34 On the Force of Percussion. 
mechanic force to bodies of equal or unequal magnitude 
have been so distinctly treated of by Smeaton, in a series of 
most direct experiments *, that it would be a needless waste 
of time to reconsider them in this place. So also, on the 
coutrary, the quantities of extended mechanic effect pro- 
ducible by bodies moving with different quantities of im- 
petus, have been as clearly traced by the same accurate ex- 
perimentalist t. 
But there is one yiew in which the comparative ores of 
impact of different bodies was not examined by Smeaton, 
and it may be worth while to show that when the whole 
energy of a body A is employed without loss in giving ve- 
locity to a second body B, the impetus which B receives is 
in all cases equal to that of A, and the force transferred 
to B, or by it to any third body C, (if also communicated 
without Joss, and duly estimated as a mechanic force,). is 
always equal to that from which it originated. 
As the simplest case of entire transfer, the body A may 
he supposed to act upon B in a direct line through the me- 
dium of a light spring, so contrived that the spring is pre- 
vented by a satchet from returning in the direction towards A, 
but expands again entirely in the direction towards B, and 
by that means exerts the whole force which had been wound 
up by the action of A in giving motion to B alone. In this 
case, since the moving force of the spring is the same upon 
each of the bodies, the accelerating force acting upon B at 
each point is to the retarding force opposed to A at the cor- 
responding points in the reciprocal ratio of the bodies, and 
the squares of the velocities produced and destroyed by its 
action through a given’space will consequently be in that 
same ratio, The momentum, which is in the simple reci- 
procal ratio of the bodies, might consequently be increased 
at pleasure by the means proposed, in the subduplicate ratio 
of the bodies employed ; and if momentum were an efficient 
force capable of reproducing itself, and of overcoming fric~ 
tion in proportion to its estimated magnitude, the additional 
force acquired by such a means of increase might be employed 
* Phil. Trans. vol. lxvi. p. 450. t Ibid. vel. lxxii. p. 337, 
for 
