The Progress of Invention in the Nineteenth Century Part 21

Multiplying the dimensions of the smallest cells to more than a thousand times their size, it has brought into range of vision an unseen world, developed new sciences, and added immensely to the stores of human knowledge. To the biologist and botanist it has yielded its revelations in cell structure and growth; to the physician its diagnosis in urinary and blood examinations; in histology and morbid secretions it is invaluable; in geology its contribution to the knowledge of the physical history of the world is of equal importance; while in the study of bacteriology and disease germs it has so revolutionized our conception of the laws of health and sanitation, and the conditions of life and death, and is so intimately related to our well being, as to mark probably the greatest era of progress and useful extension of knowledge the world has ever known. In the useful arts, also, it figures in almost every department; the jeweler, the engraver, the miner, the agriculturalist, the chemical manufacturer, and the food inspector, all make use of its magnifying powers.

To the microscope the art of photography has lent its valuable aid, so that all the revelations of the microscope are susceptible of preservation in permanent records, as photomicrographs. A curious, but very practical, use of the microscope was made in the establishment of the pigeon-post during the siege of Paris in 1870-71. Shut in from the outside world, the resourceful Frenchmen photographed the news of the day to such microscopic dimensions that a single pigeon could carry 50,000 messages, which weighed less than a gramme. These messages were placed on delicate films, rolled up, and packed in quills. The pigeons were sent out in balloons, and flying back to Paris from the outer world, carried these messages back and forth, and the messages, when reaching their destination, were enlarged to legible dimensions and interpreted by the microscope. It is said that two and a half million messages were in this way transmitted.

_The Spectroscope._--To the popular comprehension, the best definition of any scientific instrument is to tell what it does. Few things, however, so tax the credulity of the uninformed as a description of the functions and possibilities of the spectroscope. To state that it tells what kind of materials there are in the sun and stars, millions of miles away, seems like an unwarranted attack upon one's imagination, and yet this is one of the things that the spectroscope does. A few commonplace observations will help to explain its action. Every schoolboy has seen the play of colors through a triangular prism of gla.s.s, as seen in Fig.

198, and the older generation remembers the old-fas.h.i.+oned candelabras, which, with their brilliant pendants of cut gla.s.s cast beautiful colored patches on the wall, and whose dancing beauties delighted the souls of many a boy and girl of fifty years ago. This spread of color is called the _spectrum_, and it is with the spectrum that the spectroscope has to deal. The white light of the sun is composed of the seven colors: red, orange, yellow, green, blue, indigo, and violet. When a sunbeam falls upon a triangular prism of gla.s.s the beam is bent from its course at an angle, and the different colors of its light are deflected at different angles or degrees, and consequently, instead of appearing as white light, the beam is spread out into a divergent wedge shape, that separates the colors and produces what is called the spectrum. This discovery was made by Sir Isaac Newton, in 1675.

[Ill.u.s.tration: FIG. 198.--PRISM AND SPECTRUM.]

In 1802 Dr. Wollaston, in repeating Newton's experiments, admitted the beam of light through a very narrow slit, instead of a round hole, and noticed that the spectrum, as spread out in its colors, was not a continuous shading from one color into another, but he found black lines crossing the spectrum. These black lines were, in 1814, carefully mapped by a German optician, named Fraunhofer, and were found by him to be 576 in number. The next step toward the spectroscope was made by Simms, an optician, in 1830, who placed a lens in front of the prism so that the slit was in the focus of the lens, and the light pa.s.sing through the slit first pa.s.sed through the lens, and then through the prism. This lens was called the "Collimating" lens. With these preliminary steps of development, Prof. Kirchhoff began in 1859 his great work of mapping the solar spectrum, and he, in connection with Prof. Bunsen, found several thousand of the dark lines in the spectrum, and laid the foundation of _spectrum-a.n.a.lysis_, or the determination of the nature of substances from the spectra cast by them when in an incandescent state.

[Ill.u.s.tration: FIG. 199.--KIRCHHOFF'S FOUR-PRISM SPECTROSCOPE.]

The form of Kirchhoff's spectroscope is given in Fig. 199. The slit forming slide is seen on the far end of the tube A, and is shown in enlarged detached view on the right. The collimating lens is contained in the tube A. The beam of light entering the slit at the far end of the tube A, pa.s.ses through the lens in that tube, and then pa.s.ses successively through the four triangular prisms on the table, and is successively bent by these and thrown in the form of a spectrum into the telescopic tube B, and is seen by the eye at the remote end of said tube B. The greater the number of prisms the wider is the dispersion of the rays and the longer is the spectrum, and the more easily studied are the peculiar lines which Wollaston and Fraunhofer found crossing it. It was the presence of these black lines on the spectrum which led to the development of the spectroscope and established its significance and value. The work which the spectroscope does is simply to form an extended spectrum, but this spectrum varies with the different kinds of light admitted through the slit, the different kinds of light showing different arrangement of colored bands and dark lines, and such a definite relation between the light of various incandescing elementary bodies and their spectra has been found to exist, that the casting of a definite spectrum from the sun or stars indicates with certainty the presence in the sun or stars of the incandescing element which produces that spectrum. This application of the spectroscope is called _spectrum-a.n.a.lysis_, and by rendering any substance incandescent in the flame of a Bunsen burner, and directing the light of its incandescence through the spectroscope, its spectrum gives the basis of intelligent chemical identification. So delicate is its test that it has been calculated by Profs. Kirchhoff and Bunsen that the eighteen-millionth part of a grain of sodium may be detected.

The useful applications of the spectroscope are found princ.i.p.ally in astronomy and the chemical laboratory, but some industrial applications have also been made of it in metallurgical operations, as, for instance, in determining the progress of the Bessemer process of making steel, and also for testing alloys. Many hitherto unknown metals have also been discovered through the agency of the spectroscope, among which may be named caesium, rubidium, thallium, and indium.

The field of optics is so large that many interesting branches can receive only a casual mention. The polarization of light, first noticed by Bartholinus in 1669, and by Huygens in 1678, in experiments in double refraction with crystals of Iceland spar, were followed in the Nineteenth Century by the discoveries of Malus, Arago, Fresnel, Brewster, and Biot. Malus, in 1808, discovered polarization by reflection from polished surfaces; Arago, in 1811, discovered colored polarization; Nicol, in 1828, invented the prism named after him. The Kaleidoscope was invented by Sir David Brewster in 1814, and British patent No. 4,136 granted him July 10, 1817, for the same. The reflecting stereoscope was invented by Wheatstone in 1838, and the lenticular form, as now generally used, was invented by Sir David Brewster in the year 1849.

Among the more recent inventions of importance in optics may be mentioned the Fiske range finder (Patent No. 418,510, December 31, 1889), for enabling a gunner to direct his cannon upon the target when its distance is unknown, or even when obscured by fog or smoke. The Beehler solarometer (Patent No. 533,340, January 29, 1895), is also an important scientific invention, which has for its object to determine the position, or the compa.s.s error, of a s.h.i.+p at sea when the horizon is obscured. There is also in late years a great variety of entertaining and instructive apparatus in photography, and improvements in the stereopticon and magic lantern.

The most interesting of the latter is the Kinetoscope, for producing the so-called moving pictures, in which the magic lantern and modern results in the photographic art, have wrought wonders on the screen. The old-fas.h.i.+oned magic lantern projections were interesting and instructive object lessons, but modern invention has endowed the pictures with all the atmosphere and naturalness of real living scenes, in which the figures move and act, and the scenes change just as they do in real life.

The foundation principle upon which these moving pictures exist is that of persistence of vision. If a succession of views of the same object in motion is made, with the moving object in each consecutive figure changed just a little, and progressively so in a constantly advancing att.i.tude in a definite movement, and those different positions are rapidly presented in sequence to the eye in detached views, the figures appear to constantly move through the changing position. The theory of the duration of visible impressions was taught by Leonardo da Vinci in the fifteenth century, and practical advantage has been taken of the same in a variety of old-fas.h.i.+oned toys, known as the phenakistoscope, thaumatrope, zoetrope, stroboscope, rotascope, etc.

The phenakistoscope was invented by Dr. Roget, and improved by Plateau in 1829, and also by Faraday. A circular disk, bearing a circular series of figures is mounted on a handle to revolve. The figures following each other show consecutively a gradual progression, or change in position.

The disk has radial slits around its periphery, and is held with its figured face before a looking gla.s.s. When the reflection is viewed in the looking gla.s.s through the slits, the figures rapidly pa.s.sing in succession before the slits appear to have the movements of life. The thaumatrope, which originated with Sir John Herschel, consists of a thin disc, bearing on opposite sides two a.s.sociated objects, such as a bird and a cage, or a horse and a man. This, when rotated about its diameter, to bring alternately the bird and cage into view, appears to bring the bird into the cage, or to put the rider on the horse's back, as the case may be. The zoetrope, described in the _Philosophical Magazine_, January, 1834, employs the general principle of the phenakistoscope, except that, instead of a disc before a looking gla.s.s, an upright rotating drum or cylinder is employed, and has its figures on the inside, and is viewed, when rotating, through a succession of vertical slits in the drum.

The earliest patents found in this art are the British patent to Shaw, No. 1,260, May 22, 1860; United States patents, Sellers, No. 31,357, February 5, 1861, and Lincoln, No. 64,117, April 23, 1867. In Brown's patent, No. 93,594, August 10, 1869, the magic lantern was applied to the moving pictures, and Muybridge's photos of trotting horses in 1872, followed by instantaneous photography, which enabled a great number of views to be taken of moving objects in rapid succession, laid the foundation for the modern art.

[Ill.u.s.tration: SHOOTING GLa.s.s b.a.l.l.s.

FIRING DISAPPEARING GUN.

FIG. 200.]

In Fig. 200 is shown a succession of instantaneous photographs of a sportsman shooting a gla.s.s ball, and the firing of a disappearing gun. A multiplicity of views extending through all the phases of these movements, when successively presented in order, before a magic lantern projecting apparatus, gives to the eye the striking semblance of real movements. In practice these views are taken by special cameras, and are printed on long transparent ribbons that contain many hundreds, and even thousands of the views. Edison's Kinetoscope is covered by patent No.

493,426, March 14, 1893, and his instrument known as the Vitascope, is one of those used for projecting the views upon a screen. In Fig. 201 a similar instrument, called the Biograph, is shown, in which the seeming approach of the locomotive makes those who witness it shudder with the apparent danger.

[Ill.u.s.tration: FIG. 201.--BIOGRAPH IN THE THEATRE.]

To secure the best results, the ribbon with its views should remain with a figure the longest possible time between the light and the lens, and the s.h.i.+fting to the next view should be as nearly instantaneous as possible. This problem has been admirably solved by C. F. Jenkins, who, in 1894, devised means for accomplis.h.i.+ng it, and was one of the first, if not the first, to successfully project the views on a large screen adapted to public exhibitions. His apparatus is shown in Fig. 202. An electric motor, seen on the left, drives, through a belt and pulley, a countershaft, and also through a worm gear turns another shaft parallel to the countershaft, and bearing a sprocket pulley, whose teeth penetrate little marginal holes in the ribbon of views, and, drawing it down from the reel above, deliver it to the receiving reel on the right.

On the end of the countershaft, just in front of the sprocket wheel, is a revolving crank pin or spool, which intermittently beats down the ribbon of views, causing the latter to advance through the vertical guides in front of the lens by a succession of jerks. This holds each view for a maximum period before the lens, and then suddenly jerks the ribbon to bring the next view into position. In the Kinetoscope the animated pictures not only present the movements of life, but, by a combination with the phonograph, the audible speech, or music fitting the occasion, is also presented at the same time, making a marvelous simulation of real life to both the eye and the ear.

[Ill.u.s.tration: FIG. 202.--JENKINS' PHANTASCOPE.]

Among the latest promises of the inventor is the "Distance Seer," or telectroscope, which, it is said, enables one to see at any distance over electric wires, just as one may telegraph or telephone over them.

The surprises of the Nineteenth Century have been so many and so astounding, and the principles of this invention are so far correct, that it would be dogmatic to say that this hope may not be realized.

To the sum total of human knowledge no department of science has contributed more than that of optics. With the telescope man has climbed into the limitless s.p.a.ce of the heavens, and ascertained the infinite vastness of the universe. The flaming sun which warms and vitalizes the world, is found more than ninety millions of miles away. The nearest fixed stars visible to the naked eye are more than 200,000 times the distance of the sun, and their light, traveling at the rate of 190,000 miles a second, requires more than three years to reach us. Although so far away, their size, distance, and const.i.tution have been ascertained, and their movements are scheduled with such accuracy that the going and coming thereof are brought to the exactness of a railroad time table.

The astronomer predicts an eclipse, and on the minute the spheres swing into line, verifying, beyond all doubt, the correctness of the laws predicated for their movements. The wonders of the telescope, the microscope, and the spectroscope are, however, but suggestions of what we may still expect, for science abundantly teaches that the eye may yet see what to the eye is now invisible, and that light exists in what may now seem darkness.

No man may say with certainty what thought was uppermost in Goethe's mind when, grappling in the final struggle with the King of Terrors, he exclaimed "Mehr licht!" It may be that it was but the wish to dispel the gathering gloom of his dimming senses, or perchance the unfolding of an illuminated vision of a brighter threshold, but certain it is that no words so voice the aspirations of an enlightened humanity as that one cry of "More light!"

CHAPTER XXIV.

PHOTOGRAPHY.

EXPERIMENTS OF WEDGEWOOD AND DAVY--NIePCE'S HELIOGRAPHY--DAGUERRE AND THE DAGUERREOTYPE--FOX TALBOT MAKES FIRST PROOFS FROM NEGATIVES--SIR JOHN HERSCHEL INTRODUCES GLa.s.s PLATES--THE COLLODION PROCESS--SILVER AND CARBON PRINTS--AMBROTYPES--EMULSIONS--DRY PLATES--THE KODAK CAMERA--THE PLATINOTYPE--PHOTOGRAPHY IN COLORS-- PANORAMA CAMERAS--PHOTO-ENGRAVING AND PHOTO-LITHOGRAPHY--HALF TONE ENGRAVING.

"Art's proudest triumph is to imitate nature."

When nature paints she does so with the brush of beauty, dipped in the pigment of truth. The tender affection of a ray of light touches the heart of a rose, brings a blush to its cheek, and life, becoming the bride of chemical affinity, blooms into surpa.s.sing beauty and loveliness. Photography is closely allied to nature's painting, for just as light brings into existence nature's living beauties, so does light fix, preserve, and perpetuate these beauties by the same subtile and mysterious agency of a quickened chemical affinity. Photography is both an art and a science, and as such is both beautiful and true. It is an art intimately a.s.sociated with the tenderest affections of the human heart in keeping alive its precious memories. By it the youthful sweetheart of long ago, the loving face of the departed mother, and the cherished form of the dead child are brought back to us in familiar presence, while our great men have become the every-day friends and ideals of the common people. What an enrichment and satisfaction it would have added to our lives if the art had been coeval with history, and all the world's exalted scenes and faces had come to us through the camera with the knowledge of absolute truth and fidelity. But not only in portraiture is photography a great art, for it catches the stately pose of the mountain, the grandeur of the sea, the beauty of the forest, or the majesty of Niagara Falls, and brings them all home to us, even to the vision of the bed-ridden invalid. The camera alike records the secrets of the starry heavens and the bacteria of the microscopic world.

Hanging on the tail of a kite it photographs the face of mother earth, and, acting quicker than the lightning, it catches and defines the path of that erratic flash. It plays the part of a private detective, and its testimony in court is never doubted. The architect, engineer, and ill.u.s.trator find it in constant requisition. By the aid of the Roentgen Rays, it locates a bullet in a wounded soldier, and takes a picture of one's spinal column. In fact, it sees and records things both visible and invisible, acts with the rapidity of thought, and is never mistaken.

The art of photography, named from the two Greek words f?t?? ??af? (the writing of light), is a comparatively new one, and belongs entirely to the Nineteenth Century. It was known to the ancient alchemists that "horn silver" (fused chloride of silver) would blacken on exposure to light, but there was neither any clear understanding of the nature of this action, nor any application made of it prior to the year 1800. We now know that the art of photography is dependent upon the actinic effect of certain of the rays of the spectrum upon certain chemical salts, notably those of silver and chromic acid, in connection with organic matter. The rays which have this effect are the blue and violet rays at one end of the spectrum, and even invisible rays beyond the violet, the red and yellow rays having little or no such actinic effect.

That which made photography possible for the Nineteenth Century was the philosophical observation of Scheele, in 1777, upon the decomposing influence of light on the salts of silver, and the superior activity of the violet rays of the spectrum over the others in producing this effect. In 1801 Ritter proved the existence of such invisible rays beyond the violet end of the visible spectrum by the power they possessed of blackening chloride of silver.

_Earliest Application of Principles._--The first attempt to render the blackening of silver salts by light available for artistic purposes, was made by Wedgewood and Davy in 1802. A sheet of white paper was saturated with a solution of nitrate of silver, and the shadow of the figure intended to be copied was projected upon it. Where the shadow fell the paper remained white, while the surrounding exposed parts darkened under the sun's rays. There was, however, no means of fixing such a picture, and in time the white parts would also turn black.

_Introduction of Camera._--The camera obscura, a very old invention designed for the use of artists in copying from nature, was at a very early period brought into this art, but it was found that the chemicals employed by Wedgewood and Davy were not sufficiently sensitive to be affected by its subdued light. In 1814, however, Joseph Niceph.o.r.e Niepce, of Chalons, invented a process that utilized the camera, and which was called "Heliography," or sun drawing. In 1827 he discarded the use of silver salts, and employed a resin known as "Bitumen of Judea" (asphaltum). A plate was coated with a solution of this resin and exposed. The light acting upon the plate rendered the resin insoluble where exposed, and left it soluble under the shadows. Hence, when treated with an oleaginous solvent the shadows dissolved out, and the lights, represented by the undissolved resin, formed a picture, which was in reality a permanent negative. The process, however, was slow, requiring some hours.

_The Daguerreotype._--In 1829 Niepce and Daguerre became partners, and in 1839, after the death of the elder Niepce, the process named after Daguerre was perfected (British patent No. 8,194, of 1839). He abandoned the resin as a sensitive material, and went back to the salts of silver.

He employed a polished silver surfaced plate, and exposed it to the action of the vapors of iodine, so as to form a layer of iodide of silver upon the surface, which rendered it very sensitive. By a short exposure in the camera an effect was produced, not visible to the eye, but appearing when the plate was subjected to the vapor of mercury. This process reduced the time required from hours to minutes, and as it involved the production of a latent image, which was subsequently developed by a chemical agent, it represented practically the beginning of the photographic art as practiced to-day. Daguerre sought also to permanently fix his pictures, but this was accomplished only imperfectly until 1839, when Sir John Herschel made known the properties of the hyposulphites for dissolving the salts of silver. In 1844 Hunt introduced the protosulphate of iron as a developer.

_Production of Positive Proofs from Negatives._--This was first done by Mr. Fox Talbot, of England, between 1834 and 1839. In his first communication to the Royal Society, in January, 1839, it was directed that the paper should be dipped first in a solution of chloride of sodium, and then in nitrate of silver, which, by reaction, produced, on the face of the paper, chloride of silver, which was more sensitive to the light than nitrate of silver. The object to be reproduced was laid in contact with the prepared paper, and exposed to the light until a copy was produced which was a negative, having the lights and shadows reversed. A second sheet was then prepared, and the first or negative impression was laid upon it, and used as a stencil to produce a second print which, by a reversal of the lights and shadows, formed an exact reproduction of the original. In 1841, British patent No. 8,842 was obtained by Mr. Talbot, for what he called the "Calotype," and which was afterward known as the "Talbotype." A sheet of paper was first coated with iodide of silver, by soaking it alternately in iodide of pota.s.sium and nitrate of silver, and was then washed with a solution of gallic acid containing nitrate of silver, by which the sensitiveness to light was increased. An exposure of some seconds or minutes, according to the brightness of the light, produced an impression upon the plate, which, when treated with a fresh portion of gallic acid and nitrate of silver, developed into the image. After being fixed it formed a negative from which any number of prints might be obtained. The Talbot process represented a great advance in this art. Gla.s.s plates to retain the sensitive film were introduced by Sir John Herschel in 1839, and were a great improvement over the paper negatives, which latter, from lack of transparency and uniformity in texture, had prevented fine definition and sharpness of outline. Blue printing was also invented by Sir John Herschel in 1842, and he was the first to apply the term "negative" in photography. In 1848 M. Niepce de St. Victor, a nephew of Daguerre's former partner, applied to the gla.s.s a film of alb.u.men to receive the sensitive silver coating.

_Collodion Process._--The most important step in the preparation of the negative was the application of collodion. This is a solution of pyroxilin in ether and alcohol, which rapidly evaporates and leaves a thin film adhering to the gla.s.s. M. Le Gray, of Paris, was the first to suggest collodion for this purpose, but Mr. Scott Archer, of London, in 1851, was the first to carry it out practically. A clean plate of gla.s.s is coated with collodion sensitized with iodides of pota.s.sium, etc., and is then immersed in a solution of nitrate of silver. Metallic silver takes the place of pota.s.sium, forming insoluble iodide of silver on the film. The plate is then exposed and the latent image developed by an aqueous solution of pyrogallic acid, or protosulphate of iron. When sufficiently developed, the plate is washed, and the image fixed by dissolving the unacted-upon iodide of silver with a solution of cyanide of pota.s.sium or hyposulphite of soda. This completed the negative or stencil from which the positives are printed by pa.s.sing rays of light through it upon sensitive paper.

_The Ambrotype_ succeeded the Daguerreotype, and was produced by making a very thin negative by under exposure on gla.s.s, using the collodion process, and, after drying, backing the gla.s.s with black asphaltum varnish or black velvet, causing the dense portions of the negative to appear white by reflected light, and the transparent portions black.

Such pictures were quickly made, and were much in vogue forty years ago, but are now obsolete. A modification of the ambrotype, however, still survives in what is known as the "tin-type" or "ferro-type." In the tin-type the collodion picture is made directly upon a very thin iron plate, covered with black enamel, which both protects the plate from the action of the chemicals in the bath, and forms the equivalent of the black background of the ambrotype.

_Silver Printing._--A sheet of paper, previously treated with a solution of chloride of sodium and dried, is sensitized in an alkaline bath of nitrate of silver. When the paper is exposed under a negative, the light through the transparent parts of the negative reduces the silver, converting the chloride, it is supposed, into a metallic sub-chloride of silver which becomes dark or black, and const.i.tutes the main portion of the picture. The image is then fixed by dissolving out the chloride of silver unaltered by light in a bath of hyposulphite of soda. After fixation, the image is well washed in several changes of water to eliminate all traces of the hyposulphite of soda and prevent the subsequent fading of the darkened portions of the picture and the yellowing of the whites. If the printed image is immediately fixed, it will have a red color. To avoid this it is washed first in water and then immersed in a chloride of gold toning bath and fixed.

_The Platinotype Process_ is one in which pota.s.sium chloroplatinite and ferric oxalate are converted by light into the ferrous state, and metallic platinum is reduced when in contact with the ferrous oxalate of potash solution. The unacted upon portions are dissolved out by dilute hydrochloric acid, leaving a black permanent image. This process is characterized by simplicity, sensitiveness in action, permanence of print, and a peculiarly soft and artistic quality in the picture.

British Patent No. 2,011, of 1873, to Willis, is the first disclosure of the platinotype.

_Carbon Printing_ is a process in which lampblack or other indestructible pigment is mixed with the chemicals to render the photograph more stable against fading from the gradual decomposition of its elements. Mungo Ponton, in 1838, discovered the sensitive quality of pota.s.sium b.i.+.c.hromate, which led up to carbon printing. Becquerel and Poitevin, in Paris, in 1855, were the first to experiment in this direction, and Fargier, Swan, and Johnson were successors who made valuable contributions.

_Emulsions._--A photographic emulsion is a viscous liquid, such as collodion or a solution of gelatine, containing a sensitive silver salt with which the gla.s.s plate is at once coated, instead of coating the plate with collodion or gelatine, and then immersing it in a sensitizing bath. The desirability of emulsions was recognized as early as 1850 by Gustave Le Gray, and in 1853 by Gaudin. Collodion emulsion with bromide of silver was invented by Sayce and made known in 1864. In 1871 Maddox published his first notice of gelatine emulsion, and in 1873 the gelatine emulsions of Burgess were advertised for sale. In 1878 Mr.

Charles Bennett brought out gelatino-bromide emulsion of extreme sensitiveness, by the application of heat, and from this time gelatine began to supersede all other organic media.

_Dry Plates_ were a great improvement over the old wet process, with its tray for baths, its bottles of chemicals, and other accessories.

Especially was this the case with out of door work, which heretofore had involved the carrying along of much unwieldy and inconvenient paraphernalia. With the dry plate process only the camera and the plates were needed, and this step marks the beginning of the spread of the art among amateurs, and the great snap-shot era of photography, growing into a distinct movement about the year 1888, has since spread over the entire world. The first practical dry plate process (collodion-alb.u.men) was published in 1855 by Dr. J. M. Taupenot, a French scientist.

Russell, in 1862; Sayce, in 1864; Captain Abney, for photographing the transit of Venus in 1874; Rev. Canon Beechey, of England, in 1875; Prof.