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. [Illustration: FIG. 205.--HAND PREMO.]