116 



ANIMAL MECHANISM. 



centre rises, that it is altered if we raise our arms, that, in 

 fact, it describes within the interior of the body all sorts of 

 movements, as soon as we cease to be motionless, it is easy 

 to understand that it will be impossible to refer to this 

 ideal and movable point, the reactionary movements produced 

 by the pressure of the feet upon the ground. It will be 

 better to choose a determinate part of the trunk of the body, 

 the pubis, for example, in order to study its movements in the 

 act of walking. 



Fig. 21. — Transmission of an oscillatory movement to the registering apparatus. 



The instrument which we have already employed will be 

 applicable to the study of these displacements. 



Let there be two lever drums, united by a long tube T T T. 

 Let a vertical oscillary movement be given to one of these 

 levers, so as, for example, to carry the lever L downwards 

 into the position indicated by the dotted line, the other lever 

 will be displaced in the opposite direction, and will assume the 

 position also shown by the dotted line near it. Under these 

 conditions the lowering of one lever corresponds with the ele- 

 vation of the other, since the compression of the air in one of 

 the drums must lead to its expansion in the other. If we 

 wish to obtain from the two parts of the apparatus indications 

 in the same direction, it would be necessary to turn one of 

 the drums, so as to place its lever downwards. 



Vertical oscillations of the body. — Let us suppose that one of 

 these levers traces a curve on the registering apparatus, while 

 the other rests, by its point, on the pubis of a man who is 



