Mr. vince’s Invejiigation , &c. 547 
of gravity and point of contaCt lie in thedine of direc- 
tion of the ftriking body, yet few writers on mechanics 
have extended their enquiries any further than this Am- 
ple cafe. It muft however be acknowledged, that 
the action of bodies on each other, in directions not 
palling through their center of gravity, affords a fub- 
jeCt at leaft curious in fpeculation ; for my oyra part, 
I have little doubt but that it might be rendered ex- 
tremely ufeful to the practical mechanic. 1. Bernoulli 
was the firft who publifhed any thing on this fubjeCt. 
He found the point about which a body at reft would 
begin to revolve w'hen ftruck by another body, obferv- 
ing however that d. Bernoulli had alfo difcovered the 
fame : he has alfo mentioned the curve defcribed by 
that point in the progreffive motion of the body, and 
has directed a method of enquiry by which the veloci- 
ties of the bodies may be found after the ftroke, which 
comprehends all he has done on the fubjeCt. Two years 
afterwards d. Bernoulli publifhed a paper on progref- 
live and rotatory motion, containing nothing more than 
what 1. Bernoulli had before given us, and, what is a 
little extraordinary, fays in the introduction, de tali 
quidem percujjione nihil adbuc , quantum /do, publid juris 
faclurn fuit ab iis, qui de motu corporum a percuffione ege- 
runt . Euler has alfo inveftigated the velocities of the 
Vol. LXX. 4 G bodies 
