CANNON. A military engine for pro jecting balls, shells, &e., by the force of gunpowder. The principal parts of a cannon arc : 1. The breech, which is the solid metal from the bottom of the bore, or concave cy linder, to the extremity of the cascabel, a. 2. The true nions,b b, which project on each side, and serve to sup port the cannon in equili brio, their axis being in the vertical plane passing through the centre of gra vity, but intersecting it be low that point. 3. The bore or cylindrical cavity. This in several sorts of cannon is made of smaller diameter towards the breech, thus assuming 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 gunpowder, 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 brass, 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 gunpowder was discovered, cast iron, though possessing less tenacity than gun metal, has been substituted for ship, gar rison, and battering guns. But the small er species of cannon (field-pieces) con tinue to be made generally of brass : for by reason of the rapid cooling of the iron in small masses its strength is considera bly 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 less 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 succes sively increased.