THE REVERSING ENGINE — MARINE ENGINE SPEED GOVERNORS — THE STEERING ENGINE — BLOWING AND VENTILATING APPARATUS — PUMPS — FEED HEATERS — FEED-WATER FILTERS — DISTILLERS — REFRIGERATORS — THE SEARCH-LIGHT — WIRELESS TELEGRAPHY INSTRUMENTS — SAFETY DEVICES — THE TRANSMISSION OF POWER ON A SHIP

With many travellers by sea the first impulse, after bunks have been visited and baggage has been safely stored away, is to saunter off to the hatches over the engine-room and peer down into the shining machinery which forms the heart of the vessel. Some engine is sure to be at work to remind them of the great power stored down there below, and to give a foretaste of what to expect when the engine-room gong sounds and the man in charge opens the huge throttle controlling some thousands of horse-power.

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.

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.

This chapter will deal with the auxiliaries to be found in large vessels designed for peaceful or warlike uses. Many devices are common to ships of both classes, and some are confined to one type only, though the "steel wall" certainly has the advantage with regard to multiplicity.

We may begin with

THE REVERSING ENGINE

All marine engines should be fitted with some apparatus which enables the engineer to reverse them from full speed ahead to full speed astern in a few seconds. The effort required to perform the operation of shifting over the valves is such as to necessitate the help of steam. Therefore you will find a special device in the engine-room which, when the engineer moves a small lever either way from the normal position, lets steam into a cylinder and moves rods reversing the main engine. By a link action (which could not be explained without a special diagram) the valves of the auxiliary are closed automatically as soon as the task has been performed; so that there is no constant pressure on the one or the other side of its piston. To prevent the reversal being too sudden, the auxiliary's piston-rod is prolonged, and fitted to a second piston working in a second cylinder full of glycerine or oil. This piston is pierced with a small hole, through which the incompressible liquid passes as the piston moves. Since its passage is gradual, the engines are reversed deliberately enough to protect their valves from any severe strains. These reversing engines can, if the steam serving them fails, be worked by hand.

MARINE ENGINE SPEED GOVERNORS

When a ship is passing through a strong sea and pitches as she crosses the waves, the screw is from time to time lifted clear of the water, and the engines which a moment before had been doing their utmost, suddenly find their load taken off them. The result is "racing" of the machinery, which makes itself very unpleasantly felt from one end of the ship to the other. Then the screw, revolving at a speed much above the normal, suddenly plunges into the water again, and encounters great resistance to its revolution.

A series of changes from full to no "load," as engineers term it, must be harmful to any engines, even though the evil effects are not shown at once. Great strains are set up which shake bolts loose, or may crack the heavy standards in which the cranks and shaft work, and even seriously tax the shaft itself and the screw. On land every stationary engine set to do tasks in which the load varies—which practically means all stationary engines—are fitted with a governor, to cut off the steam directly a certain rate of revolution is exceeded. These engines are the more easily governed because they carry heavy fly-wheels, which pick up or lose their velocity gradually. A marine engine, on the other hand, has only the screw to steady it, and this is extremely light in proportion to the power which drives it; in fact, has scarcely any controlling influence at all as soon as it leaves the water.

Marine engineers, therefore, need some mechanical means of restraining their engines from "running away." The device must be very sensitive and quick acting, since the engines would increase their rate threefold in a second if left ungoverned when running "free"; while on the other hand it must not throttle the steam supply a moment after the work has begun again when the screw takes the water.

Many mechanisms have been invented to curb the marine engine. Some have proved fairly successful, others practically useless; and the fact remains that, owing to the greater difficulty of the task, marine governing is not so delicate as that of land engines. A great number of steamships are not fitted with governors, for the simple reason that the engineers are sceptical about such devices as a class and "would rather not be bothered with them."

But whatever may have been its record in the past, the marine governor is at the present time sufficiently developed to form an item in the engine-rooms of many of our largest ships. We select as one of the best devices yet produced that known as Andrews' Patent Governor; and append a short description.

It consists of two main parts—the pumps and the ram closing the throttle. The pumps, two in number, are worked alternately by some moving part of the engine, such as the air-pump lever. They inject water through a small pipe into a cylinder, the piston-rod of which operates a throttle valve in the main steam supply to the engines. At the bottom of this cylinder is a by-pass, or artificial leak, through which the water flows back to the pumps. The size of the flow through the by-pass is controlled by a screw adjustment.

We will suppose that the governor is set to permit one hundred revolutions a minute. As long as that rate is not exceeded the by-pass will let out as much water as the pumps can inject into the cylinder, and the piston is not moved. But as soon as the engines begin to race, the pumps send in an excess, and the piston immediately begins to rise, closing the throttle. As the speed falls, the leak gets the upper hand again, and the piston is pushed down by a powerful spring, opening the throttle.

It might be supposed that, when the screw "races," the pumps would not only close the throttle, but also press so hard on it as to cause damage to some part of the apparatus before the speed had fallen again. This is prevented by the presence of a second control valve (or leak) worked by a connecting-rod rising along with the piston-rod of the ram. The two rods are held in engagement by a powerful spring which presses them together, so that a hollow in the first engages with a projection on the second. Immediately the pressure increases and the piston rises, the second valve is shut by the lifting of its rod, and so farther augments the pressure in the cylinder and quickens the closing of the throttle valve. This pressure increase must, however, be checked, or the piston would overrun and stop the engines. So when the piston has nearly finished its stroke the connecting-rod comes into contact with a stop which disengages it from the piston-rod and allows the second control valve to be fully opened by the spring pulling on its rod. The piston at once sinks to such a position as the pressure allows, and the action is repeated time after time.

The governing is practically instantaneous, though without shock, and is said to keep the engine within 3 per cent. of the normal rate. That is, if 100 be the proper number of revolutions, it would not be allowed to exceed 103 or drop below 97. Such governing is, in technical language, very "close."

The idea is very ingenious: pumps working against a leak, and as soon as they have mastered it, being aided by a secondary valve which reduces the size of the leak so as to render the effect of the pumps increasingly rapid until the throttle has been closed. Then the secondary valve is suddenly thrown out of action, gives the leak full play, and causes the throttle to open quickly so that the steam may be cut off only for a moment. By the turning of a small milled screw-head a couple of inches in diameter the pace of 5,000 h.p. engines is as fully regulated as if a powerful brake were applied the moment they exceeded "the legal limit."

STEERING ENGINES

The uninitiated may think that the man on the bridge, revolving a spoked-wheel with apparently small exertion, is directly moving the rudder to port or to starboard as he wishes. But the helm of a large vessel, travelling at high speed, could not be so easily deflected were not some giant at work down below in obedience to the easy motions of the wheel.

Sometimes in a special little cabin on deck, but more often in the engine-room, where it can be tended by the staff, there is the steering engine, usually worked by steam-power. Two little cylinders turn a worm-screw which revolves a worm-wheel and a train of cogs, the last of which moves to right or left a quadrant attached to the chains or cables which work the rudder. All that the steersman has to do with his wheel is to put the engine in forward, backward, or middle gear. The steam being admitted to the cylinders quickly moves the helm to the position required.

A particularly ingenious steam gear is that made by Messrs. Harfield and Company, of London. Its chief feature is the arrangement whereby the power to move the rudder into any position remains constant. If you have ever steered a boat, you will remember that, when a sudden curve must be made, you have to put far more strength into the tiller than would suffice for a slight change of direction. Now, if a steam-engine and gear were so built as to give sufficient pressure on the helm in all positions, it would, if powerful enough to put the ship hard-a-port, evidently be overpowered for the gentler movements, and would waste steam. The Harfield gear has the last of the cog-train—the one which engages with the rack operating the tiller—mounted eccentrically. The rack itself is not part of a circle, but almost flat centrally, and sharply bent at the ends. In short, the curve is such that the rack teeth engage with the eccentric cog at all points of the latter's revolution.

When the helm is normal the longest radius of the eccentric is turned towards the rack. In this position it exerts least power; but least power is then needed. As the helm goes over, the radius of the cogs gradually decreases, and its leverage proportionately increases. So that the engine is taxed uniformly all the time.

Some war vessels, including the ill-fated Russian cruiser Variag, have been fitted with electric steering gear, operated by a motor in which the direction of the current can be varied at the will of the helmsman.

All power gears are so arranged that, in case of a breakdown of the power, a hand-wheel can be quickly brought into play.

BLOWING AND VENTILATING APPARATUS

A railway locomotive sends the exhaust steam up the funnel with sufficient force to expel all air from the same and to create a vacuum. The only passage for the air flying to fill this empty space lies through the fire-box and tubes traversing the boiler from end to end. Were it not for the "induced draught"—the invention of George Stephenson—no locomotive would be able to draw a train at a higher speed than a few miles an hour.

On shipboard the fresh water used in the boilers is far too precious to be wasted by using it as a fire-exciter. Salt water to make good the loss would soon corrode the boilers and cause terrible explosions. Therefore the necessary draught is created by forcing air through the furnaces instead of by drawing it.

The stoke-hold is entirely separated from the outer air, except for the ventilators, down which air is forced by centrifugal pumps at considerable pressure. This draught serves two purposes. It lowers the temperature of the stoke-hold, which otherwise would be unbearable, and also feeds the fires with plenty of oxygen. The air forced in can escape in one way only, viz. by passing through the furnaces. When the ship is slowed down the "forced draught" is turned off, and then you see the poor stokers coming up for a breath of fresh air. In the Red Sea or other tropical latitudes these grimy but useful men have a very hard time of it. While passengers up above are grumbling at the heat, the stoker below is almost fainting, although clad in nothing but the thinnest of trousers.

In the engine-room also things at times become uncomfortably warm. Take the case of the United States monitor Amphitrite, which went into commission in 1895 for a trial run.

Both stoke-hold and engine-room were very insufficiently ventilated. The vessel started from Hampton Roads for Brunswick, Georgia. "The trip of about 500 miles occupied five days in the latter part of July, and, for sheer suffering, has perhaps seldom been equalled in our naval history. The fire-room (stoke-hold) temperature was never below 150°, and often above 170°, while the engine-room ranged closely about 150°. For the first twenty-four hours the men stood it well, but on the second day seven succumbed to the heat and were put on the sick list, one of them nearly dying; before the voyage was ended, twenty-eight had been driven to seek medical attendance. The gaps thus created were partially filled with inexperienced men from the deck force, until there was only a lifeboat's crew left in each watch.... On the evening of the fourth day out our men had literally fought the fire to a finish and had been vanquished; the watch on duty broke down one by one, and the engines, after lumbering along slower and slower, actually stopped for want of steam.... At daybreak the next morning we got under way and steamed at a very conservative rate to our destination, fortunately only about ten miles distant. The scene in the fire-room that morning was not of this earth, and far beyond description. The heat was almost destructive to life; steam was blowing from many defective joints and water columns; tools, ladders, doors, and all fittings were too hot to touch; and the place was dense with smoke escaping from furnace doors, for there was absolutely no draught. The men collected to build up the fires were the best of those remaining fit for duty, but they were worn out physically, were nervous, apprehensive, and dispirited. Rough Irish firemen, who would stand in a fair fight till killed in their tracks, were crying like children, and begging to be allowed to go on deck, so completely were they unmanned by the cruel ordeal they had endured so long. 'Hell afloat' is a nautical figure of speech often idly used, but then we saw it. For a month thereafter the ship was actively employed on the southern coast, drilling militia at different ports, and sweltering in the new dock at Port Royal. One trip of twenty-nine hours broke the record for heat, the fire-room being frequently above 180°. All fire-room temperatures were taken in the actual spaces where the men had to work, and not from hot corners or overhead pockets."[16]

The ventilators were subsequently altered, and the men enjoyed comparative comfort. The words quoted will suffice to establish the importance of a proper current of air where men have to work. One of the greatest difficulties encountered in deep mining is that, while the temperature approaches and sometimes passes that of a stoke-hold, the task of sending down a cool current from above is, with depths of 4,000 ft. and over, a very awkward one to carry out.

On passenger ships the fans ventilating the cabins and saloons are constantly at work, either sucking out foul air or driving in fresh. The principle of the fan is very similar to that of the centrifugal water pump—vanes rotating in a case open at the centre, through which the air enters, to be flung by the blades against the sides of the case and driven out of an opening in its circumference. Sometimes an ordinary screw-shaped fan, such as we often see in public buildings, is employed.

PUMPS

Every steamship carries several varieties of pump. First, there are the large pumps, generally of a simple type, for emptying the bilge or any compartment of the ship which may have sprung a leak. "All hands to the pumps!" is now seldom heard on a steamer, for the opening of a steam-cock sets machinery in motion which will successfully fight any but a very severe breach. It is needless to say that these pumps form a very important part of a ship's equipment, without which many a fine vessel would have sunk which has struggled to land.

The pumps for the condensers form another class. These are centrifugal force pumps; their duty is to circulate cold sea-water round the nests of tubes through which steam flows after passing through the cylinders. It is thus converted once more into water, ready for use again in the boiler. Every atom of the water is evaporated, condensed, and pumped back into the boiler once in a period ranging from fifteen minutes to an hour, according to the type of boiler and the size of the supply tanks.

Some condensers have the cooling water passed through the tubes, and the steam circulated round these in an air-tight chamber. In any case, the condenser should be so designed as to offer a large amount of cold surface to the hot vapour. A breakdown of the condenser pumps is a serious mishap, since steam would then be wasted, which represents so much fresh water—hard to replace in the open sea. It would be comparable to the disarrangement of the circulating pump on a motor-car, though the effects are different.

We must not forget the feed-pumps for the boilers. On their efficient action depends the safety of the ship and her passengers. Water must be maintained at a certain level in the boiler, so that all tube and other surfaces in direct contact with the furnace gases may be covered. The disastrous explosions we sometimes hear of are often caused by the failure of a pump, the burning of a tube or plate, and the inevitable collapse of the same. The firms of Weir and Worthington are among the best-known makers of the special high-pressure pumps used for throwing large quantities of water into the boilers of mercantile and war vessels.

FEED HEATERS

As the fuel supply of a vessel cannot easily be replenished on the high seas, economy in coal consumption is very desirable.

If you put a cold spoon into a boiling saucepan ebullition is checked at once, though only for a moment, while the spoon takes in the temperature of the water. Similarly, if cold water be fed into a boiler the steam pressure at once falls. Therefore the hotter the feed water is the better.

The feed heater is the reverse of the condenser. In the latter, cold water is used to cool hot steam; in the former, hot steam to heat cold water. There are many patterns of heaters. One type, largely used, sprays the cold water through a valve into a chamber through which steam is passed from the engines. The spray, falling through the hot vapour, partially condenses it and takes up some of its heat. The surplus steam travels on to the condensers. A float in the lower part of the chamber governs a valve admitting steam to the boiler pumps, so that as soon as a certain amount of water has accumulated the pumps are started, and the hot liquid is forced into the boiler.

Another type, the Hampson feeder, sends steam through pipes of a wavy form surrounded by the feed water, there being no actual contact between liquid and vapour.

An ally of the heater is the

FEED-WATER FILTER,

which removes suspended matter which, if it entered the boiler, would form a deposit round the tubes, and while decreasing their efficiency, make them more liable to burning. The most dangerous element caught by the filters is fatty matter—oil which has entered the cylinders and been carried off by the exhaust steam.

The filter is either high pressure, i.e. situated between the pump and the boiler; or low pressure, i.e. between the pump and the reservoir from which it draws its water. The second class must have large areas, so as not to throttle the supply unduly.

Many kinds of filtering media have been tried—fabrics of silk, calico, cocoanut fibre, towelling, sawdust, cork dust, charcoal, coke; but the ideal substance, at once cheap, easily obtainable, durable, and completely effective, yet remains to be found.

A filter should be so constructed that the filtering substance is very accessible for cleansing or renewal.

DISTILLERS

We now come to a part of a ship's plant very necessary for both machines and human beings. Many a time have people been in the position of the Ancient Mariner, who exclaimed:—

"Water, water, everywhere,
But not a drop to drink!"

Water is so weighty that a ship cannot carry more than a very limited quantity, and that for the immediate needs of her passengers. The boilers, in spite of their condensers, waste a good deal of steam at safety valves through leaking joints and packings, and in other ways. This loss must be made good, for, as already remarked, salt water spells the speedy ruin of any boiler it enters.

The distiller in its simplest form combines a boiler for changing water into vapour, with a condenser for reconverting it to liquid. Solids in impure water do not pass off with the steam, so that the latter, if condensed in clean vessels, is fit for drinking or for use in the engine boilers.

A pound of steam will, under this system, give a pound of water. But as such procedure would be extravagant of fuel, compound condensers are used, which act in the following manner.

High-pressure steam is passed from the engine boilers into the tubes of an evaporator, and converts the salt water surrounding it into steam. The boiler steam then travels into its own condenser or into the feed water heater, while the steam it generated passes into the coils of a second evaporator, converts water there into steam, and itself goes to a condenser. The steam generated in the second evaporator does similar duty in a third evaporator. So that one pound of high-pressure steam is directly reconverted to water, and also indirectly produces between two and three pounds of fresh water.

The condensers used are similar to those already described in connection with the engines, and need no further comment. About the evaporators, it may be said that they are so constructed that they can be cleaned out easily as soon as the accumulation of salt and other matter renders the operation necessary. Usually one side is hinged, and provided with a number of bolts all round the edges which are quickly removed and replaced.

The United States Navy includes a ship, the Iris, whose sole duty is to supply the fleet she attends with plenty of fresh water. She was built in 1885 by Messrs. R. and W. Hawthorn, of Newcastle-on-Tyne, and measures 310 feet in length, 38 1 / 2 feet beam. For her size she has remarkable bunker capacity, and can accommodate nearly 2,500 tons of coal. Fore and aft are huge storage tanks to hold between them about 170,000 gallons of fresh water. Her stills can produce a maximum of 60,000 gallons a day. It has been reckoned that each ton of water distilled costs only 18 cents; or, stated otherwise, that 40 gallons cost one penny. At many ports fresh water costs three or four times this figure; and even when procured is of doubtful purity. During the Spanish-American War the Iris and a sister ship, the Rainbow, proved most useful.

REFRIGERATORS

Of late years the frozen-meat trade has increased by leaps and bounds. Australia, New Zealand, Argentina, Canada, and the United States send millions of pounds' worth of mutton and beef across the water every year to help feed the populations of England and Europe.

In past times the live animals were sent, to be either killed when disembarked or fatted up for the market. This practice was expensive, and attended by much suffering of the unfortunate creatures if bad weather knocked the vessel about.

Refrigerating machinery has altered the traffic most fundamentally. Not only can more meat be sent at lower rates, but the variety is increased; and many other substances than flesh are often found in the cold stores of a ship—butter and fruit being important items.

Certain steamship lines, such as the Shaw, Savill, and Albion—plying between England and Australasia—include vessels specially built for the transport of vast numbers of carcases. Upwards of a million carcases have been packed into the hull of a single ship and kept perfectly fresh during the long six weeks' voyage across the Equator.

Every passenger-carrying steamer is provided with refrigerating rooms for the storage of perishable provisions; and as the comfort of the passengers, not to say their luxury, is bound up with these compartments, it will be interesting to glance at the method employed for creating local frost amid surrounding heat.

The big principle underlying the refrigerator is this—that a liquid when turned into gas absorbs heat (thus, to convert water into steam you must feed it with heat from a fire), and that as soon as the gas loses a certain amount of its heat it reverts to liquid form.

Now take ammonia gas. The "spirits of hartshorn" we buy at the chemist's is water impregnated with this gas. At ordinary living temperatures the water gives out the gas, as a sniff at the bottle proves in a most effective manner.

If this gas were cooled to 37·3° below zero it would assume a liquid state, i.e. that temperature marks its boiling point. Similarly steam, cooled to 212° Fahr., becomes water. Boiling point, therefore, merely means the temperature at which the change occurs.

Ammonia liquid, when gasifying, absorbs a great amount of heat from its surroundings—air, water, or whatever they may be. So that if we put a tumbler full of the liquid into a basin of water it would rob the water of enough heat to cause the formation of ice.

The refrigerating machine, generally employed on ships, is one which constantly turns the ammonia liquid into gas, and the gas back into liquid. The first process produces the cold used in the freezing-rooms. The apparatus consists of three main parts:—

(1) The compressor, for squeezing ammonia gas.

(2) The condenser, for liquefying the gas.

(3) The evaporator, for gasifying the liquid.

The compressor is a pump. The condenser, a tube or series of tubes outside which cold water is circulated. The evaporator, a spiral tube or tubes passing through a vessel full of brine. Between the condenser and evaporator is a valve, which allows the liquid to pass from the one to the other in proper quantities.

We can now watch the cycle of operations. The compressor sucks in a charge of very cold gas from the evaporator, and squeezes it into a fraction of its original volume, thereby heating it. The heated gas now passes into the condenser coils and, as it expands, encounters the chilling effects of the water circulating outside, which robs it of heat and causes it to liquefy.

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.

Large arc-lamps slung on yards over the deck give great help for coaling and unloading vessels at night time. The touch of a switch lights up the deck with the brilliancy of a well-equipped railway station. The day of the "lantern, dimly burning," has long passed away from the big liner, cargo boat, and warship.

WIRELESS TELEGRAPHY INSTRUMENTS

Solitude is being rapidly banished from the earth's surface. By solitude we mean entire separation from news of the world, and the inability to get into touch with people far away. On the remote ranches of the United States, in sequestered Norwegian fiords, in the folds of the eternal hills where the only other living creature is the eagle, man may still be as conversant with what is going on in China or Peru as if he were living in the busy streets of a capital town. The electric wire is the magic news-bringer. Wherever man can go it can go too, and also into many places besides.

We must make one exception—the surface of the sea. Cables rest on ocean's bed, but they would be useless if floated on its surface to act as marine telegraph offices. Winds and waves would soon batter them to pieces, even if they could be moored, which in a thousand fathoms may be considered impracticable.

So until a few years back the occupants of a ship were truly isolated from the time that they left port until they reached land again, except for the rare occasions when a passing vessel might give them a fragment of news.

This has all been changed. Stroll into the saloon of one of our large Atlantic liners and you will see telegram forms lying on the tables. In the 'nineties they would have been about as useful aboard ships as a mackintosh coat in the Sahara. A glance, however, at pamphlets scattered around informs you that the ship carries a Marconi wireless installation, and that a Marconi telegram, handed in at the ship's telegraph office, will be despatched on the wings of ether waves to the land far over the horizon.

Inside the cabin streams of sparks scintillate with a cracking noise, and your message shoots into space from a wire suspended on insulators from one of the mast heads. If circumstances favour, you may receive a reply from the Unseen before the steamer has got out of range of the coast stations. The immense installations at Poldhu, Cornwall, and in Newfoundland, could be used to flash the words to a ship at any point of the transatlantic journey. Owing to lack of space, and consequently power, the steamer's transmitting apparatus has a limited capacity.

The first shipping company to grasp the possibilities of the commercial working of the Marconi system was the Nord-Deutscher-Lloyd, whose mail steamer, Kaiser Wilhelm der Grosse, was fitted in March, 1900. At the present time many of the large Atlantic steamship companies carry a wireless installation as a matter of course, ranking it among necessary things. The Cunard, American Atlantic Transport, Allan, Compagnie Transatlantique, Hamburg-American, and Nord-Deutscher-Lloyd lines make full use of the system, as the conveniences it gives far outweigh any expense. A short time since maritime signalling was extremely limited in its range, being effected by flags, semaphores, lights, and sounds, which in stormy weather became uncertain agents, and in foggy, useless. Also the operations of transmitting and receiving were so slow that many a message had to remain uncompleted.

The following paragraph, which appeared in The Times of December 11th, 1903, is significant of the very practical value of marine wireless telegraphy. "The American steamer Kroonland, from Antwerp for New York, which, as reported yesterday, disabled her steering gear when west of the Fastnet, and had to put back, arrived yesterday morning at Queenstown. The saloon passengers speak in the highest terms of praise of the utility of the Marconi wireless telegraphy with which the liner is fitted, and of the facility with which, when the accident occurred, the passengers were able to communicate with their friends, in England, Scotland, and the Continent, and even America, and get replies before the Irish coast was sighted. The accident occurred on Tuesday about noon, when the liner was 130 miles west of the Fastnet, and communication was at once made with the Marconi station at Crookhaven. Captain Doxrud was enabled accordingly to send messages to the chief agents of the American line, at Antwerp, stating the nature of the damage to the steering gear of the steamer, and that he would have to abandon the idea of prosecuting the western voyage. Within an hour and a half a message was received by the captain from the agents instructing him what to do, and at once the Kroonland was headed for Queenstown. Three-fourths of the total number of the saloon passengers and a goodly number of the second cabin sent messages to their friends in various parts of the world, and replies were received even from the Continent before the Fastnet was sighted. Seven or eight passengers telegraphed to relatives for money, and replies were received in four instances, authorising the purser to advance the amounts required, and the money was paid over in each case to the passengers."

The possibility of thus communicating between vessel and land, or vessel and vessel, removes much of the anxiety attending a sea voyage. Business men, for whom even a few days' want of touch with the mercantile markets may be a serious matter, can send long messages in code or otherwise instructing their agents what to do; while they can receive information to shape their actions when they reach land. The "uncommercial traveller" also is pleased and grateful on receiving a message from home. The feeling of loneliness is eliminated. The ocean has lost its right to the term bestowed by Horace—dissociabilis, "the separator."

Steamship companies vie with one another in their efforts to keep their passengers well posted in the latest news. Bulletins, or small newspapers, are issued daily during the voyage, which give, in very condensed form, accounts of events interesting to those on board. "The amount of fresh news a steamer gathers during a passage is considerable, and is greatly relished by the passengers, who are invariably ravenous for signs of the busy life they left behind, more especially when they have departed on the verge of some important event taking place; and the bulletins are eagerly sought for when it is announced that an inward-bound ship is in communication. The shipowners realise the importance and usefulness of being able to communicate with their commanders before the huge vessels enter narrow waters, and issue instructions concerning their movements.

"The stations, which are placed at carefully-selected points at well-adapted distances around the coast, are connected with either the land telegraph or telephone line, or are close to a telegraph office. They are kept open night and day, as the times of the ships passing are, of course, greatly dependent on the weather encountered during the voyage. For those on shore who are anxious to greet their friends on arrival—with good or bad news, as the case may be—this arrangement enables them to be informed of the exact time of the ship's expected arrival, and they are left free to their own devices, instead of enduring long waits on draughty piers and docks—which, on a wet or windy day, are almost enough to damp the warmest and most enthusiastic welcome.

"Cases have occurred where a telegram, sent from the American side to an outlying English land-station two days after a ship has left, has been transmitted to an outgoing steamer, which in turn has re-transmitted it to the astonished passenger two days prior to his arrival off the English coast; and it has now become quite a common thing for competing teams on vessels many miles apart, and out of sight of each other, to arrange chess matches with each other, some of these interesting events taking two or more days to be played to a finish."[17]

For naval purposes, wireless telegraphy has assumed an importance which can hardly be overestimated, as the whole efficiency of a fine fleet may depend upon a single message flashed through space. All navies are fitting instruments, the British Admiralty being well to the fore. Even in manoeuvres and during the execution of tactical formations the apparatus is constantly at work. The admiral gives the word, and a dozen paper tapes moving jerkily through Morse machines, pass the message round the fleet. The Japanese naval successes have, doubtless, been largely due to their up-to-date employment of this latest development of Western electrical science. No one knows how soon the time may come when the fate of a nation may depend on the proper working of a machine covering a few square feet of a cabin table; for, rapid as has been the growth of wireless telegraphy, it is yet in its infancy.

SAFETY DEVICES

A ship is usually divided into compartments by cross bulkheads of steel. In event of a collision or damage by torpedoes or shell, the water rushing through the break can be prevented from swamping the ship by closing the bulkhead doors.

Messrs. J. Stone and Company, of Deptford, have patented a system of hydraulically operated bulkhead doors, which is finding great favour among shipbuilders on account of its versatility. Each door is closed by an hydraulic cylinder placed above it. The valves of the cylinder are opened automatically by a float when the water rises in the compartment, and every cylinder is also controllable independently from the bridge and other stations in the ship, and by separate hand levers alongside the bulkhead.

The doors can therefore be closed collectively or individually. Should it happen that, when a door has been closed, someone is imprisoned, the prisoner can open the door by depressing a lever inside the compartment, and make his escape. But the door is closed behind him by the action of the float.

THE TRANSMISSION OF POWER ON A SHIP

There are four power agents available on board ship, all derived directly or indirectly from the steam boilers. They are:—

(1) Steam.

(2) High-pressure water.

(3) Compressed air.

(4) Electricity.

On some ships we may find all four working side by side to drive the multifarious auxiliaries, since each has its peculiar advantages and disadvantages. At the same time, marine engineers prefer to reduce the number as far as possible, since each class of transmission needs specially trained mechanics, and introduces its special complications.

Let us take the four agents in order and briefly consider their value.

Steam is so largely used in all departments of engineering that its working is better understood by the bulk of average mechanics than hydraulic power, compressed air, or electricity. But for marine work it has very serious drawbacks, especially on a war vessel. Imagine a ship which contains a network of steam-pipes running from end to end, and from side to side. The pipes must, on account of the many obstacles they encounter, twist and turn about in a manner which might be avoided on land, where room is more available. Every bend means friction and loss of power. Again, the condensation of steam in long pipes is notorious. Even if they are well jacketed, a great deal of heat will radiate from the ducts into the below-deck atmosphere, which is generally too close and hot to be pleasant without any such further warming. So that, while power is lost, discomfort increases, with a decided lowering of human efficiency. We must not forget, either, the risk attending the presence of a steam-pipe. Were it broken, by accident or in a naval engagement, a great loss of life might result, or, at least, the abandonment of all neighbouring machinery.

For these reasons there is, therefore, a tendency to abolish the direct use of steam in the auxiliary machinery of a modern vessel.

High-pressure water is free from heating and danger troubles, and consequently is used for much heavy work, such as training guns, raising ashes and ammunition, and steering. One of its great advantages is its inelasticity, which prevents the overrunning of gear worked by it. Water, being incompressible, gives a "positive" drive; thus, if the pump delivers a pint at each stroke in the engine-room a pint must pass into the motor, assuming that all joints are tight, and the work due from the passage of one pint is done. Air and steam—and electricity too, if not very delicately controlled—are apt to work in fits and starts when operating against varying resistance, and "run away" from the engineer.

An objection to hydraulic power is, that all leakage from the system must be replaced by fresh water manufactured on board, which, as we have seen, is no easy task.

Compressed air, like steam, may cause explosions; but when it escapes in small quantities only it has a beneficial effect in cooling and freshening the air below decks. The exhaust from an air-driven motor is welcome for the same reason, that it aids ventilation. On a fighting ship it is of the utmost importance that the personnel should be in good physical condition; and when the battle-hatches have been battened down for an engagement any supply of fresh oxygen means an increased "staying power" for officers and crew. Poisoned air brings mental slackness, and weakening of resolve; so that if the motive power of heavy machinery can be made to do a second duty, so much the better for all concerned.

Compressed air also proves useful as a water-excluder. If a vessel contain, as it should, a number of water-tight compartments, any water rushing into one of these can be expelled by injecting air until the pressure inside is equal to that of the draught of water of the vessel outside.

On land compressed-air installations include reservoirs of large size in which air can be stored till needed, and which take the place of the accumulator used with hydraulic power. On shipboard want of space reduces such reservoirs to minimum dimensions, so that the compressors must squirt their air almost directly into the cylinders which do the work. When the load, or work, is constantly varying, this direct drive proves somewhat of a nuisance, since the compressors, if worked continuously at their maximum capacity, must waste large quantities of air, while if run spasmodically, as occasion demands, they require much more attention. It is therefore considered advisable by some marine engineers to make compressed air perform as many functions as possible when it is present on a vessel. The United States monitor Terror is an instance of a warship which depends on this agency for working her guns and turrets, handling ammunition, and—a somewhat unusual practice—controlling the helm. The last operation is performed by two large cylinders placed face to face athwart the ship. They have a common piston-rod, in the middle of which is a slot for the tiller to pass through. Air is admitted to the cylinders by a valve which is controlled by wires passing over a train of wheels from different stations on the ship. An ingenious device automatically prevents the tiller from moving over too fast, and also helps to lessen the shocks given to the rudder by a heavy sea.

We now come to electricity, the fourth and most modern form of transmission. Its chief recommendation is that the wires through which it flows lend themselves readily to a tortuous course without in any way throttling the passage of power. And as every ship must carry a generating plant for lighting purposes, the same staff will serve to tend a second plant for auxiliary machinery. Electric motors work with practically no vibration, are light for their power, and can be very easily controlled from a distance. They therefore enjoy increasing favour; and are found in deck-winches, anchor-capstans, ammunition hoists, ventilation blowers, and cranes. They also control the movements of gun-turrets, having been found most suitable for this work.

If the current were to get loose in a ship it would undoubtedly cause more damage than an escape of compressed air or water. Electricity, even when every known means of keeping it within bounds has been tried, is suspected of causing deterioration to the metalwork of ships. But these disadvantages are not serious enough to hamper the progress of electrical science as applied to marine engineering; and the undoubted economy of the electric motor, its noiselessness, its manageableness, and comparatively small size will, no doubt, in the future lead to its much more extensive use on board our floating palaces and floating forts.

FOOTNOTES:

16. F. M. Bennett, in the Journal of the American Society of Naval Engineers.

17. Charles V. Daly, in The Magazine of Commerce.