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IIII

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Originally appearing in Volume V26, Page 516 of the 1911 Encyclopedia Britannica.
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IIII 01111181 QI Ilk0 Imo". II' ' , M I ggllhiilhmlll !I Illllll See also:

horizontal resistance and its electrostatic capacity are then measured. These tests are in some cases repeated at another temperature, say 5o° F., for the purpose of obtaining at the same See also:time greater certainty of the soundness of the core and the See also:rate of variation of the conductor and See also:dielectric resistances with temperature. The subjection of the P=h{w–(A/See also:sin i)f(u–v See also:cos i)} (a) core to a See also:hydraulic pressure of four tons to the s9uare See also:inch and an and w cos i = Bf (v sin i) (S), electric pressure of 5000 volts from an alternating-current trans- where f stand for " See also:function." The factors Af (u–v cos i) and former has been adopted, by one manufacturer at least, to secure Bf (v sin i) give the frictional resistance to sinking, per unit length the detection of masked faults which might develop themselves of the See also:cable, in the direction of the length and transverse to the after submergence. Should these tests prove satisfactory the core length respectively). It is evident from See also:equation (0) that the is served with jute See also:yarn, coiled in See also:water-tight tanks, and surrounded See also:angle of See also:immersion depends solely on the See also:speed of the See also:ship; hence with See also:salt water. The insulation is again tested, and if no See also:fault is in laying a cable on an irregular bottom it is of See also:great importance discovered the served core is passed through the sheathing See also:machine, that the speed should be sufficiently See also:low. This may be illustrated and the See also:iron sheath and the See also:outer covering are 'laid on. As the very simply as follows: suppose a a (fig. lo) to be the See also:surface of cable is sheathed it is stored in large water-tight tanks and kept the See also:sea, b c the bottom, and c c the straight See also:line made by the cable; at a nearly See also:uniform temperature by means of water. then, if a See also:hill H, which is at any See also:part steeper than the inclination When the cable is to be laid it is transferred to a cable ship, of the cable, is passed over, the cable touches it at some point t provided with water-tight tanks similar to those used in the factory before it touches the part immediately below t, and if the See also:friction Laying, for storing it. The tanks are nearly cylindrical in See also:form between the cable and the ground is sufficient the cable will either and have a truncated See also:cone fixed in the centre, as shown break or be See also:left in a See also:long span ready to break at some future time. at C, fig. ~9. The cable is carefully coiled into the tanks in It is important to observe that the See also:risk is in no way obviated by the except in so far as the amount of sliding which the strength of the cable is able to produce at the points of contact with the ground may be thereby increased.

The speed of the ship must therefore be so regulated that the angle of immersion is as great as the inclination of the steepest slope passed over. In See also:

ordinary circumstances the angle of immersion i varies between six and nine degrees. The " slack See also:indicator " of Messrs See also:Siemens See also:Brothers & Co. yields a continuous indication and See also:record of the actual slack paid out. It consists of a and coiled towards the centre. The different coils are prevented long See also:screw spindle, coupled by suitable gearing with the cable from adhering by a coating of whitewash, and the end of each nautical mile is carefully marked for future reference. After the cable has been again subjected to the proper See also:electrical tests and found to be in perfect See also:condition, the ship is taken to the See also:place where the See also:shore end is to be landed. A sufficient length of cable to reach the shore or the cable-See also:house is paid overboard and coiled on a raft or rafts, or on the See also:deck of a See also:steam-See also:launch, in See also:order to be connected with the shore. The end is taken into the testing See also:room in the cable-house and the conductor connected with the testing See also:instruments, and, should the electrical tests continue satisfactory, the ship is put on the proper course and steams slowly ahead, paying out the cable over her stern. The cable must not be overstrained in the See also:process of submersion, and must be paid out at the proper rate to give the requisite slack. This involves the introduction of machinery for measuring and controlling the speed at which it leaves the ship and for measuring the pull on the cable. The essential parts of this apparatus are shown in fig. 9.

The See also:

lower end e of the cable in the tank T is taken to the testing room, so that continuous tests for electrical condition can be made. The upper end is passed over a guiding quadrant Q to a set of wheels or fixed quadrants I, 2, 3, . . . then to the paying-out See also:drum P, from it to the See also:dynamometer D, and finally to the stern See also:pulley, over which it passes into the sea. The wheels i, 2, 3, ... are so arranged that 2, 4, 6, . . . can be raised or lowered so as to give the cable less or more See also:bend as it passes between them, while I, 3. 5, ... are furnished with brakes. The whole See also:system provides the means of giving sufficient back-pull to the cable to make it to the See also:piston P. The newly coated See also:wire is passed through a long trough T, containing See also:cold water, until it is sufficiently cold to allow it to be safely See also:wound on a bobbin B' This operation completed, the wire is wound from the bobbin B' on to another, and at the same time carefully examined for See also:air-holes or other flaws, all of which are eliminated. The coated wire is treated in the same way as the See also:copper strand—the See also:die D, or another of the same See also:size, being placed at the back of the See also:cylinder and a larger one substituted at the front. A second coating is then laid on, and after it passes through a similar process of examination a third coating is applied, and so on until the requisite number is completed. The finished core changes rapidly in its electric qualities at first, and is generally kept for a stated See also:interval of time before being subjected to the specified tests. It is then placed in a tank of water and kept at a certain fixed temperature, usually 75° F., until it assumes approximately a See also:constant electrical See also:state.

Its conductor and dielectric grip the drum P, See also:

round which it passes several times to prevent slipping. On the same See also:shaft with P is fixed a See also:brake-See also:wheel furnished with a powerful brake B, by the proper manipulation of which the speed of paying out is regulated, the pull on the cable being at the same time observed by means of D. The shaft of P can be readily put in See also:gear with a powerful See also:engine for the purpose of hauling back the cable should it be found necessary to do so. The length paid out and the rate of paying out are obtained approximately from the number of turns made by the drum P and its rate of turning. This is checked by the mile marks, the known position of the See also:joints, &c., as they pass. The speed of the ship can be- roughly estimated from the speed of the engines; it is more accurately obtained by one or other of the various forms of See also:log, or it may be measured by paying out continuously a See also:steel wire over a measuring wheel. The See also:average speed is obtained very accurately from See also:solar and stellar observations for' the position of the ship. The difference between the speed of the ship and the rate of paying out gives the amount of slack. The amount of slack varies in different cases between 3 and to per cent., but some is always allowed, so that the cable may easily adapt itself to inequalities of the bottom and may be more readily lifted for See also:repairs. But the See also:mere paying out of sufficient slack is not a See also:guarantee that the cable will always See also:lie closely along the bottom or be See also:free from spans. Whilst it is being paid out the portion between the surface of the water and the bottom of the sea lies along a straight line, the component of the See also:weight at right angles to its length being supported by the frictional resistance to sinking in the water. If, then, the speed of the ship be v, the rate of paying out u, the angle of immersion i, the See also:depth of the water h, the weight per unit length of the cable w, the pull on the cable at the surface P, and A, B constants, we have of Submarine Cable.

drum, and thus rotating at the speed of the outgoing cable; on this screw See also:

works a See also:nut which forms the centre of a thin circular disk, the edge of which is pressed against the surface of a right circular cone, the line of contact, as the nut moves along the screw, being parallel to the See also:axis of the latter. This cone is driven by gearing from the wire drum, so that it rotates at the speed of the outgoing wire, the direction of rotation being such as to cause the nut to travel towards the smaller end of the cone. If both nut and screw are rotating at the same speed, the position of the former will remain fixed; and as the nut is driven by friction from the surface of the cone, this equality of speed will obtain only when the product of the See also:diameter (d) of the cone at that position multi-plied into its speed of rotation (n) equals the product of the diameter (a) of the disk multiplied into the speed of rotation (N) of the screw, or N/n=d/a, and thus the ratio of cable paid out to that of wire paid out is continuously given by a pointer controlled i See See also:Sir W. See also:Thomson (See also:Lord See also:Kelvin) Mathematical and See also:Physical Papers, vol. ii. p. 165. by the disk, for any difference in speed between nut and screw will cause the nut to move along the screw until the diameter of the cone is reached which fulfils the above conditions for equality in speed. In fig. i i the edge of the disk serves as the pointer and the See also:scale gives the percentage of slack, or (N—n)/n. The wire being paid out without slack See also:measures the actual distance and speed over the ground, and the engineer in See also:charge is relieved of all anxiety in estimating the depth from the scattered soundings of the preliminary survey, or in calculating the retarding See also:strain required to produce the specified slack, since the brakesman merely has to follow the indications of the See also:instrument and regulate the strain so as to keep the pointer at the figure required—an easy task, seeing that the ratio of speed of wire and cable is not affected by the See also:motion of the ship, whatever be the state of the sea, whereas the rl~li 'i/i/r/19/ i/ihUhphh/Ihhli/i o q io !o ip do FIG. ii.—Slack Indicator strain will in heavy See also:weather be varying 50 per cent. or more on each See also:side of the mean value. Further, the preliminary survey over the proposed route, necessary for deciding the length and types of cable required, can afford merely an approximation to the depth in which the cable actually lies, since accidents of See also:wind and weather, or lack of observations for determining the position, cause deviations, often of considerable importance, from the proposed route. From the continuous records of slack and strain combined with the weight of the cable it is a See also:simple See also:matter to calculate and See also:plot the depths along the whole route of the cable as actually laid. Fig. 12, compiled from the actual records obtained during the laying of the Canso-See also:Fayal See also:section of the Commercial Cable See also:Company's system, shows by the full line the actual strain recorded which secured the even See also:distribution of 8 per cent. of slack, and by the dotted line the strain that would have been applied if the soundings taken during the preliminary survey had been the only source available, although the conditions of sea and weather favoured See also:close adherence to the proposed route.

The ordinates of the See also:

curve give the strain in cwts., and the abscissae the distance in See also:miles measured from the Canso end; as the strain is proportional to the depth, 18 cwts. corresponding to See also:i000 fathoms, the See also:black line represents to an exaggerated scale the See also:contour of the sea See also:bed. Owing to the experience gained with many thousands of miles of cable in all depths and under varying conditions of weather and See also:climate, the risk, and consequently the cost, of laying Repairing, has been greatly reduced. But the cost of effecting a repair still remains a very uncertain quantity, success being de-pendent on quiet conditions of sea and weather. The modus operandi is briefly as follows: The position of the fracture is determined by electrical tests from both ends, with more or less accuracy, depending on the nature of the fracture, but with a probable See also:error not exceeding a few miles. The steamer on reaching the given position lowers one, or perhaps two, See also:mark buoys, mooring them by See also:mushroom See also:anchor, See also:chain and rope. Using these buoys to See also:guide the direction of See also:tow, a grapnel, a See also:species of five-pronged anchor, attached to a strong See also:compound rope formed of strands of steel and See also:manila, is lowered to the bottom and dragged at a slow speed, as it were ploughing a furrow in the sea bottom, in a line at right angles to the cable route, until the behaviour of the dynamometer shows that the cable is hooked. The ship is then stopped, and the cable gradually See also:hove up towards the surface; but in deep water, unless it has been caught near a loose end, thecable will break on the grapnel before it reaches the surface, as the See also:catenary strain on the See also:bight will be greater than it will stand. Another See also:buoy is put down marking this position, fixing at the same time the actual line of the cable. Grappling will be recommenced so as to See also:hook the cable near enough to the end to allow of its being hove to the surface. When this has been done an electrical test is applied, and if the See also:original fracture is between ship and shore the heaving in of cable will continue until the end comes on See also:board. Another buoy is then lowered to mark this spot, and the cable on the other side of the fracture grappled for, brought to the surface, and, if communication is found perfect with the shore, buoyed with sufficient chain and rope attached to allow of the cable itself reaching the bottom. The ship now returns to the position of original attack, and by similar operations brings on board the end which secures communication with the other shore.

The See also:

gap between the two ends has now to be closed by splicing on new cable and paying out until the buoyed end is reached, which is then hove up and brought on board. After the " final splice," as it is termed, between these ends has been made, the bight, made fast to a slip rope, is lowered overboard, the slip rope cut, and the cable allowed to sink by its own weight to its resting-place on the sea bed. The repair being thus completed, the various mark buoys are picked up, and the ship returns to her usual station. The grappling of the cable and raising it to the surface from a depth of 2000 fathoms seldom occupy less than twenty-four See also:hours, and since any extra strain due to the pitching of the See also:vessel must be avoided, it is clear that the state of the sea and weather is the predominating See also:factor in the time necessary for effecting the long See also:series of operations which, in the most favourable circumstances, are required for a repair. In addition, the intervention of very heavy weather may See also:mar all the See also:work already accomplished, and require the whole series of operations to be undertaken de novo. As to cost, one transatlantic cable repair cost £75,000; the repair of the- See also:Aden-Bombay cable, broken in a depth of 1900 fathoms, was effected with the See also:expenditure of 176 miles of new cable, and after a See also:lapse of 251 days, 103 being spent in actual work, which for the See also:remainder of the time was interrupted by the See also:monsoon; a repair of the See also:Lisbon-Porthcurnow cable, broken in the See also:Bay of See also:Biscay in 2700 fathoms, eleven years after the cable was laid, took 215 days, with an expenditure of 300 miles of cable. All interruptions are not so costly, for in shallower See also:waters, with favourable conditions of weather, a repair may be only a matter of a few hours, and it is in such waters that the See also:majority of breaks occur, but still a large reserve fund must be laid aside for this purpose. As an ordinary instance, it has been stated that the cost of repairing the See also:Direct See also:United States cable up to 1900 from its submergence in 1874 averaged £800o per annum. Nearly all the cable companies possess their own steamers, of sufficient dimensions and specially equipped for making ordinary repairs; but for exceptional cases, where a considerable quantity of new cable may have to be inserted, it may be necessary to See also:charter the services of one of the larger vessels owned by a cable-manufacturing company, at a certain sum per See also:day, which may well reach £200 to £300. This See also:fleet of cable See also:ships now See also:numbers over See also:forty, ranging in size from vessels of 300 tons to 10,000 tons carrying capacity. The See also:life of a cable is usually considered to continue until it is no longer capable of being lifted for repair, but in some cases the duration and frequency of interruptions as affecting Life. public convenience, with the loss of See also:revenue and cost of repairs, must together decide the question of either making very extensive renewals or even abandoning the whole cable. The possibility of repair is affected by so many circumstances due to the environment of the cable, that not even an approximate See also:term of years has yet been authoritatively fixed.

It is a well-ascertained fact that the insulator, See also:

gutta-percha, is, when kept under water, practically imperishable, so that it is only the original strength of the sheathing wires and the deterioration allowable in them that have to be considered. Cables have frequently been picked up showing after many years of submergence no appreciable deterioration in this respect, while in other cases ends have been picked up which in the course of twelve years had been corroded to See also:needle points, the result probably of metalliferous deposits in the locality. It is scarcely possible from the preliminary survey, with soundings several miles apart, to obtain more than a See also:general See also:idea as to the average depth along the route, while the nature of the constituents of the sea bed can only be revealed by a few small specimens brought up at isolated spots, though fortunately the globigerine See also:ooze which covers the bottom at all the greater ocean depths forms an ideal bed for the cable. The experience gained in the earlier days of ocean telegraphy, from the failure and See also:abandonment of nearly 5o per cent. of the deep-sea cables within the first twelve years, placed the probable life of a cable as low as fifteen years, but the weeding out of unserviceable types of construction, and the general improvement in materials, have by degrees extended that first estimate, until now the limit may be safely placed at not less than forty years. In depths beyond the reach of See also:wave motion, and apart from suspension across a submarine See also:gully, which will sooner or later result in a rupture of the cable, the most frequent cause of interruption is seismic or other shifting of the ocean bed, while in shallower waters and near the shore the dragging of anchors or fishing trawls has been mostly responsible. Since by See also:international agreement the wilful damage of a cable has been constituted a criminal offence, and the cable companies have avoided See also:crossing the fishing See also:banks, or have adopted the See also:wise policy of refunding the value of anchors lost on their cables, the number of such fractures has greatly diminished. Instruments for See also:Land Telegraphy.—At small See also:country towns or villages, where the See also:message See also:traffic is See also:light, the See also:Wheatstone " A B C " instrument is used. In this apparatus electric A B C currents are generated by turning a handle (placed in instru- front of the instrument), which is geared, in the instru- ment. ments of the most See also:recent See also:pattern, to a Siemens See also:shuttle See also:armature placed between the two arms of a powerful See also:horse-See also:shoe permanent magnet. When one of a series of keys (each corresponding to a See also:letter) arranged round a pointer is depressed, the motion of the pointer, which is geared to the shuttle armature, is arrested on coming opposite that particular See also:key, and the transmission of the currents to line is stopped, though the armature itself can continue to rotate. The depression of a second key causes the first key to be raised. The currents actuate a ratchet-wheel mechanism at the receiving station, whereby the See also:hand on a small See also:dial is moved on letter by letter. A noticeable feature in the See also:modern A B C indicator, as well as in all modern forms of See also:telegraph instruments, is the See also:adoption of " induced " magnets in the moving portion of the apparatus.

A small permanent magnet is always liable to become demagnetized, or have its See also:

polarity reversed by the See also:action of See also:lightning. This liability is overcome by making such movable parts as require to be magnetic of soft iron, and magnetizing them by the inducing action of a strong permanent magnet. Although formerly in very extensive employment, this instrument is dropping out of use and the " sounder " (and in many cases the See also:telephone) is being used in its place. At offices where the work is heavier than can be dealt with by the A B C apparatus, the " Single Needle " instrument has been Single very largely employed; it has the See also:advantage of slight needle liability to derangement, and of requiring very little instru- See also:adjustment. A fairly skilled operator can See also:signal with it ment. at the rate of 20 words per See also:minute. The needle (in the modern pattern) is of soft iron, and is kept magnetized inductively by the action of two permanent steel magnets. The coils are wound with copper wire (covered with See also:silk), to mils. in diameter, to a See also:total resistance of 200 ohms. The actual current required to work the instrument is 3.3 milliamperes (See also:equivalent approximately to the current given by t See also:Daniell See also:cell through 3300 ohms), but in peactice a current of to milliamperes is allowed. A simple, but important, addition to enable the See also:reading from the instrument to be effected by See also:sound is shown in fig. 13; in this arrangement the needle strikes against small tubes formed of See also:tin-See also:plate. Although a most serviceable instrument and cheap as regards See also:maintenance, the " single needle " has (except for railway telegraph purposes) been discarded in favour of the " sounder," to secure the advantage of using one general pattern of apparatus, as far as possible, and to avoid the See also:necessity of two different types of instrument being learnt by the telegraphist. The well-known See also:code of signals (fig.

14) introduced by See also:

Morse is still employed in with See also:sounding arrange- international code in See also:vogue in See also:Europe ment. differs only slightly from it. The instruments used for land telegraphs on this system are of two types—" sounders," which indicate by sound, and " recorders," which record the signals. Recorders vary in details of construction, but all have the same See also:object, namely, to record the intervals during which the current is applied to the line. In the earlier forms of instrument the record was made by See also:embossing lines on a ribbon of See also:paper by means of a See also:sharp See also:style fixed to one end of a See also:lever, which carried at the other end the armature of an electromagnet. The form of Morse See also:recorder almost universally used in Europe makes the record in Morse See also:ink, and hence is sometimes called the "ink-writer." writer. This method has the advantage of distinctness, and so is less trying to the eyes of the operators. Although the " ink-writer " is still in use it is practically an obsolete instrument, and has been displaced by the " sounder." Operators who used the recorder soon learned to read the message by the click of the armature against its stop, and as this left the hands and eyes free to write, reading by sound was usuallypreferred. Thus, when it is not necessary to keep a copy, a much simpler instrument may be employed and the message read sounder, by sound. The earliest successful form was " See also:Bright's See also:bell " sounder, which consisted, of two bells of distinct See also:tone or See also:pitch, one of which was sounded when the current was sent in one INTERNATIONAL CODE A • O --- 4 B —... P •--• 5 C - - Q --•— 6 C h ---- •—• 7 D — g ... 8 E T 9 U ••— 0 G-- V ... O 3 P 4 Q ..—.

8 R .. 6 S 7 T — 8 U 9 0 J K Y .. .. , —..-- L Z t ----• M -- 1 .---. & ... N direction and the other when it was reversed. This instrument was capable of giving very considerable speed, but it was more complicated than that now in use, which consists only of an electromagnet, with its armature lever arranged to stop against an See also:

anvil or screw in such a way as to give a distinct and somewhat loud sound. Dots and dashes are distinguished by the interval between the sounds of the instrument in precisely the same way as they are distinguished when reading from the recorder by sound. Fig. 15 shows the modern pattern of " sounder " as used by the See also:British See also:Post See also:Office. The magnet is wound to a resistance of 40 ohms (or 900 ohms when worked from accumulators), and the instrument is worked with a current of 400 milliamperes (25 milli-amperes with accumulators). Methods of Working Land Circuits.—The arrangement on the " open-See also:circuit " system for single-current working is shown in fig.

16, in which Li represents the line, G a See also:

galvanometer, used simply to show that the currents are going to line when the message is being transmitted, K the transmitting key, B the See also:battery, I the receiving instrument, and E the See also:earth-plate. The See also:complete circuit is from the plate E through the instrument I, the key K, and the galvanoscope G to the line Li, then through the corresponding instruments to the earth-plate E at the other end, and back through the earth to the plate E. The earth is always, except for some See also:special See also:reason, used as a return, because it offers little resistance and saves the expense and the risk of failure of the return wire. The earth-plate E ought to be buried in moist earth or in water.

End of Article: IIII

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