28 ESSAYS anv OBSERVATIONS 
fiftance of a body is always lefs than the im- 
prefled force, the refifting body, after its re- 
fiftance is overcome, mutt neceflarily be car- 
ried along with the body which impinges up- 
on it. And, being once putin motion, its 
own vis infita preferves it in the fame degree 
of motion. Iam here putting the fimpleft. 
cafe, that of a body in motion, impingeing 
upon one at refit; and, for the eafe of the 
imagination, I fhall fuppofe thefe two bodies 
equal. In this cafe it is afcertained by expe- 
riments, that the two bodies in contact, go 
on with halfthe celerity which the impinge- 
ing body had before the collifion. For it is 
a general rule in the percuffion of hard bo- 
dies, that the »omentum or force, directed to 
the fame point, continues the {ame after con- 
ta& as before. There is no difficulty here: 
for after half of the force of the impingeing 
body is deftroyed, by the refiltance of the 
body at reft; the other half remains, with 
which the impingeing body moves, and car- 
ries along with it the other body from reft to 
motion. When the refiftance of the body 
at reft is once deftroyed, it yields to the im- 
prefied force without any further oppofition ; 
and 
