man. Man cannot control the power of Niagara or the thunder-storm;
but he can control the power of a fleet.

Speaking, then, from the standpoint of the human being, one may say
that the fleet has the element of controllability, while Niagara
and the thunder-storm have not. One man can make the fleet go faster
or slower or stop; he can increase its power of motion or decrease
it at his will; he can reduce it to zero. He cannot do so with
the forces of nature.

_Directability_.--Not only can one man control the power of the
fleet, he can also direct it; that is, can turn it to the right
or the left as much as he wishes. But one man cannot change the
direction of motion of Niagara or the lightning-bolt.

_Power, Controllability, and Directability_.--We may say, then,
that a fleet combines the three elements of mechanical power,
controllability, and directability.

_The Unit of Military Power_.--This is an enormous power that has
come into the hands of the naval nations; but it has come so newly
that we do not appreciate it yet. One reason why we do not and cannot
appreciate it correctly is that no units have been established by
which to measure it.

To supply this deficiency, the author begs leave to point out that,
since the military power of every nation has until recently been
its army, of which the unit has been the soldier, whose power has
rested wholly in his musket, the musket has actually been the unit
of military power. In all history, the statement of the number of