5 63 Mr. vince’s Investigation of the 
nued uniform. In the following Propofitions, there- 
fore, we fuppofe the axis of the body, after the com- 
mencement of the motion, to continue perpendicular 
to the plane palling through the direction of the force, 
and the center of gravity of the body, and that the 
body itfelf is orthographical 1 y projected upon that plane ; 
alfo in the cafe of the action of two bodies on each 
other, the plane palling through the direction of the 
(hiking body and point of percuffion is fuppofed to pafs 
through the centers of gravity of each body; that 
the axis of each body after it is ftruck continues per- 
pendicular to that plane, and that each body is reduced 
to it in the manner above defcribed. 
P R O P. X. 
determine the point about which a body , when Jlruck , 
begins to revolve . 
Let lmso (fig. 7 .) reprefent the body, g the center 
of gravity, and pa the direction of the force adling at a, 
which produce till it meets ln, palling through g, per- 
pendicularly in the point d ; draw pb perpendicular to pc, 
on which (produced if neceffary) let fall the perpendicular 
hw ; c being fuppofed the point about which the body be- 
gins to revolve, and which, from the laft Propofition, is 
fomewhere in the line ln. Becaufe the body, in con- 
fequence 
