112 MOVEMENT 



The gelatine plates, sensitized with bromide of silver, 



Fig. 76.— Details of the interior of the photographic gun. 



on which the photographs were taken, were cut with a 

 diamond to a circular or octagonal shape, as is shown 



at the butt end, is a large cylindrical breech which contains the cluck- 

 work mei-hanism. The axis of the breech is seen projecting at B. 

 When the trigger is pulled the wheels begin to rotate and transmit 

 the necessary movement to the different parts of the instrument. A 

 centml axis, which revolves 12 times in a second, controls the move- 

 ment of all the individual parts of the apparatus. In the first place 

 (Fig. 76), there is an opaque metal disc provided with one small 

 opening. This disc constitutes the shutter, and only allows the light, 

 which passes through the objective, to gain an entrance 12 times in a 

 second, and then on y for a period of y-^ part of a second. Behind 

 the first disc there is another provided with 12 openings which 

 rotates freely on the same axis as the first, and behind these, again, 

 there is room for the sensitized plate, which may be circular or 

 octagonal in shape. This fenestrated disc should rotate inter- 

 mittently so as to come to rest 12 times in t. e second just opposite the 

 beam of light which penetrates the instrument. 



