4§ ESSAYS AND OBSERVATIONS 



bodies left free at any height, fall to the 

 earth with an accelerated mat ion. When 

 applied to the latter, it is commonly called 

 gravity ; when to the former, attra£iion. 

 Sir Ifaac Newton, to whom the great dif- 

 covery was referved, that the defcent of 

 heavy bodies, and the curvilinear motioii 

 of the planets, are eflFeds of the fame 

 caufe, chufes to talk of this property of 

 matter with great circumfpedlion and re- 

 ferve. He pretends only, in his Principiaj 

 to have afcertained the fadts, without ven- 

 turing to point out the caufe. In the ge- 

 neral fcholiutn, which concludes that ela- 

 borate work, he fatisfies himfelf with ha- 

 ving explained " the motion of the cele- 

 " dial bodies, and of the fea, by the force 

 ** of gravity, without afEgning the caufe 

 ** of gravity," He only obferves, ** That 

 " gravity muft be the efFedl of fome caufe, 

 ** which penetrates into the very center of 

 ** the fun and planets, and which ads not 

 ** in proportion to the furfaces, but the 

 " folid quantity of matter ; its adlion on- 

 " ly decreafing in a duplicate ratio of the 



** diHances, 



