Heavy Ordnance Described. The Armstrong gun is thus fabricated. A long bar of iron, say 3 by 4 inches in section, is wound into a close coil about 2 feet long and of the required diameter,say 18 inches. This is set upon end at a welding heat under a steamhammer and "upset" into a tube which is then recessed in a lathe on the ends so as to fit into other tubes. Two tubes set end to end are heated to welding, squeezed together by a heavy screw passing through them, and then hammered lightly on the outside without a mandrel. Other short tubes are similarly added. Five tubes of different lengths and diameters are turned and bored and shrunk over one another, without successively increasing tension, however, to form a gun. The breechend of the second tube from the bore is forged solid so that its grain will run parallel with the bore and give the gun longitudinal strength. Both the wedge and the screw breech-loading apparatus are employed on guns of 7 inches bore (110-pounders) and under. It will thus be seen that the defects of large solid forgings are avoided; that the iron may be well worked before it is formed into a gun; and that its greatest strength is in the direction of the greatest strain; and on the other hand, that the gun is weak longitudinally and excessively costly, (the 7-inch gun costs $4,000, and the 10-inch, $9,000,) and that the material, although strong and pretty trustworthy in the shape of bars, has insufficient elasticity and hardness. Still, it is a formidable gun, especially when relieved of the weak and complex breechloading apparatus, and used with a better system of rifling and projectiles than Armstrong's. The 110-pounder Armstrong rifle has 99 inches length and 7 inches diameter of bore, 27 inches maximum diameter, and weighs 44 tons. The "300-pounder" smooth-bore has 11 feet length and 10 inches diameter of bore, 38 inches maximum diameter, and weighs 10 tons. The Mersey IronWorks guns are of wrought-iron, and

are forged solid like steamboat-shafts, or hollow by laying up staves into the form of a barrel and welding layers of curved plates upon them until the whole mass is united. But few of these guns have been fabricated. The most remarkable of them are, 1st, the Horsfall smooth-bore, of 13 inches bore, 44 inches maximum diameter, and 24 tons weight, price, $12,500; 2d, the "Alfred" rifle, in the recent Exhibition, of 10 inches bore,-price, $5,000; 3d, the 12-inch smooth-bore in the Brooklyn Navy-Yard, which, though very light, has fired a double 224-pound shot with 45 pounds of powder: if properly hooped, it would make the most formidable gun in America. Blakely has constructed for Russia two 13-inch smooth-bore guns, 15 feet long and 47 inches maximum diameter, of castiron hooped with steel: price, $10,000 each. He has also fabricated many others of large calibre, on the principles before mentioned. The 15-inch Rodman smooth-bore cast-iron gun is of 48 inches maximum diameter, 15 feet 10 inches long, and weighs 25 tons. The cost of such guns is about $6,000. The Dahlgren 15-inch guns on the Monitors are about four feet shorter.

Results of Heavy Ordnance. The 10inch Armstrong gun sent a round 150pound shot, with 50 pounds of powder, through a 5-inch solid plate and its 9inch teak backing and §-inch iron lining, at 200 yards, and one out of four shots with the same charge through the Warrior target, namely, a 43-inch solid plate, 18-inch backing, and §-inch lining. The Horsfall 13-inch gun sent a round 270pound shot, with 74 pounds of powder, entirely through the Warrior target at 200 yards, making an irregular hole about 2 feet in diameter. The same charge at 800 yards did not make a clean breach. The Whitworth shell burst in the backing of the same target has been referred to. Experiments on the effect of the 15-inch gun are now in progress. Its hollow 375-pound shot (3-inch walls) was broken without do

ing serious damage to 104-inch laminated armor backed with 18 inches of oak. The comparative test of solid and laminated armor has already been mentioned. The best 44-inch solid plates, well backed, are practically proof against the guns of English iron-clads, namely, 68-pounder smooth-bores and Armstrong 110-pounder rifles, the service charge of each being 16 pounds.

Rifling and Projectiles. The spherical shot, presenting a larger area to the action of the powder, for a given weight, than the elongated rifle-shot, has a higher initial velocity with a given charge; and all the power applied to it is converted into velocity, while a part of the power applied to the rifle-shot is employed in spinning it on its axis. But, as compared with the rifle-shot, at long ranges, it quickly loses, 1st, velocity, because it presents a larger area to the resisting air; 2d, penetration, because it has to force a larger hole through the armor; and 3d, accuracy, because the spinning of the rifle-shot constantly shifts from side to side any inaccuracy of weight it may have on either side of its centre, so that it has no time to deviate in either direction. Practically, however, iron-clad warfare must be at close quarters, because it is almost impossible to aim any gun situated on a movable ship's deck so that it will hit a rapidly moving object at a distance. It is believed by some authorities that elongated shot can be sufficiently well balanced to be projected accurately from smooth-bores; still, it is stated by Whitworth and others that a spinning motion is necessary to keep an elongated shot on end while passing through armor. On the whole, so far as penetrating armor is concerned, the theory and practice favor the spherical shot. But a more destructive effect than mere penetration has been alluded to, the bursting of a shell within the backing of an iron-clad vessel. This can be accomplished only by an elongated missile with a solid head for making the hole and a hollow rear for holding the bursting charge. The

rifle-shot used in America, and the Armstrong and some other European shot, are covered with soft metal, which in muzzle-loaders is expanded by the explosion so as to fill the grooves of the gun, and in breech-loaders is planed by the lands of the gun to fit the rifling, —all of which is wasteful of power. Whitworth employs a solid iron or steel projectile dressed by machinery beforehand to fit the rifling. But as the bore of his gun is hexagonal, the greater part of the power employed to spin the shot tends directly to burst the gun. Captain Scott, R. N., employs a solid projectile dressed to fit by machinery; but the surfaces of the lands upon which the shot presses are radial to the bore, so that the rotation of the shot tends, not to split the gun, but simply to rotate it in the opposite direction.

Mounting Heavy Ordnance, so that it may be rapidly manœuvred on shipboard and protected from the enemy's shot, has been the subject of so much ingenious experiment and invention, that in a brief paper it can only be alluded to in connection with the following subject:

THE STRUCTURE OF WAR-VESSELS.

Size. To attain high speed and carry heavy armor and armament, warvessels must be of large dimensions. By doubling all the lineal dimensions of a vessel of given form, her capacity is increased eight fold, that is to say, she can carry eight times as much weight of engines, boilers, armor, and guns. Meanwhile her resistance is only quadrupled; so that to propel each ton of her weight requires but half the power necessary to propel each ton of the weight of a vessel of half the dimensions. High speed is probably quite as important as invulnerability. Light armor is a complete protection against the most destructive shells, and the old wooden frigates could stand a long batItle with solid shot. But without superior speed, the most invulnerable and

heavily armed vessel could neither keep within effective range of her enemy, nor run her down as a ram, nor retreat when overpowered. And a very fast vessel can almost certainly run past forts, as they are ordinarily situated, at some distance from the channel, without being hit. Indeed, the difficulty of hitting a moving object with heavy cannon is so great that slow wooden ships do not hesitate to encounter forts and to reduce them, for a moving ship can be so manœuvred as to hit a stationary fort.

The disadvantages of large ships are, first, great draught. Although draught need not be increased in the same degree as length, a stable and seaworthy model cannot be very shallow or flat-bottomed. Hence the harbors in which very large vessels can manœuvre are few, and there must be a light-draught class of vessels to encounter enemies of light draught, although they cannot be expected to cope very successfully with fast and heavy vessels. Second, a given sum expended exclusively in large vessels concentrates coast-defences upon a few points, while, if it is devoted to a greater number, consisting partly of small vessels, the line of defences is made more continuous and complete.

System of Protection. But the effectiveness of war-vessels need not depend solely upon their size. First, twice or thrice the power may be obtained, with the same weight of boilers and machinery, and with considerable economy, by carrying very much higher steam, employing simple surface-condensers, and maintaining a high rate of combustion and vaporization, in accordance with the best commercial - marine practice. Second, the battery may be reduced in extent, and the armor thus increased rather than diminished in thickness, with a given buoyancy. At the same time, the fewer guns may be made available in all directions and more rapidly worked, so that, on the whole, a small ship thus improved will be a match in every respect for a large ship as ordi

narily constructed. Working the guns in small revolving turrets, as by Ericsson's or by Coles's plan, and loading and cooling them by steam-power, and taking up their recoil by springs in a short space, as by Stevens's plan, are improvements in this direction. The plan of elevating a gun above a shotproof deck at the moment of aiming and firing, and dropping it for loading or protection by means of hydraulic cylinders, and the plan of placing a gun upon the top of the armor-clad portion of the ship, covering it with a shot-proof hood, and loading it from below, and the plan of a rotating battery, in which one gun is in a position to fire while the others attached to the same revolving frame are loading,-all these obviously feasible plans have the advantages of avoiding port-holes in the inhabited and vital parts of the vessel, of rendering the possible bursting of a gun comparatively harmless to the crew and ship, and of rapid manoeuvring, as compared with the turret system, besides all the advantages of the turret as compared with the casemate or old-fashioned broadside system. The necessity of fighting at close quarters has been remarked. At close quarters, musketballs, grape, and shells can be accurately thrown into ordinary port-holes, which removes the necessity of smashing any other holes in the armor.

Protection at, and extending several feet below the water-line, is obviously indispensable around the battery of a vessel. It is valuable at other points, but not indispensable, provided the vessel has numerous horizontal and vertical bulkheads to prevent too great a loss of buoyancy when the vessel is seriously damaged between wind and water. Harbor-craft may be very low on the water, so that only a little height of protection is required. But it is generally supposed that sea-going vessels must be high out of water. Mr. Ericsson's practice, however, is to the contrary; and it may turn out that a low vessel, over which the sea makes a clean breach, can be

made sufficiently buoyant on his plan. If high sides are necessary, the plan of Mr. Lungley, of London, may be adopted, -a streak of protection at the water-line, and another forming the side of the battery at the top of the structure, with an intermediate unprotected space. A shot-proof deck at the waterline, and the necessary shot-proof passages leading from the parts below water to the battery, would of course be necessary.

Considering the many expedients for vastly increasing the thickness of armor, the idea, somewhat widely expressed, especially in England, that, in view of the exploits of Armstrong, Clay, and Whitworth, iron-protection must be abandoned, is at least premature. The manner in which the various principles of construction have thus far been carried out will be noticed in a brief

Description of Prominent Iron-Clad Vessels. CLASS I. Classified with reference to the protection, the dimensions of the English Warrior and Black Prince are, length 380 feet, beam 58 feet, depth 33 feet, measurement 6,038 tons. Their armor (previously described) extends from the upper deck down to 5 feet below water, throughout 200 feet of the length amidships. Vertical shot-proof bulkheads joining the side armor form a box or casemate in the middle of the vessel, in which the 26 casemate-guns, mostly 68-pounder smooth-bores, are situated and fired through port-holes in the ordinary manner. Their speed on trial is about 14 knots,

at sea, about 12. The Defence and Resistance, of 275 feet length and 3,668 tons, and carrying 14 casemate - guns, are similarly constructed, though their speed is slow. All these vessels are built entirely of iron.

CLASS II. This differs from the first mentioned in having protection all around at the water-line. The New Ironsides, (American,) of 3,250 tons, 240 feet length, 583 feet beam, 28 feet depth, and 15 feet draught, and built of wood, has 44-inch solid armor with 2 feet

backing, extending from the upper deck down to 4 feet below water, with vertical bulkheads like the Warrior, making a casemate 170 feet long, in which there are sixteen 11-inch smooth-bores and two 200-pounder Parrott rifles. A streak of armor, 4 feet below water and 3 feet above, runs from this forward and aft entirely around the vessel. Her speed is 8 knots. The Stevens Battery, (American,) 6,000 tons, constructed of iron and nearly completed, is 420 feet long, 53 feet wide, and 28 feet deep from the top of the casemate, and is iron-clad from end to end along the water-line. As proposed to the last Congress, the central casemate was to be about 120 feet long on the top, its sides being inclined 27 degrees from the horizon, and composed of 63 inches of iron, 14 inches of locust backing, and a half-inch iron lining. Upon the top of it, and to be loaded and manœuvred from within it, were to be five 15-inch smooth-bores and two 10-inch rifled guns clad with armor. The actual horse-power of this ship being above 8,000, her speed would be much higher than that of any other war-vessel. Congress, declining to make an appropriation to complete this vessel, made it over to Mr. Stevens, who had already borne a considerable portion of its cost, and who intends to finish it at his own expense, and is now experimenting to still further perfect his designs. The Achilles (English) now building of iron, about the size of the Warrior, and of 6,039 tons, with a casemate 200 feet long holding 26 guns, belongs to this class. The Enterprise, 180 feet length, 990 tons, 4 casemate-guns, and the Favorite, 220 feet length, 2,168 tons, 8 casemate-guns, are building in England on the same plan. The Solferino and Magenta, (French,) built of wood, and a little longer than the Royal Oak, (see Class III.,) are iron-clad all round up to the main deck, and have two 13gun casemates above it.

CLASS III. The Minotaur, Agincourt, and Northumberland, 6,621 tons, and 390 feet length, resembling, but

somewhat larger than the Warrior, in all their proportions, and now on the stocks in England, are built of iron, and are to have 5-inch armor and 9inch backing extending through their whole length from the upper deck to 5 feet below water, forming a casemate from stem to stern, to hold 40 broadside - guns. Five vessels of the Royal-Oak class, 4,055 tons, building in England, 277 feet long and 58 feet wide, are of wood, being partially constructed frigates adapted to the new service, and are iron-clad throughout their length and height to 5 feet below wa

ter.

They are to carry thirty-two 68pounders. The Hector and Valiant, 4,063 tons, and 275 feet long, are English iron vessels not yet finished. They are completely protected, and carry 30 casemate-guns. All the above vessels are to carry two or more Armstrong swivel-guns fore and aft. Four ves

sels of La Gloire class, (French,) 255 feet long and built of wood, resembling the Royal Oak, carry 34 guns, and are completely clad in 4-inch solid armor. Ten French vessels, of a little larger dimensions, are similarly constructed. The Galena (American) is of this class as to extent of protection, The quality of her armor has been referred to.

CLASS IV. Ships with Revolving Turrets. The Roanoke, (American,) a razeed wooden frigate of 4,500 tons, is 265 feet long, 52 feet wide, and 32 feet deep, and will draw about 21 feet, and have a speed of 8 to 9 knots. This and all the vessels to be referred to in this class are iron-clad from end to end, and from the upper deck to 4 or 5 feet below the water-line. The Roanoke's plates (solid) are 4 inches thick, except at the ends, where they are 3, and are backed with 30 inches of oak. She has three turrets upon her main-deck, each 21 feet in diameter inside, 9 feet high, and composed of 11 thicknesses of 1-inch plates. Her armament is six 15inch

iron, two now building are to be seagoing and very fast, and are to act as rams, like several of the other vessels described. One of these, the Puritan, is 340 feet long, 52 feet wide, and 22 feet deep, and will draw 20 feet. The armor of her hull, 10 inches thick, composed mostly of 1-inch plates and 3 feet of oak backing, projects beyond her sides by the amount of its thickness, and overhangs, forming a solid ram 16 feet long at the bow. The whole upper structure also overhangs the stern, and protects the screw and rudder. This vessel will carry two turrets, 28 feet in diameter inside, 9 feet high, and 2 feet thick, composed of 1-inch plates. Each turret contains two 15-inch guns. The other vessel, the Dictator, is similarly constructed, except that it has one turret, two guns, and 320 feet length. The upper (shot-proof) deck of these vessels is 2 feet out of water. The 18 smaller Ericsson vessels, several of which are ready for service, are 18 inches out of water, of light draught, and about 200 by 45 feet. Their side-armor, laminated, is 5 inches thick, upon 3 feet of oak. They have one turret, like those of the Roanoke, and carry one 15-inch gun and one 11-inch smooth-bore, or a 200pounder rifle. The original Monitor is 174 by 44 feet, with 5-inch side-armor, and a turret 8 inches thick, 20 feet in diameter inside, and armed with two 11inch guns. These vessels of Ericsson's design are each in fact two vessels: a lower iron hull containing boilers and machinery, and an upper scow overhanging the ends and sides, forming the platform for the turret, and carrying the armor. The Onondaga, now constructing, is an iron vessel of 222 feet length, 48 feet beam, and 13 feet depth, with 4-inch solid armor having no backing, and without the overhanging top-works of the Monitors. She has two turrets, like those of the Roanoke, and four 15inch guns. Nearly all the vessels of Class IV. are without spars, and have a pilothouse about 6 feet in diameter and 6 feet