MODES OF PROGRESSION USED BY MAN. 131 



corresponds with the moment when the two feet are in 

 the air. 



Fig. 81. — Man galloping with the right foot first. Step-curves and re- 

 actions. There is an encroachment of one curve over the other, and then 

 a suspension of the body. The curve O, which corresponds with the 

 re-actions, shows the effect of the two successive impulses exerted on 

 the body by the feet. 



4. Of leaping. — Although leaping is not a sustained mode 

 of progression in human locomotion, we will say a few words 

 about it, in order to complete the series of the movements 

 which man is able to execute. 



The two feet being joined together, we can make a series 

 of leaps, and advance thus, by imitating the mode of locomo- 

 tion of some birds, or of certain quadrupeds, as the kangaroo. 



Fig. 32.— Leap on two feet at once, D and G. The line R, the curve of re- 

 actions, shows that the maximum of elevations corresponds with the 

 middle of the pressure of the feet. 



The apparatus intended to illustrate the vertical oscillations 

 of the body, being placed on the head of the experimenter, 



