KINEMATOGRAPH A general outline of the whole process or manner of taking and projecting kinematograph pictures must be given to render intelligible a description of the necessary mechanism. Briefly, the camera consists of a light-tight chamber fitted at the top with a magazine for holding a long roll of negative film ; a similar magazine at the bottom of the chamber for the reception of the film after exposure ; mechanism for drawing the unexposed film from the top magazine, passing it intermittently past the exposure aperture, and finally winding it up in the lower magazine ; and an optical system for projecting the image upon the film. A negative obtained in this camera is taken under cover to a dark-room with the usual ruby illumination ; wound on a frame, and developed in large tanks. After develop ment and washing, the negative is wound on large drums, provided for the purpose, in hot-air chambers. When dry, it is put through u contact-printing-machine, in which an un exposed film (the positive stock) is placed in contact with the negative film and the two run together with the celluloid side of the neg ative next to the illuminant and the positive film behind the negative, both in contact, gelatine to gelatine. The positive, or so-called print, is treated in the same manner as the negative, and dried on drums or on frames. When dry the films are ready to be exhibited, for which purpose projecting machines are required. All projecting machines in general use are built on the intermittent principle. The entire apparatus consists of an arc-lamp (sometimes a high-power limelight jet), lantern body, film mechanism, and optical system. Projecting consists in feeding the mechanism with a positive film from spools designed for the purpose, and winding it up as used, the images being projected upon a screen.
In many of the early kinematograph machines the film travelled through its requisite path from spool to spool with a continuous movement, whilst the optical system was made relatively stationary by following the motion of the film and being then brought back to its starting point with a jerk. In practice this was unsatis factory, and it has been superseded by what is known as the " intermittent movement," according to which the film comes to a standstill for a fraction of a second and is held stationary during exposure. Three distinct methods are
now in general use, namely, the pin movement, the dog movement, and the Maltese-cross move ment.
The three forms of intermittent movement will now be referred to. The pin movement mechanisu, is illustrated at A. A shaft Z, slotted at D, and carrying a pin at the top, oscillates on a fixed point c. The lower end of the shaft E is pivoted at B to a cam A, which, on rotation in the direction of the arrow, causes the pin shaft to rise and fall, and at the same time to make a forward and backward move ment. The dotted line at it indicates the edge of the film, the alternate open spaces indicating the perforations. The figure shows the pin about to enter a perforation. On rotating the cam A, the pin will enter the perforation, and as the cam continues to revolve, the pin will pull down the film the distance of one picture space, being ultimately released as the revolution of the cam continues and brought into position for re-engagement with the film perforation. In practice, the cam A rotates sixteen times per second ; hence the film will be moved sixteen times and as often allowed to remain stationary.
The Maltese-cross movement is shown at B. A sprocket-wheel E carries teeth which engage with the film perforations. Fixed to its side is a Maltese cross D. A disc B, carrying on its side a second disc A, and a pin at G, is made to rotate continuously in the direction of the arrow. During its motion, the pin G enters the slot E, and at a certain point begins to turn the Maltese cross ; the points of the cross pass into the notch a of disc A and thus allow the sprocket-wheel to make one quarter revolution ; then it is brought to a standstill and held steady by the concave edge I coming opposite to the convex plain edge of disc A. When disc A has made a complete revolution, the same action takes place, and so on, on each corner of the cross.