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the strength for laying and picking up, and to protect the whole from the varied dangers which menace the cable in its watery bed. In tropical seas, where the teredo and the sawfish make this human contrivance the subject of almost fiendish attacks, there has to be a thin brass ribbon wound helically over the guttapercha; and in northern oceans, as on the Newfoundland Banks, where many cables cross, the armor must be especially heavy, to prevent the cables being broken by icebergs grounding and crushing them.
Laying a Cable When the cable is made, it is loaded on board the cable ship which is to lay it. The fleet of steamers now used for lay
DEEP-SEA CABLE, AND HEAVILY SHEATHED SECTION
SECTIONS OF CABLES. Showing how they are made.
sea or general type of cable. The payingout process is continued day and night, at a rate of seven to ten knots, as the weather warrants. The Anglo-American cable of 1880 was laid between Valentia, Ireland, and Heart's Content, Newfoundland, in twelve days, without hitch or stoppage, this being the record so far in Atlantic cable laying.
The paying-out of the cable is registered by a variety of machines and contrivances to ensure its being perfectly accomplished. A light iron frame called a "crinoline" is fixed in the tank, to prevent the cable "kinking” and thus causing a foul or fracture. The snake-like line is wound around huge drums on
ing and repairing cables throughout the world, numbers forty-two, and includes vessels of 10,000 tons. The cable is stored in tanks in the hold; and on reaching her destination, the vessel sends to land a "shore-end”—a section bound with steel to the thickness of a man's arm, to withstand the chafing of the surf, tides, and currents. This is taken to the cablehouse, and the ship steams seaward, paying the cable out over a drum on her stern, as she goes. To the shoreend is attached an “intermediate” section, not so heavily sheathed, but sufficiently armored to protect it against the wave action, fishermen's anchors, and oceanic rivers; and to this, in turn, is attached the deep
DEEP-SEA SECTION OF THE "ANGLOS."
Largest Atlantic Cable.
of light from an oil lamp is thrown on the mirror, which reflects it on a proper scale. This beam of light is technically known as the "spot.” When there is no electricity energizing the galvanometer, the "spot" is at zero in the center of the scale; but when a positive or a negative current is applied to it, the “spot" flies to one side or the other of the scale. If a fault or break develops in the cable, it is detected by this instrument, for an infinitesimal current actuates it. The defective portion is then cut out and a new splice made; and "paying out” is resumed as soon as the revival of energy in the spot shows that the continuity of the metal artery is again unbroken. In splicing a cable, the gutta-percha has to be laid on by hand; and as this requires the most delicate manipulation, the cable official entrusted with this task always wears gloves except when at his particular work, so that his fingers may be soft and delicate in touch. On laying the cable across the seas to within a few miles of its other terminal, the wire is buoyed, and the ship proceeds to land, sends in the second shore-end, and returns, paying it out as she comes, till she reaches the buoyed section, when the final splice is made, and the completed cable is allowed to sink into its ocean bed.
Cable laying is not without its adventurous features, especially on seaboards inhabited by savage peoples. In the tropical regions, more than one cable has had to be landed under the protection of a warship's guns, and turbulent tribes have on occasions attacked the cable sta
deck, which carry it outboard; and a strophometer indicates how many miles have been paid out; while a dynamometer exhibits the strain on the cable. The enormous strain may be best understood from the fact that, if paying out in 2,600 fathoms (3%2 miles) of water, at the rate of seven knots an hour, the distance from the stern of the ship to where the cable touches the ooze is no less than twenty-seven miles; and it takes three hours for a particular point of the cable to reach the bottom after it passes over the drum. The "commercial” cable laid across the Atlantic in 1894, weighed, in air, 36 cwt. to the mile, and its breaking strain was eight tons.
From the time the shore-end is connected with the instruments in the station on land where the ship left, till her work is completed, there is constant electrical communication, through the cable on board, with the testing room on the ship, in order that no mishap may occur; and every five minutes, signals are exchanged between the two staffs ; while never for a single instant is the close scrutiny relaxed, which, through the mirror of the galvanometer, enables the observer to determine if all is well. The galvanometer is a coil of wire of high resistance, in the center of which a tiny circular mirror (about the size of a dime) is suspended. Attached to the back of the mirror is a small magnet; and a beam
tions and besieged the inmates. Getting transmitter" is employed. In using it, the cable to the shore, too, has frequently the original messages are first handed to proved a task of extreme difficulty, owing men known as “punchers," who sit beto storms and surf; and once, in East fore small instruments termed "perAfrica, a cable ship's landing staff was forators," consisting of three small metal kept in quarantine for three weeks by the discs—for dots, dashes, and spaces. Portuguese officials, on suspicion of some Across these a paper tape is drawn by disease existing on the ship, the cable mechanical agency; and in it the “punchbeing almost destroyed in consequence. er,” armed with two small wooden hanSending and Receiving Messages—The dles tipped with rubber, cuts the Morse Automatic Transmitter
equivalent for the letters in the message An ocean cable, once having been laid before him. This tape is then fed to the and taken over by its owners, commer- “Wheatstone transmitter,” which can cial business is transacted. For this, consume the material supplied by five
manual and automatic instruments are used, the latter, which work at a high speed and sometimes send 250 letters a minute, being employed when the traffic is greater than the human operators can dispose of. These operators, who send about 100 letters per minute, do so by means of an instrument known as a "double" or "reversing” key. It consists of two light spring levers, crossed at right angles, above and below, by contact-bearing metallic bars. The cable is connected to one lever, and a ground wire to the other; while to the two transverse bars are connected, respectively, the positive and negative poles of a battery of electrical cells. For the automatic despatch of messages, a machine known as the “modified Wheatstone
or six punchers. The transmitter works on the same principle as the hand-key, the motive power being mechanical instead of manual. The idea of the machine was taken from the Jacquard loom; and its speed is, practically speaking, limited only by the type of conductor and insulator adopted when the original cost of the cable. was considered. Sometimes it is found in actual practice that the cable is of insufficient dimensions for its length, as the working speed depends inversely on the product of the conductor resistance and the electrostatic inductive capacity, and varies inversely as the square of the length; that is, if a cable of a given type is doubled in length, the working speed is reduced to one-fourth of the original.
invention of Lord Kelvin (Sir William Thomson), the famous scientist. This consists of a rectangular coil containing many turns of very fine silk-covered copper wire, suspended between the poles of a powerful magnet; and a fine glass tube, no thicker than a coarse hair, bent in the form of a siphon, and attached to a very fine stretched wire, leaving it free to move backwards or forwards as in
fluenced by the moveCABLE STAFF AT MIDWAY ISLAND,
ments of the rectangular
coil, to which it is atThe “automatic transmitter” adds tached by an almost invisible thread greatly to the accuracy and speed of the of silk. The higher leg of the cables, the mechanism combining the ut- siphon dips into a small trough of most uniformity of signal with rapidity specially prepared ink; while past and tirelessness unattainable by hand. its lower end is drawn, by a suitable All ocean cables are, moreover, "du- motor, a continuous tape of white paper, plexed,” which doubles their capacity. along the middle of which, when the This renders possible the transmission siphon is at rest, is thus traced a fine, and reception of a message over the one clear ink line. The siphon must not wire at the same time, accomplishing come in contact with the paper, as the this seeming marvel by providing an friction between them would impede the artificial cable made up of a number of movements of the delicately suspended "condensers”—boxes of paraffin and tin coil; and through the bore of the siphon, foil in alternate layers, forming im- which is so small that ink will not flow proved Leyden jars of sufficient electrical through it, the liquid must be forced energy to counterbalance that of the either by electrification or by vibration, cable itself. This “artificial line” is either of these methods causing the ink placed in a dark room, with double doors to spurt out with sufficient force to keep and walls padded with sawdust to preserve an equal temperature, and, being connected with the instrument to which the cable is attached,“splits” the current, and thereby renders the joint passage of two sets of signals, one in each direction, quite feasible.
The Siphon Recorder
The receiving of messages at the opposite end of a cable is accomplished by means of a "siphon recorder," an
U. S. Pacific CABLE STATION ON MIDWAY ISLAND. A lonely landing station for the cable from Honolulu to Guam and the Philip
pines.-The Midway group lies northwest of Hawaii, and is an
outcropping of the same submarine range as the latter