iv.] MECHANICAL AID OF THE RIDER. 57 



the resistance of the ground is complete, the reaction, 

 which is precisely equal and in a contrary direction to the 

 action, will throw the body of the man upward and 

 forward, and by clasping with his legs he will draw the 

 chair also with him. But he can only accomplish in this 

 way a very little distance with a very great exertion. If 

 the jockey made this muscular exertion every time that 

 his horse struck with his hind feet, his strength would be 

 employed on the foreign fulcrum, the ground, through the 

 medium of his horse's bony frame. Thus the jockey 

 would contribute to the horizontal impulse of his own 

 weight, and exactly in proportion to the muscular power 

 exerted by the jockey, the muscular system of the horse 

 would be relieved. At the same time no additional task 

 is thrown on the bony frame of the horse, since, if 

 the jockey had not used his muscular power on it in 

 impelling his own weight, the muscular system of the 

 horse must have been so employed. It is true, that not 

 much is done after all with a prodigious exertion, but if 

 that little gains six inches in a hardly contested race 



