52 MECHANICAL AID OF THE RIDER. [CHAP. 



own energies. If by pulling, and giving him pain in the 

 mouth, you force him to throw up his head and neck, you 

 prevent his seeing how to foot out any unsafe ground, 

 or where to take off at a fence, and in the case of stumb- 

 ling you prevent an action practically dictated by nature 

 and theoretically justified by philosophy. When an 

 unmounted horse stumbles, nature teaches him to drop 

 his head and neck ; philosophy teaches us the reason of it. 

 During the instant that his head and neck are dropping 

 the shoulders are relieved from their weight, and that is 

 the instant in which the horse makes his effort to recover 

 himself. If by giving him pain in his mouth, you force 

 him to raise his head and neck instead of sinking them, 

 his shoulders will still remain encumbered with the 

 weight of them ; more than this, as action and reaction 

 are equal and in contrary directions, the muscular power 

 employed to raise the head and neck will act to sink the 

 shoulders and knees. The mechanical impossibility of 

 the rider assisting his horse when falling may be demon- 

 strated thus : no motion can be given to a body without a 



