v.] MECHANICAL AID OF THE RIDER. 53 



foreign force or a foreign fulcrum. Your strength is not 

 a foreign force, since it is employed entirely on the horse. 

 Nor can it be employed on the foreign fulcrum, the 

 ground, through the medium of your reins ; as much as 

 you pull up, so much you pull down. If a man in a hoat 

 uses an oar, he can accelerate or impede the motion of 

 the boat, because his strength is employed through the 

 medium of the oar on the water, which is a foreign 

 fulcrum. But if he takes hold of the chain at the head 

 of the boat, his whole strength will not accelerate or 

 impede the motion of the boat, because there is neither 

 foreign force nor foreign fulcrum. His whole strength 

 is employed within the boat, and as much as he pulls 

 backward with his hands, he pushes forward with his 

 feet. The baker can lift his basket, but not when he 

 is himself in it. 



All the arguments which I have heard adduced against 

 the doctrine here laid down would also go'to prove that 

 a horse cannot fall which has a bearing-rein and a crupper, 

 that is, whose head is tied to his tail. Sir Francis Head's 



