PHYSICAL AND LITERARY. 71 



muft be meafured by the 'velocity, which 

 is the efFect. But, when we confider an- 

 other branch of its operations, viz. its ni- 

 Jus to overcome every obftrudlion to the 

 equable motion, we have no other means 

 to eftimate this nifus, but its efFeas ; for, 

 however probable it may be, it does not 

 jiecefTarily follow, that this n'lfiis muft al- 

 fo be meafured by the velocity. Fads 

 and experiments, then, are the only means 

 by which we can determine this contro- 

 verfy ; and, when we look about for fads 

 and experiments, there can be none left 

 liable to exception than thofe, where the 

 ^uis infita of one body is oppofed to the 

 vh inftta of another, by collifion and per- 

 cuflion. If a pendulum of one pound 

 weight be let down from fuch a height, 

 as to acquire at the loweft point the velo- 

 city of 10, it will exadlly balance a pen- 

 dulum of two pounds weight, let down 

 from fuch a height as only to acquire the 

 velocity of 5, and the two bodies will be 

 at reil upon their collifion. The remain- 

 ing at reft upon contad, is compleat evi- 

 dence, that the forces of the two bodies 



are 



