44 ESSAYS AND OBSERVATIONS 



chiefly to account for this effe6l : If fo, 

 it is extremely rafli in philofophers to ap- 

 ply it, as they do, in every cafe where 

 there is the leaft appearance of action and 

 reaction, as if it were an univerfal law of 

 nature that muft pbtain in every cafe 

 whatever. It was not difcovered, it would 

 feem, that the equality of motion before 

 and after percuflion, is the genuine eflPed: 

 of the vis refiflentidB. Therefore, to ac- 

 count for this phsenomenon, a new law 

 inuft be invented ; which, to difguife the 

 matter, muft be confidered as a general 

 law : For, had it been plainly fpoke out, 

 what in efiecl is faid by Dr Keill, that this 

 law is only applicable to the percuflion of 

 bodies j every perfon would be fenfible, 

 ^hat accounting for the law of percuflion 

 in this manner, was doing no more than 

 repeating the fa 61 itfelf in diflferent words » 

 For, to fay that the adlions of two bodies 

 in percuflion are equal and in oppofite di- 

 rections, is, in an obfcure and indiftindt 

 manner, redly faying no more, than that 

 a force is generated in the one body, equal 

 to that which is loft in the other. 



In 



