Air-gun.

Air-gun. There are several forms of this weapon, but it is commonly made like a fowling-piece or musket, with lock, stock, and barrel. In one of the simplest kinds there is an air-chamber placed above the barrel, and the two communicate by a valve opening just behind where the bullet is placed. By means of a syringe in the stock, the air is condensed in the chamber. On pulling the trigger the valve opens, and immediately the bullet is projected with considerable force by the elasticity of the compressed air behind it. In air-guns, the reservoir of condensed air is usually very large in proportion to the tube which contains the ball, so that its elastic force is not greatly diminished by expanding through it. These guns commonly propel a bullet to a distance of from 60 to 80 yards. One form of air-gun contains several bullets in a receptacle or channel under the barrel; by the movement of a cock or lever, one of these bullets can readily be shifted into the barrel; and thus several successive discharges can be made after one loading—on a principle somewhat analogous to that of the revolving pistol. Some varieties of air-guns have the condensing syringe detached, by which means greater condensation of air may be produced; this done, the air-chamber is again attached to the barrel. A pressure of as much as 500 atmospheres has been attained with a powerful condenser, but even this is only about half the elastic force of fired gunpowder. Those air-guns which present the external appearance of stout walking-sticks, and are thence called air-canes, have a chamber within the handle for containing condensed air, which can be unscrewed, and subjected to the action of the condensing syringe. The air-gun was known in France more than two centuries ago; but the ancients were acquainted with some kind of apparatus by which air was made to act upon the shorter arm of a lever, while the larger arm impelled a bullet. Among the English patents which have been taken out for peculiar forms of air-guns in comparatively recent years are the following: P. Giffard in 1872; A. Pope (H. M. Quackenbush) in 1874; G. G. Bussey in 1876; and F. Wirth (M. Weber) in 1877. Inventions for using compressed air to fire large shot with pieces of ordnance have been patented by Bessemer (1867) and others. Lieutenant Zalinski of the U.S. army invented in 1886 a large 'pneumatic gun' for throwing shells containing dynamite. The gun was of iron, 60 feet long, 8 inches in the bore, and $\backslash frac\{1\}\{2\}$ inch thick. Air at 1000 lb. pressure, supplied from eight reservoirs, each 20 feet long by 12 inches in diameter, was admitted through one of the trunnions to a chamber in the gun just behind the projectile. An automatic valve permitted a volume of the compressed air to escape into this chamber. A shell containing 100 lb. of explosives was thrown 3000 yards (see CANNON, p. 714). This gun, condemned in 1889, was improved in 1890-94; a special steamer was built for the armament, with which extensive experiments were made; and New York and San Francisco harbours have powerful pneumatic dynamite guns amongst their defences.