PHYSICAL AND LITERARY. 65 



return, it is carried down by gravity 

 without any counter-adion. At firft 

 view, the afcent will be confidered as the 

 operation of two powers adling in oppo- 

 fite dire(5lions ; the efFedl of which com- 

 monly is, to produce an equable motion 

 with the difference of the forces. And, 

 were the ad:ion of gravity one uniform 

 action, like that of the vis infua^ fuch 

 would truly be the effedl : But, as gravity 

 is exerted by repeated impulfes, a diffe- 

 rent effedl muft follow. The very firft 

 impulfe of gravity takes off from the force 

 of the vis inftta; what remains is leffen- 

 ed by the fecond impulfe ; and fo on, till 

 the vis infita, gradually decreafing by the 

 repeated counter-acftions of gravity, be 

 annihilated altogether. In the return 

 downwards, gravity being exerted with- 

 out an antagonift, every new impulfe pro- 

 duces an acceleration of motion ; and, 

 thefe impulfes being repeated inceffantly, 

 the acceleration goes on, till the flone 

 touch the groud. 



It remains only to be obferved, that, 

 as the force of gravity is accurately pro- 



VoL.I, I - portioned 



