At St. Sebastian, in 1813, cast-iron guns threw tons of shot at a range of 1,500 yards; some particular guns firing as many as 3,000 rounds, and yet it is more than probable that had the same guns been used in the Crimea, they would have burst with one-fourth the number of rounds. Experience proves that it is not the great number of rounds fired which strains and destroys the gun, but the high elevation at which these guns are placed, in order to get range; this it is which shakes and disintegrates the crystalline structure of the metal, and thus extreme range is obtained at extreme cost. A gun which at 6° of elevation could stand without a strain 200 rounds, would be likely at an elevation of 30° to burst before 50 rounds were fired. The explanation of this is sufficiently simple. A gun fired at 6° recoils as the projectile is projected forward, in proportion to its relative weight and friction; but when brought up to an elevation above 30° the gun is entirely out of the horizontal, and cannot recoil as it does at an elevation of 6°: the force is now exerted downward, and the gun impinges on its support--_i. e._, either upon its bed on the deck of the ship, or on the solid earth of the battery, which is comparatively immovable; thus the force which displaced the gun in the first instance is now exerted on the sides of the gun, and the projectile receiving additional force is projected further. But this increased range is obtained at the expense of the gun, which is rapidly destroyed: 50 rounds being sufficient to render it unfit for service. To obviate this rapid destruction of cannon, the metal has been changed from the molecular to the fibrous; that is from cast iron to wrought iron. One object of this chapter is to point out the difficulties which arise in determining what the best metal for cannon really is, and to show the advantages to be gained by attending to the proper construction of projectile engines, without attaching undue importance to the _material_ of which they are made.