It needs no argument to convince the reader that the aim of a naval architect should be to combine in the best manner available, strength and lightness. The dimensions and outside form of the ship in great part determine her displacement; and her capacity to carry weights depends largely on the actual weight of her own hull; while the room within partly depends on the thinness or thickness of her walls. Now, we have seen that in wooden ships the hull weighs more than in iron ships of equal size; and it will be apparent that what is gained in the latter case can be applied to _carrying_ so much the more iron armour. Hence, distinguished authorities do not believe in the wood-built ship _carrying_ heavy armour, nearly so much as in the ironclad, iron-_built_ ship.(62) The durability and strength are greater. The authority of such a man as Mr. J. Scott Russell, the eminent shipbuilder, will be conclusive. In a pamphlet,(63) published in 1862, he noted the following ten points: 1, That iron steam ships-of-war may be built as strong as wooden ships of greater weight, and stronger than wooden ships of equal weight. 2, That iron ships of equal strength can go on less draught of water than wooden ships. 3, That iron ships can carry much heavier weights than wooden ships [hence they can carry heavier armour]. 4, That they are more durable. 5, 6, 7, 8, 9, That they are safer against the sea, against fire, explosive shots, red-hot shots, molten metal; and 10, That they can be made impregnable even against solid shot. [Illustration: THE “WARRIOR.”] The last point, alas! is one which Mr. Scott Russell himself would hardly insist upon to-day. When he wrote his pamphlet, five or six inches of armour, with a wood backing, withstood anything that could be fired against it. When the armour of the _Warrior_, our first real ironclad, had to be tested, a target, twenty feet by ten feet surface, composed of four and a half inch iron and eighteen inches of teak backing—the exact counterpart of a slice out of the ship’s side—was employed. The shot from 68-pounders—the same as composed her original armament—fired at 200 yards, only made small dents in the target and rebounded. 200-pounders had no more effect; the shot flew off in ragged splinters, the iron plates became almost red-hot under the tremendous strokes, and rung like a huge gong; but that was all. Now we have 6½-ton guns that would pierce her side at 500 yards; 12-ton guns that would put a hole through her armour at over a mile, and 25-ton guns that would probably penetrate the armour of any ironclad whatever. Why, some of the ships themselves are now carrying 30-ton guns! It is needless to go on and speak of monster 81 and 100-ton guns after recording these facts. But their consideration explains why the thickness of armour has kept on increasing, albeit it could not possibly do so in an equal ratio.