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 men in each army has been put forward by historians as giving the most accurate idea of their fighting value; and in modern times, nearly all of these men have been armed with muskets only.
It has been said already that the main reason why the invention of gunpowder was so important was that it put into the hands of man a tremendous mechanical power compressed into a very small space, which man could use or not use at his will.

This idea may be expressed by saying that gunpowder combines power and great controllability.

But it was soon discovered that this gunpowder, put into a tube with a bullet in front of it, could discharge that bullet in any given direction.

A musket was the result, and it combined the three requisites of a weapon--mechanical power, controllability, and directability.
While the loaded gun is perhaps the clearest example of the combination of the three factors we are speaking of, the moving ship supplies the next best example.