By craning forward over the edge of the ship, a jet of water may be seen spurting from a hole in the side just above the water-line, denoting either that a pump is emptying the bilge, or that the condensers are being cooled ready for the work before them.
Towards the forecastle a busy little donkey engine is lifting bunches of luggage off the quay by means of a rope passing over a swinging spar attached to the mast, and lowering it into the nether regions where stevedores pack it neatly away.
In a small compartment on the upper deck is some mysterious, and not very important-looking, gear: yet, as it operates the rudder, it claims a place of honour equalling that of the main engines which turn the screw.
To the ordinary passenger the very existence of much other machinery--the reversing engines, the air-pumps, the condensers, the "feed" heaters, the filters, the evaporators and refrigerators, and the ventilators--is most probably unsuspected. The electric light he would, from his experience of things ashore, vaguely connect with an engine "somewhere." But the apparatus referred to either works so unobtrusively or is so sequestered from the public eye that one might travel for weeks without even hearing mention of it.
On a warship the amount of machinery is vastly increased. In fact, every war vessel, from the first-class battleship to the smallest "destroyer," is practically a congeries of machines; accommodation for human beings taking a very secondary place. Big guns must be trained, fed, and cleaned by machinery; and these processes, simple as they sound, need most elaborate devices. The difference in respect of mechanism between the _King Edward VII._ and Nelson's _Victory_ is as great as that between a motor-car and a farmer's cart. It would not be too much to say that the mechanical knowledge of any period is very adequately gauged from its fighting vessels.
A gigantic sheer-legs used for lowering boilers, big guns, turrets, etc., into men-of-war. The legs rise to a height of 140 feet, and will handle weights up to 150 tons.]
During the last twenty years marine engines have been enormously improved. But the advance of auxiliary appliances has been even more marked. In earlier times the matter considered of primary importance was the propulsion of the vessel; and engineers turned their attention to the problem of crowding the greatest possible amount of power into the least possible amount of space. This was effected mainly by the "compounding" of engines--using the steam over and over again in cylinders of increasing size--and by improving the design of boilers. As soon as this business had been well forwarded, auxiliary machinery, which, though not absolutely necessary for movement, greatly affected the ease, comfort, and economy of working a ship, got its share of notice, with the result that a tour round the "works" of a modern battleship or liner is a growing wonder and a liberal education in itself.