PHYSICAL AND LITERARY. 151 



things. If all the motions and changes 

 of bodies are performed immediately by 

 thefe bodies themfelves, without the influ- 

 ence of other matter, or any other power, 

 there is an end of all inquiries into 

 caufes and efFe(5ls ; philofophy mufl be 

 degraded to a bare knowledge of fa(5ls, a 

 hitlory of nature. 



There is an argument, in the form of 

 a redu6iio ad ahfurdum, brought againft 

 the received opinion of the equality of 

 acflion and reaction, which had almoft 

 been overlooked. The fubftance of it i& 

 this, that as the prefTure undequaque is a 

 confequence of the law of equal action 

 and rea(5lion in fluids ; fo the fame fore 

 of preflure ought to be a pro perty of fo- 

 lid bodies likewife, if the i.ame law be 

 univerfally extended to all bodies, folids 

 as well as fluids. For a rea dy anfwer to 

 this objedion, we need only recolle(ft the 

 definition of a fluid, as diftin guiflied from; 

 a folid body. An undequaque- ^veOhre can- 

 not obtain in a folid body, Uwnlefs the par- 

 ticles of it did yield to any force exereifed 

 upon them ; and, in yieldi; jg, were eafily 



put 



