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Chrono-Photography

film, motion, twelve, plate, fig, passes and exposures

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CHRONO-PHOTOGRAPHY (synonym, photo-chronography).—A term applied to the photography of objects or animals in motion at regular intervals of time. Muybridge, Dickson, Edison and Jenkins of this country, Marey of Paris, and Anschtitz of Lissa, have made a special study of chronophotography, and the value of their researches in the science of motion cannot be over-estimated.

For making chrono-photographs we require a camera capable of making a number of successive exposures. There are several kinds.

Professor Marey's apparatus is arranged so that a number of successive exposures can be made upon one roll of sensitive film which passes behind the lens. In order that the negatives should be sharp it is, of course, necessary that the film be motionless during exposure. Where fifty _ _ intervals of exposure are very short (forty or ty a second), the rate of motion of the mechanism is necessarily very rapid. Of course it would be out of the question to stop this motion suddenly; equally so to stop the motion of the film while the spools kept on working; and the difficulty has been surmounted very ingeniously by Professor Marey. At the point where the film passes behind the lens, a compressing-roller forces it for an instant against the central partition, thus arresting its movement. But, before reaching this point, the film passes around a flexible plate, against which presses a spring, the result of which is this: that while the film is momentarily arrested, back of the lens, the spool continues to unwind, and the slack, so to speak, is taken up into a loop, by the plate, actuated by the spring; when the film is liberated this loop flies into position and makes its momentary stay while the flexible plate comes back to its original position and again takes up a loop of the film, and during the successive exposure.

In order that the actuating machinery may attain a uniform speed before any exposures are made, it is arranged to be thrown in and out of gear, so that the handle can be turned without moving the spools.

The apparatus used by Londe is constructed on a different plan. It consists of a battery of lenses, each provided with a shutter. By an

electric attachment these lenses can be fired off in rapid succession.

In Fig. 107, A is the covering plate carrying the objectives, shutters and electric gearing; B, thirteen-wire contact; C, camera; D, focusing rack.

Fig. rob shows the current distributor. A, clockwork case; B, brush; C, ivory disk; D, one of the twelve contacts; E, insulating tube; F, the twelve wires connected with th-2 ter minals G, G; return wire; H, escapement; I, armature; J, electro magnet; L, regulation of the counter spring; N, terminals for the current of the transmitter.

The camera is provided with twelve objectives arranged in three parallel rows so as to give the twelve images upon a 9 x 12 plate. Each objective is provided with a shutter of the Londe & Dessoudix system.* The freeing of the shutters is done electrically. Fig. io8 shows the electro-magnets and their armatures placed near each objective. The connection of the various wires is effected at a single stroke by means of the piece, B, which is put in communication with the distributer by means of a flexible 13-wire cable, twelve of the wires being in communication with the twelve electro-magnets, and the thirteenth serving as a common return wire.

The apparatus is mounted upon a lab oratory stand or a field stand, permitting of transporting it with sufficient facility.

Monsieur Marey has made a complete study of the motion of all kinds of animals. He employs a very ingenious method, in some cases to avoid the confusion from the super positives of images when using fixed plates. Such parts of the object as are not required are blackened so as to become practically invisible while those parts the movements of which are to be studied are picked out in white. In the study of the motion of a man for instance, he dresses him up in black velvet as shown in Fig. 113, with light spots and stripes on his limbs. In the chronophotograph (Fig. 1) all the positions assumed by the limbs are indicated by white lines. The number of images is con siderable while the space occupied is considerably limited without confusion.

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