PHYSICAL AND LITERARY. 35 



the momentum of the body which is put 

 in motion, is equal to the momentum 

 loft by the impinging body. Therefore 

 the momentum of the impinging body 

 is to the refiftance of the body at refl, as 

 the quantity of matter of both bodies is 

 to the quantity of matter in the latter. 



This power of refiflance in matter, 

 ■which is never exerted but when an im- 

 pulfe is made upon it, is of fo lingular a 

 nature, as to lead us to expecl fome wife 

 contrivance. Writers have given very 

 little attention to the laws of motion, con- 

 fidered in the light of final caufes, tho' a 

 xaoft beautiful fpeculation. It would, 

 carry me too far from my prefent pur- 

 pofe, to enter diredly upon it : I take 

 liberty only to make a fingle obfervatioix 

 with refpe(5t to the property of refiftance. 

 Gravity, an univerfal law of matter, ferves 

 the nobleft purpofes. In conjuncflion with 

 the vis infita, it preferves the folar fyflem 

 in order. The vis infita is ufeful in ano- 

 ther refpedl; becaufe by its means, we 

 can apply force greatly fuperior to our 



own. 



