5*2 



PHYSIOLOGICAL PHYSICS. [Chap. XLIII. 



of the toes. At this instant the leg behind begins 

 the advance by giving the body an impulse forwards 



from its point of sup- 

 port. The force acts 

 in the direction J'F. 

 Let GF represent the 

 intensity of the force. 

 If a parallelogram be 

 constructed, of which 

 GF is the diagonal, the 

 force GF is evidently 

 resolvable into GV, an 

 upward force acting 

 against gravity, and 

 neutralised by it and 

 a force GH, which is 

 the part of the impulse- 

 that d eter mines the 

 forward movement. If 

 the upward movement 

 GV is quite neutralised 

 by the downward force 

 of gravity, the body 

 will simply be ad- 

 vanced in a horizontal 

 line, and it is found, 

 as a fact, that up and 



}' L > 



Fig. 218. The Dynamics of Walking. 



down oscillations of the 



body are of very small 

 amount. To give the forward impulse, the leg that is 

 behind is extended, and in continuation of that action 

 the heel is raised from the ground by the extension of 

 the ankle joint, till the leg rests on the ground by the 

 tip of the toes only (Fig. 219, 1, hkfm). By this exten- 

 sion the leg finally leaves the ground, as represented by 

 the thin line of 3. Meanwhile, to permit the exten- 

 sion referred to, the forward leg is slightly bent at the 



