a 
PHYSICAL ann LITERARY 93 
ties mutt always be proportional to the times 
7 which they are deftroyed. From whence 
it is manifeft, that a ball ftriking with a velo- 
city as 2, muft make an impreffion fourfold 
of what it makes with a velocity as 1; be- 
caufe it continues likewife for double the 
time. In uniform motions, a double veloci- 
ty and a double time, muft always give a 
fourfold fpace: and the fame thing muft ob- 
tain in equably retarded motions; the {paces 
defcribed being exa@tly the half of what 
would have been defcribed by the uniform 
motions. But, tho’ the impreffion be four- 
fold, the real effect, by which the force ought 
to be meafured, is only double; for it has on- 
ly undergone a double refiftance. For the 
fame reafon, triple the velocity makes a nine- 
fold impreffion. And, in general, the {mall 
 impreffions made upon the furface of foft 
clay, (or even upon marble) by bodies « ftri- 
_ king upon it, muft, caeteris paribus, be as 
4 the fquares of the velocities. Thefe impref- 
_fions, made in oppofition to the uniform re- 
fiftance of cohefion, are no better meafures 
of forces, than the heights to which bodies 
are thrown near the earth, in oppofition 
to the uniform power of gravity. The 
jae heights 
