64 ESSAYS ann OBSERVATIONS 
means by which we can determine this con. 
troverfy; and, when we look about for fats 
and experiments, there can be none lefs liable 
to exception than thofe, where the «7s infita 
of one body is oppofed to the vis infita of an- 
other,’ by collifion and percuffion. Ifa pen- 
dulum of one pound weight be let down from 
fuch a height, as to acquire at the loweft 
point the velocity of ro, it will exadtly ba- 
lance a pendulum of two pounds weight, let 
down from fuch a height as only to acquire 
the velocity of 5, and the two bodies will be 
at reft upon their collifion. The remaining 
at reft upon contact, is compleat evidence, 
that the forces of the two bodies are equal ; 
confequently that their forces are as their 
quantities of matter multiplied upon their ve- _ 
locities ; and therefore that the force of the 
fame body is always as its velocity. A thou- 
fand different experiments of the fame kind, 
make it evident, that the force of every mo- 
ving body is in the precife ratio of its velo- 
city. And thofe experiments muft be abfo- 
lutely unexceptionable, in which we compare 
the force of one body, with the force of ano- 
ther equal body moving with a different ve- 
locity ; for this is in effect comparing the dif- 
ferent 
