266 



ANIMAL MECHANICS. 



Marey, using but one camera, provided with a rotating series of diaphragms, 

 obtained a series of exposures ten a second, each lasting -gj^ second 

 upon his single plate. In photographing a man running, he caused him 

 to pass in front of a black background, consisting of an enormous box, 

 blackened on the inside, and opening towards the camera, and protected from 

 the direct influence of the sun's rays. He thus obtained a series of photo- 

 graphs, say at intervals of y 1 ^ second. When, however, he dealt with slow 



movements, as in the case of 

 a walking man, or when the 

 object photographed was of 

 considerable extent in the 

 direction of movement (the 

 horse, for instance), super- 

 position of the photographs 

 occurred. To overcome this 

 difficulty, Marey reduced the 

 figure by blackening it over, 

 only indicating the joints 



FIG. 155.-Marey's curves obtained from a man run- and axes of . the limbs in 

 ning; o, oscillations of the centre of gravity ; d, curve white (see Fig. 157). 

 described by pressure of right foot ; g, the same of In this way he could 



left foot. obtain photographs which 



gave the position of these 

 parts during each phase of even a slow motion. 



A second method consisted in using a sensitive plate, or preferably a roll 

 of sensitised gelatin, which travelled at a known rate, and was at intervals, say, 

 of y 1 ^- of a second, brought to a standstill. At each moment, during which 

 the plate became stationary, the shutter of the camera was automatically 

 opened and a photograph taken. In order to keep the camera pointed at 

 the moving object a bird, for instance the camera was reduced as much 

 as possible in size, 

 sighted like a gun, 

 and moved after the 

 bird by the observer. 

 W. Braune and 

 Fischer 1 used a modi- 

 fication of Marey 's 

 method. The person 

 under observation 



FIG. 156. Chrouographic record of the periods of contact of the 

 feet of a man executing various paces. The contact of the 

 right foot is represented by a white band, that of the left 

 foot by a shaded band. After Marey. 



1. Represents walking on the level ground. 



2. Represents walking upstairs. 



3. Represents running. 



4. Represents running at a greater speed. 



and upon important 

 parts of the head 

 and limbs a series of 

 eleven Geissler's 

 tubes were attached. 

 They were filled with 

 nitrogen, and con- 

 nected with the secondary coil of a Ruhmkorff 's machine. In the primary 

 coil was placed an interrupter, which caused a current to pass through the 

 tubes at regular intervals of ^ of a second. The experiment was conducted 

 in a dark room, and the periodic flashes of the Geissler's tubes were photo- 

 graphed. Nitrogen was placed within the tubes, because its light is especially 

 rich in chemically active rays. The most important advance made by these 

 observers was the exact record of their results in relationship to co-ordinate 

 planes. The observed person's movements were recorded by cameras placed 



1 " Dcr Gang des Menschen," Leipzig, 1895. 



