by franklin matthews.

ii.

just outside the door of the captain's cabin, on every ship of the navy, there stands a sentry. he paces up and down for a distance of about ten feet. on one of the sides of the cabin is an electric indicator similar to those seen in the large hotels back of the clerk's desk. the sentry on the ship passes that indicator every time he paces from one end of his limited beat to the other. he cannot escape hearing its bell when it rings, and his eye at once sees whence the signal comes that is telegraphed to the captain in time of emergency. that indicator is placed there so that, when necessary, there shall be instant communication with the captain. some of the dials tell stories of the utmost importance to the safety of the ship. they tell these stories automatically.

let us see how one of the most important of these dials may perhaps save the ship from destruction. down in the coal-bunkers there is a little instrument attached to the side of each compartment that looks like a little thermometer. it is not more than four or five inches tall. it is simply a thermometer with an electric attachment. a fire has started in a coal-bunker, as happens sometimes on large steamships, through what is known as "spontaneous combustion." it may smoulder for several days and give no indication of its existence. at last it breaks into a flame. some one has felt a hot deck through his shoes as he has walked along, or perchance has accidentally placed his hand on the iron-work of the compartment and found it blistering hot. instantly the fire-alarm is rung, and if the fire is not too far advanced the ship may be saved. on war-ships, however, no such risk must be run. in the economy of space on such ships it frequently happens that these coal-bunkers are placed very near, and sometimes next to, the powder-magazines. a fire in the coal-bunkers would mean an awful explosion, the loss of the ship and hundreds of lives.

here is where that little thermometer plays its heroic part. it is called a thermostat, and it is so arranged that as the heat increases, the mercury in the bulb slowly rises to what is known as the danger-point. when the heat reaches that point the mercury sets an electric current going. at once the bell on the indicator where the sentry outside the captain's door stands rings violently. the sentry hurries to it and sees a fire-alarm from a certain compartment, and he hastily awakes the captain. the latter presses a button, perhaps without getting out of bed or up from his chair, and instantly there rings the general fire-alarm throughout the ship, and every man on board is called to quarters. for a few seconds it is time of immense confusion and noise. great gongs are ringing in various parts of the ship. men are hurrying half dressed, if it be in the night, here and there, and there is much shouting in the giving and passing of orders. in a twinkling, however, order prevails, and through the aid of that little automatic thermometer the ship and the lives of those on board are saved. this thermostat is an insignificant-looking affair—a mere trifle in the ship's construction—but see what an important thing it really is. these instruments are used in many buildings on land, but nowhere are they of such importance as when placed in coal-bunkers or on the outside walls of magazines in war-ships.

another dial on the indicator where the sentry paces also plays an important part in war-ships. it is called the water-alarm. all modern war-ships have what are known as double bottoms. they are built to prevent the ship from sinking or from becoming flooded in the chief compartments of the vessel below the water-line. sometimes a ship may scrape along the top of an unknown rock or reef, or may strike some obstruction floating unseen beneath the waves. no one on board may feel the shock, especially if it is a light one. the water may rush into one of these double bottoms, and although the ship may be safe from sinking, the danger in time may be most grave. as the water fills the compartment which has been broken, a little piece of wood rises with it, and finally, when it reaches a certain height, it too establishes an electric current, and the alarm rings outside the cabin door of the captain. again the alarm sounds through the ship, and if possible, the break is mended temporarily, and the pumps set going to clear the compartment of the water.

a torpedo bursting an outer compartment.

in time of battle, however, this water-alarm may tell a more important story. perhaps a torpedo from the enemy has struck the ship, and a gaping wound has been torn not only in the outside bottom of the ship, but through the inner hull as well. instantly the news reaches the captain through the water-alarm. the captain simply presses a button, and at once not only does the general alarm ring, but the "siren" whistle on the ship is set to shrieking most horribly. those siren whistles are seldom heard either in port or at sea. they begin their noise with a low[pg 89] moan, and run up to an awful shriek, with a thin, ear-piercing note that is almost unendurable. the siren may be blown by electricity as easily as an electric door-bell may be rung. when the siren is heard it is a signal throughout the ship to close all the water-tight doors in the various compartments, and thus confine the inrushing waters to a limited space. if only one or two compartments are torn open by the torpedo, the ship may be saved from sinking and a great tragedy of war may be averted. when the siren howls, however, there is such a scurrying on shipboard as is never seen at other times. nearly every compartment has men in it at work. the alarms and the whistles are their only warning, except, perhaps, the shouts of their companions. a mighty rush is made to get out of some of these compartments. no time must be lost, and there can be no waiting for a man to escape. if shut in, he may be drowned. it is a question of his life or that of the ship and the lives of the rest of the crew, and there is only one way to answer that question.

these water-alarms are used in many large buildings in connection with the fire-alarm, but one can see how much more important they are on ships, especially on war-ships, than on land. they are a most simple contrivance, and, like the thermostat, mere trifles; but they may turn the tide in a naval battle, and directly or remotely settle the fate of a nation.

in the early days of steam navigation the captain of a vessel could speak to the engineer through a tube and regulate the speed of the ship. when the vessels grew larger, the signalling was done by means of bells. that method is in common use to-day in many vessels that ply in harbors, such as river steamboats and tug-boats. as the ocean-liners increased in size the bell system of signalling became antiquated. the captain or the navigator was 300 or 400 feet away from the engineer, and from 20 to 40 feet above the engine-room. in time of emergency it became necessary to send word to the engineer exactly what to do in half a dozen different cases. he must stop, back, go slow now with one engine and now with another, or with both. a long chain was run from a contrivance on the bridge to the engine-room. when the captain pressed forward or backward a handle on a vertical dial, a handle in the engine-room would move on a similar dial, and a bell would ring to call attention to it, and the engineer knew at once what to do. this system is in use at the present time on all large passenger-ships and most war-ships in the world.

electricity has invaded this field also, and on the newer war-ships of the navy we have the signalling done by this agent. by the electric-engine telegraph, which lieutenant fiske of our navy has invented, not only does the engineer know at once when to go at full speed, half-speed, when to stop and back, and all that, but the captain can tell at an instant, by looking at a little dial attached to his signalling apparatus, whether his orders have been understood. the little dial is connected with that part of the signalling apparatus in the engine-room on the same electric circuit, and thus the captain knows exactly what is going on in the engine-room. but the new invention goes farther than that. it tells the engineer just how many revolutions of the screws a minute the captain desires the engines to make. full speed, for example, in the old way of signalling may mean anywhere from 80 to 90 or 100 revolutions of the screws. half-speed may mean anywhere from 60 to 80 revolutions. the engineer in those cases has to use his own judgment as to what speed to employ, unless a message is sent especially to him from the captain. in the electric device which we are just beginning to use there are certain notches on the dials, and the captain can signal exactly the number of revolutions he desires each engine to make. he not only gets a signal back, but he has a telltale instrument before his eyes which shows that the engines are making 59, or 73, or whatever number of turns the captain wishes them to make.

now this regulation of the revolutions of the ship's engines has a most important part to play in warfare. one of the most essential things in naval man?uvring is that ships shall keep a certain distance from one another. it avoids collisions, and preserves regularity in fire and in changing positions at critical times. it is as essential as[pg 90] that soldiers shall present a solid line to the enemy in battle on land. a helter-skelter fleet would be beaten from the start in a fight. it is most difficult for ships to keep at regular intervals. the engines of one turn just a little faster than the engines of another, and little by little a ship creeps up or drops away from its fellows. sometimes the distances are preserved by guess-work. lately a little instrument has been invented by which the captain can see at a glance how far he is from the ship ahead of him. it is a modification of the sextant. the height of a certain object on the ship in front is known. that is the base of a triangle. the size of the angles at the end of that base are seen at a glance by the observer, and by the manipulation of a screw or two the captain of a ship can see on a sliding-scale whether he is going too slow or too fast. in either case he signals a change or two in the number of revolutions he wishes the engines to make, and he preserves his required distance. accuracy in this matter may win a battle.

so great is the din and confusion on war-ships in time of battle that what are called "visual signals" are demanded. this has brought several contrivances into operation that are new. for example, we have a transmitter of orders. it tells the gunners when and what guns to load, and with what kind of shot; when to stand ready to fire; when to fire, and when to cease firing. in the old days, and even in the present days, such orders are conveyed in speaking-tubes or by telephone on most ships. in the great noise an order may be mistaken, but with a visual signal in the shape of an indicator, operated by the mere pressing of a button, orders from the captain may be conveyed clearly and instantly.

another apparently trifling thing in the development of navigation is an electrical signalling device for indicating the exact angle the captain wishes the helm set in making a turn. he presses a button, and the man at the wheel sets the rudder accordingly. a dial informs the captain that the rudder is set as required. this is most important, because it tends to avoid collisions as the war-ships suddenly change their positions in column. we all remember how serious a collision, even going at slow speed, may be when we recall how three years ago the camperdown sunk the victoria of the english mediterranean squadron on a peaceful day off the coast of africa, in going through some simple evolutions, and when hundreds of brave sailors, including the admiral of the fleet himself, were drowned, as the victoria went down before the small boats of the other vessels of the fleet could reach them.

the admiral working signals at night.

one of the great problems in naval tactics is to secure an effective method of signalling orders from ship to ship. in the night it is comparatively easy. a string of red and white alternating electric lights is strung from a yard downwards. an operator sits in front of a little box in which there are a lot of black keys on which are stamped a certain number of red and white dots. as he presses these keys, which are arranged in a circle and look like so many fancy dominoes, the red and white lights flash out in certain combinations. the operators see them, and signal back the same light. each key pressed down means a certain letter, and it takes little time to send an order. in the daytime signals must be sent by flags, or by means of a contrivance with long arms such as we see on signal-towers on a railroad. as these arms are jerked into certain positions they tell a story of their own.

during a battle by day or night all such systems are of little value because of the smoke. whistles can be of little use, because the noise of battle would drown them. electrical experts are trying to devise a system of telegraphing through the water, of course without the use of wires, but the outlook in that direction is not promising at present.

then there are important new devices which we can only mention. one of them is the sounding apparatus, by which the depth of water can be taken when going at full speed. the pressure of water on a column of air varies at certain depths of the ocean. this pressure is marked by the discoloration of a fluid in a tube through the agency of the salt water. the electric firing of guns is also interesting. a current of electricity is passed through a filament, such as we see in the incandescent lamp of a house electric light, and at once the heat sets the gun off as effectively as if a spark had ignited the powder. then there is the aerophone, or fog-indicator, which points out the exact direction of some noise-making object by cutting the sound-wave in two, so as to send it first in one ear and then the other of the man who operates the invention, until finally he gets it in equal volume in both ears, and the dial on the machine points straight to the object which cannot be seen.

all these inventions, which of themselves seem mere trifles, are necessary in these days, because of the wonderful advance in warfare and the construction of ships. in the old days the captain could roar his orders out and make himself heard almost everywhere. nowadays a fraction of a second may determine the outcome of a battle. he must be able to find the distance of his enemy, must fire his guns without aiming them in the old way, must regulate the speed of his ship to the single turn of a screw, must put his own helm at a certain angle to a degree. without electricity he would be helpless in the noise and confusion. even with electricity he is hampered, and so we may expect that the invention of these little devices will go on, until one man in a ship may control that engine of war as completely as if he were in every vital place in the ship at one and the same time.