CHRONOPHOTOGRAPHY ON MOVING PLATES 115 



regard, if one can use the expression, the object from 

 different points of view. Now, these variations in 

 perspective, although presenting few difficulties when 

 operating from afar on objects of large size, would 

 make the study of small objects at close quarters a 

 matter of great difficulty,* still less would they permit 

 one to photograph objects of microscopical size. 

 For this reason we determined to employ a single 

 objective. 



In order that we might simplify the instrument as 

 much as possible, we united in a single apparatus all 

 the accessories necessary for chronophotography on 

 fixed or moving plates, as well as for regulating at 

 will the frequency and duration of the exposures. 



Fro. 79.— Enlargement of one of the photographs obtained with the photographic gun. 



Principles of Chronophotography on Moving Plates. — 

 The weak point of the photographic gun was princi- 

 pally that the images were taken on a glass plate, the 

 weight of which was exceedinglv great. The inertia 

 of such a mass, which continually had to be set in 

 motion and brought to rest, necessarily limited the 

 number of images. The maximum was 12 in the 

 second, and these had to be very small, or else they 

 would have required a disc of larger surface, and 

 consequently of too large a mass. 



These difficulties may be overcome by substituting 

 for the glass disc, a continuous film very slightly coated 

 with gelatine and bromide of silver. This film can be 

 made to pass automatically with a rectilinear move- 

 ment across the focus of the lens, come to rest at each 



* See Chap. v. p. 81. 



