CHEONOPHOTOGKAPHY ON MOVING PLATES 113 



in Fig. 78. In this photograph the successive 

 positions of a flying gull are shown at intervals of j\ 2 



Fig. 77.— Special box for holding the photographic plates. 



of a second. These little images, when enlarged by 

 projection, furnish curious details with respect to the 

 position of the wings, and the torsion of the remiges 



An eccentric, E, placed on the central axis, produces this intermit- 

 tent rotation, by transmitting a regular to-and-fro movement to a rod 

 which is furnished with a catch, C. At each oscillation this catch is 

 held by one of the teeth which form a sort of circlet round the fenes- 

 trated disc. 



A special shutter, O, effectually prevents the light from penetrating 

 into the instrument as soon as all twelve photographs have been taken. 

 There are other arrangements for preventing the sensitized plate from 

 passing, by reason of its acquired velocity, the position assigned to it 

 by the catch, and where it should remain perfectly still during the 

 period of illumination. 



A pressure button, b, Fig. 75, is brought into close contact with the 

 plate, as soon as the latter is introduced into the gun. Under the 

 influence of this pressure the sensitized p'ate sticks firmly to the 

 posterior surface of the fenestrated disc, which is covered with india- 

 rubber to prevent it slipping. 



The object is brought into focus by elongating or shortening the 

 barrel, and thus removing or approximating the lens, and finally the 

 process is corrected by looking with a microscope through an opening, 

 O, made in the breech of the gun, and observing the definition on the 

 ground glass. 



