^o ESSAYS AND OBSERVATIONS 



motion, without acceleration or retardar 

 tion : And, on the other fide, every va-r 

 ried efTedl which is gradually diminifhed 

 or augmented, muft proceed from a va- 

 ried caufe. 



This difficulty is endeavoured to be 

 explained in the following manner : Gra- 

 vity, it is faid, has a remarkable proper- 

 ty, * That it acfls with the fame force 

 " upon a body that is already in motion, 

 " as upon a body that is at reft, fo as to 

 " produce equal accelerations in falling 

 " bodies in equal times V* But this 

 manner of conceiving the effedt qf gravi- 

 ty, whatever obfcurity it may occafion, 

 tends not to remove the difficulty. One 

 thing is extremely clear, that we h^ve no 

 means ajSbrded us to ellimate the force 

 of any power, other than the eiFe<5ts pro- 

 duced by it ; which holds in general, 

 whether the pov^er be internal or external. 

 From the uniformity of the effecfls, we 

 conclude the vis infita to be an uniform 

 power ; and we have the fame founda- 

 tion, 



• AI'Laurin's account of Newton's philofophy, p. 248. 



