(1.) Absence of vibration. Reciprocating engines, however well balanced, cause a shaking of the whole ship which is very unpleasant to passengers. The turbine, on the other hand, being almost perfectly balanced, runs so smoothly at the highest speeds that, if the hand be laid on the covering, it is sometimes almost impossible to tell whether the machinery is in motion. As a consequence of this smooth running there is little noise in the engine-room--a pleasant contrast to the deafening roar of reciprocating engines. (2.) Turbines occupy less room. (3.) They are more easily tended. (4.) They require fewer repairs, since the rubbing surfaces are very small as compared to those of reciprocating engines. (5.) They are more economical at high speeds. It must be remembered that a turbine is essentially meant for high speeds. If run slowly, the steam will escape through the many passages without doing much work. Owing to its construction, a turbine cannot be reversed like a cylinder engine. It therefore becomes necessary to fit special astern turbines to one or more of the screw shafts, for use when the ship has to be stopped or moved astern. Under ordinary conditions these turbines revolve idly in their cases. The highest speed ever attained on the sea was the forty-two miles per hour of the unfortunate _Viper_, a turbine destroyer which developed 11,500 horse power, though displacing only 370 tons. This velocity would compare favourably with that of a good many expresses on certain railways that we could name. In the future thirty miles an hour will certainly be attained by turbine-driven liners. [7] Even at this speed the wheel has a circumferential velocity of two-thirds that of a bullet shot from a Lee-Metford rifle. A vane weighing only 250 grains (about 1/2 oz.) exerts under these conditions a centrifugal pull of 15 cwt. on the wheel! Chapter IV. THE INTERNAL-COMBUSTION ENGINE. The meaning of the term--Action of the internal-combustion engine--The motor car--The starting-handle--The engine--The carburetter--Ignition of the charge--Advancing the spark--Governing the engine--The clutch--The gear-box--The compensating gear--The silencer--The brakes--Speed of cars. THE MEANING OF THE TERM "INTERNAL-COMBUSTION ENGINE."