“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 surpassing 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 associated 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 illustrator 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 NicÉphore NiÉpce, of ChalÔns, 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 NiÉpce and Daguerre became partners, and in 1839, after the death of the elder NiÉpce, 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 potassium 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. Glass 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. NiÉpce de St. Victor, a nephew of Daguerre’s former partner, applied to the glass a film of albumen 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 glass. 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 glass is coated with collodion sensitized with iodides of potassium, etc., and is then immersed in a solution of nitrate of silver. Metallic silver takes the place of potassium, 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 potassium or hyposulphite of soda. This completed the negative or stencil from which the positives are printed by passing 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 glass, using the collodion process, and, after drying, backing the glass 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 constitutes 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 potassium 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 potassium bichromate, 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 glass 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-albumen) 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. John W. Draper, of the University of New York, and the Eastman Walker Company, of Rochester, were the chief promoters of dry plate photography. The practical introduction began about 1862 with the application of the alkaline developer.

The progress of the photographic art may be approximately noted as follows:

Mechanical Development.—The photographic camera is but an adaptation of the optical principles of the old camera obscura, which has been credited to various persons, including Roger Bacon in 1297, Baptista Porta about 1569, and others. The essential elements of the camera obscura are a dark chamber, having in one end a perforation containing a lens, and opposite it on the back of the chamber a screen upon which an image of the object is projected by the lens for the purpose of enabling it to be directly traced by a pencil. The photographic camera, introduced by Daguerre in 1839, adds to the camera obscura some means for adjusting the distance between the lens and the screen on which the image falls. This was accomplished by making the dark chamber adjustable in length by forming it in two telescopic sections sliding over each other, and in later years by the well-known bellows arrangement. A luminous image of any object placed in front of the lens is thrown in an inverted position upon the screen, which is of ground glass, to permit the image to be seen in focusing. When the proper focus on this ground glass is obtained a sensitive plate is put in the plane of this screen to receive the image.

It is not possible to trace all the steps of development of the camera which have brought it to its present perfection. Most of the improvements have had relation to the lens in correcting chromatic and spherical aberration, and in shutters for regulating exposure, in stops for shutting out the oblique rays and holders for the sensitive plate.

The “Iris” shutter, so-called from its resemblance in function to the iris of the eye, consists of a series of tangentially arranged plates which open or close a central opening symmetrically from all sides.

The ordinary camera of the photographic artist is too familiar an object to require special illustration. It has been looked into by the rich and the poor, and the high and the low, all over the whole world. Between the traveling outfit, and the “look pleasant, please!” of the peripatetic artist, and the handsome studios of the cities, it is hard to find an individual in the civilized world who has not posed before its lens. Through its agency the great man of the day has found himself in evidence everywhere; the country maiden has many times experienced the delicious thrill of satisfied vanity as she posed before it, and the superstitious savage is paralyzed with fear lest the mysterious thing should steal his soul.

In 1851 the first instantaneous views were made by Mr. Cady and Mr. Beckers, of New York, and also by Mr. Talbot, who employed as a flash light a spark from a Leyden jar. In 1864 magnesium light was employed by Mr. Brothers, of Manchester, for photographic purposes, and about 1876-8 Van der Weyde made use of the electric light for the same purpose.

The roller slide, or roll film, was invented by A. J. Melhuish, in England, in 1854 (British patent No. 1,139, of 1854). The films were, however, of paper. In 1856 Norris produced sensitized dry films of collodion or gelatine (British patent No. 2,029, of 1856). In later years apparatus for utilizing the roll film has been greatly improved and extensively applied by Eastman, Walker & Co., of Rochester, N. Y.About 1888 a new thing in the photographic world made its appearance. It was a little black leather-covered rectangular box, about six inches long, with a sort of blind eye at one end closed by a cylindrical shutter, substantially as seen in Fig. 203. This shutter was wound up by a spring operated by a pull cord. In the back of the box was a film or ribbon of sensitized paper wound upon one spool, and unwinding therefrom and winding onto another spool, and being distended as it passed so as to form a flat surface which was directly in rear of the lens. A thumb piece or key on the top, and a push button on the side, were the only suggestions of the operative mechanism within. When the button was pressed the shutter for an instant passed from in front of the lens, and as quickly covered it again, but in this brief interval an image had been flashed upon the sensitive ribbon or film, and a snap-shot picture was taken. By a simple movement of the thumb piece or key, the receiving roll was made to take up the exposed section of the sensitive film and bring another section into the range of the lens, for a repetition of the operation. This little instrument was slung in a case looking like a cartridge box, and its sensitive roll was able to receive 100 successive pictures. When the roll was exhausted, it was removed and developed in a dark room. The device was placed upon the market by the Eastman Company, and it was called the “Kodak.” The advertisement of the company, that “You press the button and we do the rest,” was soon realized to be founded in fact, and in a short while the great era of snap-shot photography had set in. To-day this form of camera is a part of the luggage of every tourist, traveler, scientist, and dilletante. In fact, it has become the familiar scientific toy of man, woman, and child, interesting, instructive, and useful to all. In Fig. 204 is shown a modern form of Kodak, which is made in various sizes and is foldable for compact and convenient portability.

A very convenient and useful development in films is to be found in the cartridge system, by which the film may be placed in and removed from the camera in broad daylight. The film has throughout its length a backing of black paper which extends far enough beyond the ends of the film to allow it to be unwound, so far, in making connection with the roll holder, without exposing the film to light, and also to allow it to be removed without exposure to light, after all the exposures have been made.

Among the many other ingenious and useful hand cameras may be mentioned the “Premo,” made by the Rochester Optical Company, and shown in Fig. 205. The “Premo” is arranged for either snap-shot or time exposure, is adapted to be either held in the hand or mounted upon a tripod, and is furnished for use either with glass plates or roll films. In Fig. 206 is shown the “Premo” for stereoscopic work, in which two pictures are taken at once, a sufficient distance from each other to produce the effect of binocular vision and give the appearance of relief when viewed through the stereoscope. Brett’s British patent No. 1,629, of 1853, appears to be the earliest description of a stereoscopic camera.

There have been 2,000 United States patents granted in photography, most of which have been taken in the past thirty years, and great efficiency and detail in both the chemical and mechanical branches of the art have been obtained.

The useful applications of the art have been numerous and varied. Portrait making is probably the largest field. This was first successfully accomplished in 1839 by Professor Morse, of telegraph fame, working with Prof. John W. Draper, of the University of New York.

Celestial Photography began with Prof. Draper’s photograph of the moon in March, 1840, and Prof. Bond, of Cambridge, Mass., in 1851. In 1872 Prof. Draper photographed the spectra of the stars, and in 1880-81 the nebulÆ of Orion, and in 1887 the Photographic Congress of Astronomers of the World, organized in Paris, began the work of photographing the entire heavens. In late years notable work has been done at the Lick Observatory by Prof. Holden. In 1861 Mr. Thompson, of Weymouth, photographed the bottom of the sea, and Prof. O. N. Rood, of Troy, N. Y., the same year described his application of it to the microscope. In 1871 criminals were ordered to be photographed in England, and in America the Rogues’ Gallery became an institution in New York as early as 1857, ambrotypes being first used. In 1876 the Adams Cabinet for holding and displaying the photos was invented. To-day the New York collection amounts to nearly 30,000, while that of the National Bureau of Identification at Chicago approximates 100,000. It is a striking illustration of the law of compensation that the counterfeiter who invokes the aid of photography to copy a bank note is, by the same agency of his photo in the Rogues’ Gallery, identified and convicted.Photography in Colors has been the goal of artists and scientists in this field for many years. Robt. Hunt, in England, in 1843, and Edmond Becquerel, in France, in 1848, made evanescent photographs in colors, but little progress was made until about the last decade of the Nineteenth Century. Franz Veress in 1890, F. E. Ives (United States patent No. 432,530, July 22, 1890), W. Kurtz (United States patent No. 498,396, May 30, 1893), Gabriel Lippmann in 1892 and 1896, Ives in 1892, M. LumiÈre in 1893, Dr. Joly in 1895, M. Villedien Chassagne, and Dr. Adrien, M. Dansac and M. Bennetto, all in 1897, represent active workers in this field.

Among recent developments of the camera may be mentioned the wide angle lens, which permits larger images to be made on the plate from small near-by objects, and the telephotographic camera, which gives a large image of remote objects, such as an enemy’s fort, and the panorama camera, which is designed to cover a broad field. For this purpose the lens is movably mounted for a semi-circular swing, and the image is flashed across a curved film in the case. The Eastman Panoram-Kodak, seen in Fig. 207, is an external illustration of this type, and in Fig. 207A is shown a sectional view of another make of panorama camera which clearly shows the internal construction.

As allied branches of the photographic art, photo-engraving, photo-lithographing, and half-tone engraving are important developments of the Nineteenth Century.Photo-engraving is a process by means of which photographs may be used in forming plates from which prints in ink can be taken. The process depends upon the property possessed by bichromate of potassium, and other chemicals, of rendering insoluble under the action of light, gelatine or some similar substance. A picture is thus produced on a metal plate, and the blank spaces are etched out by acid, leaving the lines in relief as printing surfaces. When the operation is reversed, and only the darks are etched in intaglio, to be filled with ink, as in copper-plate engraving, it is called photo-gravure. Mungo Ponton, in 1839, discovered the sensitive quality of a sheet of paper treated with bichromate of potash. In 1840 Becquerel discovered that the sizing had an important function, and Fox Talbot, in 1853, discovered and utilized the insolubility of gelatine exposed to light in presence of bichromate of potash. In 1854 Paul Pretsch observed that the exposed parts of the gelatine did not swell in water. One of the first suggestions of photo-engraving appears in the British patent No. 13,736, of 1851, of James Palmer. In recent times great perfection in details has been obtained by Mr. Moss, of the Photo-Engraving Company, and others. The Albert-type and Woodbury-type are early modifications of this art.

In photo-lithography the photograph is transferred to the stone, and the latter then used to print from, as in lithography. The operation consists: 1, in making the photographic negative; 2, printing with it upon transfer paper coated with gelatine and bichromate of potash: 3, the transfer paper is then given a coat of insoluble fatty transfer ink from an inking stone; 4, all ink on surfaces not reached by the light being on a soluble surface is washed off, leaving the insoluble lines acted upon by light forming the picture; 5, the washed transfer sheet is then applied to the stone, and the remaining inked lines of the design are transferred to the stone; 6, the stone with transferred lines will now receive ink from the ink rolls on these lines, and repels ink from all other surfaces, which latter are made repellent by being kept constantly wet, as in ordinary lithography. The first attempts in this art were by Dixon, of Jersey City, and Lewis, of Dublin, in 1841, who used resins. Joseph Dixon, in 1854, was the first to use organic matter and bichromate of potash upon stone to produce a photo-lithograph. In 1859 J. W. Osborne patented in Australia, and in 1861 in the United States, a transfer process which gave such great impetus to the art that he may be considered its founder and chief promotor. His United States patents are No. 32,668, June 25, 1861, and No. 33,172, August 27, 1861.

For photo-lithography only line drawing, type print, or script, without any smooth shading, can be employed. The most extensive application of photo-lithography is in the reproduction of the Patent Office drawings, which amount to about 60,000 sheets weekly. The contracting firm, which is probably the largest in the world, also prints each week by photo-lithography 7,000 copies of the Patent Office Gazette, of about 165 pages each, including both drawings and claims, and also reproduces specifications without errors or proof reading, thus saving about 200 per cent. in cost over type setting. This art is also largely employed for printing maps, and the reproduction of the pages of books by this process has flooded the stores and news stands with cheap literature.

Half-tone engraving enables a photograph to be reproduced on a printing press, and for faithfulness in reproduction and low cost has revolutionized the art of illustrating, as nearly all books, magazines, and newspapers are now illustrated by this process. Before its introduction it was not possible to reproduce cheaply in printers’ ink shaded pictures like photographs, brush drawings, paintings, etc. Half-tone engraving renders it possible to thus print on a press, with printers’ ink, reproductions of photographs or any shaded picture, in which the soft shadows fade away in depth to white by an imperceptible tenuity. It does so by breaking up the soft shadows into minute stipples which form inkable printing faces in relief, by the interposition of a fine reticulated screen between the camera lens and the sensitive plate. This forms a sort of stencil negative through which the copper plate is etched, which latter is thus converted into a relief plate whose raised surfaces left by the etching may receive ink and print like an ordinary relief plate. By making the screen lines very fine (80 to 250 meshes to the inch), the visible effect of the shading is so far preserved that the photograph may be reproduced in printers’ ink with but little depreciation. At first, bolting cloth was used for the screen, but at present two glass plates, with closely ruled lines, laid crosswise upon each other, form the screen. A characteristic distinction of half-tone work is the regularly stippled surface, formed by the stenciling out of a portion of the picture by the screen, which may be easily seen with any magnifying glass. It is called half-tone process because half of the tones or shadows are preserved, the other half being stenciled out. The use of gauze screens was first described by Fox Talbot in British patent No. 565, October 29, 1852.

In the making of a half-tone negative, the photograph, painting, or wash drawing which is to be reproduced, is set up in front of the camera, which is arranged on an inclined runway, as seen in Fig. 208, and an exposure is made on a plate prepared by the wet collodion process (see page 304). The shadows of the picture are broken up into stipples or dots by the interposition of a cross-lined screen arranged in the plate holder between the lens and the sensitive plate, so that the picture taken is “half-toned” or stippled. Fig. 209 illustrates the relation of the parts, in which the picture to be copied is seen on the right, the camera lens in the middle, and the cross-lined screen on the left in front of the sensitive plate.

The image on the plate is then developed and fixed, and in order to secure a printed image exactly like the copy as to right and left position it is necessary to reverse the negative. This is done by cutting the film square, as seen in Fig. 210, and then peeling it off the glass, as seen at Fig. 211, and transferring it to another glass plate in reversed relation. The copper printing plate is produced as follows: The plate is first polished, as seen at the top of Fig. 213, and is then sensitized with a solution of organic matter and an alkaline bichromate. The face of the reversed negative is laid flat against and in direct contact with the face of the sensitized copper plate, and tightly held thereto by the screw clamps of the half tone printing frame. The printing on the sensitized copper face through the stippled or half-tone negative is then effected either by daylight or by the electric light. The application of the electric light for this purpose is shown in Fig. 212. The copper plate is then taken out and subjected to the three lower operations seen in Fig. 213. It is first developed under a stream of water from a faucet, seen on the left, and is then taken in a pair of pliers and held over a gas stove, as seen at the bottom, to “burn-in” the image, and then placed in a tray containing an etching bath of chloride of iron seen on the right, by which the copper is eaten away around the little stipples, and the latter, representing the half tones of the original picture, are left raised, or in relief, to form the inkable surfaces of the printing plate. So fine are these stipples, however, that the picture is to the eye perfectly reproduced. The several views illustrating this process are made in this way, the lines of the reticulated screen being 175 to the inch. The plate is next subjected to the mechanical operation of “routing out” or cutting away the undesirable portions by a routing machine, seen in Fig. 214. It then receives further mechanical treatment to correct imperfections and finish its edges, and is finally mounted upon a block ready for the printer.

The most striking application made of photography in recent years is in the production of so-called moving pictures, in which a series of photographic figures thrown upon the screen have all the motion of animated scenes which have been caught and imprisoned by the swiftly acting and never failing memory of the camera, to be again turned loose in active play through the Kinetoscope or Biograph. Perhaps the most valuable contribution to science at the end of the century made by this art is in surgery, for photographing through opaque bodies by the aid of the Roentgen rays, but for the latter subjects treatment in separate chapters must be reserved.