The Frazer gun is a modification of the Armstrong; the number of coils being lessened, cheaper iron used for the outer coils, which are shrunk on with the trunnion piece, and the arrangement of shoulders and recesses, to prevent separation of the parts, being improved. Whitworth guns are made of a substance called "homogeneous iron," a species of low steel said to be made by melting short bars of Swedish iron and adding a small amount of carbonaceous matter.

Fig. 5. - Diagram of Gun Carriage. 1, 1. Foot Boards. 2. Pintle Hook. 3. Pole. 4. Prolonge. 5. Trace Hooks.

6. Ammunition Chest. 7. Elevating Screw.

Fig. 6. - Dahlgren Gun.

Fig. 7. - 13-inch Mortar.

Fig. 8. - Field 6-pdr. smooth-bore Bronze Gun.

Fig. 9. - Armstrong Gun.

The smaller Whitworth guns are forged solid; the larger built up with coils or hoops, which are forced on by hydraulic pressure, being made with a slight taper and the ends joined by screw threads. The hoops are first cast hollow and then hammered out over a steel mandrel, or rolled out in a machine like that used for forming wheel tire; before receiving their final finish, they are subjected to an annealing process for three or four weeks, which, though making the metal very ductile, slightly impairs its tenacity; the breech pin is made with offsets in such a way as to screw into the end of the barrel and the next two surrounding hoops, the breech in the larger guns being hooped with a harder and higher steel than that used for the barrel. The cross section of the bores of the Whitworth guns is a hexagon with rounded corners, and the twist is very rapid. The projectiles are very long, those intended for armor punching being made of hardened iron or steel with very thick flat heads to prevent glancing; shells of this kind have no fuse, the bursting charge being ignited by the heat generated by the violent blow of the projectile on the plate; the powder before being inserted is wrapped in one or more thicknesses of flannel, thus interposing a slow conductor between it and the heated metal, and delaying the explosion until the shell has completed its penetration.

The principal Whitworth guns are the 120, 70, and 12-pdrs. of 6.4, 5, and 2.75 inches diameter respectively, and firing 151, 81, and 12-lb. projectiles. - The Blakely gun combines in its construction the principles of initial tension and varying elasticity, the object being to bring the strength of all the metal of the piece into simultaneous play to resist explosion. The inner tube or barrel is made of low steel, having considerable but not quite enough elasticity; the next tube is made of high steel with less elasticity, and is shrunk on the barrel with just sufficient tension to compensate for the insufficient difference of the elasticity between the two tubes; the outer cast-iron jacket, to which the trunnions are attached, is the least elastic of all. and is put on with only the shrinkage obtained by warming it over a fire. The steel tubes are cast hollow and hammered over steel mandrels, under steam hammers; by this process they are elongated about 130 per cent., and the tenacity of the metal is increased; all the parts are annealed. Blakely guns are rifled with one-sided grooves, and are tired with expanding projectiles.

The principal calibres are the 700, 550, 350, 250, 200, 120, and 100-pdrs., the diameters of the bore varying from 12 inches to 6.4 inches, and the weights of projectiles from 700 to 100 lbs. Palliser's manner of making a gun consists in introducing into a cast-iron gun a hollow cylinder of coiled wrought iron, of such thickness in proportion to its calibre that the residual strain borne by the tube has such a relation to the strain it transmits to the surrounding cast iron as is best proportioned to their respective elasticities; and by varying the thickness of the tube, the transmitted strains can be regulated with the greatest nicety. In the larger guns he proposes to use two or more concentric tubes; in the very largest, three tubes, the inner one to be of the softest and most ductile wrought iron, the next of a stronger and harsher quality, and the third of steel for some distance in front of the chamber. Old smooth-bored guns, chiefly 68-pdrs., reamed out and strengthened in this way, have shown remarkable endurance, and have been thus utilized in large numbers.

Parsons's plan of conversion consists in introducing a tube with a jacket, both of steel, through the breech of a gun, which is afterward stopped up by screwing in a large cascabel; though stronger than Palliser's method, it is much more expensive. Mon-crieff's counterpoise gun carriage is designed to shield heavy guns from direct fire, and enable them to be loaded under cover. Having given satisfactory results upon its trial in 1808, the British propose to use it extensively for coast defence, particularly in low sites where the batteries are but little above the water level. The top carriage rests on a strong bolt connecting two elevators, curved in rear, and with a box between them for the counterpoise, which is rather heavier than the gun. Upon firing the recoil makes the elevators roll backward on the chassis, the gun descending and the counterpoise rising. The weight of the latter gradually checks the motion and brings the piece to rest below the parapet, where a brake holds the elevators down until the loading is completed. - During the past decade the Prussian artillery has taken the foremost place, a consequence in great part of Krupp's excellent system of breech-loading rifled cannon.