1820. In 1850, Mr White tells us, out of 133,700 tons of shipping added to the British Mercantile Marine, only 12,800 tons, less than one-tenth, were iron ships. In 1860, out of 212,000 tons added to the navy, 64,700 tons, nearly onethird, were iron ships. In 1875, out of 420,000 tons of newly-built ships, 374,000 tons, nearly ninetenths, were built of iron. If steam-vessels alone are regarded, the change is still more complete. During 1875 a tonnage of 179,000 was added to British steam shipping, and of these 176,000 tons were iron built.

Iron shipbuilding originated in England, and has received its most important development in English dockyards. It has rendered the country independent of foreign powers for the supply of materials for its navy. All the ships added to the Royal Navy within the last ten years have iron hulls, and not a single wooden vessel is now in course of construction for the Royal Navy.

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The special advantages of iron, as compared with wood, are thus stated 1. Superior lightness combined with strength; 2. Superior durability, when properly treated; 3. Superior ease and cheapness of construction and repair; and, 4. Superior safety, when properly constructed and divided into compartments. On the other hand, it is admitted that the bottom of an iron

vessel is more easily damaged by contact with rocks or shoals; and that the fouling of the bottom, and consequent loss of speed, is more rapid in an iron than in the case of a wooden vessel. One feature of the iron ship, which at one time seemed likely to render the use of the material altogether unsuitable-that is, the disturbance of the compass-has been satis

factorily compensated and corrected.

As to comparative lightness, the percentage of nett to tare displacement has been materially improved by the introduction of iron as a material. In wooden merchant ships, the weight of the hulls were from 35 to 45 per cent. of the total displacement, leaving from 55 to 65 per cent. for the cargo. In iron merchant ships ten per cent. of the former division of weight is deducted from the hull, and added to the cargo. In the mastless type of ironclad war vessels the weight of the hull is from 30 to 35 per cent. of the displacement, leaving 65 to 70 per cent. for the cargo; and in the Russian circular type the proportions are stated at 20 and 80 per cent. respectively, of the total floating

power.

The size of vessels has increased in proportion to the greater power given to the constructor by the use of iron as a material for shipbuilding. The St. Vincent, one of our largest men-of-war in 1815, was 205 feet long, 533 broad, and had a displacement of 4700 tons. The Inflexible, the latest type of mastless sea-going men-of-war, has a displacement of 11,400 tons; her dimensions are 320 feet by 75, and her engines work to an indicated power of 8000 horses. The Great Eastern, completed by Mr. Brunel in 1858, had a length between perpendiculars of 680 feet, a breadth of 83 feet, a depth of 58 feet, and a displacement, at 30 feet draught of water, of 27,419 tons; the engines were of 2600 nominal, working up to 6600 indicated, horse-power. The weight of the hull, as launched, was 11,000 tons.

The use of iron as a material for shipbuilding has had two distinct

tons.

But the draught of 50 feet of water is too much for any ship. If the depth be reduced, by flattening the bottom, to 20 feet, the vessel would no longer float, as the buoyancy will have diminished more rapidly than the weight. The displacement will then be reduced to 4250 tons, and, in order to make the vessel float, the thickness must be reduced to 19 inches. But the least wave would sink a vessel of such exact equilibrium. The displacement would support the deck alone, leaving no buoyancy for vertical sides, bulwarks, deck, armament, cargo, and crew. To provide engines and boilers of an indicated horse-power of 3600 horses, 600 tons weight must be added, and an equal amount for coals. The weight of 1200 tons would be equal to that of about 5 inches of iron all over the shell. But we have seen that the hull displacement of a war ship should not exceed 35 per cent. of its total displacement. We can, therefore, afford only 1500 tons for the weight of the hull, which would reduce the general thickness to a little under 10 inches. This, then, may be taken as indicating a limiting proportion between the size

and the thickness of a wholly armoured vessel of this capacity, constructed so as to have the largest amount possible of buoyancy.

It will be observed that it is not the case that this mode of construction has as yet been used in our dockyards. The idea of a circular ship is taken from the Russian navy; and Mr. Froude pointed out, during the discussion cited, that the resistance to the passage through the water of such a vessel would be three times that of one constructed on more shipshape lines. It is only at and above the water-line that solid armour has been hitherto applied. But Mr. Reed contemplates the probability that it will hereafter become necessary to plate the keel of a war ship heavily, in order to resist torpedoes. The deck must be no less strong, in order to resist vertical fire. The limits of flotation are therefore pretty clearly indicated, and are not very narrowly to be approached. Had a vessel of the given displacement of 4250 tons been constructed 245 feet long, and 40 feet wide, Mr. Reed says that the thickness of the armour must be from 5 to 6 inches less than that of the before-mentioned

"soup-plate" pattern. We are thus driven to suppose an enormous displacement necessary for any vessel that is to be covered, above, below, and on her sides, with more than 12 inches of iron. The limit of size and of resistance is readily attained. The limit of cost will be no less restricted.

On 26th September, 1854, Capt. Ericsson, formerly well known in England as a competitor with George Stephenson for the prize for a locomotive engine offered by the Liverpool and Manchester Railway Company in 1829, forwarded to the French Emperor Louis Bonaparte a design and

specification of an iron-clad steam battery, with revolving cupola. The object which the inventor desired to achieve was the solution of the following problems: 1. The construction of a self-moving, shotproof vessel. 2. That of an instrument capable of projecting very large shells at slow velocities, but very accurately, in accordance with previously determined rate. 3. A shell not subject to rotation in the direction of its course, and so contrived as to explode with infallible certainty at the instant of contact. 4. A shell capable of being projected under water (or what is now called a torpedo), certain to explode on contact, together with an instrument for projecting such a shell from the vessel at a certain depth below the water line.

The idea of a submarine shell, or mine, had been not only struck out, but carried to a high degree of perfection, in 1810, by Fulton, who also designed a boat which would sink at will and move beneath the surface of the water, in order to approach the vessel which it was intended to attack without being discovered. On 20th August, 1842, Colonel Samuel Colt utterly destroyed a schooner given for the purpose of experiment by the Government of the United States on the Potomac River, while stationed himself no less than five miles from the scene. Colonel Colt claimed to possess a secret, which died with him. But the peculiarity of Ericsson's vessel was, not that it should approach an enemy unseen, or indeed under water, as was the case with Fulton's torpedo boat, but that it should be an iron-clad battery, self-moving, and strong enough to resist the shot that would be directed on it from the enemy it wished to destroy.

This forlorn hope of the war navy of the future was composed entirely

of iron. The midship section is triangular, with a broad hollow keel, loaded with about 200 tons of cast-iron blocks to balance the heavy upper works. Thus carefully did this great engineer provide against such a disaster as the capsizing of the Captain. The ends of the vessel are moderately sharp. The deck, made of iron, is curved both longitudinally and transversely, the curvature being 5 feet; it is made to project 8 feet over the rudder and propeller. The entire deck is covered with a lining of sheet iron 3 inches thick, with an opening in the centre of 16 feet in diameter. Over this opening is placed a semi-globular turret of plate iron 6 inches thick, revolving on a vertical column by means of steam power and appropriate gear work. The vessel is propelled by a powerful steamengine and screw propeller. Air for combustion under the boiler and for ventilation is supplied by

large self-acting centrifugal blower, the fresh air being drawn in through numerous small holes in the turret.

A tube for projecting the shells of 20 inches diameter of bore, was placed on the platform of the revolving turret. It was loaded through a valve, and the shell was to be projected by the direct action of steam from the boiler. Two similar tubes were placed in the body of the vessel, at a fixed inclination of 22°, revolving on vertical pivots. The shell was of cast iron, with a tail of thin plate iron in the form of a cross attached, to prevent rotation in the line of flight. A percussive hammer and wafer were attached to the anterior part of the shell, giving an explosion at the moment of contact. The hydrostatic javelin, or torpedo carrier, for the discharge of a shell under water, is described with no less minuteness.

given, should the necessity of the defence demand it. The next ten years may see the introduction of cannon which shall bear the same relation to the 22-inch plates of the present that these do to the 4-inch plates of sixteen years ago." It is, however, rather to the defence of land forts than to that of sea-going vessels that the gallant officer probably refers. For resisting the projectile of the 100-ton gun a thickness of about 4 feet of cast iron chilled on the outer side is suggested by Com. Grenfell. The proportions of targets to guns are shown by Mr. E. H. Knight in his "Practical Dictionary of Mechanism," from the thickness of 4 inches of iron, backed by 18 inches of timber and a 1-inch skin of iron, which has been pierced by a 7-inch gun with a 301b. charge, throwing a 115lb. projectile 1200 yards; up to a 16in. plate, with 18-inch backing and 14-inch skin, pierced by the 700lb. bolt of the 12-inch 35 ton gun at 500 yards.

the

The penetrating power of this series of weapons rises from 54 foot tons per inch of the circumference of the shot in the first instance, to 188 foot tons in the last. But the mighty race has advanced rapidly since the publication of this well-designed table. The powder chamber of the 100ton gun at Spezia has been enlarged, and the use of cake, or very large-grained, powder has enabled the artillerist to increase muzzle velocity of the 20001b. projectile, with a reduction of the tearing strain on the interior of the gun. By the enlargement of the chamber, the muzzle velocity has been increased from 1424 to 1585 feet per second, and the energy of the projectile from 28,130 to 34,836 foot tons. With the coarse powder, a velocity of 1661.5 feet per second has been attained, giving an energy of

38,316 foot tons. If the same rule were applicable to so tremendous a shock as that which has been found approximately to hold good in the series before mentioned, at least 30 inches of solid iron armour would be required to oppose penetration from such a missile.

It has thus become apparent to the naval constructor that the day of wholly armoured vessels is nearly over. The increase of projectile power is already so great that no ship, of whatever form may be proposed, could swim if clad in armour which would be impenetrable to the projectiles of guns that are now ready for use. The mode, therefore, in which the designer of floating batteries is now endeavouring to keep out the shot is this. A central citadel, of an adequate thickness to resist the expected blow of the enemy's shot, is to be constructed, and an unarmoured prow and stern are to be attached, which shall be so lined with compartments filled with cork as to preserve flotation and stability even if riddled with shot. For the central citadel it is evident that independent stability is necessary. Not only must it be strong enough to resist horizontal and vertical fire, but, as Mr. Reed anticipates, it must be armoured below. It is not, indeed, proposed that this floating castle should be also navigable; the navigability is to depend on the unarmoured part. But the citadel must be able to float, independently of any aid from the rest of the ship; and, not only so, but she must possess a degree of stability sufficient to prevent any danger of her being capsized by a shock such as that which her armour is intended to resist. It is evident that the elements of the problem are such as to render the solution a matter of very great nicety.

But let us see whether we are