420 MOVING PICTURE FILM AND MECHANISM [Cn. XI 



from a right-hand rotation of the crank. If the crank is turned to 

 the left the film will be pushed upward by the intermittent sprocket 

 instead of being pulled downwards as it should be. This would 

 most likely result in crumpling and breaking the film. 



586. Operation and speed. After the machine is threaded 

 the lamp is pulled toward the operator so that the light shines upon 

 the aperture plate. 



In starting the machine do not start with a jerk but start grad- 

 ually (1-2 seconds), otherwise an unnecessary strain is put upon the 

 gears. The crank is turned in a right-hand (clockwise) direction 

 at such a speed that the film passes at the rate of 16 pictures per 

 second. If the gearing is arranged so that the intermittent 

 sprocket would move 16 times for each revolution of the crank, this 

 would require i revolution per second or 10 revolutions of the 

 crank every ten seconds. One should practice the speed for a 

 while with no film in the machine, looking at the second hand of a 

 watch and turning with a uniform speed until there are just 10 

 revolutions every time the second hand passes a ten second division. 

 This should be practiced for some time until the proper speed can 

 be maintained with certainty. After the film is in, the action in 

 the scene will serve as a guide for the proper speed, as some films 

 are improved by being shown at a slower or faster rate than they 

 were taken, i. e., the standard given above. 



See Richardson's Handbook, p. 219. 



587. Automatic fire shutter. As the machine starts, the 

 automatic fire shutter (fig. 228) opens and allows the light to fall 

 upon the film. If the picture is not at the right height on the 

 screen it can be "framed up" by moving a lever which raises or 

 lowers the mechanism and film. 



If an old machine is used that does not have an automatic fire 

 shutter, one must be extremely careful never to allow the light to 

 fall upon the film except when it is in motion, otherwise one or two 

 seconds will suffice either to ruin the film if non-inflammable film 

 is used or to start a conflagration if celluloid film is used. The 

 danger from this source is so great that we strongly recommend 



