CH. XI] MOVING PICTURE FILM AND MECHANISM 419 



The gate D is then opened and the idlers, iii are pushed away 

 from the sprocket wheels a, b and c. A sufficient length of film 

 is unrolled from F to reach to the take-up reel G and the film 

 is put under the sprocket wheel a, so that the teeth fit into the holes 

 at the edges of the film. Care must be taken that the film goes 

 over or under the sprocket wheels in such a way that as the crank 

 is turned forward all of the sprocket wheels tend to move the film 

 in the same direction, otherwise they will tear it apart. The 

 arrangement may differ in different machines. 



After putting the film on the sprocket wheel a, so that the teeth 

 pass through the holes of the film, the idler i, is pushed over to hold 

 the film in place. This can be done with one of the fingers while 

 holding the film in place with the thumb and forefinger. The film 

 is then engaged with the lower sprocket wheel b, leaving an extra 

 length of film to form the two loops L and M. This can best be 

 determined by experience, it must be enough so that the inter- 

 mittent sprocket will not jerk the film in two and not long enough 

 so that the loops will strike any shields there may be to cover them. 



The film is held against the intermittent sprocket c, so the loops 

 L and M, are about equal in size and held straight on the tracks of 

 the aperture plate when the gate D, is closed. 



The end of the film is now pushed through the fire-trap opening 

 in the lower magazine and fastened to the take-up reel G. This is 

 accomplished by slipping the end under the spring on the spindle 

 of the reel, in such a direction that the film will not be folded as the 

 reel is turned. The reel is turned to insure the end of the film 

 being well fastened. Fig. 233 shows a mechanism with the film in 

 position and ready to operate as soon as the magazine doors are 

 closed. 



If the picture is not directly in front of the aperture plate but is 

 above or below (misframed) , it can be put in its proper position by 

 a lever which lowers the mechanism and film without disturbing 

 the position of the aperture plate and objective. 



585. Direction of motion. The normal direction of motion 

 to secure the proper sequence of events in the order in which they 

 occurred is secured by moving the film downward, and results 



