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that of a sphere, which is, that although the energies of a sphere and of a cylinder of equal weight, and having equal velocities, would be the same, in the case of the cylinder the energy would be concentrated upon a smaller surface, thereby increasing the intensity of attack upon each unit of area of the surface struck; in fact, the same cause that enables the long projectile to cleave the air in a manner superior to that in which the spherical projectile can pass through it, enables the long projectile to penetrate a solid resistance more readily than it can be penetrated by the sphere—an imperative reason for adopting the elongated form when it is remembered, that the object to be penetrated (when attacking a ship) is no longer wood, but is armour-plate. Thus it is that the cannon-ball has, after so many years of use, disappeared from modern guns, and that its place is taken by an elongated projectile with a head in the form of a Gothic arch, and having a total length of some 3 to 3⅝ calibres.
The alteration of the form of the projectile, it will be seen, gives us the power of passing through the air to the object to be struck, without losing so much of the initial velocity as was lost by the old spherical form, and also the greater power of attack, per unit of area struck; but there are difficulties of a serious character attendant upon this change.
We have hitherto regarded the subject, from the point of view that a certain muzzle velocity existed, without considering how that muzzle velocity was produced; but we must now enquire into the main duty of the gun, which is the production of the muzzle velocity.
From this point of view the change of form of the shot is a very grave matter. It is a matter involving no less, than the change from smooth-bore to rifle-bore, the change in the length of the gun, the change in the nature and in the quality of the powder, and eventually, as will appear, the change from muzzle loading to breech loading.
Let us now look into these questions. Obviously that which gives the velocity to the shot, must be the pressure of the powder,
