ii6 ESSAYS AND OBSERVATIONS 



no lefs difficulty here, than in the com-r 

 munication of motion. If two pieces of 

 clay pppofing each other with equal for- 

 ces, had any real adivity of their own, 

 it might be expedted, that, though they 

 both ftopt at their firft meeting, this was 

 only done by fufpending the effedl of each 

 other's adion ; and that they would rcr 

 fume their former degree of motion, upon 

 being feparated by a man's hand. We 

 find, however, that the motion of both bo- 

 dies is irrecoverably loft by fuch a colli- 

 fion. If then the force of one body is loft 

 or confumed by deftrpying force in an- 

 other, Why may not one body as well 

 lofe force by producing it in another? Be- 

 fides, were there any real adiye oppofition 

 in the body at reft, to the body in motion, 

 part of the force ought to be loft on that 

 account, and the fum of the motions after 

 the ftroke would be lefs than the motion 



before it. 



When a horfe pulls a ftone forwards, 

 it is commonly faid, that the ftone pulls 

 the horie back, with a force equal to that 

 with which the horfe pulls the ftone fore- 

 wards. 



