When repeating-rifles and machine-guns came into general use a smokeless powder became necessary. Such powders as a rule contain nitro-cellulose (gun-cotton) or nitro-glycerine, or both. These are combined into a plastic, gluey composition, which is then made up into sticks or pellets of various shapes, and usually of large size to lessen the extreme rapidity of their combustion. Substances such as tan, paraffin, starch, bran, peat, &c., &c., and many mineral salts, are used in forming low explosives from high ones. To secure complete combustion some of the larger pellets are made with a central hole, or even pierced by many holes, so that the fire penetrates the entire mass and carries off all its explosive qualities. Our _cordite_ consists of nitro-glycerine dissolving di-nitro cellulose by the acid of a volatile solvent and a mineral jelly or oil. This compound is semi-fluid, and being passed like macaroni through round holes in a metal plate it forms strings or cords of varying size according to the diameter of the holes. Hence the name, cordite. Many experiments in search of more powerful explosives resulted in an almost universal adoption of picric acid as the base. This acid is itself produced by the action of nitric acid upon carbolic acid, and each nation has its own fashion of preparing it for artillery. The French began with _mélinite_ in 1885, this being a mixture of picric acid and gun-cotton. The composition of _lyddite_ (named from its place of manufacture, Lydd, in Kent) is a jealously-guarded British secret. This substance was first used in 5-inch howitzers during the late Soudan campaign, playing a part in the bombardment of Omdurman. The effect of the 50-lb. lyddite shells upon the South African kopjes is described as astounding. When the yellow cloud had cleared away trees were seen uprooted, rocks pulverised, the very face of the earth had changed. Several attempts have been made to utilise dynamite for shells, some of the guns employing compressed air as their motive power. The United States some years ago went to great expense in setting up for this purpose heavy pneumatic plant, which has recently been disposed of as too cumbrous. Dudley’s “Aërial Torpedo” gun discharged a 13-lb. shell containing explosive gelatine, gun-cotton, and fulminate of mercury by igniting the small cordite charge in a parallel tube, through a vent in which the partially cooled gases acted on the projectile in the barrel. This was rotated in the air by inclined blades on a tailpiece, as the barrel could not be rifled for fear of the heat set up by friction. Some guns actuated on much the same principle are said to have been used with effect in the Hispano-American war. Mr. Hudson Maxim with his explosive “maximite” claims to throw half a ton of dynamite about a mile, and a one-ton shell to half that distance.