21 
on the Force of Percussion . 
from the centre ; and since the space through which the body 
would move to lose its whole velocity would be reciprocally 
as the retarding force, the angular motion of the lever and 
space through which the spring must bend, would be the 
same, at whatever point of the lever the body acted. And 
conversely, the reaction of the spring upon any other body B, 
would in all positions communicate fo it the same velocity. 
It may be remarked, however, that the times in which 
these total effects are produced may be varied at pleasure in 
proportion to the distances at which the bodies are placed 
from the centre of motion ; and it should not pass unob- 
served that, although the intensity of any vis motrix is 
increased by being placed at what is called a mechanical ad- 
vantage, yet on the contrary, any quantity of mechanic force 
is not liable to either increase or diminution by any such 
variation in the mode of its application. 
Since we can by means of any mechanic force consisting of 
a vis motrix exerted through a given space , give motion to a 
body for the purpose of employing its impetus for the produc- 
tion of any sudden effect, or can, on the contrary, occasion a 
moving body to ascend, and thus resolve its impetus into a 
moving force ready to exert itself through a determinate 
space of descent, and capable of producing precisely the same 
quantity of mechanic effect as before, the force depending on 
impetus may justly be said to be of the same kind as any other 
mechanic force, and they may be strictly compared as to 
quantity. 
In this manner we may even compare the force of a body 
in motion to the same kind of force contained in a given 
quantity of gunpowder, and may say that we have the same 
