Moving Force. 139 
obtains in all cases of rotatory motion about 
fixed axes; and that the measure composed of 
the mass into its velocity, when applied to the 
same cases, fails ; “a given quantity of motion 
thus estimated, being alterable in any assigned 
ratio.” 
But authors on mechanics generally concur 
in the following conclusion: that “a distinc- 
tion is always to be made between the actions 
of bodies when at liberty, and when they 
revolve about a centre or axis. In the first 
case, the motion lost is always equal to the 
motion communicated m an opposite direc- 
tion: m the second, the motion lost is to be 
encreased or diminished in the ratio of the 
levers before it will be equal to the motion 
communicated.”’* 
We do not find, however, that the absolute 
forces, or their effectt$_can be encreased or 
diminished by any alteration in the lengths of 
the levers. For if the arm H G, for example, 
be extended to any assumed length, the same 
velocity will still be produced in m by the 
motion of P through the same space. It is 
true the velocity will not be produced in the 
same time ; but the result will be the same, in 
whatever time, or by whatever complication of 
levers or wheels, it may be produced. 
* Dr. Milner. Philos. Trans. 1776, pe 371. 
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