is a wonderful piece of mechanism, so wonderful that to the ordinary spectator it seems almost endowed with intelligence. To see it lying in its cradle ashore it is simply a beautifully polished smooth steel cylinder. The fore end is blunt and with an innocent-looking steel spike projecting from the centre of its rounded front, but it is this spike which strikes the object aimed at and causes the ignition of the explosive an inch or two behind it in the head of the cylinder. The torpedo has a fine run aft for about a third of its length, and at the after end are two vertical and two horizontal rudders, and two screws revolving in opposite directions. It is some time since compressed air was adopted as the motive power. The efficacy of the compressed cold air has been increased to an extraordinary degree by the introduction of an apparatus for heating the air. A torpedo fitted with a heater can travel over double the distance at a given speed and the same expenditure of air that a torpedo without a heater can. “If a torpedo be run for the same distance with a heater as a similar torpedo without a heater, a 100 per cent. gain of power would be realised by increasing the speed, and at a range of 2,000 yards this increase is from 26 knots to 33.5 knots, the highest which has ever been realised with a torpedo over a range of 2,000 yards.”[56] The newest form of torpedo is that in which hot air instead of cold air is used. [Illustration: A TORPEDO. DISCHARGED FROM A DESTROYER, TRAVELLING BY ITS OWN ENGINES TOWARDS AN ARMOURED BATTLESHIP.] In the case of the latest pattern 18-inch Whitehead torpedo, a speed of 28 knots for 2,000 yards, or 34½ knots for 1,000 yards when using the ordinary cold air, has been obtained. For longer distances, such as 3,000 and 4,000 yards, the speed is proportionately less, falling to about 20 knots for the 4,000 yards range. When using the heater, “the same torpedo maintains a speed of over 40 knots for 1,000 yards, 37 knots for 2,000 yards, 30 knots for 3,000 yards, and 27 knots for 4,000 yards. The speeds are quite extraordinary, as they represent exactly 100 per cent. more power from the engines, and it is further pointed out that the heater is extremely small, simple, and burns any ordinary lamp oil, and is capable of being fitted to practically any existing type of torpedo. The Admiralty has never been slow to adopt improvements in the torpedo armament of the fleet, and for years Great Britain has led in the matter of submarine tubes for firing torpedoes.”[57] The explosive carried, usually gun-cotton, weighs 200 lb. An ingenious arrangement of gyroscope, valve and pendulum causes the torpedo to remain at the required depth, and to return to it if it should be diverted from it.