74 ESSAYS AND OBSERVATIONS 



height. The retardation, therefore, of 

 motion, in bodies thrown up with diffe- 

 rent velocities, laying afide the refiftance 

 of the air, may be a nieafure of the force 

 ot gravity, of which it is the effedl ; but 

 can never be a meafure of the force with 

 which the body is thrown up, of which 

 it is r.'Ot the effecSt. And, from the fa(5l 

 of a body's arriving at four times the 

 height with double the velocity, to infer, 

 that the momentum^ at its out-fetting, muft 

 be as the fquare of the velocity, is really 

 not more juft, than to infer, when one 

 body is let drop from four times the 

 height of another body, that it muft ac- 

 quire four times the force of the other bo- 

 dy, though it acquire but double its velo- 

 city ; which does not afl^brd the fhadow 

 of an argument. When a body is thrown 

 up with a double velocity, and confe- 

 quently with a double force, the reafon 

 why it afcends four times its former 

 height is plainly this, that the counter- 

 aftion of gravity, while it has a double 

 force to ftruggle Vv-ich, has bur half the 

 time in any given fpace to produce its ef- 

 "- ' fed; 



