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. [Illustration: 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.