The amount of work performed by gunpowder, when exploded in a gun, is a
subject which has engaged a vast quantity of attention, and some highly
ingenious methods of calculating it have been put forward. Owing,
however, to the impossibility of ascertaining how fast the combustion
of large grains and prisms proceeds, a very considerable amount of
experience is required to enable the gunmaker to apply the necessary
corrections to these calculations; but, on the whole, it may be said
that, with a given charge and weight of shot, the muzzle velocity may
now be predicted with some accuracy.

You now have the chief data on which the designer bases his proposals,
and lays down the dimensions of the gun to suit such conditions as it
may be required to fulfill. In actual practice, the conditions are
almost always complicated, either by necessities of mounting in
particular places, such as turrets and casemates; or by the advantages
attending the interchangeability of stores, or other circumstances;
and it requires great watchfulness to keep abreast of the ever-growing
improvements of the day.

I will now conclude with a few words on the power of heavy guns, when
employed in various ways. The first consideration is accuracy of fire.
No matter how deadly the projectile may be, it is useless if it does
but waste itself on air. Accuracy is of two kinds--true direction and
precision of range. All modern guns are capable of being made to shoot
straight; but their precision of range depends partly on the successful
designing of the gun and ammunition, so as to give uniform velocities,
and partly on the flatness of the trajectory. The greater the velocity,
the lower the trajectory, and the greater the chance of striking the
target. Supposing a heavy gun to be mounted as in the fortresses round
our coasts, and aimed with due care, the distance of the object being