It is next slowly admitted through the expansion valve into the evaporator. Here it gradually picks up the heat necessary for its gaseous form: taking it from the brine outside the coils, which has a very low freezing-point. The brine is circulated by pumps through pipes lining the walls of the freezing-room, and robs the air there of its heat until a temperature somewhat below the freezing-point of water is reached.
The room is well protected by layers of charcoal or silicate cotton, which are very bad conductors of heat. How the chamber strikes a novice can be gathered from the following description of a Cunard liner's refrigerating room. "It is a curious and interesting sight. It may be a hot day on deck, nearing New York, and everyone is going about in sun hats and light clothes. We descend a couple of flights of stairs, turn a key, and here is winter, sparkling in glassy frost upon the pale carcases of fowls and game, and ruddy joints of meat, crystallising the yellow apples and black grapes to the likeness of sweetmeats in a grocer's shop, gathering on the wall-pipes in scintillating coats of snow nearly an inch deep. You can make a snowball down here, if you like, and carry it up on deck to astonish the languid loungers sheltering from the sun under the protection of the promenade-deck roof. Such is the modern substitute for the old-time salt-beef cask and bags of dried pease!"
The larder is so near the kitchen that while below decks we may just peep into the kitchens, where a white-capped chef presides over an army of assistants. Inside a huge oven are dozens of joints turning round and round by the agency of an invisible electric-motor. But what most tickles the imagination is an electrical egg-boiling apparatus, which ensures the correct amount of cooking to any egg. A row of metal dippers, with perforated bottoms, is suspended over a trough of boiling water. Each dipper is marked for a certain time—one minute, two, three, four, and so on. The dippers, filled with eggs, are pushed down into the water. No need to worry lest they should be "done to a bullet," for at the expiry of a minute up springs the one-minute dipper; and after each succeeding minute the others follow in due rotation. Where 2,000 eggs or more are devoured daily this ingenious automatic device plays no mean part.
THE SEARCH-LIGHT
All liners and war vessels now carry apparatus which will enable them to detect danger at night time, whether rocks or an enemy's fleet, icebergs or a water-logged derelict. On the bridge, or on some other commanding part of the vessel's structure, is a circular, glass-fronted case, backed with a mirror of peculiar shape. Inside are two carbon points almost touching, across which, at the turn of a handle, leaps a shower of sparks so continuous as to form a dazzling light. The rays from the electric arc, as it is called, either pass directly through the glass lens, or are caught by the parabolic reflector and shot back through it in an almost parallel pencil of wonderful intensity, which illumines the darkness like a ray of sunshine slanting through a crack in the shutter of a room. The search-light draws its current from special dynamos, which absorb many horse-power in the case of the powerful apparatus used on warships. At a distance of several miles a page of print may be easily read by the beams of these scrutinisers of the night.
The finest search-lights are to be found ashore at naval ports, where, in case of war, a sharp look-out must be kept for hostile vessels. Portsmouth boasts a light of over a million candle-power, but even this is quite eclipsed by a monster light built by the Schuckert Company, of Nuremberg, Germany, which gives the effect of 816,000,000 candles. An instrument of such power would be useless on board ship, owing to the great amount of current it devours, but in a port, connected with the lighting plant of a large town, it would serve to illumine the country round for many miles.
In addition to its value as an "eye," the search-light can be utilised as an "ear." Ernst Ruhmer, a German scientist, has discovered a method of telephoning along a beam of light from a naval projector. The amount of current passing into the arc is regulated by the pulsations of a telephone battery and transmitter. If the beam be caught by a parabolic reflector, in the focus of which is a selenium cell connected with a battery and a pair of sensitive telephone receivers, the effect of these pulsations of light is heard. Selenium being a metal which varies its resistance to an electric circuit in proportion to the intensity of light shining upon it, any fluctuations of the search-light's beams cause electric fluctuations of equal rapidity in the telephone circuit; and since these waves arise from the vibrations of speech, the electric vibrations they cause in the selenium circuit are retransformed at the receiver into the sounds of speech. This German apparatus makes it possible to send messages nine or ten miles over a powerful projector beam.
In the United States Navy, and in other navies as well, night signals are flashed by the electric light. The pattern of lamp used in the United States Navy is divided transversely into two compartments, the upper having a white, the lower a red, lens. Four of these lamps are hung one above the other from a mast. A switch-board connected with the eight incandescent lamps in the series enables the operator to send any required signal, one letter or figure being flashed at a time. During the Spanish-American War the United States fleet made great use of this simple system, which on a clear night is very effective up to distances of four miles.