Moving Force. iti 
Here the force of P is twice that of Q, but 
the effects of these forces, if estimated by the 
product of each mass into its velocity, are equal. 
3. In treating of rotatory motion ;—in find- 
ing, for example, the centre of gyration of a 
mass revolving about a fixed point, the rotatory 
force of each particle is universally understood. , 
to be as the square of its distance from that 
point, or as the square of its velocity. Ifa 
body, A, (fig. 3.) be made to revolve about 
the centre C, bya force acting at P; four times 
that force, applied at the same point, P, will 
be required to make a body, B, equal to A, 
placed at twice the distance of A from C, 
revolve with the same angular velocity, that 
is, with twice the absolute velocity of A. Hf 
both the bodies be disengaged from C, they 
will each ‘continue to move with the same 
velocity as before, but in rectilinear directions; 
and then the force of B is said to be only 
twice that of A. But it is not alledged that 
A can gain, or B lose force, by the mere cir- 
cumstance of being disengaged from C. How 
then is this change in their relative forces 
- to be accounted for ? 
4. Let the lengths of the arms AF, FB, 
(fig. 4.) of the balance beam, A B, be in the 
proportion of 1 to 2, and let the weight of the 
ball, m, be to that of n, as2tol. If they 
