2 
236 On the Force of Percussion. 
other body B, would in all positions communicate to it the 
same velocity. 
It may be remarked, however, that the times in which 
these total effects are produced may be varied at pleasure im 
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 motria is in- 
creased by being placed at what is called a mechanical ad- 
vantage, yet, on the contrary, any quantity of mechanic 
force is not hable 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 
production of any sudden effect, or can, on the contrary, 
occasion a moving body to ascend, and thus resolve its im- 
petus into a moving force ready to exert itself through a de- 
terminate space of descent, and capable of producing pre- 
cisely 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 
quantity of mechanic force at command, whether we have 
1 lb. of powder, which by its expansion could give to one 
ton weight a velocity sufficient to raise it through 40 feet, 
or the weight actually raised to that height and ready to be 
let down gradually, or the same weight possessing its ori- 
ginal velocity to be employed in any sudden exertion. 
By making use of the same measure as in the former 
ceases, a distinct expression is likewise obtained for the quan- 
tity of mechanic force given to a steam-engine by any quan- 
tity of coals; and we are enabled to make a comparison of 
its effect with the quantity of work that one or more horses 
may have performed in a day, each being expressed by the 
space through which a given moving force is exerted. In 
the 
