When a projectile is thrown from a gun, although it is not heated appreciably, yet heat-energy represented by its velocity is absorbed from the expanding gases of the powder charge. When a 12-inch projectile weighing a thousand pounds is thrown from one of our long naval guns, it has a striking energy, fifty feet from the muzzle, of about 50,000 foot-tons--that is to say, it strikes with a force equal to that of 50,000 tons falling from a height of one foot, or one ton falling from a height of 50,000 feet. As the 12-inch naval gun weighs about 50 tons, the energy absorbed from the gases in the shape of velocity of the projectile is sufficient to lift a thousand 12-inch guns to a height of one foot. As a projectile weighs half a ton, the force of the blow is about the same as though the projectile were to be dropped from a height of twenty miles, with no deduction for the resistance of the atmosphere. When the projectile is stopped, a quantity of heat is re-developed exactly equal to that absorbed from the powder gases in giving the projectile its high velocity; and the quantity of heat absorbed from the powder gases in throwing a thousand-pound projectile from our big naval guns is sufficient to melt 750 pounds of cast iron, which is enough to heat the projectile white hot. Obviously, when the projectile strikes armor-plate, either the plate or the projectile must yield, for the reason that the projectile brings to bear upon a 12-inch plate an energy sufficient to fuse a hole right through it, and this is substantially what it does. The hard and toughened steel of the plate is heated and softened by the force of impact, and, although the projectile may be cold after it has passed through, it actually does fuse a hole through the plate, the metal flowing like wax from its path. The introduction of smokeless cannon-powder was followed by a recession from guns of great weight and caliber, to guns of smaller weight and smaller caliber, the aim being to make up for the greater smashing power of huge projectiles, thrown at a lower velocity, with projectiles of smaller size, thrown at much greater velocity and having a greater power of penetration of armor-plate, which was constantly being made thicker and tougher and harder in order to resist the impact of armor-piercing projectiles. As armor-plate continued to increase in thickness and in powers of resistance, guns of bigger and bigger caliber had to be made, capable of withstanding the enormous pressure necessary to throw projectiles of sufficient size and at sufficiently high velocity to penetrate any armor-plate that could be opposed to them. With every improvement in armor-plate, the gun and the projectile have been improved and enlarged, until now no armor-plate carried by any ship can withstand the naval guns of largest caliber. In its race with armor-plate, the gun has thus far been the winner.