the screw, and so of the ship, but yet allowed the actual engines to run comparatively slowly. This toothed wheel idea was a better method than that employed in the _Great Britain’s_ engines, though it was only just one stage better. There was a rooted objection in the early days of the screw to running the engines at a great speed, and thus it was only by some such means of gearing that the propeller was made to revolve quickly. In the course of time, when a wider experience and knowledge of engineering matters had been obtained, the gearing was done away with and the engines became direct-acting, and so there ensued far less friction, an absence of complication, and less expense caused by gearing. At the same time the power obtained by the newer method became more direct. A customary apparatus nowadays adopted for steamships is the surface condenser, and in the effort to increase the steam pressures this has been a potent factor. But it had already been tried by Watt, by David Napier, and re-introduced by Samuel Hall in 1831. The surface condenser consists of a number of brass tubes about three quarters of an inch in diameter, through which a stream of cold water circulates. This necessarily keeps the pipes cool, and thus condenses the exhaust steam which is thrown on to them from the cylinder; it is practically a kind of tubular boiler. Instead of the jet, as in the older form of condenser, it is the outside of the pipes which performs the office, and the air-pump does its work as before. The condensed steam is now available for feeding the boiler, and after being filtered the feed pump draws it into a heater and thence it is led into the boiler once more. If the reader will now turn to the illustration facing page 132 once more, he will see in the right hand of the picture that in the _Candia_ the feed and bilge pumps were worked by small beams from an eccentric. By being able to use this water for the boilers a great economy was effected, but in some of the P. and O. liners the boilers suffered rather badly, since an injurious chemical action was set up owing to the continuous return of the same water backwards and forwards from the condenser. Nowadays the problems connected with the condenser have been fully mastered, and the advantage of being able to use distilled water is obvious; for one of the surest and quickest methods of bringing about ruin is to use sea-water for the boiler, over which it will lay a thick crust of salt.