HUMAN LOCOMOTION. 53 



seen in Fig. 3. The drum is provided with a piece of lead placed at 

 the extremity of its lever ; this mass acts by its inertia. While the 

 body oscillates vertically, the mass of lead resists these movements, 

 and causes the membrane of the drum to sink when the body rises, 

 and to rise when the body descends. From these alternate actions a 

 current of air results, which, transmitted by a tube to a registering 

 lever, shows by a curve the oscillatory movements of the body. 



A complete horizontal oscillation occupies the time of two steps, 

 and, consequently, of two vertical oscillations. The body is carried 

 toward the right side, at the moment of the maximum of elevation, 

 which corresponds with the middle of the pressure on the right foot, 

 and toward the left at the middle of the pressure on the left foot. This 

 lateral swaying of the trunk is the consequence of the alternate pas- 

 sage of the body into a position sensibly vertical over each foot. 



The body is advancing at every moment during the step, but at 

 some parts of it more rapidly than at others. The greatest rapidity 

 of advance is at the end of the pressure of the foot. 



With this brief sketch of the movements of the limbs and body in 

 walking, and of the apparatus employed by M. Marey for studying 

 these movements, we are prepared to consider the different paces com- 

 mon to man. 



Fig. 6. Tracing produced by, Walking Up-stairs. D, tracing of the pressure and rise of the 

 right foot (full line) ; G, tracing of the left foot (dotted line). 



In walking, the body does not leave the ground, the footsteps fol- 

 low each other without any interval, and the weight of the body passes 

 alternately from one foot to the other. The tracings in Fig. 4, ob- 

 tained by walking on a level surface, illustrate these points. There 

 are exceptions, however, to this definition. For example, in mounting 

 a staircase it will be observed that the step-curves encroach on each 

 other (Fig. 6), showing that each foot is still pressing on its support 

 when the other has already planted itself on the next step. Besides 

 this, it is at the time of this double pressure that the lower foot exerts 

 its maximum force ; it is at this moment, in fact, that the work is pro- 

 duced which raises the body to the whole height of a step. Nothing 

 like this is observed in the descent of a staircase ; the step-curves cease 

 to encroach on each other, following one another very much as in or- 

 dinary walking on level ground. 



Running, though more rapid than walking, consists like it in alter- 

 nate treads of the two feet, whose step-curves follow each other at 

 equal intervals ; but it presents this difference, that in running the 



