CANNON

A military engine for projecting balls, shells, . by the force of gun-powder. The principal parts of a cannon are, 1. The breech, which is the solid metal from the bottom of the bore c or concave cylinder to the extremity of the cascabel, a. 2. The trunnions, b b, which pro- 'ect on each side, and serve to support the cannon inequilibrio, their axis being in the vertical plane pa ing through the centre of gravity, but intersecting it below that point. 3. The bore or b cylindrical cavity. This in several sorts of cannon is made of smaller diameter towards the breech, thus a uming the shape of two cylinders united by a portion of a spherical surface. The smaller part of the bore is of such a length as to receive the maximum service charge of gun-powder, and is called the chamber. The entrance of the bore, c, is called the mouth or muzzle. Cannon are made either of cast iron or bra , the latter being an alloy of copper and tin in the proportion of about 10 parts of copper to 1 of tin, and called gun-metal. This has a greater tenacity than iron, but is objectionable on account of its greater density and higher price, besides being liable in rapid service to soften and droop at the muzzle, whereby it is rendered unserviceable. Since the advantage of using smaller charges of gun-powder was discovered, cast iron, though po e ing le tenacity than gun metal, has been substituted for ship, garrison, and battering guns. But the smaller species of cannon (field-pieces) continue to be made generally of bra : for by reason of the rapid cooling of the iron in small ma es its strength is considerably impaired, so that it is difficult to be procured of the requisite quality. Cannon were formerly cast with a cave or hollow, but they are now always cast solid; experience having shown that when cast solid they are stronger, and le liable to burst; that the metal is freer from honeycombs; and that the bore can be rendered more perfect, and its axis made to coincide more accurately with that of the piece. In boring cannon, the gun itself is made to revolve about the bit or borer, the size of which is succe ively increased. In service cannon are mounted on carriages, by which they may be removed from place to place. They are supported on the carriage by the trunnions, about which they move as on an axle; and the form of the carriage is such as to admit of their being elevated or depre ed a few degrees above or below the horizontal plane. See Gun, Gunnery, Howitzer, Mortar. See Greener on* Gunnery; and Wilkinson's Engines of War. [s. 206]