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:

_Process._ _Time Required._ _Introduced._ Heliography 6 hours' exposure 1814 Daguerreotype 30 minutes' exposure 1839 Calotype or Talbotype 3 minutes' exposure 1841 Collodion process 10 seconds' exposure 1851 Collodion emulsion (dry plate) 15 seconds' exposure 1864 Gelatine emulsion (dry plate) 1 second exposure 1878

_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 gla.s.s, to permit the image to be seen in focusing. When the proper focus on this ground gla.s.s is obtained a sensitive plate is put in the plane of this screen to receive the image.

[Ill.u.s.tration: FIG. 203.--KODAK.]

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 ill.u.s.tration. 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 superst.i.tious savage is paralyzed with fear lest the mysterious thing should steal his soul.

[Ill.u.s.tration: FIG. 204.--FOLDING KODAK.]

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 pa.s.sed 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 b.u.t.ton on the side, were the only suggestions of the operative mechanism within. When the b.u.t.ton was pressed the shutter for an instant pa.s.sed 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 repet.i.tion 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 advertis.e.m.e.nt of the company, that "You press the b.u.t.ton 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.

[Ill.u.s.tration: FIG. 205.--HAND PREMO.]

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 gla.s.s 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.

[Ill.u.s.tration: FIG. 206.--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, Ma.s.s., in 1851. In 1872 Prof. Draper photographed the spectra of the stars, and in 1880-81 the nebulae 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 inst.i.tution 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 ill.u.s.tration 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. Lumiere in 1893, Dr. Joly in 1895, M. Villedien Cha.s.sagne, and Dr.

Adrien, M. Dansac and M. Bennetto, all in 1897, represent active workers in this field.

[Ill.u.s.tration: FIG. 207.--PANORAM-KODAK.]

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 ill.u.s.tration of this type, and in Fig.

207A is shown a sectional view of another make of panorama camera which clearly shows the internal construction.

[Ill.u.s.tration: FIG. 207A.--SECTIONAL PLAN OF PANORAMIC CAMERA.]

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 pota.s.sium, 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 s.p.a.ces 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.

[Ill.u.s.tration: FIG. 208.--PHOTOGRAPH GALLERY.]

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.

[Ill.u.s.tration: FIG. 209.--DIAGRAM SHOWING PRODUCTION OF DOT.]

_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 ill.u.s.trating, as nearly all books, magazines, and newspapers are now ill.u.s.trated 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 gla.s.s 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 gla.s.s. 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.

[Ill.u.s.tration: FIG. 210.--Tr.i.m.m.i.n.g FILM.]

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 ill.u.s.trates 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.

[Ill.u.s.tration: FIG. 211.--STRIPPING FILM.]

[Ill.u.s.tration: FIG. 212.--PRINTING BY ELECTRIC LIGHT.]

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 gla.s.s, as seen at Fig. 211, and transferring it to another gla.s.s 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 ill.u.s.trating 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.

[Ill.u.s.tration: FIG. 213.--TREATMENT OF COPPER PLATE.]

[Ill.u.s.tration: FIG. 214.--ROUTER AT WORK ON HALF-TONE PLATE.]

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.

CHAPTER XXV.

THE ROENTGEN OR X-RAYS.

GEISSLER TUBES--VACUUM TUBES OF CROOKES, HITTORF AND LENARD--THE CATHODE RAY--ROENTGEN'S GREAT DISCOVERY IN 1895--X-RAY APPARATUS-- SALVIONI'S CRYPTOSCOPE--EDISON'S FLUOROSCOPE--THE FLUOROMETER--SUN BURN FROM X-RAYS--USES OF X-RAYS.

The majority of people have been accustomed to regard light as something to be excluded and controlled by opaque screens just as effectively as rain is excluded by a tin roof, or cold is kept out by a brick wall. The shady retreat furnished relief from the garish day to the primitive man, and the opaque shades and Venetian blinds of modern civilization exclude the excess of light at our windows. Sunshine and shadow have, in fact, been correlated conditions to the ordinary observation of man since time began. The last few years of the Nineteenth Century, however, were to witness the discovery of a new kind of light ray which, in its behavior, subverted all previous conception of the nature and action of light. It was a species of electric light, which we are accustomed to regard as brilliant, but this light ray was invisible to the eye. It could not be refracted or bent from its course by a prism or lens, and it was so subtle, penetrating and insidious, that it could not be barred out like sunlight, but pa.s.sed readily through many opaque substances, such as wood, flesh tissue, paper (even a book of 1,000 pages), as well as some of the metals. The lighter the weight of the substance, or less its density, the easier these rays pa.s.sed through it, or the more transparent such bodies were to the rays. The heavier metals, like platinum, gold and lead, were practically opaque, or allowed none of the rays to pa.s.s through them, while the very light metal aluminum was about as transparent to these rays as was gla.s.s to ordinary light, and for that reason this metal could form window panes for such rays, while excluding other light. Most organic substances are transparent or semi-transparent to these rays, and hence such rays readily pa.s.s through the body of an individual, being only intercepted in part by the denser parts of the anatomy, such as the bones, so that a man in such light no longer casts a well-defined shadow of his outline, but the shadow disclosed is that of a skeleton, by virtue of the greater density of the bones. Any object of higher density, such as a ring upon the finger, clearly establishes its shadow by virtue of its greater density.

Likewise, any foreign object in the body, such as a bullet from a gun-shot wound, or a foreign body accidentally swallowed, is perfectly disclosed and located by the shadow which it casts. As these light rays have been characterized as invisible, it may be difficult to understand how invisible rays can cast a visible shadow, and it should be here stated that when these unseen rays fall upon certain chemical substances the latter are made to glow with a peculiar fluorescence, and a screen made of such fluorescing materials will light up where the rays fall upon it, and remain dark at the points where the rays are intercepted by a substance opaque to such rays, thus outlining a shadow.

Not only do these light rays in pa.s.sing through the body tissues (transparent to them) cast a shadow of the bones or any foreign objects, but by the application of photography to these shadow pictures a species of photograph, called a radiograph, or skiagraph, may be taken, and thus any foreign body, such as a bullet, may be definitely located in the human body and quickly extracted, without the element of doubt which beset the old method of diagnosis, which, at best, was only intelligent guessing. Not only are foreign bodies so located, but the fractures of the bones may also be accurately observed, studied and adjusted. Stone in the bladder may be discovered, and the condition and movements of the heart and lungs ascertained.