Thus the force was not destroyed, but only converted into another form.
And if we should follow out the natural effects of this heat into which the motion of the bullet was transferred, we should find it rarefying the air around the place of concussion, and thus lifting the whole mass of the atmosphere above it, and producing currents of the nature of wind, and through these producing other effects, thus going on forever; the force changing its form, but neither increasing or diminishing its quantity through a series of changes without end.
_The Arrest and temporary Reservation of Force_.
Now, although it is thus impossible that any force should be destroyed, or in any way cease to exist in one form without setting in action a precisely equal amount in some other form, it may, as it were, pass into a condition of _restraint_, and remain thus suspended and latent for an indefinite period--ready, however, to break into action again the moment that the restraint is removed.

Thus a perfectly elastic spring may be bent by a certain force, and retained in the bent position a long time.

But the moment that it is released it will unbend itself, exercising in so doing precisely the degree of force expended in bending it.

In the same manner air may be compressed in an air-gun, and held thus, with the force, as it were, imprisoned, for any length of time, until at last, when the detent is released by the trigger, the elastic force comes into action, exercising in its action a power precisely the same as that with which it was compressed.
Force or power may be thus, as it were, stored up in a countless variety of ways, and reserved for future action; and, when finally released, the whole amount may be set free at once, so as to expend itself in a single impulse, as in case of the arrow or the bullet; or it may be partially restrained, so as to expend itself gradually, as in the case of a clock or watch.

In either case the total amount expended will be precisely the same--namely, the exact equivalent of that which was placed in store.
_Vegetable and Animal Life_.
There are a vast number of mechanical contrivances in use among men for thus putting force in store, as it were, and then using it more or less gradually, as may be required.