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( 13 ) be pardoned for a somewhat lengthy digression, to bring before your minds a circumstance which is so often overlooked.

It must not be supposed that the energy of the powder is all utilised in driving out the projectile, and in giving it rotation. On the contrary, a very considerable percentage is employed in moving the powder itself along the gun in the rear of the shot, while as regards the question of recoil, a large portion of this is due to the energy required to expel the whole of the powder gases, at the enormous velocity at which they are expelled, after the exit of the shot has left them free issue. One's feeling is that it cannot need much work to expel a mere gas, but you may depend upon it that if 700 lbs. of powder are put into a gun in the solid state—in which condition you would agree they could not be expelled from the gun, with less absorption of energy than would be needed to expel a shot of the same weight, issuing at the same velocity—the fact of having converted this 700 lbs. of solid into gas, will not make it weigh less, and thus, as I have said, a considerable proportion of the energy will have to be expended, to move the gases along the bore in the rear of the shot, fortunately, at a mean velocity much less than that of the shot. As tested by the recoil, however, a much larger proportion of the energy will be found to be expended in causing the vehement rush of powder gas, after the shot has left the gun. About the effects of powder gas I shall have something to say further on.

We have now traced the change from the smooth-bore gun firing a spherical shot, to a rifled gun firing an elongated projectile; needing heavier total pressure per inch of surface to propel it; pressure to be obtained, partly by increasing the weight of the charge (involving a greater length of powder-chamber), and partly by increasing the length of the gun for the travel of the shot, both alterations demanding the production of a much longer weapon.

The question now arises, How are these longer guns to be loaded?

Breech-loading presents, as I will show you later on, enormous