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562 THE PHOTOGRAPHIC NEWS. LSEPTENIBER 7, 1883. aluminium is between these lenses and the sensitive plate, being revolvable by clockwork, and having in one part a rectangular opening. When the disc is at rest, this opening is in one of the intervals between the lenses, and therefore the sensitive plate is covered. But an electric communica tion permits of releasing the disc at any moment, and this, on revolving, unmasks one lens after another. The advantage of this system is obvious. The physician can stand close to the patient and watch every movement, while the camera is at some distance. With one hand on an electric key, he makes exposure as he pleases, and thus secures a series of photographs which present all the changing phases that the patient undergoes. Fig. 1 shows the general arrangement of camera, electric battery, key, physician, and patient. The rapidity with which the disc revolves governs the intervals between the successive photo graphs ; thus a long period may elapse between each exposure, or the whole nine pictures may be taken within the hundredth part of a second, or even less, by a quick revolution of the disc. In a word, by means of an automatic arrangement any desired velocity may be given to the revolving disk. Another apparatus, for securing photographs at equally measured intervals, will be seen in with a number of small lenses, arranged in the form of a circle, all possessing the same focus. A disc of blackened | the disc Fig. 2.—PHOT-ELECTRIC Apparatus for taking Pictures at Regular Intervals. A,'Camera; B, battery ; 0, metronome; D, electric key : E, mercury bath. J fig. 2. In this case, application is made of the electric pendulum—or, rather, metro nome—of M. Gaiffe. The front of the camera is shown with its nine lenses, while the little needle in the middle indicates which of the lenses are being exposed at the moment. The exposures take place automatically, the elec tric current from the battery coming with every swing of the metronome, which causes a metal point to dip into a mercury bath, and thus make contact at every oscillation. When the camera has been focussed, the metronome is regulated to the desired speed ; the latter is then put in action, and as soon as the time arrives for the experiment, the electric current is brought into circuit. Not only for physiological and medical research generally is this photo-electric camera of use, but also for scientific and military purposes. Thus, in the discharge of torpedoes, and possibly even in that of modern artillery, application might be made of the apparatus to teach us something more of the force of explosives and the firing of a shot. To give our readers some idea of the results of the photo-electric camera, a series of photo graphs is here shown of two individuals in the act of walking during the exposure of the apparatus (fig. 3). H. .—DEKIES of FnorouxaPHS obtained by PHOrO-ELECTRIC Camera SILVER PRINTS MOUNTED ON GLASS MEDALLIONS, AND HOW TO PRODUCE THEM. Thanks to the energy so often displayed by the publishing houses, combined with their vast resources, ideas which in many cases originate at one or other of the photographic society’s meetings are so far modified or developed into a practical shape as to become of ihe utmost utility, not only to the fraternity, but to the general public also. Sometimes an idea is grasped and made use of at once, or months and even years may elapse before it is deemed of sufficient importance to warrant serious consideration. Such has been the case in the subject we are dealing with —viz., attaching as a permanent support, silver prints in optical contact with glass plates. Twenty years have elapsed since Mr. Rawlinson, as well as Mr. Tunny in Scotland, mounted photographs on glass plates by means of gelatine much in the same manner as we practise the pro cess to-day; and shortly afterwards Mr. V. Blanchard described his method of stripping the photograph from a glass plate previously collodionized. The method pro posed by the latter gentleman has been in use all over the civilized world almost daily since its publication, but the former was allowed to lie dormant, or nearly so, until the energy of Mr. Payne Jennings aud a few other exhibitors brought it once more to the fore. Mr. Jennings’ method of mounting has already been described in these columns,