Photography

fo-tog'ra-fy, the art of taking pictures by means of light. It is hard to say when the effect of light on color became a subject of study. In the eighteenth century Scheele, a Swedish chemist in the University of Upsala, found that the violet rays of the solar spectrum darken silver chloride. In 1839 Daguerre, a Paris scene painter, published a method of taking pictures. His process consisted in coating a silver plate with iodide, then exposing it in a camera. The different degrees of light proceeding from the light and dark places of the object produced corresponding differences on the iodide of the plate. This difference was brought out and fixed by a subsequent bath in vapor mercury, the mercury adhering to the several parts of the plate in proportion to the extent to which it had been affected by light. This sort of picture was named a daguerreotype in honor of the inventor. The first sun-lit picture of a human face was taken by Professor John Draper of the University of New York. In 1840 he took a daguerreotype of his sister Dorothy. It is still in existence in the family of William Herschell of England, to whom it was sent as a scientific curiosity. Daguerreotypes were expensive. They required a long, tedious sitting, and then only one picture could be produced. An account of the various substitutes for silver and iodine and the improvements which enable a photographer to produce an unlimited number of photographs from one plate are too technical for our purposes.

A method of instantaneous photography has been developed, so short a time exposure--a mere fraction of a second--that it is practicable to obtain a clear picture of objects in motion, as a moving train or a trotting horse. In 1888 George Eastman, of Rochester, New York, devised a miniature hand camera which he named the kodak. It contains a reel of sensitive paper on which many impressions may be taken to be developed later. The manufacture of kodaks has risen to commercial importance. It still centers at Rochester.

Photography has acquired an importance among scientists. Descriptions may err or fail to carry an intended meaning. Sunlight records facts or, at least, appearances. In legal affairs a photograph is accepted as the best of evidence. The astronomer uses the camera. During an eclipse the observer busies himself taking a series of photographs to be studied at leisure. Astronomers are employed busily photographing the heavens as a record of the present position of the stars. A score of telescopic cameras are at this work in various parts of the world. Naturalists are taking photographs of lions in Africa, elephants in their native jungles, and of bird, beast, and fish everywhere. The hunter with camera, instead of rifle, creeps up or lies in wait. If in darkness, he uses a flashlight--a moment of exposure--and he has his picture faithful to life. To obtain a photograph of a bird on her nest the naturalist resorts to the device of setting the camera in position. He then retires to a place of concealment at a distance, and at the right moment exposes by pulling a long cord. Cameras, and indeed, series of cameras, are sent aloft by means of a kite and are operated by a cord to obtain views of the horizon, of fortifications, and bird's-eye views of cities and landscapes. A tiny self-acting camera strapped to the breast of a pigeon has been sent aloft. It has been suggested that pigeons be trained to spy on the movements of armies in the field.

Not least among the services of the photograph is its use in education and in art. At a cost of a few cents each it is now possible to bring pictures into the schoolroom and to decorate the home with photographic reproductions that are excellent from an artistic point of view. Although persons are yet living who can remember the interest aroused by the first daguerreotype, the business of manufacturing photographers' supplies has risen in the United States alone to the value of $30,000,000 a year.