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 THE MODERN HIGH- ANGLED OBJECTIVES, AS COMPARED WITH THOSE OF MEDIUM APERTURE; WITH INSTRUCTIONS AS TO THE SELEC- TION AND USE OF AMERI- CAN OBJECT-GLASSES OF WIDE APER- TURES. ar J. EDWARDS SMITH, M. D., PROFESSOR OF PJSTOLOUY AND MICROSCOPY IN THE CLEVELAND (O.), HOM- EOPATHIC HOSPITAL COLLEGE; CORRESPONDING MEMBER OF THE SAX FRANCISCO, THE DUNKIRK, AND ILLINOIS. STATE MICROSCOPICAL SOCIETIES; MEMBER OF THE AMERICAN ASSOCIATION FOR THE ADVANCEMENT OF SCIENCE, ETC. ILLUSTRATED. CHICAGO : DUNCAN BROTHERS. 1880. Copyrighted by DUNCAN BROTHERS, 131 and 133 South Clark street, CHICAGO. r DEDICATION: TO THE HON. P. H. WATSON, WHOSE FRIENDSHIP HAS ENCOURAGED AND WHOSE PARTICIPATION HAS GIVEN DOUBLE PLEASURE TO THE INVESTIGATIONS RECORDED IN THESE PAGES ? THE TRUE FRIEND, AND THE LIB- ERAL PATRON OF SCIENTIFIC EXPERI- MENT, THIg LITTLE BOOK IS DEDICATED BY THE AUTHOR. PREFACE. INTRODUCTORY AND APOLOGETICAL. In the spring of 1874 I received from K. B. Tolles, Esq., (the well-known optician of Boston, Mass.,) a one-sixth immersion object glass, which he requested me to study carefully, and to report the results to him. The angular aperture of this new one-sixth was said to be 180, and the objective was one of the tirst " du- plex " or four-system glasses devised by Mr. Tolles, and destined, in a few short months, to create quite a stir in microscope circles. Having, at that date, leisure at my command, and being very much interested in the performance of ob- ject glasses, I was very glad to give this objective careful and prolonged attention. The result was, that after thirty days' experience I had arrived at a settled con- viction that Mr. Tolles had made a decided advance in the construction and performance of microscope object glasses. Believing this experience of mine to be of value to microscopists, I wrote a short account of the perform- ance of this one-sixth, which was published in the Cin- cinnati Medical News. Shortly afterwards Mr. Tolles kindly sent me another of the " duplex " or four-system objectives, this time a 10 PREFACE. one-tenth. This glass also occupied my leisure time for a considerable interval. The performance of the one-tenth fully sustained the high appreciation I had formed of the performance of the duplex glasses. In some respects the work of the one- tenth excelled that of the one-sixth. The article published in the Cincinnati Medical News was therefore supplemented by several other communi- cations written by me, giving my further experience with the duplex objectives. Among the conclusions I had arrived at from the study of the new four-system glasses were to be found em- bodied ideas radically opposed to popular dogmas which were at that date fully received and accepted by micro- scopists generally as settled matters of fact. For in- stance, it was claimed for the duplex one-sixth and one- tenth that either of these objectives would not only do the work of, but excel the performance (under amplifi- cations from 275 to 4,000 diameters) of any one-fiftieth extant. Furthermore, it was claimed that the central light work of the new wide apertured duplex objectives would surpass that of the low angles. Referring to the resolution of the severest test objects, it was the express purpose of the said contributions to the Cincinnati Medical News to claim and insist on, as a stubborn fact, that the work of the duplex one-sixth or one-tenth excelled that of any glass extant, " be it a one-fifth or a one-fiftieth." These, as well as other statements so thoroughly hete- rodox to established belief, met, as a matter of course, PREFACE. 11 with earnest opposition from my readers. A large cor- respondence ensued, while many microscopists visited me for the purpose of witnessing, by way of ocular demonstrations, the performance of the duplex glasses. Meanwhile, in London, England, a lively controversy, known in microscope circles as " the war of the aper- tures," appeared in the columns of the London Monti tly Journal of Microscopy, in which controversy the posi- tions assumed by Mr. Tolles were assailed by Mr. F. A. Wenham. The issues involved, however, appertained only to optical possibilities, the performance of the du- plex objectives being an entirely outside matter. During the London battle Mr. Tolles was ably assisted by Dr. J. J. Woodward, of Washington, D. C., and by Piof. Keith of Georgetown. Suffice it here to say, that froir the standpoint of optical science Mr. Tolles maintains his positions, a fact, I believe, now generally admitted t And now, after a period of nearly six years, it is to me a matter of pride to here record that of the several 4 ' heterodox " positions I had assumed in public print, there has occurred, neither in the interim, or at this present writing, no occasion to retract one word of what was claimed by me in my former contributions to the Cincinnati Medical News. The duplex objectives have steadily, and perforce of intrinsic worth, forced their way into general use, while the leading opticians are exerting themselves to still further improve their performance. Having, as I have above briefly set forth, had a very large experience with the four-system objectives, it was 12 PREFACE. suggested to the author that a small work, giving in detail the manipulations of the new objectives, with, perhaps, some other items resulting from an experience of over fifteen years as a microscopist, would not only be acceptable, but would fill a place at present unoccu- pied; and it is in response to this suggestion this little book is presented, with the hope that it may prove of some service to some of my brother microscopists. The book is entirely innocent of literary pretensions. It has been my aim to express myself in the simplest possible manner. The diction is at times redundant, gossipy and commonplace, the dominant idea through- out being to hold a good natured chat with my readers* During the past eight years the author has received thousands of letters asking for information in the mat- ter of microscope object glasses, and especially has his experience been called on as to methods of manipulation involved in the use of wide apertured objectives. In the following pages he has endeavored to supply this in- formation, introducing, it is believed, the first attempt to teach the difficult art of collar adjustment, as will be seen in the graduated series of lessons, which, imperfect as they are, it is hoped will nevertheless be of value to those commencing to use the four-system objectives. A.nd now, by way of apology, it remains to state that circumstances entirely unlocked for, and entirely beyond the author's control, have caused a delay in the publica- tion, and many have suffered disappointment therefrom. This delay, however, has furnished me with the oppor- tunity to revise the MS., rendering it, I trust, more PREFACE. 13 acceptable. It has also given me the opportunity to introduce new matter not originally contemplated. During the period of delay above mentioned the writer was in receipt of hundreds of letters of enquiry from as many kind friends. It was impossible to reply to all of these. He, however, improves the present as a fit- ting occasion to return his grateful thanks to those of his correspondents for the tangible evidences of confi- dence and esteem thus manifested. And to the Messrs. Duncan Bros., too, is he under obligations for the hearty manner in which they took the little brochure under their wing, pushing the same through the press with their accustomed energy. 323 Euclid Avenue, Cleveland, O., September 1880. ACME STAND. CONTENTS. PAGE. Introduction and Apologetical ..... 5 CHAPTER I. Something about American Stands, etc. . IT Zentmayer's American Centennial Stands. ... 34 The American Histological Stand 39 Tolles' large " B B " Microscope 47 Tolles' Largest " A " Microscope 48 Tolles' Student's Microscope 49 The Professional Microscope 53 Large Student's Microscope 46 Family Microscope 57 Bulloch's First-Class Microscope 59 Small best Stand " A B " . 67 Mr. Bulloch's " D " Stand . . . . . . . 67 Mr. Bulloch's New Biological Stand .... 68 R. &. J. Beck's Microscope . 71 Beck's Popular Microscope, Minocular or Binocular . 72 Beck's Economic Microscope 72 Beck's New Histological Dissecting Microscope . . 79 The New National Microscope 80 The New Acme Stand 84 13 14 CONTENTS. CHAPTEE II. What is Augnlar Aperture 93 Angular Aperture ... .... 93 How Shall we Measure Angular Aperture ... 95 Object Glasses . , 97 Something Further about Objectives .... 108 Balsam Apertures 123 Flatness of Field , 126 Mounting of Objectives 129 Nomenclature of Objectives 130 Table of the Magnifying Power of Single Convex Lenses 134 CHAPTER III. Objectives Continued 137 Objectives of Lower Balsam Angle 144 Adjustable Objectives ........ 148 Eye-Pieces . 156 CHAPTER IV. Manipulations Wenham's Reflex Illuminator . . 157 The Woodward Illuminator ...... 163 Tolles' Traverse Lens 179 CONTENTS. 15 CHAPTER V. Illumination . . .183 Sunlight .......... 186 Artificial Light 187 CHAPTER VI. Choice of Objectives for Regular Work ... 202 Selection of Covering Glass 213 Bull's Eye Condenser 225 Working with Low Powers 225 The Spencer one-inch of 50 Broad Guage Objectives, .etc. 230 CHAPTER VII. Work with the Higher " Powers " . . . . . 235 Position of Observer 246 Mean of ten Measurement of Moller Test Plates . . 253 Position of Observer '289 Work over dry Mounts with high Aperture Objectives . 298 Oil Immersion Object Glasses .... 309 Oil Immersion Objectives 310 16 CONTENTS. CHAPTEE VIII. A Word or two on Volumetric Analysis . . . 318 Apparatus necessary 320 Analysis of Urea, etc 325 Analysis of Sugar, etc 332 Preparation of Urinary Constituents 339 APPENDIX. Names and Address of Dealers in Microscopes, Object- ives, etc., Alphabetically Arranged .... 341 The Investigator Microscope 345 International Microscope Stand, 348 Prices of Accessories 352 SUPPLEMENT. Contributions to the Cincinnati Medical News . . 358 High Angles . 359 Angular Aperture and Central Illumination . . . 361 On the Performance of Objections 368 Angular Aperture once More 370 The use and abuse of the Microscope .... 375 A Chapter on Elementary Physics , 393 Choice of Objectives .,,..... 397 Microscopical Examinations of Oleomargarine . . .400 HOW TO SEE WITH THE MICROSCOPE. CHAPTER I. SOMETHING ABOUT AMERICAN STANDS, ETC. The choice of a stand is a matter of interest to every working microscopist, and to most of us it has been a source of much annoyance and needless expense. It may be safely affirmed that most workers have wasted more money in previous purchases of unsatisfactory stands than would suffice to pay for the one at present in use ; very many indeed would feel grateful to be let off with this record. I therefore propose to assist the novice in the important matter of the selection of a stand, and shall, with this end purely in view, give him fearlessly what, in my opinion, will be sound advice. And be it known again that there will be some adver- tising done in this department. As I have before inti- mated, it is quite impossible to say what I shall have to say, of real value to the reader, without giving promi- nence to one or more of the several makers. The re- sponsibility is mine, and I accept it. It has been my province, in times past, to select many stands for my friends and acquaintances ; those who have visited me with the special object to ascertain my methods of using and working objectives have, in many instances, fol- 18 HOW TO SEE WITH THE MICROSCOPE. lowed my recommendations as to stands, and in every case, I believe, have expressed to me their satisfaction. The author has not in the past stood so much alone as to his ideas of a stand as was the case with his opinion *of objectives. Now, in what follows, it is to be assumed that the reader desires one stand, and one only, and that he wishes to invest his money to the best advantage, i. e., make the same go as far as possible ; that he desires a really good and reliable instrument, and one that will last for a lifetime. During the past three or four years, the microscope stand has been greatly improved, both in Europe and America, and as a rule, really serviceable instruments *can now be obtained either of American or London -workmanship, and at a moderate cost. It is to be re- :gretted that our German friends have not followed suit, but, on the contrary, have been content with the old form of stands which were patent ten years ago. In the late improvements by the American and Lon- don makers, it is first noticealle that the weight of the stand has been considerably reduced ; the old idea, that to secure sufficient solidity it was necessary to employ stands weighing from twenty to forty pounds, being now practically abandoned. Again, it was formerly considered a sine qua non that the microscope stage be thick enough, heavy enough, and solid enough to bear the whacks from a sledge- hammer. It must be here kept in mird that years ago there SOMETHING ABOUT AMERICAN STANDS, ETC. 19 were no such things as wide-angled objectives, and, as a matter of course, the work was principally done with central or centrally disposed light. To this the old and heavy stage offered no objection, for it was quite possible, with the aid of achromatic condensers, prisms, etc., to work with all the obliquity the objective would respond to, using a stage two or three inches in thickness. Luckily, there were those who would at times "fight objectives," play with diatoms, etc., and in response to their demands the optician increased his angles and working force of the object-glasses. To meet this in turn called for the construction of condensers of greater angle; until finally it occurred that the aper- ture of the objective had arrived at proportions to which the condensers did not satisfactorily respond. Something had to be done, and something was done, for necessity is the " mother of invention." The simplest way is the best, and this was to reduce the thickness of the stage. The "fighter" of objec tives had discovered the fact that a stage, one-fifth of an inch in thickness, was solid enough for any and all of the delicate work required by the microscopist, while at the same time he derived a great advantage in thus pro- viding play for the aperture of his objectives. The writer remembers with pride that he " took a hand"" at this; he remembers, too, the unalloyed satis- faction he experienced in seeing two heavy, lumbering, and expensive stages, alone costing several hundred dol- lars, removed from imported stands, and their place substituted by plain, thin plates made by the local 20 HOW TO SEE WITH THE MICROSCOPE. watchmaker; he recollects, also, the exclamation of one of his friends, after looking at an object as dis- played by the improvised stage : " Well, I declare ! This instrument was made for any thing in creation but to see through." Hence it was, responding to the increasing call, our American and London makers decreased the thickness of their stages. While it is yet true that many of the present stages are unnecessarily thick, the reduction is still palpably manifest. It may be remarked, then, that the real improvement of late years in the construction of American and Lon- don stands may, as a rule, be manifested in these two items, viz., reduction of weight and thickness of stage. We have learned something from the Germans, too, within the past few years. It has been well known that they favored the vertical stand with its short tube. Our experience has taught us that both of these have their advantages, and our later instruments are so con- trived as to be used with short, and also with standard tube, and in a vertical or inclined position. I desire in this place to record the fact that the stands made in the United States are not excelled in any qual- ity or condition going to make a number one, reliable instrument. ^The stands produced by our home makers are quite equal in every respect to those of any- other countries, while their cost is not one whit higher. Those contemplating the purchase of a stand will, as a matter of course, consult their individual taste and inclinations to a considerable extent : thus, A may select SOMETHING ABOUT AMERICAN STANDS, ETC. 21 a large and heavy stand, while B would prefer a smaller and lighter one. The party, too, will naturally take into consideration the particular field of work he may have in contemplation. It is quite possible to give the latter consideration too much weight. It will be found, as a rule, better policy in the long-run to purchase a stand capable of doing almost any work, and thus avoid the possibility of being compelled to sell at some future date, at a heavy discount, and purchase another and more capable stand. Fortunate it is that one can now purchase, at moderate figures, reliable and well-made stands, suitable for almost any purpose of tl e micro- scopist. In the reference that has been made to American stands, it is proper to state that the Messrs. Beck, of London, have a regular agency here for the sale of their wares, and that this agency is in charge of an American gentleman. There can be no good reason to regard them as other than home folks. At all events, the author is of this opinion, and will act accordingly. Among the essentials that deserve attention in the selection of a reliable stand may be mentioned : FIRST. See that the stand is well balanced in every position that it manifests no disposition to topple either one way or the other; that it stands tolerably firm (for its weight) on its legs. SECOND. If it has coarse adjustment by rack and pinion, see that the movement is as smooth as oil; reverse the milled heud between the thumb and finger promptly, and notice if there be any lost motion; try 22 HOW TO SEE WITH THE MICROSCOPE. this test all the way of the "run" of the rack, and if there be " lost motion" detected discard the stand. THIRD. Examine carefully the bearings on which the body slides; these should be broad, and the fitting of the body to the limb accurate; test by placing a small object on the stage a circular diatom will be the thing; now examine with a half-inch glass; rack the tube up and down a little, and see if the object keeps its centre ; seize the body-tube near the eye-piece, and twist it a bit from right to left, and vice versa, noticing whether the object "travels" or not; repeat this ex- periment by punching holes in a card-box, say three- quarters of an inch thick, thus forming a supplemental stage ; focus again and try the twist once more. The instrument that will stand this test is all right as to its bearings. FOURTH. Place the diatom on the stage, under the half-inch, as before, and if the instrument has fine ad- justment by nose-piece, test by moving the fine wheel quickly either way, and see if the object " travels." If satisfactory with the half-inch, try an eighth, or tenth ; test also by taking hold of the objective as one would in the adjustment for cover, by giving it a little twist right and left, and see if the object changes its position. Finally, examine the run of the fine adjustment; see if it is quick and sensitive to the touch, without "jump;" if satisfactory so far, so good. FIFTH. Should the stand have concentric stage, test the accuracy of its fittings with diatom and half-inch glass. If the stand has suffered transportation, or has SOMETHING ABOUT AMERICAN STANDS, ETC. 23 in any way been submitted to fatigue, the probability will be that the stage has become somewhat decentred, and any effort of your own to re-adjust will be likely to make things worse. The very best stages will not remain centred long if roughly used. Still, with your half-inch and the diatom you can manage to get some idea, which will be better than none at all. Centre your diatom, and focus; now seize opposite edges of the stage with both hands, hold it firmly, giving it "jerks" either way, right and left, but not sufficiently to absolutely move the stage on its centre. If you suc- ceed in moving your object, with a corresponding move- ment of the stage, then the latter is not accurately fitted, and cannot be accurately centred. This "slip" can be detected with the hands alone. SIXTH. It the stand be furnished with mirror fitted to radial arm, see that all these fittings are strong and likely to last. This portion of the stand meets with more fatigue than any other. See that the friction sur- faces are not both the same metal ; this will apply, too, to any part of the stand. Notice particularly whether the universal motions of the mirror are properly con- structed, and likely to last for years; this is a most im- portant point. FINALLY. It will be well to see that the joint for inclining the instrument at various angles is strong and well made, and that it have compensation for wear. Notice the general " get up" the general finish of its various parts. And now, having received a lesson on the use of diatoms, you may put the little fellow away until again wanted. 24 HOW TO SEE WITH THE MICROSCOPE. Aside from these matters involving sound mechanism, there remain other points connected with the choice of a stand, which may, to some extent, be regarded as a matter of election. For instance, some of the most costly stands are furnished with mechanical stages whereby motions are given to the object-carrier by various milled heads. I have used these stages in times past, anc 1 have to record my disapprobation of them, and for the following reasons : FIRST. They are an impediment to quick work. It is much quicker to run from one end of an object to another by one single movement given by hand than to wait the slow motions of the screws. There are, how- ever, some advantages arising at times from the use of the mechanical staore, e. g., in adjusting the image of an object to the eye-piece micrometer, etc. Nevertheless these slight conveniences are sadly outweighed by the positive objection to their use. SECOND. A mechanical stage, to be good for any thing must be nicely made ; hence they are costly, and further, seldom keep in order for a great length of time, however well made. THIRD. As generally modelled, they increase the thickness of the stage, and the screws are always more or less in the way. FOURTH. Those who rely on their mechanical assist- ance seldom arrive at that delicate finger manipulation so necessary to be acquired by the observer. Any one of the objections above named ought, in my opinion, to 1x3 sufficient and determinate. SOMETHING ABOUT AMERICAN STANDS, ETC. 25 Many of the first-class stands (so called) are fitted with sub-stages, provided with rack and pinion, and centering screws. In the latter models these accessories in common parlance, constitutes a high-angled glass. The writer has already in print stated his individual views which have since undergone no change. As a rule, refer- ence being made to wide apertures, most persons are prepared for some great show of figures, such as "175" or "179"; others might call for nearly "180"; and then again, others there are who would insist on pass- ing the " impossible" 180 corner, and revel among the 104 HOW TO SEE WITH THE MICROSCOPE. balsam angles to the tune of 100, or even higher. In dealing with objectives of short focal distance, all this may be well enough; the writer, however, prefers to regard as high-angled, any, and all glasses, without reference to their focal lengths, which are endowed with the widest apertures obtainable. If this platform be accepted, then it will occur that a one-inch of 50 should be classed as a high-angled objective, and simi- larly, a two-inch of 25. And, again, it would also then occur that a one-sixth of 130, which fifteen years ago ranked as a wide, would now be classed as a glass of medium aperture. And furthermore it may possibly (yea probably} have place, that there are many observers to-day, loud in their denunciations of the "wide-angles," falling back on "The Microscope and its Revelations" for authority, who, in their habitual use of what are now known as medium apertures, are in truth the real culprits, to whom and for whom were Dr. Carpenter's original remarks intended. As has been suggested on a previous page, there may be seriously some question, not only as to angular aper- ture per se, but as to what constitutes the measure of the same. It is one thing to get light through an ob- jective, and quite another to bring said light into the traces, and render it of use to the observer. There are, too, scores of high-angled glasses (so-called) sold as having angle of i?5, and possibly more, that are entirely worthless when worked with pencils beyond 130 ; indeed, many that I have seen would utterly fail when compared with a really good glass of 115. OBJECT GLASSES. 105 The writer has before him a glass of the latter angle, (115,) made by C. A. Spencer & Sons. It is what they call one of their " professional series" a dry one- fourth ; the makers ought not to expect that this glass should be called on for work requiring oblique pencils greater than 100. Now this glass this professional one-fourth will give me real good shows, even when worked at all the 53 o 7 obliquity obtainable on my Zentmayer stand ; and thus have I seen with it the longitudinal markings on the balsamed surriella of the* Moller test-plate, and this is a test that will defeat many dry eighths, engraved by their makers as having 160 or more angle. From this little experiment one that the writer has repeated scores of times in the interests of his friends some curious conclusions might be arrived at, which, although possibly coherent and plausible in detail, become absurd when considered collectively; thus it might be held : First. That both glasses having at least 160 of aper- ture, are in fact high-angled glasses. Second. That of the two named, the Spencer is the better glass. Third. That the Spencer objective has really but an angle of 115, as marked by its maker; that its capa- bility of admitting working beams up to 140 gives it no real claim to those figures. Fourth. That, as any good eighth of 140 will easily show the longitudinal markings of the surriella, it is proven that the one referred to has not that angle 106 HOW TO SEE WITH THE MICROSCOPE. at all, and is, in fact, but a medium power glass the general verdict being that it is an indifferent one at the best. Fifth. That the capacity of an objective to display markings on balsamed and difficult tests, at or near the limits of its aperture, is no index of angular aperture. In the case presented, if it so be that the eighth, when worked at 140, gave fair and distinct images of the sur- riella, then there is no reason to dispute the angle a& claimed for the glass ; let the experiment be repeated an using angle of 120, and over dry as well as bal- samed mounts. The above may be taken as representing individual differences of opinion. Either of the conclusions pre- sented have been urged on our attention time and time again. To the second, third, and fourth, the author gives his assent, and has never allowed an opportunity to pass without exposing by actual demonstration the fallacy contained in the fifth. From the preceding, then, it becomes apparent that there is much difference of opinion as to what consti- tutes angular aperture or the measurement thereof. Until there can be some more precise plan arrived at, let the purchaser of any objective imperatively demand : First. That the objective, in general, work with its full vim fully up to the* limits of the aperture claimed for it; that the images be strong, vigorous, brilliant, and without distortion, and that such images shall not be surpassed in any particular by any similar glass, without reference to its angle. If it be that you have OBJECT GLASSES. 107 a wide aperture in hand, see that its work by central or centrally disposed light is not excelled by any objective of narrow angle extant. In calling on the glass at the limits of its aperture, demand, and see to it particularly, that there be no letting down of general performance, that the images remain strong and vigorous, that the corrections are not impaired, and even with the widest apertured objective known, that there be no sensible distortion of the image. Again, if it so be that you desire thus to test an ob- jective claiming considerable aperture, say 170 or 175% and adjustable, note whether there be any special ad- justment required when worked at or near the limits of its aperture, other than necessary for its correct per- formance by central light; if this be found the case, the indications are that the two sets of pencils are not in harmony with each other as the Germans say, are not "married." It will be necessary to use a little discretion here, for some of the very finest glasses re- quire a slight change of adjustment under the condi- tions named. The less of this especial adjustment, however, the better. Any objective that will stand acceptably the fore- going- tests may be allowed to ' ' pass muster " as to its aperture sans peur et sans rejiroche. In the act of writing the above, the author was inter- rupted by a friend with the remark, " Are you not screwing things down pretty fine? Don't you see that your method not only is a severe test as to working 108 HOW TO SEE WITH THE MICROSCOPE. -angle, but is also a severe test as to the general quali- ties ot an objective?" In response to this interrogatory, I reply, that it's high time things were "screwed down." As to the latter portion of the remark of my friend, it may be observed that the directions given indicate a part, and part only, of the course to be pursued in testing the performance of a really first-class American objective of wide aperture. The plan proposed is liable to another, and, in the minds of some, a most serious objection; says one, " Don't you see that you have advanced no positive guage? Your idea simply is to compare one glass with .another in short, it means 'fighting objectives" Selah! SOMETHING FURTHER ABOUT OBJECTIVES. There is another matter of common acceptance which has in the past made some mischief; I refer to the fact that the focal or working distance of an objective has been and is considered the index of its capacity for cer- tain classes of work. Thus, the incli has been set apart for the study of such objects as required examination, with powers from 50 to 150 diameters, and where its comparatively long working distance was desirable, while the one-fiftieth, whose lowest power of 2,500 diameters and its exceedingly short working distance, <;ould not perform the work of the inch the one- fiftieth being reserved for the investigation of the most minute organisms, and under the highest amplifications. SOMETHING FURTHER ABOUT OBJECTIVES. Now, in the instance cited the popular idea is correct. The inch cannot do the work of the fiftieth, nor can the fiftieth do the work of the inch, and each, as to the other, are to be appropriately brought into use. But, as is well-known, between and intermediate to the scope of the two glasses named, there are several objectives having not only intermediate but variable focal lengths. Among these latter, too, are to be found the objectives known as " medium powers," and it is with reference to these that it may be affirmed that the broad rule governing the inch and the fiftieth does not hold good. Some four or five years since, the author, in writing to a brother microscopist, hazarded the statement that the time would surely come when the optician would furnish one-sixths, capable of performing all the work then done with the one-fiftieth. The principal reason advanced at that date, in support of his opinion, was, First, assuming the case of a perfect objective with a perfect eye-piece, he claimed that it made no difference to which end of the tube the power should be applied. Second, the nearer perfection arrived at in the con- struction of the objective and eye-piece, the higher may be the power of the latter ; and Third, as we have no right to expect absolute per- fection in the construction of objectives, it nevertheless seemed reasonable to infer that the optician could bet- ter handle and adjust a lens of sensible dimensions, such as are used in the manufacture of the medium 110 HOW TO SEE WITH THE MICROSCOPE. powers, than could be possible with the merest speck of glass forming the fronts of the one-fiftieth. Whether the ideas thus advanced were correct or not, the fact is patent that in less than two years from the date of the said letter, Mr. Tolles produced a one-sixth, that excelled for any and all work the performance of any one-fiftieth on record. This one-sixth is still in the possession of the author, who, ere the glass was thirty days old, pitted it against the finest fiftieth to be found in the country. The battle waged for an entire week, but the result was decisive. It was David vs. Goliath, and David had the best of it. Scarcely had another month elapsed before Mr. Tolles again sent the writer another glass this time a tenth which, in turn, eclipsed the previous inimitable work of the sixth; while at a still later day, Mr. Herbert Spencer produces a tenth, made on a somewhat differ- ent formula, the performance of which is not excelled by any glass yet made, " be it a fifth or a fiftieth." Without reference to the " impossible 180," it may be positively claimed that either of three glasses named have greater aperture than is possible (or has thus far been possible) to obtain with the fiftieths. As has already been stated in the introduction, the writer was the first to call public attention to the claims of American objectives of medium power. Statements so radically at war with the generally accepted popular belief were destined, as a matter of course, to meet with opposition. Microscopists from almost every section came in person to see for themselves, many of them SOMETHING FURTHER ABOUT OBJECTIVES. 11] bringing their favorite high-power glasses for compari- son, and returning to their homes satisfied with the trip, leaving the one-sixth and the tenth to encounter the next comer. It being probable that there are others who yet re- main to be convinced as to the accurary or validity of the claims of the " medium powers," it may be stated that at this late day the writer is no longer in a minor- ity of one. Microscopists of note have studied the situation, arriving at similar results. About twelve months ago, Mr. John Mayall, Jr., a well-known and talented microscopist of London, wrote as follows: " I am not going to enter into a mass of details of the various trials I have made with Tolles' one-fourth and one-eighth. Suffice it to say that no lenses that have been in my hands have ever been so thoroughly tested against the best lenses by English, French, and German opticians (here Mr. Mayall presents a list of seventeen recent immersion objectives by the most re- nowned makers in Europe); and without reserve of any kind, I say these lenses are the finest I have ever seen. * * I affirm, then, that with cen- tral and oblique light on all the objects that are known here as tests, Tolles carried the palm. I find, on the most severe tests, there is in Tolles' lenses a better cor- rection for spherical aberration, the image is more crisp and clear. By difficult tests, I mean, for instance, sur- rirella gemma with central light, or amphipleura pellu- cida with oblique light. I urge that low-angle lenses will not exhibit the definition these 112 HOW TO SEE WITH THE MICROSCOPE. lenses will show, and that if one takes a higher power that will show the images, he will find, by comparison, the higher power will be the more difficult to manage. The whole question tums upon results ; if you are con- tent with medium images, use medium or low-angle objectives; if you train your eye for fine images, you must use high-angled objectives." In 1876, Dr. J. Gr. Hunt, of Philadelphia, a widely known and expert microscopist, after having given the new American objectives of medium power close study, writes as follows ; and believing that the doctor's letter will be found of general interest, we give it entire* The glass he makes reference to was a Tolles tenth : " I can now report to you that the one-tenth you sent me is grand. It contains more good qualities than are to be -found in many first-class lenses perfect mechanical workmanship, large field, gives sharp image on the margin of field, decision of definition leaving- nothing doubtful or foggy, equal penetration with reso- lution; thus being superior for his tological work. I could engrave it all over with marks of admiration. . . . For the best work of the botanist or histologist it has a definition which can be retained, with an amplification such as I have not seen in any one twenty-fifth or one-fiftieth that has come under my notice. ... I see in its con- struction more finger skill, more time and conscious brain patience than mathematics. Hence its charac- ter; it has no precedent, but is wholly original, and unlike any other ma&e, English or continental." SOMETHING FURTHER ABOUT OBJECTIVES. 113 The preceding quotations are thus presented to the reader because the issue we have under consideration is therein discussed typically (I may say) from both the American and English standpoints. To the testimony cf these talented gentlemen the author could, did his- space allow, add a mass of similar evidence. I repeat, it is not consistent with the limits of this little book to further discuss the issue in question. The author therefore dogmatically asserts that his positions taken in public print relative to the matter we have been considering, were then correct, and have so re- mained up to the present date. But mark this point: the claim thus established in favor of "medium powers" of the widest apertures has no reference whatever to hosts of objectives made and sold with high-sounding figures attached. Keep this fact in lively remembrance. We are now prepared to return directly to the point from which we started. We have seen by our digres- sion that the relations existing between the inch and the one-fiftieth are to be essentially modified, relatively, as to the nature and performance of a one-sixth as compared with that of a one-fiftieth. For instance, if it were true, as has formerly been accepted, that it is the province of the inch to assist in the study of the simpler organisms, and that of the fiftieth for the in- vestigation of the mostjlelicate structures, it does not hold good at this present writing that a one-sixth or tenth (generally classed as medium powers) are the proper objectives for an intermediate class of work only. 8 Microscopy. 114 HOW TO SEE WITH THE MICROSCOPE. It is obvious also that, if the one-sixth and the one- tenth are more than capable of doing the work formerly set apart for the employment of the one-fiftieth, the former have the better right tp be regarded as "high powers." Furthermore it occurs in the present advanced stage of optical science that it is really quite impossible to precisely define what constitutes a " medium power " glass, or for what particular class of work would such glasses (if defined) be characteristically adapted. The ^author confidently believes that still further and greater improvements in American objectives are yet to be ac- complished. He believes, too, confidently that, as the instrument shall approach perfection, and still higher ye-pieces be brought into requisition, he may yet live to see the Nobert nineteenth band with a half-inch ob- jective and a one-sixteenth eye-piece. It therefore seems to him that any discussion as to the characteristic duties of an object-glass based entirely on the focal length of the same may wisely be dismissed as being (for the present at least) impractical, if not impossible. And now for some remarks that are not only possible, but can, if the reader elects, be made eminently practical, closely related, too, to what has just been written; and in these the author hopes to render some service at least to a portion of his readers. A fine objective is in its very nature a costly instru- ment, while on the other hand, it often happens that the true lover of nature has unfortunately a light purse. In fact, this whole situation is to be regretted, and cer- SOMETHING FURTHER ABOUT OBJECTIVES. 115 tainly to be ameliorated if possible. It happens, too, that the so-called " high powers," such as one-twenty- fifths, one-fiftieths, and one seventy-fifths, cost in them- selves more than the majority of observers could afford to pay for an entire outfit, and thus have been accessi- ble to only a favored few. The price of the fiftieth, as furnished by eminent makers may be quoted at from $250 to $300. I dare say that more than one of my readers, earnest workers with the microscope have yearned time and time again, as they have read of some wonderful things accomplished with a twenty-fifth or one-fiftieth, for the means to enable them to pursue similar investigations. Let all such hail with joy the announcement that these costly glasses are no longer a necessity, and that their work can be not only done, but better and with greater ease accomplished, with what are known as medium-power glasses of wide apertures; that there is no longer, too, any necessity of going abroad, or paying duties thereby; that a one- sixth, or, at the furthest, a one-tenth, costing from 60 to $85, will (if properly selected) compete in perform- ance with any one-fiftieth extant a fact, reader, worth knowing. Another dogma in the popular mind has very general acceptance to wit : that angular aperture can only be obtained at the sacrifice of working distance. The old saying is, that " it's a poor rule that won't work- both ways;" hence it should obtain conversely, that with the sacrifice of working distance, angular aperture ought to be obtained; but this is not always the case. For in- 116 HOAV TO SEE WITH THE MICROSCOPE. stance, one -sixth are now made with apertures we will say (to keep out of controversy) up to 180, and with a working distance of one-fiftieth of an inch. Now the widest angled one-fiftieth in existence, with a working distance le^s than half that of the one-sixth, will be found to measure less than 170, and in the latter glass it is evident that working distance has been sacrificed without corresponding increase of angular aperture. The case cited is an instance notably in point, and one that cannot be dodged, and yet to a certain extent the same will apply to some of the intermediate objectives. Take again the befors-mentioned sixth of the widest angle known, and its working distance of one-fiftieth of an inch. It will be found that, although it is possible to obtain the same aperture for the tenth, the working distance will sufier decrease ; and here again is another instance where sacrifice of working distance is not accompanied by corresponding increase of aperture. The subject is by no means exhausted, and is well worth a little ventilation. We can better get at the situation by supposing a case which might possibly occur in practice. Suppose then, reader, that you desire five one-inch glasses, each glass to have a work- ing distance of five-tenths of an inch, and each to mag- nify with the two-inch ("A") eye-piece, fifty diameters, and that you gave these five glasses respectively to five opticians, to be made as per the conditions named. Now, it will most probably occur that when you get these five glasses in hand, the working distance and the magnifying powers of each are true to the specifications, SOMETHING FURTHER ABOUT OBJECTIVES. 117 and further, that no two of the five glasses will have the same angular aperture. It's well enough to pause here and allow the approach of a deluge of threadbare argument. Says one, "All this proves nothing. It's quite possible that the glass with the narrowest aperture may be the better corrected. Let your own rule be here applied, and the quality of the apertures tested; nothing short of a competitive examination can be determinate." To this the writer says amen ; but the reader is again reminded that this is nothing more or less than "fight- ing objectives." This is the course, too, which the author has pursued in the way of making competitive examinations of objectives in his own interests, and in behali of those of his pupils, his friends, and his corre- spondents. The result being, in nineteen cases out of twenty, that the glass with the wider aperture proved in every other respect the better glass a result, too, not improbable in its nature, when it is borne in mind that those of our opticians who have given great attention to the development of aperture are no ways behind-hand in their general professional attainments. Again, (to steer clear of cavil or controversy,) suppose that of the five glasses before named, all having the same working distance and amplification, the one with the lower aperture being made by Mr. X., and the other of wider angle being by Mr. Y., both objectives being, too, equally well corrected. That such a condition of things is possible no one will attempt to deny. Here is M condition to which the popular dogma can be 118 HOW TO SEE WITH THE MICROSCOPE. applied to advantage to wit: we can send to Mr. Y. for another inch similar to the one in hand, but with a lower aperture, and corresponding to that of Mr. X., and it will obtain that Mr. Y., in cutting down the aperture of his inch to that of Mr. X., will increase his working distance; and here (comparatively) we gain working distance without loss, or, as it has been termed, sacrifice of angular aperture. Hence we arrive at the conclusion that the function recognized as "angular aperture "per se is not a fixed and definite quantity nor one that can be fenced in and subjected to any fixed rules. Nothing definite in the way of rigid law can be applied to it. In the case just mentioned, another curious conclusion might be arrived at, and justly too. For instance, the decrease of aper- ture from that of the wider aperture to that of the lower would not only be accompanied (accepting the popular dogma), which in the case in question would hold true by an increase in the working distance, but the penetra- ting power of the glass w r ould thereby be enhanced, and this, too (comparatively), without loss of angle. The facts presented are valuable, are significant, and worth careful thought and study. The author has never seen them in print, and they are, as suggested, the result of an active experience. And this brings us to the consideration of another matter; I refer to the popular dogma of "penetration." This has been the biggest toad in the puddle, and has exercised an active agency in roiling and mystifying the mind of the microscopist. The doctrine of penetration SOMETHING FURTHER ABOUT OBJECTIVES. 119 as generally taken and accepted may be thus stated: objectives of low angular aperture are endowed with a peculiar inherent and intrinsic power, by virtue of which they enable the observer to see and study struc- tures situated .in different planes of the object. For example, if the objective be focussed accurately to details occupying an intermediate plane of the object to be examined, then will the low-angled glass allow the observer, without change of focus, to study other details of the said object, situated in planes either nearer or more remote. We have been taught that this is a most valuable property, and one due to the employ- ment of low angles only the idea thus conveyed being that the low angles possess a peculiar and accommodat- ing power of great value to the microscopist, to which the wide apertures stand inflexibly opposed, and defiant. In support of the doctrine of penetration , it has been customary to present the case of the optical principles governing the action of low apertures, contrasting the same relatively with similar conditions involved in the , use of the high angles ; thus we have been taught that the narrow-angled glass admits as a matter of course, but a narrow cone of light, the pencils crossing at the focal point at a very acute angle. Hence it is "obvious" that it matters not whether the object to be viewed be placed exactly at the crossing point or a little within or without the said focus. The accompanying and sup- posed increase of working distance attributable to the narrow aperture of course is not lost sight of; and we are here admonished to keep in mind the fact that, with 120 HOW TO SEE WITH THE MICROSCOPE. 'an infinite working distance, there would be no need of special focal adjustment, and hence the longer the work- ing distance the better. On the other hand, we are told that objectives with very high apertures admit a much wider cone of light, the lateral rays of which cross in the focal point, at a more obtuse angle, and hence the necessity of placing the object to be viewed exactly in the local plane. On all other planes, nearer or more remote, the object being out of the crossing of the rays, cannot be well defined; and here again, conversely the presumed decrease of the working distance due to the increase of aperture is held prominently in view. To all of the above, which has proved so acceptable to the world of microscopists, the author long ago pub- lished his dissent. He never did, and does not to-day, take the least stocK in the aforesaid enunciation of the so-called doctrine of penetration. Admitting, as in the case of the two objectives pre- sented, that the cone ot light illuminating the field from the high-angled objective is wider, and that the lateral pencils cross in the focal point at a more obtuse angle than can occur in the case of the narrow-angled glass, it is nevertheless true (and singularly this little fact seems to have been entirely lost sight of), that the wider cone of light due to the employment of the wide aperture includes all of the central pencils present in the case of the narrow-angled glass. In other words, there are just as many central pencils at work (and remember that these are the fellows that cross the focal plane at such an acute angle, thus furnishing the beloved pene- SOMETHING FURTHER ABOUT OBJECTIVES. 121 tration) in the making up of the wider cone as can occur with the use of the narrow aperture ; furthermore, that it would be not only possible, but eminently prac- ticable, by the use of a diaphragm, to cut clown the cone of the wider aperture objective to correspond with that of the low-angled glass ; hence it is obvious that in this latter case the two objectives would be worked under similar conditions as respects the angle at the crossing of the rays, and, applying the argument based thereon, neither glass can be endowed with the greater penetration. Says one, "How about the working distance?" The relations of angular aperture to working dis- tance have already been discussed, and intentionally, with the view of preparing the mind of the reader for the above interrogatory. But there remain other con- siderations bearing on the matter of working distance, and the clinching 1 argument on the part of the writer remains to be presented. In doing this, the author is compelled to deal in assertions dogmatically. In the handling and compar- ing of object-glasses, he has had a very large experience, and he feels that he has the same liberty to speak ex cathedra as has been granted to others. Moreover, what he now has to say is " important if true," and he is as well assured ot their correctness as of any other fact within his knowledge and experience, nor is he alone in the matter about to be stated. Without exception, all who have experimented in the proper direction assent to all that will be here claimed, while 122 HOW TO SEE WITH THE MICROSCOPE. those who have not, may reasonably be expected to> know not. Let it be required to display an object under the microscope, and under a given amplification. It matters not what the object may be be it a diatom, or a bit of voluntary muscle, or what not; nor dees it matter as to the amplification be it 60, 600, or 6000 diameters, as the case may be. Now, to attack this object, we will provide two sets of objectives, including all the focal lengths, say from the inch, upwards, to the one-fiftieth these glasses to be the very finest of their kind made at the present day, and notably of low apertures ; the other set to be simi- lar as to the range of focal length and quality, but notably to possess the highest apertures (respectively)* known. Now choose. your object, select your amplification,, and display the former, using the low angles with their very best foot foremost. This done, allow me to remove the objective, replacing in its stead the suitable high-angled glass, and I affirm pointedly that the object shall be equally well displayed, under the same amplifi- cation, etc., and by an objective, too, having greater working distance than the low angle first selected. It should be contemplated, in any competitive com- parisons of this kind, that they be conducted without prejudice, and solely in the interests of science, and when so conducted, and by observers fitted for the emergency, the author apprehends that his statements, will be found correct. BALSAM APERTURES. We have thus again endeavored to make manifest that the idea that angular aperture is accompanied by a sacrifice of working distance has no real existence that is, in the form popularly accepted. Thus far we have discussed ' ' angular aperture" in its popular signification, and, in several of its aspects, from the definition given from the micrographic dic- tionary. Taken in conjunction with the remarks we- have thus far had occasion to offer, the reader would probably infer as axiomatic that the range of apertures would necessarily be confined within the axial pencil and the one striking the underside of the slide at near coincidence, thus traversing and limited by an arc measured by nearly 90 the latter being equal to 180 of aperture. This, too, is the precise aspect to which the author desired to restrict his observations. Now there is another kind of aperture of which very little is generally known, we refer to BALSAM APERTURES. From a theoretical or mathematical standpoint, the study of balsam angles fairly bristles with difficulties; it has been to us a problem to which our school boy wrestlings with Euclid seem a pleasant and simple exer- cise. While we frankly admit our incompetency to properly present the subject, we have to remark, on the other hand that we were not willing to send forth this little book without at least some mention of the matter. Observers interested in the history of the American 124 HOW TO SEE WITH THE MICROSCOPE. objective (and American observers ought to be, to a man) will find the subject ably discussed in the columns of the London Microscopical Journal, reference being made to the celebrated controversy on the subject of angular aperture between Mr. K. B. Tolles, of Boston, Mass., and Mr. Wenham of London. In this discus- sion, the American side of the question was ably assisted by Col. J. J. Woodward, of the U. S. Army, and Prof. Keith, of Georgetown, D. C. The entire controversy is well worth reprinting in a consolidated form, and should find an appropriate place in the library of every American observer. No attempt will, tor the reasons given, be made to discuss the subject of balsam apertures in these pages. We shall, however, try and give the novice an idea or two connected with balsam angles without which some things which will hereafter be presented, would be wholly unintelligible. Suppose we put a ray of light down the tube of the microscope, thus reversing the usual order of things, and that said pencil have an angle of 41. This pencil traversing a suitable objective in position over a bal- samed mount, will find emergence into air at 90 ; equal to what is recognized as 180 of aperture. Such an objective would be said to possess a balsam angle of 82, in other words (rejecting fractions), the balsam angle of 82 is said to equal an air angle of 180. Now it is claimed by certain American opticians, that it is possible to construct immersion lenses that are capable, when worked over balsam mounts, of recogniz- BALSAM APERTURES. 125 \i\cr interior pencils greater than 41. Mr. Tolles claims for some of his recent immersion objectives, balsam angles as high as 120.* We have devoted a great deal of time to the study of this class of objectives. These glasses were generally known here at home as " duplex," or four system immersions, as distinguished from the older form having a single front. Many of these objectives, ranging in their claims as to balsam angle from 82 to 100, have passed through our hands, and have been submitted to close and careful study ; one object on our part being to determine, if possible, whether a glass said to be of a lew balsam angle was in any respect characteristically different from another claiming a higher balsam angle, and in this way to arrive at some determination as to the existence or val- idity of the claims resting on the recognition of the an^le itself. O As a result obtained from close, tedious and pro- tracted observations, dating from the present date back to that of the first " duplex" made, we unhesitatingly affirm that it is quite possible to distinguish the per- formance of a duplex objective of 82 balsam angle, from a similar glass of 100, otherwise we would have had no occasion to have introduced the subject at all. Now, in the effect of balsam aperture, we recognize in the high balsam angles precisely what has been at- tributed to high air apertures, namely, a decrease of working distance, as the balsam angle is increased, and * Messrs. Tolles & Spencer are now (1880) making objectives of 120 balsam aperture. 126 HOW TO SEE WITH THE MICROSCOPE. a corresponding increase of definition, when worked by extremely oblique light over balsam mounts of " diffi- cult tests." These characteristic differences in perform- ance are so palpable, as to enable us to select in less than fifteen minutes' use of two glasses over the Moller probe plate, the higher-angled glass (balsam) from the lower. It has been claimed by some who have used the duplex glasses, that the higher performance by central light is obtained with those of the smaller balsam angle. My own experience does not authorize me to endorse these conclusions. Certain it is, that when the higher angles Are used by central illumination, their immense power of light will, if the matter receive not proper atten- tion, defeat the glass, and again, even with oblique illumination, the high-angled objectives require the most careful attention and expert handling. We are, therefore, prepared to endorse to some ex- tent, referring to high balsam angles, the remarks which have been quoted from " The Microscope and Its Reve- lations." FLATNESS OF FIELD. It is, of course, desirable that an object known to be ilat should so appear when viewed under an objective. The optician, however, has thus far found it impossible to secure perfection in this respect, combined with the highest aperture obtainable, and this might be urged as an objection to the use of wide-angled objectives. The slight error shown by the glasses referred to, has rn uch FLATNESS OF FIELD. 127 more weight on paper than occurs actually in practice, where the great increase in definition obtained causes the slight deficiency in flatness of field to sink into utter insignificance. Hence, in testing the qualities of an object-glass, the flatness of its field would hardly be called into requisition. Nevertheless, flatness of field must have its due weight, and the performance of a first-class objective should not betray any serious error. It will be well, then, when examining an objective, to look after the quality referred to. The careful testing of an object glass in this particu- lar, is not such an easy and oft-hand matter as might at a glance be presumed; the manipulator may arrive at incorrect results, and thus condemn a glass without due cause therefor, and a word or two as to the proper mode of conducting this test may not be amiss. First, it is of the first importance that the object be in itself flat when presented to the objective. Errors may creep in first, because the object is not in itself flat, or, second, because it is mounted on an improper slide, or on the cover thereof very few slides are flat, and covers are notoriously " in wind;" third, the stage of the microscope may not be at right-angles to the optical axis, and fourth, the eye-piece may not suit the objective. To guard as far as possible against these sources of error, proceed thus : Select a fine itage micrometer, having a band of lines just about as close as the objective can well display when viewed with nearly central light, and if you have 128 HOW TO SEE WITH THE MICROSCOPE. no conveniences of your own, take this to the machin- ist, or the watchmaker, either of whom will allow you the use of a steel " straight edge," with which you will be enabled to ascertain with tolerable exactness whether one side of the micrometer is truly a plane. This clone, by the aid of a suitable " guage," you will also deter- mine as to the other face. ' If, in a process of this kind the micrometer betrays defects, it should be discarded and another one chosen in its place. In our own prac- tice we always use a Nobert test-plate, which has been found to be very reliable. To avoid the third source of error, view the lines, selecting as close a band of lines as possible, and using, as before named, nearly central light, and the two-inch eye-piece, with the micrometer placed horizontally and vertically on the stage, examining the bands from end to end as they appear in the field. Repeat the experi- ment, but reversing the micrometer in each position end for end. Any error due to the pose of the stage is thus made manifest. Should you have reason to suspect trouble from the eye-piece used, repeat the entire test on the stand of some friend, always using the two-inch, or lowest eye- piece. This ocular furnishing the more severe test. Finally, let it be known that all the eminent makers, both American and English, furnish glasses that are not to be rejected for non-flatness of field. We would rather trust to the reputation of these gentlemen, than to the test conducted by the novice. A little practice on the other hand on the part of the latter will not be a waste of time. MOUNTING OF OBJECTIVES. 129 MOUNTING OF OBJECTIVES. Having glanced briefly at the optical portion, a few words in reference to the mechanism of the instrument may not be out of place. Adjustable glasses are provided with movable or stationary fronts, that is to say, in the process of re- volving the correction collar the front lens also revolves, or remains stationary, as the case may be. The station- ary front being the mobt expensive mounting, it is gen- erally adopted in first-class American or London glasses of short focal distance. In the use of objectives of tolerably long focal dis- tance, the necessity for the stationary front is not so apparent, and some first-class makers adopt either form of mounting for such objectives. It behooves the buyer to keep in mind this difference in the cost of the two mountings, for of two glasses, both equal in optical performance, the one adjusting with stationary front ought to be the most costly. Generally, the mechanism of the collar adjustment should be first-class. There should be no "slip," "back- lash," or " dead-point;" the collar should rotate with a certain firmness of action, and yet run as " smooth as oil;" there should be no undue rubbing or grating, nor "hitch or hindrance" of any kind. With a one-half inch, or a four-tenths, a slight " slip" or " back-lash" need not defeat an otherwise satisfactory objective; but, on the other hand, nothing of this sort can be allowed in the higher and first-class objectives. If the 9 Microscopy. 130 HOW TO SEE WITH THE MICKOSCOPE. collar be adjusted by the maker to rotate under high pressure only, regard this with suspicion, and examine for back-lash closely, or what is perhaps the better way, get the opinion of a skillful mechanic. The models of some of our American objectives are, in the opinion of the writer, far too large and clumsy, and the fronts too large and too flat. We decidedly prefer the conical front the more conical the better. The new tenth of Mr. Herbert Spencer, which we have before found occasion to mention, was, beyond all cavil, the most beautifully mounted glass we had ever seen, and in which the last-named objections were almost wholly avoided. NOMENCLATURE OF OBJECTIVES. American and English microscopists usually class their objectives on the basis of their focal length, it being arbitrarily assumed that the inch s^lass worked with ten-inch tube and with two-inch eye-piece, should give an amplification of fifty diameters. Hence, the half-inch glass would give one hundred diameters, the one-fourth two hundred, the one-eighth four hundred, the one-tenth five hundred, and so on. It very seldom happens, however, that an object-glass will exactly re- spond to the designation given it by the maker some opticians over, while others under-rate their instru- ments ; and then again with an adjustable glass the power will change in different positions of the adjusting collar, the amplification being greater with the systems at closed than when at "open-point." Even when due NOMENCLATURE OF OBJECTIVES. 131 allowance has been made for this last condition, we have seen English eighths having really higher power than some American one-twelfths. Again, but a few weeks since, we handled a foreign one-sixth which was superior in amplification to a Spencer one-eighth. We, here at home, have scolded a good deal at this state of things, and at times have rated our English cousins for thus underrating their objectives. It is quite unneces- sary here to traverse the ground we have already dis- cussed, to render it evident that as the objective ap- proaches perfection, these nominal distinctions, based on focal length, fail to have particular force. If, for example, it were possible to produce a two-inch objec- tive, which, under extremely high eye-piecing, would more than do the work of our present tenths, then we could afford to work pretty much with one objective, and to the eye-piece look for the determination of the power. Until, however, some such " possibility" shall occur, our present nomenclature will be invested with some force, no matter how variable this force may be. It is, therefore, desirable sometimes to determine the actual rating of an objective. The method usually employed, is to place a stage micrometer in position, using a ten-inch tube, and pro- jecting the image by aid of the camera lucida on a screen ten inches distant. Knowing, then, the actual value nothing can be seen, precisely as in the case of dry ob- jectives. 2d. Those which have sufficient angle of aper- ture to admit rays of this obliquity, but are incapable of bringing them to an image-forming focus ; with these the field appears well illuminated, but the objects are not well defined. 3d. Those which not only admit rays- of this obliquity, but form well-defined images with them. To this class belong not merely immersion ob- jectives with the so-called duplex fronts, but others; and I may add, not merely objectives of American make,, but some constructed by a well-known English house. As might be expected, the quality of the image formed by the direct rays of the sun thrown through a pin hole at this excessive obliquity varies very greatly in differ- ent cases. I will state, however, that I have thus far found at least seven objectives, some of English, others- of American make, which define sufficiently well under these circumstances to resolve Amphipleura pellucida mounted in Canada balsam. With the objectives which performed best, the field was of exceeding whiteness and brilliancy, but by 110 means dazzling, the frustule undistorted, and the striae clean and black on the white ground, very little color aberration being perceived. With other objectives there was more ot less color aber- ration and distortion, both which faults were in one or two cases very conspicuous, although in the part of the frustule most sharply focussed upon the striae were handsomely brought out. The objectives with which I thus succeeded ranged all the way from one-fourth to- one-sixteenth immersion. I will add that the objectives- 170 HOW TO SEE WITH THE MICROSCOPE. which resolved Amphipleura pellucida under these try- ing circumstances, when used in the ordinary way with this or other test-objects, displayed an exquisite perfec- tion of definition which it would be hopeless to expect to attain with objectives of less angular aperture. " As it is no part of my purpose in this communication to provoke ill-tempered discussion of the merits of indi- vidual makers, I will not append a list of the results obtained with the various immersion objectives I have tried* in this way. The apparatus can be constructed for a few shillings, and those who take the trouble to use it will soon see to which of the three classes any particular objective they may test belongs." Subsequent to the date of the reading of the preceed- ing communication, Dr. Woodward proposed some slight changes in the form of his prism. Having had consid- erable experience with the prism as now used, we append the following description, and also the manner of work- ing the instrument. Essentially, it consists of a triangular prism of crown glass. In the form adopted by Dr. Woodward the ob- tuse angle is 98 and the two acute angles 41 each. The prism may be used unmounted, by simply attach- ing the same to the under surface of the slide containing the objects to be examined, a drop of glycerine or oil of cloves serving to secure optical contact, and at the same time acting as cement to retain the prism in place. Notwithstanding this is the arrangement employed by many observers, it is but a faulty plan, in fact, a regular THE WOODWARD ILLUMINATOR. 171 " make-shift " arrangement. With the prism thus mounted any movement of the object-slide will of course cause a corresponding movement and decentering of the prism; furthermore, such object-slides can only be Avell examined when posed in nearly the horizontal position on the stage; it often, too, occurs that the intermediate drop looses its hold, suffering the prism to slide or even to loose its attachment entirely; and then, again, I have frequently got the very best work when the facet of the prism was slightly depressed from the under surface of the slide. It is far better, then, and for the reasons given, to have the prism mounted, and to those who propose to adopt my method of illumination, I will say that much depends on the proper mounting, and that any piece of sub-stage apparatus which shall impede the passage of rays from the lamp to the mirror, or from the mirror to the prism, will defeat the maximum working of the latter. Hence, as a rule, it cannot be well mounted in the usual sub-stage, the latter obstructing top much light. After much experiment, and with the hearty co-opera- tion of Mr. Sidle, I am now in possession of the Wood- ward prism, suitably mounted and adapted to the " his- tological" of Mr. Zentmayer, as will be seen from inspection of the cut on the following page. This accessory, as above delineated in plan and sec- tion, is easily placed in position on any of the histolo- gical stands. Provision is also made for centering in a lateral direction. The prism can also be revolved so as 172 HOW TO SEE WITH THE MICROSCOPE. to use either angle. It can at will be raised or lowered, or clamped in any desired position. o. Vertical vi*w. b. Sectional view. c. Prism three-fourths full size. In the adaptation of this useful accessory to the acme stand Mr. Sidle has been singularly fortunate. This neat and compact little device screws, as I have had occasion, on a previous page, to state, into the well-hole of the acme stage. It is thus 4< on and off'" THE WOODWARD ILLUMINATOR. 173 in a moment's time. All the necessary motions are pro- vided for, and it may be depended on for first-class performance. From what has already been stated, it is almost need- less to repeat that when either of the mountings de- scribed are to be used on the histological or acme stands the sub-stage must be removed. It is quite possible that the mountings presented may, with slight modifications, be fitted to other microscope stands. The form of prism (angles 98, 41 and 41), as sug- gested by Col. Woodward, will be found to do very acceptable work. It occurred to me, after having had considerable experience with this accessory, that there was nothing gained by having the acute angles equal, but on the other hand advantages would be insured by an inequality of these angles, either of which might be used as occasion required. I therefore begged Mr. Sidle to make me a prism with an obtuse angle of 93, one of the acute angles to be 47, the other to be 40, and this is the form I have adopted, believing it to be the most seviceable arrangement yet proposed, and especially adapted to the general run of modern wide-apertured objectives. To provide one's self with two or more forms of prisms will not involve serious expense. Either of the mountings I have described can be modified so that the prism can be removed and others substituted in its place. To use the Woodward prism we will suppose on the acme stand first, screw the accessory into the well- hole of the stage securely; next, place the slide to be 174 HOW TO SEE WITH THE MICROSCOPE. examined on the stage. With a one and one-half or two-inch objective (having raised the prism so as to contact nearly the under surface of the slide), focu& entirely through the body of the prism, so that its lower edge may be seen in the field, and by turning the prism in its mounting make this line, by estimation, as nearly vertical as possible. If, perchance, this line appears ta the eye considerably to the right or left of the centre of the field there is no harm done ; but you must make a note of the fact; this would indicate, however, that either the stage is out of centre, or the mounting of the prism has been injured. Next, rack back the objective and remove the slide, place a drop of glycerine on the top face of the prism ; replace the slide and raise the prism so as to make con- tact with its under surface. Having made this contact exactly, depress the prism, say, about one-fiftieth of an inch. Focus again with the low power, and bring the lower edge truly vertical, as before instructed. Eemove the low power and substitute the wide-aper- tured objective, and by way of illumination provide a small kerosene hand lamp, the flame of which ought not to be higher than two-thirds the distance from the table to the stage of the microscope; remove, also, the sub- stage. Now, if the lower edge of the prism was seen to the right of the field place the lamp to the right of the stage; on the contrary, if the edge was seen to the left, pla,ce the lamp to the left ; and in either case swing the THE WOODWARD ILLUMINATOR. 175 mirror away from the lamp, placing it so that the gradu- ating wheel shall read at about 34, 35 or 36 degrees. The lamp being passed to the right or left of the stage, as the case may be, and about four inches distant there- from, bring the edge of the flame to the mirror; now move the lamp to or from the front edge of the table, so that the edge of the lamp frame, prism and centre of mirror shall form approximately a straight line parallel with the front edge of the table, From the position described it will be seen that the ordinary sub-stage would be entirely in the way; hence the necessity for its removal. Making immersion contact, focus your objective, and, without changing the position of the swing bar, manip- ulate the mirror so that the field may be nicely illumi- ated, select your object, which we take it for granted will be 3ome difficult lined test. Next, interpose the large bull's-eye condenser (flat side to the lamp), thus concentrating light on the mir- ror ; adjust the object glass. It will be well now to try the effect of various degrees of obliquity, remembering that any considerable move- ment of the swing- bar will necessitate a new adjustment of the condenser. A slight change, too, in the position of the lamp will sometimes be attended with excellent results, keeping, in all cases, however, its edge to the mirror. The above includes the author's method of working the Woodward prism ; but as this accessory bids fair to come into general use he will now traverse the ground 176 HOW TO SEE WITH THE MICROSCOPE. over again, feeling sure that many there are who will not object to some further discussion of the subject. In the initial attempt to use the prism, the observer should select an object (balsam mounted) with which he is tolerably familiar. The collar adjustment, also, should have been previously ascertained. The next step is to decide on the proper position of the radial bar, i. e., its distance from axis, the extent of this distance will be demonstrated by the illumination becoming too feeble, the images, also, becoming generally unsatisfactory. The remedy is, in such cases, to cause the radial bar to approach nearer to an axial position, until the field can be suffi- ciently lighted and the object displayed with tolerable vigor. Thus the operator has the means of " gauging " his objective. The mirror being properly posed, it re- mains to obtain the best possible illumination, which is 'effected by slight changes of the mirror, condenser, and finally the lamp. When things are generally about right, a little movement of the lamp (grasping it firmly by the bowl), sometimes twisting it to the right or left, so as to get the flame exactly edgewise to the mirror (which is best determined in this way), will result in very nice effects, bringing out the stria? on such tests as the Moller test-plate in a very satisfactory style. Resolutions of difficult test objects are accomplished with this illuminator in a very handsome manner. It is an easy instrument to use, and will adapt itself kindly to the objective, of course; the higher the balsam angle of the object glass, the better the definition. It has, in its ease of adaptation a decided advantage over THE WOODWARD ILLUMINATOR. 177 the Wenham forms, and in the comparative examina- tion of objectives, the wedge illuminator is an exceed- ingly handy accessory. In the determination of the collar adjustment corresponding to the point of maximum aperture, the same holds true. We have spent two or three entire evenings in the at- tempt to determine which of the two illuminators is the most effective ; and our experience leads to the conclusion that the " reflex " is somewhat the superior instrument in the resolution of the most difficult lined tests; never- theless, we are glad to give the newcomer a place in the accessory box, and expect to make it very useful. It is easily made and mounted, and ought not to be expensive. Another matter closely allied to the new illuminator may as well be mentioned here. Learning that the Messrs. Spencers had just completed a new one-fourth inch objective, which was to be sent to the Paris Expos- ition, we wrote to these gentlemen asking the loan of the glass for examination, the Messrs. Spencers re- sponded promptly, and it occurred that we received the one-fourth and the new illuminator the same day. We were thus enabled to put the illuminator to practi- cal use at once, in this manner: First, we took our one- sixth, working it with the illuminator over the No. 20 of the Moller plate getting the radial bar as far from axis as the objective would allow and preserve a good display of the striae. This done, we substituted the one-fourth in place of the one-sixth, keeping the illum- ination, etc., carefully in the same position, (the cover of the plate was as well adapted to the one glass as the 178 HOW TO SEE WITH THE MICROSCOPE. other.) We found at once, that in order to obtain suf- ficient light, and retain the general vigor of the image, it was necessary to approach the radial bar to the axis -und the required movement of the latter was quite per- ceptible. It was therefore accepted that the one-sixth faad the higher balsam angle. The question then turned, as a matter of course, on the respective working dis- tances; that of the one-sixth was known. It remained, therefore, simply to measure that of the one-fourth, resulting as follows : The working distance of the one- sixth is twenty-four-thousandths of an inch; while that cf the one-fourth was found to be thirty-two-thou- sandths of an inch, a difference of 33 per cent in favor of the one-fourth. Thus it will be seen that in this instance the question as to superiority may be further taken under advisement. We relate this bit ot " prac- tice" with the illuminator in illustration of the pre- ceding remarks. One thing was proven even by the above experiment, to wit: Having our tenth on hand, held in reserve for especial demands, we would greatly prefer the one- fourth as an intermediate s^lass. This fact is too obvious to need further comment, and, in general, we are glad to add that the new one-fourth of the Messrs. Spencer is indeed a lovely glass, and if properly exhibited in Paris, will be an honor to the talented makers. The modified illuminator above described (obtuse angle, 98, acute angles, 41 each) will work very well with objectives having wide air apertures only; hence, like the modified " reflex," it will work over dry mounts, THE WOODWARD ILLUMINATOR. 179 in such cases, in common with the modified " reflex," its action, to some extent, is crippled; nevertheless, nice resolutions are to be obtained with either instru- ment, with either of which we are able to instantly display the transverse striae of amphipleura pellucida, frustulia saxonica, etc. The simplicity of Dr. Wood- ward's device, its ease of working, and the facility it affords for the comparison of objectives are in them- selves strong points in its favor, and to these may be added the satisfactory character of the resolutions ob- tained. We gladly accord to Dr. Wood ward our appre- ciation of the value of his illuminator. We are informed by General Cox that the pin hole apertures are only used when working with sunlight illumination ; they also serve a useful purpose as an assist- ance in measuring with greater precision the obliquity of the illuminating pencils employed, thus enhancing the value and capacity of the instrument. It now remains to present to the reader the Tra- verse Lens, devised by Mr. R. B. Tolles. The follow- ing is the inventor's own description of this valuable accessory, and is taken from the American Journal of Microscopy : 6 ' With the advent of objectives of increased interior angle aperture, the indispensableness of equivalent ac- cessory means for the illumination of the object became immediately evident.* * See"M. M. J.," July, 1871, p. 38. 180 HOW TO SEE WITH THE MICROSCOPE. " III my first construction of such object-classes I therefore required to provide means which proved so suitable that I have adhered to their use to the present time. "The first appliance was a deep plano-convex lens, cen- trally mounted below the object, and having its centre of curvature in the object place. Afterwards I adopted a plano-cylindrically convex lens, equal to a hemisphere less the thicknsss of the object-slide, which was placed iji immersion contact with the base of the slide, so that the object itself formed the centre of curvature of this illuminating lens. Around the convex surface of this central lens moved a shutter to regulate and limit the o access of light, and it was provided also with a small plano-concave lens which, applied by its concave to the convex surface of the larger lens by immersion contact, cancelled the refracting surfaces and allowed a perpen- dicular beam of light to reach the suitably immersed object without refraction.* " The device in a more complete form is represented in the annexed figure, where P is the basilar plate of the whole traverse system, having a circular groove and track in which the carriage, C, moves. On a projecting arm, A, of the carriage, C, are mounted whatever ap- pliances are to be used to modify or direct the light upon the traverse lens, T, in the direction of the object at the centre of the system. " In the figure, the concave lens, N, is shown in posi- tion on the arm. Thus situated, the interior convex * M. M. J M May, 1873, p. 213. TOLLES" TRAVERSE LENS. 181 and concave surfaces being of no effect, the two exterior plane surfaces of the traverse system constitute it a prism, and every slightest movement of this concave facet lens on the traverse lens, T, would give a different prism to infinite variety. In this arrangement the concave mir- ror can be used in the ordinary manner and condense light enough upon the object for all ordinary purposes. The full interior aperture of a dry objective would be reached at the very convenient obliquity of 41; i. e., at less than the critical angle, or angle of total internal reflection between crown-glass and air. L is a double convex condensing lens, that may be placed at about its principal focal distance from the object. " For a condenser, with the size of apparatus as drawn in the figure, a simple lens of 1J inch focus, and about ten (10) degrees of aperture, is convenient, and if the lens is movable along the arm, A, it can be focussed readily on the object, the position being fixed by inspec- tion. This would be well for parallel rays. If diverg- ing rays are used another lens of two or three inches focus, mounted on the arm, A, will conveniently take 182 HOW TO SEE WITH THE MICROSCOPE. up the rays from the radiant at the distance of the focus of this supplementary lens. " The plate, P, is graduated on its circular edge, as in the figure, to two degrees, and the arm, A, has a swing of seventy degrees of arc each way from the axis of the microscope. An index-line is marked on the bevelled edge of the carriage 10 from the axis of the condenser, which must be added to or subtracted from the real ob- liquity of the illuminating rays. " It is obvious that any observation made and duly re- corded as to its conditions, as of obliquity of incidence of illuminating pencil or ray, form of the pencil or beam, focal length and distance of the condenser, such obser- vation could be successfully repeated. The record of the obliquity of the most oblique rays reaching the ob- ject directly, and giving view of it at the eye-piece with luminous field, would express the 'balsam' aperture, or more correctly, the half interior aperture of the ob- jective when the front lens of the objective and the traverse system are of glass of similar refraction. " Having thus the ' balsam ' angle, we readily calcu- late or learn the corresponding angle for glycerine, or water, or any medium of which we have the index of refraction. A corresponding notation, perhaps for air, might be engraved in juxtaposition on the basilar plate." CHAPTER V. ILLUMINATION. Ordinary daylight is the cheapest; and for a great many purposes the microscopist will find it amply suffi- cient. It will be found a great convenience to have the light enter the room considerably to the left of the microscope, in which case we naturally adjust the mirror with the right hand. Placing the instrument directly before the window is objectionable, and such a position should be avoided if possible. The quality, as well as the quantity of daylight illumination will, as a matter of course, vary with the particular aspect of the day. In bright sunny weather the light from a white cloud, as has often been recommended, is pure and pleasant to vvork with, and can be used with tolerably high ampli- fications with good success. In cloudy, rainy weather it is still quite possible to work with powers up to, say 200 diameters. The recent introduction of the swing- ing sub-stage has worked somewhat of a revolution in our own practice. For years we have steadily eschewed the achromatic condenser as being a costly and incon- venient affair, making more " bother" than it was worth. The principal objection I had to urge against its use was that it was a fixture beneath the stage, thus preventing me from varying the obliquity of the illumination at will, as I desired, and, as a rule, practically I got better 183 184 HOW TO SEE WITH THE MICROSCOPE. effects without than with it. The former condensers were generally of short focal length, and of consider- able aperture. In the late stands having swing sub- stages, it being possible to swing sub-stage and con- denser together bodily, there seems to be no further use for condensers of wide angles, while on the other hand one is enabled to use in the place thereof cheaper and much less expensive instruments, and the lower the angle the better, and one need not be very particular as to the matter of achromatism. On commencing the use of the little Histological, it occurred to the author (and probably to scores of others) that its swinging stage was a strong invitation to experi- ment again with sub-stage condensers, not for the pur- pose of resolving difficult tests by extremely oblique illumination, for in this work the achromatic condenser is of no manner of account, but, per contra, it seemed obvious that by the use of a narrow apertured lens placed below the stage, and so arranged that its inclina- tion might be changed at will, good effects might be secured in two directions : First, by the concentration of a narrow cone of light immediately upon the partic- ular portion of the object under examination, thus en- abling the observer to sharply illuminate a certain point of his object, and with less danger of drowning out details in a general flood of light. Secondly, such a contrivance would do good service by daylight in dark and rainy weather. It required but few experiments to demonstrate that there was force in the above reasoning, and the next thing in course was to ascertain what par- ILLUMINATION. 185 ticular form of condenser would be the best adapted for the purpose. In determining how far it would be practicable to cut down the angle of the, condenser, thus reducing the illuminating cone of light, we have made countless ex- periments, while the low stage of the Histological ren- dered it imperative that the focal length of the lens should be such as would best accommodate the little stand. To sum up all these trials, we find that the cheapest inch objective made by Mr. Grundlach, or the inch of the Messrs. Beck's " National Series," are, either of them, well adapted for the purpose. Mr. Gundlach's inch has a rubber front which can be removed, while the setting of the Beck " National " is extremely short, and thus suited in this respect for the purpose. This, then, is the author's arrangement for work with low or moderate powers by daylight illumination, and the condenser described has become almost a fixture. In the darkest days there will be plenty of light, using the concave mirror, while in bright, sunny days the plane can be substituted. The general amount of illu- mination can be changed at will by merely raising or lowering the sub-stage, and the nicest effects in the way of definition obtained. The swing-bar can also be placed so as to afford central illumination, or it may (condenser and all) be swung laterally up, say to an angle of 40 or 50 degrees from the axis; and it further remains to say that either of these cheap objectives are real good, honest glasses for the money. 186 HOW TO SEE WITH THE MICROSCOPE. SUNLIGHT. In the study of very minute and delicate structures requiring- the utmost separating or resolving power of the objective, remarkable effects are to be secured by condensing sunlight on top of the object by means of the concave mirror, the object being mounted with a cover in the usual way. The objective used should of course have wide aperture. The mirror being posed slightly above the level of the stage, the sunlight is thrown on the surface of the cover, and making a very acute angle therewith. Although not absolutely neces- sary for this purpose, those stands furnished with swing- ing sub-stages, allowing the mirror to rise above the level of the stage, are extremely handy and convenient. By the employment of this illumination in conjunction with object-glasses of wide angles, the most difficult diatoms, such as amphipleurapellucida,f?*ustulia saxon-ica, etc., are easily and forcibly displayed. The advantages- attending the use of monochromatic sunlight, as ob- tained by the intervention of the cupro-ammonia cell, or a plate of blue glass, have long been known. Thi& illumination is procured most easily as follows: Cut with a diamond, or the point of a file, a small piece of the blue glass roughly to fit the cap of the eye-piece, p.o that when the cap is restored to its place the blue glass shall be between the eye and the eye-lens of the eye-piece, and the light is thus modified before it reaches the eye. This is the handiest method of obtaining mo- ARTIFICIAL LIGHT. 1ST nochromatic illumination we have ever tried, and the- resolutions are quite as strong 1 and effective as when the cupro-ammonia cell is used in the usual manner. In working with sunlight by either of the methods de- scribed, care should be taken to exclude the full strength of the solar beam ; that is, if the sun be clear and bright. Too much light, supposing the manipulations are tolera- bly well attended to, will be manifest by the appearance of a multitude of diffraction lines, and these as a rule may be recognized by their extending beyond the ob- ject observed. Under very high amplifications, involv- ing the use of powerful eye-pieces, we can of course- help ourselves to a little more of the solar beam. When the sun is very clear, the beam being condensed on the top of the cover, as above described, there is danger sometimes, if the object be balsam mounted, of the heat starting the balsam. In this way we once ruined a Moller probbe plate. A very little attention will, how- ever, provide against accidents of this nature. ARTIFICIAL LIGHT. For the ordinary purposes of the microscopist the St. Germain or German Student's Lamp, 0. A. Kleemann's patent, or a similar lamp made by the Cleveland Com- pany, will be found quite satisfactory. This style of lamp is too well known to require any extended descrip- tion. The flame is bright, clear and intense, and its height can be changed at will. It is easily kept in order, and has the advantage, too, of being well adapted for ordinary household purposes. The breakage of 188 HOW TO SEE WITH THE MICROSCOPE. chimneys has been a serious objection to its use ; a brand of chimney known in Cleveland as the " Crown" (each chimney having a crown ground in the glass) seem to be very free from breakage. Non-combustible wicks are to be obtained, fitting the Kleeman lamp. These are clean and handy, obviating the necessity of occa- sional cutting and trimming ; but to our mind the light is not so intense, and therefore we prefer to use the old -style of wick. These lamps burn very steadily, and are not easily affected by occasional drafts, and this is a strong recommendation in their favor, as is also the ease with which they are kept in order. For investigations of ^exceedingly difficult objects the circular wick is not so well adapted, and recourse must be had to lamps carry- ing flat wicks. The best lamp we know of, of the lat- ter style is the Mechanical Lamp, manufactured in New York City. The lamp stands about ten inches in height. The height cannot be changed, and this is an objection. It burns kerosene oil, without any chimney. The body contains a movement which, on being wound like a clock, drives a blast wheel, and thus supplies a current of air at the point of combustion. Although there is a peri- odicity noticeable in the burning of this lamp, never- theless the flame is very steady, is very intense, and superior to gas. Like the St. Germain, this lamp is very handy to have in the house, and it takes but little trouble to keep it in order. The movement should be cleaned once a year, and any one possessed of fair me- chanical skill will be competent to do this. While burning, the clock-work makes scarcely any noise. An- ARTIFICIAL LIGHT. other form of this lamp has the movement placed in the case flatwise, thus allowing the flame to burn within three or four inches of the table. The lamp is thus ren- dered very handy for use when direct light is wanted. The author has found, as a result of thousands of ex- periments, that the very best artificial light for the pur- pose of the microscopist is only to be had from a small but very intense flame. The smaller the flame the better, owing to the fact that there is less light diffused. We therefore use and strongly recommend the smallest ker- osene hand-lamp procurable, and fitted with a well-be- haved burner of the smallest capacity. If possible let the lamp bowl be so low that the flame will be, say three or four inehes only above the table, thus adapting the lamp for use by direct light. On other occasions the lamp can be supported in a more elevated position. With a little lamp of this description, in proper order r all the most difficult tests known to the microscopist can be well displayed, provided, obviously, that the ob- jective, etc., shall be competent for the work. It is of importance, when any lamp provided with a chimney is to be used, that the latter be kept scrupulously clean,, especially from a whitish film that forms on the interior. A chimney may appear to be perfectly clean while cold, but when heated the aforesaid film can be detected, and should be removed, if delicate observations are in hand, in which case it will be well, too, if the wick be three or four weeks old, to remove the same and substitute a fresh one. Even in the case of the small pattern of lamp recommended there will be no occasion to force 190 HOW TO SEE WITH THE MICROSCOPE. the combustion to the fullest extent such a burner will ^afford. A flame with the lamp burning' at one-half its capacity will be amply sufficient, and even this would be too much for the proper display of some of the most difficult tests. Attempts have been made to modify artificial illumina- tion by the introduction of blue tinted chimneys, white ground illuminators, etc. We have patiently tried the ^entire list, and reject them all, from the fact that there is no real advantage secured by their adoption which cannot be obtained in a simpler way without them. The neutral tint " Light Moderator," so called, is a pleasant thing enough for use with moderate amplifi- cations ; yet there is nothing seen with it that cannot be as well shown without it. The blue tinted chimney cuts down seriously the in- tensity of the lamp illumination to an extent which will defeat the resolution of any severe test, while, on the contrary, any and all work with the lower powers can be as well accomplished without its aid. The reader has thus before him all the various kinds of illumination we use. A great deal of the profes- sional routine of work not requiring, us a rule, the em- ployment of the highest amplifications (such as the examination of urinary deposits, malignant growths, etc.,) we try as far as possible to accomplish in the day time, and by the use of diffused daylight. If the sun happen to shine, and it be desirable to cross-question some preliminary examination under the highest pow- ers, we generally use the sunlight condensed on the top ARTIFICIAL LIGHT. 191 of the cover, or perhaps v/ith the aid of the bit of blue glass in eye-piece. For work at night we employ at times all the lamps we have described. Should the routine examinations be prolonged into the evening, we use the German student's lamp for preliminary work, the same as we use diffused daylight in the day time. But should the higher amplifications become necessary, we bring the mechanical or the little hand-lamp into play. The German student's will still do service in the lighting up generally of the work-table at intervals. For the showing of such objects as the Nos. 18, 19, and 20 of the Moller plate by lamplight, of course the little hand-lamp, or the lower model mechanical is impera- tively employed, especially when the Wenham " reflex " illuminator is selected. There remains yet another method of sunlight illumina- tion which will be found useful at times. I refer to the use of the* 'reflex" illuminator with direct sun-light. In this case the solar beam can be received through a closed window (quite a boon in the winter season) and reflected from the plane mirror. This illumination is only suitable for work with wide apertures, and ever the most minute objects, and the mount must be free from surrounding objects of a coarse character, else, from the extremely oblique character of the illumina- tion these stronger and coarser objects will project their strong shadows across the field, causing nothing but contusion and chaos. With the genuine form of the Wenham " reflex " an epithelial scale would hardly be recognized were there several in the field. The princi- 192 HOW TO SEE WITH THE MICROSCOPE. pal advantage in the use of the " reflex " with sunlight is in arriving at a knowledge of surface markings, and for this purpose it is indeed very valuable. Thus work- ing the " reflex " by sunlight, the mirror must be manip- ulated so as to produce the same effects as have been described by moving the hand-lamp and conversely. The mirror may be substituted for the hand-lamp when working in the evening, but the most favorable results are obtained with the light direct. This reflex and sun- light illumination is especially desirable when one wishes to trace out structure situated in one particular plane^ to the exclusion of that lying in adjacent planes. In the general squabble to produce the so-called penetra- tion, this very important item has been lost sight of. We are now ready to consider a matter which has been alluded to on a preceding page. It has been already stated that the maximum performance of ad- justable objectives can only be secured when such object- glasses are worked at the point of their maximum aper- ture, and that this point is by no means a fixture but varies with different objectives. Every observer should then ascertain for himself as to the proper handling of his object-glasses in this particular. Methods will now be given which, although but approximate, are suffi- ciently precise for the use of the practical manipulator. For the purpose of testing the point of maximum aperture for object-glasses having apertures, say from 40 to 175, proceed thus: Place the objective in posi- tion on any good stand having a thin stage and mirror attached to radial arm. Commence by focussing any ARTIFICIAL LIGHT. 193 suitable object on the stage, with the mirror in a central position, the collar of the objective being set at the ex- tremity of its range. Now, by degrees, swing the radial bar carrying the mirror, meanwhile adjusting the mirror so as to secure all the illumination possible, just as would occur in arranging for greater obliquity of illumination, until the obliquity of the light becomes as great as the objective will bear; i. e., until the greatest degree of obliquity has been obtained that will secure a tolerably well-lighted field. Now move the radial bar a little, and but a little further from axis, meeting this change by the proper manipulation of the mirror, and so as still to secure all possible light. The object now ought not to have more than one-fourth the usual illumination, but should nevertheless be distinctly seen. Next, revolve the collar and notice the effect. If you get less and less light as the collar is turned towards the other extremity of its range, it would show that it was already at the point of its maximum aperture ; on the contrary, should you get more light, it will be apparent that the aper- ture increases as the collar is turned, and thus turning the collar by degrees, move also the radial bar still fur- ther from axis, manipulating the mirror as before, and to the same end, and so proceed as long as the change of the collar gives more light. You have then, by simple inspection of the position of the adjustment, a tolerable idea where the maximum of the objective is to be found. Note this : Now remove the object, place the stand in a horizontal position, and, without changing the adjustment of the objective, proceed to measure its 13 Microscopy. 194 HOW TO SEE WITH THE MICROSCOPE. angle by the method previously given. Note again the angle obtained. Next, change the collar adjustment a division or two, and again measure the aperture. Com- paring results, it will become obvious which of these two positions of the collar corresponded to the larger angle. Should the latter measure prove the least, it will be necessary to reverse the movement of the col- lar, placing it a division or two from the previous posi- tion but in the reverse direction, and by a few measures of this kind, which, by the way, are quickly accom- plished, the point in the collar adjustment correspond- ing to the maximum aperture on the glass will be ascer- tained with considerable precision. In the method just described the primary object was to get an approximate idea as to the point of largest aperture, and with the least outlay of time, and subsequently, by actual trial, to arrive at a more precise determination. The whole process involves but little outlay of time, ten minutes being quite sufficient for the purpose. With objectives of high balsam angles it will be neces- sary to employ th6 genuine Wenham " reflex " illumina- tor (angle of facet 26). With this instrument proceed as has already been advised until, by the lateral move- ment of the lamp at either the extremes, right or left, the illumination commences to die away, the field being blue or red, according to the position of the lamp. It will generally be a saving of time to start with the collar of the objective at " closed." Having found the best position for the lamp, as we have before directed, move it still a little further laterally until the field of ARTIFICIAL LIGHT. 195 the instrument shall only be illuminated sufficiently to enable you to see your object distinctly. Now, keeping things thus, revolve the collar, and notice the effect on the illumination, and thus, as in the case already presented, you have the means of judging as to the aperture of the objective. And as an example I now relate a bit of experience not twenty-four hours old : We have just had in hand an objective claiming to have high balsam angle, and we desire to know some- thing about it. First, we look to its working distance and find that it will work through covers one-fiftieth of an inch thick, its distance is therefore ample. Applying the Wenham " reflex " we test as to aperture, and pre- cisely as has been above described, thereby learning that its greatest angle occurs when the systems are at "closed." We find, too, that as the collar is revolved towards the " open point," the angle goes down rapidly. We therefore conclude that to work this glass at its maximum performance it will be necessary to use covers thick enough to cause the objective to "correct" at or near " closed.' 5 It will take but a moment to try the actual experiment, aud to see if theory holds good in practice. For this 'purpose we place the "reflex" in position and the No. 20 of the balsam Moller plate on the stage, making immersion contact with water. Next, we attempt the resolution of the shell, and with the best manipulations at our command succeed in getting but a tolerable show of the striae. I have the blue field in hand, with the lamp at the extremest point to the left: the best display being thus obtained, as the lamp 196 HOW TO SEE WITH THE MICROSCOPE. was thus shoved to the left the definition was improved, but we were compelled to desist from this movement owing to the loss of light, and were therefore content with the lamp as far to the left as was possible without sacrifice of the illumination. Of course the objective was adjusted with all possible care, the collar standing within three divisions from " open point." We now carefully raise the objective, and removing the water with a bit of blotting paper, we substitute a drop of glycerine, focussing and adjusting the glass again with the glycerine intermedium ; the glass now ad- justs at nearly closed, the collar having made nearly two full revolutions from its former position. It is further obvious that we have now more light generally; we can, too, move the lamp to a greater distance right or left without loss of illumination. In fact, things in the tube have a sunshine appearance that is very accept- able. We now attempt again the resolution of the same shell, using the blue field as before. Finding that the lamp will bear to be shoved further to the left than before. And now, even before arriving at the limit of light, i. e., the lamp not so far to the left as we might place it, we are rewarded by a splendid display of the transverse striae, this, too, with illumination, I was going to say in excess, at all events enough to allow the use of the one-halt and the one-fourth solid eye-pieces. We have thus described this experience taken from our private practice, giving the actual results obtained. Well, now, suppose that with the Wenham reflex the experiment had turned out a total failure; i. e., that we ARTIFICIAL LIGHT. 197 could get no light through the objective, showing that in this case the accessory was a reflex and no mistake ; or, suppose that our best efforts were only rewarded by a dim view of the diatom seen doubled up endwise amid a plexus of indeterminate undefinable diffraction lines, the entire field miserably illuminated, of a muggy, smoky, dingy yellow, as if a piece of yellow flannel had been used in place of the lamp, and that we could only get this much in just one solitary position of the lamp ; then the experimsnt is quite as interesting, quite as valuable, and if made in due time will amply repay its cost. As a matter of course, the lower the balsam aperture the lower will be the grade of its work with the " re- flex ;" nevertheless, the point of maximum performance can be ascertained by the method above given, and in the testing of object-glasses I make it a point to look after the balsam angle and the point of maximum aper- ture at the same sitting, the only additional trouble involved being the change in the thickness of cover, or, as in the instance named, substituting glycerine in place of water. We have entered into these details, feeling assured that the facts are worth knowing, and that many there be who have not given these things due attention. Of those who have visited us, eight out of ten saw the work- ing of the "reflex" lor the first time, while without exception all have seemed greatly pleased and interested with such comparative experiments as we have just de- scribed. Let the reader rest a moment here and I will relate a little incident : 198 HOW TO SEE WITH THE MICROSCOPE. Not long since I was honored with a call from a gen- tleman who had put himself to some little trouble in visiting Cleveland. Said he: "I have been for some time desirous of visiting you ; I have read all your ar- ticles in the journals, and have been permitted to read your letters to our mutual friend, . I want to know something more about the " balsam angle " business; ditto, about the " 180"; I confess these ex- treme apertures seem to me " impossible"; and then, again, we have high authority that the true aperture of any object-glass cannot exceed 120 and the assertion is fortified with reasoning that I cannot well dodge. I have brought with me an excellent glass purporting to have corrected angle up to 140, and would like to have some comparisons made with your own. I am after the facts, and have no personal bias in any direction," etc., etc. He also went on to state that Mr. Wenham had expressly asserted that direct light could be obtained with the " reflex." At his suggestion I showed him the No. 18 of the balsam Moller probbe plate illumina- ted with the genuine " reflex." The field was brilliantly lighted with just enough of the blue in to take off the intensity of the glare. The shell appeared without sen- sible distortion, edges sharp and clean, and with a full stand of lines from end to end. Revolving the stage so as to place the saxonica in a diagonal position, we had little difficulty in obtaining simultaneous views of both transverse and longitudinal strise, thus cutting the valve into checks or squares. The same little hand-lamp was used, and we had nice shows with eye-pieces up to the one-fourth inch. ARTIFICIAL LIGHT. 199 My visitor was- delighted, nor did he attempt to con- ceal his delight. " Now," said he, "just keep all things just as they are, but take off your glass and put on mine." The same was accordingly done, and the result was that we could not see the diatom at all, nor could we, by the best possible manipulation of the Limp, see it well enough to recognize it. I suggested the possi- bility that the glass might not be truly centered, and thus to some extent be defeated. Attention was there- fore given to this, but without avail. My friend's ob- jective positively refused to have anything to do with the reflex illuminator. Now, I have found, by countless experiments, that of two objectives, the one working well with the genuine " reflex," and another refusing to so work at all, the former will be far the superior glass for any and all work; a fact which, after a little subsequent experi- ment my visitor was not slow to accept. I am of course referring to objectives generally known under the ap- pellation of " high powers." Thus it will be seen that the Wenham " reflex " is for any of these purposes quite a handy and effective little instrument, and ought to have its place in the accessory box of every microscopist. It will serve, too, in its legitimate capacity as designed by its inventor, i. e as a " dark ground illuminator;" but herein will be found its least value. To return directly to our subject: I cannot too strongly recommend that every one inter- ested in microscopical work requiring the employment of high amplifications with fine defining power, should 200 HOW TO SEE WITH THE MICROSCOPE. study their objectives, and if for the sake of practice only, those of their friends to which they can have access. There is no time lost in this occupation ; on the other hand, it will usually result in economy of time. For instance, if your glass totally refuses to asso- ciate with the genuine " reflex," you are hereby informed that such a glass is totally unfit for any such purpose as resolving the last numbers of the Moller probbe plate, or for any kind of duty requiring the recognition of lines as close as 80,000 to the inch. Thus, by the method described you can, in less than ten or fifteen minutes time, settle definitely any such question as to the capacity of your object-glass. This matter is suggestive, and with the reader's per- mission I desire to " switch off on a side track " again, for we have " an ax to grind." We often, yea, almost every day, hear those who regard the study of objectives as one worth attention, roundly condemned by workers in natural history, biology, etc. The former are said to be " only diatom crackers," wlio do nothing but fool away their time over difficult diatoms, and are said to have angular aperture " on the brain." Now, reader, when you shall be permitted to peep behind the curtain as often as I have had the chance in the past (which, by the way, I have improved), you will find that the very gentlemen who make all this hue and cry are the very ones who have been and still are " fooling away" their time. You will find, as a rule, that each and every one of them have their little cabinet of " difficult tests," over which they spend (sub rosa) night after night in ARTIFICIAL LIGHT. 201 an absurd attempt to display the hateful markings ; an attempt, too, as futile and puny as that of the child who cries for a piece of the moon. And why? Simply be- cause the object-glass employed is not suited to the work in hand. Nor is the picture overdrawn, as more than one lady can attest, or the " looker on in Venice " vouch for. To all such, to all who value the microscope as an aid to scientific investigation, let me urge the importance of studying well the nature, capacity and capabilities of the objective, and to this end, and in the special line we have been discussing, the Wenham " reflex" will prove itself a valuable and important accessory, and a time saver of the very first water. CHAPTER VI. CHOICE OF OBJECTIVES FOR REGULAR WORK. Practically, for the past four years, we have confined ourselves to the use of four object-glasses, namely, an inch or two-thirds inch of 45 or 50. A one-half inch of 38. A one-sixth immersion, balsam angle ranging from, say 87 to 95, according to the position of its collar, and a one-tenth immersion having a constant angle of 100. Of the last two glasses, the one-sixth has a working distance of one-fiftieth of an inch. The one-tenth will work readily through covers one-one- hundredth of an inch thick. The orthodox theory has been, and I suppose still is, that each worker ought to select his stand, objectives,, accessories, etc., with special reference to the particular line of investigations he may elect to pursue; and since, as before intimated, there may be more or less force attached to such a platform, I neither accept it nor reject it; nor am I " on the fence," halting between two con- flicting opinions. Without going into any special dis- cussion of the pros or cons, we will proceed to state the character of the work in which we have been engaged, accompanied with a recital of the special methods, etc., employed. First; we use the microscope constantly from January to December in examination of urinary deposits, and for the study and detection of malignant growths. In CHOICE OF OBJECTIVES FOE REGULAR WORK. 203 conjunction therewith the aid of medical chemistry is constantly sought, especially in the diagnosis of renal diseases. Work of this description is continually on the tapis " all the year round." In addition to this we use the instrument as a necessary aid in our daily lec- tures, and for the private instruction of students at the college on matters pertaining to our Chair of Histology and Microscopy. Besides these duties we have more or less private instruction entirely outside of the college to attend to. The range of work then to be accom- plished is by no means a narrow one, and anything in the way of instrumentation that would assist either teacher or pupil will find at all times in my laboratory a ready market. We thus state the character of the work we have in hand, and also the instrumentation employed for its ac- complishment; perhaps a leaf or two from our daily practice may prove acceptable, and with this hope we proceed : We have said that a large amount of our work is over urinary deposits. For this purpose we use the " histological " stand of Mr. Zentmayer, the tube short and the stage level. Nine physicians out of ten engaged in similar examinations use their instruments in an in- clined position, covering their preliminary mounts, absorbing the superfluous moisture with a bit of blot- ting paper, employing, too, an objective as high as the one-fourth, or perhaps higher. Now nine-tenths of all work of this description can be accomplished with a wide angled inch or two-thirds, and by keeping the tube short 204 HOW TO SEE WITH THE MICROSCOPE. and the stage level there will be found, in ninety-live cases out of the hundred no necessity for covering the mount. I simply place on a clean glass slide a drop of the specimen to be examined and, without covering it at nil, place the same on the stage, the spring clips being turned back out of the way, for even these are a draw- back to rapid work. It will be often necessary to use re-agents, and to this end the long working distance .affords every facility. With this two-thirds or the inch I ivm enabled, by eye-piecing, to get nice definition up, say to 200 or 250 diameters. Here we have & practical ad- vantage arising from the use of a high -angled glass, and one of the greatest value. In thus being able to dispense with the use of covers a wonderful saving of time is accomplished; the objective, too, is far enough out of the way, so that it does not become clouded by the evaporation, nor injured by the fumes of the re-agents. Any desirable change in amplification that can ordina- rily occur is furnished instantly by changing the e}'e- piece. And here let me say that the oculars should slip in and out of the tube just as easily as possible without decentering the object viewed. A tight fitting eye-piece is an abomination of the first order; any ocular of mine will drop out of the tube instantly by tipping the stand " upside down." Now the advantage of the short tube is this: You are enabled to work over a table of the ordinary height, and to view your object comfortably, at the same time the table forms a very acceptable rest for the forearm ; on the other hand, by keeping the tube its standard length one must use a lower table, and the CHOICE OF OBJECTIVES FOR REGULAR WORK. 205 rest for the arms can no longer be obtained unless some recourse be had to blocking up by books and the like. Now in an examination involving three or four hours' time, it is quite possible that it may be desirable to sub- stitute in the place of the two-thirds a glass that will give higher amplifications. In this case the two-third would be removed'and the one-sixth called on to take its place. Now I have previously found out that the one- sixth has maximum performance when worked over the thickest covers. These I have already selected and placed in a little box by themselves, one of which is carefully cleaned and placed over my object, the micro- scope tube pulled out to the standard length, the instru- ment inclined to a suitable angle, and thus the exam- ination goes on. In extreme cases the one-tenth would be again substituted for the one-sixth. With this glass, having as it has, maximum performance at any point f its cover adjustment, there need be no particular care exercised as to the selection of the cover, further than to see that the same be thin enough. It will be noticed that with the employment of the immersions the tube should be restored to the standard length. This is an important item, and should never be omitted when there is nice work in hand. These wide- apertured glasses are especially intended by the optician to be worked with tubes of standard lengths. The range of collar adjustment, too, is in many instances arranged conformably thereto. In observations over urinary deposits I contrive to do a great deal of work with the one-half inch. Of the 206 HOW TO SEE WITH THE MICROSCOPE. two, the two-thirds or the wide-angled inch is much the superior glass ; but I value these so highly that I dread to use them over the fumes of chemicals. Hence I make the cheaper glass do all that I possibly can, and in this kind of a way the glass is really useful to me. It will doubtless be observed that in changing from the inch or two-thirds to the one-sixth or one-tenth I make a pretty big jump. This has often occurred to me, and has led to the trial of several intermediate powers, resulting in every instance in my going back to first principles; we are still of the notion that a No. 1, four-tenths, or say three-tenths of the very highest aperture possible, would be a valuable glass in the lab- oratory, especially in such examinations as those of urinary deposits or histological work generally, and we hope before long to own just such a glass, which, if a success, shall not be allowed to le glass. Nor need one hunt long or dig very deep to find other " authorities" teaching that all this handling" " although essential to the optician" is no manner of use to the practical observer, unless he has so far degenerated as to aspire to the distinction of being simply a " handler " and a " fighter." Let the author, then, and in view of the situation as presented, inform those proposing to study the microscope with the intention of becoming in due time accomplished observers, that there is no " royal road " to success ; that to become even so sufficiently expert as to enable one to follow out (leaving original work out of considera- tion) the investigations already made and published by eminent microscopists, will require quite as much effort and study as would be called for in graduating from any college in the United States. The curriculum is a broad one in its very nature, involving a thorough knowledge of instrumentation, and when by means thereof we are enabled to see well, it then becomes a positive necessity to judge well of what is seen, and this in turn can only be well accomplished by those having eyes well trained to the work in hand. There is, moreover, work for the brain outside of the functions of the optic nerve. In the micrographic dictionary, by Messrs. Griffith & Henfrey, I find, (page 11,) the following: " Above all. WOKK WITH THE HIGHER " POWERS." 237 however, it must never be forgotten that microscopic investigations require more time and patience than per- haps any others, even in regard to the determination of simple facts of structure and qualitative composition ; and although it is not very uncommon to hear those en- gaged in them sneered at as wasting their time over a very simple plaything, this may be regarded as arising from one of those prejudices which will exist so long as people will venture to express opinions upon matters with which they are unacquainted, and which are beyond their comprehension." The above quotation is well worth reprinting on its intrinsic merits, and it may be that we shall find some especial use for it bye-and-bye. Meanwhile, this mat- ter of eye training calls for a word or two, for, among the accomplishments tha/t go to make the first class ob- server, this education of the eye. is generally supposed to be quite as much a myth as the capacity to " handle " an object glass. Let us take an item or two from our personal experience : Not long since the author had the honor to address a select party of gentlemen at the parlors of a private residence. In the course of his remarks the matter of " eye-training " was brought prominently forward and its usefulness urgently insisted on. Subsequent to the close thereof a gentlemen present stepped up to him, saying, " I want a little talk with you about that eye business, which you seem to regard as a sine qua non. I do not see that thing as you do. You and I are about the same age. We have both of us necessarily been 238 HOW TO SEE WITH THE MICKOSCOPE. using our eyes constantly all our days. If I look across the street and see a house, why, so can you; and thus we have been respectively seeing houses as well as other things all through life. In short, our eyes have been constantly at work, and have thus been as constantly trained. It may be that you have abused yours by over work with the microscope if that be the case, I reckon mine have the best of it. At all events, I can't see how you can establish any individual superiority as to vision." At this moment Prof. Huber had seated himself at the piano and was entertaining the company by his superb renderings from classical authors. In reply, I said: what you affirm as to the eye must be similarly true of the hands. Prof. Huber and yourself are apparently of the same age, and both of you have been using your hands " all your days." Whence comes that lightning rapidity of action; that wondrous delicacy of touch? Think you that the professor has abused his muscles by over work with his five finger exercises, or that you have any claim to digital superiority? But to confine the case strictly to the eye alone; how comes it that the mariner can, not only detect a " sail " near the distant horizon, but can also state with accuracy whether it be a ship, brig, or schooner, and the direction the " sail" may be pursuing, to all of which the passengers present will be totally blind? Noi need we " go to sea " to find instances illustrative of the issue in hand. The eye of the artist recognizes, perforce of his experience with the esthetics ot nature, WORK WITH THE HIGHER " POWERS." 239 beauties, to which that of the shepherd boy is innocently enough a stranger, and of the two, permit me to inquire which would make the better rnicroscopist? As far as our auditor is concerned, we rest the issue on its merits. A few years ago we purchased for a gentleman well known in microscope circles, a wide apertured objective. The party was no novice, but on the contrary a real hard and close worker with the instrument; and fur- thermore, the gentleman had formerly filled the chair of microscopy in one of our most honored colleges. After working with this glass for about one year, he applied to me for instruction in the use of this instru- ment, proposing to spend his vacation with me, and for this purpose the author was delighted with the proposal and the arrangement was consummated by unanimous consent. Now the main point actuating my honored pupil was this : He had used his glass considerably enough to discover that there were conditions involved that he could not control as he desired. Sometimes he could see better than at others; sometimes the glass would work good naturedly, and then again, at others, it wouldn't work well. In the course of instruction which followed, a slide of navicula rkomboides was se- lected (this, by the way, was a diatom) and placed on the stand for examination with the objective named. In point of " difficulty" these shells would have been regarded as average specimens. We then look some little time to explain as well as we could the behavior of the object glass when in and out of adjustment, as 240 HOW TO SEE WITH THE MICROSCOPE . exhibited by the object selected. Our reason for mak- ing at this time the particular selection was this : When the objective was in perfect adjustment, the striae were admirably well seen when the inch ocular was employed,, but were assumed to be invisible under the two inch. Next, the pupil was required to adjust the object glass using the two-inch ocular only, acting, of course, under the general instructions he had received. This done he was to apply the higher eye-piece and learn of his suc- cess, practically. Our friend went at his task manfully, and fought that slide of diatoms three hours or more daily for more than a full week, constantly improving in its manipulations. Then it occurred that, getting somewhat weary of his protracted efforts over one and the same slide, he began to beg for a change to do some- thing else. Nevertheless, he was put off time after time, until nearly at the close of a long evening's work he jumped up from his table, and running towards me, his eyes beaming with joy, exclaimed, " I have it! I see it! It's all plain sailing now!" "Well," said I> "what is it?" He replied, " I can see any shell on that slide, I care not how small nor how close the striae, and as well with the two-inch ocular as with any other; and more than that, I can put the correction collar right on the dot without humming or hawing, and do it every time." To this we responded: " You have now solved your problem, and are ready to tackle another mount at our next sitting. Now, reader, here is a practical case in point: My pupil had not only been improving himself in the "hand- WORK WITH THE HIGHER "POWERS." 241 ling " of the object glass, but all this time his eye was becoming educated. At the commencement it would have been an utter impossibility for him to have recog- nized the striae of the rhomboides with but the two- inch eye-piece, nevertheless the writer saw them splen- didly, and with that exquisite definition which per- tains only to the work of these high-angled glasses. Had 1 told my pupil this at the start, he would proba- bly have received the assertion in a becoming manner, meanwhile entertaining some " first class doubts " under his sleeve;" full fledged doubts, too, and simply wait- ing for a fine day to fly. Place the microscope in the hands of the shepherd boy ; its total defeat is established. Adjust, if you will, The objective with the utmost nicety, and arrange the illumination to perfection, and total defeat still reigns tiiumphant. He neither has the capacity of seeing well nor of judging well of what may be seen, neverthe- less, he can honestly and innocently look you squarely in the face and assert that he has as good a pair of eyes ' as the next man." We have thus taken some little pains, and hope not without profit to the reader, to establish a fact well knwn to all who are expert in the use of the microscope. If our views are correct, it obtains that no inconsider- able amount of time and patient care and study are each individual elements in the outlay necessary in the effort to become an accomplished observer, and if this is to be considered in the light of an evil, then let it be remem- bered that " there are no evils unless attended with Microscopy 16 242 HOW TO SEE WITH THE MICROSCOPE. some corresponding good." And fortunate it is, in the case before us, there is a fascination accompanying the intelligent use of the microscope knowing neither limit nor bounds, and the task of becoming well acquainted with the use of the instrument is merely a labor of love. There is another aspect of the matter which deserves a word or two, to wit: The popular idea with many is, that if there be a certain amount of eye training essen- tial in the use of the " high powers," this has no appli- cation to those who use the lower amplifications. Says one, " you are all right about your ey^ education when there is such nice work as showing the 19th band in hand ; but then you see most of my work is done with the inch, and that's quite another thing." Now there is just as much error here, but it is of a less serious character. The truth is, the expert can see more with the inch, and by the "expert" I mean (for the time being) those referred to who are able to display hand- somely such tests as the 19th band. Every day expe- rience with pupils in the laboratory demonstrate this fact pointedly. Thus: At the commencement of his practice, the novice is quite content with the meanest French triplet the premises afford, but in less than a month he will hold it in perfect contempt, and his sub- sequent progress will to a great extent be properly measured or indexed by the constantly increasing capa- city to handle even these non-adjusting glasses. In thus insisting on the necessity of the proper edu- cation of the eye, let us look for a moment to its im- portant bearing on a particular class of observations. WORK WITH THE HIGHER " POWERS." 243 We intended to refer to this bye-and-bye, but it finds an appropriate place right here. We may, however, refer to it at some future time. I allude to that class of work intimately connected with the use of object glasses of wide apertures, and over exceedingly difficult lined structures; for instance, 'the display of the stride of amphipleura pellucida. But let the reader remember that this class of work is not confined to the study of diatoms. To illustrate what we have in hand, reference is made to the following sketch : Let C-D and G-H be a sec- tional view of some " difficult " diatom, such as amphr pleura pellucida or the like, the short lines 1, 2, 3, 4 ? etc., representing in section the elevations of the striae; M and N being views " in plan" as seen conditionally in the microscope. Let us first consider the effect of illuminating C-D with direct central light, as indicated by the line A-B. The effect will be as shown in plan at N, to wit : There will appear but a series of exceed- ingly fine lines; so fine (mark the words, not necessa- rily close) that it will be impossible to see them with any glass extant. Recourse must then be had to " ob- lique illumination." Now let C-D, as duplicated at G-H, be illuminated by the oblique beam E-F. The effect of this is shown in section at 1', 2', 3', etc., and in plan at K, where we have the view as displayed in the microscope. Here we have tAVO things successfully accomplished; the strise which in the former case were so " fine " as to be invisible have now become broad and can easily be distinguished by the eye ; and, secondly, 244 WORK WITH THE HIGHER " POWERS." 245 this last display is as false, as to many it has been ac- ceptable. Now let down the obliquity of the illumina- tion, as indicated by the line I-J; the effect is noted on the sketch at L, and with a first class high balsam angled objective and an eye well trained, it may be that the striae are not only discernable in the microscope, but the observer will further be able to note the intervening spaces also; and this, too, which the certain knowledge that of the varying condition set forth, the latter dis- play is not only the most satisfactory in general terms, but the most truthful. It is also apparent that the more we decrease the angle of the illuminating beam the louder the call on' the defining power of the object glass and the greater the demand for education on the part of the eye. In other words, the expert, all other things being equal, with a pair of eyes trained by long practice in his profession, has the better chance of see- ing things as they actually are. From the illustration given we deduce several propositions, viz: First, it is always better to see structure somehow than not at all. Let those addicted solely to the use of narrow apertures ponder this well. Secondly, when engaged in investigations of " diffi- cult" structure similar to the case presented, and calling at the best for light of considerable obliquity, the less of the obliquity, as a rule, and within certain limits, the better ; and the more perfect the education of the eye the less will be the call above mentioned. Third, the higher the balsam angle of the glass the LESS will be the obliquity required. Let those who 246 HOW TO SEE WITH THE MICROSCOPE. favor work with centrally disposed light make a note ol this. Says one (alluding to the second proposition), I don't exactly see that thing as you do. Suppose, for instance, that the objective and the eye were both so perfect as to allow the illumination to become axial, as in your first illustration, wouldn't that be better still? We reply, ask the artist if he would prefer the land- scape thus lighted. The architect of the universe ex- pressly arranged ^things to prevent such a catastrophe. A certain amount of shade is as necessary as that of light. Such a thing as " dead central illumination," although often talked about, is a myth. Feeling deeply the importance of calling the atten- tion of the reader to an element which we regard as of O vital importance, we have accordingly done so at the risk of being somewhat tedious. POSITION OF OBSERVER. Our experience is, that in sixty cases out of the hun- dred, having made some preliminary examination of an object under study, and thus demonstrating the neces- sity of the use of higher amplifications, that with the latter comes also the necessity of a long and protracted sitting ; in fact a downright seige is inaugurated. It is better in all such cases to postpone work until evening, or at least so to arrange that the observer shall have perfect immunity trom interruptions of any nature; and at the commencement of such work it is of para- mount importance that the operator adopt such a posi- PO6ITIO^ OF OBSERVER. 247 tion at the work table as will allow him to observe for hours without serious fatigue. Such a table as has already been recommended, with two front drawers, will be just what is wanted. The novice is here re- minded that in working with the higher powers, after having placed the object in position under the objective, the latter being correctly adjusted, there will be no longer use for the coarse adjustment. Having, then, our table, place the chair adjacent thereto, but in place of putting its front edge parallel to the front of the table, as is generally done, turn the chair to the right until the front and left-hand sides form equal angles with the front of the table, the angular point formed by the meeting of the front and left-hand edges of the chair being adjacent to the table. Now let the observer seat himself, placing the shank of the left shoe on the left-hand round of the chair. Pull out both drawers, so that the edge of these, assisted by the edge of the table, shall form a double rest for the forearm. Now place the stand in such a position, that is, with refer- ence to the front of the table, that the left hand finds its way easily to the fine adjustment, while that of the right grasps the mirror bodily, the tube being mean- while adjusted to the standard length, and the whole instrument properly inclined. Let the reader practice these directions thoroughly until he shall be able to thus sit at his instrument firmly wedged to it. It will be noticed that, once in this position, either hand can grasp the object slide for the purpose of making any neces- sary change, and without seriously disturbing the double 248 HOW TO SEE WITH THE MICROSCOPE. adjustment for the forearm, while the right hand, being thus so nicely supported, is enabled to manipulate the mirror with almost mathematical precision. At the first, as might easily be supposed, the sharp edges of the table and drawers will be a source of some little incon- venience. This can be remedied by placing a pair of napkins thereon; but the better way is to endure this slight annoyance for a little time, when the forearm will be found to have adapted itself to the situation. The position thus described we have represented as far as possible in the frontispiece, using such furniture as was at hand in the photographer's gallery This pose can be varied at times by bringing the left knee in use so that it may support the left elbow. Thus we get three rests tor the left arm, and sometimes we get the shank of the right foot on to the front round of the chair, spreading the knee open a bit and wedging it under the right hand draw. Other little changes are o o practicable and need not be detailed here. Of all the manipulations connected with the use of the higher powers, the adjustment ot the objective (sup- posing, of course, that it is a good one, one that will respond to the collar adjustment), is of pa/ramount im- portance. For reasons previously stated, two elements are involved, namely, the behavior of the object glass and the education of the eye ; and here the use of the diatommecaB is imperative. We have insisted on this for years. These little organisms are the most con- venient, and then, again, any little deviation from the perfect correction of the objective is sure to " stick out " POSITION OF OBSERVER. 249 ;and be detected. This is not the case with other objects. Show the tyro a scale of podurae under a tolerably nar- row angled one-tenth, and likewise display the same with a similar object glass of the higher balsam angles. There will be as much difference in the quality of the two exhibits as there is (I was going to say) between light and total darkness ; and yet, nevertheless, the nov- ice will be as well satisfied with the one as with the other; but let the experiment be repeated, using in the place of the podura a balsam mount of surriella gemma, both glasses doing their best, as before, and the tyro is no longer " at sea " as to his choice. Moreover, at this stage of his experience he will be fully prepared to blow his trumpet in the support of one of the most absurd and stupid errors that has ever been promulgated since the time of Adam, to wit, " High angled glasses are only fit for work over diatoms ! ! " When we say that diatoms are the most convenient objects over which to study the adjustment of the ob- jective, we mean it, and thereto attaches greater force than the casual reader may suppose. If it be imagined that these objects are " convenient" because their gen- eral proportions are about the thing because they can be purchased at slight expense, or, if preferred, pre- pared by the observer himself, or even be it granted that the markings on the more difficult of these shells will only surrender to a first-class objective in perfect adjustment, we admit the facts, but the story is not fully told. The grand, the culminating convenience attending 250 HOW TO SEE WITH THE MICROSCOPE. the use of diatoms in the study of the objectives used under high amplifications, is this : We are enabled to- display on one and the same mount, shells of the same family and species, differing only in size, and we thu^ are on the instant ready to study the work of the ob- jective over each. Now if it so be, and we make it a point that it shall so be that the smaller shell is in all respects the more difficult of the two. Then it occurs- that the student, having mastered such smaller frustule can examine at his leisure the larger ones, and with the certainty that his objective is in at least approximate adjustment; hence he is further prepared to note the difference in the behavior of the object glass over the different diatoms, and thus he arrives at items of the utmost value; all this, too, ^without any change of the mount. Still other conveniences there are attending the use of the diatom, their extreme thinness preventing the shadow of one shell from interfering with the defini- tion of another, thus getting rid of a complication which would prove of serious detriment in the early studies of the student, while by and by he can essay ai> attack on the very problem named by merely selecting sueh positions of the amount as contain the little organisms huddled together. Thus learning their char- acter and being thus forewarned, is fore-armed against the time when he shall be brought in contact with other slides presenting the same difficulty, but in a more determined manner. But let the reader note this fact. It is one thing to POSITION OF OBSERVER. 251 look at diatoms, and quite another to study them with the especial object of becoming acquainted with the behavior of the objective, while it must be admitted that there is a fascination and charm per se 9 connected with diatom examinations under the microscope. It is- equ.dly true that the student can use them legitimately and for the purpose named, without establishing any claim to the functions of the diatomist. Referring to the especial purposes we have been con- sidering, the following list of objects will amply suffice, for the study of the one-sixth or one-tenth objectives,, viz: 1. Navicular Rhomboides, Monmouth, Maine, Balsam Mount 2. Navicular Rhomboides, Cherryfleld, Balsam Mount. 3. Erustulia Saxonica, Leipsig, Germany, Balsam Mount. 4. Frustulia Saxonica, Isle of Shoals, U. S., Balsam Mount. 5. Amphipleura Pellucida, Bridge of Allan, Scotland, Balsam Mount. 6. Amphipleura Pellucida, Aberdeen, Scotland, Balsam Mount. 7. Surriella Gemma, Balsam Mount. Of the above list, Nos. 1 and 2 can readily be ob- tained of the dealers. As to the others named, Prof. H. L. Smith, of Geneva, .N. Y., has a large supply of the material, and has kindly supplied the author and his friends with excellent mounts and at figures much below the usual list prices. In addition to the diatoms, a genuine mount of English podura will be a capital thing to have on hand for occasional comparisons, but the student must on no- account select the slide himself. Poor scales are simply good for nothing, while perfect ones are held by the opticians in the highest esteem, and are constantly used 252 HOW TO SEE WITH THE MICROSCOPE. by them in the final corrections of the objective. Of all the scales of podura we have yet seen, a mount was shown us last summer by Mr. Herbert Spencer, which was perfection itself. As an index ot the value Mr. Spencer attached to this mount, I will add that he had once offered one of his first class one-tenth objectives in exchange for it I Every microscopist needs a suitable stage micrometer and very few have reliable ones. We gladly state that Prof. W. A. Rogers, of Cambridge, Mass., has after years of careful study succeeded in making rulings on glass rivaling if not excelling those of Noberl himself. Not long since Prof. Rogers ruled for us a plate, con- taining lines 100, 1,000, 2,000, 5,000, 10,000, 20,000, 40,000 and 80,000 to the inch, which was a marvel in point of accuracy and delicacy. Subsequently Prof. Rogers ruled a plate for us up to 120,000 lines to the inch. This band the author has seen well and has shown to his friends. We therefore recommend first, that every student should be possessed of a micrometer ; and secondly, that the same be procured from Prof. Rogers. It will be well while one is about it, to order a plate ruled as high as 80,000 to the inch, inasmuch as the cost is not materially enhanced, the plate will thus do double service not only as a stage micrometer, but as a test plate for the comparison and study of objec- tives. In this connection the reader will remember that we have advised that eye-piece micrometers be ruled 600 lines to the inch. Hence, if our advice is followed, let the stage micrometer have a similar band. POSITION OF OBSERVER. 253 The positive convenience resulting from this in the measurement of the focal length of objectives by the method previously described is too obvious to need further comment. The series of graduated diatoms by Moller of Wedel, Germany, and generally known as the Moller test Plate, is now to be found in the cabinet of nearly every uiicroscopist, and can be advantageously supple- mented to the list above given. A table showing the mean of the measurement of ten of these plates will be now furnished and thus the plate can on a pinch be made to do approximate duty as a stage micrometer. MEAN OF TEN MEASUREMENTS OF MOLLER TEST PLATES,. BY PROF. E. W. MORELEY, M. D., OF HUDSON, OHIO. 1. Triceratium Favus 3.1to 4. 2. Pinnularia Nobilis 11.7 to 14. 3. Navicula Lyra , 14.5 to 18. 4. Navicula Lyra 23.0 to 30.5. 5. Pinnularia Interrupta 25.5 to 29.5. 6. Stauronesis Phoemcenteron 31. to 36.5. 7. Grammatophora Marina 36. to 39. 8. Pleurosigma Balticum 32. to 37. 9. Pleurosigma Acurninatum 41. to 46.5. 10. Nitzschia Amphoyx 43. to 49. 11. Pleurosigma Angulatum 44. to 49. 12. Grammatophora Oceanica=G. Subtilissima 60. to 67. 13. Surriella Gemma 43. to 54. 14. Nitzschia Sigmoidea 61. to 64. 15. Pleurosigma Fasciola 55. to 58. 16. Surriella Gemma. Longitudinal 64. to 69. 17. Cymatopleura Elliptica 55. to 81. 18. Navicula Crassinervis, Frustulia Saxonica 78. to 87. 19. Nitzschia Curvula 83. to 90. 20. Amphipleura Pellucida 92. to 95. 254 HOW TO SEE WITH THE MICROSCOPE. THESE FIGURES DENOTING THE NUMBER OF LINES IN .001 OF AN ENGLISH INCH. As a matter of convenience to those having the cele- brated Nobert 19 band test plate, we present the fol- lowing tabulated values of the rulings. The first column contains the value in Paris lines. The second the number c f lines in .001 of an English inch, as ruled in the several bands. NUMBER. PARIS LINES. IN .100 ENO. IN. 1 1,000 11.26 2 1,500 16.89 3 2,000 22.52 4 2,500 28.13 5 3,000 33.78 6 3,500 39.41 7 4,000 45.04 8 4,500.... 50.67 9 5,000 56.30 10 5,f>00 61.93 11 6.000 67.56 12 6.500 73.19 13 7.000 78.82 14 7,500 84.45 15 8,000 90.08 16 8,500 95.71 17 3,000 101.34 18 9,500 106.97 19 10,000 112.60 Returning now to our original list of diatom mounts we proceed to give such a description of the same as will enable the student to approach them intelligently, iind without undue loss or waste of time. The first two slides are pretty much the same thing, both contain POSITION OF OBSERVER. 255 tine shells of navicular rhomboides, and nicely assorted as to size and "difficulty." The larger, or even the medium sized shells are easily displayed (we refer to the transverse striae) by such a glass as the Spencer dry one-fourth of 115, when nicely adjusted, while the smaller frustules are more "difficult" than the No. 18 of the Moller plate. These mounts are therfore valu- able on account of their range, and the reader has .already our reasons governing the selection thereof. When these slides are thoroughly mastered, the student will be ready to attack the Saxonica from Leipsig. These vary also, a medium shell being about as obsti- nate as the No. 18 of the Moller plate, and will defeat the Spencer one-fourth. The Saxonica from the Isle of Shoals is still more bothersome. These frustules are very small i nd very thin, and at the start the .student should select the very largest and most vigorous shell he can find on the mount, proceeding carefully as he may acquire skill, to the smaller ones, and before he can establish any claim to have mastered this slide he must be able to show the very smallest and thinnest shell acceptably. In point of "difficulty" these smaller diatoms rival the No. 19 of the Moller plate, while the .smallest and the very thinnest are a fair match for the No. 20. Of the amphipleuras, that from the " Bridge of Allan," Scotland, is the easier of the two, and should be studied first. This slide in common with the two last mentioned calls for object-glasses of high apertures. To attack them with any of the low angled glasses is but a waste of time and patience. The mount 256 HOW TO SEE WITH THE MICROSCOPE. of surriella gemma is selected for reasons very much akin to the mention that has been made of podura. These shells are not suited for the purpose of study, but are admirably adapted for comparisons. The actual structure of this diatom is yet a matter sub judice. Now let us go back again to the first mounts named in the list. We have had occasion before to assert that one of the advantages resulting from the study of di- atoms is due to the fact that the student in mastering one of the smaller and more difficult ones becomes fortified as to the adjustment of his glass. Supposing then that by some good luck he has succeeded in dis- playing the smaller frustules of the Monmouth or Cherry field. He can return to the larger shells with tolerable assurance that his glass is in fair correction. But mark this. In order to show the little fellows, there was need of greater obliquity of illumination, which, when return shall be made to the larger shells can profitably be dispensed with. Now although the slide of diatoms offer special conveniences, let the student adopt this line of study, no matter what may be the character of the object under his objective, select- ing the most obscure and diaphanous structure possi- ble to bring into the field, and making sure that there is a sufficiency of oblique illumination. From what has been said it may be adduced as a gen- eral rule that it is advisable to study the corrections of the objective by the aid of oblique light, and over the finest structure the mount can be made to exhibit, and POSITION OF OBSERVEH. 257 to the beginner no better advice can be given. It is simply impossible for the novice to study the correc- tions of a high angled object-glass by centrally disposed illumination. In the selection of the ohjects recommended to the student, we have been governed by these and similar considerations. All of the slides named contain frus- tules requiring the use of light at least 40 from axis r and the student will in his first attempts be compelled to go considerably higher than that figure. The exact amount of obliquity essential to the best display he can possibly make, will depend on his object-glass the cor- rectness of its adjustment, and the education of his eye. We shall, on some succeeding page have a few words to say as to the management, etc., of high balsam apertures by centrally disposed light. With this one exception only, anything that we may have to offer in the way of instruction bearing on the use of these glasses will be confined to the study of the diatoms which have been presented. The student who can properly display the seven mounts to which his atten- tion has been invited, together with the Moller plate and the podura, can safely be allowed to shift for him- self. We, however, fear that our ability to teach this much will not now keep pace with our sincere desire. Competent, or incompetent, we propose to try. A singular fact it is, that among all the works thus far written on the microscope not one word of instruction can be found as to the management of objectives of Microscopy 17 258 HOW TO SEE WITH THE MICROSCOPE. wide apertures. It is therefore high time that some one k< assume the judicial." Any endeavor on the part of anyone to teach the management of wide apertured object-glasses must in the nature of things be incom- plete, and at the best but approximative. Notably so as to written instructions, no two objectives work exactly alike, and appearances in the field will be mod- ified by the individual corrections of the particular glass employed. Of two objectives, one may be supe- rior to the other. Hence the student not being a con- noisseur becomes environed with doubts that the ex- pert might easily cause to vanish by a little personal interference. Object-glasses, too, wcrk differently over different objects. The appearance of a dry mounted object is characteristically at variance with the appear- ances presented by balsam mounts, and here is our reason for selecting in every instance the latter for the instruction of the beginner. Neither is it possible for the professional philologist by mere force of word pic- turing to convey to the mind of the learner just what may be desired. And even should the teacher be fortu- nate enough to employ the most accurate descriptions language can afford, then he has no assurance of being perfectly understood by the pupil. The author being no philologist, and having but a little command of language desirous of using none other than the simplest words, thus adapting this little book to the compre- hension of all, can but essay his best and only hope for partial success. A word or two further before we proceed with our POSITION OF OBSERVER. 259 tuition. The remark is often of late made, "what does all this talk about the handling " of objectives mean? Are we to understand that the real work of the micro- scopist consists in the resolution of a few diatoms, or the exhibition of the rulings of the 19thNobert band? To this we reply, that all this is implied and a very great deal more ; it means that the microscopist shall know as much of the microscope as it is expected of the engineer to know of his level or transit. In O geodesy the value of entire systems of costly triangu- lations are wholly dependent on the accuracy of the original base line, and in a similar manner is the work of the microscopist affected. We often hear old ob- servers claim that all work worth having with the microscope is accomplished with amplifications less than 300 diameters ; and then again the scientific contribu- tions resulting from the use of the finest English objec- tives in the hands of physicists like Professors Tyndall and Huxley dependent on amplifications of 5,000 and 6,000 diameters, have been seriously called in question, yea, disputed by those working with objectives not worth the weight of their brass mountings! We repeat, that it is eminently the business of the would- be microscopist to know all that can be known of his instrument ; if, when he has to an acceptable extent ac- quired this knowledge, if so be that he prefers not to devote his time and microscope to investigation, he has the satisfaction of being conscious that what was done was well done. Had the engineers employed in meas- uring the original base on which the coast survey was 260 HOW TO SEE WITH THE MICROSCOPE. founded, chosen to have abandoned the work on the completion of the base, there would have been no time lost or wasted ; per contra, had the base been but im- perfectly measured, and the engineers proceeded to build the other triangles resting thereon, they would not long have continued in the service, but would have been furnished with palpable reasons for leaving! Again, the question is ofttimes asked, do you require that the observer shall be familiar enough with his ob- jective as to work it up to the same force as its maker could? Its the legitimate business of the optician, and he can thus afford to spend his time on a matter which to him is a necessity, but to demand this much of the practical observer seems uncalled for. In answer to this oft-repeated remark, we wish it distinctly under- stood that it is eminently the business of the observer to fully understand the practical woiking of his objec- tives. The man who cannot make his object-glass per- form as well as when in the hands of its maker, is using an instrument that he does not fully understand, of which the fact becomes incontestible proof. If it be necessary that the optician be able to work an objec- tive to its maximum, it is imperative that the micro- scopist should do as much. Until this shall be the case, absurdities will abound. Take for instance a con- dition that often occurs. The microscopist orders a new objective from the optician. The specifications are complete, and the glass is made conformably thereto. In due time the purchaser receives his glass, and can do nothing with it, and it is returned in high dungeon to POSITION OF OBSERVES. 261 its maker. And why? Simply because the purchaser was as incompetent to " handle " the instrument, as perchance he might have been to manipulate a piano- forte or church organ. And then again through his ignorance he might have possibly ordered the very glass he did not want. What would we say to the invalid who on summoning the attendance of the physi- cian should undertake to dictate as to the treatment! Again, we have often been requested b}' our friends and visitors to examine objectives and give our opinion thereon ; and, as a rule, five minutes Avill suffice for this. But, says the owner, "you must be prejudiced against my glass. No man could give a well grounded opinion in the few moments you have occupied." Nevertheless, we have given hundreds of just such opinions without having had occasion to modify or retract, and here is an illustration showing that time spent in the study of objectives is neither totally lost nor without its compen- sations. We reiterate, let the microscopist understand well his tools, and in the hope of being at least some assistance to the student we are ready to proceed with our instructions. In the lessons which follow the reader is presumed to employ a wide apertured one-fifth, one-sixth or one- tenth immersion. We shall try, as far as possible, to make them applicable to the use of any good glass hav- ing air angle up to 175. The higher balsam angles will, however, when attainable, be the better instrument, with which, too, the instructions will be the better un- derstood. The student is also reminded that with the 262 HOW TO SEE WITH THE MICROSCOPE. particular objective he may employ he may be in some measure defeated in his efforts; still we have to hope that his endeavors will not result in time " totally lost." Lesson First. Place the mount of Monmouth rhom- boids on the stand, select the two-inch ocular, mak- ing immersion contact with water or glycerine, as has previously been directed. Place the collar of the ad- justment in the middle of its run ; use the light from the smallest kerosene hand lamp, placing the same about seven inches to the left of the stage, the flame to be on a level with the same, edgewise to the mirror, and two inches in advance of the front edge thereof. Removing all sub-stage appliances, swing the radial bar so that the mirror shall give illumination, say from 70 axis; ma- nipulate so fts to light up the field, using about one-half the sized flame your lamp will allow. Now focus, and having taken a general look at the " tout ensemble," select a frustule somewhat below a medium one in size, and bring to the centre of the field, the valve in a hor- izontal position. Now focus again carefully, adjusting the mirror so as to get the very best view attainable. Now study for a moment the general character of the image. Notice particularly if there be any distortion, or whether the two ends are more or less indistinct or obscured. Slide the object carrier and hunt up several other shells and examine individually, that ;you may be assured that you have a fair specimen to deal with. Next, notice the edges of the valve ; compare the upper with the under; note if these are tolerably clean and POSITION OF OBSERVER. 263 sharp, or whether they are more or less woolley. Com- pare the median line with the upper and lower edges. Manipulate the fine adjustment and notice as to any change of focus necessary as between the edges and the median line; study this median line well, and you will probably detect a shadow from it shading, but only per- haps slightly, the lower entire half of the shell. Grasp the mirror firmly and change its position (not the radial arm) a little in every direction, meanwhile studying the effect of the shadow on the lower half of the frustule. Hunt up other frustules and study them in like man- ner, changing the focus from time to time as may be necessary. Selecting an average shell, and placing the same in the centre of the field, and focus sharply. Having ar- ranged the mirror to the best advantage, grasp the collar of the objective with the fingers of the right hand (which now leaves the mirror just as it was), those of the left hand being in contact with the fine adjustment, withdraw the eye for an instant and turn the collar of the adjustment briskly nearly a full half revolution; placing again the eye in position, focus quickly and sharply. Now undertake to decide instantly as to the effects produced. Is there more or less distortion at the ends of the shell than before? How are the edges? Cleaner and sharper, or the reverse? How is that shadow below the median line? Does it shade the en- tire half of the valve more than was the case formerly, or has it consolidated itself to a narrow band under the median line? If you find the least trouble in assuring 264 HOW TO SEE WITH THE MICROSCOPE. yourself instantly, repeat the program me until you can. Now, reader, one-half hour conscientiously spent at this exercise will assist you more than a half year of pro- miscuous practice. Let me advise you to hang- well to it. You must learn to judge instantly as to the appear- ances to which your attention has been called, nor can the least " guess-work" be allowed. Well, now, premising that you have had sufficient of this practice, so that you are able to assert, without fear of contradiction, that after the turn of the collar adjust- ment, there was, as we will assume, evidently more dis- tortion noticeable at the ends of the valve, nor were the edges as sharply defined, (it may be that one edge cannot now be seen without specially focussing therefor.) The shadow, too, under the median line is not only en- tirely over the entire lower half of the shell, but it has become deeper and more offensive than before. The fact, then, becomes apparent that you turned the collar in the wrong direction. Therefore, place the adjust- ment in its original position ; look your shell well over, thus to fortify yourself. It will be well, now, to repeat the experiment, selecting various valves of the rhom- boides, and, having become accustomed to the change in appearances, then you may try many of the other diatoms to be found on the mount. No matter what particular one may be selected, you will in due time be able to note the characteristic effect of this change in the adjustment. Lesson Second. Having replaced the collar adjust- ment to its first position, and selecting a tolerably small POSITION OF OBSERVER. 265 shell of the rhomboides, place it in the centre of the field, the focus well adjusted, etc. Devote a few mo- ments to a general consideration of the nature of the changes wrought by the turn of the collar. Endeavor to gather up, as it were, the experience gained by les- son first. This done, removing the eye for a moment, turn the adjustment in an opposite direction to that of lesson first, but not so far in extent, and immediately looking through the tube, adjust again the focus, and if necessary adjust also the mirror until the best view of the shell shall be obtained. Now if the preceding lesson has been well studied, the learner ought to recognize a decided improvement, and there ought, withal, to be more general brilliancy to the image. The shell should, so to speak, lay flatter in the field. In short, things ought to assume an encouraging .appearance. Repeat the experiment several times, but with greater or lesser changes of the collar adjustment, until you arrive at a particular point in the adjustment which seems to be about the thing. Having thus deter- mined this point, the student may now, by way of en- couragement, shift the position of the object carrier and bring one of the larger shells to the centre of the field, when, with a slight alteration of the mirror, he will probably be rewarded with a fair view of the trans- verse strife. Assuming this to be so, let the student examine progressively other and smaller frustules, and selecting one of the very smallest that he can see, bring it to the centre of the field. Lesson Third. Replace the collar to the initial po- 266 HOW TO SEE WITH THE MICROSCOPE. sition, as per lesson second, focus your new shell and 1 examine it critically, as has already been directed ; next* repeat the turn of the collar, in the same direction, but varying the extent of the movement, focussing' again as before. Bye-and-bye, when the collar shall have been turned to approximately the correct place, the striae will of course be again visible, and it is more than probable will be even better seen than before. If this shall be the case, try, by slight manipulations of the mirror alone, to obtain the very best display of the lines. And we now approach close work. If the eyes are tired, or the general condition of health be below par, it will be better, if any further work be determined upon, to go back and take a review of what has already been accom- plished ; but on the other hand, if conditions are gen- erally favorable, proceed thus : Lesson Fourth. With your frustule as nicely exhi- bited as possible, the shell selected being as small as you can successfully attack to show well the striae, examine it well closely; see if the upper and under edge are both equally well in focus. It may be that one edge is- much better defined than the other, or it may be that one edge cannot be seen at all. This indicates that the valve lies side wise in the balsam, in which event discard the shell and hunt up another that lies exactly flat, and of the same size. Now work over this diatom, generally as you have been instructed in the foregoing lessons, accepting the position you now have of the adjustment as the base of farther trials. Change the collar to the right or left. POSITION OF OBSERVER. 267 noticing all the points to which your attention has been called ; but these various changes of the collar should be much less limited in extent. We have now further items for you to observe. Examine the strice carefully; see if they continue quite to the edge of the shell, or do- they stop a little short thereof, the edge becoming as clear, sharp and distinct as that of a razor. Look with an eagle eye, too, into that shadow under the median line. Has it become almost self-luminous and trans- parent? And has it drawn itself upwards and together, forming a narrow but brilliant band (so to speak) ad- jacent to the under side of the median line? Have all appearances of diffraction lines left? Does the shell lay well down and flat? All of these interrogatories must receive your devoted attention. When things are just right, the valve laying flat iiu the balsam, the striae will not quite extend to the edge of the shell. The dark band under the median line will be contracted as described, but in the place of the former dark and muggy shadow, it will have become lively and brilliant. Ditto, as to all the other shadows- seen in the field. In fact, everything has improved, be- it a diatom or a patch of dirt. The edge of your shell ought to be sharply distinguishable, not by a line of varying thickness, for there is no line there, and there- fore you ought not to see anything of the kind. If the adjustment be a trifle out, it will sometimes occur that the valve will seem to "rise up;" i. e., appear nearer to the eye than it should. It is impossible to describe- on paper just what I mean by this. I have no trouble, 268 HOW TO SEE WITH THE MICROSCOPE. however, in getting- pupils to appreciate this phenome- non. This effect is the more palpable under a high oc- ular, say the one-fourth inch. Let the student try the highest one he has, and he will notice that a slight change of the collar will cause the shell to " lay down " prop- erly. But he must nevertheless be able to make this correction from noticing the condition when employing the two-inch eye-piece. And here it may be observed that with different objectives some leeway must be allowed. It is hardly probable that the student can take his particular object glass and follow me to the very letter; or is it even certain that the author could, with said glass, demonstrate to an expert what has been written in these instructions ; yet after allowing due and proper margin, the hints presented must prove of value, and if we could have been told as much eight years ago it would have saved us hours and hours of the toughest work. And right here a thought presents itself, for- eign, perhaps, to these lessons, but let it go on record, namely : If it be so that we can assist the student, we have in very truth no mean reward for time spent in the past in the study of object glasses. Lesson Fifth. Having noted the division correspond- ing to the exact adjustment of your objective, so that you shall be able to place the collar at the right spot at once, without loss of time, leave the rhomboides and examine your mount generally. Notice the play of light and shade over the several diatoms. Hunt up those por- tions of the slide containing a mass of the larger forms huddled together; in other places you will probably POSITION OF OBSERVER. 269 find sediment congregated together in little colonies, the O O O coarser particles throwing an individual shadow over the others. Observe these appearances closely. Now place the collar intentionally out of adjustment (prefer- ably opening the systems), and thus look over your mount again. See, how the shadows have become mixed up! What a labyrinth there is to be sure! A perfect plexus of indeterminable, indefinable shadows proceed- ing from nowhere and ending nowhere. The thickened edges of the diatoms seem to cast a shadow on their own account. Notice, too, how that some of these large shells seem to have become badly distorted. Find those little colonies again, and note that the individual particles thereof have lost their brilliancy have become muggy and indefinite. Here, too, are all sorts of shad- ows, and more or less confusion generally. Return,, now the collar to its proper place and review your mount. Now, see how things have improved in general brilliancy ; see how the shadows have become harnessed properly into the traces. You can trace them now, and get an idea of what they mean, where they came from,, and where they end. Look at the little colonies once more. Now they are all alive with brilliancy and sparkle like very diamonds. When the student feels that he can follow me thus far, let him study the tone of his objective. This will depend on the object-glass employed. All superfine objectives should be under corrected, i. e., there should be a preponderance of the blue; but hardly any two good objectives are exactly alike, some being under- 270 HOW TO SEE WITH THE MICKOSCOPE. corrected to a greater extent than others.* Whatever may be the correction of a given object-glass, there will be a corresponding tone to the field, and it's the business of the learner not only to know the fact but to be competent to recognize the characteristic appear- ance presented not by the particular object viewed alone, but by the entire field of view. And here again comes some nice eye work. The artist can look at the landscape and recognize the very "atmosphere" not so the shepherd's boy. The former might talk until dooms-day to the latter as to " atmosphere." Now every good object-glass has an "atmosphere" of its own, peculiar to itself, and depending on the individual corrections of the glass. A moment's con- templation of the situation teaches the difficulty attend- ing any effort on the part of the author to make him- self understood so as to be of service to the learner. Nevertheless, the attempt shall be made. Lesson Sixth. Place the shell of rhomboides exactly in- the centre of the field, and adjust the object-glass. Arrange the mirror with its radial bar, so as to illumi- nate at about 45 or 50 from axis. Focussing sharply, examine well your diatom as to color; the chances are that both blue and red are to be observed. Select in turn several shells and thus examine, and finally in- spect all the objects on the mount before mentioned. A little patient attention will teach you that there is something apparently clue to the blue that does not attach to the red. For instance, the shells may have a slight lavender tint ; as soon as one can detect any- POSITION OF OBSERVER. 271 thing in this way that is presumed to be characteristic, then put the object-glass out of adjustment and focus- sing anew make the comparison. If the student has hit the proper effect, he will notice that with the glass out of adjustment, said effect has vanished. Should (as will most probably be the case with his first efforts) he fail to mark any characteristic difference in color or tint, replace the collar adjustment and repeat the ex- periment; selecting, as near as he can judge, some "probability," and again throwing the glass out of proper adjustment examine again. The process must be repeated time after time until the end shall be gained. When by dint of practice the learner begins to feel that he " sees the point" let him in a similar manner examine all of the other diatoms on the mount until he shall have become perfectly familiar with the tone of his objective. Lesson Seventh. Having mastered tolerably well the previous instructions, let the learner now turn his atten- tion to the tone of his field. This is a finer "point" than that of the preceding lesson, and demands in turn more of the eye-training. The problem is in all respects similar to that concerning the tone of the objective, differing in this one element only. The student must now endeavor to recognize a particular tone to the whole field when the object glass is in per- fect adjustment. The instructions are quite of the character as those of the last lesson, an 1 need not be repeated. The two lessons might have been reduced to one, were it not that a little practice on the former 272 HOAV TO SEE WITH THE MICROSCOPE, will, and for the reason named, be advantageous before studying the tone of the field. These last two lessons should not only be well studied, but the student ought constantly to endeavor to improve in his recognition of tone. Once having become tolerably, I may say, com- fortably expert, its practice becomes a second nature and will be persisted in from choice, meanwhile the observer becoming daily more and more proficient. This characteristic tone of the field is more apparent in objectives of the highest balsam angles, with the super-excellent object-glasses of the Messrs. Spencer or Mr. Tolles, when the glass is exactly in correction, the tone of the field becomes a peculiar and exceedingly delicate shade of apple green, which one soon learns to. recognize by aid of the teacher. In the studies we have thus far presented, and which ought to enlist the occasional attention of the pupil for at least a month or six weeks, it is taken for granted that he will meanwhile use the instrument as he may elect, and either for pleasure or such profit as he can arrive at on his own account. There will undoubtedly be other objects brought into requisition not named in our lists. Now, whatever practice he may have of this description, there are some general conditions concern- ing high-angled objectives which ought not to be un- heeded, for example, let the learner discover as near as possible the point ot the maximum aperture of his glass ; it will be well, too, that he pay attention as to thickness of the covers used. These two points have a direct bearing on the pupil's progress and must not be- neglected. POSITION OF OBSERVER. 273 Hand the expert a strange mount of the Monmouth or Cherryfield rhomboides. It is possible for him with- out looking at it, and by the sense of feeling alone to state thus: " This slide cannot be used with the one- tenth and glycerine contact. Use water and with the collar nearly at closed. If the one-sixth be employed use glycerine, and the objective will correct within four or five divisions from the closed point." Either statement being found on the actual test or trial to be the fact. In truth, any such statement from the expert founded on his sense of feeling alone would be worth more than two hours spent over the tube by the novice. Hence the importance of the learner's acquiring the same tact (" knack " is the popular word), nor is there anything so very difficult in its acquisition. Lesson Eighth. Returning to the slide of Monmouth Rhomboides, and choosing a frustule somewhat larger than a medium one, place it in the centre of the field, adjusting the objective, and displaying the striae, em- ploying an obliquity of say 70 from axis. Next rotate the stage through an arc of 45 ; if necessary centre the object again. It will now have assumed a position in- termediate between the horizontal and the vertical. Attempt, by slight changes in the position of the mirror, to display simultaneously both sets of lines. The inch ocular may now be substituted in place of the two inch. To do this nicely, getting both sets with equal force, requires indeed some little " knack." The collar ad- justment being already correct, the manipulation will entirely be confined to the illumination. Possibly it 18 Microscopy. 274 HOW TO SEE WITH THE MICROSCOPE. may be well to shove the lamp a little farther away from you ; i. e., a little more in advance of the front edge of the stage, or perhaps raising or lowering the wick, thus increasing or diminishing the amount of light, may be of service. This is all that can be written, and the learner must simply make the most of and help himself. Rest assured that both sets of lines are there, and if it be that they are not shown, the diatom is not to blame. In case of total failure the observer may select one of the larger shells, proceeding to the smaller one? carefully and by degrees. With the illumination at present employed he cannot expect thus to show both sets on frustules smaller than a medium one. After having mastered, as well as may be, the Monmouth, substitute the Cherryfield, readjusting the objective, as a matter of course. There now remain, for future consideration, on the slides of Monmouth and the Cherryfield, the smallest frustules of the rhomboides. These we will pass over for the present, and in the next lesson proceed to attack the Saxonicas, from Leipsic, Germany. Lesson Ninth. The student will recognize the frus- tules on this slide by their similarity to the two slides preceding. The valves are on an average smaller and thinner, and in consequence weaker objects to deal with ; as the saying is, they are more " difficult." Select one of the largest and most vigorous shells ; bring to the centre of the field, and, employing the inch ocular, focus, the illumination being about 70 from axis. Now ex- amine closely your diatom, and see if you can bring POSITION OF OBSERVEK. 275 your past experience to bear. Without attempting- to observe as to the striae, reckon up the general appear- ances and form some verdict as to whether the glass is in adjustment. If you decide that it is not, make up your mind to what extent. This done, proceed, if ne- cessary, to adjust, following the directions already given, bearing now in mind that all the phenomena previously described will be much fainter and less decided than was the case of the Cherryfield or the Monmouth. Let the student assure himself that the shell before him lays perfectly flat in the balsam. If this is not the case, it will be impossible to see both the upper and under edges simultaneously. These frustules are ex- tremely thin, and when one edge is the lower of the two in the mounting medium, it will appear to vanish out of sight. Accepting that the diatom is a favorable one for study, the learner will notice that the upper and lower edges, as the adjustment approaches the proper position, behave better than was the case with the Cher- ryfield or the Monmouth. This is owing, of course, to the diaphanous character of the Leipsic. He will there- fore endeavor to render these edges considerably sharper and cleaner than could possibly have been the case when working over the former slides. Let the pupil observe closely the behavior of the shadow under the median line. As has already been remarked, the effects are quite similar, but in a less marked degree. The eye must be educated to the situation. Notice, too, that as the ad- justment becomes more perfect this shadow contracts, assuming the form of a narrow band immediately adja- 276 HOW TO SEE WITH THE MICROSCOPE. cent to the median line, while the entire lower half of the shell is of a lower tone than that of the upper. Should the tryo have got along- thus far tolerably well, it is more than probable that he will have been rewarded by at least a glimpse of the transverse striae. He may now, by minute changes of the mirror, and by raising or lowering the wick of the lamp, endeavor to show the markings as strongly (that's a bad word) as neatly as possible. Having thus succeeded, look sharply and see if the lines extend quite to the edges of the frustule ; it may be that some of them will be found to project ; in either case something is wrong. Look first to the illumination, and, observing the shadow line under the median line, endeavor to contract and render this as narrow as possible. If this does not prevent the striae from showing to the extreme edges of this valve, then recourse must be had to slight alterations in the position of the collar adjustment. It may be advisable to try a stronger ocular, say the " D " solid, if one is at hand. If under this the lines seem to " rise," try and correct this, as before instructed. This apparent "rising" will perhaps strike the reader as something novel. Certain it is that we have never seen anything of the kind in print. The effect was, however, noticed long ago by the author, and it soon became one of his " points" in the tuition of his pupils, the latter, at the onset, seldom ever get his meaning. Nevertheless, in a very little time they " see it " plain enough. We have not command of a word that will precisely and accurately express what we desire. It POSITION OF OBSERVER. 277 may be advantageous to the student if we repeat ejacu- lations such as are heard from scholars, thus : " I can't make this shell lay down." " I have a tolerably good show, but the valve is restless." " You seem to anchor your diatoms; mine are all out at sea." "The valve will float in spite of me." "I have it; the shell lays as quiet as a summer morn." "This valve seems to come right up to the eye-piece," (referring generally to the one-half or one-fourth inch.) Such and similar ex- pressions we have heard over and over again. The student can select the one that will be of the most service. The tone of the objective should be studied with the Leipsig, just as has before been noticed when discussing the Monmouth and the Cherryfield. The observer may, at the commencement, entertain the notion that in re- gard to tone, the objective behaves very differently when over the more difficult mount. If, however, the pre- ceding lessons have become perfectly familiar there will be but little trouble in recognizing the same peculiar and characteristic tone not only pervading the valve, but the entire field of the instrument. Suppose, now, that the manipulator, having followed the author with satisfactory success through the Mon- mouth and the Cherryfield, should fail thus to do when the Leipsig is taken in hand, thus: There appears a cer- tain indistinctness accompanying the images of the latter, besides, the valves seeui considerably distorted, and the band of light behaves badly; so much so that the direc- tions cannot be followed with any degree of certainty, 278 HOW TO SEE WITH THE MICROSCOPE. and that several trials have been ineffectually made ; all of which lead to the same result. In this case the prob- abilities are that the objective is at fault, and that any attempt to work it by anyone, however expert, will only result in a waste of time. . The student ought not to decide definitely until by practice he shall be entirely competent to judge for himself. We mention the fact here, because we know full well that some who may read these pages will try and follow the author, employ- ing such objectives as they may have at hand. Now it might occur that an object glass capable of showing a medium Cherryfield or a Monmouth very well indeed, even cutting the larger shells into checks or squares, responding, too, to all the conditions we have presented, and yet entirely fail when worked over any but an ex- ceptionally large shell of the Leipsig. It may be apropos hereto discuss another point which is suggested as we write: It will be noticed that all along- in the course of these lessons we have made it obli X 0.50, 228 = unity. Use of the standard solution in the ordinary testing for sugar. The practitioner will very often have occa- sion to simply test for the presence of sugar, when the exact amount is not necessary. In fact, after becoming thoroughly familiar with the behavior of the chemicals, he will be enabled to give a close guess as to quantity. The urine should in all cases be cleared from albumen. To merely detect the presence of sugar it is only neces- sary to pour a dozen drops or so of the copper solution into one of the largest test tubes (these are always bet- ter when there is boiling to be done), and to add twice the volume of the caustic solution. Bring to the boil- APPARATUS. 337 ing- point, and add urine to the tube directly, continuing such additions and bringing' to the boiling point sub- stantially as in performing the regular analysis. If, when the amount of urine thus introduced shall be equal to the original volume of the test solution, and there be no change of color, it may safely be assumed that sugar is not present. Even when the regular analysis is contemplated, the preliminary trial test should be instituted. For instance, we do not care to attempt the regular analysis, when by the rough test we are assured that there is no sugar in the specimen.- Again, when, by the trial test, it shall be found that sugar is present, and in large amount, then it may sometimes be better to dilute the urine with an equal, or even six times its volume of water; of course, allowing for this reduction in the computa- tions after reading the burette; the accuracy of the analysis is enhanced by the dilution ot the urine. It may be further remarked that different specimens be- have somewhat differently. The directions given will, however, be found ample, and the practitioner having frequent use for the sugar test in a short time becomes perfectly at ease with the manipulations. Analysis for Albumen. The volumetric method, one of "trial and error," involving several nitrations, is somewhat tedious ; too much so for the-practical pur- poses of the medical practitioner. The author was hence induced to experiment with the "Marais" ap- proximate tubes comparing results with those obtained by two of the regular methods. These were so far sat- 22 Microscopy. 338 HOW TO SEE WITH THE MICROSCOPE. isfactory as to lead to the employment of the approxi- mate tabes in his general practice ; and the degree of accuracy afforded by the use of these tubes is quite equal to the ordinary demands of the medical profession. The principal source of error arises, as we believe, from the fact that the coagulated albumen will at times pack closer in the tube than at others. By using three or four tubes in one and the same analysis, taking the mean of the results, the approximate process will, in most instances, be all that can be desired. Proceed as follows: In a clean evaporating dish, or a Florence flask, coag- ulate by heat three fluid ounces of the urine to be tested; set aside until nearly cold; shake, well; now take three marais tubes, fill the first full, also the second with the treated urine and coagulum ; pour the Temainder into the third tube, rinsing the dish with a little water, adding the wash to the several tubes. The three tubes can be thus made to contain the entire coagulum from the three ounces of urine; set aside for twenty-four hours, after which time read the several tubes ; add the readings together and divide by three, and every two whole cubic centimetres will represent one grain of albumen to the ounce of urine. In the daily routine it will often suffice to use but one tube, in which case all that is necessary will be to coagulate a single fluid ounce of the urine; when cool, shake, and pour into the approximate tube, rinsing the dish as before, adding the wash to the tube ; at the end of twenty-four hours read off the amount of coagulum ; APPARATUS. 339 every two whole c. c. will equal one grain of albumen to the ounce of albumen. Reaction. Urines being at times either acid, neutral, or alkaline, it is often interesting, not only to observe as to the fact, but also as to the degree of acidity or alkalinity; to accomplish this prepare the following solutions: Test Solution for Acidity. In 1,000 grains of dis- tilled water dissolve ten grains of pure hydrate of soda. Test Solution for Alkalinity . In 1,000 grains of distilled water dissolve 15.75 grains of pure oxalic acid. Equal volumes of these two solutions will exactly neu- tralize each other. To Test the Degree of Acidity in a Sample of Urine. Fill the burette with the soda solution ; measure one- halt fluid ounce of the urine into a wine-glass ; deliver the soda from the burette into this a few drops at a time, stirring well after each addition and testing with litmus paper; when the mixture fails to affect the latter, read the burette twice, the figures read will indi- cate the number of grains of the solution employed required to neutralize a fluid ounce of the urine. To test for alkalinity proceed as above, using the acid solu- tion in place of the soda, and also red litmus paper in place of the blue. The daily variations in any particu- lar case can in this manner be determined and recorded. Proportion per tluid Ounce of certain of the Urinary Constituents. The estimates given in this part of the table are roughly ap- proximative, and represent the widest variations consistent with 340 HOW TO SEE WITH THE MICROSCOPE. normal conditions. The variations, always considerable, are particularly marked as regards the uric acid . Urea 6'50 to 10'50 grains. Chlorine (1*30 to 3'60 s rs. of chloride of sodium) 0'80 " 2'15 Sulphuric acid (1-30 to 3'20 grs. of sulphates) 0'66 " T62 ** Phosphoric acid (2- 10 to 4'00 grs. of phosphates) 1'17 2'25 " Do do combined with alkalies (phosphate of soda and phosphate of magnesia) 0'78 ** T40 " Do do combined with earths (phosphate of lime and ammonio-magnesian phos- phate) 0-39 " 0'85 * Uric acid (0.40 to 0-70 grs. of urates) 0'23 " 0'40 " TABLE FOB REDUCING THE INDICATIONS OP A GLASS UBINOMETEB TO STANDARD TEMPERATURE (60 Fahr.) WHEN THE SPECIFIC GRAVITY HAS BEEN TAKEN AT A HIGHER TEMPERATURE. (BlHD, Urinary Deposits. etc., Philadelphia, 1859 p. 7J.) Tempera- ture and degree. 60 61 62 63 64 95 66 No. to be added to the indi- cation. o-oo 0-08 0-16 0-24 0-32 0-40 0'50 0-70 Tempera- ture and degree. No, to be added to the indi- cation. Tempera- ture and degree. No. to be added to the indi- cation. 69 0-80 78 1-70 70 0.90 79 1-80 71 1-00 80 1-90 72 1-10 81 2-00 73 1-20 82 2-10 74 1-30 83 2-20 75 1-40 84 2-30 76 1-50 85 2-40 77 1-60 APPENDIX. As a matter of convenience to the student we present the addresses of American dealers in Microscope Stands, Objectives, etc. The list is compiled from the various catalogues and other sources of information which hap- pened to be in our possession. It is therefore probably incomplete, but nevertheless will be found to comprise most, if not all of the leading dealers. Of the latter, those marked with an Asterisk (*) issue illustrated cat- alogues, which can be obtained on application, free of expense : NAMES AND ADDRESS OF DEALERS IN MICROSCOPES, OBJECT- IVES, ETC., ALPHABETICALLY ARRANGED. (*)Bausch & Lomb Optical Company, 37 Maiden Lane, New York; factory at Rochester, New York. (*)R. & J. Beck, (London); American Agency in charge of W. H. Walmsley, Chestnut street, Philadel- phia, Pa. (*)W. H. Bulloch, 126 Clark street, Chicago, 111. F. J. Emmerich (Importer), 38 Maiden Lane, New York. E. Gundlach, L. R. Sextcn, agent, Rochester, New York. (*)T. H. McAllister, 49 Nassau street, New York. Pike (Dealer), 518 Broadway, New York. 341 342 HOW TO SEE WITH THE MICROSCOPE. (*)James W. Queen & Co., 924 Chestnut street, Phil- adelphia, Pa. William A. Kogers (Micrometer Plates, etc.,) Cam- bridge, Mass. (*)Messrs. C. A. Spencer & Sons, (Objectives, Ac- cessories, etc.,) Geneva New York. L. Schraner, 50 Chatham street, New York. (*)J. W. Sidle & Co., Lancaster, Pa. (*)Robert B. Tolles, Hanover street, Boston, Mass. Charles Stodder, Agent, Devonshire street, Boston, Mass. (*)George Wale, Patterson, N. J. George Wale & Co., Hoboken, N. J., Agents. (*) William Wales, Fort Lee, New Jersey. (*)Joseph Zentmayer, 147 South Fourth street, Phil- adelphia, Pa. The following price list of stands, etc., is only in- tended to include those previously described in this book. Several of the makers therein mentioned manu- facture various models not included in our list. The stands ot the Messrs. Spencer's have been intention- ally omitted, as we learn that they are now devoting their entire attention to the production of objectives. The list of objectives is similarly incomplete. With the glasses of Messrs. Tolles and Spencer we have had a large experience. Several months ago the Messrs. Bausch & Lomb sent us a line of their objectives for study, all of which, after working with the same more or less for nearly a year, proved reliable glasses for their cost. APPENDIX. 343 The entire list may be understood to include only such objectives as we have used to a greater or less extent in practical work, and of which we can therefore speak from experience, and without prejudice to other reliable makers. We earnestly advise the student contemplating the purchase of object glasses, especially when ordering the same to be made by the optician, to seek the advice of some expert friend. Protection is thus afforded both to the maker and the buyer, and it has often happened that the latter, through sheer incompetency, returns a really fine glass to its maker, with the assertion that it has proved unsatisfactory. While on the other hand, especially in glasses of high balsam angles, there IS a choice in the work of the very best makers. The ex- pert, too, will render valuable assistance in specifying the exact kind of objective desired. MICROSCOPE STANDS, BY W. H. BULLOCH, NO. 126 CLARK STREET, CHICAGO, ILL. Large best stand, Al, binocular, iris diaphragn, with the latest improvements, draw-tube, 5 eye pieces $300 00 Same as above, but monocular, iris diaphragm, with three eye pieces 250 00 Polished mahogany case, with side case for accessories. 25 00 Small best stand, A. B., binocular, 4 eye pieces and iris diaphragm 225 00 Monocular, two eye pieces and iris diaphragm 175 00 Polished mahogony case 20 00 " D " stand, all brass, 2 eye pieces and case 75 00 " D " stand, all brass except the base, 2 eye pieces and case.., 67 00 344 HOW TO SEE WITH THE MICROSCOPE. MICROSCOPES AND OBJECTIVES BY THE BAUSCH & LOMB OPTICAL COMPANY. The Professional Microscope, with the following acces- sories : Hemispherical immersion condenser and ob- lique light projector, plain and concave mirrors, sub- stage, receiving accessories of standard English size, two revolving diaphragms, sub-stage with internal *' society screw," 2 slot diaphragms for mirror, 3 Gund- lach's periscopic eye pieces (B, C and D), four object- ives, viz : 2-inch, l-5th inch, 3-4th inch and l-8th inch immersion, with adjustment for cover, magnifying powers from 30 to 800 diameters, eye piece micrometer, camera lucida, bull's eye condenser, the whole in upright walnut case, with handle, lock and key, and drawer for accessories $200 00 Large Student's Microscope, plain and concave mirrors, sub-stage of extra size to receive standards, English accessories, revolving diaphragm, etc., all attached to the swinging mirror bar ; sub-stage and mirror are re- movable ; three eye pieces, A, B and C, three object- ives, 2-inch, 3-4th inch and t-5th inch, magifying from 22 to 375 diameters, eye piece, micrometer, camera lucida, in upright walnut case, with handle, lock and key, and drawer for accessories 90 00 Family Microscope, concave mirror, adjustable for ob- lique light, one (B) eye piece, one first-class achromatic objective (one-half inch dividing) powers, 50 and 100 diameters, in upright walnut case, with handle, lock and key 20 00 The Messrs. Bausch & Lomb have brought out a new model which they term the Physicians' Stand, which may be thus de- scribed : Large, heavy cast iron foot, rack and pinion for coarse adjustment, draw-tube, allowing 2 1-2-inches shorten- ing, fine adjustment by a new friclionless motion, large hard rubber stage, sub-stage of standard size, carrying APPENDIX. 345 three diaphragms, which, when pushed up, will closely reach the object slide, plain and concave mirrors, ar- ranged so that their distance from the object may be varied, 2 eye pieces, A. and C, 2 objectives, 3-4ths inch and l-5th inch, magnifying powers, when the tubes are completely drawn out, from 50 to 375 diameters, eye piece, micrometer and camera lucida, in upright wal- nut case, with lock and key 60 00 The past twelve-month has witnessed unusual activity on the part of: microscope makers. Mr. Zentmayer, in the production of his " Histological," (as also the advent of the Acme Stand) stimulated other makers to increased energy in the production of small, low-priced and reliable stands capable of performing the work.of larger and costly instruments. At the late (August, 1880) meeting of the American Society of Microscopists, held at Detroit, Michigan, two medium-priced stands were exhibited which were regarded bv competent judges as being quite equal to the Acme Stand. One of these was made by Mr. Bullock, of Chicago, and its cost as near as I can learn will be about $50. The other stand referred to was exhibited by the Messrs. Bausch & Lomb, of Rochester, N. Y. It is called the tw Inves- tigator." Messrs. B. & L, have furnished the author with the following description of THE INVESTIGATOR MICROSCOPE. In this stand we confidently claim to have reached a higher degree of perfection than is possessed by any one approximat- ing it in price. We have combined in it the qualities of a first-class and high-priced stand, and at no sacrifice of its working qualities. The different parts are ingeniously com- bined, are strong and firm, and in the parts subject to friction we have introduced, as much as possible, new compensating bearings, which insure the retention of smooth and reliable movements with any amount of work. Working microscopists will understand the value of this quality. When contracted it stands but 11 high, but can be extended to 18 inches. 346 HOAV TO SEE WITH THE MICROSCOPE. The base is of the tripod form, neatly japanned ; pillar and arm of brass, connected by a solid joint, which allows inclina- tion of body to any angle; rack and pinion for coarse adjust- ment, tine adjustment by our patent frictionless motion ; main tube with two draw tubes. This is an entirely new feature in microscopes, which is an unquestionable improvement. It per- mits the use of standard length of tube for quick adjustment in outside tube, same as in instruments without rack and pinion adjustment ; the same for any low power objective and the use of amplifier in either combination. The outside tube has ,a broad gauged screw, and adapter with society screw. The stage lies in the same plane as center of movement for mirror, is of brass, and has concentric, revolving motion with removable clips. It is thin to allow great obliquty, and as it rests upon a strong projecting arm, is perfectly firm under any manipulation. The mirror bar swings with a perfectly easy but firm motion, upon one bearing to any obliquity below, and above the stage for the illumination of opaque objects, and has affixed to it a secondary bar, to which the mirror is attached and which allows the separate use of the latter in any position of the sub-stage. It is provided with a sliding arrangement, whereby the mirror may be moved to and from the object. The mirrors are plain and concave, and of large size. The substage is adjustable along the mirror bar, and entire removable. It contains a diaphragm which may be brought directly under the stage. The- ring is of standard size and is easily centered by a set screw. The stand is furnished with an eye piece of any power. In black walnut case, with receptacles for eye pieces and objectives, drawer for accessories, handle and lock, price $40.00. Same, with C Eye Piece, arranged for micrometer, camera lucida, micrometer, 3-4 inch and 1-5 inch objectives, $65.00. BAUSCH & LOME OBJECTIVES. Deg. Price. 2inch 18 $1200 2inch 12 600 linch 36 2000 linen. . 20 6 (K> APPENDIX. 347 Deg. Price. 3-4inch 27 800 l-2inch 72 2200 1-2 inch 40 9 00 4-10 100 20 00 3-10 75 11 00 1-4 100 .', 14 00 1-5 108 1500 1-6 inch 180 Adjusting 30 00 1-8 Immersion 180 Adjusting 4000 MICROSCOPES OF THE MESSRS. R. & J. BECK, OF LONDON. AMERICAN AGENCY IN CHARGE OF W. H. WALMSLEY, ESQ , 1016 CHESTNUT STREET, PHILADELPHIA, PA. Popular Microscope stand, binocular, with one pair of eye pieces, concave mirror, diaphragm, forceps, glass plate, pliers, etc $6500 Same, but monocular 40 00 Economic Microscope, as furnished by the makers, mo- nocular, with sliding coarse adjustment, 1 inch and 1-4 inch object glasses, 1 eye piece, concave mirror, condensing lens, glass plate with ledge, brass pliers and diaphragm, in mahogany case 35 00 The same, with rack and pinion, for coarse adjustment, concave and plane mirrois, stage forceps, etc., in ma- hogany case 50 00 (Both of the above stands are fitted with fine adjust- ment screw.) Extra eye pieces, each 4 00 The Messrs. Beck have just published a large and com- plete illustrated catalogue of their microocopes and other scientific instruments, which they furnish to any one on application. Among their later models of mi- croscope stands we notice the u New National," cost- ing, with one eye piece, concave and plane mirrors, diaphragm, stage forceps, glass plate pliers, etc 40 00 Mahogany cabinet for the same 10 00 348 HOW TO SEE WITH THE MICROSCOPE. Since the chapter on stands was written we have received the following description of BECK'S INTERNATIONAL MICROSCOPE STAND. The improved large best or international microscope stand has a tripod (A) for its base, upon which is placed a revolving fitting (B), graduated to degrees, by which means the micro- scope can be turned round without its being lifted from the table, and the amount of such rotation registered ; upon this fitting two pillars are firmly fixed, and between them the limb My third improvement consists in the addition of a graduated sectorial arc to microscope concentric to the plane of the object " in, situ,"' on which either the afore- said prism or other suitable illuminator is made to slide, thereby producing every kind of illumination required for microscopic examination, and also the means of registering or applying any definite angle of illumination at pleasure." With but slight modification, this is the plan adopted in this stand. The sub-stage is also fitted with complete centering and rotat- ing adjustments, the latter having a graduated circle attached, and fittings for carrying Barker's series of selenites, blue glass disks for modifying the light, etc. In all the requirements of an instrument of precision, and fully meeting the wants of the most advanced modern workers, it is confidently believed that this new stand has no rival. The price of the International Stand, Binocular, with five eye- pieces, concave and plane mirrors, and right angle prism, stage forceps, pliers and glass plate with ledge, is . . $325.00 The price of the International Stand, Monocular, with three ye-pieces, and the same fittings as above, is, . . $275.00 (The Messrs. Beck manufacture several grades of objectives, as will be seen by reference to their published catalogue.) J. W. SIDLE & CO., LANCASTER, PA., ACME MICRO- SCOPES AND ACCESSORIES. We here quote the prices of the Acmes, and a few of the more important accessories. 3a. Acme Monocular, with brass tripod base, rotating stage, iris diaphragm and substage fitting with Society screw for using objectives as condensers ; in walnut case with lock and handle, and drawer for accessories, $ 50.00 352 HOW TO SEE WITH THE MICROSCOPE. 36. Acme Binocular, with one pair oculars, and outfit as above 75.00 3c. Acme Monocular, as above, with i objective of 32 and i of 100, and small bull's eye condenser, . . 75.00 3d. Acme Binocular, as above, with f of 32, i of 100 and bull's eye, -.' 100.00 2a. Large Acme Monocular, r6tating glass stage, sub- stage, with rack and pinion, in polished mahogany case with side case for accessories, 100.00 26. Large Acme Binocular, same as above,with addition- al nose-piece, as per circular, . . . . . 135.00 2c. Large Acme Monocular, as above, with mechanical stage and 2 pair oculars, 135.00 2cZ. Large Acme Binocular, as above, with mechanical stage and 2 pair oculars, . . . . * 170.00 PRICES OF ACCESSORIES. Mechanical stage for Acme No. 3, .... $16.00 Walnut base with lamp and adjustable stand, with brass fitting to receive lower end of pillar, converting the Ac- me into a Class Microscope, . * . . ; . . 5.50 Camera Lucida, . . . v * . . . 5.50 Neutral Tint (Beale's)^ . * .. <. -. ; . 3.00 Iris Diaphragm, .' 4.50 Sub-stage fitting for using objectives as condensers, . l.Oi) Woodward's prism, unmounted, 1.50 " " mounted to screw in stage, . . 4 00 Mechanical Stage, . 25.00 Sliding Object Carrier, fitted to stand, . . . . 4.00 Paraboloid, plain, i . ' . 8.50 Parabolic Illuminator, " . . 8.50 Polarizer for Acme, selenite screwing in stage, to rotate independently of Nichol prism, 13.50 Polarizer, best, with large prism, 18.00 Mechanical Finger, 6.50 Solid Ocular, i, i, i inch, 8.00 APPENDIX. 353 CONGRESS TURN TABLE. This table has made a reputation for itself. Retail price $6.50 PRICES OF ACME SERIES OF OBJECTIVES. 2 inch, 15 ... $13.00 ' 3-10 inch, 115 non adjust- able, . . $16.00 H " 18 ... 14.00 3-10 u 115 adjustable, 20.00 1 " 36 ... 15.00 1-4 " 100 non-adjust- able, . . 14.00 f " 32 ... 12.00 1-5 " 120 non-adjust- able, . . 16.00 f " 36 ... 15.00 1-5 " 120 adjustable, 20.00 | * 60 ... 14.00 Other lenses quoted in Catalogue. MICROSCOPE OBJECTIVES, BY MESSRS. C. A. SPENCER & SONS, GENEVA, N. Y. FIRST CLASS. Size. Deg. Price. 3inch 13 $1800 2 inch.. 20 2500 1 inch 50 4500 2-3inch 47 3200 1-2 inch 100 Adjustable 50 00 1-4 inch, dry and immersion 180 6500 1-6 inch, " " 180 7000 1-8 inch, " u 180 7000 l-lOinch, u " 180 8000 1-16 inch," " 180 11500 PROFESSIONAL SERIES. 3inch 13 $1800 2inch 16 1800 1 inch 33 1800 2-3inch 36 2000 23 Microscopy. 354 HOW TO SEE WITH THE MICROSCOPE. 1-2 inch . 65 2500 1-4 inch, Adjustable 115 24 00 1-6 inch, " 175 Dry and immersion 3400 1-8 inch, " 175 u " 40 00 1-15 inch, " 175 " " 50 00 STUDENTS' SEBIES. 3 inch 8 $6 00 2 inch 10 6 00 linch 22 1000 2-3 inch 32 , 1200 l-2inch 50 1500 1-4 inch 100 16 00 1-8 inch 135 25 00 "Wenham's Reflex Illuminator 10 00 (The Messrs. Spencer & Sons furnish a full line of goods desir- able by the microscopist, such as solid eye pieces camera lucidas, and accessories generally. Their former connection with the Optical Company has been dissolved, and they now continue business on their own account, as above stated, at Geneva, 1ST. Y.) MICROSCOPES AND OBJECTIVES, BY R. B. TOLLES, BOSTON, MASS. Tolles' Large Microscope, ' B," no objectives $225 00 Student's stand, 1 inch E. P., 1, and l-4th inch object- ives, packed in black walnut case 50 00 Additions, etc., to the above- Extra eye pieces, each 4 00 Camera lucida 5 00 Sub-stage, for accessory apparatus 5 00 Sliding stage, giving horizontal and vertical movements by hand 15 00 Fine adjustment by lever and micrometer screw 20 00 Rack and pinion for coarse ad j ustment 12 00 Draw tube 4 00 Plain mirror 3 00 Thin glass stage to rotate on the optical axis 10 00 Packing boxes for transportation, extra 1 00 APPENDIX. 355 Student's Microscope, with one inch and one - fourth inch objectives (second quality) one ocular, rack and pinion, lever, fine adjustment for focus, sub-stage for Illuminating apparatus, revolving diaphragm, plain and concave mirrors, side stand for illuminating opaque objects, black walnut case 90 00 TOLLES' FIRST CLASS OBJECTIVES. Size Degrees. Price. 1-2 inch, Angle apertured 60 to 90 $4000 4-10 .... 90 to 120 4500 4-10 u ik 135 to 145 6500 1-4 or 1-5 u " .... 120 to 130 4500 1-4 " - .... 150 55 00 1-4 4 - l - 180 70 00 1-6 ' lt 180 75 00 1-8 " " 180 80 00 1-10 " " .... 180 85 00 TOLLES' PATENT SOLID EYE PIECES. l-2inch,"D" $800 1-4 inch 8 00 Either of the above, for his Student's Microscope 6 00 Wenham's Reflex Illuminator 1000 MICROSCOPE STANDS, BY JOSEPH ZENTMAYER, 147 SOUTH FOURTH STREET, PHILADELPHIA, PA. American Centennial Stand, binocular, with 5 eye pieces $300 00 Same, but monocular, 3 eye pieces 250 00 Concentric adjustable stage, extra 20 00 Best mahogany case, with fine handle and side case 30 00 American Histological Stand, with plain and concave mirrors attached to swinging radial bar, carrying, also, sub-stage and diaphragms having three apertures, 1 (B) eye piece, no case 30 00 Extra eye pieces, each 5 00 NOTE. The following extras can be obtained of Mr. Zentmayer at the prices below given. They are fur- 356 HOW TO SEE WITH THE MICROSCOPE. nished at the suggestion of the author, who invariably orders them for his friends and pupils. The instru- ment is thus rendered efficient for all the ordinary pur- poses of the working microscopist : Supplemental revolving stage $1 00 Sub-stage adapter, to carry condenser, society screw 1 00 Eye-piece adapters, ready to carry solid cells, each 1 00 8TAC4E MICROMETERS, TEST PLATES, ETC., BY W. A. ROGERS, CAMBRIDGE MASS. Mr. Rogers has just completed his new machine, in the con- struction of which several important improvements have been secured. We cheerfully add our endorsement as to the regu- larity and delicacy of his rulings. One of his plates, ruled up to 120,000 lines to the inch, now in our possession, is a marvel of art. Owing to the extreme shallowness of Mr. Rogers' finer rulings, they are more difficult tests than similar bands by Nobert. Mr. Rogers furnishes a great variety of work. Some of his regular plates may be thus described : Stage Micrometer, consisting of 10 lines, 100, and 10 lines, 1,000 to the inch $125 Stage Micrometer, consisting of 25 lines, 200 to the inch, 10 lines, 1,000, 10 lines, 2,000, 10 lines, 4,000, 10 lines, 5,000, 10 lines, 10,000, 10 lines, 20,000, and 10 lines, 30,000 to the inch 4 00 Stage Micrometers, ruled 1,000, 10,000,20,000, 30,000, 40,000 and 50,000 to the inch 500 Same as above, to 60,000 600 " to 70 ,000, $7.00; to 80,000, $8.CO; to 90,000 900 ^ " to 100,000 1000 (Closer rulings by special contract.) Standard half-inches, with 50 subdivisions of l-100th inch and 10 subdivisions in the centre of l-100th inch : 3 00 Standard centimeters, with 100 subdivisions 4 00 (At double the above prices Mr. Rogers furnishes a complete discussion of the errors of the plates, and a APPENDIX. 357 table showing the corrections to be applied to each ruled space to reduce it to the United States standard.) Standard half metres and standard metres, either on glass, steel, iron or nickel surface, from $25.00 to 100 00 Test plates, micrometers, etc., are also ruled by Mr. Charles Fasoldt, 594 Broadway, Troy, N.Y. The author has one of Mr Fasoldt's 120,000 band plates, which he values very highly. He regrets not being able to give Mr r Fasoldt's Catalogue of Prices. SUPPLEMENT. CONTRIBUTIONS TO THE CINCINNATI MEDICAL NEWS. Inasmuch as the author's contributions during the past six years to the pages of the Cincinnati Medical News, and also the American Journal of Microscopy contain instructions more or less interesting to those commencing the study of the micro- scope, it is thought desirable to present them in this supplement. It was however found on inquiry that the back numbers ot the Cincinnati journal were not to be obtained. Dr. Blackham, of Dunkirk, N. Y.. kindly placed his bound volumes of the News in the hands of the writer, thus enabling him to give the reader the following references, dates, etc., to the several articles contained in the Medical News. 1875. January, " Microscope Objectives," p. 41 ; February " Measurements of Moller Probbe Plate," p. 92; March "Wide us. Low Angled Objectives," p. 129.; April; "Diagnosis of Blood Stains, Dr. Woodward vs. Dr! Richardson," p. 177.; April, " A Simple Method of Demonstrating Aug. Aperture," p. 1-83.; May, u Wide vs. Low Angled Objectives," p. 228.; June, " Dr. Ches- ter Morris' Reports on Objectives," p. 281.; November, " Wide vs. Low Angled Objectives," p. 515. 1876. January, kl Battle of the Object-Glasses," p. 41.; Febru- ary, " The Mic. and Its Mis-iriterpretataions," p. 86.; March, " A New Microscope Stage," p. 232.; April, "Nobert's 19th Band," p. 287.; July, " Wythe's Ampli- fiers," p. 433.; August, " Prof. J. E. Smith us. the Nachet l-5th," p. 485.; August, " Trichiniasis," p. 488. October, " Necessary Manipulation of the Microscope; to Exhibit Fine Striae," p. 533.; December, " Torula Cerevisse in Human Urine," p. 677. 358 SUPPLEMENT. 359 1877. January, " Wenham's Reflex Illuminator," p. 74.; July, " R. Hitchcock, Esq., vs. High Angles," p. 504. The past contributions to the American Journal of Microscopy will, owing to the kindness of Prof. Phin be given in full. PROF. B. HITCHCOCK VS. HIGH ANGLES. In the May number of the American Journal of Microscopy , I find an article containing a good-natured criticism of a paper read by me before the Dunkirk Microscopical Society last October. Mr. Hitchcock candidly states that he has only seen a short - abstract of this paper, and has but an imperfect knowledge of it. He further suggests that his main object was to call further attention to my views, and he suggests that I put them in form, so as to be published iu the American Journal. For the benefit of Mr. Hitchcock, I will state, that my views have been clearly stated in a series of articles, which have been published in the Cincinnati Medical News during the past three years, under the caption of " High us. Low Angles," and have thence been quoted from and reprinted in various publications ; certainly I cannot be expected to go over the ground anew at this late day. It is true that I exhibited before the Dunkirk Microscopical Society the No. 20 of the balsam Moller probe platte, and also the 19th Nobert band, both so plainly that all who were present saw without difficulty. These tests were not difficult for the glasses employed, as was attested by the fact that they were shown in a crowded room, amid the attendant jars and vibrations, my object being to demonstrate the facility with which my Tolles' duplex glasses handled these so-called difficult tests. To show the work of these same lenses by central light, I selected the same test.Nav. Angulatum which the biological committee at Philadelphia has declared impossible to be shown at a less angle than 20 degrees from axis, with any medium power glass. This test was displayed illuminated by light through a central aperture placed close to the object, just large enough to light the field, the diameter of the aperture being 360 HOW TO SEE WITH THE MICROSCOPE. about 1-200 of an inch, direct light being used, i. e., without mirror or condenser. The ease with which the duplex handled this test was made amusing and apparent by my picking up the stand, walking around the room, sitting it down again hap- hazard before the lamp, when the resolution was found by a gentleman appointed to examine to be unimpaired. This was repeated three times. Will Mr. Hitchcock repeat, using a low angle glass, be it a one-fifth or a one-fiftieth, and report? I had other tests for central light work, including histological and pathological preparations. It was impossible to show all of these to so many people as were present, as it was, the entire evening after the readingjof my paper was occupied. Hence, it will be seen that I fought the low angles on their own chosen ground, and with the express view of demonstrating that the very best preformance of the duplex lenses is seen by central light, Mr. Hitchcock further says that " the universal testimony of our best authorities, who have spent their lives in microscopical work, is against Prof Smith." It was just this kind of testimony that affirmed a few years ago, ths highest possible aperture of an object glass to be 135 degrees; that the resolution of the Nobert 19th band was a matter of faith rather than of sight, etc., etc. Mr. Hitchcock is welcome to the witnesses. Note this fact, to- wit, in original investigations, the advanced worker must necessarily be in a minority. I rejoice that some of Mr. Hitchcock's witnesses have lately found cause to change their opinions. Dr. Carpenter will no longer assert that the resolutions of the Nobert 19th band is a k ' matter of faith, rather than of sight." On the other hand, he has given unqualified endorsement to the superiority of the duplex glasses. Mr. Hitchcock desires to ask iohy I think that most of the work in histology and pathology already" done" with the so-called " working lenses" of narrow angles would require further atten- tion, and with wide angled glasses I reply, that in the past four years great advances have been made in the construction of objectives, and in the manipulation of the microscope ; what was considered a " good working glass" ten years ago, would SUPPLEMENT. 361 mow be totally valueless for advanced work. We now demand, as near as may be, perfect lenses, and superior dexterity in handling them ; and these two conditions are inseparable. The finer the objective the louder the call for expert manipulations. That well-known term, " working lenses of narrow angles" means, when stripped stark naked, easy going lenses, with no screw collar to bother ; good working lenses, that a child or sleepy adult without experience can use right along, will work through covers of common window glass, big working distance, and all that, etc., etc. Such are admirably adapted to the use of those who use the microscope as a plaything ; admirable things, too, to prove that " a little knowledge is a dangerous thing." Be it known, that I do not condemn an objective simply because it has a narrow aperture ; conversely, I do not endorse a glass on account of its wide angle. I have seen scores of wide angle glasses not worth the cost of their brass mountings. As to "errors in interpretation," the more perfect the lens, and the more expert the manipulator, the less chance of error. Under high amplifications, a superior wide-angled glass, properly handled, will generally prove the more reliable ; and in advanced work cannot be dispensed with, be the illumination central or oblique. Finally, I have to thank Mr. Hitchcock for his friendly criti- cism. He seems, evidently, to be after the facts. I have re- sponded to his request as well as I could with my limited time and space. Two hours "over the tube" would demonstrate more than volumes of print. J. EDWARDS SMITH. Note. On my last visit to the Dunkirk Society, May, 1877, 1 showed, I believe, for the first time, the Nobert 19th band as an vpaqvx object, with my Tolles' one-tenth duplex, Beck's vertical illuminator being used. It is obvious that the pencils of light traversing that band were at least centrally disposed. J. E. S. ANGULAli APERTURE AND CENTRAL ILLUMINATION. In my reply to Prof. E. Hitchcock, reprinted in the August number of this journal, I endeavored to respond to his court- 362 HOW TO SEE WITH THE MICROSCOPE. eous request. My position had been placed fairly before the public for years, and I was. for the nonce, content in maintain- ing silence, feeling assured that when attention should be thoroughly aroused as to the claims of high-angled glasses, that I would be better understood. I think I can to-day safely assert that my expectations have been realized, and to a greater extent than I had any reason to anticipate. Prof. Hitchcock has done me the honor of an extended reply in the September number of this journal. It is noticeable that he still preserves the same courteous bearing which character- ized his previous paper ; indeed he pays me a compliment ("We have his plain statements, and we accept," etc., p. 110). All this, as an index of his good nature, is very acceptable. Nevertheless, be it remembered that it has been no part of mv purpose to obtain acceptance per se of my positions. On the contrary it has been my earnest endeavor to excite attention,. and to induce my readers to experiment for themselves. Hence the results of my tedious and protracted experience with the duplex lenses were printed in forcible terms (heterodox as they must have seemed to many), allowing no loop-hole for retraction or qualification on my part. Hence it was, too, that I requested Prof. Hitchcock to repeat some of my experiments ; Prof. II. is compelled to decline, because he has not the objectives at command. This I sincerely regret. Premising that my time is fully occupied, and that it will be impossible to reply directly to Piof. Hitchcock's last, and inter- esting paper, I proceed to offer a few thoughts suggested by -ne same. First, what, in common parlance, constitutes a high-angled objective ? I think I understand Prof. Hitchcock perhaps not let us see. It may be that in arriving at a mutual under- standing on this point, we may get, generally, nearer coinci- dence. Now, most observers associate with the term " high- angled objectives," some great display of figures. Thus, 175 r 178, or the " impossible " 180. Others might go still further, turning the 180 corner, and thus revel in the" balsam angles* say, up to 100 or higher. Such are not exactly my own notions. I regard as high-angled, all objectives from a 4-inch to a SUPPLEMENT. 363 l-75th, having respectively the highest possible attainable aper- ture. If this definition be accepted, then it occurs that what was known as a high-angled l-10th of 130 ten years ago, would now be classed as a medium-angled glass, and further, that au inch objective of 45 would take rank as a high-angled glass, and to the latter class of objectives do I refer as giving me the best results for any and all work, selecting from this class of objectives the one best adapted for the work in hand. Let me illustrate by selecting a case that I almost daily have in practice to- wit : Suppose, for instance, I am making preparations, say, of malignant growths (notice that this is not a diatom), it would doubtless be desirable tirst to make a preliminary examination. I should, from the high-angled class of objectives, select the above named inch of 45. Why ? First, because it has large working distance, which is not disturbed by high eye-piecing. I am also enabled to bring the mirror above the stage, and thus easily condense light on the object ; and further, the working distance is so large that little changes in the same do not disturb the object to such an object- ionable extent as would occur had a higher power been selected. Second, because this inch will show me structure up to 30,- 000 lines to the inch. It will not only bear the l-4th solid eye- piece, but will give with it added force of definition, with increased amplification. Third, (result of first and second), because of all glasses I have ever handled, I can get the most work (I have in hnnd) out of it. For instance, its large reach, due to its working dis- tance (the so-called penetration), enables me to focus through the different planes of the object, while the entire specimen remains fairly in view. I am further enabled to search through my mount, with the least danger of allowing important struc- tural elements to escape my attention an important item. .N"ow, should such preliminary examination suggest the pres- ence of structure calling for an objective capable of recognizing lines 100,000 to the inch ; the inch of 45 would be removed, and a l-6th, having the widest aperture known, and working dis- tance of one-fiftieth of an inch, substituted. With this supe- 3(34 HOW TO SEE WITH THE MICROSCOPE. rior defining glass I have still working distance enough to illuminate my object by condensing sunlight on top of the cover, thus securing exquisite definition under amplification of more than 5,000 diameters. Here, again, with said l-6th, I get better work than I can with any other style of glass. Again, should it be desirable to cross-question my specimen still closer, it would become necessary to remove the l-6th and substitute a bran-new l-10th not yet a month old, the master- piece of a young American optician. This l-10th has also the widest aperture known, combining still more exquisite defini- tion w^th sufficient working distance to allow the use of sun- light as above named, while its glorious performances by central light eclipse, yea, distance the work of any low-angled glass extant, this beyond the ghost of a doubt. (And right here I beg Prof. Hitchcock to be lenient, and to allow me a little mar- gin ; it's hard to keep cool over the central-light performance of this new MOth). But, with the employment of this l-10th, we get into tolerably close quarters, the " difficulty of working " is enhanced. It won't do to put the screw-collar somewhere between " zero " and somewhere else. And then, too, there has got to be a good deal of that ik handling " attended to that Prof. H. says will do so well to talk about before an audience. Prof. Hitchcock here applies the great American question, and asks if all this bother will pay. I reply, u Yea, verily I" I shall be very grateful if Prof. Hitchcock will point me to glasses that will take the place of those above mentioned. It has so happened that those who have thus far undertaken this task (and some have traveled hundreds of miles to accomplish it) have resigned their previous ideas in my favor. In fact, I have scores of friends made in just this kind of a way, and I hope to add Prof. H. to the list. Having thus given my ideas as to the nature and performance of high-angled objectives, I beg to add that I see no necessity for backing down from my original statements, although chal- lenged by Prof. H. On the contrary, the advent of the new l-10th serves to clinch the nail that I had previously well-driven home with the duplex. And I now place again on record my deep- SUPPLEMENT. 365 seated convictions that the use of such lenses as I have de- scribed will be of the greatest use in histological observations. Prof. Hitchcock's remarkable statement that ' much of the very best class of work is being done with second-class lenses,'* is, J fear, a slip of the pen. I, for one, certainly cannot agree with him, even if so be, that I am found in a u minority.' 7 Prof. Hitchcock has, I fear, found out my weak side, and punches me sorely with Helmholtz's formulas. He has got things nicely tabulated, to show at a glance just what can be done and what can't. Now, I own up that of all the annoying things on this mundane sphere (to me), these confounded tables take the lead. Years after others as well as myself, saw the 19th Nobert band as clearly as we saw anything, came the tables to prove that the thing was an utter impossibility I It was noticeable too that, year after year, the tables got changed, in fact, improved, to approximate more closely to the facts. Verb. sap. Again, Mr. Hitchcock informs us that " to attain the best possible results from an objective, the angle of the illuminating- pencil must be the same as the angular aperture of the objec- tive." This, he says, is the " chosen ground " for any lens. To put it mildly, this is another most remarkable statement. I dismiss it with the remark that my own experience teaches me that such manipulation would defeat ninety low angled glasses out of the hundred. He also, referring to my exhibition of the 19th Nobert band, with the vertical illuminator, sug- gests the employment of a diaphragm to the back lens, pre- dicting that the resolution would " doubtless be greatly improved." I had already tried the experiment (and scores of others); the result was nil. Prof. Hitchcock further says that " Prof. Smith has not taught us anything new about objectives." Well, doubtless a little setting back of this kind will be of benefit to me, and may prevent the growth of undue conceit. I confess, that I really did entertain the notion that some of my " shows " before the Dunkirk Microscopical Society were novel. For instance, the exhibition of the Nobert 19th band as an opaque object ; ditto, the showing of 30,000 lines to the inch with an inch objective, and under an amplification of 740 diameters, etc. 366 HOW TO SEE WITH THE MICROSCOPE. It was my intention to pass over one or two points presented by Prof. Hitchcock, but fearing that silence may be miscon- strued, a word or two may not be amiss. Prof. Hitchcock does not deny that Dr. Carpenter has lately (note that point) given his unqualified endorsement to the superiority of the duplex glasses, but he adds, " so does everybody else." This, too, must be another slip of the pen, for it is all, yea, more than I have claimed, for at the date of my Dunkirk lecture, the claims of the duplex were not admitted by everybody. During the past four years I have, myself, received hundreds of letters from as many sceptics. Prof. Hitchcock states that he was taken "a little by surprise" by my claim that the " very best work of the duplex is seen by central light," and with singular tact allows the little fact to remain intact. This is too bad, for right here I expected the thickest of the fight. It was, in fact, " my chosen ground." Prof. H. is too much for me on tactics. In this connection, I beg the reader to bear in mind that while Prof. II. admitted the superiority of wide angles for the resolution of " diatoms and Robert's test-plates," he neverthe- less held that this did not support my view that high angles are " universally preferable," (see this journal, May, 1877). To meet this point, I stated in my response (this journal, August, 1877,) that I had not omitted such tests as are generally consid- ered " chosen ground " for small apertures, i. e., what is gener- ally understood and accepted as dead central illumination ; and further, that among other tests I selected Navicula angulata illuminated by central light, because such resolution had been publicly declared impossible. In reply Prof. II. kindly admits, and in complimentary terms, all that I had claimed as to cen- tral light work, and he frankly adds, " they are just what we would naturally expect a priori." Having made this full admis- sion, Prof. H. seems to repent a little, and reverts to the sub- ject again (page 112), still yielding that the high angles are superior, both with oblique or central illumination, but for reso- lutions only, because he says, the low angles have the greater penetration. The nature of this, his residual error, is mani- festly indicated in the piesent paper. Less than IV Uvo hours SUPPLEMENT. 367 over the tube " would convince Prof. Hitchcock that u the very best performance (penetration, depth of focus, reach, or what not included) is seen by central light. I again invite investi- gation. The passage from Frey was original with Dr. Carpen- ter ten years ago. I have no objection to urge. A word, and let it bo with due respect to Dr. Carpenter. His advanced age and failing eyesight, together with his many duties and cares, forbid that he should continue to be the authority he has been in the past. Singularly enough, the doctrines advanced by Dr. Carpenter twelve years ago are still endorsed by many to-day. This operates as a brake to the wheel of progress ; surely Dr. C. is not to blame. Mr. Hitch- cock asks if Dr. C. has changed his opinion since the fifth edi- tion of his work ; in reply, I can say that the latest information I have bearing on this point is this; about eighteen months since a friend of mine was in London attending medical lect- ures. He sought Dr. Carpenter's advice as to objectives ; Dr. C. advised him to go home and purchase the duplex, and my friend did so purchase. Be all this as it may, while I enter- tain the highest respect and admiration for his medical and scientific attainments his life of unceasing toil in his profes- sionI cannot, and for the reasons presented, attach impor- tance to Dr. Carpenter's endorsement of the duplex glasses. In other words, I should prefer the testimony of American experts. To resume, Mr. Hitchcock further says that " two hours over the tube " has demonstrated something, he don't say exactly what. At anyrate he volunteers his thanks, which I joyfully accept. I should have said that " two hours jointly over the tube " would demonstrate more than volumes of print. 1 hope yet to enjoy such a tete-a-tete with friend Hitchcock, and prom- ise in advance to delight him with the new wide-angled l-10th before referred to. The new glass, too, confirms in a truly practical manner the positions I have heretofore taken in print. In conclusion, I have again to thank Prof. Hitchcock for his good natured review of my previous article, and hope that he will find nothing in this hastily written article objectionable. 368 HOW TO SEE WITH THE MICROSCOPE. A FEW WORDS CONGE LINING THE PERFORMANCE OF OBJEC- TIVES. Ed. Am. Jour. Microscopy Referring to the letters of Mr. E. Gundlach, printed in the August issue of the Cincinnati Medi- cal News, it was noticed that Mr. Gundlach bases his optical laws on the performance of his own objectives, or at least he appeals confidently to his objectives to sustain his positions, as to working distance, resolution and angular aperture. Mr. Gundlach certainly has the right to state the principles which govern him in the construction of object-glasses, and it would be well if other makers would follow his example. But his readers must keep constantly in mind that while the general principles he sets forth may not, as a rule, differ materially from those actuating other opticans, each and every one has a handling characteristically his own, and that a necessary result of his will be recognized in the characteristic performance of various so-called first-class objectives ; and further, that between the extremes comprised in the " handling" above named, a large margin obtains, sufficient to warrant the acceptance of one ob- jective to the exclusion of another. The potency of these considerations is enhanced when we remember that the slightest superiority in an objective is of the highest importance. Beale says ("How to Work with the Microscope," p. 285) "It is certain that the slightest advantage iii defining power ought not to be underrated. * * * Im- provement in the means of observation is of the utmost im- portance, and however slight, always leads to the discovery of new facts." Again Dr. Beale writes (p. 283) - l The best object-glasses will define clearly and accurately bodies which, from their trans- parency, are quite invisible under objectives only slightly in- ferior to the first." It therefore becomes apparent that these little differences, perhaps due to " handling" on the part of the optician, while they are invaluable to the working microscopist, may also be referable to the genius of the optician to a particular method of "handling" known optical laws. SUPPLEMENT. 369 By way of illustrating these "little differences," it may be mentioned that among first- class objectives of the same mag- nification, aperture and resolving power, greater and lesser working distance will be found, and right here is the solution of the dogma of (bo-called) penetration, for, of the glasses above mentioned, that one having the greater working distance will be endowed with the greater penetration. This is the whole thing in a nutshell, as set forth by the writer years ago. If, in the comparison of two objectives, alike in magnification, aperture and resolving power, one shall be found to have the longer working distance, then is its superiority demonstrated, and, be it remembered, that comparisons of objectives ought always to be made in this kind of a way, otherwise any attempt at comparison would be as futile as if we were to compare a tur- nip with an orange. Again, ij it can be shown that a medium power glass, say a l-6th or a 1-lOth having the widest aperture known, and also com- paratively large working distance, say l-50th of an inch, will more than do any work that can be done with objectives of ex- ceedingly high power, and correspondingly short working dis- tance [excess of aperture being barred by the above named conditions), it will be obvious that the former will be eminently the superior glass. Now the facts warrant the assertion that just such one-sixth and one-tenth are made, and by American opticians. The writer has had, and still has in his possession just such glasses. His first contribution to the columns of the News, four years since, set forth their claims, and he has never had occasion to make either modification or retraction of his original statement. When such occasion shall occur, the readers, of this journal will be promptly advised ; until then I claim (especially for the one- sixth) unequaled intensity of definition, widest known aperture, combined with large working distance in other words, without that sacrifice of " working distance" alluded to by Mr. Gundlach. I embrace this, my first opportunity, to say that I have lately examined at length a new duplex one-tenth, the work of a young American optician. This new one-tenth is similar in 24 Microscopy. 370 HOW TO SEE WITH THE MICROSCOPE. aperture and has greater working distance than my own one- tenth ; its work over such tests as the Nobert and Moller (balsam) plates was quite equal to that of its formidable competitor, while the views it gave by central light were simply glorious, excelling the old one-tenth. This, as a first attempt on the part of a young optician, is truly encouraging. These new duplex glasses will receive my earnest attention, and I may have, in the future, something more to say about them. Allow me to further state, that, being desirous of acquainting myself with the work of our own opticians, I wrote to the Rochester firm, asking the loan of objectives for examination and study. They responded promptly, sending me by return mail a full line of Mr. Gundlach's lowest priced " Student's" work. They certainly had no time to select exceptional glasses. My time has been so thoroughly occupied, I have not yet given them the attention they deserve, but as far as they have been examined J am much pleased with them a three-fourth inch at $6, a one- half inch at $8, and a three-tenths at $11 , are very finejindeed for their cost. ANGULAR APERTURE ONCE MORE. Ed. Am. Jour. Microscopy. The discussion between Prof. Hitchcock and myself, which, during the last few months you have done us the honor to print, seems to have become some- what of a rambling nature. Prof. Hitchcock " changes base " so often, that it would bother a streak of lightning to catch much less corner him. Be this as it may and perchance he might return the compliment, 1 can only say that I have endeav- ored to stick to the points at issue the merits of high, as com- pared with low angles, I have attempted to set forth from a practical standpoint, being tolerably familiar with the use of either style of glass. I have tried my best to have Prof. Hitchcock examine high- angled glasses for himself, and report results, but, as your read- ers are aware, from his own assertions, Prof. Hitchcock does not claim a practical knowledge of them, and as a matter of course he cannot see what that " handling " (of which it will do SUPPLEMENT. 371 so well " to talk about before an audience ") amounts to. Of a piece with this comes his statements that such and such posi- tions of my own are ** not proved," and that before he accepts them he " must know why." I submit : that the only possible method of convincing Prof. Hitchcock will be the practical one, in this instance, however, quite impracticable, to-wit : " two (or more) hours conjointly over the tube," or until he shall have done me the honor to adopt my suggestion, and experiment with the high angles for himself ; in the latter case, obviously, he ought not to expect nrst-class results from the wide angles until at least he shall have learned that something is due to " handling." I repeat that until one or the other expedient is adopted, we might con- tinue the present discussion until doomsday, and on my part without a vistige of any chance of convincing Prof. Hitchcock. I therefore offer the following brief remarks by way of closing a controversy which, in the nature of things cannot lead to any fixed results. Prof. Hitchcock asks, " Why strain a one-inch to see 30,000 lines to an inch, with a deep eye-piece, when the half-inch would do the same work without being pressed so hard ?" Well, let us strip things " stark naked," and find out tk why." First, with the inch I get better definition ; second, longer working distance ; and, third, because the inch, with deep eye- piecing " is not pressed so hard as the half-inch and this is my reply to Prof. Hitchcock. As a matter of course he will come back at me with the stereotyped assertion, " I must know why." He says, too, u Until his (my) experiments are published and subiected to public examination they are not to be accept- ed, etc." Well, by the laws, my experiments have been both published and subjected to public examination. But, unfortu- nately, Prof. H. wasn't there ! Note that. Further, I now propose to put the inch and half-inch to a practical test. Thus, let Prof. Bodgers, of Cambridge, rule a band of 40,000 lines to the inch, and let Prof. Hitchcock count them if he can with a low half-inch (say of 40). I hazard the prediction that he will fail, and furthermore, that I will be enabled to count them with an inch of 45. I am ready for such test in any shape that Prof. Hitchcock may suggest. 372 HOW TO SEE WITH THE MICROSCOPE. To get back to our " moutons." When I stated 30,000 as the limit for definition of the inch, I held a good large margin (to swear by) in reserve. This, as the 30,000 was " millions " as far as establishing my point was concerned, now that the readers of this journal have got used to the ' 30 " I will add that I have no trouble in seeing the 40,000 band of a Rodger's test-plate, and most beautifully ruled they are. Here is an added strain of ten thousand on the inch, but it is as good as ever ! (One of these days I must give your readers a description of an exquisitely ruled plate, up to 80,000 to the inch, an.d by the same talented artist.) But to business. I have as fine a half-inch of 38 as I have ever seen, a glass selected with much care, having spent consid- erable time in making the selection, so as to have the very best; for, be it known, I sometimes (not often) have use for just this sort of glass. Well, now, this half-inch has shorter working distance, and, as a matter of course, less penetration than has the inch of 45, while the last-named inch of 45 has much the superior definition. Now, I am perfectly acquainted with the u points " of these two objectives, and can make either put its '" best foot fore- most," (hence the " handling " may be counted out.) Both are my own, and I can at will use ths one that I prefer. Which would Prof. Hitchcock use under tbe same circumstances ? Or, leaving the Professor out, which would the reader select ? Which glass would be " strained " the most ? Prof. Hitchcock reminds his readers that he has " already ad- mitted to Prof. Smith that Tolles and Spencer are making won- derful glasses, etc." Yes, so he did, but he put a fence round them ; thus he adds " but for resolutions only." When Prof. Hitchcock shall become as well acquainted with the work of Spencer and Tolles as are others, that fence will step down and out. I accept no loop-hole, but stand to the position heretofore assumed, to-wit, that the above named glasses are not equalled for kt any and all work," a set forth in my last paper. Now about Dr. Johnson's showing the 19th band as an opaque object in the year 1872 or thereabouts. Here is a legitimate chance to try on Pro'f. Hitchcock's conditions, to-wit: Were SUPPLEMENT. 373 Dr. Johnson's experiments with the 19th band published ? (as were my own). Again, were they " subjected " to public exam- ination ?" (as were -my own.) Let the Professor's rule work both ways. Meanwhile I no*v assert, and know whereof I affirm, that a Powell & Lealand l-10th of 1872 cannot be forced to show the 19th band by lamplight. In gen- eral, I don't propose to accept anything done with the 19th band live years ago, as comparable with what is being done in 1877. Again, all who have seen the 19th band as displayed with the duplex and modified Beck illuminator, instantly admit that for wondrous delicacy of definition, the total absence of the "ghost" of a diffraction line, all other methods of illumination (by arti- ficial light) are simply " nowhere." And further, that any attempt at photographing these wonderful lines has been but approximative. To be more definite, the best photograph of the 19th band yet made is simply a caricature. Nevertheless it is wonderful that Col. Woodward has succeeded as well as he has, and his photographs are the best that I have seen. A word as to the mathematical tables. There can be no pos- sible objection to these, when (it's my chance to say " when " now) they agree with obvious facts ; they are objectionable when they are not in accord with facts. I stand ready to accept truth in any form ; ditto, to repel error. Now the facts are, that from a mathematical standpoint the limits of vision have been erroneously " set " again and again. I simply protest against fighting facts with mathematics simply this, and nothing more. In drawing towards the close of this article, I desire, as apro- pos to the question at issue, to state a little bit of personal expe- rience, viz : About a year ago a gentleman, a professor occupy- ing a responsible position, gave me a carte blanche to provide him with a medium power lens. He was particular to state that he was engaged in histological studies, and wanted the glass for such and similar purposes. In response, he was furnished with a l-6th duplex. Last summer he visited me during his vacation and became my pupil. He was, of course, an apt scholar, and quick to learn. He spent with me weeks in acquiring the man- ipulations of this glass, and became quite expert. When he left me he said, " I have now learned practically what was done for 374 HOW TO SEE WITH THE MICROSCOPE. me in the selection of the objective, which I now prize more than ever, and it is astonishing how much is due to handling. I had no idea of it." A few weeks ago he wrote me that he was doing finely with the duplex, and had succeeded with it in trac- ing structure (histological) that could not possibly have been seen with any low-angled glass. Further, that the very best makes of the low angles were constantly within his reach. Now it is a fact that before I furnished this gentleman with the duplex, he was as fully committed in favor of low angles as Prof. Hitchcock can be ; but, unlike Prof. H., he commenced the study of high apertures, and with the sure results above narrated. His address will be furnished to any one desiring it. Prof. Hitchcock says something (I quote from memory) about " accepting defeat in a becoming manner." I desire most earn- estly to advertise the fact that it is not, has not, been any part of my purpose to u defeat " Prof. Hitchcock, and as I have understood the gentleman from the very onset, he is not, nor has he been, in a position to suffer defeat. He simply wants the facts, and I have endeavored to furnish them, and if so be that any good has been brought about by this discussion, your readers are quite as much indebted to Prof. Hitchcock as to any one else. In conclusion, I return Prof. Hitchcock my sincere thanks for the courteous and gentlemanly consideration he has ever extended me. It has been my intention to reciprocate, and with the hope that I have been in a measure successfnl, and with the kindest feelings towards Prof. Hitchcock, to you Mr. Editor, and to your many readers, I remain sincerely yours, J. EDWARDS SMITH. NOTE. In your October number, page 132, an obvious error occurs. For " what was known as a high-angled l-10th of 180 ten years ago," read lk 130 ten years ago," etc. J. E. S. SUPPLEMENT. 375 DISCURSORY THOUGHTS RELATING TO THE USE AND ABUSE OF THE MICROSCOPE. An Address delivered by Prof. J. Edwards Smith, before the Dunkirk Microscopical Society, Tuesday Evening, October 31, 1876. To the Members of the Dunkirk Microscopical Society : GENTLEMEN: About twelve months ago a friend of mine and a brother microscopist, ordered from London a low-angled l-4th inch objective ; my friend was engaged in histological investiga- tions, and felt the need of a reliable medium-power glass. He had been told that wide-angled glasses, although very suitable for the purposes of the diatomist, were hardly suitable for the work he had in hand ; he was told, too, that the thing needed was a glass of low or moderate angle, say from 50 to 70, and one that had great working distance ; in short, as the saying goes, he needed a good " working glass." In due time the objective was received, and one very pleasant evening my friend called on me expressly to show the work of the lens. I remember that we had a very enjoyable time, amus- ing ourselves by looking over a variety of specimens suitable for the glass. In the course of the evening he exhibited a beau- tiful section of a human tooth, and placing the same under the l-4th, called my attention to the "Nasmyth's membrane," described by Frey and others. This was a matter of interest to me, for I had heard much of this " Kasmyth's membrane ;" I had examined human teeth time and time again with my own wide-angled glasses, but had never been able to discover the same. I was, in fact, somewhat curious about the matter. It seemed odd, to say the least, that my glasses, which would show me clearly and accurately, lines as close as 120,000 to the English inch, should fail to show me the existence of a membrane said to be about 1-6,000 of an inch in thickness ; and then again I had hunted with a low-angled l-4th of my own without success. Hence it was with expect- ancy and interest that I put my eye to the tube ; I saw a decided thickening of the margin of the crown of the tooth, and was informed that this was the veritable "Nasmyth." But, 376 HOW TO SEE WITH THE MICROSCOPE. said I, " is this thickened edge not the fault of the objective, and suppose that we examine the specimen with another glass?" Removing the London lens, I substituted a wide-angled l-6th of plus 180 of aperture, and on adjusting carefully to the thick- ness of covering glass, I soon had a splendid view of the pre- paration, by far finer than that shown by the London glass ; and as I had supposed would be the case, I now had a nice clean edge in the place of the thickened one before mentioned. The superiority of the definition over that of the l-4th was apparent; and tht capacity of the 1 -6th to bear the 1 -4th inch solid eye-piece and amplifier thus carrying the amplification up to nearly 4,000 diameters was in a few moments demonstra- ted, but the Nasmyth's membrane was not to be seen uitder any amplification. At this time it occurred to me that I might possibly make a membrane as described by the books, and as shown by the Lon- don lens. Turning the collar of the l-6th so as to throw the glass considerably out of adjustment, and again focussing the object, I was much amused to find that I had the identical membrane, as shown by the imported glass, and also, that as tht collar was moved, the membrane could be made thick or thin to suit I The result of this little episode was simply this my friend now owns and uses on histological work an American made l-6th of 180 of aperture. I have related, as briefly as possible, this little incident, and exactly as it occurred. I desire to say, however, that I do not deny the existence of " Nasmyth's membrane," described in the various works on physiology and histology. Nevertheless can- dor compels me to state that I have in times past made diligent search, and have failed to recognize a structure which is taught even in our elementary school books, as if it were a common- place thing ! Months ago it occurred to me that the membrane referred to might only be found on teeth of the first dentition, and obvi- ously would be found wanting on the tooth of an adult. This idea sent me to the dentist's office : such specimens were pro- cured, but the u Nasmyth " still defeated my search therefor. SUPPLEMENT. 377 Some months ago I was engaged in teaching microscopy in one of our public schools. At that time I had the class in physiology in hand, and it was my especial purpose to show them actually, structures which were described and pictured in the text book used. I had not proceeded far before we ran against this " Nasmyth's membrane," and I was compelled to state substantially the experience which I have now related to you. There is not a class of persons on earth Jess appreciated or more poorly paid than those engaged in histological investiga- tions, and for their indefatigable perseverance I entertain a profound respect ; but it has often occurred to me that as a class they have been content to work with very poor tools, and it is safe to say that a great deal of the ground already studied will have to be reinvestigated, and with better glasses with a bet- ter knowledge of those manipulations requisite to the use of wide-angled lenses. Nor can the necessary manipulations be acquired in the ordinary routine of investigation ; it is an art of itself, and calls for special attention, requiring as much study as the art of manipulating a pianoforte or an organ. It is a very commonplace remark, that, for the purposes of the histologist, low-angled glasses, of moderate definition, are the best suited. And yet, if we consult their latest works, we will find structures described that call for the best lenses of the widest angles. Take, for instance, the muscle sheaths, or the axis cylinders of the nerves described by Frey, in his last edition. Coming down to commonplace things, I affirm that the simple trachea of a bee cannot be studied with advantage with other than lenses of the widest angles. There is perhaps no microscopic object more common than these tracheaes. They are to be found mounted in the cabinet of every microscopist, and we have all of us read about them in the books ; we have examined them again and again, times without number, with objectives ranging from the inch to the l-5th, or perhaps to the l-10th. Now I ask you take a look at them on my account, and if possible inform me how these tracheal coils terminate : what is the structure at their very last end? What is the least diameter of these terminal coils V Here 378 HOW TO SEE WITH THE MICROSCOPE. you have a problem in hand, to which, for exquisite intensity of definition, or nicety of manipulation, the resolution of the Moller or Nobert plates are child's-play matters ! And if you should be desirous of testing your lenses as to their capacity for histological work, the trachea will be found to be one of the very best test objects in existence, and will surely furnish you valuable ideas as to the relative value of wide and low angled glasses for the purposes of histological research. Not long since one of our most skilful physicians sent me a sample of urine from a child supposed to be suffering from a disease of the kidneys. Jt was a perplexing case, and the med- ical gentleman in charge hoped that the microscope would give some light on the case ; when examined with a low power l-5th of 70 Q aperture, the specimen appeared in every respect healthy ; but on further examination with a wide-angled glass, and with an amplification of nearly 4,000 diameters, it was- found to be literally swarming with vibriones. There were bil- lions upon billions of them in every field examined, all of which were totally invisible to the low-angled l-5th. We often hear the remark, that wide -angled glasses are just the thing for the display of lined objects, surface markings r diatoms, etc., but that owing to their short focal length, and limited working distance the trouble attending the adjustment of collar and in general, the difficulties pertaining to their use r that they are unsuited to the purposes of the histologist ; white on the contrary, low-angled glasses of greater working distance requiring no skill in management, are the tools with which the real work of the microscope has been, and will continue to be done, and such are fondly termed good, honest and reliable " working glasses." 1 can never listen to this line of argument without entertain- ing the suspicion that sloth and inactivity lay at the bottom. We never hear astronomers complain of the care they are compelled to use in instrumentation ; on the contrary, they pride them- selves on the accomplishment of being able to work instruments- requiring a great amount of skill and precision in manipula- tion. The objection of short working distance originated years ago SUPPLEMENT. 379 when German pathologists were in the habit of using common window glass to cover their mounts, and at that time the extremely thin glass, now so easily obtainable, was unknown. All this is now changed ; the widest angled lenses known giving all desirable amplification, will admit the use of covers l-50th of an inch thick, while covering glass measuring .003 can easily be procured. A vast amount of work has been done with these kl honest and reliable working glasses," and, as I have before said, will have to be done over again, and this revisory work is now in progress. But while there is some excuse for the investigators of the past, who used the best instruments then obtainable,, what shall we say of those of to-day who persistently refuse to avail themselves of the wonderful progress the optician is able to demonstrate in this centennial year V I have advanced the idea that working pathologists were too often content to work with poor tools. 1 made that remark in- good faith, and believe tnat it will be found to be trne. Never- theless the pathologists of the past, or even of the present day,, are by no means wholly at fault, when we remember that the entire corps .of observers to whom we are indebted for all that has been taught through the aid of the microscope, were men who were regularly engaged in the respective duties of their several professions, and that most of them have rilled profes- sional chairs in various institutions of learning. These men, in studying the use of the microscope, each and every one of them were compelled to dig and trench for themselves; -the instru- ment which to them was as all-important as the compass to the navigator, was far, very far, from being as true and reliable as- kk the needle to the pole." Once launched on the unknown, but to them, fascinating sea of scientific investigation, every spare moment that could be snatched from their regular engagements was devoted to its exploration. It was a tiny sea, within a microcosm, replete with interest, and capable, as if by the touch of the optician's wand, of boundless expansion ! These self-abnegating, self-sacrificing men fully accomplished their task. It was a labor of love, and the results they obtained were given to the world without money and without price. 380 HOW TO SEE WITH THE MICROSCOPE. Among the investigators of our own day, 1 will refer you to one whose untiring industry has earned for him a world-wide reputation. I allude to Dr. Lionel S. Beale, F. E. S. Dr. Beale, as you are aware, has been contemporary with, and the supporter of, Dr. Carpenter's heretofore universally received opinions as to the relative capacity of wide and low angled objectives. Dr. Beale, in his work, " How to Work with the Microscope," I quote from the third edition, page 7 says as follows : " For ordinary work it will be found inconvenient if the object-glass when in focus comes too close to the object. This is a defect in glasses having a high angle of aperture. * * Glasses with a high angle of aperture admit much light, and define many structures of an exceedingly delicate nature, which look confused when examined by ordinary powers. For general work I recommend glasses with an angle of not more than 50Q to 1000 lk Mr. Boss has lately made glasses having an angle of 170, which are valuable for investigations upon very delicate and thin structures, such as the diatomaceae ; but such powers are not well adapted for ordinary work. The importance of arranging the object very carefully, and the necessity of paying .great attention to the illumination, render these glasses incon- venient for general observation. The penetrating power of .glasses with a low angle is much greater than in those of a high angle of aperture, so that exact focussing is much more impor- tant in the latter than in the former." This, in its popular acceptation, is the square doctrine first advanced by Dr. Carpenter, and it has suffered no loss by its filtration through the mind of Dr. Beale. It is the doctrine which has been generally received and accepted. It is the dogma which ten years ago I thought ought not to be true, and of which to-night I stand before you the prince of sceptics I In the quotation which 1 have presented, there are two domi- nant ideas ; the one displays the inconvenience attending the use of wide-angled glasses, and to this objection I have already paid my respests in due form ; the other presents the theory of ** penetration " as originally advanced by Dr. Carpenter, sup- SUPPLEMENT. 381 ported by Dr. Beale, and generally endorsed by microscopists of Europe and America. I have not the time this evening, nor would I weary your patience by the discussion of this dogma of penetration, any further than to admit that it was true ten years ago, when first announced by Dr. Carpenter, but can .have no possible present force in reference to the wide aperture glasses of to-day. I am also quite prepared to grant that a spectacle lens of sixty inches- focus needs less skill in management than a duplex l-10th of plus 180 of aperture ! After all, I get considerable comfort out of -the quotation already presented. Dr. Beale says, " that glasses with a high angle of aperture admit much light, and define many structures of an exceedingly delicate nature, which look confused when examined by ordinary powers." Notice the wording ; he does not say diatoms. He does say, u many structures of an exceed- ingly delicate nature, which look confused when examined by ordinary powers." It is a candid and manly admission, and E honor his candor. It is the truth, the whole truth, and nothing but the truth ; while for brevity of form, or clearness of expres- sion, these half dozen words leave nothing to be desired beyond what is here so forcibly stated ; and I bet? of you not to lose sight of the fact that if this was true of wide- angled glasses made in 1865, it is equally so of those of 1876. Another fact will bear to be borne in mind. It is this : when Dr. Beale wrote in 1865, he was very far from being expert in the use of wide apertures. I wiH read to you further from the same paragraph : " In order to adjust the object-glass, it is- first arranged for an uncovered object ; then any object covered with thin glass is brought into focus by moving the body of the- microscope ; next, the ring which carries the third lens is screwed round until any particles of dust upon the upper sur- face of the glass are brought into focus. The glass is then cor- rected for examining the covered object which may be brought into focus." It will be seen that the method of adjustment adopted by Dr. Beale is precisely the same as that used by many for measuring the thickness of covering glass, and when the milled head of the fine adjustment is properly graduated, and 382 HOW TO SEE WITH THE MICROSCOPE. the " run" of the fine adjustment is known, the plan is a con- venient one, and will give measures tolerably correct ; but for the purpose of adjusting an object-glass it is obviously fanlty, and would in almost every instance defeat such wide angled lenses as I am in the habit of using. Dr. Beale's instructions MS to the adjustment of wide-angled lenses must be taken "cum grano salis," aud will indeed be more honored in the breach than in the observance. It is with pleasure that I now turn to page 217, and read as follows: "Besides extreme minuteness in mere size, extreme tenuity or transparancy may interfere with the definition of an object. Now the greatest difference is observed in object- glasses in this particular. The best object-glasses will define dearly and accurately mark the words," clearly and accurately" bodies which, from their transparency, are quite invisible under objectives only slightly inferior to the first." Now the question arises at once, Where shall we find these best object-glasses, which define so clearly and so accurately such delicate and transparent objects? Referring again to page 7, Dr. Beale responds thus : " Glasses with a high angle of aperture admit much light, and define many objects of an exceedingly delicate nature, which look confused when exam- ined by ordinary powers." The Doctor having thus squarely settled the question, most kindly goes on to tell us where we can get these wide-angled glasses, and I read right along, as before quoted : " Mr. Ross has lately made glasses having an angle of 170, which are valu- able for investigations upon very many delicate and thin struc- tures," etc., etc. It is especially a part of my purpose in appearing before you this evening to show you " clearly and accurately," and by the aid of glasses of American manufacture, which for width of aperture have never been excelled, some of these extremely thin and transparent objects, and thus prove to you the truth of Dr. Beale's assertion ; and relying on the correctness of the old adage that " seeing is believing," I can hardly fail in the demonstration of the accuracy of Dr. Beale's position. Pardon a momentary digression, and allow nie to turn to page SUPPLEMENT. 383 216. Here I read : u If any one makes out new points of struc- ture by any new method, all that such an authority who differs has to do is to state that he has not been able to see the struc- ture described so and so. Authority too often denies the ex- istence of what it has itself been unable to see. Many auth- orities deny the existence of what they haye not seen, while they have not taken the pains to try the only method of demon- stration by which the appearances in question could be seen." Now we perceive that the Doctor is in a complaining mood. The root of the matter was simply this : Dr. Beale paid great attention to instrumentation ; the first l-25th arid the first l-50th objectives in existence were made for him ; he was not very par- ticular as to their angle, although it is noticeable that he claimed for them " plenty of light." But the fact is indisput- able that his instrumentation has been in advance of that of the London microscopists. Dr. Beale was in fact in a position very similar to those of the present day, who, conscious of the superi- ority of their glasses, are disposed to regard the blind " authori- ties " referred to as unworthy of special consideration. I desire in this connection to call your attention to the history of the diatom of which we have all of us heard so much about during the past nine years. I refer to Amphipleura pellucida. Who of us here cannot recall the time when the existence of striae on this shell was stoutly denied V We can remember, too, when Dr. Woodward settled this much vexed question by pro- ducing his photographs displaying the striae on what he was pleased to call " this well-marked diatom." And now that these markings are no longer to be questioned, as exhibited on dry mounts, and by the employment of monochromatic sunlight, full eighty per cent, of our American observers fail to exhibit 41 this well-marked diatom" by lamp illumination, even when dry mounted. I have a balsam mount of this shell with me, and hope to show you the lines of No. 20 of the Holier plate this eyening before we part, and also the 19th band of the Nobert test plate, and by the aid of American made lenses of medium power. Let me call your attention, for a few moments only, to another subject. We often hear the diatomist spoken of in terms, 384 HOW TO SEE WITH THE MICROSCOPE. almost, of contempt. They are too often regarded by the hist- ologist as a class of observers who use the microscope as a mere plaything ; and the fact that the diatomists are not altogether agreed as to the structure of some of their favorite shells, is. often used as an argument to show the folly of studying the diatomacese at all ! All 'this, my friends, is sheer sophistry. The study of the dia- tomacese is as legitimate as that of any other branch of the science of biology, and the labors of the diatomists have not been for naught ; it is to them, and to their constant demands on the optician, that we are indebted for the wonderful improvements which have been made in object-glasses; and I am bold enough to tell you that skillful diatomists can tell you a much concerning the structure of a diatom, as can the patholo- gistequally skilled inform you as to the structure of a blood corpuscle ! But to the student, to those who desire to prepare themselves for advanced work, the study of the diatomaceae cannot be neg- lected. No line of practice has yet been discovered that will teach the student the use and management of his tools, that can at all compete with the superior claims of these minute 'org- anisms. It is said that " adversity tries us and shows up our best qualities." These little shells, too, will try the would-be- manipulator, and, like the country judge, show up his worst qualities. It was not my purpose to enter at all into the details concern- ing the use of objectives ; but it will perhaps be well not to let the opportunity pass without alluding to the fact that a wide- angled glass requires totally different management, in some respects, from those of narrow apertures. Those who have been accustomed to the use of the low angles will, on a slight acquaintance with glasses possessing wide aper- tures, almost invariably assert that the latter do not give as good results, when worked by central, of centrally disposed light, as they are accustomed to get from the former. A moment or two devoted to the consideration of the situation, will, I think, furnish the key thereto. When we use a narrow-angled objective, the oblique or lateral SUPPLEMENT. 385 rays are per force excluded. The objective will not receive them, and there can be no possible doubt but that such work is being done with centrally disposed light, such as the observer desires ; there is no special manipulation or management neces- sary to secure this, for the objective will admit centrally dis- posed rays, and none other. But in the handling of a wide-angled lens the conditions are essentially changed, and this change of condition involves in turn a change of handling, and of management. Hence it occurs, that in using a wide-angled glass by central or centrally disposed light, some arrangement must be provided for the purpose of shutting out the lateral rays ; these the glass will admit, and in default of the provision referred to, will steal in, cause interference, and defeat both observer and objective. To shut out these lateral pencils would seem eminently the bus- iness of the usual diaphragm box. This provoking little piece of apparatus, this diaphragm box, is supplied with almost every stand in use, and is as faulty in operation as human ingenuity in construction could devise ; in general these boxes are furnished with a shutter pierced with openings of various sizes, and placed from one-half to one inch below the object-carrier of the stage. Now, suppose we are using a wide-angled lens, and being desirous of central light only, we attempt the use of the smallest opening of the shutter. What now is the result ? It is as follows : the pencils of light enter the small aperture, emerge and diverge within, and fill the box with simply light of low intensity. It has now become a washed-out, wire-drawn light, lacking force, and, I may say, velocity ; the objective now in turn receives this much- abused illumination, not only the central pencils thereof, but lateral ones also ; and the working angle used will be determined by the depth and diameter of the diaphragm box. A proper diaphragm for general use not diaphragm box, for the less of the box the better is a plate pierced with a central opening of about the size of a large needle, and so mounted as to approach the iower edge of the mount closely as possible without suffering actual contact. To construct this little piece 25 Microscopy. 386 HOW TO SEE WITH THE MICROSCOPE. of apparatus will not make any very severe demands on your mechanical skill. Those of my hearers who read the London Monthly Micro- scopical Journal will remember that the capacity to display the markings of Navicula angulata by central light, was considered a feat only to be performed by low-angled glasses of superior excellence. Some of you, too, may have read the report of a certain biological committee who met in Philadelphia last year for the purpose of testing the object glasses of several makers ; one of the tests used was the exhibition of the markings of this same dry mounted Navicula angulata by central light. I was simply astounded when I read the report, in public print, of this biological committee, and learned that in their hands that Angulata had defeated a wide-angled American l-10th, and I immediately repeated the experiment, using a similar l-10th, by the same maker, and worked with a dia- phragm plate perforated with an opening, say, l-200th of an inch in diameter, and placed almost in contact with the under sur- face of the mount. The result was amusing enough ! I instantly had the markings " clearly and accurately " defined ; the prob- lem was, indeed, to avoid seeing them I In fact nothing short of sheer intention, or, what is worse, bad manipulation, could have defeated the objective. I then repeated the experiment, using this time a balsam mounted Angulata the !No. 11 of the Moller plate and was almost instantly rewarded, as in the pre- vious instance. I am prepared to again repeat this experiment this evening should you so desire. Again, the converse of what has been said is also true, namely in working with a wide-angled objective, and with.oblique light, it is important to shut out the central pencils. About a year ago, I devised a simple little instrument, which gave access only to a narrow wedge of oblique light, and thus gave added force to the definition of the objective and this "oblique dia- phragm " was permanently fitted to the stage of my stand. The most efficient instrument of this nature, however, is "Wenham's reflex illuminator," an ingenious accessory, and so contrived as to shut out all rays less than 41 interior, which, of course, has emergence at 90 into air. The reflex illuminator, SUPPLEMENT. 387 which was designed by its inventor to give a dark field, becomes, when used on balsam mounts, with American object- glasses, having balsam angles ranging in the nineties, not a reflex, but a direct illuminator, and a most efficient aid to the definition of the lens. By it I am enabled to show the trans- verse striae of Ko. 20 of the Holier plate so clearly that any old lady who can read her family bible could hardly fail of recog- nizing the striae on "this well-marked diatom." I have the instrument with me, and shall be happy to show you its work on the Moller plate. * It was mainly the purpose of these desultory remarks to call your attention to the importance of instrumentation ; absolute perfection has not been, and never will be obtained. There never has been, nor will there ever be made, an instrument of precision that does not embody inherently some radical weak- ness, some dangerous fault. The practical astronomer is not only early taught the nature and use of the various instruments to be found in the observatory, and made acquainted with their several imperfections, both optical and mechanical, but he is compelled to acquaint himself thoroughly with the methods employed to eliminate these imperfections. Having thus per- force of his preliminary study acquired a thorough perception of the Scylla and Oharybdis which environ the use of instru- ments, it becomes in turn a life's study to further remove exist- ing difficulties, or to provide better and more competent means of compensation therefor. I have no doubt but that it would be interesting and instruc- tive to detail some of .the exquisitely precise methods employed by the astronomer to detect and compensate for the unavoidable errors of instrumentation, but time forbids. I will, however, * immediately after the introduction of the " reflex," mod. neat ions, by changing- the angle cf the facet, were made by the London opticians, so as to adapt the instrument to their variously-angled objectives, similar modi- fications were also made here in this country, by Messrs. Tolles & Spencer. Three years ago the writer consulted a skilled artist with the view of mak- ing- the " reflex" in three separate mountings, changing the angle of the facet in each. Nevertheless, the idea is Weuham's. The mere matter of changing the angle of the facet would naturally occur to any one using the instrument J. E. S. January, 1878. 388 HOW TO SEE WITH THE MICROSCOPE. notice th nature of one or two difficulties which may be said to infest the observatory. We are all familiar with the purpose for which the transit instrument is employed, namely, to observe the transit of celes- tial bodies across the meridian in which the transit is adjusted. To accomplish this, it is evident that the instrument must be permanently placed in that meridian ; bnt, unfortunately, the block of stone has yet to be found solid enough for the purpose. Hence it is usual to ascertain the direction and amount of error and thus correct the results obtained by observing with the instrument while out of the plane of the meridian. The alti- tude and azimuth instrument, too, requires frequent and careful attention. To be assured that its object-glass may swing in a vertical plane, observations are nightly made by observing a distant star directly, and immediately afterwards its image as seen in the mercurial horizon. By this means a truly vertical line millions of miles in length is obtained. Reflecting instruments constructed on the model of the sex- tant, are cross-questioned by observations on east and west stars, and errors due to eccentricity thereby avoided. Not only do these painstaking men study their instruments, but they in like manner study themselves, and their capacity to observe is cross-questioned in the severest manner. It is to them well known that the observations of some first-class observers are constantly affected with a plus sign ; while, again, those of other equally good observers are affected in a contrary direction. This individual condition is called " personal equa- ion," and has to be thoroughly known and compensated for; and this you. must bear in mind, that the amount of error due to personal equation is always comparatively small, and as a con- sequence is only recognized in the observations of professional experts, trained to machine-like, impassive regularity. My initial remarks, in which the kt Nasmyth's " membrane of the books was discussed in a somewhat discursory manner, were intended as an example, and to give you an illustration in refer- ence to a radical evil, which has in times past tainted the obser- vations of many who use the microscope I refer to diffraction lines and diffraction borders. To avoid these spectral, illusory SUPPLEMENT. 389 appearances, is a consideration of the very first importance- requiring, too, the employment of the finest object-glasses, and that technical skill in the adjustment thereof, which is only acquired by long practice ; and to this end the study of the dia- t^macese will be found in the highest Degree advantageous. Moreover, one must devote a good deal of study to this ghostly parasite, which t:oo often infests, and to a greater or less extent defeats the unsuspecting observer. And here again the little diatom will render yeoman's service. Some months ago, Dr. Woodward, to whom we are all so much indebted published in the London Monthly Microscopical Journal, for the express purpose of displaying these illusory ap- pearances, a lithograph from his photograph of Frmlulia, Sax- onica. The objective used by Dr. Woodward was an American l-18th, and was the same glass with which his inimitable photo- graphs of the 19th Kobert band were accomplished. I took it for granted that the lithograph of Fmstulia Saxonica was made with the glass intentionally placed out of adjustment, and for the purpose of creating these particular lines. A copy of the London journal is placed at our service this evening, and I invite your inspection of the plate referred to. The whole shell of the diatom will be seen badly distorted, the striae badly denned, and the diffraction lines are immense I" * *I may here remark that only a few hours ago my attention was called to a report of a meeting: of the London Microscopical Society, held April 5, 1876, and t eported in the May number of the London Microscopical Journal. Alluding: to the photographs of Frustulia Saxonica, Mr. John Mayall said: " Kvery one who is familiar with the Frustul'a Saxonica, photographs of which Dr. Woodward sent in illustration of his paper in December, knows it to be one of the most difficult test-objects a diatom that ranks next to Amphipleura pellucida. That particular form of Frustulia is one that I have rare y seen resolved, except by lenses of the highest excellence. I consider Dr. Woodward's photographs of it as in every way most remark- able, evincing first-rate skill brought to bear on one of the finest known lenses." It is hard to tell which is the most "remarkaole," the photographs, or this statement of Mr. Mayall's. As there seems to be much difference of opinion as to these representa- tions of Frustulia Saxonica, both at h me and abroad, a word or two may be admissable. When the lithographs first made their appearance in the Lon- don Monthly MicroscopiealJournal^ one of our most talented experts wrote 390 HOW TO SEE WITH THE MICROSCOPE. Now, after seeing and learning what can be accomplished with a superior objective, when out of adjustment, it will be instructive, and I shall beg your permission, by the employ- ment of a superb glass, accurately adjusted, to show you a sim- ilar, but more difficult tiaxonica, as illuminated by the most oblique beams my extremely thin stage will admit. Thus han- dled the resolution of JFrustulia Saxonica becomes one of the most charming and fascinating objects that can well be imag- ined. We shall thus see the frustule without sensible distortion the striae displayed with such exquisite beauty of definition as must command your admiration, and minus, too, the suspicion of a diffraction line I The attention of Andrew Boss, while examining Podura scales with glasses of his own manufacture, was called to the thickened edge, the " Nasmyth membrane " so plainly seen with the non-adjustable glass he then employed, and to him are we indebted for the collar adjustment now so common to all first- class objectives. Now, my friends, good object-glasses, like astronomers, have their " personal equation." They alone are the ones to be most affected by collar adjustment; an ordinary glass, furnished with compensating screw, is scarcely superior to an ordinary non-adjustable lens ; one may turn the collar through its entire range, without sensible or corresponding change in definition. me saying that he was surprised that Dr. Woodward should have allowed the publication of prints giving- such indifferent ideas of the work of American lenses. I replied, that as I then understood the mat 1 er, it was Col. Woodward's intention to show the work of the objective purposely placed out of adjustment, and I so continued to think at the date of the above lecture, a fact obvious to the reader. I also su-rgested that the litho- graphs might not fairly represent the photographs ; that if it was the case, Col. Woodward would surely make the fact known. His silence, however, authorized the inference that the original photos had not suffered at the hands of the lithographer. I th nk I can now safely affirm that the general opinion is that one of these lithographs was intended by Col. Woodward to give a correct idea as to the appearance of P. S ixonica when property resolved, i. e., that it might be contrasted with the others then presented. Be all this as it may, I am prepared to asse- t that no one of said lithographs gives any idea of the proper resolution of Fr istulia Saxonica. J. E. S.. January, 1878. SUPPLEMENT. 391 On the contrary, objectives of: the widest apertures, and capable of yielding intense definition, require the strictest attention to their adjustment. * Nor is this all. It is quite possible to accurately adjust a first- class objective, and, nevertheless, in this very act defeat the maximum performance of a first-class glass 1 When working with oblique light, the maximum performance of a superior glass will be obtained at maximum aperture ; if this maximum aperture obtains, with the systems ' closed," as is often the case, it is then manifestly our business to use covers of such thickness as will " correct" the objective at " closed," and to work such a glass over thinner covers, requiring the lens to " correct " at, or near bk open point," would surely defeat its best performance. It being possible that we may have time in the course of the evening to practically discuss this point, I have brought here an objective which, in any position of its collar, has plus 180 of aperture ; its balsam angles are at " closed," 97i; at half way between " open " and 4 * closed " 95 ; at open point, 85. It will be an easy matter to demonstrate that this glass is defeated by the thin covers of the Moller plates, over which the glass will " correct " near to " open point," and conversely, of the decided increase of definition obtained (and angle also) when worked through a supplemental cover of sufficient thickness to cause adjustment with the systems at, or near " closed." I have brought here another, and a totally different objective; this glass has a constant bals,im angle of 100 through nearly the whole run of its adjusting screw. Manifestly, when using this glass, there need be less attention paid to the thickness of cover, a fact which is demonstrated in practice. * In an article contributed by Mr. P. B. Wenhana see London Microsr.op- icalJournal for March, 18761 read, as follows : "The adjustment seems to be a stumbling- block for those advocating an extra immersion theory. We have now in use thousands of serviceable im nersion object-glasses, capa- ble of denning most tests, and whic-i have no adjustment, as they are set for an average thickness of cover. They answer well, because in the im mersion system the errors of cover aberrations ara nearly eliminated, and with a balsam intermedium they would be inappreciable." (Ill) J. E. S. 392 HOW TO SEE WITH THE MICROSCOPE. These two objectives were constructed expressly for me, and were especially intended for conjunct use they are in truth, companion glasses ; either of them will display the 19th band by oblique use of artificial light, and also the markings of An- gulata by central lamp illumination. Of the two, the first- named has the greatest working distance, and, for reasons already given, will work at maximum performance over covers l-50th of an inch in thickness, and in the hands of one thor- oughly conversant with its functions, it is, perhaps, the most generally useful glass. I have here still another objective of plus 180 of aperture. This glass was intended to be a compromise, and to serve to a great degree the purposes both of the l-6th and the l-10th before mentioned. The glass I now refer to has at u closed " a balsam angle of 97 ; at open point, 92. The compromise is thus appar- ent : this l-6th was made to my order for the gentleman who tills the executive chair of this society. It asks no favors of M. Kobert, nor of a centrally posed Angulata, and when one is con- fined to a l-6th alone, a glass of this construction will prove of great value. These conditions, which have still greater force when we include the work of various opticians, need attention and study in default of which you may expect diffraction lines and dif- fraction borders; and, perchance, our old friend, the fct Nas- myth," may put in an appearance ! I repeat, that it was the dominant purpose of these desultory remarks to call your attention to the importance of microscope instrumentation, and to the manipulations connected therewith. To the fact that it is a study, a profession in itself, and an accomplishment that must be fully mastered at the outset, before one can investigate with precision, or have claim to the confidence of others. In point of fact, the most expert manip- ulator will constantly have something to learn there is no landing place where one can stop and rest. The world pro- gresses, and so should the microscopist pari passu. I take it for granted that nothing I have said will lead you to suppose that I am opposed to the legitimate use of low-angled objectives; nothing could be further from my purpose. When SUPPLEMENT. 393 properly used, for preliminary examinations, they are convenient and useful, but for advanced work they should be abandoned, and in favor of more inconvenient glasses of wider apertures. A wide-angled lens, incapable of receiving and utilizing cen- tral beams, is a faulty and undesirable objective ; it is, in fact, but half a glass. And on the other hand, a low-angled objec- tive, incapable of receiving lateral beams, is. in my opinion, equally undesirable, unless, indeed, when we are prepared to sacrifice force of definition to convenience of handling. It must be admitted that there are functional and character- istic differences in the performance of the two classes of objec- tives; for instance, a wide-angled glass of relatively shorter focal length will not see so far around an object as will one of narrow aperture and longer focal distance.- This, as well as other considerations which might be mentioned, offer no rebut- ting testimony to the statement already advanced, that the principal advantage presented by the low angles is their con- venience in manipulation. In conclusion, I have to thank you for your kind attention to the rambling remarks I have had the honor of presenting. Dur- ing the few short hours that I have been in your city, the earth has not had time to make one rotation ; but I have had a plenty -of time to experience and enjoy a generous hospitality. I am now ready to show you the promised objects, and shall be happy to see what you have to offer. You will find me ready, willing and ardent to be taught, and in microscope matters be assured I am as absorbent as a sponge. A CHAPTER ON ELEMENTARY PHYSICS. (Dedicated to Prof. Hitchcock.) Part First The Sun. u The luminous orb, the light of which constitutes day ; the central body around which the earth and planets revolve ; a celestial body which can be seen almost any fair day through a piece of smoked glass." I beg my friend to read the above little monograph on ele- mentary astronomy carefully. Assuming his compliance with this request, I go on to say that just after sundown this evening, my attention was called to his really kind notice of myself, as 394 HOW TO SEE WITH THE MICROSCOPE. well as my Dunkirk lecture. Allow me to assure you, my dear professor, that although we have been pulling at opposite ends of the rope for some months, the generosity I have experienced at your hands has been vastly in advance of what I. could have returned, and has placed me in position to receive any criticism that you might offer with the best possible grace. I now propose to jerk my end of the rope in a manner that will make things lively with you I The fact is, when I get after you with a " sharp stick " you become unusually brilliant with the jerk responsive 1 I like it. I admit that you are one " who demands accuracy of expres- sion in every branch of science" "that the scientist has no right to say what he does not mean, and he has no right to pre- sume that his readers will understand him if he uses incorrect language." I therefore have placed the above little monograph on elementary astronomy at your service, and in timely season r fearing otherwise you might be led astray by my use of th& word " sundown "you will see the point. It's true that Joshua of old commanded the sun and moon to stand still, and the-' story is found in a book generally admitted to be a classic, but no matter. Now, professor, I fear that you do not practice what you preach ; for I read (page 92), " if this question were put to a thorough physicist * * * knowing nothing about balsam or fluid mounts, etc." Isn't there an " impossibility ' r here ? A thorough physicist knowing nothing, etc. There's a screw loose somewhere. liight on your next line is another jumble. Here is a want of accuracy or what not which is it ? You say " Must the scien- tist be led by the nose," etc. If this expression is accurate, 1 want you to tell me just how this kind of a thing is accom- plished ; give me the p-r-a-c-t-i-c-a-l details, just as it would be done in the flesh, including the " adopt " and the " teach ' r before an audience, too, without " apology " and the why of it. " It's the right and duty of every man of science to ask this little question whenever it occurs to him." " The scientist has no- right to say what he does not mean." Let us have the facts. Part Second. 180, plus 180, 180 -f 45. It is true, my dear SUPPLEMENT. 395 sir, that in my Dunkirk lecture I did use the words u plus 180 of aperture/' Now that select and intelligent audience (com- prising physicists who did know something about " balsam angles,") so far from demanding an " apology," generously and unanimously gave me a vote of thanks. Curious, wasn't it ? I remember well my delight in there meeting the veteran Dr. J. W. Armstrong, Principal of the Fredonia Normal School, and one of the leading educators of your state; another physicist, too, who can talk intelligently as to " balsam angles," and who- has made the apertures of objectives an especial study, and who afterwards became one of my most valued correspondents. Nor did we have any quarrel about the " plus 180 Q ." Most of the audience had read about Joshua, and doubtless would not baulk at such expressions as " sunrise '' or " sunset." After all, professor, admitting that the " plus 180 " might have courted sor~.e such gentlemanly criticism as it finally got from you, I reckon I was as near right as Joshua. But before I can lift you over this stile, I must s.coop you up ! get you together in some shape, so you can be handled. First of all T you seem to put the 180, plus 180, 180 x 45, all in one boat together; you regard them as synonyms. And, secondly, I have to learn some things from you. Messrs. Tolles and Spencer you denounce because they mark their objectives 180, which you say is not only " impossible,"" but " absurd," and that one of these gentlemen (you don't say which) attempts to lead the scientist " by the nose." And you further say that one ot them (I don't know which, again,) " might as well add 45 to said 180. Well, here is material enough to commence on. Now, my dear professor, you maintain it to be the " right and duty " even of every man of science to ask this little question whenever it occurs to him the " why" part you know). That I have been engaged in a controversy with you for months, demonstrates, my claim as a " man of science." You can't dodge that, and the "occur " part is present and up to the high-pressure notch. Now, I want to know " why " it is that 180 of aperture is- impossible ; "why " that plus 180 of aperture is impossible and absurd. We have your assertions, but minus the ghost of a dem- onstration. 396 HOW TO SEE WITH THE MICROSCOPE. Why do you accuse Messrs. Tolles and Spencer of perpetrat- ing acts that are absurd and impossible ; and why do you ven- ture to hint that one of these gentlemen attempts to " lead scientists by the nose," (whatever that may mean). The names of Spencer and Tolles are revered by American microscopists, and their unrivaled efforts in the improvement of object-glasses have won for them a world-wide reputation. The chances are that they know more of microscope optics than you and I put together; and these are the men who mark their objectives 4t 180." Why should there be kt a law to prevent it V" Now, professor, if this 18*0 is impossible and absurd, will you kindly inform the readers of this journal what figures Tolles and Spencer ought to engrave on their wide-angled objectives in place of the awful tfc 180." Will you be kind enough to name the extreme angle immediately adjacent, but not contact- inQ the impossible and the absurd ? Again I read, " plus 180 does riot mean 97 balsam." Did I assert this V Now, I ask what does 97 balsam mean ? Let's have it, and the a why" thereof. Unless you can tell me exactly what the 97 balsam angle is, I shall not take any stock in your above assertion. Once more, you say that "true apertures can be measured and definitely stated." I wish that you would tell Mr. Wenham how the thing is done ; he tried for a whole year to measure one of Tolle's objectives, without getting any two results alike ! But I am after you, not Wenham. I desire to learn irom you precisely what " true aperture is." When thus taught, then 1 desire to know by what physical process the same can be meas- ured " definitely" you know. "Accuracy" is the thing we scientists want. Now, my dear sir, I call on you to answer all of these inter- rogatories, and when you shall have proven that 180, plus 180, or 180 X 45, are one and the same thing ; when you shall show that Messrs. Tolles and Spencer are asserting absurd and impossible things, and more, are trying to lead scientists " by the nose ;" when you shall prove that a thorough physicist can know nothing of balsam or fluid mounts ; when you shall have demonstrated that I should have apologized to my Dun- SUPPLEMENT. 397 kirk audience ; when you shall have proven what 97 of balsam angle is ; ditto as to " true aperture," and how to "definitely measure " the same then and riot until then will I take the "plus 180 " under advisement. Meanwhile we will be good friends, and with Gen. Grant say, " Let us have peace." Don't omit reading the reprint of Wenham's article on angular aper- ture, pages 74 and 75. CHOICE OF OBJECTIVES. Ed. Am. Jour. Microscopy. It was with real pleasure that I read the article entitled " Dr. Carpenter on Angular Aperture," by W. G. Lapham, Esq., in your May issue. First of all, it is very satisfactory, from the fact that Mr. Lapham speakes from a practical standpoint. The gentleman is- an entire stranger to me, but the fact that his conclusions are drawn from his personal, and, I doubt not, protracted experi- ence, is evident from the ability with which he handles his- subject. Your readers are well aware that I have often complained that I have been compelled to fight theory with practice and that no effort on my part sufficed to induce my opponents to abandon their theoretical ideas, and to examine practically as to the truth of the positions advanced by myself. In Mr. Lap- ham, however, I resognize a co-worker, and althiugh the results he arrives at are not in perfect coincidence with my own, I find nothing to criticize, but am simply desirous of further comparing notes with the gentleman, in the hope that some- thing to the advantage of microscopy may be developed. I propose to present a few thoughts for Mr. Lapham's con- sideration, requesting the gentleman to give them whatever study and attention he may elect, and to advise your readers- as to the conclusions he arrives at; and, as before intimated, nothing that I have to say ought to be taken in the light of a criticism of his really excellent paper. First, I desire to ask if Mr. Lapham does not attach too much importance to the so-called " penetration." Is there in esse, any such thing as "penetrations?" Perhaps it will be well, first of all, to settle this point. 398 HOW TO SEE WITH THE MICROSCOPE. Now I hold as follows : We will take, for example, two glasses, both possessing the same amplifications and the same apertures ; now of these two glasses, the one having the greater working distance will exhibit structures situated slightly out of the precise focal plane, or what amounts to the same thing, will be less susceptible to slight changes in the focal distance, or again, to use the words of Dr. Carpenter, will have the greater pene- tration. In extreme cases, the item of aperture may be dis- regarded. For instance, as stated in my Dunkirk lecture, a spectacle lens of sixty inches focal length will be endowed with greater penetration than a To'les duplex objective. But in the Dunkirk address, I did not avail myself fully the demonstration afforded by the spectacle lens, but now invite Mr. Lapham's attention, thus : If it so be that with the spectacle lens I am enabled to see with perfect clearness of vision objects across the road, it will surely occur that when I attempt to read fine print, that the lens will defeat me. I will, to be sure, see the lines of the print, will recognize the contour of the book, and larger objects in immediate proximity, etc. Here is an example from everyday life, to-wit : The glasses suitable for reading will not answer for observations at a dis- tance. True it is that with such glasses, with which we read with ease, we may also see the general forms of things across the road, yet they suffice not to render clearly the details thereof. Hence we have all of us observed that many persons wearing convex glasses often use two pairs of spectacles, one for near and one for distant vision. Now in this everyday case we are taught a ICLSOH, that, from some cause or other, has been a slow one to acquire. First ** penetration," in its naked aspect, is simply a function depend- ing upon working distance ; and secondly that "penetration," unless acccmpartied with a certain amount of definition* is practi- cally worthless. I ask Mr. Lapham's close attention to this point, one that has been terribly overlooked. Now, if Mr. Lapham's one-sixth of 180 happens to just " turn the corner," i. e. have balsam angle, say, about 85, I would feel sure that a little observation would lead him to the same opinions I have arrived at, and I only fear that he has SUPPLEMENT. 399 chosen one of the highest balsam angles, in which case he will have to fall back on his four-tenths. Nevertheless, let him, if he will, try the experiment, and report as to whatever is gained in point of penetration by the use of his one-forth of 50 over and above what can be obtained by the use of the one-sixth, or the four-tenths. The point I have to make is this the one- fourth of 50 will have the greater penetration (so-called, like the spectacle lens) but will lack definition, to the end that more is lost in the latter element than is gained in the former. I state as a matter of fact, but with no desire to bias the further observations of Mr. Lapham, that I have used just such a one-fourth as he describes, but have ultimately discarded it, and in favor of a one-sixth marked by the maker 180 Q , which I find will do all the work (penetration included) of the one-fourth of 50 and a great deal more besides. But behind this one-sixth, I hold a one-tenth of 100 balsam angle in reserve, for work where " penetration" is ruled out. As to the other point suggested. Is there not undue weight attached to this "penetration?" With me, I have often been obliged to take special measures to get rid of this function, and for this purpose use the Beck illuminator, which gives me only surface structures. I mention the fact, but am willing to admit that a certain amount of " penetration" is at times desirable, and should be provided for as perfectly as possible. Mr. Lapham recommends a four-tenths of 100. I have often thought that such a glass, or a half-inch of the same angle, would be desirable, and, as a luxury, arn still of the opinion. It must be remembered that he very properly rules out the item of cost ; wnile on the other hand I have made it a study to avoid expense, where my opinion has been solicited in the matter of selection of objectives. Mr. Lapham recommends a certain number of low-angled glasses, all others to be of the highest angles, and of the best quality and well corrected. Why not amend this by insisting that all glasses have the highest attainable angles? selecting of such the one suitable for the work in hand. Again, Mr. Lapham states that we have no need to consider objectives of lower power than the half-inch for " they are not 400 HOW TO SEE WITH THE MICROSCOPE. made with angles sufficiently high to injure penetration." Here is involved an error in fact, one quite pardonable too. Not long- since a German gentleman remarked to the writer that it seemed to him that when the London opticians demonstrated a certain opticial law, some Yankee optician would be just mean enough to make an objective that would upset the whole arrangementl And it is perforce of this fact that Mr. Lapham becomes involved in his very pardonable error. Now I have in my possession a two- thirds of the Messrs. Spencers of 48 aperture. They have lately made to my order an inch of 47. The clear diameter of both glasses is about the same; the working distance of the two-thirds is 25-100ths of an inch, while that of the inch is but 13-100ths of an inch, and the '"penetration" of the latter (so- called) is less than that of the 2-3ds. In fact the penetration of the inch is ''injured," as compared with one of 30. The reader will notice that Mr. Wenham's pet theory gets also into grief. I assure Mr. Lapham that this new inch is a glorious glass, pene- tration or no penetration. Finally, I desire to extend to Mr. Lapham personally my thanks for his instructive and interesting article. It will be a pleasure, and, I doubt not, profit to compare notes with him r and, in the words of my very generous opponent, Prof Hitch- cock, I will add that all I desire is "the facts." Mr. Lapham r by the way, will be pretty sure to catcli it, about that 180 Q , from Prof. H., on the " impossible" and the " absurd." It may be well enough to add that my first impulse was to- write Mr. Lapham privately for an interchange of personal experiences, but on reflection chose this, the more public plan, hoping to enlist the attention of others in the same direction. OLEOMARGARINE AGAIN. Ed. Am. Jour. Microscopy: The article giving " The Micro- scopical Examinations of Oleomargarine," by Prof. Michels, which appeared in a recent issue of this journal, was perused by me with much interest, and I at once resolved to repeat the experiments as detailed. The first thing requisite was to secure authentic specimens of SUPPLEMENT. 401 oleomargarine. In order to do this, I solicited the friendly aid of a prominent gentleman of this city, who is also well known in business circles in New York. I also wrote, independently T to a gentleman in your city, urging him to obtain for me the samples required. Desiring also to procure a specimen of genuine dairy butter, I applied to a well-known citizen of this city, who procures his supplies directly from a farmer. After an interval of ten days, I was, in response to my solici- tations, in possession of three samples of oleomargarine, and one sample of pure dairy butter. The three samples of oleo- margarine are directly from the manufacturers at Xew York city, and will be referred to as Nos. 1, 2, and 3. The four samples were subjected to examination under the microscope ; tha objectives used were a l-4th inch of 100 by Tolles, and Spencers late duplex l-4th of 180. Samples Nos. 1, 2 and 3, and also the specimen of pure dairy butter, showed many crystals of chloride of sodium ; the crys- tals furnished by the pure butter were, however, cleaner, and more acceptable generally than those exhibited by Nos. 1, 2 and 3. Samples Nos. 1, 2 and 3, in addition to crystals of chloride of sodium, displayed other crystals, those of nitrate of soda being prominent ; while forms closely resembling crystals of choleste- nne were found in considerable numbers. Regarding Nos. 1, 2 and 3, it may be remarked that Nos. 1 and 2 were, to outward appearance, tolerably fair imitations of genuine butter, and might by the ordinary purchaser be accept- ed and bought as such. N"o. 3 was a poorer counterfeit, and would probably be rejected by most buyers ; but if mixed in equal parts with the genuine article, the mixture would be likely to deceive the purchaser. In samples Kos. 1 and 2 the microscope displayed the ' feathery crystals" (margarine) described by Prof. Michels, although these were not constantly present in every field exam- ined. By moving the slide, other fields were brought to view in which these crystals were much more prominent than those given in the cut accompanying Prof. Michels' paper. The crys- 402 HOW TO SEE WITH THE MICROSCOPE. tals of nitrate of soda and cholesterine (?) were to be seen in every slide prepared from the samples named. Besides the crystals named, samples Nos. 1 and 2 gave " sus- picious cells " in large numbers, accompanied by shreds and tissue fibres, many in a broken down condition, while others seemed to be in a tolerably normal stdte, sufficient almost to establish the presence of voluntary muscle. Bundles of these fibres were closely examined with the duplex l-4th, under powres as high as 1,600 diameters, with the endeavor to bring out the transverse markings ; this was not accomplished owing, doubtless, to the nature of the vehicle (my observations in this direction will be continued). Many of the bundles seen were completely broken down, and the elementary fibres detached. Sample No. 3, when examined under the microscope, displayed fewei f the "feathery crystals;" nevertheless, this was the most u buspicious " specimen of the three ; there were multi- tudes of " suspicious cells," shreds and patches of tissue, in a more or less broken down state. In one field I felt tolerably sure of finding encysted hydatids. This slide unfortunately, was accidentally destroyed by the water getting under the cover. To give an intelligent description of this material (No. 3) would require far more time to its study than I have at my com- mand at present ; but I hope to attack it again, and at an earlr day. Suffice it now to say that this specimen contains verymani " suspicious " elements, and that its behavior under the objec- tive (here I also include Nos. 1 and 2), is with the exception of the crystals of chloride of sodium, and the presence of a few fatty globules totally different from that of pure dairy butter. The sample of pure dairy butter gave fields just as represented by Prof. Michels, with the exception that crystals of the chlor- ide were almost constantly present. Having established, to my own satisfaction, at least, the in- tegrity ot the observations of Prof. Michels, I therefore hold that the gentleman should be regarded in the light of a public benefactor ; the matter he has presented will be found worth serious and careful investigation. In one of my recent lectures before the medical class of this SUPPLEMENT. 403 College, on the JSntozoa.t I quoted (substantially) from Dr. liob- erts, as follows : " A marvelous light has been thrown in recent years on the zoological position of the Entozoa, chiefly by the researches of Siebold .and Van Beneden. It has been ascertained that the hy- datid worm found in man, constitutes the encysted phase in the developement of a very minute tape-worm which infests the dog. The tape- worm in question is the Tcenia, echinococcus ; the entire adult animal is so small that it scarcely exceeds the size of a millet seed. It consists of but three segments, of which three, the last only is fruitful. When this segment arrives at maturity, it is cast off, and a new one developed in its place. Myriads of these worms are sometimes found in the intestine of the dog, and their eggs are discharged in countless numbers with the excrements, the eggs so discharged are scattered far and wide ; and some of them find their way with the food into the stomachs of men and other creatures suitable for their de- velopment. Arrived there, the embryo is liberated ; and after penetrating the mucus membrane, it burrows its way, or is car- ried by the blood current to some distant organ, where it is arrested. Having thus lodged itself, it presently reappears as a hydatid vesicle, in which are developed the echinococci, as be- fore explained. Dogs in their turn become infested with the corresponding tsenia by feeding on the offal of slaughtered sheep, pigs, etc., which had been infested with hydatids. The echinococci therein contained develop in their intestines into the tsenia echinococci, and thus the circle of transformation and development recommences." By similar cycles of transformation and development, do we arrive at a class of parasites known in medicine as the ectozoa. This term may be said to include, or be applied to, worms or larvae of insects that have been introduced into the intestinal canal by accident. Animalcules, such as the hair worm, grub of the fly, may be mentioned ; also the larva of the bee, the spi- der, etc. Among animals, the disease known popularly as the botts, to which the horse is frequently a victim, is caused by such animals swallowing the ova of the oestrus or gad-fly. That oleomargarine manufactured from refuse animal fats, 404 HOW TO SEE WITH THE MICROSCOPE. in the manner described by Prof. Michels, and at a temperature not above 120 F., may be a highway through which " eggs so discharged " find their way into the stomachs of men, is too pal- pably evident to need further comment. INDEX. Acetate of soda, solution, 329. Acme microscope, 84. Adjustable objectives, 148. Adj ustable glasses, 129. American stands, 17. American stands compared with German, 18. American histological stand', 39. Analysis, chemicals for, 322. Analysis, chloride of sodium, 328. Analysis for albumen, 337. Analysis for glasses, 103. Analysis, earthy phosphates, 331 Analysis, phosphoric acid, 330. Analysis, sugar, 332. Analysis, sulphuric acid, 331. Analysis, urea, 323, 325. Analysis for sugar, 335. Angular aperture, what is it? 93. Angular aperture defined, 93, 370. Angular aperture illustrated, 94. Angular aperture, how to meas- ure, 95. Angular aperture, versus work- ing distance, 115, 121. Angular aperture and central illumination, 361. Angular aperture and penetra- tion, 118. Angle high glasses, 103. Apparatus for micro-chemical use, 320. Apertures, angular, 93, 405 Aperture, angular balsam, 123. Artificial light, 187. Balsam apertures, 128. Balsam angles, advantages of, 141. Balsam angle, management of 257, Balsam angle, and working dis- tance, 142. Balsam angle, low objective 144. Baryta solution, 324. Bausch & Lomb's microscopes, 50. Bausch & Lomb's microscope, professional, 53. Bausch & Lomb's microscope, students, 66. Bausch & Lomb's microscope, stands, 344. Bausch & Lomb's objectives, 346. Beck's microscopes, 72. Beck's microscope stands, 347. Beck's vertical illuminator, 217. Beck's vertical illuminator, how to use, 221 Binocular, objections to, 30. Binocular, versus monocular, 29. Biological microscope, 68. Bull's eye condenser, 225. Bull's eye condenser, how to use, 227. ' Bullock's microscope, first- class, "A. 1." 59. 40G INDEX. Bullock's microscope, 59. Bullock's microscope, D stand, 57. Bullock's microscope, small, best, 67. Bullock's microscope stands, 343. Carbonate of soda, 324. Carpenter on object glasses, 97. Centennial stand, Zentmayers, 34. Centennial stand and A. 1. com- pared, 63. Central light and high angles, 257 Choice of objectives, 397. Choice of objectives for regular | work, 202, Chemicals for analysis, 322. Chloride of sodium, 327. Chromate of Potash, 327. Collar adjustment, objections to, 208. Concentric rotating stage, 25. Condenser, Bull's eye, 225. Condenser, small diameter, 308 Contributions to the Medical News, 358. Covering glass guage, 216, Covering glass, selection of, 213. Daylight, how to use it, 1*3. Diatoms, examinations of, 255. Diatoms tor test, 251. Diatoms, order for test, 254. Diatoms resolution as objective test, 249. Diatoms resolution, with high i powers, 245. Diatoms resolution, with low i powers, 245. I Diatoms, resolution, 243. Draw tube, advantages of, 136. Dry mounts, list of, 305. Dry mounts, \vith high objec- tives, 298. Duplex glass, the first, 9. Essentials of a reliable stand, 21. Examination of morbid pro- ducts, 206. Examination of urinary depos- its, 203. Examination of oleomargarine, 400. Eye pieces, 256. Eye pieces high, 146. Eye pieces fittings, 33. Eye pieces solid, 156. Eye pieces should fit loosely 204. Eye training, 287. Eye training illustrated, 239. Family microscope, 57. Fasoldt's micrometer, 357. Fehling's solution, 333. Ferro cyanide of potassium so- lution, 329. Field, flatness of, 126. Fighting objectives, 117. 140. Flatness of field, 126. Four system glasses, 9. G Glasses, high angle, 103. Glasses, high angle history of 100, Glasses, testing aperture, 192. German stands compared with American, 18. INDEX. 407 German student lamp, 187. Handling objectives. 259. High angles, 103. High angles balsam, 125. High angles, discursion of , 359. High angles, objectives, 100. High, eye piecing. 146. High objectives, with dry mounts. 298. Higher powers, work with, 235. History of high angle objec- tives, 100. Histological stand, 39. Illumination, artificial, 187. Illumination, daylight, 183. Illumination small best, 189. Illumination, sunlight, 186. Illumination, varieties of, 183. Illuminator, Beck's vertical, 217 Illuminator, modified, 219. Illuminator, Wenharn's reflex, 157. Illuminator, Wenham's with sunlight, 191. Illuminator, Woodward's, 163. Immersion, 125. Kerosene oil immersion lens, 316. Lens, Tolles' traverse, 179. Lessons on seeing with the mi- croscope, 261. Lesson first, 261. Lesson second, 262. Lesson third, 265. Lesson fourth, 266. Lesson fifth, 268. Lesson sixth, 270. Lesson seventh, 271. Lesson eighth, 273. Lesson ninth, 274. Lesson tenth, 280. Lesson eleventh, 282. Lesson twelfth, 284. Low balsam angles, 144. Low powers, working with, 225. Management of high angles, 257. Manipulations, microscopic, 157. Marais' approximate tubes, 330. Measuring bottle, 324. Medium power of glass 144. Micrometer, necessity for, 252. Micrometer, Fasoldt, 357. Micrometer, Rogers', 356. Micro-chemical apparatus, 320. ! Micro-chemical examination of urine, 318. Microscope, Acme, 84. Microscope, Biiusch & Lomb, 51. Microscope, Beck's, 72. Microscope, Bullock's, 59. Microscope, dissecting, Beck's 79. Microscope, "D," 67. Microscope, economic, 72. Microscope, family, 57. Microscope, first-class A 1, 59. Microscope, international, 348. Microscope, investigator, 345. Microscope, new biological, 68. Microscope, new histological, 79. Microscope, monocular vs. bin- ocular, 80. 408 INDEX. Microscope, national, 29. Microscope, popular, 72. Microscope, professional, 63. Microscope students, 56. Microscope, Sidle's, 84, 351. Microscope selection, 147. Microscope, Tolles , 47. Microscope, Zentmayer, 34. Microscope, use and abuse of 376. Microscopic manipulations, 157 Mirrors, concave, 32. Mirrors, hangings strong, 38. Mirrors mountings, 32. Mirrors, plain, 31. Mirrors used as condensers, 229. Mirrors where attached, 226. Monocular vs. binocular, 29, 80. Moller's test-plates, measure- ments of, 253. Mounting of objectives, 129. Names of microscopic dealers, 341. Robert's test-plate, 254. Objections to mechanical stages 24. Objections to binoculars, 30. Objectives, adjustable, 148. Objectives, broad guage, 230. Objectives, balsam, 141. Objectives, choiceiof, 397. Objectives, Dr. Carpenter on 97. Objectives, fighting, 117, 140. Objectives, high angle, 97.. Objectives, high angle, testing ot',107. Objectives, low balsam angle, 144. Objectives, one-sixth preferred to one-fiftieth, 109. Objectives, immersion, 125. Objectives, experience with, 202. Objectives, for physicians, 207. Objectives for regular work, 202. Objectives, test with diatoms, 249. Objectives, testing aperture of 192. Objectives, testing, 198. Objectives, wide angle, what is it ? 137. Objectives, working distance of, 1Q6. Objectives, mounting, 129. Objectives, oil immersion, 310, Objectives, Spencer's, 353. Objectives, Tolles', 354. Objectives, performance of, 368. Observer's position, 246, 289. Oil immersion objectives, 309. Oil immersion, objectives, expe- rience with, 315. Oil immersion objectives of Zeiss, 310. Oleomargarine examinations, 400. Penetration and angular aper- ture, 118. Physicians, objectives best for, 207. Physics, elementary hints on, 393. Pod ura, scale resolution of, 299. Position of observer, 246,289. Professional microscope, 53. Rising of the object. 276. INDEX. 409 Reaction of urine with tests, 339. Rogers' micrometers, 356. Selection of covering glass, 213. Selecting a stand, Sliding tube, advantages of, 44. Short tube stands, 25. Small light best, 189. Small kerosene lamp, 189. Society screw, 232. Society screw not sufficient for high angles, 88. Specific gravity and tempera- ture, 340. Spencer's objectives, 353. Spencer's one inch of 50, 230. Stage, thin, improvised, 39. Stage swing and mirror best, 91. Stage, concentric, rotating, 25. Stage, mechanical objections to 24. Stage, room necessary, 26. Stage used by the author, 27. Stand, Acme, 84. Stand, American, 17. Stand, American Centennial, 34. Stand, Bausch & Lomb's, 50. Stand, Beck's, 72. Stand, Bullock's, 59. Stand, essential of a reliable, 21. Stand, Economic, 72. Stand, Histological, 79. Stand, "D,"67. Stand, Investigator, 345. Stand, International, 348. Stand, large and small, 26. stand, large " BB," 47, Stand, large " A," 48. Stand, new biological, 68. Stand, new National, 80. Stand, first class " A. 1." 69. Stand, small best, 67. Stand, popular, 72. Stand, Sidle's, 84. Stand, Tolles', 47. Stand, students', 49, 56. Stand, small and cheap, best, 92. Stands, with short tubes, 25. Stands, Zentmayer's, 34. Students microscopes, 49, 56. Sunlight illumination, 186. T. Table for work, 229. Temperature and Urine specific gravity, 340. Testing high angles, objective, 107. Thin stage necessary, 90. Tight fitting eye pieces, 204. Tolles' first duplex, 9. Tolle's microscopes and objec- tives, 354. Tolles' traverse lens, 179. Tolles' large " BB "stand, 47, Tolles' large " A " itand, 48. Tolles' students' stands, 49. Traverse lens, 179. Tube casts,, no genuine seen, 319. Tube sliding, advantages of, 44. U. Urinnry constituents, propor- tion of, 339. Urinary deposits, examinations of, 203. Use and abuse of the microscope 375. V. Volumetric analysis, 318. 410 INDEX. w. Weights recognised, 321. Wenham's reflex illuminator, 157. Wide apertures, lessons in the use of, 261 Wide apertures, management of 258. Wide angle objectives, 137. Wide angle objectives and col- lar adjustment. 139. Wide angle objectives and illu- mination, 140. Wide angle objectives and working distance, 137. Work table, 229. Working with higher powers, 285. Working with lower powers, Working distance of high an- gles, 137. Working distance of high bal- sam angles, 143. Working distance of objectives* 108. Working distance vs. angle aperture, 115,121. Woodward's illuminator, 163. Woodward's illuminator modi- fled, experience with, 177. Z. Zentmayer's stands, 34, 355. Zentmayer's American Centen- nial, 34. Zentrnayer's American Histo- logical, 39. SPECTACELS ; AND HOW TO CHOOSE THEM. BY C. H. VILAS, A. M., M. D. Professor of Diseases of the Eye and Ear in the Hahnemann Medical College, and Ophthalmic and Aural Surgeon to the Hahnemann Hospital, Chicago, etc., etc. This book is full of interest and instruction to readers of all classes. Designed more especially for the profession, it never- theless does not deal in technicalities or obscure terms and will doubtless tind a large demand among non-professional people. In a clear and comprehensive manner it treats of a most important subject, a subject concerning which, far too many er- roneous and dangerous notions prevail. It's aim is to dissemin- ate knowledge, and to prevent the common haphazard custom of choosing Spectacles, a custom so often disastrous to vision or fruitful to discomfort. The Author points out how, within a comparatively recent period, what was once veiled in mystery, has attained a sure place among the sciences ; how the know- ledge of the proper construction, adaptation, and uses of Spec- tacles has grown to great proportions, and has led to a revolu- tion in the treatment of eye affections. Many popular delusions will be dispelled by reading this book. It is valuable alike to the physician and the layman. The former may utilize it in practicing his profession ; the latter will prepare himself to avoid errors fatal to vision. All the new and useful cases of trial lenses are described and illustrated and their respective merits and demerits are pointed out. It is clearly shown how the low prices, at which a good set of trial lenses can be obtained, will enable the physicians in general practice to give attention to the titting of Spectacles and to treating ordinary defects of the vision, thus preventing the frauds so often practiced by itinerant venders. The Author's well known accomplishments in this depart- ment of science, have eminently prepared him to skillfully treat so important a subject. The work is illustrated and full of practical hints. Price bound in cloth, $1.00. DUNCAN BROS., Publishers. 131 & 133 S. Clark St. , CHl CA G O. THE NURSE; OR, HINTS ON THE CARE OF THE SICK; INCLUDING MOTHERS AND INFANTS, AND A DIGEST OF DOMESTIC MEDICINE. By CHARLES T. HARRIS, A.M., M.D. Elegantly bound in Cloth - Price, 60 cents. "Every Nurse should have a copy." "Every Mother should possess this useful work." " It will not hurt physicians even to glance over the pages devoted to mothers and nurses, and this little treatise ought to become one of the tracts domiciled in every household." North Am. Journal of Homoeopathy. This is a valuable volume to professional nurses and mothers, the natural nurses. The author strongly advocates the importance of intelligent, self- sacrificing nurses. The instruction the book contains is clearly and con- scientiously given. Boston Inventors & Manufacturers' Gazette. Such a work is very much needed. Itis simply and clearly written, giv- ing hints on all the points which a nurse ought to know. We cordially recommend this little work to the attention of mothers and nurses who will find it a valuable vade mecum. Monthly Homoeopathic Review, London. A neatly printed, handsomely bound work of over a hundred pages, written with the endeavor, as stated in the preface, to make their scope 44 broadenough to cover the wants of two classes; the conscientious and ambitious professional nurse, and the faithful and loving mother." The matter of the worfc, from the introduction to the last page, seems well and carefully written and very sensible. Ypsilanti Sentinel. It is written in simple and concise style and free from all technicalities, and abounds in valuable facts and directions to those who have health as well as to those who are called to nurse in the sick room. It is a book every mother could read with profit. Skilled and trained nurses are not a ways in reach, and the lives of those deartoihe family are of ten imperiled by simple ignorance of what every intelligent person should know. Good nursing, every intelligent physician will say, is of more value than drugs. The hand- some little volume should find its way into many homes, and by the intelligent observance of its rules, blessings alone will result. The News. ^B^May be ordered through your physician, or newsdealer, or will be sent to you direct on receipt of price. DUNCAN BROS., Publishers, 113 Madison and 131 & 133 Clark St., Chicago. HOW TO BE PLUMP. OR TALKS ON PHYSIOLOGICAL FEEDING. BY T. C. DUNCAN, M,D., Author of a Professional Treatise on Diseases of Infants and Children and their Homoeopathic Treat- ment; Editor " United States Medical Investigator, etc. etc." Finely bound in Cloth .... Price, 5O Cents. It is an admirable work on hygiene, as far as i't relates to eating Ohio. Farmer. These " Talks " have their own charm, for most of us like to be plump. Women's Journal, Boston. Certainly all thin people should ponder well its suggestions and put them into practice. Voice of Masonry. A brochure which many persons of lean inclinations will be glad to read and may be able to profit by. Banner of Light. The little volume contains riuch sensible professional advice upon healthy and morbid digestion, and the occasions of it. Zion's Herald. The book is intended to indicate how anyone may become fat, fair and jolly, and a careful perusal affords proof thst the author is fully conversant with his subject, and that he has done it full justice. The Cmcdgo Grocer. It is a common sense volume, that believes in rational and practic I methods of preserving health, beautv and happiness. It is not a receipt book of impos-ibilities; it is a bright, genial book, that understands itself from first to last. The Chicago Cosmopolitan. We do most warmly applaud its purpose, and especially commend its philosophy to theunnaturaliy It an, and still mor *. to mothers in the training of delica e children whose physical stamina hardly equals that of a full- grown rye-stalk. Theirs is a leanness to be built up into steady strength and picturesque plumpness of limb and face. The Standard. CHICAGO, Sept 18, 1878. The case referred toon page 45 of " How to be Plump" is our little boy, who was certainly rescued from death's door. This summer he began to run down again. After Dr. Dun an had tried several medicines without benefit he i gain advised " inunction." and again with the same happy effect. The little fellow is now plump and well. CH A i> LKS WALES. ^P~May e ordered through your physician, or newsdealer, or will be sent direct on receipt of price. DUNCAN BEOS,, Publishers, 113 Madison and 131 & 133 Clark St., Chicago. DOCTOR, WHAT SHALL 1 A HAND BOOK OF DIET IN DISEASE. BY CHAS. GATCHELL, M. D., Formerly Professor of Practice, University of Michigan. It is highly endorsed by the Profession and Medical Press. How often do we hear that same question. Doctor; what shall I eat? and though there are text books enough on the Pathology and Treatment of Diseases, there is hardly ever a word found in them about the Hygiene in Disease. Gatchell as a teacher, found out this want, and thus probably originated this little treatise,* lor which we most heartily thank the author. We consider the recipes in it a little Materia Medica for itself, but follow instructions closely ; not quantity, but quality of food deserves our consideration. North American Journal of Homcepaihy. MILWAUKEE, Wis. "I consider your work on "Diet ii Disease" to be the most practical, and therefore the most useful, work on the subject with which I am acquainted. No physician should be wlthoutit; every mother should have it. It is in use in many of the households in which I practice." C. C. OUHSTEAD. M. D. President of the Wisconsin Hommpathic Medical Society. "This work is plain, practical and valuable, It is really a clinical guide on diet, and one the profession will find reliable and correct." United States Medical Investigator. "By far the best work on the subject in pur literature. I find it of use every day. I want one in every household in which 1 practice." Oak Park, HI. F. G. FOLSOM, M. D. "Evidently much investigation, thought and carefulness have entered into the production of this work, and we believe it to be worthy a place in every household." The Magnet. * * * "w e have carefully examined the work and s^all cheerfully recommend it for family use. The directions as to what food and drinks, and modes of preparation are very judicious." * * * Resp. Yours, Janesville, Wis. DR. G. W. UHITTENDEN & SON Professor Charles Gatchell's Manual of 'DIET IN DISEASE' is the best book on the subject for the people. It contains in 160 pages an astonishing amount of condensed information on a subject of great importance, and one but little understood. Its style is admit able, pithy and to the point. The book has no padding about it and deserves an immense sale." SAMUEL POTTER. M. D., President, Milwarikee Academy of Medicine, Aathor of Index of Comparative Therapeutics, etc. etc. 1&ff~ Sent free on receipt of price, $ 1 .OO. DUNCAN BROS., 131 & 133 S. Clark St. CHICAGO. THE FEEDING AND MANAGEMENT OF INFANTS AND CHILDREN, AND THE HOME TREATMENT OF THEIR DISEASES. By T. C. DUNCAN, M. D., PRESIDENT OF THE AMERICAN REDOLOGICAL SOCIETY. CONSULTING PHYS- ICIAN TO THE CHICAGO FOUNDLINGS' HOME. CLINICAL LECTURER ON DISEASES OF CHILDREN. AUTHOR OF "A PROFESSIONAL TREATISE ON THE DISEASES OF CHILDREN" (2 large volumes). EDITOR OF THE UNITED STATES MEDICAL INVESTIGATOR, 'ETC., ETC. MRS. J. E. JOICE writes : "I find it a very useful book and full of practical information, especially about diet for children." L. PAULY M. D. writes : "I am glad to know that we are going to have a German edition of The Feeding and Management of Infants and Children. I know of no such book in German of a similar character and am confident that it will be welcomed by all thinking German mothers." MRS. T. WILCE, President of the Mother's Society of Chicago, says : "It is the most instructive book for mothers and c specially young mothers, that has come to my notice and I earnestly arlvise all prospective mothers to read it. Would to God that I had had such a book years ago. MRS. H. E.REDEKER of Kenosha, Wis., writes: "I think it isthe best work of the kind I have seen. 1 am glad that I shall have Dr. Duncan at hand ready to consult at any moment for I have the greatest confidence in all that he says. It is a book that it seems to me every mother would like to have." DR. EDWARD CRANCH, Secy, of the American Paedological Society (com- posed of the leading physicians interested in Children's Diseases), says : " I have carefully examined the work and unhesitatingly pronounce it a most necessary book for all families. It ought to go into every intelligent household where the health of the little ones is valued." 'Prevention is better than cure," and many a babe will fare better if the mother follows the advice given by that great friend of our bebies, T. C. Duncan. It is a work, whose first par c we can fully endorse, and since I studied th^se alkaline and acid babies, my endeavors are to have my little patients alkaline. The artificial feeding of children is a most interesting study even to an old physician and only by following closely the rules laid down, can we prevent the necessity of studying the secoud part. North American Journal of Homwpaihy. The Organon of London, Eng., says: "Paedology is Dr. Duncan's Specia- lite and we may be sure that what he writes on tnis subject contains some- thing worth reading. His Encyclopedia on Diseases of Infants and Child- ren is a work for the profession ; this one is for the public, and a better work on the subject we do not remember to have seen. * * Every day rules for diet and regimen generally, are what the public should know, and without these the skill of the physician is daily thwarted ; iu this respect Dr. Duncan has performed his work almitably. The book is elegantly gotten up." SOLD ONLY BY SUBSCRIPTION. Price, Cloth, $2.00 ; Half Morocco, $2.75, Agents wanted in every town. Ladies sell it rapidly. Address for terms and territory, DUNCAN BROTHERS, 131 <& 133 Clark St., CHICAGO. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. OCT 17 1934 OCT 15 1937 LD 21-100m-7,'33