The _Pom-pom_, of which we have heard so much in the late war, is a large edition of the Maxim automatic system with some differences in the system. Its calibre is 1-1/2 inches. Instead of bullets it emits explosive shells 1 lb. in weight, fitted with percussion fuses which burst them into about twelve or fourteen pieces. The effective range is up to 2000 yards, and it will carry to 4000 yards. An improved _Pom-pom_ recently brought out hurls a 1-1/4 lb. shell with effect at a mark 3000 yards away, and as far as 6000 yards before its energy is entirely exhausted. The muzzle velocity of this weapon is 2350 feet a second as against the 1800 feet of the older pattern. They both fire 300 rounds a minute. The _Colt_ automatic gun is an American invention whose automatic action is due to explosion of the charge, not to recoil. The force by which the motions of firing, extracting, and loading are performed is derived from the powder-gases, a portion of which--passing through a small vent in the muzzle--acts by means of a lever on the mechanism of the gun. This is also in two parts: (_a_) _barrel_, attached to (_b_) breech-casing, in which gear for charging, firing, and ejecting is contained. The barrel, made of a strong alloy of nickel, has its cartridges fed in by means of belts coiled in boxes attached to the breech-casing, the boxes moving with the latter so that the movements of the gun do not affect it. These boxes contain 250 cartridges each and are easily replaced. The feed-belt is inserted, and the lever thrown down and moved backward--once by hand--as far as it will go; this opens the breech and passes the first cartridge from the belt to the carrier. The lever is then released and the spring causes it to fly forward, close the vent, and transfer the cartridge from the carrier to the barrel, also compressing the mainspring and opening and closing the breech. On pulling the trigger the shot is fired, and after the bullet has passed the little vent, but is not yet out of the muzzle, the force of the expanding gas, acting through the vent on the piston, sets a gas-lever in operation which acts on the breech mechanism, opens breech, ejects cartridge-case, and feeds another cartridge into the carrier. The gas-lever returning forces the cartridge home in the barrel and closes and locks the breech. The hammer of the gun acts as the piston of an air-pump, forcing a strong jet of air into the chamber, and through the barrel, thus removing all unburnt powder, and thoroughly cleansing it. The metal employed is strong enough to resist the heaviest charge of nitro-powder, and the accuracy of its aim is not disturbed by the vibrations of rapid fire. It does not heat fast, so has no need of a water-jacket, any surplus heat being removed by a system of radiation.