72 



MOVEMENT 



In front of the opening there is a track paved with 

 blackened wood, along which, when it is necessary 

 to analyze any particular kind of movement, the man 

 or animal is made to walk. Theoretically, an indefinite 

 number of images may be taken in front of a dark 

 background without any impressions of outside objects 

 appearing on the plate. Practically, when several 

 hundred successive images of a luminous object have 



Fig. 49. — Arrangement of the dark background at the Physiological Station. In front 

 of it there is a small chamber running on rails for keeping the apparatus. Above 

 the dark background a framework is arranged for holding the camera at a distance 

 of 12 metres, when it is necessary to photograph from above. 



been taken, the plate sometimes appears "fogged" 

 in the areas which correspond to the dark background. 

 This proves that a small quantity of light emanates 

 from this source. The appearance of "fogging" 

 curtails the duration of development, and diminishes 

 the intensity of the image. The slightest reflection 



