i serious objection to silver-bromide, the sensitive salt in the ordinary photographic plate, is the fact that it is so much more sensitive to the blue-violet than to the green and red of the spectrum as to give a very false rendering of color values or luminosities, the darker colors showing as the lighter and vice-versa. Dr. W. H. Vogel was, perhaps, the first to find that the addition of certain dyes to the emulsion tended, to a large extent at least, to equalize the sensi tiveness; and to plates prepared with such an emulsion or soaked in the dyes after prepara tion, he gave the name of orthochromatic or isochromatic. But even the most evenly sensi tive of such plates are still more sensitive to the blue-violet than to the red and green and for the best results — the true rendering of color luminosity, it is desirable to employ color filters or screens that will absorb the excess of blue violet.
The beginning of the moving picture idea was early in 1878, prior to the introduction of the present rapid dry plate, by E. J. Muybridge, a photographer in San Francisco, Cal., who photographed the movements of a racing horse owned by Leland Stanford by having a series of individual cameras placed in a row about one foot apart, the shutters of which were electri cally operated automatically, as the horse moved forward. This first experiment proved that a trotter's feet are entirely off the ground to gether twice during the making of a stride. In 1896 Edison and others perfected the moving film system in combination with a shutter. See MOVING PICTURES.
In scientific investigation, photography has been remarkably helpful. It has taken the place of manual labor in record-keeping, measured the velocity of flying bullets, shown the true positions of animals in motion and created the ((new astronomy.) As early as 1840, Draper had made photographs of the moon; in 1857 De la Rue established heliographic observation of sun spots, a work begun at Kew and con tinued at Greenwich till the present time. Em ployed in every solar eclipse since 1860, photog raphy has told us all that we know of the i corona and chromosphere; it has revealed the mystery of the hitherto puzzling nebula, and, by virtue of the fact that the light action is cumulative, has told of the existence of stars so far away as to be beyond the ken of the human eye, aided by the most powerful telescope yet made. At the Astro-photographic Con gress that met in Paris in 1887, it was resolved to make a photographic survey and star-map of the heavens and at present there are 18 telescopes, each of 13-inch aperture, engaged in that work in various parts of the world, while in most of the more important observa tories protography and the spectroscope are joined together and made daily, or rather nightly, to tell us more and more of the mystery of the heavens.
As an educational adjunct, photography has played an important part. The projection lan tern finds a place in every well-equipped lecture room, and the photographic lantern-slide lends itself equally to the teaching of science and the illustration of travel. The beauty and ac
curacy of the photographic lantern-slide and the ease with which it is made make it equally available to the college professor and the itin erant lecturer, enabling the one to show to a whole class what otherwise would require to be handled by the members one by one; and giving to the other an opportunity of making a comfortable living and in some cases amass ing a fortune, by amusing and instructing the popular audience. Hardly less important, al though much less popular, is the enlarging of small objects, In bacteri ology, histology, etc., its importance can hardly be overrated, affording, as it does, illustrations in works dealing with such subjects that are without a suspicion of the imperfections of draftsmanship and showing, as they do, when orthochromatic plates are employed, the differ ent luminosities of the various stains.
Nor is photography less important from a social point of view. While it displaced minia ture painting, a style that only the rich could enjoy, it gave a better likeness of loved ones equally available to rich and poor. It has given us correct instead of fancy or distorted views of the manners, customs and scenery of distant lands; enabled the cottager to decorate his walls with better pictures than were available to his richer neighbor previous to its advent and given a new interest to periodical literature by the low cost and excellent quality of its illustra tions. Not less wonderful has been its influence commercially. It has created new branches of trade and manufacture and largely increased many that were in existence before, furnishing well-paid work to hundreds of thousands of both men and women. The glassmaker and the optician have wrought together till they have given us lenses as nearly perfect as we can hope to see; the chemist has given us new material and improved the old, building factories for the manufacture of some by the ton that, pre vious to the advent of photography, were only known as curiosities of the laboratory; while the camera-maker has so exercised his inge nuity as to give us cameras of perfect workman ship and almost automatic in their action. In 1914 there were 87 establishments in the United States manufacturing photographic apparatus, of which 21 made almost exclusively cameras and 21 motion-picture machines. In the same year there were reported 59 factories making photographic materials of the gross value of $4,273,000. This latter industry employed 6,658 people and made gross products of $34,768,000.
Harrison, 'History of Pho tography' (1887) ; Wall, 'Dictionary of Pho tography' (1897),; Payne, 'Wet Collodion Pro cess' (1907) ; Derr, 'Photography for Students' (1906); Holme, 'Colour Photography' (1908); Cassell, 'Cyclopedia of Photography' (1911) ; Jones, 'Photography of To-Day' (1912) ; Hance, 'Commercial Photography' (1914) ; Roebuck, 'The Science and Practice of Photog raphy' (1918) ; files of The Camera, Photo graphk Journal, etc. See PHOTO-ENGRAVING.