pre- vented from moving when the forceps are removed by in- Fig. 71. sorting a common pin in the slit seen in Fig. 71. When using the forceps shown in Fig. 70, 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. Fig. 70. 219 SUDE HOUXER. 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 c 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 t limbs of the forceps part of the g 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. 72 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 clothes-pin, so as to prevent tipping 220 SELECTION AND USE 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 the joints (cover and all, of course,) tightly soldered. A small tube, closed with a cork, serves to admit the water. SPRING CUPS. One of the first of the needs which impress themselves upon the mind of the beginner, is the necessity foi 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. 73, and which we have used for Fig. 73. 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 OF THE MICKOSCOPE. % 221 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 VABNISHES. 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 222 SELECTION AND TJSE be laid orer an old one, the old layer will be softened, and if there should be any tendency to a vacuum in the cell, 4w softened cement will be unable to resist the outside Fig. 74. 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 ijnmersed 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 them. 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, though 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 wouli be OF THE M1CEOSCOPE. 227 very laborious to get the air out of this by means of the air pump, while by soaking successively in water, alcohol, and tur- pentine, it can be mounted with great ease without a bubble. Let us now take the c^se 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 which 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 ceissnt 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 I 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 recom- 228 SELECTION AND USE 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. In most cases it will be found unnecessary to cover the cells 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 Fig. 75. It consists of a metallic cell, having a broad flange like the rim of a hat, which is cemented to an ordinary Fig. 75. 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. Some persons object to any slide that is mounted without a glass cover. It must be acknowledged, however, that while glass covers add to the appearance of the object and serve to protect it, they interfere somewhat with its examination, as it cannot be so brilliantly illuminated, and the rays in their passage OS* THE MICROSCOPE. 229 to the objective are interfered with to a considerable extent. The objections to mounting opaque objects in cells with mov- able covers are that even during the short period in which they are exposed for examination they are liable to be contaminated with dust, the cover is liable to be lost, and the object when exposed is liable to mechanical injury. Therefore, while a few brilliant and striking objects, such as minerals, seeds, etc., may well be mounted in open cells, all delicate and valuable objects should be permanently covered. Of late years the most popular cell for opaque objects is un- doubtedly that devised by Prof. Hamilton L. Smith, and known as the wax cell. Various methods of making it are in use, the following being that originally published by the inventor: Take a circular disc of thin sheet wax, which is easily cut with a common gun punch from the sheet wax ordinarily used for making flowers, and attach it by means of heat to the cen- tre of a glass slide. A brass curtain ring, of which the inte- rior is the same size as the disc, is then slightly warmed and laid on the wax, to which it, of course, adheres. 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 thereto with a little cement, and the whole may then be finished off on the turn-table. The appearance of objects mounted in this way is very ele- gant, and consequently it has become a general favorite. It has, however, recently been condemned in most unsparing terms by the inventor, who has found that the under surface of the cover becomes in time coated with a deposit which causes a glare that entirely prevents clear vision. As soon as this difficulty was announced, an animated correspondence took place in the scientific journals, and it was found that while some microscopists had experienced this difficulty, it had never occurred to others. The final conclusion seems to be that the difficulty arises from the kind of wax used, and the method of attaching the object to it. The wax should have been thoroughly melted at a temperature as high as it will bear, so as to drive off all volatile matter, and instead of using discs punched from sheets, the wax should be applied in a 230 SELECTION AND tfSE melted condition, by means of a brush, to the warm glass slide. The object should not be stuck on with turpentine or similar cement, but should be attached to the wax after a small spot on the latter has been softened by bringing near it a hot wire. Objects mounted in this way, in cells so prepai'ed, seem to re- main in good condition for years. A very ingenious cell has been devised by Mr. D. B. Scott. This cell is punched out of thin sheet metal, as shown in plan and section in figures 76 and 77. The cell is formed by the Fig. 77. METAL SLIDE AND CELL FOR OPAQUE OBJECTS. central depression, and there is a turned-down edge all round the slide which gives it strength, and causes it to lie steadily on any flat surface. The cell has a ledge, or rebate, as seen in figure 77, for the purpose of supporting the thin glass cover. When made of tin the whole slide is japanned; those made of brass are lacquered, and the interior of the cell is covered with black asphalt, or some similar dark varnish. The objects are attached to the surface of the varnish by means of gum water, to which a very little glycerine has been added, and the thin glass cover may be cemented down and varnished on the turn- table in the usual manner. Fig. 78. CELL FOR OPAQUE OBJECTS. The alleged failure of the wax cell gave rise to a great many devices, one of which, proposed by Mr. Atwood, consists of a vulcanite or hard rubber cell, of which a sectional view is given in figure 78, the dotted lines showing the thin glass OF THE MICBOSCOPE. 231 cover. The base is solid, thus giving a black back-ground of rubber; around the top is a ledge fitted to receive a one-half inch cover glass; this being secured by a trifle of shellac or any similar cement, completes the mounting. The cell may be attached to a glass slip by any cement, before or after preparation. For exchanges it offers superior advantages, in- asmuch as the cell, with objects enclosed, may be sent through the mails independent of the glass slips, the recipient attach- ing them. Cells similar in construction to the hard rubber cell may be moulded out of melted shellac by any one who is possessed of a proper die or mould. The die is easily turned out of a piece of brass, and with two or three moulds of different sizes, and a little shellac colored black, the microscopist may easily and cheaply provide himself with a supply of cells suitable for almost any object. The idea is due to Dr. Dayton, of Cleve- land, and the details of the process may be found in the Ameri- can Journal of Microscopy for June, 1881. 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 cement it is easy to make as many cells as may be wanted, by laying on a ring with a brush while the glass slide revolves on the turn-table. As soon as the rings or cells are made, dust finely-powdered litharge over them until they are covered a sixteenth of an inch deep; allow them to stand a few minutes, and then shake off 1 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, level, 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. Any turn-table with stout spring clips will hold a slide with sufficient firmness to allow of such soft material being turned quite true and smooth. Of course the tables which grasp the slides by the corner are best for this purpose. Such cells, after 232 SELECTIOK ASTD USE 7 a few weeks, become very hard, and may be finished so as to be very neat. When covered with a few coats of shellac var- nish or pure gold size, and completely dried, they hold liquids very well. They adhere so firmly to the slide that on several occasions when the slide has been broken by a fall, the cell has not parted from the glass. The only objection which we find to them is the length of time which it takes them to harden. Tin foil, which may be had of various thicknesses from that of thin paper to a sixteenth of an inch, makes a capital mate- rial for cells. It is difficult to get the inner and outer circles which form the ring, concentric, except by the use of special tools. Prof. Chester avoids this difficulty by placing a large number of rings on a rod or mandril which just fits the open- ing, and after screwing the rings tightly endwise, he turns off the outside so as to leave it perfectly true and even. Mr. A. Y. Moore cements the sheet of tin foil to the slide by means of shellac, and cuts out the ring on the turn-table by means of a sharp knife or chisel. Finishing tlie Slides. The appearance of a collection of slides depends very much upon the style in which they are finished, and although in some instances it may be said that the finish does not affect the intrinsic value of the object, it is generally the case that a well-finished slide is more durable than one that has not been properly completed. The old sys- tem of covering the slides with paper is now entirely obsolete, and properly so. It was troublesome, unsightly, unless in pro- fessional hands, and not very durable. Fortunately slides with ground and polished edges are now so cheap that there is no occasion to resort to the paper cover. Objects mounted on these slides, whether in cells or otherwise, are in general cov- ered with round covers, which are adjusted on the turn-table so as to be perfectly central. After the mount has been com- pleted so far as fastening down the cover is concerned, the edge of the latter is finished with a neat coat of varnish. 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 caae of Canada balsam it is of use, for if gold size be used as the var- OF THE MICROSCOPE. 233 nish, 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 turn-table, and a neat ring of varnish, either plain or colored, is run around the edge. The varnish used for this purpose should be selected according to the material in which the object is mounted. Thus, for ob- jects in glycerine, glycerine jelly, or gum, the best coating is shellac varnish, which may be left quite transparent and colored with some of the aniline colors. Shellac also answers on Canada balsam, when the latter has become hard, but gold size is better, and the gold size may either be colored with the ordinary artists' colors, which are sold in -tubes, and which give an opaque-colored ring, or transparent colors may be used. Labeling tlie Slides. The proper labeling of slides and material is a most important matter. All bottles should be labeled, not only on the bottles themselves, but on the corks or stoppers, and the slides should be kept labeled or numbered during every stage of their progress. Our system is as follows : Before the object is mounted the slide is labeled on the under side with a very thin gummed label. Numbering with the writing diamond is deferred until the mount is completed, be- cause, if spoilt, the whole may be thrown into a jar to be soaked off, and this cannot be done with figures written or scratched in with a diamond. As soon as the slide is finished the regular label is attached, and the slide numbered with a writing dia- mond. 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 provided; 234 SELECTION AND USE and unfortunately it sometimes happens that labels drop off either from exposure to moisture or excessive dryness. 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. The only suggestion that we would make is that severe simplicity be adopted as the rule. Complicated and fancy labels look well at fii'st, but they soon pall, and we get tired of them. It is well to have a large blank label at one end, on which memoranda may be written, such as the power best adapted to show the object; whether it is best seen by reflected, transmitted, or polarized light; the location of interesting points as determined by the Maltwood Finder, etc., etc. An important point also is the direction in which the reading should run whether across or lengthwise of the slide. There seems to be no rule on this point, and it would be well for our societies to discuss this subject, and establish a rule for the benefit of exchangers. Nothing is more aggravating than a lot of slides labeled in different ways. The direction will de- pend, of course, upon the kind of cabinet used. For cabinets with racks, either way will answer, though the lengthwise direc- tion is somewhat the most convenient. For the old style Eng- lish cabinet, in which the objects lie flat and endwise to the front of the drawers, the writing should run across the slide. For our American cabinets with drawers having spaces divided off for each slide, the writing should be lengthwise of the slide. In short, when the slide lies in its proper position in the drawer, the lines of writing should run parallel with the front edge of the drawer. Cabinets. The value, either for work or for exhibition, of a collection of microscopic objects, is greatly enhanced when they are properly arranged and easily accessible. Conse- quently every microscopist who possesses even a small number of slides, should provide some kind of a case or cabinet for keeping them. The simplest form of case is one with racks, and these are made in a great variety of styles, forms, and sizes, from the simple mailing box, holding two or three slides, to large and expensive cabinets. The common box, with a hinged lid, and OF THE MICKOSCOPE. 235 holding twenty -five objects, answers well for carrying a few objects to exhibitions and the like. The chief objections to this style of cabinet consist in the difficulty of lifting out any particular slide and of reading the names. The latter difficulty may be obviated by writing the names on the bottom of the box on a line with the slide; the first objection may be miti- gated by placing the spaces in the rack as far apart as possible. These rack boxes make altogether the cheapest cases, and when placed in cabinets holding, say, a dozen boxes, or three hun- dred slides, they form a very economical and convenient ar- rangement. The cabinet, or outer case, should, of course, be so made that the boxes will stand on end, as in this way the slides lie flat a most important point. Cases or cabinets of shallow drawers in which the slides lie flat, with the labels fully exposed to view, are, however, alto- gether the best. They have been made of various forms. A cheap, simple case, holding about six dozen slides, may be had, in which the drawers do not slide in grooves, but lie one above the other. The only objection to this plan lies in the fact that all the drawers must be taken out if we wish to get at the lowest one; but where there are not more than a dozen drawers this is not a very serious difficulty, and the compactness, lightness and cheapness of the arrangement make it quite a favorite. In the English cabinets the slides lie with their ends towards the front of the drawer, so that the motion of pulling the drawer out or pushing it in, does not cause the slides to slip over each other. This is a very excellent arrangement, and one which we like better than any other. In the American cabinets as hitherto made, the slides lie with the long edges towards the front of the drawers, and are prevented from slipping over each other by small partitions which divide the rows into spaces one inch each in width. This is, theoretically, the most perfect arrangement, but it requires a little more room than the other. The American cabinets have, however, one feature which is a most important one: The spaces in which the slides rest have a depression under the ends of the slides, and by pressing on the end, the slide is lifted so that it is very easily grasped. In the English cabinets this feature is wanting, and it is only with great trouble that a tightly-fitting slide can b SELECTION AND USE taken from its place. Fortunately, any drawer which is deep enough, may have this device applied to it by simply glueing a thin strip of wood or pasteboard on the bottom of the drawer so as to raise up the part on which the slides rest, but leaving a space of about three-quarters of an inch under the end of the slide, into which the latter may be tipped. Tiie Maltwood Finder. This is a most important ac- cessory to every microscope, as it not only facilitates inter- change of notes between microscopists living at a distance from each other, but it enables observers to make an accurate record of the position of any object, and thus make sure of its identity when under ex- amination at different times. MALT WOOD'S 'V :: V ::: S ;: FINDER III *-<* STOP. Fig. 79. It consists of a glass slip, a lit- tle wider than an ordinary slide, upon which is a photograph occupying a space 1 by 1 inch, as shown in figure 79. This space is divided into 2,500 squares (50 divisions on each side) and each of these small squares contains two numbers, one of which indicates its position from bottom to top, while the other marks its position from right to left. Thus the square which lies on the tenth line from the bottom, and the fifteenth from the right-hand side, would be j. The method of using the Finder is as follows: Placing on the stage an object mounted on an ordinary slide, with its lower edge against a ledge of some kind, and its left-hand edge against a stop (the stop and ledge both being movable as regards the stage), we bring some particular spot into view. Bernoving the slide, we now place the finder in its place, and read off the two numbers. It is now evident that if at any future time we should place the finder against the movable ledge and stop, and bring the same numbers into view, then on removing the finder and placing the slide on the stage and against the ledge and stop, which, of course, must occupy the same position that they did when the finder was in place, the precise spot origin- ally under examination will be in view. We can therefore OF THE MICROSCOPE. 237 easily register the location of any object of interest, and so be certain of finding it at any future time. The mechanical stage, or the ordinary movable glass stage, described at page 110, or that shown in Fig. 24 (page 111) af- fords special facilities for using the Maltwood Finder. But un- less fitted with some special contrivance, microscopes which have only the ordinary clips, are unsxiitable for this purpose. A movable ledge and stop, which may be used with the common spring clips, is, however, easily devised with a little projection on the edge near one end. The wooden slide must be thicker than the glass slide which carries the 6*bject to be registered, as it is necessary that the springs should hold the wooden slide firmly in place, while the object-slide moves freely below the springs. A piece of vulcanite or hard rubber about the eighth of an inch, thick and the size of the usual 3x1 glass slide answers admirably. It should have a stop fastened to one end, as shown in figure 80, where a is the hard rubber slide, and b is a small piece of brass, let into the end and screwed fast. Microscopical Misinterpretations. The observer who iises the compound microscope labors under certain dis- advantages which do not affect those who examine large ob- jects which can be handled, and thus subjected to the scrutiny of several senses. The fallacies to which the microscopist is liable in this way deserve special attention and special precau- tions. We have already (page 198) alluded to certain fallacies of another kind, which must be avoided by such careful and extensive study as will enable us to recognize foreign matter when we see it; the fallacies now under consideration can only be avoided by careful study of the laws of optics, and by intro- ducing considerable variety of methods into our examinations. One of these sources of fallacy arises from the liability which most persons have to see objects pseudoscopically, as it is called that is to say, hollows appear to be elevations, and elevations appear to be hollows. The extent to which this tendency ex- ists is not generally recognized. Taking a gold coin, on which the letters, etc., were known to be raised, we placed it under the microscope, and submitted it to seven intelligent persons. Out of these, five declared that they saw the letters sunk into 238 SELECTION AND TJSE OF THE MICROSCOPE. the metal; two said they Avere raised. In objects too small to be felt, and where sections cannot be made, the truth may be ascertained by watching the effect of raising or lowering the object glass in focussing. Another fallacy of this kind has led to the belief that hairs and many similar bodies are hollow. Seen under the micro- scope, a hair looks just as if it were a tube but then, so does a wire, which is known to be solid. The test in thjs case is to make a cross section of the object. The true form of objects may frequently be determined by studying the effect of light and shade produced by sending the light across them in different directions. This is most readily effected by means of the revolving stage, which, for this purpose, should have very accurate rotation in the optic axis. The most singular fallacies, however, are those arising from certain illusions of vision, which affect every one, and which in ordinary practice, are easily corrected. For a full account of these, the reader is referred to the works of Helmholtz; a brief account of the most common cases is given in the Young Scientist for 1881. The one which is of most interest to microscopists is the famous optical illusion of Nachet, of which a figure is given below. In the course of his examination of the markings on the Pig. 81. XATCHET'B OPTICAL ILLUSION. P. Angtdatum, M. Nachet found that if a series of round black dots be arranged on a white ground, as in Fig. 81, the dots, when viewed from a distance of twelve to twenty inches, will appear to be hexagonal, though we know that they are round. Plato I. ROSS MODEL. As made by Ross & Cc Plate II. JACKSON MODEL. As made by Bausch & Lomb Optical Company. Plate III. NEW BIOLOGICAL STAND. As made by W, H. Bulloch, Plate IV. THE HISTOLOGICAL MICROSCOPE. As made by Joseph Zentmayer. Plate V. THE INVESTIGATOR MICROSCOPE. As made by Bausch & Lomb Optical Company. Plate VI. THE ACME BINOCULAR MICROSCOPE. As made by J. W. Sidle & Co. CATALOGUE OP Books and Periodicals PUBLISHED AND FOR SALE BY THE INDUSTRIAL PUBLICATION COMPANY, 14 Dey Street, New York. 3&~Any of these Books may be obtained from any BookseUer or Newsdealer, or will be sent Free by mail to any part of the United States or Canada ONEECEIPT OF PRICK The Amateur's Handbook of Practical Information, For the Workshop and the 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, etc. ; and for Solder* ing, Brazing, Lacquering, Bronzing, Staining and Polishing Wood, Tempering Tools, Cutting and Working Glass, Varnishing, Silvering, Gilding, Preparing Skins, etc., etc. The New Edition contains extended directions for preparing Polish- ing Powders, Freezing Mixtures, Colored Lights for tableaux, Solu- tions for rendering ladies' dresses incombustible, etc. There has also been added a very large number of new and valuable receipts. Rhymes of Science: Wise and Otherwise. By O. W. Holmes, Bret Hart, Ingoldsby, Prof. Fortoes, Prof. J. W. McQ. Rankine, Hon. R. W. Baymond, and others. With Illustrations. Cloth, Gilt Title. - 50 cents Section Cutting. A Practical Guide to the Preparation and Mounting 01 Sections for the Microscope ; Special Prominence being t^iven to the Subject of Animal Sections. By Sylvester Marsh. Beprinted 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 direc- tions, illustrated with engravings, for selecting and sharpening knives and razors. A Book for Beginners with the Microscope. Being an abridgment of " Practical Hints on the Selection and Use of the Microscope." ByJohnPhia. Fully illus- trated, and neatly and strongly bound in boards. 30 cts. This book was prepared for the use of those who, having no know- ledge of the use of the microscope, or, indeed, of any scientific appar- atus, desire simple and practical instruction in the best methods o! managing the instrument and preparing objects. How to Use the Microscope. " Practical Hints on the Selection and Use of the Micro- scrope." Intended for Beginners. By John Phin, Editor of the "American Journal of Microscopy." Fourth Edition. Greatly enlarged, with over 80 engrav- ings in the text, and 6 full-page engravings, printed on heavy tint paper. 12mo., cloth, gilt title, - $1.00 The Microscope. By Andrew Boss. Fully Illustrated. 12mo., Cloth, Gilt Title. 75 cents. This is the celebrated article contributed by Andrew Boss to the "Penny Cyclopaedia," and quoted so frequently by writers on the Microscope. Carpenter and Hogg, in the last editions of their works on the Microscope, and Brooke, in his treatise on Natural Philoso- phy, 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 simple language, free from abstruse technicalities. The Microscopist's Annual for 1873. Contains List of all the Microscopical Societies In the country, with names of officers, days of meeting, etc. ; etc. ; Alphabetical and Classified Lists of all the Manu- facturers of Microscopes and Objectives, Dissecting Ap- paratus, Microscopic Objects, Materials for Microscopists, in Europe and America, etc., etc. ; Postal Hates, Eules and Regulations, prepared expressly for microscopists ; Weights and Measures, with tables and rules for the con- version of different measures into each other; Custom Duties and Eegulations in regard to Instruments and Books ; Value of the Moneys of all Countries in U. S. 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, etc., etc. ; Focal Value of the Objectives of those makers who Number their Objectives (Hartnack, Nachet, etc.) ; Focal Value of the Eye-pieces of different makers ; Magnifying Power of Eye-pieces and Objectives, etc., etc. The whole form- ing an indispensable companion for every working micro- scopist. Limp Cloth, Gilt - - 25 cents, J83- The " Annual " for 1880 is in a forward state of preparation, and will be uniform in size and price with that for 1879. Microscope Objectives. The Angulai Aperture of Microscope Objectives. By Dr. George E. Blackham. 8vo., Cloth. Eighteen full page illustrations printed on extra fine paper. $1.25. Sold only by Subscription. This is the elaborate paper on Angular Aperture, read by Dr. Blackham before the Microscopical Congress, held at Indianapolis. Kutzing on Diatoms. Nearly ready. 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The splendid full-page engravings, printed on tinted paper, in the highest style of the art, are univei sally conceded to be the finest architectural and mechanical engravings ever published in this country. "We have on hand a few complete sets, which we offer for $16.00, handsomely and uniformly bound in cloth. We have also a few extra sets of Vols. IE to VHI Inclusive. Thess? six volumes we offer for $8.00 bound in cloth. As there are but a very few sets remaining, those who desire to secure them sheuld order -inimediatelj NOTE. The above prices do not include postage or express charges 'Ihe set weighs altogether too much to be sent by mail. Shooting on the Wing. Plain Directions for Acquiring the Art of Shooting on the "Wing. "With Useful Hints concerning all that relates to Guns and Shooting, and particularly in regard to the art of Loading so as to Kill. To which has been added several Valuable and hitherto Secret Eecipes, of Great Practical Importance to the Sportsman. 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Also, its application in obtaining the Bevels and Cuts for Hoppers, Spring Mouldings, Octagons, Stairs, Diminished Stiles, etc., etc., etc. Illustrated by Over Fifty Wood-cuts. By Fred. T. Hodgson, Editor of the " Builder and Woodworker." Cloth, Gilt, - - 75 cents. Mechanical Draughting. The Students' Illustrated Guide to Practical Draughting. A Series of Practical Instructions for Machinists, Me- chanics, Apprentices, and Students at Engineering Establishments and Technical Institutes. By T. P. Pemberton, Draughtsman and Mechanical Engineer. Illustrated with Numerous Engravings. Cloth, Gilt, - - $1.00 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 direc- tion of a teacher. Map of the Moon. This is a copy of Webb's reduction of Baer & Maedler's .' celebrated Map of the Moon. 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Full of interesting facts, stated in simple and forcible language. PHYSIOLOGY. By F. le Gros Clarke, F.R.S., St. Thomas's Hospital The object of this elementary treatise is to teach some of the simple truths of Human Physiology, such as may be intelligible without any extended knowledge of other branches of science. But it is hoped, by the avoidance of technical terms, when possible, and their definition when essential, and also by a familiar explanation of any natural law which may be referred to, that there will be no material difficulty in under- standing the simple principles and details which will be taught in these pages. Aether's Introduction. FOURTH EDITION. Greatly Enlarged, -with over 80 illustrations in ike Text and (s full page Engravings, printed on Heavy Tint Paper, i Vol. izmo., 240 Pages. Neatly Bound in Cloth, Gilt Title. Price $1.00. HOW TO USE THE MICROSCOPE. A SIMPLE AND PRACTICAL BOOK, INTENDED FOR BEGINNERS. BY JOHN PHIN, Editor of " The American Journal of Microscopy." CONDENSED TABLE OF CONTENTS. THE MICROSCOPE. What it Is ; What it Does; Different Kinds of Microscopes; Principles of its Construct on; Names of the Different Parts. SIMPLE MICROSCOPES. Hand Magnifiers; Doublets; Power of Two or More Lenses When Used Together; Stanhope Lens; Coddington Lens; Achromatic Doublets and Triplets ; Twenty-five Cent M icroscopes and How to Make Them; Penny Microscopes, to Show Eels in Paste and Vinegar. DISSECTING MICROSCOPES. Essentials of a Good Dissecting Microscope. COMPOUND MICROSCOPES. Cheap Foreign Stands; The Ross Model; The Jackson Model; The Continental Model; The New American Model; Cheap American Stands; The Binocular Microscope; The Binocular Eye-piece; The Inverted Micro- scope; Lithological Microscopes; The Aquarium Microscope; Microscopes for Special Purpo>es; "Class" Microscopes. OBJECTIVES. Defects of Common Lenses; Spherical Aberration; Chromatic do. ; Corrected Objectives; Denning Power ; Achromatism; Aberration of Form ; Flatness of Field; Angular Aperture; Penetrating Power : Working Distance; Immersion and "Homogeneous" Lenses; Duplex Fronts; French Triplets, etc., etc. TESTING OBJECTIVES. General Rules; Accepted Standards Diatoms, Ruled Lines, Artificial Star; Podura; Nobert's Lines; Moller's Probe Platte, etc., etc. SELECTION OF A MICROSCOPE Must be Adapted to Requirements and Skill of User; Microscopes for Botany; For Physicians; For Students. ACCESSORY APPARATUS. Stage Forceps; Forceps Carrier; Plain Slides; Concave Slides ; Watch-Glass Holder; Animalcule Cage; Zoophyte Trough ; The Weber Slide ; The Cell-Trough; The Compressorium ; Gravity Compressonum; Growing Slides; Frog Plate; Table; Double Nose-piece. ILLUMINATION. Sun- Light; Artificial Light Candles, Gas, Lamps, etc., etc. ILLUMINATION OF OPAQUE OBJECTS. Bulls- Eye Condenser; Side Reflector; The Lieberkuhn; The Parabolic Reflector; Vertical Illuminators. ILLUMINATION OF TRANSPARENT OBJECTS. Direct and Reflected Light; Axial or Central Ligh ; Oblique Light ; The Achromatic Condenser; The Webster Condenser, and How to Use it; Wenham's Reflex Illuminator, and How to Use it; The Wenham Prism; The "Half-Button;" The Woodward Illuminator; Tolles' Illuminating Traverse Lens; The Spot Lens; The Parabolic Illuminator; Polarized Light. How TO USE THE MICROSCOPE. General Rules; Hints to Beginners. How TO USE OBJECTIVES OF LARGE APERTURE. Collar-Correction, etc. CARE OF THE MICROSCOPE. Should be Kept Covered; Care of Objectives: Pre- cautions to be Used when Corrosive Vapors and Liquids are Employed ; To Protect the Objectives from Vapors which Corrode Glass ; Cleaning the Objectives; Cleaning th Brass Work. COLLECTING OBJECTS. Where to Find Objects ; What to Look for; How to Capture Them. THE PREPARATION AND EXAMINATION OF OBJECTS. Cutting Thin Sections of Soft Substances ; Valentine's Knife ; Sections of Wood and Bone; Improved Section Cutter; Sections of Rock; 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; Refractive Powers of Different Liquids ; lod-Serum; Artificial lod-Serum; Covers for Keeping Out Dust; Errors in Microscopic Observations. PRESERVATIVE PROCESSES. General Principles; Preservative Media. APPARATUS FOR MOUNTING OBJECTS. Slides; Covers; Cells; Turn-Tables, etc. CEMENTS AND VARNISHES. General Rules for Using. MOUNTING OBJECTS. Mounting Transparent Objects Dry; m Balsam ; in Liquids; Whole Insects; How to Get Rid of Air-Bubbles ; Mounting Opaque Objects. FINISHING THB SLIDES. Cabinets ; Maltwood Finder ; Microscopical Fallacies. - THE WORKSHOP COMPANION. A Collection of* Useful and Reliable Recipes, Rules, Processes, HolSiod*. Wrinkles, and Practical Hints, FOR THE HOUSEHOLD MJTD THE SHOP. CONTENTS. Abyssinian Gold: Accidents, General Rules; -Alabaster, how to work, polish and clean; Alcohol; Alloys, rules fqt making, and r6 recipes; Amber, how to work, polish and mend; Annealing arm Hardening ghss, copper, steel, etc.; Arsenical Soap; Arsenical Powder; Beeswax, how to bleach; Blackboards, how to make; Brass, how to work, polish, color, varnish, whiten, deposit by electricity, clean, etc., etc. ; Brazing and Soldering; Bronzing brass, wood, leather, etc.; Burns, how to cure; Case-hardening; Catgut, how prepared ; Cements, general rules for using, and 56 recipes for preparing; Copper, working, welding, depositing; Coral, artificial; Cork, working; Crayons for Blackboards; Curling brass, iron, etc.; Liquid Cu- ticle; Etching copper, steel, glass: Eye, accidents to;--Fires, to prevent; Clothes on Fire; Fireproof Dresses; Fly Papers; Freezing Mixtures, 6 recipes; Fumigating Pastils; Gilding metal, leather, wood, etc.; Glass, cutting, drilling, turning in the lathe, fitting stoppers, removing tight stoppers, powdering, packing, imitating ground glass, washing glass vessels, etc. ; Grass, Dry, to stain ; Guns, to make shoot close, to keep from rusting, to brown the barrels of, etc., etc.; Handles, to fasten ; Inks, rules for selecting and preserving, and 54 recipes for; Ink Eraser; Inlaying; Iron, forging, welding, case-hardening, zincing, tinning, do. in the cold, brightening, etc., etc. ; Ivory, to work, polish, bleach, etc. ; Javelle Water ; -Jewelry and Gilded Ware, care of, cleaning, coloring, etc. ; Lacquer, how to make and apply ; Laundry Gloss ; Skeleton Leaves; Lights, signal and colored, also for tableaux, photography, etc., 25 recipes ; Lubricators, selection of, 4 recipes for ; Marble, working, polishing, clean- ing; Metals, polishing; Mirrors, care of, to make, pure silver, etc., etc.; Nickel, to plate with without a battery; Noise, prevention of; Pairting Bright Mefals; Paper, adhesive, barometer, glass, tracing, transfer, waxed, etc. ;-^Paper, to clean, take creases out of, remove water stains, mount drawing paper, to prepare for varnishing, etc., etc. ; Patina; Patterns, to trace; Pencils, indelible; Percil Marks, to fix; Pewter; Pillows for Sick Room, cheap and good ; Plaster-of- Paris, how to work; Poisons, antidotes for, 12 recipes; Polishing Powders, preparation and use of (six pages); Resins, their properties, etc.; Saws, how to sharpen;- -Sieves; Shellac, properties and uses of; Silver, properties of, oxidized, old, cleaning, to remove ink stains from, to dissolve from plated goods, etc., etc. ; Silvering metals, leather, iron, etc. ; Size, preparation of various kinds of; Skins, tanning and curing, do with hail on; Stains, to remove from all kinds of goods; Steel, tempering ani,V working (six pages); Tin, properties, method's of working; Varnish, 21 recipes for; ^Varnishipg, directions for; Voltaic Batteries; Watch, care of; Waterproofing, 7 recipes for; Whitewash; Wood Floors, waxing, staining, and polishing; Wood, polisHtg. ~> Wood, staining, 17 recipes; Zinc, to pulverize, black varnish for. 164 closely-printed pages, neatly bound. Sent bv mail for 36 oenvfl (postage stamps received). Specimen pages free. INDUSTRIAL PUBLICATION COMPANY, 14 Dey Street, New York. SCIENTIFIC LIBEAEY FOR TOUNG PEOPLE. C.EOLOGY. By the Rev. T. G. Bonney, M.A., F.G.S., Fellow and late Tutor of St. John's College, Cambridge. In the following pages I have attempted to set down briefly the principal facts of Geology, and the conclusions which have been drawn from them ; to indicate the nature of the earth's crust, the processes which have acted and are still acting upon it, and the probable history of that little portion of it on which we live. I was requested, before commencing my task, to avoid the use of long words and the discussion of doubtful points, and have done my best to attend to this request. Author's Preface. CRYSTALLOGRAPHY. By Henry Palin Gurney, M.A., Clare College, Cambridge. Crys allography has been hitherto strangely neglected in this country as a branch of education. Its great importance to the chemist, the physicist, and the geologist cannot be questioned, and it is full of interest for all. No study is better calculated to sharpen at once the observing and the reasoning faculties of youth. There is nothing repulsive in crystals. Their beauty is often more attractive, as it is more enduring, than that of the fairest flowers. Their symmetry illustrates the rhythm and the harmony that pervade the universe. They have already suggested the most important law of modern chemistry. They tell us more about the properties of atoms than any other form of substance. Author's Prefaci. SPECTROSCOPE, THE WORK OF THE. By Richard A. Proctor, Esq. I have endeavored to make this little treatise on the Spectroscopic Analysis clear and simple for beginners, but at the same time accurate, and as complete as possible within so limited a space. * * * I have endeavored to give a full account of all the prin- ciples on which the application of spectroscopy depends, and also of all the chief methods of observation and their results. Autlwr's Preface. ELECTRICITY. By Fleeming Jenkins, F.R.S., Professor of Engineering in the University of Edin- burgh. Gives the most recent views of scientific men, and an account of the latest dis- coveries and the principles upon which they are founded such as the telephone, microphone, photophone, etc. Jg^'These ten volumes ftrm the most complete popular Scientific Library now accessible to the student. If the ten volumes are ordered at one time they will be sent free to any part of the country for $3.50. INDUSTRIAL PUBLICATION COMPANY, 14 I>ey Street, New York. Hand-Book of Urinary Analysis, f 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 University of New York; Member of the N. Y. County Medical Society; Member of the New York Microscopical Society, etc. Illustrated, Limp Cloth, Gilt, 25 eta. 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 bed-side 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 busy practitioner. Free by Mail on receipt of price. JUST PUBLISHED. HOW TO SEE WITH THE MICROSCOPE. Being Useful Hints Connected with the Selection and Use of the Instrument; also Some Discussion of the Claims and Capacity of Modern High-Angled Objectives, as Compared with those of Medium Aperture. With Instructions as to the Selection and Use of American Object-Glasses of Wide Apertures. By J. EDWARDS SMITH, M. D. Professor of Histology and Microscopy; Corresponding Member San Francisco, Dunkirk, and other Microscopical Societies, etc., etc, Handsomely Illustrated. Prof. Smith is well known as the most expert manipulator in this country, as regards objectives of wide aperture, and in this volume he gives, in a clear and practical man- ner, all the directions necessary to attain the surprising results which he has achieved. No microscopist that uses anything better than French triplets can afford to be without it. Price, $2,OO. Free by Mail on recent of price. Address To be completed in Six Monthly Parts. Price $T.s.oo,*payabZe in advance. PART I. IS NOW READY. A Manual of the Infusoria, Including a Description of all Known Flagellate, Ciliate, and Tentaculiferous Protozoa, British and Foreign, and an Account of the Organization and Affinities of the Sponges. By W. SAVILLE KENT, F.L.S., F.Z.S., F.R.M.S. This important work, the result of many years' careful labor and investigation on the part of the author, will, it is hoped, meet a want which has long existed among micro- scopists. It will consist of a volume ot text extending to about 800 pages super royal 8vo., and an atlas of 48 plates, containing upwards of 2,000 figures. Wishing to lend what little assistance we can to the publication of this valuable work, we have subscribed for a large number of copies, which we offer to the microscopists of the United States at the prices named above. As the book is large and very expen- sive, the publisher will issue very few copies beyond those for which subscriptions are received, and consequently the price will undoubtedly be advanced after the work has been Completed. INDUSTRIAL PUBLICATION CO., 14 Dey Street, New York, AGENTS FOR THE UNITED STATES. The Carpenter's Steel Square, AND HOW TO USE IT. OPINIONS OF THE PRESS. " This little work consists of a republication of some papers contributed by its talented author some time ago to the A merican Builder, and which were received with so much favor by artisans, for whom they were written, as to induce their author to collect them into the present volume." ******** The work is well illustrated by upwards of fifty cuts which have been well engraved, and can hardly fail to give any one an idea of the capabilities of the steel square, and what can be accomplished from it when in skilful hands. " Journal of Franklin Institute, Phila. " A most valuable little treatise of 70 pages upon that commonplace subject, the ' steel square, ' being a description of that useful tool, and its uses in obtaining the lengths and bevels of rafters, hips, groins, braces, brackets, purlins, collar beams and jack lafters, and its application in obtaining the bevels and cuU for hoppers, spring moldings, octa- gons, stairs, diminished stiles, etc., illustrated by over 50 wood cuts. Mr. Hodgson has succeeded admirably in demonstrating that the study of the value and use of the square is by no means the dry subject one would suppose, and that as a tool in the hands of an intelligent workman, its possibilities are far beyond the standard usually conceded to it. It is a valuable book for the use of the carpenter, and should be upon the office desk of every retailer of lumber, from the valuable hints it will give him as a guide to his negotiations with his customers in figuring out their wants. It is, in fact, well adapted to the wants of every man who has a shed or fence to erect upon his premises, or who wishes to keep a check upon his builder." Northwestern Lumber- man, Chicago, III. "This is a little book that no carpenter, joiner, cabinetmaker, or amateur' wood- worker, can do without, if they wish to keep up with the times in their several branches of trade. "We believe this is the first and only book that has been written on this subject alone, and we must say, that ihe duty of writing it fell into good hands, as the author has handled his subject in a masterly manner. One is struck with astonishment at the number of difficult and apparently intricate problems this simple instrument the square is made to solve, and in such a manner that any mechanic who can read the figures on the tool can work out the solutions. The lengths and bevels of rafters, hips, braces, trusses, purlins, collar beams, and jack rafters are obtained as if by magic, and without thought or calculation. "The work is handsomely gotten up, printed on heavy white paper, substantially bound, and cleanly turned out. The some fifty odd wood cuts are almost equal to steel engravings, and the whole get-up is a credit to both author and publisher, and the low price at which it is sold, (75 cents), places it within reach of every wood-worker, no matter how poor he may be." Enterprise, Collingwood, Ont. " It is a timely book on the subject in hand, and we can safely recommend it as com- petent to fill a long felt vacancy in the mechanics' library. The work presents a valu- able collection of rules and data connected with the framing square, to the solution of roofing problems, braces, hoppers, etc., etc." Orillia Packet, Ont. " Some fifty engravings aid in the description of the square and its uses in obtaining lengths and bevels of all kinds; also, its application in obtaining the bevels and cuts for all conceivable shapes used in the wood shops. Any wood-worker possessing this book will find its cost, seventy-five cents, is not to be compared with its real vaUA and usefulness in the shop." The Carriage Monthly, Phila. " The work is n very valuable one, and should be in the hands of every carpenter." Messenger, Collingwood, Ont. Tfc; work will be of very great service to carpenters and builders." Bulletin, Ont. A 'New and Live Book on the Gun. Just Published. Price 75 cents, in cloth. PLAIN DIRECTIONS FOR ACQUIRING THE ART OF SHOOTING ON THE WING. With Useful Hints concerning all that relates to Guns and Shoot- ing, and 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 GAMEKEEPER. Sent free by mail on receipt of price. Opinion* of the fret*. The directions are so plain that they cannot well be mistaken, and they are expressed in the fewest possible words. Turf, Field and Farm. Facing the title-page is one of the handsomest, best-executed woodcuts, we have ever seen. It is entitled "The Wounded Snipe," and almost equals a steel engraving. Baptist Union. From its pages we should think even the most experienced sportsman might derive some new ideas, while the beginner will find it an invaluable assistant. Country Gentleman. For concise instructions as to how to shoot, to select, load, carry, and keep a gun in order, etc., it cannot be surpassed. Western Rural. \. pleasantly written, and, it seems, to us, correct and practical treatise on the sportsman's art; a modest little book, but one from the reading of which a good deal of the right kind of knowledge is to be gained. Applelon's Journal. A practical and well-written handbook, especially adapted for tne use of young sportsmen, as it gives sensible advice on the manipulation of firearms, and the rules and etiquette of the field. Scientific American. GENESIS AND GEOLOGY. The only really scientific and logical system of harmony between Genesis and Geology is to be found in a little work, just published, and entitled THE CHEMICAL HISTORY The Six Days of Creation. BY JOHN PHIN, C. E., EDITOB OF " HANDICBAFT. " 1 vol., 12mo., cloth. 75 cents. In this work an attempt is made to show that the account given of the Creation, in the first chapter of Genesis, agrees literally with the record developed by the investigations of modern science. May be ordered through any bookseller. Single copies sent by mail, on receipt of price, The following are a few of the Opinions of the Press : Tfcis 4s a small book, bet full of matter. The author believes in the book of Genesis M the 'work of Moses, and believes in the entire correctness of the statements made by Moaeg .in regard to the work of creation. He defends the accuracy of the first chapter of Genesis, and defends it from a scientific standpoint. We think this book is full of interest and value ; and as the discussions concerning the harmony of science and v the In- dustrial Publication Co., contains EVERY THIUfG relating' to Medical Matters that appears in the original London edition. THE LANCET is the oldest and most Practical Medical Journal published in the English language, and is the national British organ of Science in its relations to the human frame. THE LANCET is edited by a corps of the most distinguished physicians of the British Metropolis, and numbers among its con- tributors, the best medical and surgical talent of Europe. THE LANCET for 1881, will contain over 1200 double-column pages of closely printed matter, exclusive of the advertising sheets. The type is clear, and printed on the very best calendered book paper. Our pages contain nearly twice as much reading matter as any other monthly medical journal published on this side of the Atlantic. Every effort will be made to continue this Work, as it ever has been, the Standard Journal of Medicine and Surgery. Illustrated with engravings by the best artists. Subscription $5.00 per year. Single Numbers 50 cts. each. Specimen Copies (our . election), 25 cents. For Club Rates, Subscriptions, Advertisements, etc,, address THE INDUSTRIAL PUBLICATION COMPANY, 14 Dey Street, New York. THE YOUNG SCIENTIST, A Practical Journal for Amateurs. ISSUED MONTHLY. Price 5O Cents per year. It is characteristic of young Americans that they want to be DOING something. They are not content with merely knowing how things are done, or even with teeing them done; they want to do them themselves. In other words, they want to experiment. Hence the wonder'"! demand that has sprung up for email tool chests, turning lathes, scroll saws, er line. As postal currency has nearly disappeared from circulation, we receive post age stamps ol the lower denominations (ones, twos and threes) at their full value. Postal orders are, however, much safer and more convenient. To avoid delay and mistakes address all communications to " THE YOUNG SCIENTIST, Box 8859, New York," and make all checks and orders payable to John Phia. WHAT PEOPLE SAY OF US. In a letter to the Editor, Oliver Wendel Holmes, the genial "Autocrat of the Breakfast Table," says: "I am much pleased with the YOUNG SCIENTIST. It makes me want to be a boy again." "It is a little publication, calculated to call out and educate all tbe latent ingenuity and thirst for knowledge which the youthful mind pos- sesses, and we hope it will win its way into every household in the land." [Scientific Press. "We have never seen a periodical, designed for youth, which came nearer to our ideal of what such a journal should be." [Canadian Phar- maceutical Journal. "The YOUNG SciENriSTis one of the choicest publications for juvenile minds in this country. Every page treats on subjects of importance to young and old, portrayed in a clearly comprehensive manner, which at once interests the young idea in its careful perusal." [Lapeer Clarion. "It seems to fill the bill." [Newport Daily News. "It is pleasing to note that its youthful subscribers will not be misled by clap-trap advertisements or advertisements of patent medicines, which will not be received at any price. The YOUNG SCIENTIST is doing good work in setting its face against this class of humbugs." [Manufacturing and Trade Review. " The work is a copiously illustrated monthly, and is full of practical hints that will instruct and amuse the young folks." [Industrial School Advocate. "A small but elegant and very instructive monthly." [Pittsburg Chronicle. " Contains the best possible reading for the young of both sexes." [Ottawa Journal. " We can safely recommend this magazine as one of the very best "nblications for the young folks." [The Independent, Fenton, Mich. 'This journal occupies a new field, and is needed to put the minds of our youth on the right track to secure a correct understanding of the nature of things." [Wayland Press. "It is ably edited by John Phin, who will make a large place in the heart of the rising generation, if he persists in his venture. We hope his success in the field will be equal to the article furnished first best." [Sunset Chimes. "The articles are written in a popular, readable style, and profusely illustrated." Akron City Times. "The YOUNG SCIENTIST is excellent in conception, and well designed to amuse and instruct young people." [Chicago Evening Journal. "The YOUNG SCIENTIST is a handsome monthly magazine, each number containing about 16 pages, handsomely illustrated. It will supply a place which has been heretofore unoccupied. The copy before us comes fully up to the promise of the prospectus." [The Times, Iroquois, Mich. "It is a journal which should be in the hands of both young and old, and is a great benefit to the young scientist as well as the advanced pro- fessor. It is a thousand times more valuable than the dime novel series, so much read by boys. Parents would do well to have it in their house- holds." [The Iron Home. "This publication is a new launch, and it i" very gratifying to witness the ableness which pervades its pages." AL Lerst Free Press. THE AMERICAN Journal of Microscopy. PROSPECTUS-SIXTH YEAB-1881 The object of the JOURNAL OF MICROSCOPY is to diffuse a knowledge of the best methods of using the Microscope; of all valuable improvements in the instrument and its accessories ; of all new methods of microscopical investigation, and of the most recen* results of microscopical research. The JOURNAL does not address itself to those who have long pursued certain special lines of research, and whose wants can be supplied only by elaborate papers, which, from their thoroughness, are entitled to be called monographs rather than mere articles. It is intended rather to meet the wants of those who use the microscope for purposes of general study, medical work, class instruction, and even amusement, and who desire, in addition to the information afforded by text-books, such a knowledge of what others are doing as can be derived only from a periodical. With this object in view, therefore, the publishers propose to make the JOURNAL so simple, practical and trustworthy, that it will prove to the advantage of every one who uses the microscope at all to take it ILLUSTRATIONS. The JOURNAL will be freely illustrated by ener.ivings representing either objects of natural history or apparatus connected with the microscope. TRANSACTIONS OF SOCIETIES. THE AMERICAN JOURNAL OF MICRO- SCOPY is not the organ of any Society, but it gives the proceedings of all Societies whose officers send us a report. As the JOURNAL is devoted wholly to Microscopy, and is in good form and size for binding, no better medium can be had for preserving the scientific records of any Society. Matters of mere business routine we are frequently obliged to omit for want of room. EXCHANGES. An important feature of the JOURNAL is the exchange column, by means of which workers indifferent parts of the country are enabled, without expense, except for postage, to exchange slides and materials with each other. Published Monthly at $1.00 a year. SPECIMENS FREE. Four copies for three dollars. Those who wish to economize in the direction of periodicals, would do well to examine our dubbing list. FOREIGN SUBSCRIBERS. The JOURNAL will be sent, postage paid, to any country in the Postal Union for $1.24, or 5 shillings sterling per year. English postage stamps, payment. In return for a ill be furnished and mailed nd postal orders payable to John Phin. te osta non or 1.24, or 5 sngs sterng per year. American currency or American postage stamps taken in pa postal order or draft for 1 55., five copies of the JOURNAL will to different addresses. Make all drafts and postal orders payab Vol. I is out of print We are occasionally able to complete volumes which, when bound, we offer for $1.50. Of Vols. II, III and IV we have a few copies on hand. Price $1.50 each. The JOURNAL OF MICROSCOPY, from its very nature, is a visitor to the very best families, and its value as an advertising medium has therefore proved to be much above that of average periodicals. A few select advertisements will be inserted at the rate of 30 cents per line, nonpariel measure, of which twelve lines make an inch. Address AMERICAN JOURNAL OF MICROSCOPY, P. O. Box 8852, New York. NEW DESIGNS FOE Fret or Scroll Sawyers, MR. F. f. HODGSON, whose admirable series of articles on the USE OF THE SCROLL SAW are now in course of publication in the YOUNG SCIENTIST, has pre- pared for us a series of SEVENTEEN DESIGNS, of which the following is a list : No. i. This shows one side, back, and bottom, of a pen rack. It may be made of ebony, walnut, or other dark wood. No. 2. Design for inlaying drawer fronts, table tops, box lids, and many other things. It is a sumach leaf pattern. No. 3. Design for a thermometer stand. It may be made of any hard wood or alabaster. The method of putting together is obvious. No. 4. This shows a design for a lamp screen. The open part may be covered with tinted silk, or other suitable material, with some appropriate device worked on with the needle, or, if preferred, ornaments may be painted on the silk, etc. No. 5. A case for containing visiting cards. Will look best made of white holly. No. 6. A placque stand, it may be made of any kind of dark or medium wood. No. 7. A design for ornaments suitable for a window cornice. It should be made of black walnut, and overlaid on some light colored hard wood. No. 8 A design for a jewel casket. This will be very pretty made of white holly and lined with blue velvet. It also looks well made of ebony lined with crimson. No. 9. Frame. Will look well made of any dark wood. No. 10. Frame. Intended to be made in pairs. Looks well made of white holly, with leaves and flowers painted on wide stile. No. 11. Horseshoe. Can be made of any kind of wood and used for a pen rack. When decorated with gold and colors, looks very handsome. No. 12. Design for a hinge strap. If made of black walnut, and planted on a white or oaken door, will look well. No. 13. Design for a napkin ring. May be made of any kind of hard wood. No. 14. Hinge strap for doors with narrow stiles. No. 15. Centre ornament for panel. No. 16. Corner ornament for panel. No. 17. Key-h ole escutcheon. t These designs we have had photo-lithographed and printed on good paper, so that the outlines are sharp, and the opposite sides of each design symmetrical. Common designs are printed from coarse wooden blocks, and are rough and unequal, so that it is often impossible to make good work from them. The series embraces over forty different pieces, and designs of equal quality cannot be had for less than five, ten or fifteen cents each. We offer them for twenty-five cents for the set, which is an average price of only one cent and a half each. Mailed to any address on receipt of price. INDUSTRIAL PUBLICATION CO., 14 De; Street, New York. SHEET NO. I. SHEET NO. 2. REDUCED FIGURES OF NEW DESIGNS FOR FRET OR SCROLL SAWYERS. SIZE OF SHEETS 28 BY 22 INCHES. (For description see preceding page.) QM 205 PS THE LIBRARY UNIVERSITY OF CALIFORNIA Santa Barbara THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW. UC SOUTHERN REGIONAL LIBRARY FACILITY 001264667 5