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IGNITION OF FILM PERMISSIBLE PULL ON THE FILM IN THE OPERATION OF THE MACHINE The take-up we have seen is a frictional device to regulate the pull on the film, as it enters the lower magazine and is wound on the reel within it. The same Society has concerned itself with this pull, and stipulates that it should not exceed fifteen ounces for a ten-inch circle. This is the circle determined by the film as wound on the reel. The diameter of this circle is constantly increasing, as the film rolls upon the reel. A high tension would operate to wind the film more closely, than a lower tension would, and the above tension is considered an advisable figure to follow in practice. If the film on the power reel increases to eleven inches in diameter an extra ounce of pull is allowed. THE DANGER OF THE FILM IGNITING The film moves in the space between the fixed aperture plate, and a perforated shutter or little door; the fixed aperture plate is behind the film, between the film and the lamp. The light from the lamp, as far as its use in the projection of the pictures is con- cerned, has to go through this aperture. The aperture is 29/32ds inch wide and 22/32ds inch high. It is quite surprising to realize how small is the picture, with which the work is done. On each side of the aperture are smooth vertical strips of metal, over which the film moves in the operation of the machine. Hinged to the plate or front of the machine, is a perforated plate, its per- foration is of the same size as that in the aperture plate. It closes over the aperture plate; on each side of its aperture are also a pair of vertical strips of metal. When the gate is closed these strips come exactly over the corresponding strips on the face of the aperture plate. They nearly touch the strips, but a sufficient space is left between the two sets of plates for the film to pass without friction. Across the top of the aperture and be- low it there is also room left for the passage of the film. DANGER OF FIRE OVERESTIMATED Thus it will be seen that the film is surrounded by metal on all sides, front and back, except for the portion being projected. A film will rarely if ever catch fire while the machine is in mo- tion. If something happens to stop the machine, and if the fire 261