Then came an invention that put a new face upon the matter,—the surface-hardening of plates, composed of a mixture of nickel with steel,—which, from one of its perfectors, is known as “Harveyizing” it. Other processes also are known. This gave to the surface of the metal such a flinty hardness that the heaviest and most highly tempered steel projectiles would almost invariably break to pieces when they struck it—the same projectiles that were able to punch a hole clear through a target-plate of ordinary wrought-steel twenty-two inches thick! Plates thus surface-hardened are now made in Europe, and as well, if not better, in the United States, where we have learned and taught the rest of the world how to make them by rolling—a much better, as well as cheaper, process than the former method of hammering them into shape. It was found that with these hard-surfaced plates much less thickness was required to contend successfully with the great guns opposed to them than had been the case before; and the great saving of weight enabled a much larger extent of armor to be borne upon a ship than was formerly possible, so arranged as to protect all her hull and vital parts. Thus, in a typical modern battle-ship, say 360 feet long, 72 feet broad, and drawing 24 feet of water, having an armor of surface-hardened nickel-steel, this armor is thus disposed: amidships, and a quarter of her length behind the point of the prow, is built up a semicircular “barbette,” or wall, of the thickest armor, behind which is a “turret,” moving to the right or left through an arc equal to half the horizon, no higher than necessary to cover and work the guns, and having its motor mechanism fully protected by the barbette. This is the forward turret—a swinging fort, carrying with it, as it turns, two of the heaviest guns in the ship. [Illustration: THE UNITED STATES BATTLE-SHIP “INDIANA.”] Half-way from the center to the stern stands the after turret and its barbette, similarly built of the strongest armor,—ten to twelve inches thick,—and sweeping with its guns half the horizon. From a point just in front of the forward barbette two walls of the heaviest possible armor, reaching vertically from four and a half feet below the water-line (loaded) to three feet above it, extend diagonally backward to the sides of the ship, then continue along its side in a “belt” to points opposite the after barbette, where they bend inward as before and meet just aft of the after barbette; but hereafter the increased efficiency of armor, by further reducing its weight, will probably enable the armor-belts to be carried to the extreme ends of the ship, which otherwise can be so seriously damaged by an enemy as to interfere with the speed and control of a ship in action, even if it does not disable her.