AIR-GUN, an instrument for projecting bullets, in which the moving power is the rush of condensed air allowed to escape, instead of the formation of gases arising from the igni tion of gunpowder.
In the stock of the air-gun is a condensing syringe, the piston of which condenses air into a cavity having a valve opening inwards, just behind the bullet. The barrel is open, and the bullet (which should just fit the barrel) is inserted in the usual way. The trigger opens the valve behind the bullet, and permits the rush of the condensed air, which propels the bullet forward. The moment the finger is withdrawn from the trigger, the air closes the valve, and remains, somewhat less con densed than before, for the next discharge.
The same principle has been variously ap plied. In the magazine air-gun, there is a reservoir of bullets, in a channel tinder the barrel, one of which is turned in by a cylindri cal Cock pierced by a tube, which in one posi tion is a continuation of the reservoir of bul lets, and in another, of the barrel. Thus by
'turning the gun upside down, and turning the cock, a bullet falls into it from the reservoir, which, on returning the cock, is of course in the barrel. In some air-guns, the cavity con taining the condensed air is a hollow copper ball, which can be screwed on to the gun after condensation. The Air-Cane is so called be cause it is usually in the form of a walking stick. The handle contains the condensed air, and can be unscrewed and filled by a separate condensing syringe.
No power, but only a convenient adaptation of power, is gained in an air-gun ; since the ,ondensation of the air itself requires an ex penditure of power. The instrument has hitherto been little more than a toy.
In 1819 a singular air-gun was invented, in which the elastic quality of gutta-percha was brought in aid of the elasticity of air, so as to charge the gun without the necessity for a condensing syringe—such, at least, was the theory of the apparatus.