CHEOXOPHOTOGEAPHY ON FIXED PLATES 61 



consists in artificially reducing the surface of the 

 object under observation. Such parts of the object 

 as are not wanted in the photograph are blackened 

 and thus rendered invisible ; on the other hand, those 

 portions, the movements of which are to be studied, 

 are picked out in white. Thus a man dressed in black 

 velvet (Fig. 41), with bright stripes and spots on his 

 limbs, is reproduced in the photograph as a system of 

 white lines, which indicates the various positions 

 assumed by the limbs. In the diagram thus obtained 



Fig. 42.— Images of a runner reduced to a system of bright lines for representing the 

 position of his limbs. (Geometrical chronophotography.) 



(Fig. 42), the number of images may be considerable, 

 and the notion of time very complete, while that of 

 space has been voluntarily limited to what was strictly 

 necessary. 



Stereoscopic Chronophotography. — In Chapter II. 

 we discussed the method of obtaining stereoscopic 

 pictures of figures described by straight or curved 

 lines moving in space. A series of separate images 

 was thus obtained, that is to say, they were produced 

 by intermittent exposure of the objective. This was 

 done with the double object of explaining the method 

 of producing figures in relief, and of showing the 



