62 ESSAYS AND OBSERVATIONS 



body, the force of gravity varies every 

 inflanr, and increales in its progrefs 

 downwards. And indeed gravity can- 

 not otherways produce acceleration, more 

 than the njis infita does. Nor is there a- 

 ny thing fingular in this property of gra- 

 vity. The vis infita has a property fome- 

 what fimilar : For, though it continues 

 invariable after the body is fet in motion, 

 yet it is not always the fame. It keeps 

 pace with the imprefTed force ; and is ve- 

 ry different, according to the different 

 forces with which bodies are put in mo-' 

 tion. In a word, iince effedls muft al- 

 ways correfpond with their caufes, the 

 gradual increafe of the force of a falling 

 body muft infer the gradual increafe of 

 the power of gravity, which is the caufe 

 of the motion. Or rather, conlidering the 

 matter in a different light, perhaps more 

 accurately, the tendency or nifus of a bo- 

 dy towards the center of the earth, which 

 is greater in motion than at reft, and 

 which gradually increafes with the velo- 

 city of the motion, being nothing elfe 

 but the exertion of its power of gravity, 



makes 



