A decisive test of the merits of the turbine engine was given in 1905, when the Cunard Company built two vessels, the _Caronia_ and _Carmania_, of exactly the same size and shape, the _Caronia_ having the highest type of quadruple expansion reciprocating engines, while the _Carmania_ was equipped with turbine engines. Here was a fair test of efficiency between the two types. And the turbine boat proved herself the better of the two by developing more than a knot greater speed per hour. Still the _Carmania_ offered no serious competition in speed to several of the German flyers. But in 1908 two more turbine ships, the _Lusitania_ and _Mauretania_ began making regular transatlantic voyages, and quickly distanced all competitors. In size as well as in speed these sister ships mark an epoch in navigation. Turbine engines take the place of the usual reciprocating type, acting on four propellers for going ahead, and two separate propellers for going astern. These engines develop 68,000 horse-power. Stated in this way these figures convey little idea of the power developed. But when we say that it would take a line of horses one hundred and twenty miles long hitched tandem to develop the power generated in the compact space of the _Mauretania's_ engine room, some idea of the power is gained. It is not the matter of power, size, or speed alone that makes the twentieth century passenger steamer so completely outclass her predecessors. It is really the matter of comfort and safety afforded the ocean travelers. Safety against sinking from injury to the hull was provided for by the introduction of watertight compartments half a century ago, as we have seen; and the size of the _Great Eastern_ has been surpassed in only a few instances. But it is since the beginning of the present century that two revolutionary safety devices have been perfected--wireless telegraphy and the submarine signaling apparatus. The wireless apparatus has been described in another chapter, and as it is used almost as much on land as at sea, cannot be considered as solely a nautical appliance. But the submarine signaling device, which is dependent upon water for transmission, is essentially a nautical mechanism. SUBMARINE SIGNALING It is difficult for the average landsman to appreciate that the one thing most dreaded by mariners is fog. Dark and boisterous nights which frighten the distressed landsman have no terrors for the sailor. Given an open sea-way he knows that he can ride out any gale that blows. It is the foggy night that fills him with apprehension.