PHYSICAL AND LITERARY. 43 



With regard to gravitation, whicK is 

 given as another inflance of the equality 

 of adion and readion ; it is very true, 

 that there is an equal tendency in every 

 particle of matter to evrery particle; but I 

 am at a lofs what farther can be made 

 of this, than that fuch is the law of gra- 

 vitation. Why then fhould we endea- 

 vour to account for this efiPecl by any fe- 

 parate law ? I might add, that this at beffc 

 is a doubtful inftance of the mutual ac- 

 tions of bodies upon each other. It will 

 perhaps, upon examination, be found the 

 more fafe opinion, that bodies a<5l not 

 upon each other by the power of gravity. 

 But of this afterwards. 



Keill, in explaining this law of na- 

 ture, feems to confine it to the percuflion 

 of bodies ; and refts it wholly upon this 

 fadl, that equal changes of motion are 

 produced upon coUifion; which is, in o- 

 ther words, that, whatever force is loft 

 by the one body, an equal force is gene- 

 rated in the other. And indeed it appears 

 probable, that the law has been invented 



chiefly 



