Page:The American Cyclopædia (1879) Volume III.djvu/719

 CANNON 709 time the diameter of the bore, H. The first reenforce extends from the base ring to the seat of the ball, and is the thickest part of the piece, for the reason that the pressure of the gas is found by experience and calculation to be the greatest before the ball has moved far from its place. The second reenforce is that portion of the piece to which the trunnions are attached, and extends from the first reenforce to the chase ; it is made thicker than is neces- sary to resist the pressure of the gas, in order to serve as a proper support for the trunnions and to compensate for defects likely to appear in all castings of irregular shapes. The chase extends from the end of the second reenforce to the muzzle, or to the swell of the muzzle, which is now generally omitted from large can- non. Trunnions, F, are cylindrical arms attach- ed to the sides of cannon for the purpose of supporting them upon their carriages, and per- mitting them to be elevated and depressed in action. On the supposition that the strain upon the trunnions is proportional to the weight of the charge, it is laid down as a rule that the di- ameter of a gun's trunnions should be equal to the diameter of its bore, and of a howitzer's equal to the diameter of its chamber. The axis Flo. 7. Dahlgren Gun. of the trunnions is placed in the same plane with the axis of the piece in all the cannon of the United States service ; and in this position the force of the charge is communicated to the trunnions directly, without producing any oth- er than the inevitable strain on the carriage and without checking the recoil. Were the axis of the trunnions above or below that of the piece, the force of the discharge would act to turn the piece slightly upward or downward, producing unequal strains. In many cannon the axis of the trunnions passes also through the centre of gravity of the piece. This arrangement was in- troduced by Gen. Rodman, who has shown that cannon constructed in this way may be fired with accuracy, and, although easily moved, do not when fired sensibly change their position be- fore the projectile leaves the bore. The weight which a cannon should have depends upon the weight of the projectile it is to throw, the maximum velocity which it may be desired to give to it, and the extent of the recoil that can be permitted. The last being limited by the conditions of service, the weight of the piece may be deduced from the principle that the quantity of motion expended on the piece, car- riage, and friction is equal to that expended on the projectile and the air set in motion by the charge. A "gun," technically speaking, is a heavy cannon, intended to throw solid shot with large charges of powder, for the purpose of attaining great accuracy, range, and pene- tration ; it is distinguished from other cannon by its great weight and length, and by the absence of a chamber. It is suitable for firing shell and solid shot. The system of Gen. Paix- hans consists in the employment of shells in heavy cannon, and not in any special form of the gun itself. The howitzer, alluded to before, is a cannon employed to throw large projectiles with small charges of powder ; it is shorter, lighter, and more nearly cylindrical in shape than a gun of the same calibre, and has a chamber for the reception of the charge. The principal advantage of a howitzer over a gun is that it weighs less, and can produce at short range a greater effect with hollow projectiles and case shot. A mortar is a still shorter cannon than a howitzer, and is employed to throw hollow projectiles at greater angles of elevation, so as to produce effect by the force and direction with which they descend upon their object. Columbiads are a kind of cannon FIG. 8. Seacoast Gun. for seacoast purposes, which combine certain qualities of the gun, howitzer, and mortar. They are long chambered pieces, capable of projecting shells and solid shot with heavy charges of powder, at high angles of elevation, and are therefore equally suited for the defence of narrow channels and distant anchorages. They were invented by Col. Bomfprd, an American officer, and were first used in 1812, previous to Gen. Paixhans's adoption of the same idea. The different kinds of cannon are made of various sizes and classifications accor- ding to their use, and are adapted to seacoaat defence, siege, and garrison purposes. Field cannon are used in the operations of armies in the field, and are divided into light and heavy piece's ; the former following the rapid move- ments of infantry and cavalry, and the latter designed to commence action at long distances, and to defend fortifications and other important positions on the field of battle. Formerly light field pieces were 6-pdr. guns and 12-pdr. how- itzers; and the heavy pieces were the 12-pdr. gun and 24 and 32-pdr. howitzers. But at the outbreak of the late war in this country, the heavy pieces were discarded, or used for arming field works and blockhouses, and their places were supplied by the light 12-pdr. smooth-bore guns and the 3-inch rifled guns. These rifle guns are made of wrought iron, by wrapping boiler plate around a mandril so as to form a cylindrical mass, which is firmly and solidly welded by bringing it to a white heat and passing it between rollers. The trunnions