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HAND-BOOK FOR DPTICIANS. — A TREATISE ON THE OPTICAL TRADE, AND ITS MECHANICAL MANIPULATIONS. BY W. BOHNE, ee OPTICIAN. a e ΡΕΟΟΝΡ ἘΒΙΤΙΟΝ, & THOROUGHLY REVISED AND GREATLY E ED. Y Ee WITH ILLUSTRATIONS. ce A ELEN BY THE AUTHOR, 7 ith A. B. GRISWOLD & CO.) Q CANAL STREET, NEW ORLEANS, La. SS 1892. EET AH EI— y - Entered according to Act of Congress, in the year 1892, by THE AUTHOR, In the Office of the Librarian of Congress, at Washington, D. C. xe Iis ri F. Shepard Memoria ram, n ois College of Οριοῴιὸ 224] S. Michigan ol 5. Chicago. lil. As bie i “PRESS” PRINT, 50 BIENVILLE ST., N. O. PREFACE TO: SECOND' EDITION: — - Since the ** Hand-Book for Opticians'' made its first appearance, I have, to my greatest satisfaction, observed a general wholesome stir among the opticians, manifest- ing itself by several new blo itions in the same line; by the increased attendance of young opticians at the different Ophthalmie. Colleges, and by the issue of a ** Monthly Journal’’ in our interest. This was my reason for taking another step in the further instruction of my companions. The first edition was merely a feeler to ascertain if a book, so different from other instruction- books, was wanted or rather needed. The favorable re- ception it received, even outside of the trade, induced me to extend its usefülness by adding some information which I purposely omitted before, judging that the medical faculty would properly attend to the theoretical part of our occupation. But their writings d« N partially scientific education which most. of KAN opticians, have. not received. ^ My explanati nay not be strictly professional$'but à diligent re: avi readily ` understand them, and — that i 18,1 in. n Qo, the prin- cipal object of all instructions.” 3e The treatise on the SUAM f the Optical Trade (Chap. XXVI), although o Y, is still insufficient in its present state ; and to $ nsate for its short-com- a ings, I have added the 1 pter, in which the gradual progress of the optica nce is individualized by a brief history of the live o$"fhose men, who attributed to the advancement of r trade and science in general. The large sy I devoted to the memory of the late Charles A. cer may be a surprise to many opticians ο ero 4 PREFACE. who perhaps never heard of him; he is better known in medical circles than among his own trade-companions; better in Europe than in America. Even the cyclopedists have neglected him; he went to the grave almost un- known to his neighbors. Spencer was the first optician who produced objectives of wide angles, and inspired the studies of scientific men in all parts of the world. With- out his genius, many of the marvelous discoveries accom- plished by the microscope could never have been made. Our country did herself a great wrong in not making more of her gifted son, and it is the sacred duty of the American opticians to prevent his name from being: for- gotten. It is with great pleasure that I acknowledge my indebt- edness to Dr. H. D. Bruns, Mr. H. Ginder, Mr. Chas. F. Prentice, Mr. J. M. Johnston and Mr. G. C. Ridgway, for their valuable assistance and kind advice in the prep- aration of this work. New ORLEANS, 1892. A xS BOHNE. o το PA TRACT FROM PREFACE OF FIRST EDITION: My object is to instruct the rising generation of our trade, and elevate them to the position of the great pro- gress optical science has made within the last quarter of the century. Iam well aware that the present work is not as complete as it ought to be, because every chapter is composed and written as something new. There is noth- ing previously published about these subjects, and my book may be the pioneer to open the road for other writ- ers. Almost every trade has its literature or hand-book of the secrets peculiar to its business; but the optical trade, as regards the mechanical part of it, has none whatever. What I offer here is the result of a life-long experience and of numerous investigations. _Workmen who find any error, or who know better methods, are cordially invited to communicate their information to the author, x vill acknowledge his obligation in a future edition. Let us remove the curse of all progress Mo keeping of our secrets and little tricks to ourselv et every workman withdraw the restriction pla pon his fel- low-laborers, forbidding them to en shop, in order to prevent them from profiting by$his Skill. This is the proper way to elevate our trade (9 a commanding posi- tion, so that we may no long Qe confounded ΤΙ street- fakirs and mere spectacle Cu My book will fur nisl Noe young man a solid foun- dation of what he φας o» know, and will enable him to master all DNA e may encounter in the pursuit of his occupation?<“@s there is no telling what demand will be laid on EO ae in the immediate future, he should S 6 PREFACE. try to understand thoroughly the fundamental laws of his trade and become a competent workman. Chapter V explains all about the optical line and center in lenses, and chapter VII, of the setting of compownd lenses; both proved for many years to be the stumbling- block of our efficiency and ability. Chapter III treats of pebbles, but differs from anything heretofore published. I hope that my experiment will be repeated by opticians and scientists in order to finally settle the vexatious ques- tion: **Shall pebbles be used or not?" Iam anxious to hear what others have to say about them. The history of the ‘‘Invention and Introduction of Spectacles,’’ is the first attempt at collecting the scanty materials about this important subject, and is far from being what its title indicates. Those of my readers, who are in possession of facts concerning this matter, will kindly communicate them to me for future use. A BOHNE. δ᾽ ANE NEw ORLEANS, 1888. CONTENTS. CHAPTER I.—Inch and Metric Systems IL— Different Qualities of Lenses III.—Merits and Defects of Pebbles. .. 1V.—Prisms, Spherical and Cylindrical Lenses V.— Optical Line and Center . VI.-—Setting of Spherical ος VII.—Measuring and Setting of ο αμα VIII —Selection of ϑροοίαοῖθβ.................. IX.—Double Focus Single and Split Glasses. X.—Colored or Tinted Glasses............. XI.—Redressing of Spectacle Frames XII.—Use of Test-Types XIII —Refraction and Dispersion of Light ... X1IV.—Achromatic Lenses..................... XV.—Anatomy of the Human Eye XVI.—Presbyopia, Hypermetropia and Myopia XVIL—Astigmatism XVIII.—Ophthalmoscope XIX.— Second Sight................ -.. XX.—Relief to Injured Eyes.. XXI.—Artificial Human Eye ..... XXII.—Caloric Rays in O ent L * XXIII.—Range of Vision * XXIV.—Tears * XXV.—Facial Expression. «* XXVL—History of the «€ XX VIII.— Mis € XXIX.—* 65 71 76 82 102 116 ABBREVIATIONS. degree. foot, also Qi, inch, al Second, D — diopter. ax <= Axis, C. or cyl. = cylindrical. ος — concave. em — centimeter. m — meter. mm — millimeter. S or sph. — spherical. — = concave. + — convex. E = combined i ΟᾺ o E / m line, roin part of an inch. ^O CHAPTER I. INCH AND METRIC SYSTEMS. Spectacle lenses are made of glass or pebbles ground to a spherical form, either convex or concave, by means of tools which are segments of a ball or sphere. ....... . ο... LN ο προς aen. ra Py . " " 0% + 4. o? + 9 * ν Pees oe E Pd Re LJ 5 e ^ ot? aes ΄ s 5 . . ο’ 9 e ier e ο ° 9 ΄ v MS «. “ «. . E *. oF ta «΄ N The dotted lines represent the whole sph Qr which but segments in form of shells or cups (e ployed for the grinding of lenses. If we use t side or hollow A part of the shell, we produce a ç lens, while the outside or rounded part is emplo fór concave lenses. NS oos ue ο USC Να. : i v a “ey m a2. Some ae are eurved only on one side, while the SS 10 HAND-BOOK FOR OPTICIANS. iu other side is flat; they are called plano-convex or plano- concave. LS Periscopic lenses are ground by spheres of different sizes, as shown in the above cuts. We have, therefore, three kinds of cx, and three | kinds of ec lenses. Cx lenses collect behind them, j by refraction, the greatest portion of the rays falling on | their surface at one common point, called the **positive focus," which is nearer to, or further from the lens according to its focal power. A concave lens, on the contrary, disperses or scatters the rays, and has a ‘‘neg- ative focus," because we only can neutralize it by a plus or positive focus lens., The term ‘‘negative lens’’ j: does not exactly cover the nature of a concave lens; M we can measure its focus also by reflection, ich gives | in front of it a positive focus, just as a ex lens 5 will do behind it when measured by C aoo For | | ee eg oe, B * * ΄ [1 * - instance, fasten a white card at the ο òf a foot-rule, go to a glass-door or window, hol ruler so that the i card is between the window and ens, approach the | concave lens until you get a EY mage of the window | 3 on the card; then see on tae Wer how many inches the lens is from the card, a if it is a double concave, multiply by two, if plane-toncave, by four, and you | have the focal lengt the lens in inches. Periscopie ` | Í lenses cannot be m dthis way. Although the latter are highly recom ded by their inventor, Wollaston, p and by other c ‘ated authorities, I, for my part, find | that the ως numbers are extremely unpleasant to | A the eye, espétially when they are used for cataracts. ii All tha{sS@laimed for their superiority may be granted | ie to eos ker numbers from one to four diopters, but 1 | ^ st oer i | SS stronger ones | INCH AND METRIC SYSTEMS. 11 Here arises the question, which of the three words is right and should be used: Dioptric, Dioptry or Diop- ter? These three scientific terms are derived from the Greek verb dioptomai (dia, through, and optomai, I see), I see through, I see completely. In Modern Greek dioptres means spectacles. ‘‘Dioptrique’’ (English **dioptrie"' ) has been adopted by the French in connection with optical measurements, as a substitute for the term meter, which latter, although denoting measure in gener- al, has no specific application to optical measurements. Originally, the French word dioptrique, both by deriva- tion and common use, does not include any idea of measure or measurement whatsoever, it only refers to the refraction of light. It is simply an old word with a new technical meaning, contrary to the logical rules of language, like many other words of foreign extraction. Dioptrique not being a noun but an adjective, and not sanctioned by scientific usage, at least not yet in the English speaking world, we should exclude it henceforth from our optical terminology in regard to measurement. Likewise objectionable is the noun **Dioptry'' as a term for expressing optical measures. The word diopter, considered as’ a contraction from **dioptometer,'" is evidently the most suitable for AUN purpose, and is strictly analogous to words like barom aik: thermometer, etc., also employed for different me ments. The word ‘‘diopter’’ also denotes a ge instrument used for leveling purposes—The søR¥itution of thé word diopter for meter has been adopt oculists and all first-class opticians since 18754 ‘der to in- troduce a uniform measurement instga he old inch measure, which considerably diffe and that cree of dis- al lenses it is 48 ` HAND-BOOK FOR OPTICIANS. cylinder, instead of the segment of a ball used for grind- ing spherical lenses. When the outside of the cylinder is employed, the lens will be concavo-cylindrical; but when the concave side of a section of the hollow cylinder is used, the lens will be convex-cylindrical. The size of the cylinder imparts to the lens its strength ; for instance, a cylinder of 5" diameter will produce a cylindrical lens of 5-inch focus, or of 8 D. Properly speaking, there is no common focus or focal point to a cylindrical lens, but instead thereof a focal line which is parallel to its so- called awis. We find here again an analogy to the pro- perties of prisms. While in spherical lenses the prisms encircle a common center or focus, they are in cylindri- cal lenses arrayed with their bases when convex, or with their apexes when concave, in a straight line across the lens, called the axis. We may say, therefore, that the fundamental forms of all lenses are but modified com- pounds of prisms; even the simple slab is a double prism, , as we have seen at the beginning of this chapter. The axis of such a lens Q along the highest or lowest ridge of it, and ‘is ο etermined by moving the lens up and down, πα by its gradual turning that line where there is ᾿ς λοίοη at all. As long as the object seen through tl,lens moves with the motion of the lens, the axis is yet found. The peculiar nf cylindrical lenses, producing an apparent leng ing or shortening of the object, alter- nately did αυτό, through a convex and concave cylindri- cal ics isot shown by the changed form of a square. Gupx- cylindrical lens with axis vertical will uA ehe horizontal sides, producing a horizontal ogram. A concavo-cylindrical lens similarly QNM. will have the opposite effect, making the paral- PRISMS, SPHERICAL AND CYLINDRICAL LENSES. 49 lelogram vertical. This explains why a convex and con- cave cylindrical lens of the same power laid together, axis upon axis, will counteract each other, and restore the parallelogram to a perfect square. When we take two cylindrical lenses of the same strength, and place the axis of one vertically, and of the other horizontally, we destroy all cylindrical action, and retain only the strength of a simple spherical lens of the same num- ber or power as that of the cylindrical lenses. Take, for j lay their axes crosswise, and you have — 2s, which is neutralized by + 2s. But, if we lay the two lenses (— 2c) axis upon axis, we double ar θές their power in getting a lens of — 4c. — My first exper- | ience with these lenses was about twenty-five years ago; : they were the plano-cylindrical, and their axis ya set | either in the vertical or horizontal meridian. I ‘ied to combine the cylindrical with a spherical l@fs, gluing them together with Canada balsam, till ΓΑΡ advised | | from Berlin and Paris, that both correct were ground | upon the same lens. Of course, 4 can opticians were promptly up to their professtayAind since several years all combinations are groupd were made from all sides, and jf\eemed almost as if this new departure was a failure, t Nachet, and afterwards | other opticians, Id trial-frame. Yet, there e. Many blunders was only a limited numb opticians who worked with the full understandj were able to convert one combination into a As to my own researches, I is must say that i me a good while before I found the T practical DIR Gop making this conversion with certainty. My ple y cess is based upon the above three fund- amental la et us bring them into such a shape that they NS remembered forever when once thoroughly as Tm 50 HAND-BOOK FOR OPTICIANS. understood. By means of these rules we can turn cross- cylinders into spherieals and compounds, and again into cross-cylinders without any trouble or error. I. Plus and minus cylinders of equal strength, and at same angles, neutralize: + le axis 90° T — 1c axis 90° — a plane. II. Two cylinders of equal strength and denomination, at same angles, double : — 16 axis 180? J — 16 axis 180? = — 2c axis 180°. III. Crossed cylinders of equal value, produce sphericals: T koas 90 ο σκι 190" — 4I. The first two laws coincide with the properties of spherical lenses and need no further explanation, but the third law throws a new light upon sphericals; it demon- strates the fact that spheres are only erossed cylinders, of which the proof is easily made. We know that -+ 2s is neutralized by— 2s; wealso know that the crossed cylinder — 2c axis 90° © — 2c axis 180°, = — 2s, and that the concave sphere (— 2s), or those concave cylinders combined, will turn + 2s into a plane or slab. Now, instead of placing both cylinders a£ once upon the: convex lens, we may take the first one at 90° atid lay it on the spherical lens. I wish, the reader ] make here this experiment for himself, as it is 6 NS. greatest interest to notice practically the changes ally brought about in the spherical lens by the at (9n, first of one and then of the other cy linder. 1e lens — 26 axis 90° represents only one half o Ko S ower necessary to ; neutralize the test-lens, its a ion to the spherical lens is quite singular, as itt alters the nature of the sphere by turning its 2e eoo half into a distinct convex cylinder axis 185, which is fully neutralized only by the addition of E. 'cond concave cylinder at the same angle [180° There are two inations of crossed cylinders: 1. Both cyg s have equal signs, but one is stronger than th er. For instance: -+ 2c axis 90 ^ E 16 axG_180°; this crossed cylinder can be converted ος € following compounds: — 1ο axis 180^, or + 1s O + le axis 90°. 7 | |Ε i |j 4 PRISMS, SPHERICAL AND CYLINDRICAL LENSES. 51 2. The cylinders have mixed signs, no matter how strong each cylinder. + 96 axis 90° C — 96 axis 180^; their equivalents are: + 2s O — 4c axis 180°, or — 2s © + 4c axis 90°. To come to the above answers, we have to turn one of the cylinders into a spherical lens, making use of the third law. For instance: + 2c axis 90°, requires the cylinder + 2c axis 180° to turn it into + aT but then we have to neutralize this first addition by — 2c axis 180°, in order not to alter the original strength of the crossed cylinder, although we have changed ‘entirely its form. Thus: +2caxis 90°S-+1eaxis 180^; by adding --2e '« 180°S—2c ** 180°, which is a plane, we receive +28 -----]ο axis 180°, the first answer. We take the same crossed cylinder, and turn the second one into a sphere. + le axis 180? 75 + 2c axis 90°; we add + le: “90°. — le. «€. 90°, = plane; and we get + ls CS + le axis 90°, the second answ Remember that each time we added something dh crossed cylinder in the problem, this something sa sented only a ος or slab, aecording to the ΦΑΝ law, although it was really a erossed cylinder i in dese: but it completely chi inged the nature of nit {ρα èns, which a plane glass cannot do. Let us now see about the seco bination with mixed signs, by making use of the E e*process. + 36 axis 90? D — ο axis RO. We again add ο. I90 x nr 20e f a) °, = a plane, and get + 2s CR Gy 180°, the first answer. We now turn the seco Sindee into a sphere: a ig 205 ΖΝ — 2c axis 180°C axis adding — 26 ** 90° 2ος m — 0, we come to — 28 + 4c axis 90°, the second answer. «Το turn a eo(pgound lens into a crossed cylinder, we make use of Same experiment of which I spoke at the beginning is article. Let us take the last answer: 52 HAND-BOOK FOR OPTICIANS. ο μα” C2 + 4ο axis 90°, and add + 26 axis 9075 — 26 ** 90°, — 0, we get — 2c axis 180^ -- 2e axis 90°, a crossed cylinder. The first cylinder of this answer [| — 2c axis 180°], may puzzle the inexpert, but Law III explains it quickly. We can neutralize — 2s either by + 2s, or, as we did in the problem, by the crossed cylinders: + 2e axis 90" 206 axis 130°. By laying 4- 2c ax. 90* on the test-lens, the remainder of it ought to be a cylinder which is neutralized by + 20 axis 180°, according to Law I. As I used in the foregoing problems the most simple values and always the same numbers, let us now select a problem with varied numerals as a further illustration. For instance: + 1.75e axis 90° 75 — 2.50c axis 180°. To turn the first cylinder into a spherical, we must combine it with + 1.756 axis 180°; then we have to add — 1.75c axis 180°, in order to ος the first addition, thus: + 1.75¢ axis 90? J — 2.50c axis 180° Adele LLCO == 4.156 ^ € 1907 = plane + 1.75s D — 4.25¢ axis xn or + 1.75c axis 90° O — 2.50c πω + 2.90e **. 90° Dd — 2.506 + 4.25c axis 90° J — 2.50s I wil direct your attention ag the important question: ‘Is there any AND) Yifference between a crossed cylinder and its er compound ?" Ap- parently there is a great di and yet there is none whatever; every S s is a crossed cylinder, and every crossed cyli s a compound lens. Let us turn, for argument.s m following erossed cylinder into a compound ig» | 1.506 NS Ὅσλ-- 2 caxis 180°; by adding + 1.50g, @NBO°S — 1.50e “180° = 0, we get zh O CS — 3.50c axis 180°. Now, us turn the compound lens again into a crosse inder. In order to dọ this according to pre- vig es, we substitute for the spherical part of that PRISMS, SPHERICAL AND CYLINDRICAL LENSES. 93 lens (+ 1.50s), its equivalent, viz. + 1.50c axis 90° D + 1.50c axis 180°, thus: + 1.50¢ ax. 90? 75 + 1.50c axis 180° 75 — 3.50c ax. 180°. This formula, as it stands, is nonsensical, because we have only two surfaces on a lens for cylindrical corrections; but by looking at it critically, we observe that + 150c axis 180° C> — 3.50 axis 180°, is only one cylinder of — 2c axis 180^; and the actual formula of that triple cylinder, therefore, is + 1.50c axis 90° C — 2c axis 180°, which is the crossed cylinder we first turned into a com- pound lens, and then again into its first form. This practical test evidently demonstrates the fact that two faulty meridians in the eye, when 90? apart, are cor- rected as well by à compound lens as by erossed cylinders. But as cross-cylinders require greater care in grinding and fitting, all competent oculists and opticians prefer to substitute compounds, as being less liable to mistakes, and aecomplishing the same visual correction. About the year 1850, a French optician, Galland de Chevreux, introduced crossed cylinders instead of spher- icals, claiming that they not only eorrected presbyopia, but also the small degree of astigmatism with which nearly every eye is afilicted. A careful com n of them with spherical lenses will show the fall ολο his claim. ‘This, and their high price, have bygght them into disuse. **In fact, it has been demonst( Ke, both by exhaustive mathematical calculation κ xperiments, that all crossed cylinders, for all devi; hae of their axes, may be replaced by sphero-cylind τ enses?’ .* The use of cylindrical glasseg P increased lately to such an extent that no optical blishment comes up to the requirements of the trade Xhout being.able to fill correctly the orders of og One-tenth of all eyes are more or less astigm: and since oculists have taken the selection of spQwMIéS in hand, the demand for cylindrie glasses is great. * **We further Qy suspect error in our estimation of the refraction of an eye seemingjo démand cylinders combined under acute or obtuse angles." DM eam ulz for Cylindrical Lenses, by Chas. F. Prentice, New York, CHAPTER V. OPTICAL LINE AND CENTER. About twenty-five years ago, a traveler for a New York manufacturing house, offered spectacles for sale which he called ** Perfected." When I asked what he meant by it, he said that the lenses were correctly set, the frames well tempered, and the whole spectacle perfect. To my great surprise, one lens of the first pair I examined was badly eentered. He exeused himself by saying that he was not an optieian, he only represented the goods ac- cording to instructions given him by his employers, and promised that all goods I might order through him should be without fault. He admitted further that no member of his firm was a practical workman, but that the factory was superintended by a competent optician. Noy, if this foreman really understood the meaning of optical center in a lens, why did he not instruct the Ns#setters how to be exact in the fitting of lenses 1e frames, especially of those ** Perfected Spect: 8j" for which they charged $4.00 a dozen more ( or other goods not st: ımped, but of the same stylee Ne quality ? I know not whether this name was inv extortion, or whether they c ^ so much more for the stamping of the temples, κο α was, indeed, nicely done in gold letters, and was sor ios new at that time. 'To be able to readil (Qytermine the optical line of a lens, is more dd or an optician than any other acquirement of cap e. It is the essential requisite for the correct facture of all optical instruments, — spectacles opera glasses, telescopes, or microscopes; the optical cdser must have its right place and position, or the ingfegment will be incorrect and worthless. The NS way to find this center is to look through the AN well-marked vertical line, drawn with pen and 5. zT h b 1 OPTICAL LINE AND CENTER. OD ink and a ruler on a sheet of paper. Hang this paper against the wall some four or more feet from you; then take the lens between the thumb and first finger, extend your arm, shut one eye and look through the lens at that line. You will observe that the line is broken in the lens, and the more so, the nearer you move the lens towards its border. Figures a or 6 represent this phe- nomenon in concave lenses, and ὦ or 7 as seen in convex lenses. \ \ & | j -X Now, move the lens slowly tabs the center till you find the line unbroken, as in fig c; mark this line with ink, and it will indicate the ic line of the lens in one direction. Then turn th ns 90°, so that the line on the paper and the max G 1e lens form right angles. Proceed in the same as before, and you will find, very often, that optic center is not always in the middle of the lens we see in figure d. The two lir Gyhould cross each other in the middle of the lens, as do in figure e. This test will do for SS | 56 HAND-BOOK FOR OPTICIANS. spectacle lenses; but the test for scientific instruments is more elaborate, as we have seen in Chapter IV. This somewhat circumstantial way of finding the center of a lens ean be shortened as suggested by Dr. H. Knapp in this manner: ‘‘ Look through the lens at two lines crossing each other at right angles; when the prolonga- tions of the lines beyond the lens are unbroken, the point of the lens through which we see the crossing of the lines is the optic center of the lens."' I would advise you now to take at random a dozen spectacles from your stock in trade, and examine them as to the correctness of their optic centers. You will find that many of them, highly valued in the market on account of their trade-mark, are greatly ipáorrect and good for nothing. It will cease to be a m ο aston- ishment that some of your customers c ot see with one pair of spectacles, and yet Foun ee of the same number pleasant and satisfactory. To decenter lenses is an easy ox» any one who un- derstands the nature of the px center. As we have seen in the previous chapter, mthe heading **Prisms,"' that we have to set them &ther base in or base out, it is sometimes necessary, in Ger to overcome certain defects of vision, also to de@yter spherical lenses, and cause OPTICAL LINE AND CENTER. 57 them to act like weak prisms. To fill such an order cor- rectly, it is necessary to first locate the optic center on the lens, then put the zinc-pattern (Chapter VI) as much as possible to one border of the lens, and make a mark around the pattern. In convex lenses the border nearest the optic center is the base; and any prescription of base in or out is cor- rectly filled, if we place this part (7) towards the nose or temple according to order. In concave lenses the base is at g, or just the opposite from that of convex lenses. The base and center of a convex lens always fall together, in concave lenses they are separated; the base is at the border of a lens, and the optic center, of course, in its middle. If, therefore, we have to decenter a concave lens, base in, the optic line will appear beyond the middle, nearer the temple, but not towards the nose, as is the case with convex lenses. In order to explain the object of decentering lenses, I draw your attention to the fact that the eyeball moves in any direction about a common center of rotation by the action of six muscles, four straight ones, the other two oblique. The first are called superior rectus, inferior rectus, external rectus and internal rectus; they move the eyeball either upward, downward, outward or inward, while the two oblique muscles with the assi of the four recti, rotate the ball in every other (y Motion. Most movements of the eyes are in P. ho nog al meri- dian, and are alternately produced Ὁ ΚΟ traction of the internal and external recti. These A muscles are constantly taxed, and it is no wor s one or the other will fail to perform its atisfactorily. In distant vision the muscles of m are almost at rest, but close work compels t ecti interni to converge in order to direct the visual(ggle of both eyes to a near point. This is the rea why the internal muscles sometimes weaken e bracing up, which is done either by prisms, or Wery slight degrees of insufficiency by decentered 1 As soon as a prism with base inward is placed Before the eye, the rays will strike it in a more paren’ lirection, as if they were coming from a distant obey; hus allowing the recti interni to relax. S E ^ CHAPTER VI. SETTING OF SPHERICAL LENSES. We work blindfolded when we are unable to find the | οι center of a lens, and it will be by mere chance, if our work is correct. Rough lenses are not always well cen- | tered; if they were, we would have simply to cut the b^ 1 size we need from their middle, and there would be no mistake. Many of them will be found so much decen- tered as to be useless for sizes 0 and 1, and are fit only | for sizes 3 and four, or they may be altogether worthless, | except for lenses to be decentered. We may take notice here of the lenses called the **in- i terchangeable".* They range from No. ὃ, the ordinary |. size of spectacles (although smaller numbers are used for |^ : children spectacles), to Νο. 2, the size of eyeglasses, up to No. 1 and 0; even to coquille sizes, No. 00. and 000. Most manufacturers of spectacles adopted thgse\standard sizes of lenses, to enable the retailer e nge the lenses from one frame to another witho ering them. A lens of No. 2 spectacles fits exactly gi @ ordinary size / of eyeglasses. If you order 1-6 9) >ctacles and eye- glasses, you can exchange the legs rom the spectacles to the eyeglasses, or vice O rou like, they always fit. In a well-centered lens S ue edges are equally thiek on their opposite bords dA a little practice will enable a frame without screws jenses to be sprung in like watchglasses. j Albert Lorsch introq Cy: e spectacle and eyeglass frames since 1869, together with finishe Ses of a certain size, about eye 2, which fitted Y he called **Lenses for the Patent Accommodating Spectacle and Ass." But the term interchangeable lenses is of a later date, and cam o general use since the Bausch & Lomb Opt. Co. ac- cepted the gandard sizes of the American Opt. Co., although other manu- η lung to their old sizes, till at present there is hardly any Ἂν Ww manufa hich will not take, and correctly fill, an order for all in- D. terch le sizes. * 'The first impulse in Wy ction was given by Noél, who patented SETTING OF SPHERICAL LENSES. 59 the eye to see at a glance, and without looking through it, whether the lens is decentered or not. This saves us a good deal of time, as the principal test is then quickly determined. But we should not rely altogether on the judgment of our eye in this regard, as it requires a good deal of practice to detect small differences in weak lenses. Any workman with good tools can perform in a short time more and better work than others who shuffle about the whole day long, wasting time and material, for want of proper implements. The most useful tool in setting glasses is the model or pattern made of thin zinc. If you have not yet made use of it, prepare a set of the different sizes and shapes of spectacles, as they come into your hands for repairs, and mark them according to the different sizes of the eye. Make a hole exactly in the middle, partly for purposes to be spoken of in the next chapter, and partly to suspend them on the wall within convenient reach, well-assorted according to size and pattern. About three dozen will fully assort you, and will save you, in the course of years, an immense amount of trouble and time. Another important tool is the marker, an instrument like a lead-pencil, mounted at one end with a small dia- mond. The marker is used to make a scratch arQund your pattern, after it is placed correctly on th gc ef will not cut the glass as a glazier's diamonc ause it is intended only for scratching purposes, andNg) therefore, very cheap. On heavy lenses it is NY o mark both sides, to prevent the breaking of © ens inside the mark. The next tool for our purposé&kis The sliding-tongs, an instrument employed by watch} kers and jewelers, who call it the ** dog-nose sliding ngs 7 itis also used by opticians to chip the MASS I have f the largest size the best for almost all every thin glasses, for instance, for lockets or : 60 HAND-BOOK FOR OPTICIANS. watches, which we may occasionally be obliged to grind, can be chipped with common flat pliers. The apprentice should practice this chipping on pieces of window glass, before he attempts to shape a lens and spoil it, perhaps, by inexperience in handling the tool. The proper tool used in factories, for doing quick and good work in this respect, is represented by the following figure. I first handled it in 1866. It was shown to me by a workman who called it the **English Shears.” As I never found them for sale, I returned to the use of the ** dog-nose sliding-tongs,”’ which answer very well the purposes of a retailing optician. The pieces a and 6 are dove-tailed into the shears and can be reneweg den used out. They are ᾗς’ broad, with ΠΤ irfaces. The rivet at c is rather loose, so that the ample play for the shanks to move freely sidewa y They are used in a similar way as the sliding-tongg C The proper way to handle this is the following: The tongs, held by the right (js should be applied loosely to the lens, and vorge we do a pair of scis- sors, with the difference at the same moment we close them, we also give thNupper part of the tongs a slight inclination to outside and downward. The lower nose is kept y n the mark by the middle finger of the left hand olds the lens. This effectually prevents the le ‘om cracking inside the mark. The outside moY(enymt of the tongs throws the chips and glass-splinters*from us, and thus saves the eyes from MERC a fine glass-dust also rises from the lens, and ig Quy pernicious to the lungs. Hold the lens, SS SETTING OF SPHERICAL LENSES. 61 therefore, nearly at arm's length, and blow the dust off before you breathe. As a rule, we should move the tongs outward; but we may come to a place which will not break readily, even by applying greater force. In this case we can some- times aecomplish our task with ease, and without the risk of spoiling the lens, by moving the tongs upwards, using the lower nose for the breaking, and the upper as a guide. This alternate turning up or down of the tongs should be well practiced by the apprentiee. In regard to the forward or backward movement of the tongs, it is immaterial which way we proceed with glass, but as to pebbles it should be always the backward movement. As every crystal has a cleavage-plane in its lateral axes, the forward movement may aceidentally cause a splitting in the direction of this plane, which rarely happens with the backward movement of the tool. It is hardly necessary to mention that the stone has to be turned from you when grinding. I have seen only one jeweler (and he, too, styled himself ‘‘optician’’), who turned the stone £o him, as he had seen done by a street- grinder. 15 it to be wondered that he CHORUS after- wards of not being able to get a smooth edge op his glasses, or that they looked as if rats had given tl the finishing η. XO I do not think it out of place to say here z (ἐν words in general about the grinding of lenses Imost all manufactories grind them into a sharp my opinion an unnecessary trouble, αἱ very little sound judgment. The Y are not pointed, but rounded off, Waether they are made of soft material or metal; and lens, to properly fill such a groove, should be also ounded off. This will have the double adv: antage eing less liable to erack, and less troublesome nish. Sharp-pointed lenses easily split shell on r frames, when the latter con- tract in cold weat] r they themselves are chipped by metal frames, wengfiey are tightly fitted. To overcome this diffieulty,,amW to establish a practical method of fitting lenses he frames, I will describe the method which I adopted. After the lens has been well 'frame 18 quiekly done, and they ay 62 HAND-BOOK FOR OPTICIANS. shaped and sufficiently reduced by the sliding-tongs, I grind off the sharp edge on one side by passing "it quickly over the revolving grinding-stone. A few revolutions will accomplish this, and will give it a small but distinctly visible bevel. Then I do the same with the other side, by turning the lens alternately edgewise, to take away its unevenness. In less than one minute my lens has a finished appearance, and needs now only the final adjust- ment. The edges of the lens have then a rounded form, and when set in frames do not show any roughness, because the polished surface of the lens touches the border of the mounting, thus relieving me of the trouble to polish the bevel, which, however, "cannot be a when the lenses are thicker than the frames, or when the grooves are very shallow. Τη regard to the present universally ER habit of polishing the edges of lenses, I must confess that I do not approve of it, for the good reason that the reflected light from such bevelled surfaces is annoying to the eyes, and ean be easily removed by giving them only a fine ground finish, which the Germans and French call «qatt." Even frameless spectacles could be made in this way and would look equally stylish. But this re- form can only be effectually introduced by "ἘΝ. nanimous co-operation of the oculists in rejecting uture all glasses with polished edges. The fitting of bevelled glasses into groove of the üs ily ground and pattern. Octagon shaped if they are of an oval or r glasses require more attentiongegpgtially when the frames are old and often repaired. Sreatest care has to be taken with skeleton and coved: glasses, as the edge must be flat, and the bev ery small. The stone should be used till the lens rightly shaped and the edge roughly flattened ; e should then finish the lens on emery paper Now Ard 2, and lastly on No. 1 and 0 for polishing purpos* If the lens has to be grooved, No. ὃ is used onl he edge, but Nos. 2 and 1 forthe bevel. It is better nish the. Πο before filing the groove, as a gare os is less liable to chip in case the file shoul ch the edges. The grooving is always done S AČ wl SETTING OF SPHERICAL LENSES. m with a round file, never with a four or three-cornered one. The file will soon be smooth if used dry; it is therefore necessary to wet it constantly either with water, turpentine, benzine, or dilute sulphuric acid; the latter is most effective. But even these will generally ruin the file after the finish of one pair of lenses, thus con- siderably increasing the cost and labor. The best fluid for the preservation of the file and drill for our purposes is one that contains an access of camphor. Any mechanic knows that a new file should not be used at once for filing hard iron or steel, without passing it first several times over a soft material, as wood, brass or soft iron, to fill up the deeper parts of the file, giving strength to the exposed sharp points of it. Camphor renders the same service to our file used for grooving glasses, without interfering with its cutting qu: ities, if the fluid evapo- 'ates quickly enough to allow the camphor to clog up the deeper parts of the file. To do this by passing it over lead, would cause it to slip without cutting the glass. The formula for this fluid is: Dpirits- o£ ‘Turpentine... 5.515 ον. l ounce. Camphor Qum iris. osc. δ ος Tu E Sulphuriedther; 12. PE EN 3 drach: A The ether facilitates the solution of the οἱ yy but volatilizes so quickly that the file would be c fter a few strokes, if the turpentine did not τοῖς its vola- tilization fora while. Keep the file, thereg&9, constantly wet while using it, and it will do LO" for a good length of time.* The drilling or boring of glgssts? for skeleton or frameless spectacles is done by(mNWrilling machine; but if you have none, it can be dove with a round file and the above fluid. Select a Qio of the size of the hole you need; break of point, and commence the hole by moving to ΤΝ the sharp edge of the file, previously dipped ipt(Whe camphor preparation. Make a mark on the EA len raise the file by degrees per- pendicularly to £heMÉns, and use it as a drill by turning it slowly bees ais fingers. Each turn of the drill * Another ont fluid for this purpose was lately introduced, called «Di UNS or drilling and filing in glass, porcelain, enamel, etc. N EN 64 HAND-BOOK FOR OPTICIANS. must make the noise of a gnawing rat, otherwise the drill does not bite. When the hole is half through, com- mence on the other side, and reduce pressure gradually, to prevent a sudden advance of the file when nearly through. The holes are finished off by a three-cornered sinker, much larger than the hole itself, which bevels the edges of it, and prevents the breaking of the lens by the subsequent insertion of the screw.* There are many devices recommended to shape drills for glass-boring purposes; all agree that they should never be pointed in the middle, but be rounded up, or be flat like a chisel. My favorite drills were always made of a round file (rat-tail), by grinding off two opposite sides, so that it had almost the shape of a square. Hold- ing the file at an angle of 60°, I smoothed the lower surface with the oil-stone, forming a slanting plane, and producing a sharp strong edge.to cut with. Another good drill is made of a three- cornered file, sharpened in the usual way, but with one corner taken off, so that the cross section of the drill near the point is that of a trun- cated cone, and the end of the drill of a narrow chisel- shape. Not all files make good drills. Eithe well tempered, or the grain of their stee k$ that pe- culiar cutting quality which we find i hers. If you see, therefore, that your drill s n&tNut readily, throw it aside and try another file, BA Qna one that works well. Ihave often rehardened O στ 'ally with- oat success; the steel was O d cisely of that quality which is necessary to m good drill. When you have secured such a flea jealous care of it; I have used some for years, al fodid them always reliable like old trustworthy, nds. are not * [tissafer to βᾷρ g as soon as we reach an opening, no matter how small, becaus&y asy που to widen tthe hole with an ordinary broach, wetted wi 3 above fluid, in the same way we enlarge a hole in a brass onm O's ed. the broach is not pressed or forced into the hole, but moves logsely in it. CHAPTER VII. MEASURING AND SETTING OF COMPOUND LENSES. Simple defects in the refraction of eyes can be cor- rected by spherical ex or ce glasses; and when their right number or strength is selected for each eye sepa- rately, and afterwards correctly set in suitable frames, such spectacles will always give satisfaction. Nine-tenths of those in need of glasses are well suited with simple spherical lenses, and can be rightly served by the opti- cian as well as by the oculist, who, if he is nevertheless consulted by over-anxious people, can do no more than we do: he uses his test-types to find the extent of the error of refraction, and selects the spectacles accordingly. But others require something more than an optician is able to do; these should be sent to an oculist, who, after a professional examination,will give his orders, gegeXally, for compound lenses. AN Compound. lenses are combinations of sphy 1, pris- matical and cylindrical glasses, of which πρ ΟΥ in some cases all three, are ground on one anc (NN same lens. The most simple combination is when 2Ng"plane sides of a prism are ground into the spherj ape of either cx e or ec, without altering the actign à prism. CI MM S. An order for such hs wil read for instance: + 3 S prism 2°, NO aps:— 2 S © prism 3°. The combinations NÉ compound glasses are so mani- fold that they | be ground always to order, as no optician can hake deem in stock. We should never rely on the faithf@yexecution of our orders by the grinder; for instangaNWe may have copied them indistinctly, οἷο. It is th re advisable to remeasure all lenses before ι ο αν XS 66 HAND-BOOK FOR OPTICIANS. we fit them to a frame. Let us take the first lens as a test. We have here a spherical + lens combined with prism of 2°. I suppose that each of my readers has a trial-box with all the different lenses; if he has not, he should procure one as soon as possible, for no optician can do without it.* We first take from our box a prism of 2° and place the thick end upon the thin one of our lens. We will see at once that the optic line, which was before near the border, is now in the center. We then take — 3 S and place it on the other side of the lens; these three together must now be a plane, or the lens is not correct. The next combination is the sphere with a cylinder. One side of the lens is ground spherically, the other side, cylindrically. Such an order reads: + 2.5 S D + 1.25 C. The test is the same as before. With — 1.25 C we neu- tralize the cylindrical action in this lens by laying the two axes so as to cover one another perfectly, and by adding — 2.5 S we must again have a plane lens. The grinder always marks the axes by little scratches upon the edges of the lenses, so that we have no trouble in measuring them. But how, when the grinder forgets to mark €he lens, or when we are compelled to find the fort QW com- pound spectacles, having no mark, hand NS by a stranger to duplieate them ? Let us first see if they are decente find one side of the lens thicker aw. : horizontal line is elevated or Joy) y turning the lens between the fingers to the rig left. When this is the case, they are combined wita prism. We neutral- ize this prismatic action Xy ring different degrees of prisms till we get the Cal line in the middle, or till there is no more brgh&(&ne of the horizontal line. By e turning the lens NA optie line will not move up or I d e so, we will other, or that a down, as it did b the prismatic action was neutral- ized. Keeping thes} two lenses in position, we notice whether E nao. formerly imported from Europe, and Natchet’s Trial Boxes w D nsidered the best; but at present, we manufacture them RR! ood and cheaper in America. S » ENS MEASURING AND SETTING OF COMPOUND LENSES. 67 WS ~ the cyl. part of the lens is cx or ce, by moving it to the pos right or left in front of a vertical line. When this line D, follows our motion, the lens is concave, and has to be defined by a ex cyl. lens. The remainder of our lens is simply spherical, and easily measured. To prove the measurement, and especially to determine the right posi- tion of the angle of the cyl. part, we first neutralize the prism, and then the sphere, and lastly find the axis of the cyl. part by following the rule given in Chapter IV. We now mark this line with pen and ink, and place our lens on the following figure. τν "A Se πος ΤΊ S Q The center of the lens νο exactly over the center of the circle, and the horiz line marked on the lens from nose to temple ηλ ών the horizontal line A B. We now observe in NX irection the ink-mark points, and we have the 6 of the cyl. axis. In making this proof we migtJhold always the outside of the lens upwards, not foggards the paper. All wis e p its of the physician refer to the position Hi. he takes SS the patient, his right is the patient's left. t 68 HAND-BOOK FOR OPTICIANS. I have made for my own use this delineation on strong paste-board, covered with white paper, and find it very handy and more accurate than anything I used before. The little lines are useful guides for finding the right position of the zinc-pattern, and dispense with the labor of searching for the true center through its hole. I have tried to explain this matter in as few words as possible, and in the most practical way; but some may think it too complicated a task, and lose confidence in their ability to overcome certain difficulties. Just try : it, and if it takes a whole hour to! measure a compound ee lens over and over again, you will laugh at this **Sphinx"* afterwards, when you will be able to solve the problem in five minutes. It is absolutely necessary to know well how to meas- ure compound lenses before we are able to set them correctly. I admit that there are difficulties which will puzzle the inexpert, and will lure him into a different calculation altogether. I give here a few illustrations: We have, for instance, a lene —0.50 8S 2 — 1 C ax 90°, if the formula of which we do not know. By looking > through the lens we see at-once that the. concavity is in » 8 excess of the convexity, if there is any at : We first i look at a vertical line, and notice whetherWiNwHI follow; ^ if it does, and we pursue our investiga Gn and correct li S | I | | } the cyl. action by a suitable cx cyl. gaps, we are on the right track. But if, perchance, turned the lens 4 of its circumference, and had ined it in this posi- tion, which is at right angle he true cyl. axis, we find that the vertical line ot follow, but acts as a ΙΙ ex cyl. lens, and we hav make the correction in this case with a concavo-cyl. The consequence will be | that we make cross-c@imders, and adding — 1 S to the | — 0.508, which i e real amount of its spherical con- n cavity, the fo ound will be — 1.50 SO 4-1€ ax 180°, whic the periscopic equivalent of the first biconcave (δι Foe andskér test let us take — 0.50 SCO + 2C ax 180°. Όρο cyl. axis is easily detected in such a lens by its on but, for argument’s sake, I suppose we have H E~ into the same error, and again produced cross- MEASURING AND SETTING OF COMPOUND LENSES. 69 cylinders, thus turning + 2C into + 2 S. Then we have to add + 2 S to — 0. 50 S, which would give + 1.50 5, and our formula would be + 1.50 S > — Qux 905 the equivalent of the test-lens. We take another lens: + 1.75 SZ + 0.50 C ax 90°, and by the same process we will get + 2.25 S O — 0.50 C ax 180°. In order to find the formula, the axis should always be marked by small seratches at the border of the lens, or by pen and ink on a lens already fitted. The fitiing of a compound lens to a frame next lays claim to all our attention, if we will do justice to the. general rule, 7. e., to bring the spherical center before the pupil of the eye. When we have marked the cyl. axis in ink across the whole lens, and have neutralized the cyl. action by its opposite, we must next observe where the optic line crosses the lens 90° from the cyl. axis and mark it likewise in ink, but in a manner differ- ent from the line of the cyl. axis, say by little dots. We now lay that point of our lens where the two lines cross, exactly over the center of the test-figure, turn the axis of the cyl. to the prescribed angle, and mark by little scratches at the edges of our lens where it touches the horizontal line A B. These marks are guid to direct us in regard to the nose-piece and temp, We must take care that the hollow side of the len upon the paper, because that side will be tows Our zinc-pattern, after which we ess have a hole exactly in the middle, ην from the hose-piece to the Eee O marked line Through the hol NEn see the point where our ink- marks cross; wW the line of the pattern so that its continuation strives the scratches made before as a guide for the nos g temple, and after ascertaining once more by ο examination that everything is right, we run ouz ker around the pattern. Before chipping off O 70 HAND-BOOK FOR OPTICIANS. the superfluous part of the lens, we take a small woóden ruler, place it on the lens, touching the two marks for nose and temple, and make two other fine scratches inside the mark just made for the size of the lens, long enough not to be ground away in the finishing process. After the chipping, we have only to pay attention that our lens retains a nice oval shape, and that the edges are well bevelled. Any optician who follows these instructions cannot fail to give full satisfaction to the most exacting oculists, no matter at what angle the axis of the lens has to be placed. I believe that some opticians are careless in marking the true center of the lens, and, to find the angle, use designs similar to the following: I republish this cut as a sample of the Byorrect man- ner in which they are generally ma nd to guard against their use by any optician. In the ***Jewelers? Circular ang ‘ological Review’’ of November, 1885, I find on 8412, the strange com- plaint of a well-known oculist, io. ** You will seldom find a workman who can exg{ly set a cylindrical lens at the axis required, unless tlÁeJixis named be 180° or 90°. You will probably hay@p tilt the frame a little, either up or down, to obtai( Ré exact position required. That they set more EN rong than right, has been my 2 experience.’ If his optimas the above design to find the angle, their lenses st, of course, be incorrectly set, except in thoseet@ directions, as they are the only correct ones. Tt iss fore, no wonder that the ‘‘ Doctor” finds faul 1 his optician. S EN DEDE SCIUNT DA CHAPTER VIII. SELECTION OF SPECTACLES. This chapter is written for young opticians and such persons as have not yet acquired sufficient experience in the selection of spectacles, to overcome the many vexa- tions incident to their particular trade. I refer first to the pupil distance, as this is the main point of a good fit of spectacles. Pupil distance is the length between the two pupils, measured from the middle of one to the middle of the other. This distance is never smaller than two, nor larger than three inches. The eyes of little children, as well as those of the largest men, are within this compass. The average pupil dis- tance of a grown person is 28 or 2$ inches, and these are the standard sizes the manwtactories use for most spec- tacles they make. But an optician is obliged to leor any emergency an assortment of all the differ ranging from 2 to 3 inches. Children re 21"; boys and young girls 24” and 23”; Yn persons with small faces use mostly 28". is at 180°, and the lens whi s to me most satisfactory and pieasant, is — 2s N "axis 90°. Butit would be an excellent illustra for the theory of apparent astigmatism had f'eQwrected my myopia by — 3s, and then the apparenthfaulty meridian by + 1c axis 180°. When we look Sethe two combinations: 28 DO — 1ο axis 90”, and NS SOF Ty ασ "e TD". 140 HAND-BOOK FOR OPTICIANS. we will find them to be equivalents, only my eye prefers | the biconcave to the periscopic form. If, therefore, the axis of the cylinder has to be placed in the direction of the apparently faulty meridian, instead of ninety degrees from it, we have simply over-corrected the hyperme- tropia or myopia of the eye, and have made an error in the selection of the spherical lens. — The lenses which correct compound hypermetropic and myopic astigmatism are called Compound Lenses. jl The third variety of astigmatism cannot be well cor- | rected without the application of a mydriatie, and is, 1 therefore, beyond our reach. | - The zrregular astigmatism even eludes the greatest | efforts of the expert oculists, because we opticians can- | not produce the suitable lens for its correction. CHAPTER XVIII. THE OPHTHALMOSCOPE. —— Prior to the invention of the ophthalmoscope it was impossible to explore the interior of a living eye. Scien- tific men tried in vain to interpret this strange fact, for apparently this should have been easily accomplished, since the depth of the eye is shallow and all the struct- ures situated in front of the retina are transparent; yet it proved to be a conundrum, until Helmholtz explained the whole mystery. The optical law that the angle of reflection is equal to the angle of incidence had been known two thousand years. Polished surfaces and the bottom of shining vessels with wide openings were used to demonstrate its correctness; but when the angle of incidence became so small as to be almost, or completely, parallel to the angle of reflection, as is the case when light enterg the eye and should be visibly reflected through the wil, this law was entirely overlooked, and many theoy: formulated to explain the black appearance o A faint luminosity of the eye, especially ir of dogs and eats, had been observed D he earliest times, and gave rise to the general ANE at the human eye was also luminous under certain(copSitions. With a kind of popular superstition it wẹ refarded as evidence of a voluntary nervous irritati the part of the ani- mal, although nothing of ZU could be perceived in the human eye. The first who opposec bian, Alhazen, and IN pupil. > tapetum general error was the Ara- rds the Italian, Battista Porta, but their protest v Ωω noticed; on the contrary, when Méry, 1704, obseNygll the retinal vessels of a cat under water, the old@yperstition was strongly revived, till in 1810, Greate and Prevost repeated the very experi- 142 HAND-BOOK FOR OPTICIANS. ment in the dark, and of course did not see anything. They, therefore, denied the self-luminosity of the eye, and referred the aforesaid phenomenon rightly to reflected light. This was the end of the old delusion, and it was reserved to our century to solve the question: why is the pupil black ? In 1846, Dr. Cumming published a paper ** On the Luminous Appearance of the Human Eye," and rarely has an observer approached closer to an important dis- covery without actually reaching it. The next year, Dr. E. Brücke published the aecount of an experiment in which he allowed the light from a lamp to: enter the observed eye, whilst he approached his own eye very closely to the flame, only protecting it from the glare and heat by a thin screen. Both, Cumming's and Brücke's principle was for the observer to regard the eye ina direction nearly parallel to the entering rays of light. But Helmholtz, in 1851, was the first who clearly per- ceived the true optical relation between the incident and reflected rays, and then was led to the invention of the eye-mirror, or as he called it, the Ophthalmoscope. Instead of placing the light in front of the patient's eye, Helmholtz put it at the side of the patient's head, and reflected the rays by a polished plate of glass into the observed eye, while, without great annonce to him- self, he looked through the i Thus BS e4into the il- luminated eye of the patient. Thus t for the first time become possible to observe the (NI: of the interior of the eye — its nerve and vesselg previous observa- tions on the human eye had a to observing sim- ply its luminosity. Notwit ing, however, the mag- nitude of Helmholtz’s dis , the difficulty of manipu- lation, the feeble ποσο power, and the limited field of view of his ophthal]miécope would in all probability have restricted its aj ation to that of a philosophical in- strument, had no rs taken up his idea and, by intro- ducing great i ements, made it forever the most im- portant τοι t to every oculist. Although Helmholtz's instrumenk was of a crude construction, it does not lessen, ame of having opened an inexhaustible mine of in ist of having shed light on an heretofore chaotic SS — M P — ΤΗΕ OPHTHALMOSCOPE. 143 darkness, and of having completely revolutionized all preconceived notions of the diseases of the deeper structures of the eye. It is a striking fact, indeed, that the almost unparalleled strides ophthalmie surgery has made within late years, date, by a remarkable coincidence, with Helmholtz's immortal discovery. The first improvement in the ophthalmoscope was made by Theodore Ruete of Leipsic, in 1852, by introducing a concave mirror as reflector, which had a small opening in the center for the observer's eye. Since then, mirrors of different shapes have completely superseded the plates of polished glass. ^ Liebreich introduced a most handy and useful instrument. He used a coneave metal mirror, about 14 inch in diameter, and of eight inches focal length. The back of the central small aperture is bev- elled off towards the edge, in order that the peripheral rays of the cone of light, which passes through it, may not be cut off by a thick, broad edge, which would make the opening a short tube. Behind the mirror, which is fixed upon a short handle, is a small clip for holding a convex or concave lens. Other improvements were made by Coccius, who introduced a plane mirror, while Zehender made use of a convex one, in order to - centrate the light upon one point. A further WÒ% 30 perfection was | made (1870) by E. G. Loring, y phy- sician of New York; his instrument eben Konstant changing of lenses behind the mirror, as AE the different convex and concave glasses i SA rotating cylinders, alternately ΤΗ “Debi gay mirror. In 1878, Dr. H. Knapp did away wi Ore s cylinders by presenting an ophthilnoscopsei ^ two undetachable but revolving dises, one of w Q containing concave, the other convex lenses. are arranged i in such a manner that they rotate pastsych other, so that the focal value of each lens can Qa ned to a greater or less degree by adding tg i various neutralizing lenses of the other disc. to e glasses are covered by a stationary metal plate to Pe soiling. In 1874, Loring simpli- fied the forego a ος and by adding a few im- provements ge ced a comparatively cheap and handy ophthal OE whieh soon took the fancy of most oculist Ν | ἃ [ir ο | ag GN 144 HAND-BOOK FOR OPTICIANS. All these instruments are monocular; Dr. Giraud- Teulon, of Paris, and Dr. J. Z. Laurence, of London, invented binoeular ophthalmoscopes by combining Helm- holtz's invention with Wheatstone's stereoscope; but they soon were dropped, the more handy monocular instruments proving preferable. The ophthalmoscope finds its greatest usefulness in the hands of expert oculists, who have all opportunities of learning how to use it. My first experiment with it was about twenty years ago. I had an instrument of Lieb- reich’s, and my workman and some trusting friends were the innocent victims of my investigating proclivity ; but they soon were frightened by the flashes of light which almost blinded them, as they were directed to look straight into the mirror, instead of looking a little side- ways. Since then, there have been published several exhaustive treatise on the use of the ophthalmoscope, which should be carefully studied before attempting to employ it. It is not my intention here to specify the many variations and their correction in the observer's and the observed eye, as this treatise is written for opticians who, perhaps, never will professionally handle an ophthalmoscope. 1, therefore, close thi\chapter with some generalities which may give the "XR an idea of the great importance of Helmholtz's Lory tion. The ophthalmoscope reveals tworkN»ortant conditions of the eye; the pathological, |l ne indirect method, where we obtain, by placing convex lens of about three inch focus in front of bserved eye, an inverted image of the dise; and the ical, by the direct method, not using the convex s, when we obtain an upright image. The indirect WmVéthod is mostly employed to as- certain the health Qr impaired condition of the inside structures of the ; the strong convex lens before the eye greatly Adtes such an examination. By means ex , of this m perts discover the beginning of certain serious dísegWes, as for instance, Bright’s Disease, before any AO. ymptoms of it show themselves. The direct metha on the contrary, reveals the optical condition ο eye with great certainty, and shows the myopie, SS Yermetropic or astigmatic errors of the eye. Wemay mazo THE OPHTHALMOSCOPE. 145 say, therefore, that ophthalmology is an exact science; in no other branch of practical medicine or surgery can an equally certain diagnosis be made. Some years ago I was introduced to one who pretended to know all about à person's general state of health and mind by looking at him without asking a single question; but, as ridic- ulous as were his pretensions, we have to bow to the expert oculist who accomplishes this feat by looking into the eye with the ophthalmoscope. To make a professional examination we first have to adjust our own eyes to the focal distance of six or eight inches, by means of the convex or concave lenses in the revolving discs attached to the ophthalmoscope; then, when we » place our eye at the given distance, and we find the retina sharply focused, the eye observed will be emmetropic. But when the image is indistinct, and we only can gain a clear view of it by changing our own correcting ‘Jens to a stronger one, there is hypermetropia present in the observed eye, and the difference between the two lenses is the amount of its ametropia. Again, when we have to reduce the power of our correcting lens to a weaker one, then the eye observed is myopic, and the difference between the two lenses represents the amount of myopia. This result is only approximative, as the obs Nd ye remains in full possession of its accommoda ^ which greatly interferes with the exact meu of its refractive errors. In many cases it i Quay to sus- pend the power of accommodation e use of a mydriatic before we can measure EN xact amount’ of the refraction, as this is not ΤΝ Oo the application of the mydriatic. Some of my ej ers may not be posted about the difference between-th Ces may nt and the refraction of the eye; it therefore, not be out of place to define in a f Quas their meaning. When the crystalline lens i 4 state of rest it still has a cer- tain amount of ref z e power, which is, as the mathe- matician would Say) ‘‘constant’’; but as long as the lens is VACUNA AE of the ciliary muscle, its power of refractio anged by the alteration of its convexity, it is ** varj > This changing of its form or shape is 146 HAND-BOOK FOR OPTICIANS. called ‘*accommodation,’’ and to suspend this **variable factor"' in order to measure only the ** constant factor,” the refraction, it is necessary to apply the mydriatic. As valuable, yea indispensible, as this instrument is to the medical faculty, it is of but small importance to the dispensing optician. It is not only difficult for us to find the many willing patients for experimental pur- poses in order to acquire expertness, but it is also a very unprofitable and time-losing business as long as patients refuse to pay for our trouble, in addition to the regular price of the spectacles we select for them. j} t i j } CHAPTER XIX. SECOND SIGHT. The eye is by no means a perfect optical instrument. Its defects are, under ordinary circumstances, suppressed by the brighter and more perfectly formed central por- tion of the retinal image, so that the defects, when not of too high a degree, are unobserved and can only be de- tected by careful experiments. Helmholtz once re- marked: **If an optician wanted to sell me an instru- ment which has all these defects, I should think myself quite justified i in blaming his carelessness in the strongest terms, and give him back his instrument." And yet, nobody can devise a better plan for the construction of this organ to accomplish all its duties with such simple means. It is the most wonderful machinery ever de- signed, although it is not perfectly achromatic, and,be- sides, suffers from spherical aberration. Yet, ve no reason to grumble at trifling imperfections; Po to accept this precious gift of nature with gratitude, and take proper care not to hag unneces- sarily its natural decline by an pe e, reckless use. But the most careful use of our e cannot defer the senile changes which take place > yes, in myopic and hypermetropie as well as in efant®fropic eyes, on ac- count of the natural developmer SY the crystalline lens. In childhood the nucleus ofzjhe"lens is firm, while the density diminishes toward jeriphery; this arrange- ment almost entirely oge s the spherical aberration, as the peripheral ἘΚ N ess refracted than they would be, if all parts o ens were of a uniform density. Hence, the sis ois rays are united at nearly the same point as,tlye, central rays; consequently, the child can have a γρ ήτσε pupil, and the peripheral rays still be united e focus of the central ones. With the 148 HAND-BOOK FOR OPTICIANS. advance of age, the outer layers increase in firmness; they gradually approach the consistency of the nucleus. The greater firmness and, more uniform consistency of the lens causes it to become fiatter, thus diminishing the reiractive power of the lens, and increasing its spherical aberration. The peripheral rays are brought sooner to a focus than the central, thus compelling the pupil to re- duce in size; the iris acting now as a diaphragm in a tel- escope. The time for the use of spectacles has arrived, and should not be overlooked by those who wish to preserve their eyesight. The increase in the strength of specta- cles will keep step with the gradual hardening and con- sequent flattening of the lens. The development of the crystalline can be compared to a fruit while growing; it takes its natural course till it is ripe. We cannot, di- rectly, weaken the lens, no matter how long it is used; but, indirectly, it is impaired by the other parts of the eye which we abuse or hurt,—as the fruit is prematurely ripened by the sting of an insect. When we unduly postpone the use of spectacles, we do not weaken the lens, but the ciliary muscle, and when we overwork the eye, it is not the lens that suffers, but the retina. By an inflammation of the cornea or iris; the lengu% only sec- ondarily affected; choroiditis and retinitiMQave the same effect. Each suffering part acts UNE upon of the others by reflex action. One of the most dreaded afii ihe eye is when the lens commences to lose its @xMasparency, when signs of cataract make their appe ty , and people anticipate blindness and misery. arect is, generally, a disease of old age; the loss o » transparency of the lens 18 chiefly due to its defigigntnutrition, dependent upon an inefficient blood sv , and consequent diminution of the watery const s of the crystalline lens. Inflam- mation of the ‘ tunies of the eye, especially of the vitreous humor, may also give rise to iris, choroj (9) cataract, hot) by an impairment of the nutrition of the lens, bu. by the inflammatory changes, implicating the inner Wypsule, and even the lens itself. — It is very diff to detect the real cause of cataract. Among the SECOND SIGHT. 149 most important of these causes is exposure to light and heat; for instance, the artisan at his work-bench, facing with his unprotected eyes a window or gas-jet for many | hours every day; the cook, bending over the heated f range; glass-blowers, bakers, blacksmiths, puddlers, l stokers and engineers are affected. A fully formed, | mature cataract may be easily recognized even with the naked eye; the pupil is no longer dark and clear, but is occupied by a whitish opalescent body, which lies close behind it. However, when cataract is incipient, and but slightly advanced, more especially when the opacity | commences at the edge of the lens, it may be overlooked, ' except when the eye is carefully examined with the ophthalmoscope. | Care must be taken not to mistake the physiological q changes which occur in the lens in old age for commenc- ing cataract. These changes consist in a thickening and consolidation of the lens substance, especially of the | nucleus, which assumes a yellowish tint. The chief à distinctive features between this and incipient cataract are, that in the former case the sight is perfect, when assisted by suitable glasses; the opacity remains abso- lutely or almost entirely stationary for a long ; BN and the cloudiness is not observable with the al- moscope, except with oblique illumination. qu ave here a clear case of second sight. Since the issue of my first book, I RAS inquiry of several cases, and learned pus thej elopment is not of such short duration as I i ed. A former customer laid aside her ο age of 66 years, and is now, after 17 years, stil oing fine needle-work | as well as ever. Of course, ay vision is poor, | and ought to be correctec concave glasses; but she | hates to commence E DX spectacles. Other cases, p of a shorter ses n to me, show that second NG of Danaus,* which ends in C eties a blessing, and a source r those people who perceive that one sight is not alwa misery, but that of great rejoicing [ ο ασ * * Danaus w e king of the most prominent province in ancient Greece. It AY that his gifts were often disastrous to the receiver. A gift, CNN iven with bad intention, is called after him. 150 HAND-BOOK FOR OPTICIANS. faculty after another gradually withers and vanishes, except their eyesight. In the development of real cataract we meet with a phe- nomenon which may falsely be taken for second sight, and cruelly disappoints the afflicted, as it is, generally, of short standing. Dr. Soelberg Wells says: **'The rate of progress of senile cataract is very difficult to determine with accuracy. Sometimes, years may elapse before it arrives at maturity. It may remain at an incipient stage for a long time without apparently making any progress, and then suddenly advance very rapidly, arriving at maturity within a few months or even weeks. We must, therefore, always be upon our guard against giving a decided opinion as to when any given case of incipient cataract will be fully formed. Patients are sure to ask this question, and we may fall into great mistakes by giving a decided answer." Another physician recently remarked: **When oculists, formerly, were consulted for relief from commencing cataract, it was their habit to acquaint the patient or his friends with the cause of the failing vision. The opinion expressed was to the effect, that forthe present nothing could be done to restore vision ; on the contrary, it would grow steadily wor, but that though blindness might and probably πους ue in one or both eyes, vision could be restored b noval of the ripe cataract. Thus the patient an e family were sent away with an abiding solicitud nging like a cloud over the household, the anxiet viated only by the prospect of a future successf, ration.”’ Such sensible remarks teaabAhe wholesome lesson to opticians, who have to dezNyith those customers, seeing the advance of this fearfülisitation, not to be indiscreet, and wantonly dispel ‘happy delusion, as nothing in the world can ar O he final course of their trouble. We may advis ahot to read or sew at night, and to spare their e NS much as possible. When in the first stage of iia cataract bright light begins to annoy their sight, *eTve them smoked glasses; they neutralize the sct ed rays which pass through the infected lens. Do x ose patience by their renewed attempts to find SS y changing their spectacles. Have always a kind a ~ — — HÀ ee SECOND SIGHT. 151 word for them, and as you cannot help them materially, let them have the full benefit of your benevolent sym- pathy. CHAPTER XX. ! c RELIEF TO INJURED EyEs. µας... This chapter is partly compiled from different sources. It would not have found a place here if it were not for : the great usefulness of these simple directions in case of emergency. Though the eyes are well protected and shielded by the forehead, the nose-bridge and the cheek-bones, they | are nevertheless exposed to accidents caused by small fly- ing objects; and although the eyelids are reliable safe- guards to keep off any foreign intruders, they may be b out-generaled occasionally when they are the least aware of any danger. Some injuries do not allow of any delay, and as medical assistance is not always to be had when mostly needed, I thought it proper to add this treatise not only for the personal benefit of my readers, but also for that of their friends and customers, whq may in their trouble come running to the optician to eq exhem relief. I was several times successful in this αν ect, and may say that I saved more than one eye f reat annoyance and danger. A very common accident is the By ing of mud, dust or insects into the eye, which, losing of the eye, en- ter between the lid and [9.47 People thus af- fected generally keep we ves closed, as the opening of the lids causes such irritation that the eye-ball is soon inflamed and shot. The quickest way to re- lieve these suffere o wash the dirt out with clean water by means of aq: air brush ora feather. This is done in the follow anner: With our left hand we take hold of t -lashes of the upper lid, drawing it for- ward ET. to allow the brush or feather, previously sl eet water, to enter between the eye-ball and lid, till Zach the inner folds. We direct the patient to RELIEF ΤΟ INJURED EYES. 153 look downward, and move the brush towards the nose, not to the outside. We have to repeat this several times with plenty of water. Then we depress the lower lid, directing the patient to look upward, and wash carefully as before, cleaning the brush after each application. In pi some trifling cases, when an insect or a few grains of dust | have entered the eye, draw the upper lid as ; far down as possible, a little outward, and push the lower one as far up as you can. Then let the upper lid fly back to its natural position, when the eye-lashes of the lower one will act as a brush, detaching any light substances, and relieving the eye instantly. “Make it a rule never to rub the eye ‘when injured, as the irritation will be increased largely by it, and soon will cause inflammation. When hard pieces are imbedded in the tender parts of the con- junctiva, which cannot be removed by the brush, it is not difficult to remove them, if they are lodged in the lower lid, by means of a handkerchief or some small pincers; but it requires some skill to remove them from behind the upper lid. In order to accomplish this, we have to evert the same, which is done by taking a good hold of the eye-lashes and the edge of the lid with the left hand, then applying with the right hand a thin pencil or any other rounded object to the middle of the lid, and b pressing the pencil, at the same time swingi left hand upward, the lid is everted and the ing posed for examination. The patient is now ted to look downward, which brings into view th Sio inner surface of the upper lid, and enables us Oo any foreign bodies, as grains of sand or by coal, yet stick- ing in the soft part of the tender Ye “A somewhat singular advice, ho& to remove grit from the eye, was lately: communicate@ Dy a railroad man. He says: ** Most persons with w or any foreign substance in the eye will instantly b o rub the organ with one NG andkerchief with the other. do, remove the offending sub- stance; but more ntly they rub until the eye þe- comes ‘inflamed, t bind a handkerchief around the head and go 1. This isallwrong. The better way is not to PUN eye with grit in at all, but rub the other hand, while hunting fo They may, and some 154 HAND-BOOK FOR OPTICIANS. eye as vigorously as possible, causing the offended eye to profusely shed tears by which the bit of sand or dust is washed out.”’ Mechanics are very often hurt by fiying particles of metal while hammering or turning, and chips may strike and penetrate to some extent the front part of the eye. If these are of iron or steel, and not imbedded too deep, we may remove them by the use of a strong magnet. In case these chips have penetrated so deeply that the con- junctiva has closed over the entrance of the wound, it is necessary to consult a physician. Such wounds are not very painful at first, and the application of water or oil may be sufficient to allow us to wait even until the next day to look for relief. Any longer delay may prove fatal, as a neglect will surely result in a violent inflam- mation, if these particles are not removed in due time. Another danger to the eyes is the splashing of quick- lime into them, causing sometimes the complete loss of sight. I myself was a victim of such an accident at the age of four years. Some workmen were slacking lime, and I was wondering how stones covered with water eould boil. Wholly absorbed by this phenomenon, one mischievous boy gave me a push, and I fell headlong into the hot lime water, but was immedigttly re escued, washed and brought to bed. I soon fel ay something soothing was applied to my eyes, whic cade them of the burning sensation. It was th Weeks before I could open my eyes again, and I rewNihber quite well the many anxious inquiries of my ts, whether I could see them. In such accidentg washed out with large water as thoroughly as po&gible, and a rag ean with sweet-oil applied, till a RDysician can be consulted. If corrosive pigme@ and acids enter the eye the whole face, eyes open, s be repeatedly dipped in water in order to dilut a ash off the acid or paint; then apply milk freely, afterward plenty of oil, till medical as- sistance gMh Net procured. Whatever is done must be done quic, as it is of the greatest importance to re- lieve « ve instantly from the ravages of such corrosive wo | } ($ d | RELIEF TO INJURED EYES. 195 In ease the eye should be scalded or injured by the spattering of hot fluids, do not apply water, but only oil or milk, and shut off light and air by a compress of soft linen, thoroughly saturated with sweet-oil, till the doctor comes. — Hot vapors of strong sulphuric or nitric acids will cause immediate blindness if they strike the eye. These directions are not intended to do away with the services of the physician. On the contrary, they are in- tended only to prevent as much as possible the pernicious consequences and further progress of such accidents, till professional aid can be procured. Sometimes five min- utes’ delay may destroy the eyesight forever, when by the prompt application of water, vinegar, milk or oil, the effects of such injuries would be diminished, and often- times removed entirely. CHAPTER XXI. ARTIFICIAL Human EYES. Long before the Christian era, artificial eyes were used in statues and busts; they were made of colored stones or metal, and inserted into the cavity expressly constructed for their reception. The deep sockets found in some statues without eyes are an evidence of this; like that of Antinous in Paris, and others in different archeologic museums. In some ancient statues the eyes were outlined by the chisel and then painted. We have no record that glass-eyes were ever used for this purpose, although colored glass was already known at that period, and the story that mummies with artificial eyes were exhumed is probably without foundation. It was abso- lutely unnecessary to ornament a body which was enveloped all over, several inches thick with bandages, and then covered hermetically with a kind of plast r cement. This outside coating was made to repres S. uman-like figure, studded with glass beads and er ornaments ; but no mummies have yet been ] with artificial eyes, except those lately discow Q in South America, which are of modern date, TN our or five hundred years old, of the time of ncient Incas of Peru. The custom of embalmingwivery common among the Incas, and was made t 1ally easy by the warm, dry climate of Peru. It ,is Stated that the embalmed were often simply placed iM sitting posture on the vast nitre beds, and left exasgedyi to the open air. For years after death they wan isited by: friends and relatives, and it was congeq(iyttly important that the semblance of life should be&njiintained as perfectly as possible. They removegs, therefore, the perishable natural eyeballs of the de and substituted the dried eyes of the cuttle fis} ich are almost indestructible, and possess suffi- SNP Sem and fire to partially simulate life. a SV Zo ARTIFICIAL HUMAN EYES. 154 The substitute for a live human eye is not older than three hundred years. We find the first authentic record of them in the Chirurgical Work of Porrée, 1582, with drawings of two kinds of eyes, one to represent the eye and the lids, in case both were removed, the other to be used when the lids were still present, and to be inserted behind them. Both kinds were made of flat or slightly curved gold, silver or copper plates, enameled and painted to imitate the other eye as near as possible. When the eyeball and lids were totally removed by the operator, as was done very often at that time, the plate had to be large enough to represent also the eye-lids, lashes and earuncle. To this plate was attached a spring covered with leather, which encircled three quarters of the head, thus pressing the plate towards the hollow orbit. This was indeed a very poor commencement of that great benefaction of to-day. Porcelain, and afterwards glass, soon took the place of metal, as Fabricius states, in 1623. From that time the manufacture of eyes has slowly but constantly improved. Dr. Mauchard, 1749, relates of a lady who had been furnished by him with an artificial eye, that she only wondered why she could not see with such a beautiful imitation. Since 1770, the eyes have been made of οἵ νὴ stead of glass, mostly in France, and for m: up to recent date, the best eyes have come jam Some of the celebrated manufacturers Wen Hazard- Micault, Noël, Boissoneau, etc. But resent good eyes are made everywhere, even in SQ ca. The best eyes I ever handled were made by( Γλιδν!ς Müller-Uri, in Germany, who lately died. x An artificial eye is a shell ο) | front of the eyeball, the los; conceal. They are so pep&éed that nobody can distin- guish them from the na ye, and they are now used by everybody who NN y can afford to pay for them. An artificial eye πο no means a luxury as in former years, when only jich people could afford to pay its price, but it is ρον altogether a necessity for everyone who is unfortune disfigured by the loss of it. The sev- eral TM it has to perform, are: S EN mel, representing the which it is intended to 158 HAND-BOOK FOR OPTICIANS. 1. The artificial eye serves as a beautifier. It restores the natural appearance of the face and preserves the regularity of the features. If, for instance, the greater part of the eye-ball is lost, the lids have no support and, consequently, shrink and shorten. When this loss happens in the earlier stage of life, the development of that side of the face becomes retarded and will present a strange appearance. Even in adults this shrinkage takes place after the lapse of a few years. It is, there- fore, wrong to postpone the use of an artificial eye, especially with children whose tissues change so rapidly, the more so, as even a child of five years can wear an artificial eye without any inconvenience. 2. The artificial eye serves asa remedy. It enables the eyelids to move freely, they can be closed and opened as before, and also restores the functions of the tear- passages. After the removal of the eyeball there is an empty space left behind the lids; the tears accumulate in this cavity, and irritate the edge of the lower lid, and frequently give rise to ulceration. ` By means of an arti- ficial eye, however, the tears are directed to their natural channel, and are removed in the usual way through the nose. It also prevents the eyelashes from turning inwards, causing inflammation and suppuration Ni constant friction upon the structures left behindøaNħe socket. It protects the latter from all outside ation, such as wind, dust, smoke, etc., which o ise might sympa- thetically exert a pernicious KA upon the remain- ing sound eye. 3. The artificial eye Os benefaction. It is a blessing to everybody,-&%w the rich as well as for the poor; but while it servè the former mostly as a beauti- fier, it very ofter tects the latter against want and misery. It is re question of existence for them, as some employ hesitate to engage a person thus disfigured ; "ust him with work that requires good sight, eva) it could be well performed with only one eye. ὃν e use of an artificial eye, however, such objecg2 are removed and he may readily find employ- m d ARTIFICIAL HUMAN EYES. 159 A judicious selection of the different sizes of artificial eyes depends altogether upon the various dimensions of Ν the cavities. Children, generally, need larger eyes than | elderly persons, and a great variety as to shape and color. is, therefore, necessary to suit all cases. The white of most artificial eyes is on one edge more or less eut out, and as a rule, this edge should be used for the upper lid, in order to allow the same as much room and liberty of mo- A tion as possible. We may classify the eyes, therefore, into right and left ones, according to the position of this cut-out. By doing this, we must bear in mind that the smaller end of the eye is the nasal part. But when the artificial eye squints upward, we have to change this rule, as the true position of the pupil and iris is the principal condition of a good fit. The eye should never cover the caruncle (the fleshy protuberance in the inner canthus, or in the corner of the eyelids near the nose), and should allow the lids to close. In order to make the artificial eye light, and save the under lid from being depressed by its weight, it is made in form of a shell with its border finished off by the melt- ing process with a pointed flame. Any alteration by cut- ting and polishing it, will render the eye useless afje\a short while. Before the insertion of an artificial eye, the Qies in the socket must be perfectly healed and cieqtNZed, and the conjunctiva free from inflammation a norbid sen- sibility. An artificial eye, besides resey g the oppo- site sound eye in prominence and in nd appearance of the iris, ought, if the stamp be to move in con- cert with it. "This it does by Mowing the motions |. communicated to the eo M: folds, into which its 1 margins are fitted, and by t ovements of the stump. It ought at the same a ıse no pain or uneasiness. | A perfect motion of e is possible only when the stump is large, and y ὃς is almost resting on it. For this purpose the dy Na es be rather flat, not too large, lest the free mo ^u be checked by its touching the sides of the ^C Ww hen the stump is small, the artificial eye must τ (22ο, high and well rounded. The inner folds of yelids are then its only support, and its S SS 160 HAND-BOOK FOR OPTICIANS. motion is, of course, little and insufficient ; the more so, if the patient insists on having the artificial eye matched exactly in size with the other, thus producing a **staring look.’’ To introduce an artificial eye, it is necessary to raise the upper eyelid and slide the eye, previously dipped in water, up behind it by the end which is to correspond to the temporal angle. Then turning the nasal part up- ward, and letting the upper eyelid fall, depress the lower forcibly, and make the lower edge οἵ. the artificial eye slip into the lower palpebral cavity. This being done, and the lower lid allowed to rise, the introduction of the eye is accomplished. The removal of an artificial eye is done in the follow- ing manner. It is withdrawn by an opposite procedure, by depressing the lower lid, and inserting the curved end of a hair-pin, or even the thumb-nail, between the eyelid and the lower edge of the artificial eye, thus hooking it out from the lower palpebral cavity, when it will oide down from behind the upper eyelid, and fall into the hand ready to receive it. In doing this himself, the patient should lean his face over a ‘soft cu hion, or the like, in order that, if the eye should slip ou vedi fingers, it may not be broken in the fall. The artificial eye is withdrawn ev be cleaned with water (which shoul of the mucus which may adheg in the artificial eye and after y rawing it, the patient should bathe the cavity o orbit and the stump of his eye with water. A tgorse@h cleaning of the artificial eye every week with μοὶ water and a soft sponge is also recommended ip Orfer to remove all fatty matter from it. But alt er objectionable is the habit of some people to ir artificial eye before inserting it, because the s membranes of the orbit do not re- quire ee ional lubrication, as long as the eye has p UM and is to ἃ tepid in winter) Before putting not lost i h.—In the course of time it becomes rough from fae Slow corrosive action of the humors which com Bontact with it, and requires to be exchanged foxWnew one. In case there should be some difficulty ovis a new eye, the old one may be repolished ARTIFICIAL HUMAN EYES. 161 and do service for a few months longer. You take a rag of cotton, form it into a small ball and fasten the eye over it with soft bee’s wax. The inside of the eye should be well filled up to prevent any accident. Then put in your hand a little alcohol or water and fine pulverized English rouge, and afterward Parisian rouge to finish, and shine the eye as you would shine a brass button. A worn-out eye causes congestion of the lids, a swell- ing of the conjunctiva and a gradual filling up of the orbit. Many unfortunate sufferers have in this way deprived themselves entirely of the great blessing of correcting their disfiguring loss by a suitable substitute. As an artificial eye is liable to be broken by accident, a person making use of it should always have several on hand. An eye will last no longer than two years on an average. From the irritation excited by the artificial eye, when it is either a bad fit or worn too long, the palpebral conjunctiva are apt to become much congested, and beset with polypus-like excrescences. In this case the use of the artificial eye should be discontinued for some time, and it is necessary for the patient to seek medical assistance. Ϊ ò ο ἀν CHAPTER XXII. CALORIC Rays IN DIFFERENT Licuts. According to the old emission theory, light is a com- pound matter; but according to the new undulatory theory, it is a compound force. It is a mixture of lu- minous and caloric waves, and is also a combination of the different colors. To resolve light into its colors has been a comparatively easy task since the properties of the prism have been known; but the complete separation of luminous from the caloric rays is yet a matter of inves- tigation. Eminent scientists have labored long to isolate one from the other, but only with partial success. Light, passing through an ice block, or through plates of mica, is not deprived of its caloric rays, although they are absorbed to a certain extent by reflection; but by means of a strong burning-glass we detect enough of them to be aware of their presence. So explorers have succeeded in completely absorbing luminous rays, and showing the presence of onl caloric rays in their full strength. The following experiment was (Ωλυπίοαίοά to me by Professor Pepper, of England, i 2, when he, on his lecture tour, passed through (Ny Orleans. I repeat it here as he explained it to Re: I have never tried this experiment myself. Ir aber with great pleasure his able lecture on ** Lightyand Heat,’’ illustrated profusely by novel and highly Aferesting experiments. The candle ὁ 6 between the glass-jar c and the concave miro he rays of the candle are thrown by the miryer he flat jar, filled with a solution of sul- phuret of Qripn and iodine, which completely absorbs the lugpisous rays. You cannot detect through the jar the le Nace of light; but if you hold your finger at the peigDvon will find that the caloric part of the light is Y SS EN | — n — CALORIC RAYS IN DIFFERENT LIGHTS. 168 concentrated there most keenly. Thisshows that the liquid absorbed only the luminous rays, and allowed the caloric rays to pass through without perceptible interference. In the same manner that luminous rays are modified or intercepted while passing through bodies of different de- grees of clearness, the caloric rays are also more or e : 28. only ithout intercepted by different substances. Mica, for ips absorbs the greater part of the caloric rays; bu substance which allows all caloric rays to p: any obstruction is clear rock-salt. Expe nts with prisms of this salt have demonstrated the Wt. that light passing through such a prism gives ty@ Soectra, one by theluminous, another by the calo: det of the light, with the remarkable difference tl{t tfe red line of the calorie spectrum is as broad as o ne other colors com- bined, from orange to violet This experiment is an un- deniable proof that the cal and luminous rays can be separated, and that both sof rays are subject to the same law of nature, t dulatory or wave theory. This theory de AF Sht as motion of such an intense velocity that we dgnJexpress it only in figures, but are utterly unable ο Ur Ap qs it. Imagine that we were able to buil achine of indestructible material, and had the p of increasing its revolutions indefinitely. Eo 164 HAND-BOOK FOR OPTICIANS. We put it into operation. As long as we can follow its movements with the eye, we have common motion. We can follow with our eyes a stone thrown to some dis- tance. This also is common motion. Let us now in- crease the speed of our machine thirty-three revolutions asecond. The eye can no longer follow it, but the ear discerns a low hum, which becomes louder and higher as the machine gradually moves quicker. We have sound. A ritle-ball is not seen, but we hear its whistling noise. When the tone has reached its highest, pitch (38,000 vi- brations in a second), our ear is unable to perceive any further increase; we feel then the effect of heat, and soon see a violet glimmer, then a transition through blue, yel- low and red into white. We now have light. The vi- brations have increased to many thousand billions a sec- ond. If our machine is not melted by this time, and is still running with increasing speed, we had better keep at a safe distance, for the next action will be the emission of electric sparks and lightning in all directions. Here science ends, and here is the limit of all power and force we can explain or comprehend. But if we al- low our imagination its widest range, and look upon this experiment only as the symbol of the univer sublime power, does it not give usa faint idea the proper mode of attaining to the knowledge of uy tima ratio, the incomprehensible omnipotence? Light and heat are always co ; there is no light without heat, for phosphores annot be regarded as light. Of all the lights in née, the natural or sun- light is the most pleasant; Khas 70% of caloric and 30% of luminous rays. The RN preponderance of the ca- loric over the lumino¢Pyrays is necessary to make our earth habitable, as i(SWiatural heat, about one hundred feet below the Gg and not interfered with by atmos- pheric change NS only 50° Fahrenheit. Although the temperature fences 1° for every 65 feet of depth, so that at twoWwges below the surface water will boil, and at ΕΙ miles, iron will melt; the inner heat, esti- Tak more than 10,000^, is not able to warm the com- RALEN ly thin crust of our earth much above the freez- S EN ο οἴασ.---- 5 y; , 5 ae iia imi " * (ΝᾺ Ὁ O .AQ g CALORIC RAYS IN DIFFERENT LIGHTS- 165 ing point. Besides, if the sun would not come to our as- sistance, we could not endure the low temperature of the Universe, which is calculated to be 2000? below zero. But the sun with her 100,000? of heat on her sur- face, overcomes all these obstacles, and sends us sufficient light and heat to make our earth the most pleasant quar- ters to live in. We must not form the wrong idea that the immense radiating heat of the sun could extend through the whole solar system and reach the last planet, Neptune; in fact, it does not reach even the nearest planet, Mercury.* — The real size of the sun can be best demonstrated by sup- posing the sun to be a hollow shell, with our earth in its center and the moon moving around the earth at the same distance. Now, if we imagine ourselves to be present on the surface of the shell, and looking at the moon through a hole, it would in its nearest position to us appear only of the same size as when viewed from the earth. Just think, the sun to be a solid body with a diameter of four times the distance of the moon from the earth, and you have an idea of its enormous size. And, further, imagine this immense ball to be in a state of combustion! Not calmly glowing as it appears to us from a distance 95 million miles, but in a state of furious uproar an un- dering convulsions. Just look at a large hous re, and notice the crackling and hissing of the fi Qi watch with awe the fearful roaring and thunderin a burning city; picture to yourself, if you can, t ‘rific reports and unearthly glare when a stream of bursts through the sides of a volcano; the vast κ aping hundreds of feet into the air, amidst th ‘ful internal rum- blings; multiply all these a mðn times, and we may get a faint idea of the sun's preSént condition. The ter- rible roaring would be he illions of miles away ; tre- mendous sheets of fla called protuberances, are thrown hundred ον miles into space; the con- stant explosions, g holes in the surface of the sun, causing the(sug-spots, which our earth would not fill: really, . C le of elements of the sublimest N grandeur. * We kno ittle of the planet, Vulcano, lately discovered, to use it here SS Ustration, LATO. um ep EMT Neu 166 HAND-BOOK FOR OPTICIANS. The atmosphere of the sun is caleulated to extend about five million miles, but its radiating heat will not reach thus far, so that the planet, Mercury, whose mean distance from the sun is 37 million miles, must have at least thirty million miles of that extreme low temperature of the universe, and our earth fully 90 million miles of it. It is, therefore, impossible that the rays of sunlight actually carry particles of its radiating heat with them. In fact, the vibrations of ether caused by the sun are by themselves neither light nor heat, until they are decom- posed under certain conditions, as in passing through our atmosphere; but how this is performed I must leave to professional scientists to explain. The sunlight is perfectly white or colorless, and is the most agreeable to the eye. The caloric part of it is greatly modified by the moist atmosphere it has to pene- trate, and by repeated reflections. "The healthy eye is well able to bear its effect the whole day long without fatigue. Next to sunlight, electric light is the strongest; it has a bluish-violet tinge, and contains 80% of "glorie and 20% of luminous” rays. The electric light not pro- duced by combustion, as we have seen in Beht, but by the intense heating and volatilizatiop! ponderable matter, because the electric spark can ass through a vacuum. It is very intense, so tha eye is dazzled, and vision becomes much more stinct than with a light of the same power giv from a lamp with a large circular wick. ey experiments with large Voltaic piles to produce electric spark, were made merely for curiosity's ss, till in 1813, Sir Humphrey Davy (1778—1829 OY ie dii English chemist, at- tached to the wire the different poles, pencils of charcoal, and y% a constant arc-light of consider- able strength. t his experiment was not followed up as arduous the time as it has been during the last twenty-fivewzZars. The scientists experimented with the Drums or calcium light, and later with Bunsen’s κ. m light, without following up Davy's temporary In fact, it was merely an experiment and of CALORIC RAYS IN DIFFERENT LIGHTS. 167 no practieal use, as the charcoal points were too rapidly consumed. A great improvement was made in 1843, by Foucault, who substituted pencils of hard gas-carbon, such as is deposited in the interior of the retorts during the manufacture of illuminating gas. Since then, many different forms of electric lamps have been devised. They are divided into two kinds: the arc-lamp, for street illumination, and the incandescent, for use in houses, offices and theatres. The latter is an invention by Thomas A. Edison. This light is preferable to gaslight on account of its cleanliness and its comparative cool- ness; it does not fill the room with impure vapors, is steady and pleasant to the eye. An important improvement in the line of illumination was, at the time, the invention and introduction of gas- light; it has only 90% of caloric rays, has a yellowish tinge, and is often flickering and unsteady and, there- fore, tiring the eye more than an improved oil-lamp. Gas is made from different combustible materials, of which the stone-coal is mostly employed. Just one hun- dred years ago, 1792, Murdoch made the first experi- ments with it; and already in 1811 some stores and streets in London were illuminated with gas taneously Lampadius experimented in Germa Lebon in France, but with little result; the En far ahead in the manufacture of gas, mostly, superior coal. Especially after they en vices of the German chemist, A. Winzex Jinsor), the gas-industry made rapid progress. llected the gas in large reservoirs or tanks, and the forced it through small gas-pipes to the different ces of consumption. He started many gas-companies WW England as well as in France. He died 1830 in, @yris. Between 1830 and 1840, almost all large NZUL their gas-works, even in America. SN Another useful fighis the ordinary oil-lamp, with its 87% of caloric ante13% of luminous rays. The best form of it is iitation of the German student's lamp, with a puse Shade; its light is preferable to all other y yer - aT ORE ee πα rider ae ον p Aches rs rrr 168 HAND-BOOK FOR OPTICIANS. artificial lights. — Lamps were known in very ancient times, and are already mentioned in Gen. 15, 17, and Ex. 21, 20. The lamps of the Jews, Greeks and Romans, were of a primitive construction ; a hollow open vessel for the reception of oil, ending in a spout to carry a coarse wick, was the whole ar rangement, though the ex- terior was often artistically sculptured. The real improvement of lamps began only in 1550, when Hieronymus Cardanus constructed a lamp with a separate receptacle for oil, which was attached to the side of the lamp, and which produced a comparatively steady light. Soon the addition of a lamp-shade followed. The next important improvement was made by the Frenchman, Leger, who invented, 1765, the flat wick, which was in 1782 improved into the circular form by Argand, who also added the glass chimney to the lamp. — The great trouble with all lamps was, that a bright light needed more oil than the wick was able to conduct to the flame, thus causing the wick to coal and compel frequent clipping. For this reason, Carcel (1800) com- bined a clockwork with the lamp to feed the flame suf- ficiently with oil. In 1809, the so-called ** Astral-lamp ”’ was introduced, which received its name from the round oil-receptacle placed below the flame; all FW hereto- fore, had their oil-vessels either sideway above the flame. A complete change in the Se of lamps was caused by the introduction of petr n, or coal oil, as a light producing agent, which geates combustible va- pors at amuch lower tempera and being a thinner fluid than other oils in use "n e hs the wick quicker and follows it to a greater he t. But such a flame requires a good ventilation, whic erves also {ο cool the burner; at the same time, thdjl-fount has to be placed far be- neath the flame to Qlkvent the heating of the oil. When the wick is flat fy irner is in need of a semi-spherieal metal cap wi RN: a little larger than the opening in the wick-¢gTige¥ to allow a free passage of the flame, and where its ors unite with the oxygen of the air, which D Cpetter combustion and prevents the flame from When the wick is circular, the metal cap is se — CALORIC RAYS IN DIFFERENT LIGHTS. 169 replaced by a chimney, where the wider lower part is suddenly reduced into a smaller cylinder, while the chim- ney of the flat wick is bellied. Another source of light is the candle, which has nearly the same proportion of caloric and luminous rays as the lamp. Candles were not known before the second cen- tury after Christ, although lamps were used for over two thousand years, before anybody conceived the idea that solid fatty matter, like tallow and wax, would answer the same purpose. Candles have the advantage that they do not smoke as much as the oil-lamps, but are more expen- sive, especially the wax-candles. For many hundred years they were used only in churches on certain solemn occasions, and by the rich and reigning households as a sign of luxury. — About the year 1700, the spermaceti- candles were introduced; their light was extremely white, but the price was considerably higher than even wax-can- dles. The spermaceti is a fatty substance from the head of the cachelot ( potfish or white whale); sometimes one single fish produces twelve barrels. Such candles were mostly used to compare and measure the intensity of different lights, but were too costly for every day use. Since 1725, the cheaper stearine-candles have been great rivals of the still crude lamps of that time, es since the invention of braiding the wick, alth improved lamps gradually superseded the ¢; complished finally by the introduction of coaJaN De Milly invented a simple and cheap ducing stearine; the manufacture of greatly revived, but their most suc rival is now the gas. The poorest light of alkkis the alcohol-lamp, which has only $% of luminous Gy, and is absolutely unfit for seeing-purposes. Q es was again It now remains to dray tion to the action of the different lights upon NA and to show the impor- tance of knowing ζω kact proportion of the luminous and caloric rays in Wher of them. We have seen in a previous chapteiQdjat the size of the pupil is governed by the action eiris, and as the iris is affected only 170 HAND-BOOK FOR OPTICIANS. by luminous rays, it is evident that light which contains the largest proportion of them will contract the pupil more than another light with less luminous rays. The 30% luminous rays of the sunlight will, therefore, contract the pupil most, and will allow but a limited amount of caloric rays to enter the eye. Any light with a less proportion of luminous rays causes the pupil to di- late, and favors the entrance of a greater amount of ca- lorie rays without improving sight. Therefore, the large quantity of calorie rays in all artifieial lights will sooner fatigue the eye than the comparatively cool sunlight. If we visit, for instance, a well-lighted theatre during a ** matinee,’’and there are exposed for hours to the daz- zling gaslight, we feel greatly relieved when sunlight again strikes our eye. | ος ας νεο ημας | | τ | | | CHAPTER XXIII. RANGE OF VISION. In Genesis, chap. 11, 1—9, we find the amusing story of the building of the Tower of Babel, ** whose top may reach unto heaven, and may be seen upon the face of the whole earth." People were afraid to stray away too far from the center of their colony, partly for fear of being lost in this wide world, but mainly for fear of tumbling down, somewhere, over the edge of the flat circle, which the ancient believed the true shape of the earth. The first one who showed practically that the earth is a globe, was Christopher Columbus (1435—1506)*, who maintained that by sailing westward, one would reach the East-Indies. sooner than by the south-east course round Africa. He explained his plan, after many pre- vious failures in Italy and Portugal, to Ferdinand and Isabella of Spain; but only after an eight years’ sfalegle with the obstacles thrown in his way by ignorMqWwe Jand malice, especially by the fanatical priests of panish Inquisition, he received three small vesgékgYwith 120 men. Eighteen years had elapsed sing first con- ceived the idea of his enterprise. Ὁ of that time * Columbus was of an engaging presence, (y ll formed and mus- cular, and of an elevated and dignified de(9eaNef. His visage was long, his nose aquiline, his eyes light-gray, : apt to enkindle. His whole countenance had an air of authority. and trouble had turned his hair white at thirty years of age. Heaps moderate and simple in diet and apparel, eloquent in discours, engag nd affable with strangers, and of great amiableness and suavity in Gompestic life. His temper was naturally irritable, but he subdued ith e/benevolence and generosity of his heart. Throughout his li was noted for strict attention to the offices of religion; nor did fRNelety consist in mere forms, but partook of that lofty and solemnffütNwiasm, with which his whole character was strongly tinctured. aJereat and inventive genius, a lofty and noble ambition, his ihe characterized by the grandeur of his views and the magnanimitf. is spirit. The treatment which he finally exper- ienced from th nish court shows that ingratitude is not confined to 172 HAND-BOOK FOR OPTICIANS. had been passed in almost hopeless solicitation, amidst poverty, neglect and ridicule; the prime of his life had been wasted in the struggle, and, when his perseverance was finally crowned with success (Oct. 12th, 1492), he was about 56 years of age. Since the real shape and size of our earth is known, we are able to estimate the longest distance at which we can see an object, either with the naked eye or with the assistance of a spy-glass or telescope; because the range of vision is not dependent only on the acuteness of vision, or on the optical strength of an instrument, but is lim- ited also by the curvature of the surface of the earth. It is well known to all engineers that, on an even plane, only the head of a man is seen through a field- glass at the distance of three miles, and that, in order to see at a longer distance, either we have to take a higher stand, or the object must be raised to a greater height. Lighthouses are erected on this principle; the farther their light is to be seen, the higher they must be built, as ships have only a limited height. The following table shows both, the distance and the height at which a light can be seen. At 5 miles, the light must be — 15 feet high. « 10 ες T 66 60 ές « 15 ες 66 ές 140 ἐς 90 66 ές 66 250 Re c6 30 é€ , ές 6“ 5 é« 66 49 ές ές ες jt 66 The rule for calculations of thi àd is: <‘ The cur- vature of the earth is taken t eight inches for the first mile, and increases acc to the square of the distance." For instance: 2-miles, 23), ON inches — 32" or 28 did Um ee 93), ο 8 66 z— ον Ὁ 4. [11 ( 4?) 6 x 8 ές — 10 ές 5 66 ( 2 5 X 8 ο cu 16 ές 10 « NA 100x 8-5: - 066 « 15 ον #225 5^ 8 ον ας 20; «e 0294 D 5, ἡ == 2600. ες The A height of lighthouses, as shown in the first table, (ly ο ue to the elevated stand of the captain on ——— Án - | 4 f ] RANGE OF VISION. 173 board the ship, which is supposed to be ten feet from the waterline, thus allowing the light to be somewhat lower.* Range of vision, practically, means ** the distance at which we are able to see." On a plane surface, our vision is limited to three miles for all objects not higher than six feet; trees, towers and mountains are seen at a longer distance according to their height. But it is not only the height of an object that makes it visible, also its width must cover.a certain space; besides, it makes a great difference if the atmosphere is clear or misty; if our eye is emmetropic or myopic; or if one object is more readily distinguished from its surroundings than another. The old rule that the width of an object must cover, at least, a visual angle of forty seconds, is super- seded by Snellen’s experiment with his test-types; and instead of seeing an object, which is not farther away than 5000 times its diameter, we have to shorten the range, according to his rule, to 3437 times. (See Chap. XII.) Thus we can find, approximately, the distance of any object, if we know its size; or its size, if we know its distance. The breadth of a man, on an aver- age, is eighteen inches (13); if we can barely see him, he is 3437 x 14’ away, or almost one mile. IN iS dressed in white, and the surroundings are dark, i tance may be set at 14 mile; if dressed in black may be only half a mile. If the back ground is dark, the imp different colors upon our eye range in th White, yellow, orange, red, green, M di»! olet and black, i. e., black disappears first, then γι etc. White on black makes the strongest impre$wjn, and is seen the farthest. Upona light- colored ‘adckground the effect is the reverse, with the ον of violet, which disap- ion of the wing order: pears before red. * There is an analogy of S ve rule in the calculation of the decreas- ing strength of light, w ually removed from us; it also loses in power just in i rie the square of the distance. "The intensity, which a light has at one ¥e6t from us, diminishes in strength four times at two feet, anden times at three feet. It requires, therefore, nine candles, three AR) “to produce the same amount of light as one candle produces at th “κ ance of one foot from our eye. S 174 HAND-BOOK FOR OPTICIANS. It is a well-known fact that all animals of prey bear the color of their hiding places. This enables them to surprise their booty without being seen from any dis- tance. The striped tiger in the Indian swamps or jun- gles resembles the environs so perfectly that his victim is not aware of its presence till it is too late. The yel- low stems of the reeds, and the darker ground, produce a striking resemblance to the skin of this voracious beast. This curious play of nature is called ** mimicry,” and benefits not only those beasts, but also many animals which are preyed upon. The hunter is thus sorely vexed, and often cannot make use of the above rule. But in military life there are many occasions where it is of an immense import- ance, by furnishing an estimate of the number of the advancing foe, and giving time to prepare for their reception. There arises another question analogous to the previ- ous one. I refer to the fact that it is not difficult to judge with any certainty the number of people congre- gated in large assemblages. The easiest way of this kind of calculation is to measure the ground in square feet, and divide the number by 4, as four square feet is ample room for a standing person. We cap measure a space by walking over it and counting the βάθρο. A full step (not a stride) measures on an av 21. Sup- pose, at a public meeting well attendoqWOhe bulk of the crowd extends in one direction Κα s (150); in an- other, 30 (75'); we have κο XO T1290 square feet, divided by 4, o and with the stray people counted in, OR 7 estimate that about 3000 people were attendi meeting. The next day we read in the different Qe ; that the attendance was immense, and that © were at least 5000 persons present. Others exaggerate the number even to | } CHAPTER XXIV. TEARS. The eyes of all vertebrates, with the exception of fishes and those amphibious animals that live in water, are provided with tear-glands, to moisten the surface of the eye and the inner side of the lids. If the tears were stopped, the outside of the eyeball would become dry and opaque, and sight be lost. As long as the tears flow they are drained through the tear-duct into the nose, and here mostly evaporate without any further annoy- ance. But, if in consequence of catarrh or any other cause, these tear-ducts are closed, the eyes fill with water which runs down the cheeks in the form of tears. This occurs in the eyes of animals as well as of men, but we cannot call it ** weeping;"' it is only due to local causes. No animal weeps. Real weeping presupposes d emotion, based on self-consciousness. Only hu uM - ings can reflect upon their own existence, ang (ία. plate themselves in an objective way. we but this great superiority over animals, we would @ unable to touch that responsive chord of our η να] existence which makes us weep for joy, grief C». Weeping* is synonymous to e» A mfort, utter violent and prolonged screams; their gyeS“are firmly closed, so that the skin round them is a¥@Akled, and the forehead contracted into a frown, Gké)mouth is widely opened with the lips idR EN a peculiar manner, which causes it to assume arish form. The firm closing of the eyelids and 4gnJequent compression of the eyeball, serves to proteqe, the eyes from becoming too much Infants, when suffering even slight pain or di * The verb “to ” comes from Anglo-Saxon wop, the primary mean- ing of which 15 y ‘‘outery.” — ** Expression of Emotions in Man Charles Darwin, 1873.” . + and Animal 176 HAND-BOOK FOR OPTICIANS. ο E gorged with blood. The contraction of the muscles (corrugator supercili) surrounding the eye produces the transverse wrinkles across the forehead, whilst the con- traction of the pyramidal muscle ( pyramidalis nasi ) causes the eyebrows to be drawn downward and inward, i producing a ‘frown.* "The muscles surrounding the eyes i are somewhat connected with those of the upper lip; if, | therefore, the former are strongly contracted, those of d the upper lip likewise contract and raise the lip. Even | in grown persons, it is observed, that when tears are re- strained with difficulty, as in reading a pathetic story, it is almost impossible to prevent the various muscles, which with young children are brought into strong action during their screaming-fits, from slightly twitching or trembling. Infants, while screaming, do not shed tears or weep until they have attained the age of three or four months. This fact is most remarkable, as, later in life, no expres- sion is more general or more strongly marked than weep- ing. When the habit has once been acquired by an in- fant, it expresses in the clearest manner suffering of all kinds, both bodily pain and mental distress, even 1 though accompanied by other emotions, such as f or rage. With adults, especially of the male se Nx soon ceases to be caused by, or to express, ΜΥ pain. This may be accounted for by its being t t weak and un- manly by men. The insane notopiQuMy give way to all their emotions with little or no XQ ¥Mtaint ; and it is ob- served that nothing is m racer of simple melancholia, than a tenc okey) weep on the slightest r | oecasions. n Weeping seems to be@De Mq and natural expres- sion of suffering of kind. But common experience shows that a NS y repeated effort to restrain weep- ing does HRS expression of the eye is due, * The human eye has two distinctive pec © which we do not find in animals: the eyebrows and the promin visible portion of the white sclerotic coat. This last characteristic fea of the human eye is perhaps the principal cause that every animal ms its eyes down or sidewise, as we can readily observe when we tak of the head of our dog, and look at his eyes. Although he may be v ond of us, he nevertheless tries to er freeing himself, he will jump avoid the fixation of our look; about. for joy, lick our handy ch down and is highly delighted with chantment of our stare. his release from that unbear This accounts for the above story, beofffis anybody is accidentally confronted by a lion, it is natural that AS stunned, motionless, or paralyzed, with eyes wide open, thus involunt®fily showing that **ominous white” to greatest advantage, which imal can face without shrinking from its magic spell. Lion-tam ake use of this weakness in all animals; they keep those beast "uS stern influence of their eyes, and awe them into TONO spite of their superior brutal strength. 180 HAND-BOOK FOR OPTICIANS. l. To the changes of its surroundings, and .2. to the position of its axis of vision. Of the part performed by the eyelids, that of the upper lid is the most important, because it is larger and more. movable than the lower one. The raised, elevated lid admits free entrance of the full light, while the drooping lid shadows and darkens it. The eyes are wide open when we listen to something of great interest, which causes either surprise or alarm. Half closed eyes indicate indifference and indolence, and produce a dull and drowsy look. * Were his eyes open? Yes, and his mouth too. — Surprise has this effect, to make one dumb; Yet leave the gate, which eloquence slips through, As wide as if a long speech were to come.” The eyelashes play also a great part in this respect. When they are long and fine, they impart to the eyeball a gentle and affectionate appearance, which the poets call.** the sweet pensive shadow." “And eyes disclos’d what eyes alone can tell." But when they are short and sparing, the look loses that mellowy appearance is rather unsymp&thetie, and gives the eye generally a cunning and sl AN The eyebrows are powerful organs o N ος. we can produce a frown by Πτα the brows, while by elevating them w, ress incredulity, surprise, or contempt almost as ly as by words. * Disdain and scorn rid ding in her eyes." The position of the ey, ως. great effect; the so-called ** deep eye," w ὄν is constantly shaded by the prominent forehead, makes a different impression from the ** shallow ’’ one (ιο deep eye is somewhat lacking the free motion o (Dy upper lid, and as it is generally of & darker tint es being shaded by the projected forehead πο row, it produces a determined, grave, often morOsey®xpression. “Set well that eye could flash resentment’s rays, Oro scornful, check the boldest gaze : ill burning passion with a calm disdain, 9 And with one glance rekindle it again." SS ό τ κο x S FACIAL EXPRESSIONS. 181 The shallow eye, mostly light colored, shows to per- fection the innumerable variations of the human look. There is first the staring look; the eye is not fixed upon any distinct object, it is immovable and indieates hope- lessness, pain, fright, terror. The :** hopeless stare,"' after the loss of all energy, is characterized by an indo- lent silence; the drooping of the upper lid produces the appearance of a weary despondency. “In those sad eyes the grief of years I trace, And sorrow seems acquainted with that face." In cases of violent excitement, the staring look is the result of the convulsive exertions of the outside muscles of the eyeball, which, by acting all at once, push the eye forward. The look of the over-joyful is just the opposite; his eye is not staring in one direction, but is restlessly wandering from one object to another, because none is able to attract his attention long enough to counter- balance the inner excitement. By the quick changing of the position of his eyes, the observer receives constantly another reflection of them; such eyes sparkle with joy. And ease of heart her every look conveyed” “The joy of youth and health her eyes ταὶ * «While pleasure lights the joyful laughing T he dif- irt at the estasy over The color of the eye is of little importan ferent expressions, but plays a promine time of courtship, when a lover goes 1 the color of the eyes of his beloved Q QUY. * Let other men bow, and u Of devotion and love thon As the sparkling black eye riumph draws nigh, Its glances upon them end. But give me the eye, which I can spy To the depth of NS zarm and true ; Whose color ma Wii the hue of the sky ; — The soft, ed ; love-beaming blue!” O All these dci f the eye are produced by the action of separate nto: Some motions are controlled by our will, others (ny acted upon by the so-called sympathetic nerves Q for instance, regulate the dilatation and con- N à Ἃ ao 182 HAND-BOOK FOR OPTICIANS. traction of the pupil, and produce other phenomena beyond our control.. But by means of an “iron will", or by long mental training, many expressions of the eye can be concealed from the observation of others. Skilled diplomatists, shrewd lawyers, professional swindlers, hypocrites and many more, often deceive others with sleek words and a trusting look; but the intelligent observer instinctively shrinks from their enticements, and is not easily caught by their deceitful schemes. The warning impression we receive as to the questionable truthfulness of their words is due to certain motions and positions of the eye, not controllable by their will. Their words do not touch the corresponding chord of our soul, they only cause dissonance and aversion of which we cannot give a clear account, but feel indi- stinctively. “O what a tangled web we weave, When first we practice to deceive.” There are persons who win our affection without any effort, although their exteriors are plain, their features irregular, their discourse lacking eloquence and depth of knowledge, and yet we are fascinated by them. This is the witchery of an expressive eye, the reflex n honest, sincere mind. “In one soft look what languag gs!” A close observer of the facial exprGNons of different individuals will find a great varit their delineation, based principally upon the digeewion of the axis of vision. In children this M 3, Imost constantly par- allel, producing the impr of thoughtlessness, or the childish innocent loo With increasing intelligence the eyes lose the parallelism by being fixed upon objects of investigation. ffections of the mind are now manifested by ¢ motions and positions of the eyes, which PS more and more convergent. The lurking loo e convict on trial, the watchful scrut- iny of the Ge uspicions, the lustful look of the liber- tine, the-piefcing glance of anger, the rude gaze of the * . mous the fearful glare of the maniae; — all are modifications of the same act, produced by an increased f the axis of tl 5. S gency of the axis of the eyes M Óá— ee ALL FACIAL EXPRESSIONS. 183 The gentle and refined affections of the mind restore to a certain degree the parallelism of the axis. It is this which appeals in the eye of the trusting; sparkles in the eye of the happy and the gay; subdues in the eyes of the affectionate and the loving; awes and elevates in upward gaze of piety and religion; or composes in the gentle regard of the devout and resigned. The eyes of a frightened person diverge; the wish to be far away from the place of danger causes the dilating of the pupils and the opening of the eyelids. In old age the axis of vision again becomes parallel. The passions of former years are calmed, and the mind, in a contemplative mood, is now diverted upon its future distant home. At last the eye dies in the absolute par- allelism of the axis of vision. CHAPTER XXVI. HISTORY OF THE INVENTION OF SPECTACLES, AND THE GRADUAL DEVELOPMENT OF THE ΟΡΤΙΟΑΙ, TRADE. (Old tradition credits Phenician merchants with the invention of glass. This nation occupied a part of the coast of Syria, between the Lebanon and the. Mediter- ranean Sea, northwest of Palestine, and was already widely known at the time of Jacob, the patriarch, about 1750 years before Christ. But it seems glass was known before that time, as there has been lately found below the ruins of old Nineveh a lens evidently used for optical purposes. A knowledge of the manufacture of glass was early aequired by the Egyptians, who improved on it, and made even colored specimens. After the Romans conquered Egypt, this art was introduced into Italy, where they soon learned to make plate-glass, and also produced a kind of glass which conld st: without in- jury the effect of hot fluids. They alsoWqNinded to have known a glass which was malleable, an Gp certain degree unbreakable.) A good story in seing Mo this states that a man once demanded to be bro efore the Emperor, to whom he presented a Te velass. The Emperor was highly pleased with th did workmanship of it, but when it passed MS o hand among the court- iers present, it accidentg\ fell to the floor, or, as it is also related, the artist V/mself threw it wilfully down. It did not break, by& yas badly dented. The man re- paired it immedi with a small hammer he had brought along with hia tís a pity that this important inven- tion is πως One Roman historian reports that Nero cou see very well, and that he made use of a large jew the shape of a lens, to enjoy a better sight of th ts of his gladiators. But this was not imitated by pe 's, and is narrated by the historian only as one HISTORY OF THE INVENTION OF SPECTACLES. 185 of the many strange extravagancies of this most remark- able man of the Roman empire. * The history of the invention of spectacles is closely connected with the general advance of science, especially as regards light. Light was a familiar phenomenon to the ancients, and from the earliest times we find man's mind busy with the attempt to render some account of it. But without experiment, which belongs to a later stage of scientifie development, little progress could be made in this direction. They satisfied themselves that light moved in straight lines; they knew also that these lines, or rays of light, were reflected from polished surfaces, and that the angle of incidence was equal to the angle of reflection. The first one who measured the refraction of glass and water at various angles, was Ptolemy, an Egyptian, about the year 150 P. C.; he states that the an- gle of refraction is always less than the angle of inci- dence.—Nine hundred years later, the Arabian mathema- tician, Alhazen, wrote a valuable book on the reflection and refraction of light, containing also a description of the eye, and a philosophy of vision. Although he gives di- rections for making experimental measures of refraction, he does not furnish any Table of the results of such ex- periments. Vitellio, a Pole, about 1250, wrote an exten- sive work on optics, including such Tables, and ts them to be derived from his own observations, 1 is very doubtful. We see that in the long period of el hundred * Nero was, perhaps, hypermetropic, but not stated. Myopia was not known in olden times Travellers have never found among uncivilized People who do not read, or do not use their €yes*é are not near-sighted. In America, which is ly an agricultural country, there are on an average twenty-five hyperrfet}opics to one myopic (cities ng was invented, there are , as it is often Ν a case of myopia. ef seeing small objects, excepted), while in Germany, where grin twenty-five myopies to one hypermetigpjc person. Myopia is often her- editary, but decreases in a few sere io when the cause for it is removed. It is simply a tempor πο) ormality, and is usually acquired as the result of certain habits? rithout doubt of modern date. The causes of hypermetropagNare not at all dependent upon the abuses of the eyes by reading oyffo&g/fine work. Many natural causes produce this abnormal conditio jua. is certainly as old as the human race, although it has been really understood and explained only in the present century. The dose iban between myopie and hypermetropic eyes, compelling both m to use spectacles for near and far, has wrongly caused many UG to make Nero near-sighted. * S X NS BH. Q 196 HAND-BOOK FOR OPTICIANS. years little progress was made in science, because the hu- man mind at that time took the opposite course of men- tal training. Instead of studying the forces of nature, f and enjoying the bountiful gifts which an exceedingly | friendly Providence had put within easy reach, people | turned their eyes to the clouds till they lost sight of | their beautiful surroundings. <‘ The men of the Middle Ages were so occupied with the concerns of a future world that they looked with lofty scorn on all things per- ἢ taining.to this one. Notwithstanding its demonstrated | failure during so many years of trial, there are still men among us who think the riddle of the Universe is to be solved by their appeal to consciousness. And, like most j people who support a delusion, they maintain theirs f warmly, and show scant respect for those who dissent from their views." This is the reason why a man like Roger Bacon was hated and hounded to death, as happened to Galilei and other men of genius. — Bacon was a pro- fessor at Oxford, England; he made many wonderful discoveries in Opties as well as in Chemistry and Phys- ics, which were regarded by his ignorant contemporaries, especially by the jealous members of his own religious order, as the work of the devil, and caused his imprison- ment, at different times, for almost twenty years. He was the first to produce, or rather c Kr e, a convex lens,* but we do not find in his work least hint that he combined these lenses into spec 4 * A spectacle lens was discovered a ay ii in 1854. This city was buried by an eruption of Vesuvius, xS e year 79 P. C., and was again discovered im 1748. + In his principal work, Opus Qe e urges the necessity of a reform in the mode of philosophizing, a ows why knowledge had not made greater progress. It contains S parts: I. On the four causes of h ignorance. 1. Authority (the f of unworthy authorities). 2. Custom (th ditionary habit). 3. Popular (the imperfection of the undisciplined senses). 4, πι) sed knowledge (the disposition to conceal our ig $fid to make ostentatious show of our knowledge. II. On the AN perfect wisdom in the sacred scripture. ΤΠ. On thes ess of grammar (regarding correct translations). VI. On thé use iness of mathematics. V. On nota Ly e Organs of vision. — κ 7 Vision in straight lines. Q 3. Vision reflected and refracted. 5 QS 4. Propagation of the impressions of light, heat, etc. S d ~ HISTORY OF THE INVENTION OF SPECTACLES. 187 He died in 1294, and only a few years afterwards this was accomplished in Italy. (We may point to the year thirteen hundred as the one in which spectacles were in- vented, if we ignore the pretensions of the Chinese, who claim to have known them long before that time. How- ever this may be, all inventions made by them were bar- ren to the rest of mankind in consequence of their exclu- siveness. An old Latin document of the year 1303, found at the Convent of St. Catherine of Pisa, tells us that a monk, Alexander of Spina, who died in 1313, was so skillful a mechanie that he could reproduce any kind of work he had seen, or which had been described to him, and that he made spectacles after having seen them, and the in- ventor had refused to communicate the true process of their manufacture.* This selfish inventor was probably SALVINO ARMATO, on whose tombstone was the inscrip- tion: Qui Giace Salvino D'Armati Degli Armato Di Firenze, Inventore Degli Occhiali, MCCCXVII. Here Rests Salvino, ete., Armato NA 9 of Florence, 3 Inventor of Spectacles, 1317. ος O The use of spectacles spread very slé&yjy, because peo- ple had little need of them. Onl ited number of men could read, books were very %carce and very dear. Printing was not yet invented, (looks were written by hand, and it was only afterwgpds, when their circulation increased, that spectacles e into demand. An old o ND. most remarkable portion of his work. cumstance to find a writer of the thirteenth nigng experiment as one source of knowledge, something far more important than men had yet VI. On experimental scienc This sixth part is undou It is indeed an extraordj century, not only rec but urging its claim been aware of. 9 * Ocularia ab er primo facta, et communicare nolente, ipse fecit et S ον NS 188 HAND-BOOK FOR OPTICIANS. chronicle of. Nuremberg, in Germany, of the year 1482, mentions that there were several manufacturers of specta- cles in that city. Spectacles were for a long while merely objects of cu- riosity, and were made use of as a conspicuous novelty, as some years ago every ** dude," male or female, had to wear blue glasses for fashion's sake. In Spain they formed a part of the costume of every well-bred person. This absurd use of glasses was meant to increase the gravity of the appearance, and consequently the venera- tion with which the wearer of them was regarded. The glasses were proportional in size to the "rank of the wearer. Those worn by the Spanish nobles were some- times three inches in diameter. The Marquis of Astorga, when having his bust sculptured in marble, particularly enjoined upon the artist not to forget his beautiful spec- tacles. After this first silly introduction of spectacles, they again fell into disuse for nearly three hundred years, dur- ing which no improvements deserving notice were made. How different were the people of that time from the pres- ent generation! In less than no time we A S have produced a concave lens also, and hav ented the world with a spy-glass. Think how q some years ago the Telephone was followed NS onograph; the l one transmitting speech, the yan) Rot i Aai d have searched in vain to find thaq Sof the inventor of | the concave lens; it was not NS e before the in- | vention of spy-glasses, I th The credit for the pL of spy-glasses, or tele- scopes, has been claime((p the friends of three parties: John Lippershey, Lepparine Jansen, both of Holland, and Galilei, of Ite ο, is no doubt that Galilei first applied AN ope for observing the stars; but he at Pekin, C old astronomical telescope which was made in 1279, under the ret f Kublai Khan. Its mounting is cast in bronze, and is still w dligaserved It was for four hundred years used as an ornament upon race in front of the imperial palace, but was removed in 1670 [ to thi servatory by order of the emperor Khang. A photograph of i ihi que instrument has arrived a few years ago in London. i * Mr. Chi ο ον Qin, has discovered lately in the Observatory na HISTORY OF ΤΗΕ INVENTION OF SPECTACLES. 189 constructed his instrument after he had learned that by a combination of convex and concave lenses distant objects would appear much nearer. ‘The real inventor of the tele- scope was without doubt John Lippershey, a spectacle maker at Middleburg, Holland. But according to Des- eartes, the inventor was Adrian Metius, who wrote on the l7th of October, 1608, to the government of Holland, stating that he, as well as the spectacle maker of Middle- burg, s Was manufacturi ing the instrument **that brings dis- tant objects near.' Another document of Oct. 2d, “1608, lately found in the government archives, is the petition from Lippershey, praying for a thirty years’ patent on his-invention. ‘This was refused him because the instru- ment could not be used with both eyes at once; and after he had made a double one, the patent was again refused, ‘because telescopes were then being made “everywhere. But as a partial compensation for his disappointment, he received an order to construct for the government two binocular instruments, the lenses of which should be of rock crystal, and for which he was to be paid 900 guild- ers, about $300 a piece. The necessarily correct finish of lenses for telescopes gave a new impulse to the manufacture of spectacles, al- though they were still made in limited quantity by oli- tary “workmen, and by hand. It is related of Wa, who died 1677, and who had learned the art Nlass- grinding to make a living while writing his ophical works, that he made a pair of spectacles the cele- brated German philosopher, Leibnitz, had formed his acquaintance at The Hague, Hollayt) The historical events which fayoked he development of this ** New Era of Science" w&re: The invention of printing, 0; the discovery of Àmeric(91492; and the gradual ο of the human mind from metaphysica BOY of th The epi NÉ lead in the march of pro- gress, and the hitķer§ð humble guild, or corporation of glass-grinders apd Coins of spectacles, had to extend their flr limited sphere to that of adroit me- chanics. ΄ not only built telescopes and other com- 190 HAND-BOOK FOR OPTICIANS. plieated instruments used for scientifie purposes, but also took personally an active part in the promotion of science by independent investigations and inventions. The hero who made the first scientific application of the new discovery was Galilei, but his telescope was very nearly the same as the modern single opera glass, being composed of one bi-convex objective lens and one bi-con- cave ocular lens. The theoretical explanation of this tele- scope was given by Kepler, 1611, who also suggested the use of a convex ocular lens, which allows a larger field of vision, but shows objects inverted. An instru- ment of this order was constructed by the capuchin, Anton De Rheita, 1645, and is called the astronomical telescope; he afterwards added to the single ocular lens four separated convex lenses, thereby restoring the up- right picture, and called it terrestrial telescope. This monk also constructed a binocular telescope which was regarded rather as a thing of curiosity than of practical utility, until in modern days his plan has been accepted in opera glasses, microscopes, etc. The great defect of these instruments was their chromatic aberration, and to overcome this, enormously long telescopes were made. Huyghens, for instance, used an instrument of his own make, with an object lens of 123 ft. i cal length; which is still in the library of the Roy: itty of Lon- don. It incited the ambition of othex construct even longer telescopes; as Divini at Ree; Campuni at Bo- logna, and Auzout at Paris. I ated that the latter made telescopes of from 300 0 feet focus, but they never could be used in pra κ ιν, In these very long telescopes RA f was employed, and they were consequently ter aerial telescopes. Huyghens finally constructed Ὃν 210 ft. long, but such instru- ments were unma fable and soon went out of use. Besides, po of the aperture of object glasses could not altww&Mer remove the coloration of the image Newtdn, who discovered the principle of the chromatic defectLin Ténses, maintained that the evil was irremedi- * . . EN 1 that any combination of lenses could no more r without producing color, than a single lens; he, GRADUAL DEVELOPMENT OF THE OPTICAL TRADE. 191 therefore, constructed, 1671, a reflecting telescope. He is not the inventor of the reflector, as James Gregory is credited with its invention, but on aecount of Newton’s effort in its favor, it rapidly came into general use in England, being called the ** Newtonian reflector, 71η op- position to the ** Gregorian," manufactured AT E by James Short and others. In 1718, Hadley made a mirror, six inches in diameter, with a focal length of 62 inches and a magnifying power of 230 diameters. In 1789, the elder Herschel constructed a reflector of forty- five feet length, with a speculum of four feet in diameter, with which he made wonderful discoveries. About the year 1747, Euler doubted the exactness of Newton's proposition, and he declared that a combina- tion of lenses of different media would give a colorless image. 'The Swedish mathematician, “Klingenstierna, confirmed the correctness of Euler’s suggestion by calcu- lation, and in 1757, John Dollond demonstrated it by in- venting the achromatic lens. It is said that Chester More Hall, was led by the study of the human eye, which he conceived to be achromatic, to construct an achromatic telescope as early as 1729, but kept his in- vention a secret. John Dollond and his son, Peter, αρη- structed achromatic telescopes of three feet, whicl Dp- duced an effect as great as those on the reflecti Vn ciple forty-five feet long. Ramsden introdu 1783, an eyepiece of two plano- convex lenses κ focus, with their convex surfaces towards each ge , and sepa- rated by a distance of two-thirds of thei mmon focal length. By this arrangement, a fla ῳ X. gained, and the chromatic and spheric: al aberre Ao Y are so much re- duced as to be practicably imper ible. The hope, now to PO struments of unlimited size, was frustrated by oO possibility of obtaining large pieces of flint gl AX there was no material improvement in this Wion for several years, till Fraunhofer, with j& Q}ristance of Frangois Guinand, gave a new ipu this branch of the optical business. Joseph Fraunhofex was born 1787, at Straubing, Bavaria; he was the so à poor glazier, and was in “his earlier years empen at the same trade. After his father’s + 192 HAND-BOOK FOR OPTICIANS. death, 1799, he entered as an apprentice the establish- ment of a mirror-maker at Munich, where he had, 1801, the singular misfortune of being buried alive by the col- lapse of his boarding house. His miraculous rescue. at- tracted the attention of the king, who made him a pres- ent of 18 ducats (about $40. 00), for which he bought a machine to grind spectacle lenses. In 1806, he accepted the position as foreman in Utzschneider's optical estab- lishment, where he soon became the greatest optician in Germany. His excellent telescopes and microscopes are known throughout Europe. Fraunhofer will always take a prominent place in the history of the optical trade; he was not only a practical and most skillful workman, but also a scientist of great renown. Still, a shadow darkens his fame, Ais selfish exclusiveness, which restrained him from making known, for the benefit of science, the true process of the manufacture of his perfected flint glass in large pieces. It was hoped that after his death some clue would be found among his writings; but, strange to say, his secret went with him into the grave.—His time can be considered as the beginning of the latest era in the development of the optical trade. The instruments for astronomical observation became an objgei\ of serious care. Extensive knowledge, intense thoaayt? and great ingenuity were requisite in the strong (yi instrument- maker. Instead of ranking with s, he became a man of science, sharing the hon © dignity of the as- tronomer himself. NS We now turn our atter S the telescope to its powerful rival, the mwoscope. The telescope had rudely dispelled our sel&éonceited error, that the earth is the pivot on whi he whole Universe revolves, by revealing myriadgQDmew worlds, thus forcibly teaching the mortifyin $N of our own insignificance. The microscope, sig as an antidote to the former, again restored allness to a state of gigantie greatness; it revealed a*wforld of hitherto invisible wonders of nature, and A manifested that everything, great or small, is DID marvelous. These two instruments have dona uM for the enlightenment of men than any. invention 1969 GRADUAL DEVELOPMENT OF THE OPTICAL TRADE. before or.since. The invention of the simple microscope is not claimed by ahy one; we do not know the inventor. The earliest magnifying lens known, if indeed it was used for this purpose, is the rude one found by the Eng- lishman, Layard, in the palace of Nimrud (at Nineveh); : it is made of rock crystal, and is far from being perfect. Aristophanes tells us that burning spheres were sold in the shops at Athens, about 400 years B. C. There is no evi- dence that lenses were used at this early date for magnify- ing purposes, but, instead of them, glass globes filled with water, which Seneca alludes to, were employed. Itis not until the seventeenth century that we find powerful magnifiers of glass, actually employed for sci- entific investigation. Most of the magnifiers used by the early observers were minute single lenses of glass, often small spheres formed by me lting threads of glass. The small single lenses of high power are usually plano-con- vex, the “plane side toward the object. Upon David. Brewster’s suggestion, lenses were ground by Peter Hill, a skillful optician of Edinburgh, and by Pritchard, of London, of garnet, sapphire and diamond.* The garnet lens was found superior to all others, being free from double refraction, and even superior to lass: Brewster also invented a very powerful single mies pa known as the Coddington Lens, w hich cong di i sphere with a deep concave groove cut e t, Rud before the Parisian Academy lenses of the diamoné phire and ruby, which were used in connection with glass lenses roscopes, but they had no advantage over glass. A letter from p rewster, lately pub- lished, explains the cause of the failure. ὧν of his own experiment, it * Some years ago two opticians of Paris, T imon ANS) berhauser, laid above mentioned: ‘‘The diamond, befor$ét was worked, had all the ap- pearance of internal brilliancy; but, after όλ) polished, it presented a series of stratified shades, which rendered it αθλίρὰς for the required purpose. I afterwards learned that lapidaries wff»,acquainted with this appearance, and were unwilling to take the ris hemselves of cutting up diamonds for optical purposes. On a mi amination of this phenomenon, it appeared that these differe s«fecurred in regular strata, each section being about the one ho art of an inch, and each stratum having & different focus, and & different degree of hardness and specific gravity. The inferenfes wn from the above facts were: that the dia- mond was a vegetable stance, and that its parts must have been held in solution and subj d to different degrees of pressure at the different stages of mane f, on the contrary, it was of mineral origin, as is generally Dele os it would be subject to the laws of crystallization, and its crystals ἕν necessarily be homogeneous and not stratified. S N = 194 HAND-BOOK FOR OPTICIANS. blackened so as to shut off the marginal pencils of light, thus giving a wider field and a more perfect image of the object. In the Stanhope Lens, the curvatures are un- equal, but its magnifying power is so strong that a drop of water may be examined by applying it to the less convex, or plane surface. In the construction and use of lenses two great diffi- culties present themselves. It is practically almost im- possible to make small lenses with any other than spherical curves, and unfortunately simple spherical lenses do not bring the rays to a perfect and exact focus. If it were possible:to construct lenses with elliptical or hyperbolic curves, the spherical aberration would be avoided; but even then, since the different rays of the spectrum are re- fracted differently, the focal length for red light would be greater than for blue, and it would be impossible to obtain a sharp image free from chromatic aberration. In order to overcome these difficulties, doublet and triplet lenses were invented and introduced, which led gradually to still greater combinations, till the simple microscope was transformed into a compound one, now the only in- strument used for minute researches. The theoretical and practical difficulties that had to be overcome in develop- ing the best modern compound microscope\from its embryonic condition were so great that, ΙΑ ithin the last seventy-five years, the very possj y of success was doubted by the highest authoritiegXNoptical science. The manufacture of microscopes much favored in England. Since the time of Ran A there has been an industrious contest among t olish opticians in per- fecting that instrument mer d more, and they were greatly encouraged by thg«Wberal support of the English people. There is hardly* college or school without it, many ships carry a g ο ο, even private studios and parlors are su with the luxury of an improved microscope. he many skillful opticians I may mention: W m, Swift, Parkes & Son, Stephenson, Smith & B ‘os., Powell & Lealand. — Other nations were not so tfberal in their support; for instance, the French. cians were chiefly dependent on the export of ERE and although they did not keep step * S Tens and eye-lens being composed of three sco GRADUAL DEVELOPMENT OF THE OPTICAL TRADE. 195 with the English manufacture, still some opticians made quite a reputation for themselves; as Chevalier, Nachet, Oberhauser, Hartnack, etc. Since the time of ποσα, the German and Italian opticians also produced fine instru- ments which could be favorably compared with the best English microscopes. There was Amici at Modena, G. p S. Merz at Munich, S. Ploessl at Vienna, C. Zeiss at Jena, and others of great ability. — America was for many years a profitable market for European instruments, but since Chas. A Spencer, Robert B. Tolles and others, we can fully compete w ith the old world as regards telescopes and microscopes. Only in the manufacture of Opera Glasses we are still in our infancy, although the demand for them is such that they form an impor- tant article of manufacture, of which Paris is the great seat. So largely and cheaply are they produced in Paris, that it has nearly a monopoly of the trade. They can be bought from 75 cents up to $30.00 a piece. The cheapest opera glasses consist of single lenses; those of the better class have one compound achromatic lens. A very ordinary construction for a medium price is to have an achromatic object-lens, and a single eye-lens. In the finest class of opera glasses, both the eye-lenses ‚and object-lenses are e achromatic. Ploessl's celebratedesyld- glasses (Feldstecher) have twelve lenses, caai ct- lenses. Almost every inventor and scientific disco has laid claim on our dexterity to execute his KO Wollaston came with his Camera Lucida, Wheat one with his Stereoscope, Daguerre with his graphic Camera, Faraday with his Electric Ma 4 Morse with his Telegraphie appliances, TE nd Bunsen with their Spectroscope, the Sugar- NA with its Polariscope, Helmholtz with his Ophth: ope and the Oculists with their Compound Lenses. ΠΝ we have to make in- struments for lees Surveyors, Navigators, Astronomers, Ch Physicists, Meteorologists, etc. ; but it is only τε 1e last century that our trade has risen to that grea prominence it occupies to-day. We are now an x pensable factor in scientifie pursuits, and furnis Nik not only the most scientific, S mapera pg a * — ει pA ο Ἕστ----- 196 HAND-BOOK FOR OPTICIANS. but also the most useful ever offered to benefit the world. We have reason to be proud of our achievement, but we must not forget that we were merely the tools, executing the order of scientists, who did the brain work for us and that we have not many opticians like Fraun- hofer and Chas. A. Spencer to boast of. The spectacle business advanced considerably after the oculists detected the asymmetrical refraction of the cor- nea, called Astigmatism. Thos. Young, of England, made the first studies in astigmatism in 1783, but it was little noticed by his contemporaries. It was only after . Donders, Helmholtz, Graefe, Javal, Knapp, and others, more than fifty years afterwards investigated it, and explained the method of its correction by means of cylindrical lenses, that it was generally understood. The manufacture of such cyl. lenses with all their combina- tions, and especially their correct setting, was a new departure in our trade, and many opticians were con- siderably troubled before they fully mastered the diffi- eulties in connection with this most delieate correcting medium in the shape of spectacles. A competent opti- cian of 1860, falling asleep like Rip Van Winkle, and awaking to-day, could not fill the simplest order of an oculist, but would have to learn his trade o again. As long as the selection of spectacles Was léft to the opticians, they contented themselves wit ae correction of a limited number of defects, and gie the remain- der incurable. They did not kn q nature of irregu- larities, such as Fy Lone OL NS Astigmatism, and were, therefore, totally in qc about their correc- tion. Oculists formerly qgnNdered it beneath their dig- nity to concern mele with spectacles, and after they had restored the Wjured or suffering eye to a healthy state, they t Bra the patient over to an optician for the proper “Or of glasses, unconcerned whether his selection w ἂν dod or bad one. It is only since prominent xe investigated such ‘‘incurable’’ cases, that they (ag"be thoroughly corrected by spectacles. Although t are manufactured by opticians, the credit of thei neficial action belongs to those eminent ex- plore(3) ho gradually wrenched their selection from the * GRADUAL DEVELOPMENT OF THE OPTICAL TRADE. 197 hands of mostly indifferent mechanies, who, destitute of the necessary scientific education, have to content them- selves at present with a secondary position under the leadership of the oculists. There is no blame attached to our present position, as it is not at all a step backward. On the contrary, the standard of our trade has advanced considerably, but it has not kept step with the gigantic progress of Ophthalmology, which has no equal in medi- cal history. In the last thirty years Ophthalmology and general Surgery have become exact sciences, while the rest of medicine is yet for the most part empirical, as was the ease with our mechanical and hap-hazard manner of selecting spectacles, when the patient was the princi- pal judge of their correctness. The selection of spectacles in complicated cases is now extensively practiced by oculists, who are, as physicians, qualified to prepare the eye for a thorough examination. Any optician, tampering with the eyes of an easily fright- ened customer, may cause himself great trouble if he cannot legally attach to his name an M. D. Only cases of simple presbyopia, manifest myopia, hypermetropia, and some cases of astigmatism, may be properly investi- gated by an optician, because the other and more προς ^ cated errors of refraction require that the ciliar scle be temporarily paralyzed by a mydriatie, and in'this state of the eye accurate and repeated meas ents be made with test-types and trial lenses. Sig&sNn the win- dows of opticians which read: ** Exami fn of the eyes made free of charge," smack of fec and should be removed. If I now allude, briefly, to thé? America has taken in the general development of ptical trade, I have to draw the attention of the Cn o the well known fact that we had during the c Al time no industry worth mentioning; we simp nged our natural and agri- cultural products fówNEhglish manufactures. Optical goods were still j Otea from Europe long after the es- tablishment of shee pofida independency from England. —The first ope, mentioned in this respect is Godfrey,” who was, ek ll, no optician but a glazier; he invented the Sex TA ie was of Philadelphia, (for many years Loo «5 198 HAND-BOOK FOR OPTICIANS. the headquarters of our slowly developing optieal indus- try); so was Rittenhouse, McAllister, Queen, Saxton, Zentmayer, etc. Other states soon followed in the path Pennsylvania had so ably opened; especially New York, with a fair line of opticians and inventors, like Fitz, Wales, Grunow, Spencer, Draper, Prentice, Fassolt, ete. Massachusetts was conspicuously represented by Tolles and Alvan Clark; even a Southern state by Riddell. At present nearly every Northern, Middle and Western state can boast of some competent opticians. Since the last fifteen years we manufacture all frames for specta- cles and eyeglasses, and also have commenced lately to grind our own lenses; I mention in this respect, Bausch & Lomb in Rochester, the American Optical Co. in Southbridge, and the Katonah Optical Co. In concluding this chapter, we must bear in mind that when we come to a great man who discovers or lays down new laws, there have always been a number of less known observers who have collected the facts from which he has formed his conclusions. Every country contributes its sharetothe development of science; wemay, therefore, say that science is international. Its achievements are open to the world at large, and the readiness with which any nation accepts and introduces them sho TW average intelligence. A superficial comparison o 10st prom- inent discoveries contributes greatl discriminate between the special characters of tl ifferent nations. France, for instance, excels in i ions for enjoying and beautifying life, thereby SQ ng the happy dispo- sition to take life mostly frém)tBe rosy side; German inventions bear a more s(Gentiüio, yea serious aspect, indieating a rigorous s ission to life's sobriety ; England, the favorite-foster-child of the world, prances proudly in the gene ce of progress, but with a sig- nificant wink to | "eg ends; and—America follows her example. It if prdualizes each step of progress by the distinction Q? tent, which is by no means an impedi- ment to piggjess, but, on the contrary, a fruitful cause of many@pportant inventions. America is the foremost advoc; e this doctrine, and is benefited by it to such t that at present our telescopes, microscopes, SS EN TL jet GRADUAL DEVELOPMENT OF THE OPTICAL TRADE. 199 J and above all, our spectacles can stand a fair comparison with the best European manufacture. Fifty years ago, we Ἐ still imported all optical instruments and appliances b from England, France or Germany; but of late we only 1 import the optical glass, and do to a good extent the grinding of lenses here as well, or even better, than they formerly did in Europe. If our glass-industry had advanced in the same proportion as the other branches of the optical trade, we also could expect in the near future an emancipation from the further importation of that article. —— ΄ DIFFERENT NAMES FOR SPECTACLES. The English word Spectacles is the plural form of spectacle, which is derived from the Latin noun Specta- culum, a sight, a show, and is formed from the verb spectare, to look at; to behold. The French word Lunettes is also the plural of lunette, which means a little moon, a ** moonlet,’’ referring to the round shape of spectacle lenses. The German word Brille, like the Dutch Bril, and the Danish Briller, is derived from -Beryl, a transparent green-bluish mineral, called by the jewelers Aqua Mne. In former years people in Germany called ε lored glass Berylle, and as a great many spectaclegN@specially ` those worn for fashion's sake, were set w m in colored glasses, this optical instrument Poe name from that mineral. The Latin name NY is berillus, the fundamental idea of which denotes iting or sparkling mineral substance, a crystal or Sey. ystal- like glass. The noun brilliant, now used only ας to diamonds, is derived through the mediu of the French word briller, to shine, to glitter, to sp@Nge (present participle, bril- lant). NC Italians say Occ; occhio = eye. Spaniards say ojos; ante — before, ojo = eye. Portuguese 8 culos, eyes. Modern Gf X. say Dioptres. Poles sa, Ιαν. 200 HAND-BOOK FOR OPTICIANS. Swedes say Glas-ógen, glass-eyes. Russians ** Ozku (atschküi); Otsko = eye. Roumanians say Ochilary (ot-chee-la-re). Hungarians ** Papaszem. Turks say G'uzlegán. Hindoos say Chasma (tchasma), frame. Hebrews ** Sechuchis l Ayin. Chinese ‘* Nong-Hieng, eye-glass. Japanese ** Megane, eye-mirror; and in Volapük, we say Liin. CHAPTER XXVII. A E n PROMINENT OPTICIANS, SCIENTISTS AND INVENTORS. | S “Tt is the commendation of a good huntsman to find game in a wide wood, but it is no imputation if he has not caught all." PLATO. ἿΝ Airy, Geo. B., born 1801, an English astronomer, first at Cambridge (1828), and since 1835, at the Green- wich Observatory. He has deservedly the reputation of being one of the most able and indefatigable of living scientists. His important contributions to astronomy, magnetism, meteorology, and other sciences are contained in leading cyclopeedias and in the annals of learned socie- ties. He ‘introduced several new astronomical instruments, among them the water-telescope, the transit-circle, and the large equatorial erected from his plans in 1859. He published, 1851, ** Six Lectures on Astronomy ”’ ; in 1 ‘ The Undulatory Theory of Optics; in λον On Atmospheric Chromatic Dispersion, " ete. Ade many researches in physics and optics, and is t gh tor of cylindrical lenses for the psa astig- matism. Alhazen, Abu Ali (died 1038 at αὖ ἠσγρί), was a great mathematician, and the first r e discoverer in optics after the time of Ptoler To him is due the explanation of the apparent inckease of heavenly bodies near the horizon; he also t@fght that vision does not result from the emission Oas from the eye, which was the favorite theox nany centuries before and after him. He wrot ok on the refraction of light, especially on atm@spfreric refraction, showing the cause of morning and & Mmg twilight. Only two of his works have been prin’ his ες Treatise on Twilight," and his es ai ον ο) ce,’’ or collection of optical facts. 202 HAND-BOOK FOR OPTICIANS. Amici, G. B. (1784-1863), a celebrated optician and astronomer at Modena, Italy; constructed the best reflec- tors and greatly improved achromatic microscopes. He invented and perfected also different kinds of camera- lucida for drawing purposes. Arago, D. F. (1786-1853), celebrated French physi- cist; discovered the colored rings of crystallized plates in polarized light. Upon this discovery is based the principle of the ** polarizer'' for testing pebbles. Archimedes (287-212 B. C.), the most celebrated ancient mathematician; invented the hollow **Archim- edes’ Screw,’’ a machine for raising water. He discov- ered the problem that a solid body, immersed in water, loses so much of its weight as the water would weigh which is removed by the body (specific gravity). In defending his native city, Syracuse (Sicily), against the Roman fleet under the command of Marcellus, he is said to have made use of powerful burning mirrors. Argand, A. (1150-1803), a Swiss chemist; invented, 1782 a lamp called after himself. The wick has the form of a hollow cylinder, through whichétéurrent of air ascends, so that the supply of oxygen iggNuvréased. This contrivance prevented the waste of n, which in the old lamps escaped in the form of &MNoóke, and it greatly increased the amount of light. also added the glass- chimney, by which a draft NG) mted and the flame ren- dered more steady. Bacon, Roger (121 ), studied at Oxford and Paris, where he received hè” degree of Doctor of Theology. After his return gland, he accepted a professorship in the C Oxford. Here he joined thé broth- erhood of NN ranciscans, and was termed by his brother 3 «* Doctor Mirabilis." His science and philosoy was almost universal, embracing Mathe- mate Y echanics, Optics, Astronomy, etc. He made ma iscoveries, or had some knowledge of the most r ‘kable inventions which were made known soon SS Ἃ ao OPTICIANS, SCIENTISTS AND INVENTORS. 208 afterwards. His principal work ‘‘Opus Majus," was addressed to Pope Clement IV (1265-68), who was formerly Legate to England, and who admired the talents of the learned monk, and pitied him for the persecution to which he was exposed.—The influence of Bacon upon his contemporaries was not great; he was suspected of magic and was placed several times in close confinement in consequence of this charge, once for ten consecutive years (1268-78). Barlow, Edward (1639-1719), an English mechanician, invented, 1676, the repeating clock and watch. Baumé, Antoine (1728-1804), a French chemist. His areometer, also called according to its applications hydro- meter, saccharometer, ete., made him widely known. It is still in use for measuring the specific gravity or density of different liquids heavier or lighter than water. Biot, J. B. (1774-1862), celebrated French mathe- matician and physicist; studied with success the dis- covery of Arago, and published some important re- searches about polarization and double refraction. He still defended Newton's emission theory .of light. Boulton, Matthew ( 1728-1809 ), a skillful Eng\ish machinist; inherited from his father an oxtensing tel manufactory, which he changed into a manut@ypry of steam engines, after he had associated να: the penniless optician, James Watt. "The im ements of steam engines were the joint efforts o h, although they are now chiefly credited to the 5 of the latter. Bradley, James ( 1692-1762 Ἂς al eminent English astronomer, was 1721 appointed fessor of astronomy at Oxford. In 1727, he angeunced the important dis- covery of the aberration of , Which serves to demon- strate the earth’s motier nd the sun. In 1741, he became the successor alley at the Observatory of Greenwich. His g «ρηι discovery was in 1747; he found that the E an of the earth's axis to the ecliptic is not constant, act which explained the precession of the nutation of the earth’s axis. This an important epoch in astronomy. 204 HAND-BOOK FOR OPTICIANS. Bramah, Jos. (1740-1814 ), an English mechanic ; invented the ** hydraulic press’’ (1795). Brandt, Geo. ( 1694-1768 ), a Swedish chemist and mineralogist; discovered, 1733, the metal Cobalt, now so extensively used in the manufacture of blue lenses. Breguet, A. L. (1747-1825), celebrated French mech- anie, made many important inventions in watchmaking as well as in physics. He invented the metal thermo- meter which consists of a thin strip of metal, composed of three layers, of silver, gold and platinum. This strip is curled up into a helix, the silver being outermost. As the temperature rises the silver expands more than the gold and the gold more than the platinum, and the helix colls itself up; in lower temperature it acts the opposite. The end of the helix carries an index by which its rota- tion is made manifest. Breisig, professor at Danzig, Prussia, invented the panorama. The first publie exhibition was made, 1787, in Edinburgh, by Robert Parker. light and in double refraction of ep the «6 kaleidoscope,” and described t, In 1832, he published his ** Treati&&von Optics," wrote many valuable articles for Des Britan- nica,” and was one of the last c ders of the ** emission theory." He is called th ther of Modern Experi- mental Opties.'' K Bunsen, R. W., wag jew 1811, professor of chemistry in Germany ; inver Qa burner which bears his name. the magnesium light which has eft in photography. The greatest dis- h his name is associated, is that of the nalysis," made in conjunction with his 22 proved so imp covery wit OPTICIANS, SCIENTISTS AND INVENTORS. 205 Celsius, A. C., (1701-44), a noted Swedish astrono- mer; divided the scale of the thermometer into one hun- dred equal parts, from the freezing point of water to its boiling point, in opposition to Reaumur and Fahrenheit. Chevalier, Arthur, born 1830; inherited, 1859, the large optieal establishment at Paris from his father, Charles Chevalier. He, as well as his father, has made many im- provements in the appliances for microscopes and other optical instruments. He published several instructive books; ** The Art of an Optician,” ‘ The Student of the Microscope,” ** The Student of Photography," ** Hand- book of the Oculist Student," ( Manuel de l'Etudiant Oculiste), etc. Clark, Alvan, (1804-87), of Cambridgeport, near Boston, is the most eminent manufacturer of telescopic lenses. He 15 a self-made optician, had never seen a lens ground; was formerly an engraver and portrait painter, but began, 1844, to study technical optics and astronomy in order to assist his oldest son, George B. Clark, a student at Andover, in his studies as engineer. Both, father and son, experimented in making a reflecting telescope, and sueceeded so well that they continue and gradually established a reputation here and in ἊΝ land. After his second son, Alvan G. Clark, a 1 machinist, joined the establishment, they tri struct ** refraetors," and increased their lege unknown before. In 1860, they construg telescope with a lens of eighteen inch Ἔρος jd it to the Astronomieal Society of Chicago. hat time, fif- teen inches had been the diameter d κα largest lens in the world.—During the war they e kept busy making binocular field glasses for the ny, but soon resumed the manufacture of telescopes( Wn 1871, they constructed a telescope for the NUN strvatory at Washington, with an objective lens enty-six ithe: in diameter; they also made a dt e of it for the Lee University of Virginia. The néw* great telescope was made for the Russian Observa e at Pulkowa; it has a clear aperture of thirty ND. a focal distance of 45 feet, and a 206 HAND-BOOK FOR OPTICIANS. magnifying power of 2000 diameters. But the greatest triumph of their technical skill is the new telescope of thirty-six-inch diameter for the Lick Observatory of the University of California. He made several discov- eries; he invented a double eyepiece, and devised a very accurate method of measuring small celestial ares. Coddington, Henry (died 1845), an English mathema- tician; published, 1829, a valuable book in two parts «System of Opties." In 1830, he published an essay ** On the Improvements of Microscopes," in which he strongly recommended the ** grooved sphere ' lens (first described by Brewster in 1820), which by his recommen- dation was brought into general use under the name of ** Coddington Lens." Cooke, Thomas (1807-68), of York, England; was originally a shoemaker in a small country village, but at the age of seventeen opened a school and in his lei- sure taught himself geometry and mathematics. His ambition was to construct a reflecting telescope, which led him to grind and polish lenses and specula, and with great perseverance and rare skill he ν᾽ his purpose. He then studied the optical a xw refraction in order to make an achromatic refract πω. one of four inches, which had an isto defining power. This telescope establishe¢Q¥name as an opti- cian; he gave up teaching a t o telescope- making. He opened, 1836, a shop i in Y Added to it the business of a general optician, Q » attending to the sale in store, "while he was work in | die back-room on tele- scopes. With the M of his brother as grinder, and his sons as mech&glics, he erected in 1855 a com- plete factory. H@ywork was always first-rate, and became known lover the world. In the same year, at the first AN. position, his six-inch equatorial tele- scope was 'ded the highest prize, a silver medal. He turnéc many telescopes, but the largest had only an aperttwé of ten inches, while Merz & Mähler, of Mun- ich, Kole some of fifteen inches, and Alvan Clarks 1860, e X ighteen inches., Cooke was too ambitious not OPTICIANS, SCIENTISTS AND INVENTORS. 201 to try to beat them; he, therefore, commenced to make one of twenty-five inches, but before it was móunted, his health broke down, he ‘died from mental anxiety and over-work. Many call him the ** English Fraunhofer." Copernicus, Nic. (1473-1543), was the founder of modern astronomy; demonstrated that the sun was the center of our system. Up to his time it was taken for granted that the earth was the center of the Universe, and that the sun with the planets, and all the stars were moving around it. His theory was received with the same opposition as, one hundred years later, Huyghen’s undulatory theory of light. The strongest opponent was the astronomer Ty cho Brahe, and the Church, which persecuted all prominent defenders of this theory. (See Galilei.) Cronstedt, A. F. (1722-65), a Swedish mineralogist ; discovered, 1751, the metal Nickel. Daguerre, L. J. M. (1789- 1851), a French painter, known as the inventor of the present photography. His pictures were called ** Daguerreotypes,’’ after his name, and were first exhibited at the Paris Academy by Arag 1839. This invention compelled the optical tra manufacture the Camera Obscura. 9 Dalton, John (1766-1844), celebrated Engliephysi- cist, and founder of the atomic theory AN émistry. He was the first who published facts wO olor-blind- ness, called foolishly after him «6 Dalt} ix Descartes, René (1596-1650), knee also by the Latin name ‘‘ Cartesius" ; was the mos&femarkable philoso- gn of his age. His oher and greatest mathemati . . Ὁ 5» . . ** Dioptrique;" published 199, is an everlasting acuteness of mind. He monument to his oN fration of a spherical lens demonstrated that the would be considerabl¢ dgMinished by increasing the con- vexity of its axis, yiz “Dy changing the spherical curve into a parabola. * also proved (1637 ) that the image ina is inverted. He is the father of formed upon t modern ANN o hy, and the founder of analytic geometry. ~ Eai S ~\ ML Y 208 HAND-BOOK FOR OPTICIANS. Dollond, John (1706-61), an English optician, well versed in mathematics; was a silk-weaver in his youth, and employed his leisure hours in the study of science. He invented the achromatic telescope, for which he re- ceived the Copley medal from the Royal Society of London (1758). Dollond, Peter (1731-1820), improved upon his fa- ther’s efforts, in conjunction with his brother-in-law, Ramsden. He published an ** Account of the discovery of refracting telescopes"" (London, 1789). Donders, F. C. (1818-89), a Dutch physician, studied at the University of Utrecht ; practiced first at The Hague, then established at Utrecht an institution for treating diseases of the eye. His principal works are: di Study of the Movements of the Eye," 1847; ** Astig- matism," 1862; ** Anomalies of Accomoda non and Refraction of the Eye," 1865. His researches regarding Hypermetropia and Astigmatism created a new epoch in Ophthalmology, and although he was ably assisted by independent discoveries, in this line, by different co-la- borers, his name will forever brightly shig& in the annals of optical science as a benefactor to m UNE 1, and as an original scientific investigator. Q Drummond, Thomas (1797-1: invented, 1825, the ** Drun ** jime or calcium ΠΟ Euler, Leonard (den. an eminent Swiss mathe- matician. In 1733 accepted the professorship of mathematics at Petersburg; in 1741, Frederick the Great, appoin m professor of natural sciences in the ly NS Academy of Sciences at Berlin; in 1766,-he r ed to St. Petersburg, where he remained to the (nd *6f his life. The last fifteen years of his Ge liehe was blind, but that did not prevent him fron ll publishing several important works. His valu- ‘ Treatise on Dioptrics’’ (Dioptrica), in three Ofumes (1769-71), was dictated by him when blind. ), a Scottish engineer; ; | Light,” also called OPTICIANS, SCIENTISTS AND INVENTORS. 209 He was a great admirer of Newton, whose marvelous achievements he investigated most critically ; this led him sometimes to correct Newton, as we see in regard to achromatism. Fahrenheit, G. D. (1686-1736). He was the first who used mercury in thermometers (1714), instead of col- oved alcohol. He determined the zero-point by mixing salt with chopped ice, contrary to Reaumur, who put the zero at the freezing-point of water. He also invented the first practical areometer, to measure the specific gravi- ty in fluids, and the first thermo-barometer. Faraday, Michael, ( 1791-1867), one of the most dis- tinguished chemists and natural philosophers of the pres- ent century. He was born near London, and was early apprenticed to a bookbinder; he devoted his leisure time to reading books and making experiments with an elec- tric machine of his own construction. Humphrey Davy, professor of chemistry at the Royal Institute, engaged him (1812) as his assistant, and here he first showed some of that extraordinary power and fertility which have rendered his name familiar to everyone acquaigted with physics. In 1827, he was appointed a regu 4 fessor of chemistry. His greatest work publist AN series of ** Experimental Researches in E which comprise all the investigations ε xo iscoveries made by him during the last forty years active life. From 1825-29, in conjunction with Sir A Horechel he tried to improve the manufacture uss for optical purposes. Practically considered &th1S jovesipstion was a failure, but the ** heavy glass’ ie; y produced led af- terward to two of his groatorh, scoveries: the ** mag- netization of light," and d lamagnetism.’ Fasoldt, Charles, -89), of Albany, N.Y., was a chronometer-mak profession, but devoted himself in his later gone t tical science. He was a mechanic of marvelous 4 g uity and wonderful exactness and skill; his gre: v^ duro Ma is a machine for micrometric rulings, NN e SS SN NO S culiar construction. His latest rulings 210 HAND-BOOK FOR OPTICIANS. were so fine that the strongest microscopes could not re- solve them, till he invented the ** vertical illuminator’’, by which some expert microscopists succeeded in the res- olution of 230,000 lines to an inch; but his machine is capable of ruling one million lines to an inch. His rul- ings are the best test to determine the strength of micro- Scopes. Fitz, Henry, ( 1808-63), a skillful telescope-maker; was a printer, but afterwards learned the trade of lock- smith. In 1835, he made his first telescope, and in 1845, he exhibited an instrument that brought him into favorable notice of eminent astronomers. He made tele- scopes for the University of Ann Arbor, Mich., for the Washington University of St. Louis, for the Dudley University at Albany, etc. His largest telescope had an aperture of thirteen inches. He was an optician entirely by his own tuition. Franklin, Benjamin, (1706-90), an illustrious Ameri- can statesman, and one of the founders of our Republic; invented the lightning-rod, and the bi-focal spectacles, which were named after him. Fraunhofer, Joseph, ( 1787-1826), κ Ger- man optician, instructed himself ir grinding, was employed, 1806, as a working optig in the establish- ment of Reichenbach & Utzschr r. While there, he acquired considerable wealtb-qÁrpugh his inventions, and became sole proprietor πο establishment in 1819. One of his first inventions was a machine for grinding and polishing mathema y uniform spherical and par- abolic surfaces; he 2 was the first who succeeded in polishing lenses an rrors without altering their curva- ture. He B NN new heliometer and a circular stage- micrometer ANN microscopes; his improved crown and flint glass/fujsetior to any English, enabled him to manu- facture hN#enowned achromatic microscopes and tele- scope ut that which rendered his name celebrated thro ut the scientific world is his discovery of the DGN n the solar spectrum ( 1815), called Fraunhofer’s I cil made L σσ. το ο) ο νι ΣΕ άν των ο ο ος ες S .AQ AV OPTICIANS, SCIENTISTS AND INVENTORS. 211 lines, which were first noticed by Wollaston in 1802, but F. published an illustrated map of fully 570 of them, assisted in his discovery by large prisms he had made of his clear flint glass. His tombstone bears this inscrip- tion: Approximavit sidera, (he drew the stars nearer). Fresnel, A. J., (1788-1827), celebrated French physi- cist and inventor. His researches on the aberration, diffraction and polarization of light, completely over- threw Newton's Emission Theory; and proved the cor- rectness of Thomas Young's defense of the Undulatory Theory of Light. His work on the ‘diffraction of light?! was crowned by the Academy of Sciences in 1819. He also considerably improved the system of illumina- tion for lighthouses. Galezowsky, Xavier, born 1833, in Poland, studied medicine at St. Petersburg; wentto Paris in 1858, became the assistant of the celebrated oeulist Desmarres, and subsequently erected a clinic for eye-patients. He in- vented the trial-frame with the half circle attached, divided into degrees, for the determination of the faulty meridian in astigmatic eyes Galilei, Galileo, (1564-1642), the Ἂν ( ον. mental science, was born at Pisa, Italy; "ovi first medicine and philosophy, then mathematj He util- ized the pendulum in the construction a ' clock for astronomical purposes, and invente Q drostatie bal- ance by which the specifie gravity oO d bodies might curac be ascertained with the nicest : He also dis- covered the laws of motion, i. at Ai falling bodies of the same specific gravitys great or small, descend with equal velocity. Am other discoveries may be noticed a certain species ermometer, a proportional compass or sector, DS construction of a refracting telescope for astrgndwcal investigations and of a micro- scope. By meanxgf his telescope he commenced his astronomical e@earches; he found that the moon was not self-IluminouewWGt owed her illumination to reflection, and D d the milky way a track of countless sep- SS Gà 212 HAND-BOOK FOR OPTICIANS. arate stars. In 1610, he discovered the four satellites of Jupiter; he also was the first to note movable spots on the disk of the sun, from which he inferred the rotation of that orb. He soon openly advocated the Copernican system, and was in consequence denounced as a pro- pounder of heretical views, and summoned {ο appear before the Inquisition. The persecutions to which he was subjected by this ** sacred court," lasted with short intervals almost twenty years. The wearisome trials and his incarcerations from time to time only ceased with his retractation. On June 22d, 1633, Galilei, at the age of seventy years, on his knees, and clad only in a shirt of sackcloth, was forced (by torture?) to pronounce in the presence of his judges and a large assembly of prelates, a most humiliating formula of abjuration. It has been asserted that he added in a whisper, ‘‘E pur si muove," (still it does move), meaning the earth. Galvani, Luigi (1737-98), an Italian physicist and celebrated anatomist; discovered accidentally the electric current produced by connecting two met: als of different density, called after him **Galvanism." ΑΙ] electro- plating is based on this discovery. Gascoigne, W. (1612-44), an English Qno and mechanie; improved the grinding of ow He was the original inventor of the wire 2 ο of its applic: ation to the telescope, and E of the telescope to the quadrant. Godfrey ‘ey, Thomas, born ae Ὃ worked as a glazier in his native city, udied mathematies with great energy; he even | en Latin in order to read mathematical works ig that language. In 1730, he communicated an im (»ement he had made in the quad- rant, and the inv( vas laid before the Royal Society in London. In mean time, John Hadley had made a very simi ention, and each of them was awarded the prize ped Godfrey died in Philadelphia in 1749. Grai ΑΙ ντο von (1828-70), the most celebrated culist; studied medicine at Berlin, Vienna and Ger S 213 4] OPTICIANS, SCIENTISTS AND INVENTORS. Paris; established 1850, at Berlin, a clinie for eye- patients, and was in 1856 elected professor of ophthal- mology. He is the founder of modern Ophthalmology, | greatly assisted by the invention of Helmholtz’s ophthal- CORN : moscope, which received in Graefe’s hands its highest | recognition. | Graham, George (1675-1751), an English watchmaker and optician; invented the con npensated mercury pendu- lum, also the cylinder escapement, and the dead-beat | escapement for clocks. He constructed the sextor with Es which Bradley, at Oxford, detected the aberration of | light, and executed a great mural-are for professor | Halley, a celebrated English astronomer (1656-1742), 1 at the Observatory of Greenwich, who calculated the course of twenty-four comets; one of them bears his | name. Gregory, James (1638-75), a Scotch mathematician, | invented at the age of twenty-four, the reflecting tele- I scope known by his name. When he went to London i with the view to the construction of his telescope, he found the opticians he employed wanting in the skill yox necessary for grinding the metal of the object-s ulum | into a conie section "to correct spherieal a ion; | therefore, he abandoned the manufacturing ain, and ju devoted. himself to the study of E ee James | | | Short. ] Grimaldi, F. M. [1613-63], great mathematician; his valuab rk on light was published two years after his Qea He was the first | 1 a ES ° : 2 i who described the ‘‘phenom of diffraction,” or the bending of waves of light ground the edges of opaque bodies. Newton could xplain this phenomenon by | his emission theory, Qt ng and Fresnel demonstrated | its correctnes ss by t ΟΡ Ave theory on the ‘‘ principle of interference. Qu. jesuit and | Guerike,, master of M air-pum © von [1602-86], the ingenious burgo- eburg, is renowned as the inventor of the “as the “originator of many experiments in S 4? 214 HAND-BOOK FOR OPTICIANS. natural philosophy. He introduced his invention by con- structing two hollow hemispheres of brass, which fitted air-tight upon each other, and which could not be pulled asunder, after he had exhausted the air out of them, but by the application of great force. They are called the Magdeburg Hemispheres, and are still used in experi- mental physies to show the immense atmospherical press- ure upon a vacuum. Guinand, Francois, (1745-1825), a Swiss watchmaker and optician, was the son of a carpenter, and first em- ployed by the celebrated mechanie Jaquet-Droz, to make wooden eases for clocks, and later on, metal cases for watches. His employer had a fine English reflector which G. so perfectly imitated that it was difficult to de- cide which of the two was better. Droz being aware of the talent of his workman, instructed him in the science of opties, in the manufacture of spectacle glasses, and in the construction of achromatic lenses. He now stud- ied chemistry, and commenced to perfect the fabrication of lenses for telescopes. Some of these coming under the observation of Fraunhofer, he engaged his services. The phenomenal improvements of achromatie instru- ments is due to the combined efforts of these Å kintal men. Qo Hadley, John, [died 1744], an En Rh astronomer, greatly improved the quadrant by t it into a sex- o tant, about the year 1731. [See Grey. ] Harrison, John, [1693-177 a' celebrated English watchmaker, learned from [ας father the trade of car- penter, made several πον ες, wood with a newly con- structed pendulum [1@§]. He then commenced to make watches of my improvements of his own invention, until «αρ * produced a marine chronome- ter for which | NS ved the medal. Captain Byron took one offfiXéhronometers along on the ** voyage round the woNd4”’ 1764-66, and it proved to be a perfect time-piese&pe, therefore, claimed the prize of £20,000, which tjr,wóvernment had offered for the best chronome- RY à OPTICIANS, SCIENTISTS AND INVENTORS. 215 Helmholtz, H. L. F., born 1821 at Potsdam, Prussia, is at present the most famed physicist in Germany. He studied medicine at Berlin, and was, 1848, appointed professor of anatomy. The next year he went to Konigsberg' as professor of physiology, where he stayed till 1855, when he was called to Bonn. In 1858 he accepted the professorship of physiology at the Univer- sity of Heidelberg. His principal publications are **Con- servation of Force," 1847; ** Handbook of Physiological Optics,” 1856; ** Theory of the Impressions of Sound," 1862; **Popular Scientifie Lectures," 1865-71; besides many other valuable scientific papers. He is the inventor of the Ophthalmoscope, an instrument which has totally revolutionized the science of Ophthalmology, and which is at present indispensable to any oculist. He is the survivor of the illustrious triumvirate ** Graefe, Helm- holtz, Donders,’’ who raised Ophthalmology to an exact science. Their names will be remembered as long as a grateful posterity will cherish the achievements of great men. Herschel, F. William [1738-1822], born in Hannover, educated a musician, emigrated 1757 to England, devoted most of his time to the study of astronomy; but being too poor to buy a telescope, he built, 1774, effector five feet long. With the assistance of his brgprt, who was a skillful mechanic, he constructed, , a tele- scope of forty feet in length, which was 10st power- ful instrument at that time, and wit ich he made many discoveries, He discovereg planet Uranus, and some of his moons, also two (o of Saturn. Herschel, Sir John, [179: 71], followed in the footsteps of his celebrated father, whom he greatly ex- ceeded in profound matl ical science, as well as in the long list of his astr ical researches and discover- ies. In 1830 he puNNRÉd a treatise ** On the Theory of Light," comprising Jis investigations in the optical department, whigh he had made in conjunction with Far- aday. In 18 ueen Victoria created him a baronet. He was an iWefatigable explorer, and the most success- ful astro r of this century. 216 HAND-BOOK FOR OPTICIANS. Heurteloup, Nic., [1750-1812], celebrated surgeon in the French army; invented the artificial leech. Hipparchus, considered the founder of the science of ' astronomy ; lived about 150 years before Christ, and was born at Nicea, Bithynia [Minor Asia]. Of his life nothing is known, and of his writings only one book has been left to us; 1 but Ptolemy tells us of his great discover- ies, and refers to him in many cases as an authority. Hooke, Robert, [1635-1703], watehmaker at London; invented, 1658, the balance spring [hairspring], also the anchor-pallets for clocks, and a sliding-weight to the pendulum, to adjust the center of gravity with greater precision. Huyghens, Christian, [1629-95], of The Hague, Hol- land; one of the greatest discoverers in mathematics, physics and astronomy. He discovered the law of double refraction in crystals with one axis, opposed the ** emis- sion theory"' against Newton, and founded the ** undula- tory theory." He improved telescopes, ground and polished the lenses himself, and νι the connec- tion of the pendulum with clock-work. o discov- ered the ring and the fourth satellite "S. In, [See alilei ] Jaeger, Edward, son of the "ey and Jae- ger, is professor of ophthalmolog the University of Vienna, Austria. In 1854, QN ished his test-types, ranging from the finest to rge letters, in different languages. Among. his n excellent publications, the most famous is his “Atlas Ophthalmology’’, the origi- nal drawings of whj vere afterwards purchased by Dr. Norris of O nia for about $2000. Johnston Cy", born 1844 in Western New York, an able optica x "ter; was educated for the Church, but ο λες] , the Johnston Optical Company. He issued ἃ ti: **Eye-Echo," the first journal in America dev xclusively to opties, and as a continuation of OPTICIANS, SCIENTISTS AND INVENTORS. 217 the former, since 1891, the ‘‘Eye-Light.’’ In 1892, he published a valuable work, ‘‘Eye Studies, a series of les- sons on vision and visual tests’’. Kepler, John, [1571-1630], a German mathematician and astronomer of great reputation; was one of the founders of modern astronomy. His three laws [Regu- lae Kepleri] of the elliptical orbits of the planets were afterwards accepted by Newton, and are still in use. iie invented the astronomical telescope in which the object- ive and ocular lenses were both convex. He was the first who explained the true theory of vision. Kircher, Athanasius, (1601-80), a very learned Jesuit ; was born in Germany, but lived mostly in France and Italy. He invented the Magic Lantern, and constructed a powerful burning-mirror with which he experimented on the Island of Malta; it is known by the name Mal- tesian Mirror. Kirchhoff, G. R., [1824-87], celebrated German phy- sicist, born at Kónigsberg, Prussia; studied mathematics and physics, went 1847 to Berlin as professor of physics, 1850 to Breslau, 1854 to Heidelberg, and 1875 again to Berlin. His scientific researches were mostly dee to electricity, galvanism, and to the peculiar i of bodies and gases. His investigations of hofer’s lines, which he made in conjunction dy Knapp, H., celebrated oculist of Rany and Amer- ica; was born 1832 in Nassau, any; studied for nine years medicine at Munich, lin, Leipzig, Vienna, Paris, London and other ce]eDw- «ted Universities. He was lecturer and later pr tor of ophthalmology in Heidelberg, but resigne 1868, and settled in New York City. Here he #hed the Archives of Ophthal- mology and Otolog founded the N. Y. Ophthalmic and Aural Isi) ο e was for several years profes- sor of ophthalmoloy at the Medical College of the Uni- versity of N mology at -X Aand is at present professor of ophthal- © College of Physiology and Surgery at 218 HAND-BOOK FOR OPTICIANS. New York. He is regarded as an authority in medical circles, in America as well as in Europe. In 1873, he introduced some very valuable improvements in the Ophthalmoscope. Lieberkühn, J. N. [1711-65], physician at Berlin; invented, 1738, the solar microscope. Lippershey, John, the inventor of spyglasses, about the year 1600, was born in Wesel, Germany; his real name was Hans Lippersheim. He established himself as an optician at Middleburg, Holland. It is told that one day his son was playing with old spectacle lenses, and accidentally put a convex lens at one end of a hollow tube and a concave one at the other end; then called the attention of his father to the strange phenomenon, that distant objects seemed to be so near-by, that he fancied he almost could touch them. Littrow, J. J., [1781-1840], studied at Prague, was engaged at different universities as professor of mathe- maties and astronomy, until in 1819, he became director of the Observatory at Vienna. Some of his theoretical publications induced the optician Ploessl to.donstruet the dialytic telescope. His most popular 1 κ λος 816: ** The Wonders of the Heavens,” ang? PW Maps of the Starred Heavens "' Malpighi, Marcello, [1628-94 Qi Italian anatomist; was the first to employ the p ( microscope to investi- gate the anatomical struetiu plants and living animals; thus he discovered the ca¥jllary circulation of the blood from the arteries to tQ@ veins. Various parts of the epidermis, spleen angkidneys still bear his name. Malus, E. educated at Q (5-1812], a French physicist, was hool of military engineers; was a great mathema but took a fancy to the study of the mathematt<él theory of optics. For the greater portion of hi Gy rt life he was attached to the French army, and tool wit in the adventurous expedition of Bonaparte DEON ER Go o Q SV n OPTICIANS, SCIENTISTS AND INVENTORS. 219 [Napoleon I] to Egypt. In 1801, he returned to Paris, and although his health was broken down, his spirit was yet in the prime of life. In 1808, the French ‘Institute of Sciences’’ offered a prize for the best essay on double ‘refraction in crystals. Malus competed for the prize, and in the course of his experiments discovered the phe- nomenon known as the polarization of light. He ad- vanced the theory **that particles of light have poles, and that on entering a doubly-refracting crystal, some of the particles forming one of the rays may be so arranged as to be transmitted through it, while the particles which should have formed the other ‘ay may be so arranged as to prevent the transmission in certain directions." This discovery introduced a new diversion of physical optics. In 1810, he published his ** Treatise on Optics,” and his P "Theory of the double refraction of light in crystals". McAllister, John, [1753-1829], born in Scotland, emi- grated to America in 1774, and started, 1796, an optical business in Philadelphia. John McAllister jr. [1786- 1877], a graduate from the University of Pennsylvania, associated with his father in 1811, and laid the foundation of an extensive business. The war of 1812 κο the importation of spectacles, and compelled them END u- facture all gold and silver spectacles δα N ‘In 1836, Walter B. Dick and. Jas. W. Queen ος part- ners, till 1853; the firm, McAllister & was then continued by him and his son, W. Y. 1812], until 1865, when the father retired. In ; W. Y. MeAI- lister took his son, W. M. [born 1! ® ; his partner; an- other son, F. W. [born 1853 ], st&ted an optical business in Baltimore, 1879, and is the Kentor of an improved nose piece.— This ge HU family of opticians"' will soon celebrate its centenni Merz & Mahler, t SE successors of Fraunhofer, at Munich; turn many astronomical telescopes, among them the ous refractor of the Pulkowa Ob- servatory in we δρ also that of the Harvard University in the U. S. h instruments contain object lenses of fifteen i NN Mus NS EN 220 HAND-BOOK FOR OPTICIANS. 1 D Mudge, Thos., [1710-94], an English mechanic; was an apprentice of the celebrated Graham, and became the most skillful watchmaker in Europe. The English government paid him for the superiority of his chronome- ters the prize of twenty-five hundred pounds sterling. ` He invented the lever escapement. Newton, Sir Isaac, [1642-1727], the most remarkable i mathematician and natural philosopher of his age, was | the founder of modern mathematical physies and physi- i cal astronomy. In 1665 he discovered the law of uni- "n versal gravitation; he then studied the nature of light, i and detected by means of prisms the composition of white light, which led him to the grinding of lenses, and to the construction of reflecting telescopes. In 1704 he UO published his *«Opties, or a treatise on the reflections, | refractions, inflections and colors of light;’’ and in 1713 DL his Principia." He was the founder of the **emis- | sion theory."' Nicholson, W. [1753-1815], English physician and chemist; invented the areometer or hydrostatic balance, that bears his name. He published aboytwenty sci- entific works mostly on chemistry. NN Nicol, W., [1768-1851], a lapidag > Edinburgh; in- vented the polarizing prism of Ice spar, which totally reflects the ordinary ray, whils extraordinary passes through, and which bears hj e. His skill as a work- ing lapidary was very Bus diy executed a number of lenses of precious stones especially of garnet, which lenses he preferred to VM ues microscopes of his time. ιο. an Italian astronomer, founded an my in Naples to which no one was ad- mitted ugfésshe had made some discovery in natural philosoph He was accused of magic and compelled pe to dissolve his academy. He wrote many 5 on natural magic, geometry, optics, ete. ; also in- the camera obscura, and demonstrated that visual Porta, Bat Brooklyn, 1854; attended the Royal "as bis AN at 8 S OPTICIANS, SCIENTISTS AND INVENTORS. 221 perception is not effected by rays emanating from the eye, but by rays reflected from objects. (See Alhazen). Prentice, James, (1812-88), eminent American opti- cian; was born in London, served an apprenticeship of seven years with Elliott & Son, opticians and mathemat- ical instrument manufacturers in London. He emigrated to America in 1842, and almost immediately secured the government patronage of the U. S., which he continued to supply with instruments until the beginning of the war, 1860. The superior excellence of his instruments gained for him a far-reaching reputation among archi- tects and engineers. He received nine medals and four diplomas of honor between the years 1842 and 1860. After the opening of the war, he devoted his entire at- tention to the store which he had just previously opened. In 1867, he invented and patented the ‘‘anatomical eye- glass," since universally known as the Prentice eye glass, which was the beginning of improvements in eyeglass- frames; numerous patents by others soon following it. Prentice, Chas. F., son of James Prentice, was born in Carlsruhe, Baden, from 1871-74. It was his AST E desire that he should give particular attention toghethar ies, physies and mathematies, in order to bec ough optician, as the father justly antici great development of the optical trade wit claim to the ability of the future optjgi After his re- turn to America, he temporarily αοάρρϑρ8 the position as mechanical draftsman at the ship$grd'of John Roach in N. Y.; but in 1878 he entered nO her's business, where he became a partner in 1883 nd since 1888 its proprie- tor. His former theoretic dies soon made him the foremost optical writer Ur ‘ica. In 1886, he published his valuable **Treatise phthalmic Lenses;"' in 1888, his mathematical : ost scientific **Dioptrie Formule for Combined Cylindrical Lenses," and in 1890, his “Metric Systetga of Measuring Prisms." He simul- taneously in d the **Prismometer," to determine the refractive pxoperties of prisms by their deviation; a new, SS Gà n a thor- that the lay greater 222 HAND-BOOK FOR OPTICIANS. simple and most ingenious method, which enables ocu- lists and opticians to experiment with prisms in a more scientific manner than ever before. t Piolemy, Claudius, an Egyptian astronomer, flour- πι ished at Alexandria in the middle of the second century after Christ. He wrote the ‘‘Syntaxis Mathematica,” ' A which is a representation of the science of astronomy of 3 that time, based partly on his own researches, partly on 1 | those of Hipparchus. As it is the only authority we | have for the views of astronomy entertained by the an- cients, and as it formed the foundation of all astronom- uU ical science down to the time of Copernicus, the book is consequently of the greatest interest. Queen, James W., [1812-90], an Ameriean optician; learned his trade at the establishment of John McAllister at Philadelphia, in which he afterwards became a part- nér. In 1853, he commenced business for himself and gradually built up the largest scientific optical house in Ameriea. Newtonian telescope at the Royal Obser Y of Green- wich. The speculum has a focal le of twenty- five feet, and a diameter of fifteengafeies. It was at that time the largest instrument ir Ramage, optician at Aberdeen; Yun Pac 1820, Ramsden, Jesse, (1735- am English optician of rare skill; was a t Pe learned engraving on copper; had to engrave & Ga of "optical i in- E struments, which indu uf to learn the trade with zB John Dollond. Alrgalyin 1763, his instruments had t] great reputation. made many improvements and in- ventions, of RO *dividing machine" is the most important. nstructed some ‘‘mural circles," one of five feg meter for Palermo, Italy, and one of eight j feet for fheJObservatory at Dublin. The error of one of / his MAE (at Padua) was only two seeonds. wmur, R. A. F., (1683-1757), celebrated French Sicist; divided the scale of the thermometer from the : OPTICIANS, SCIENTISTS AND INVENTORS. 220 freezing to the boiling point of water, into eighty de- grees. His thermometers were filled with colored alco- hol, which is preferable in great cold, as mercury will freeze at a temperature of forty degrees below zero, while the severest cold has never yet frozen pure alcohol. Reichenbach, Geo., [1772-1826], became with Fraun- hofer the ornament of the ‘‘Mechanical and Optical In- stitute of Bavaria" at Munich. His astronomical instru- ments, meridian circles, transit instruments, equatorials, heliometers, etc., made an epoch in **observing astron- omy.’ fiiddell, J. L., [1807-67], of New Orleans, was pro- fessor of botany and chemistry at the University of Loui- siana, 1836-65. He was the original inventor of the binocular microscope, 1851, which was afterwards manu- factured and introduced by J. W. Stephenson of Lon- don. He also constructed an achromatic binocular mag- nifier in the form of spectacles, leaving both hands of the operator free for manipulation, and which is still in pos- session of the well-known oculist, Dr. Cornelius Beard, formerly of New Orleans, now in Boston. Rittenhouse, David, [1732-96], an America: matician; made the first telescope ever constpye America. He learned clock-making, and ablished himself, 1751, in Norriston, near Norristom\Pa., as a clock and mathematical-instrument-maks !^ His days were spent in following his trade, (Dis nights were given to study. His orrery exhibit 10st every motion in the astronomical world; it waskeught by the Univer- sity of Pennsylvania for £400. 1770, he removed his business to Philadelphia. Hysscientific instruments dis- played unusual mechanical nathematical genius. Rochon, Alexis, grin, a French astronomer; was first abbot of gecQpWent, but quitted the church, and studied optics andggfronomy. In 1777, he constructed a micrometer oi ospck crystal to measure small angles. He made sev scientific expeditions to French colonies Hast Indies, and found in Madagascar the 224 HAND-BOOK FOR OPTICIANS. finest rock crystal which he ground into lenses; but de- clared them, afterwards, to be unfit for spectacles on ac- count of their double refraction. we ~< a I Roemer, Olans, (1644-1710), Danish astronomer; dis- covered the velocity of light by the eclipses of the first moon of Jupiter. The other three moons were not so favorable for this observation, as their mutual attraction makes their motion more complicated, and puzzled the astronomers, till Newton published his theory of univer- sal gravitation, which solved the mystery. ee ewes ei ec gu UEM Rosse, Lord W. P., (1800-67), the distinguished con- structor of the largest reflecting telescope. In 1845, he built his great reflector, which up to the present day has remained without a rival. It has a focal length of fifty- four feet, and the tube is about seven feet in | diameter. Saxton, Joseph, (1799-1873), a skillful American me- 7 chanic; was apprenticed to a watchmaker, went 1817 to n Philadelphia, where he worked at his trade, but devoted .much time to drawing and engraving. S an astronomical elock with an escapement new plan. 2 In 1828, he went to England, where he d in- genious mechanical toys, and ex xhibite Gs, a magneto- electric machine, with which he faduced a brilliant electric spark, decomposed wat rah and exhibited the electric light between σπα Arco? nts. In 1837, he re- turned to Philadelphia, and Qv the position of con- structor of the standard eing apparatus of the U. 5. mint. He invented th dal-ruler, the fountain pen, . and other useful ma oM and appliances. Short, James 10-68), born in Edinburgh; con- structed abou 5. some telescopes for his own amuse- ment. ‘st telescopes the specula were of glass, as 5 3 y Gregory, but he afterwards used metal- lic speg TH and succeeded in giving to them true para and elliptic surfaces. He then adopted tele- Ἰακίησ as his profession, and went to London. is telescopes were of the ‘‘Gregorian’’ form, and 0 oe s Bee: Fee Sti Fm ιν ARS "R ind Shee we Tomer cp SE Le OPTICIANS, SCIENTISTS AND INVENTORS. 225 some of them have retained even to the present day their original high polish and sharp definition. Snell, Willebrord, (1591-1626), a Dutch mathemati- cian; discovered the **aw of the sines,’’ i. e. that the sines of the angles of incidence and refraction are con- stant for the same medium.—Kepler tried to find this law, but did not succeed. Snellen, H., was the pupil and assistant of Donders, and since 1888, is his successor as attending oculist to the Netherland Eye Hospital; is also professor of Oph- thalmology at the University of Utrecht, Holland. In 1868, he published his test-types which virtually solve the problem of registering vision. Spencer, Chas. A., (1813-81), born in Lennox, N. Y., is considered the pioneer of scientific optics in this coun- try. He received a classical education at different col- leges, but his attention was soon drawn to more practi- cal study and experiment by himself. In 1831, he set- tled in Canastota, N. Y., as a manufacturer of telescopes and mieroscopes. He issued a descriptive catalogue, «Optical, Philosophical, Mathematical, Chemi and other Instruments and Apparatus," which cofiiintd a chiefly of the Newtonian and Gregorian Q S mm m GLOSSARY. 239 gans; so called because the ancients thought these vessels contained air, as they are empty after death. Asymmetry (Greek, a, not, syn, with, metron, meas- ure, not in measure). This word is the opposite of sym- metry, which means that the several parts of a body, or thing, are in due proportion to each other; while asym- metry means that they are out of proportion. Asthenopia (Greek, a, not, sthenos, strength, ops, eye). The eye has no strength in its muscles; sometimes **weaksightedness."' Atrophy (Greek, trephein, to nourish). A wasting away from defect of nourishment. Atropine (Greek, atropos, black,—the name of one of the Fates). A very poisonous vegetable alkaloid, ex- tracted from the plant Atropa Belladonna, the deadly nightshade; the extract crystallizes in long, white nee- dles. Axis [ Greek, axon, a straight line, real or imaginary ; on which a body revolves, or may revolve]. In opties, a ray of light from any object, which falls perpendicu- larly on the eye, called the optie or visual axis. Bi-focal. A lens having two different foci. ~\ Binocular | Latin, bini, two and two, oculus, ὁ It signifies an instrument used by both eyes at op -Binocle (French). Eyeglasses for both Brain. The mass of nervous substa contained in the cavity of the skull. Caloric (Latin, calor, heat). gh rin of heat, the agent of heat and combusti Canthus (Greek, canthos, AN ofa wheel). Angle of the eye; the inner and corners, where the eye- lids join. Capillaries: (Lati NEM hair). The smallest blood vessels bety ev arteries and the veins, so called from their minuto hair-like size. Cartilage (ση, cartilago). A firm, elastic sub- stance, like a-rubber, forming a part of the joints, wind- K and ears. E | SS SN Q V NS: 240 HAND-BOOK FOR OPTICIANS. Cataract ( Greek, catarasso, to throw down, to break or disturb). Opacity of the lens or its capsule. Catoptric (Greek, catoptron, mirror). ‘That part of opties which explains the properties of reflected light, and partieularly that which is réflected from mirrors or pol- ished surfaces. Cavity (Latin, cavus, hollow). A hollow, inclosed space. Cerebellum (Latin, diminutive of cerebrum, brain). 'The little brain situated at the back and lower part of the head. | Cerebrum. The brain proper, occupying the entire upper and front part of the skull. It is nearly divided into two equal parts, called hemispheres, by a cleft ex- tending backward from the front part of the head. Choroid (Greek, chorion, skin, eidos, form). Α brownish-black membrane forming the middle coat of the eyeball. Choroiditis. Inflammation of the choroid. Cilia (Latin). Eyelashes. C'oncave ( Latin, concavus, hollow). Curved or rounded, like the inside surface of a hollow globe. Congestion (Latin, con, together, gero, Or ng). An unnatural gathering of blood in any Mr body. Contraction (Latin, traho, to drawQf: he active short- ening of a muscle or muscular MAC Convex | Latin, conveho, to Q together]. Curved or rounded, like the outside obe. Cornea [ Latin, cornu, Bern]. The transparent, horn- like substance which cov (3 he front part of the eyeball, through which the light» passes. Crystalline Lens Oyitin, crystallum, ice,]. A trans- parent, circula Qr: rounded on its front and back sur- faces, situatedANYhe eyeball, just behind the pupil and iris. ( | | * . . . Dey nn (Latin, de, from, via, way). A turning κκ m the right way.or line. GLOSSARY. 941 Dialyte (Greek, dia^and lyo, to loosen, to separate). A telescope in which the flint and crown glass of the ob- jective lens are not glued together, but mounted sepa- rately, leaving some space between them. Diaphragm (Greek, diaphragma, partition). A plate with a circular opening, used, in instruments, to cut off marginal portions of a beam of light. Diffraction (Latin, diffringo, to break in pieces). A change which light undergoes, when, by passing near the border of an opaque body, it forms parallel bands or col- ored fringes. Dioptric (Greek, dioptomai, I see through). That branch of optics which treats of the refraction of light and the properties of lenses. Diplopia (Greek, diplos, double, ops, eye). Double vision. Dispersion (Latin, dispargo, to scatter). The sepa- ration of light into its different colored rays. Dissolving views, are produced by two magic lanterns of equal strength, whose foci are centered on the same spot of the canvas on which the picture is shown. By a skillful manipulation of the adjusting screws, one picture may gradually disappear while another almost instántly takes its place. Distance (Latin, disto, to stand apart). Ra ΝΑ, from a point nearer than twenty feet are dip@hént, and are considered as coming from a **finite e nce;" but rays coming from a greater distance th enty feet are practically parallel, and are consid 5 coming from an ‘‘infinite distance."' Duct (Latin, duco, to lead). narrow tube, usually designed to convey away a Q on from the gland in which it is produced. Elasticity ( Jd impel, or e/ao, to drive). The ρε of b NS which they recover their for- mer figure or size£ agtér the removal of outside pressure or foroe. ο eels metron, measure, emmetros, in rej) measure, o; The condition of the eye, when par- 242 HAND-BOOK FOR OPTICIANS. allel rays are brought to a focus upon the retina without any effort of the accommodation. focus (Latin, hearth, fire-place). A point in which the rays of light meet, after being reflected or refracted. Glaucoma (Greek, glaucos, sea-green). A most se- rious disease of the eye, not well understood, but charac- terized by hardness of the globe, dilatation of the pupil, and often by a greenish opaque appearance of the pupil. Goggles (this word is of Welsh origin, gogelu, to shun, to shelter; the French, coquille is only a poor substitute for the same word). Protection spectacles of colored glass in the shape of a muschel or a hollow watchglass. Granulation (Latin, granum, grain). ‘The process of forming small grain-like swellings on the tender mucous membrane of the eyelid, a disease; also the natural pro- cess by which the surfaces of ulcers and sores are cov- ered with new tissue,—granulation tissue or granulations. Horopter An obsolete denomination for Range of Vis- ion. Humor (Latin). Moisture; the humors are transpar- ent contents of the eyeball. Hyperaemia (Greek, hyper, over or αἱ τὰ haima, blood). An active superabundance of bl nan organ, or part of the body. Illusion (Latin). A deception LQ sense (sight) or brain. Indentation (Latin, in, andy , a tooth). A notch in the margin of anything. | Inflammation (Latin, Amo, to flame). A peculiar diseased condition of 2 part of an animal body, char- acterized by rednes{)gwelling, heat, pain and febrile symptoms; ther. i Gr hyperaemia and then congestion. Ingredient N ingredi, to go into]. That which enters into 4 cgmpound as one of its constituents. | in, the rainbow]. The thin muscular ring or h lies between the cornea and crystalline lens, gives the. eye its brown, blue or other color. GLOSSARY. 243 Tritis. Inflammation of the iris. Irradiation. The phenomenon by which a brilliant body (especially on a dark ground) appears larger than it is, by reason of the stimulation of the light force, ex- tending over a larger area of the retina than that occu- pied by the image of the body. Kaleidoscope (Greek, kalos, beautiful, eidos, form, skopeo, to see). An instrument which, by an arrange- ment of reflecting surfaces, exhibits an infinite variety of beautiful colors and symmetrical forms of its contents. Latent (Latin, lateo, to lie hid). Concealed, secret, hidden; not visible or apparent. Lens (Latin). A piece of transparent glass, or other substance, so shaped as either to bring together or dis- perse the rays of light. Ligament (Latin, ligo, to bind). A fibrous band or cord, serving to attach two bones to one another. Manifest [Latin]. Clear, disclosed, apparent, evident. Membrane [ Latin, membrum, a limb or member]. A thin layer of tissue serving to cover some part of the hody. Meniscus [Greek, meniskos, a little moon]. xor convex on one side and concave on the other. ον Mica [Latin, mico, to shine]. A transi mineral capable of being cleaved into elastic (ο of extreme thinness. It is a poor conductor of he Microscope | Greek, mikros, sma Ὁ An optieal instrument which magni objects. Mirage [ Latin, miror, to adnffy*]. An optical illusion arising from an unequal re e ion in the. atmosphere, and causing rémote opie o be seen double, as if reflected in a mirror, Su as if suspended in the air, like the ** Fata AN Ana.’ pi Monocle [LatiuzwAoculus, one-eyed]. A single eye- glass. o . Motor Bax moveo, motum, to move]. Causing motion; th me of those nerves which conduct to the muscles. imulus which causes them to contract. S 244. HAND-BOOK FOR OPTICIANS. Musce volitantes | Latin, musca, a fly, volito, to fly about]. The appearance of grayish motes apparently before the eyes. Mucous Membrane. The thin layer, of tissue which covers those internal cavities or passages which ‘com- municate with the external air. Mucus [Latin]. The sticky fluid which is secreted by mucous membranes, and which serves to keep them in a moist condition. Muscles [| Latin, mus, mouse, musculus, a little mouse ]. A band of fibres acting as an organ of motion in animal . r e LI . 4 bodies. The voluntary muscles act in obedience to the Pu M. will, and contract suddenly; the involuntary muscles do not obey the will, and contract or relax slowly. 1 Mydriasis [Greek]. The unnatural dilatation of the pupil. 1 Myopia [Greek, myo, to shut, ops, the eye]. Near- , | | sightedness. j Myosis | Greek ], the unnatural contraction of the pupil. glisten- i ing, white cord, connecting the brain or spinal Nord with | some other organ of the body. The nerve&&Ke the tele- graph-wires of the body. Q Neuralgia (Greek, neuron, nerve, os pain). Α peeuliar pain of a nerve of PUMA AO) sation, not pre- | ceded or occasioned by any ANS Se. Objective lens. The εκ an optical instrument n which is directed to the tct to be seen. & ὶ Nerve (Greek, neuron, ἃ cord or string). A Observatory. A plagppr building for making observ- ations on the heavenl dies. Ocular lens. (Ορ: $ of an optical instrument through 8 which the eye 1 Oculus «(5 tin, abbreviated O. D.). Right eye. Oculus nister (Latin, abbreviated O. S.). Left eye. Oph é matic SS ia (Greek, ophthalmos, the eye). Inflam- the eye. "NC $ Ü m - e. | | ' GLOSSARY. 245 Ophthalmology (Greek, logos, a discourse). The sci- ence of medicine and surgery concerning the eye. Ophthalmoscope (Greek, skopeo, to examine). The instrument for exploring the interior of the eye. Optic (Greek, opto, to see). Pertaining to the sense of sight. Opticus (Latin) Optician. Optometer (Greek, ops, eye, metron, measure). Eye- measure; an instrument for measuring. the limits of direct vision. Organ (Greek, organon, an instrument). Any part of the body which is adapted to perform a particular service, such as the eye, etc. Oxide. A compound of oxygen and a base. Oxygen ( Greek, oxys, sharp, gennaein, to bring forth). gas forming one fifth part of our atmosphere, and essential to respiration. Panorama [Gre eek, pan, all, orama, view ]. A picture presenting from a central point a view of objects in every direction. It is lighted from above, and vigwed from a platform in the center. Pantoscopic, is the Greek name for double dhe is, OF so-called Franklin glasses. Papilla [Latin]. Minute projecting the termination of nerves, as on the tor retina. Parabola. A conic section ari Gon cutting a cone by a plane, parallel to one of its-&Nes. Paralysis [ Greek, paralyg,“to loosen, dissolve or weaken]. An abolition X functions of motion. Perimeter | Greek, | ut, metron, measure]. An instrument to measur field of vision. Periphery [Gr Qs. around; phero, to bear]. The circumference of Aefrcle. Periscopic ek per δ, ar ound, sko DEO, to look]. To , 1 m look ES replied to concavo-convex lenses. S ents, being also on the 246 HAND-BOOK FOR OPTICIANS. Phantasmagoria [Greek]. A magic lantern, or its representations. Phenomenon [Greek]. Anything visible, being pres- ented to the eye by observation or experiment; an ap- pearance whose cause is not immediately obvious. Photophobia [Greek, phos, light, phobeo, to dread]. Intolerance of light. | Pigment [ Latin, pingo, to paint]. Coloring-matter. Pince-nez | French, pincer, to press, nez, nose |. Pin- cers, eyeglasses. Polarization. A change produced upon light by the action of certain media, by which it exhibits the appear- ance of having polarity or poles, possessing different properties. Polyopsia (Greek, polys, much). Seeing more objects than are present. Presbyopia (Greek, presbys, old). Old sight. Punctum proximum [Latin]. The nearest point of dis- tinct vision. Punctum remotum. The distant point of distinct vision. Pupil [Latin, pupilla]. The central, round opening in the iris, through which light passes into th 6, Range of Vision. The horizontal dist at which the eye is still able to discern objects. Reflector [mirror]. A ορ ich the rays of an object are received by a mirroyNMd from it reflected to the magnifying ocular lens Reflex action. An invol&ntaTY action of the nervous system, by which an exte impression conducted by a sensory nerve is reflected Changed into a motor impulse. Refractor. A tel je in which the rays of an object are received and ιο») ed by a set, or row of refracting N lenses. Retina (Mt rete, a net). The membranous expan- sion of the ic nerve in the interior of the eyeball, which eke the impressions resulting in the sense of vision JEN Us. Inflammation of the retina. GLOSSARY. 247 Sclerotica [ Greek, skleros, hard]. The tough, fibrous outer coat of the eyeball; the visible portion is the ‘white of the eye.’’ Sensation ( Latin, sensus, sense). The conscious per- ception of an external impression by the nervous system ; a function of the brain. Spasm (Greek, spasmos, convulsion). A sudden vio- lent and involuntary contraction of one or more muscles, or muscular fibres. Spectroscope. An instrument to decompose light by means of prisms, which is used in the researches of Spectrum Analysis. Speculum (Latin). A mirror, either plane, convex or concave. Staphyloma (Greek, staphyle, a grape). A projection of some part of the eyeball, either of the cornea and iris (Staph. anterior), or of the sclerotica and choroid (Staph. posterior). Stenopwic Slit. A blackened metal plate with a narrow slit in the middle, to detect the faulty meridian of an astigmatic eye. Stereoscope (Greek, stereos, solid, skopeo, to see). An optical instrument for giving to pictures the ay AN nce of solid forms as in nature. NS Strabismus (Greek, strabos, twisted). AA σος of an eye. Striated (Latin, strio, to fusis eth channels ). Marked with fine parallel lines. Symptom (Greek, syn, with, ¥pto, to fall). A sign or token of disease. Tapetum (Latin, tapis vestry). A shining spot to the outer side of th nerve in the eyes of certain animals, due to the ce of pigment. Temple LatinCgrpus time, tempora, the temples). The part of theshead between the ears and the forehead; so-called begs the hair begins to turn white with age in that po of the scalp. SS » NS 248 HAND-BOOK FOR OPTICIANS. Tissue. Any substance or texture in the body formed of various elements; such as cells, fibres, bloodvessels, etc., interwoven with each other. Transparent (Latin, trans, through, pareo, to appear). Capable of allowing light to pass through. Transparent bodies can be seen throngh. Vein (Latin, vena). -Α vessel serving to convey the blood from the various organs toward the heart. Vibration (Latin, vibro, to move to and fro). Quick motion to and fro. Vision (Latin). The faculty or act of seeing external objects; the symbol is V. Vitality (Latin, vita, life). The state or quality of being full of life. Vitreous (Latin, vitrum, glass). Having the nature or appearance of glass. - INDEX. Aberration, chromatic, 102. T Spherical, 105. Accommodation, 119, 119, 145. Achromatic lenses, 104, 107. Achromatism, 102, 114, 191. Acuteness of vision, 90, 172. Aluminium, 20, 233. Ametropia, 117, 238. Anatomy of the eye, 108. Angle of incidence, 99, 141. Sc reflection, 141. a refraction, 99, $6 vision, 91. Aqueous humor, 109, 238. Artificial human eye, 156. Astigmatism, 134. Axis in cylinders, 48, 69. ** in pebbles, 35. ** of vision, 180, 183, 239. Base of prism, 44, 56. Binocular ophthalmoscope, 144, 223. Blind spot, 112. Brachymetropia, 127. Caloric rays, 162, 170. Camera obscura, 108, Candle, 169. Canthus, 159, 239. Caruncle, 159. Cataract, 148, 240. Choroid, 110, 112, 240, Chromatic aberration, 102, 105. Ciliary muscle, 113, 124. Coddington lens, 193, 204. Colors, 83, 100. 4 harmony of, 85. Combinations, converting, 50. Commissure, 110, Complementary colors, 85. Q Compound lenses, 53, 65. NC c dE measuring of, NY ef Jm use of, 146: Ó Conjunctiva, 111. Q Conversion of cross-cyliggers, 50. Coquille, 87, 242. N Cornea, 109, 111, 24 Corundum, 233. (ν Cross-cylinders, 49, 53. Crown glass, 24, 33, 36. Crystalline lens, 112, 136, 145, 240. dn * capsule of, 113. Crystals, single refracting, 34. * double 23 34. Cylindrical lenses, 47, 136. Decentered Lenses, 56. Dialytes, 107, 218, 941. Diamond Oil, 63. Diaphragm 105, 109, 241. Diffraction, 213, 241. Diopter, 11. Diploma, 124, Dispersion of light, 99, 103, 241. Double focus glasses, 76. Double refraction, 32, 34. Electric light, 166. Emission theory, 96. Emmetropia, 117, 242. Equivalents, 50, 140. Ether, 96, 166. Expressive eye, 182. Eyeball, 108. Ἂ Eyebrows, 179. xS Eye-killers, 14. Φ) Eyelashes, 180. Eyelids, 180. & Eye sharpeney, Facial expre Ὁ ns, 179. Fakes, (η Fling g 3, 106. Flu for drilling, 63. F , negative, positive, 16, 47, 242. Glass, pliable, 184. Glass, drilling, 63. Goggles, 77, 242. Qo ' xlin glasses, 77, 210. o Gas light, 167. Harmony of colors, 85. Height of lighthouses, 172. Hypermetropia, 117, 121. ce absolute, 124. ο latent, 123. : 250 HAND-BOOK FOR OPTICIANS. Inch system, 12. Incidence, angle of, 99. Index of dispersion, 36, 100. Index of refraction, 36, 40, 99. Injuries of eye, 152. Interference of light, 213. Invention of spectacles, 184. Inventions, 27, 198. Iris, 109, 242. Leech, artificial, 216. Lens, Arundel, 36. * cylindrical, 47, 135. * decentered. ὅθ. * human, 112, 114. * jnterchangeable, 58. * spherical, 46, 243. Lens measure, 43. Light, 96, 162. Luminosity of eye, 141. Macula lutea, 112, 116. Measurement of prisms, 43. Meniscus, 16, 243. Meridian, faulty, 138. Metric system, 12, 17. Microscope, 107, 192, 225, 243. Musce volitantes, 112, 244. : Muscles of eye, 57, 111. Mydriatic, 124, 140, 146. Myopia, 118, 126, 244, Myopia in distans, 132. Nachet, trial frame of, 49. Near-point, 119, 246. Normal eye, 116, 119, 122. Nose-guard, 73. Nose-pieces, 72. Oil-lamps, 167. Old sight, 119, 120. Opera glass, 195. Ophthalmoscope, 141, 245. Optical center and line, 55, 56. Q Optical scale, 100. O Optic nerve, 111. Opus majus, 186 Orbit of eye, 108. O Pantoscopic Β Q 78, 245. -axis, 35. δὶ Serie BBanges in eyes, 149 , English, 60. rbwightedness, 197. Petroleum light, 168, ὶ Pigment, 119, 246. ich Plane lens 40. t Polarization, 202, 219. » Polarizer, 34. it Presbyopia, 119. 5 t Prismometer, 44. | Prism, 41. k Progressive myopia, 129. Protection spectacles, 82. | Protractor, 42. H Pupil, black, 109, 111, 142. m Pupil, distance, 71. Pyramidal muscle, 176. 1 j Quality of lenses, 19, 23. Quartz, 20. i Radiating fibres, 113, Radiating heat, 165. Radius of curvature; 14. Range of vision, 90, 173, 246. » Recti muscles, 57, 132. | y Redressing frames, 88. Reflection, 141, 185. Reflector, 104, 246. Refraction, angle of, 99. e double, 34. ες index of, 96, 40, 99. Relief to injured eyes, 152. Retina, 110, 112, 116, 24 Rock crystals, 20, y Rods and cones Sclerotica, Second si Secreti tears, 176. flicium, 20. Snow blindness, 87. Spectrum, 56, 82, 100, 103. Split glasses, 78, Squint, 124, 132. Standard sizes of lenses, 58. Stanhope lens, 194. Staring look, 160, 181. Stenopaic slit, 87, 127, 247. Sties, 125, 136. Strabismus; 124, 247. Tears, 175. Telescope, oldest, 188. Temperature of Universe, 165. - Lp INDEX. 251 k Test-types, 99, 138. Vision, direct, 116, 287, 248. } Tinted glasses, 82. Vitreous humor, 112, 248. f Trial box or case, 66 * 'Trial frame, 49. Waterglass, 21. A | Waves, aerial, 100. 4 Undulatory theory of light, 90. | i ethereal, 100, 166. { et horizontal, vertical, 138 > Velocity of light, 97. Vibration, 97, 166. Yellow spot, 112. κ ay