Another of the recent developments in cinematography is the di-optic system which aims to show every stage of the motion of figures, instead of the stage of motion every sixteenth of a second, as is in the case with the usual apparatus. The di-optic camera is simply two machines set side by side in one. It takes two loads of film, has two film gates, and two lenses, but works by turning one crank. The single shutter revolves in front of the twin lens, so that when one side is exposing a length of film the other is closed and the film is advancing. The two rolls of negative exposed in this way record the complete motions of the figures before the camera. The projector also is a di-optic machine working in the same manner as the double-eyed camera, so that when the pictures are thrown on the screen they are seen practically constantly, instead of every sixteenth of a second, for while one is hidden by the shutter, another is thrown on the screen. Also inventors are working on a scheme for taking motion pictures on glass plates instead of on films. As was mentioned previously the use of the motion-picture machine has been very valuable to science, and by adapting the cinematograph to a powerful microscope a great many motion pictures of the life of bacteria have been obtained. Also motion pictures are sometimes made of surgical operations. Carrying this work even farther still, animated photography and X-ray photography have been joined so that science now can make motion pictures of the processes that go on inside small animals. Owing to difficulties not yet overcome moving X-ray pictures cannot be taken of the human body at this time. Röntgen rays cannot be refracted, or collected in a lens. Hence the film for an X-ray picture must be equal in size to the picture desired. It is impossible to increase the size of cinematograph films with much success because of the danger of breaking or tearing them when under the strain of the rapid course they must pursue through camera and projector. These facts made it necessary for the scientists experimenting with X-ray motion pictures to photograph only animals, but they were greatly encouraged because they obtained some excellent views of the digestive processes of mice, guinea-pigs, fowls, and other small animals. The bones of the human hand also were photographed while the hand was opened and closed. M. J. Garvallo, who carried on a great many interesting experiments in France with this type of motion pictures, used a somewhat larger and more sensitive film than the standard, combined with an apparatus too complex for attention here. This phase of cinematography, however, is still in its infancy and we can look for great improvements at an early date.