PHYSICAL AND LITERARY. 39 



well as in elaftic j the efFe<5ls of collifioa 

 muft be the fame in both. Two elaftic 

 balls meeting in oppofite directions, re- 

 bound ; becaufe, after their force is fpent 

 by collision, the fame force is reftored to 

 each, by their mutual reac5lion ; and the 

 fame mult happen to hard bodies, if they 

 have the fame power of readion. In a 

 word, I cannot dillinguiih elallicity from 

 a power of readlion ; and a hard body 

 differs from an elaftic only in this, that 

 the former has no power of reaction, but 

 only of refiftance. A third difficulty is, 

 that, in the bulkof theiiiftances common- 

 ly given to illuftrate this law, I cannot 

 difcover an equality of adion and reac- 

 tion. And, laftly, what appears the moft 

 unfurmountable difficulty is, that^ except- 

 ing the cafe of elafticity now mentioned, 

 and that of fluidity to be mentioned af- 

 terwards, I have not found a fmgle in- 

 ftance of an effed produced by the action 

 of one body upon another, but what may 

 be fairly explained by acknowledged prin- 

 ciples, laying alide altogether this fup- 

 pofed equality of adioa and reaaion. 



And 



