words, that all existing forces are but the continuation or
prolongation of other forces preceding them, either of the same or other
forms, but precisely equivalent in amount; and that no force can terminate
its action in any other way than by being transmuted into some other force,
either of the same or of some other form; but still, again, precisely
equivalent in amount.

It was formerly believed that a force might under certain circumstances
be _originated_--created, as it were--and hence the attempts to contrive
machines for perpetual motion--that is, machines for the _production_
of force. This idea is now wholly renounced by all well-informed men as
utterly impossible in the nature of things. All that human mechanism can do
is to provide modes for using advantageously a force previously existing,
without the possibility of either increasing or diminishing it. No existing
force can be destroyed. The only changes possible are changes of direction,
changes in the relation of intensity to quantity, and changes of form.

The cases in which a force is apparently increased or diminished, as well
as those in which it seems to disappear, are all found, on examination, to
be illusive. For example, the apparent increase of a man's power by the use
of a lever is really no increase at all. It is true that, by pressing upon
the outer arm with his own weight, he can cause the much greater weight
of the stone to rise; but then it will rise only a very little way in
comparison with the distance through which his own weight descends. His own
weight must, in fact, descend through a distance as much greater than that
by which the stone ascends, as the weight of the stone is greater than his
weight. In other words, so far as the balance of the forces is concerned,
the whole amount of the _downward motion_ consists of the smaller weight
descending through a greater distance, which will be equal to the whole
amount of that of the larger one ascending through a smaller distance; and,
to produce a preponderance, the whole amount of the downward force must be
somewhat greater. Thus the lever only _gathers_ or _concentrates_ force, as
it were, but does not at all increase it.

It is so with all the other contrivances for managing force for the
accomplishment of particular purposes. None of them, increase the force,
but only alter its form and character, with a view to its better adaptation
to the purpose in view.

Nor can any force be ex