on the Force of Percussion. 1 <) 
impact of different bodies was not examined by Smeaton, and 
it may be worth while to shew that when the whole energy 
of a body A is employed without loss in giving velocity 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 loss, 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 be 
supposed to act upon B in a direct line through the medium 
of a light spring, so contrived that the spring is prevented by 
a ratchet from returning in the direction towards A, but ex- 
pands 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 corresponding 
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 reciprocal ratio of the 
bodies, might consequently be increased at pleasure by the 
means proposed, in the subduplicate ratio of the bodies em- 
ployed ; and if momentum were an efficient force capable of 
reproducing itself, and of overcoming friction in proportion 
to its estimated magnitude, the additional force acquired by 
such a means of increase, might be employed for counteracting 
the usual resistances, and perpetual motion would be easily 
effected. But since the impetus remains unaltered, it is evident 
D 2 
