resisting body; and
the power of a moving ship is due wholly to the mechanical energy
of the burning coal within its furnaces.

It may be objected that it is not reasonable to consider a ship's
energy of motion as an element of naval power, in the mechanical
sense in which we have been using the word "power," for the reason
that it could be exerted only by the use of her ram, an infrequent
use. To this it may be answered that energy is energy, no matter
to what purpose it is applied; that a given projectile going at
a given speed has a certain energy, whether it strikes its target
or misses it; and that a battleship going at a certain speed must
necessarily have a certain definite energy, no matter whether it
is devoted to ramming another ship or to carrying itself and its
contents from one place to another.

Besides the mechanical power exerted by the mere motion of the
ship, and often superior to it, there is the power of her guns and
torpedoes.

Perhaps the most important single invention ever made was the invention
of gunpowder. Why? Because it put into the hands of man a tremendous
force, compressed into a very small volume, which he could use
instantaneously or refrain from using at his will. Its first use
was in war; and in war has been its main employment ever since.
War gives the best field for the activity of gunpowder, because
in war, we always wish to exert a great force at a definite point
at a given instant; usually in order to _penetrate_ the bodies of
men, or some defensive work that protects them. Gunpowder is the
principal agent used in war up to the present date. It is used
by both armies and navies, but navies use it in larger masses,
fired in more powerful guns.

Of course this does not mean that it would be impossible to send
a lot of powder to a fort, more than a fleet could carry, and fire
it; but it does mean that history shows that forts have rarely
been called upon to fire much powder, that their lives have been
serene, and that most of the powder fired on shore has been fired
by infantry using muskets--though a good deal has been fired by
field and siege artillery.

Leaving forts out of consideration and searching for something
else in which to use gunpowder on a large scale, we come to
siege-pieces, field-pieces, and muskets. Disregarding siege-pieces
and field-pieces, for the reason that the great variety of types
makes it difficult to compare them with navy guns, we come to musket