From the rifle to the Gatling gun is only a step, for the latter is essentially a collection of rifle barrels fired by machinery. It consists of a number—generally ten—of rifle barrels grouped around, and parallel to, a central shaft, each barrel being provided with a lock. By turning a crank at the breech, the barrels and locks are made to revolve together around the shaft, the locks having also a forward and backward motion, the first of which inserts the cartridge into the barrel and closes the breech at the time of the discharge, while the latter extracts the cartridge after firing. Upon the gun, near the breech, is a hopper which receives the cartridges from the feed case. The cartridge falls from the hopper into the breech-block of the uppermost barrel, and in the course of the first half-revolution of the barrel it is inserted, the hammer is drawn back, and at the lowest point of the revolution the breech is closed and the cartridge is fired. As the barrel comes up in the second half-revolution the cartridge shell is extracted, and when the barrel reaches the top it receives another cartridge. The Gatling gun can be fired at the rate of 1000 to 1500 shots a minute. It generally uses the same cartridge as the infantry rifle; but some patterns of the gun fire a projectile an inch in diameter, and approximate closely in their effect to a field gun. The gun is mounted either on a carriage similar to that of a field-piece or on a tripod. Gatling guns were very successfully used by the British in the Zulu War and in the Soudan, and by our own troops in the battles around Santiago. [Illustration: GATLING GUN.] The Gardner is a lighter machine gun than the Gatling. It consists of two parallel rifle barrels, and is operated by means of mechanism at the breech, which, as in the case of the Gatling, is worked with a crank. It can fire 500 shots a minute without danger of overheating, as the breeches are enclosed in a metallic water-jacket. Its extreme portability makes it a most valuable weapon, though its firing capacity is not equal to that of the Gatling. [Illustration: NORDENFELT RAPID FIRE GUN.]