LAYING THE CABLE.] UNDULATORY FOUCE S. ELECTRO-M AGNETI SM. 



265 



it (being ignorant of its nature, it is to be hoped), was 

 about ridding himself of the incumbrance by cleaving it 

 with a hatchet ; but one of the crew, more sensible than 

 his commander, induced him to cast it overboard, and 

 so to return it to its former resting-place. 



2. THE SUBMERSION OF THE CABLE. One of the most 

 serious undertakings in connection with the submarine 

 telegraph cable, is that of "laying it," as the operation 

 is termed. Even when the finest and calmest weather is 

 experienced, many difficulties arise. The cable is coiled 

 in the hold of the vessel, and passed through an opening 

 on deck. It is then wound two or three times round a 

 large cylinder, to which is attached a break. The object 

 of this is, that the cable may be " payed out" in an even 

 manner ; for, if it were allowed to pass from the stern 

 of the vessel in an irregular manner, it would soon 

 form knots and kinks, and most probably break. The 

 regulation of its speed is a matter of great delicacy ; 

 for sufficient strain must ke kept on it to lay it straight, 

 and yet care must be taken that it is not broken by too 

 great tension, partly arising from the speed of the vessel, 

 and from the weight of the cable itself. An ordinary 

 speed of laying the cable is about four to five miles 

 per hour. When, however, a storm occurs, the diffi- 

 culties are enormously increased. As the vessel rises 

 and sinks in the trough of the waves, the tension on the 

 cable is suddenly increased or diminished ; and, unless 

 greatest care be taken, its fracture is inevitable, 

 i while the cable may appear externally to be sound, 

 possible that one or all of the wires inside it may be 

 ed ; hence telegraphic signals are constantly kept up 

 between the vessel and the station whence it proceeded. 

 In i tying the Atlantic telegraph, the two vessels started 

 from a place equi-distant from Ireland and America. 

 The cables in each vessel were spliced together, and the 

 portion between the two was gradually sunk. The 

 steamers sailed then in opposite directions, until each 

 reached its appointed port ; and, during the entire voyage, 

 the electricians kept up constant signals, acknowledged 

 and received on each vessel, which, of course, proved 

 that the conducting wire was perfect throughout. In 

 the first attempt to lay the cable, the signals were 

 interrupted, and could not bo recovered, so that it at 

 once became evident that the sunken portion had been 

 by some means injured. This, of course, necessitated its 

 loss, and both vessels returned to the port whence they 

 had started. 



We need not remind our readers, that the bed of the 

 ocean, like the surface of the land, is often exceedingly 

 irregular. Sometimes deep ravines are encountered, in 

 which the cable quickly and suddenly falls. In other 

 instances great elevations are met with, which dimmish 

 the rate of the cable's passage. All these, and many 

 other circumstances, have to be mimitely attended to ; 

 and without entering more fully into such details, we 

 have pointed out sufficient to prove, that the laying of 

 a submarine cable is a work of no ordinary difficulty and 

 importance. 



3. THE CIRCUMSTANCES WHICH INTERFERE WITH THE 

 REGULAR WORKING OF A SUBMARINE CABLE. It would 

 be impossible for us to enter into a minute examination 

 of all the circumstances which affect the regular working 

 of a submarine cable. We shall therefore only touch on 

 those which are either very important, or ordinarily found 

 to be present. The numerous accidents, of a mechanical 

 nature, to which all submarine cables are subject, have 

 been already frequently noticed, and will not require 

 further observation. There are, however, others of an 

 electrical nature, which often produce serious conse- 

 quences ; and, at times, almost forbid all chance of com- 

 munication between the two termini of the cable. 



It was found, some time since, that if a short length of 

 submerged cable formed part of a circuit between two 

 land-lines, more disturbance occurred, in the regular 

 indication of signals, than would have been the case had 

 the entire line been on land, and suspended on poles in 

 the usual manner. At first it was considered that this 

 arose from defective insulation, or from injury to the 

 conducting wire. Eventually, however, the fact was 

 VOL. i. 



discovered, that an ordinary submarine cable acquired 

 the character and qualities of a charged Leyden jar, 

 whenever a current was passed through it : indeed, its 

 construction is analogous to that arrangement ; for we 

 may suppose the wire to represent the inside of a charged 

 Leyden jar ; the gutta-percha to correspond with the 

 glass of the vessel ; and the external wires, or the water 

 surrounding them, to answer the outer coating of ajar.* 

 Now, the effect of this inductive action is not only to 

 retard the passage of a current of electricity sent from a 

 voltaic battery, but even to create an opposing force. 

 In some instances, the current is all but destroyed : 

 generally, its indications are irregular ; and if a printing 

 telegraph be employed, such as we shall shortly describe 

 it will be found, that, instead of an instantaneous signal 

 being registered, such is, generally speaking, given in a 

 slow and continuous manner, just as if the current were 

 gradually conducted by the wire. This evil increases 

 with the length of the cable. As we have already 

 stated, even a short one shows such results ; but in the 

 Atlantic wire, the effect was, as might be expected, on a 

 very large, and even alarming scale. It is a difficult 

 matter to give a popular illustration of the actual results 

 produced; but we may compare the retarded and op- 

 posed passage of a current to the position in which a 

 vessel is placed on entering the mouth of a narrow river. 

 The vessel may be urged forward by a fair or strong 

 wind, whilst the water of the river is rushing towards 

 the sea. The stream is urged into swelling waves, and 

 on these the vessel tosses, making but little progress 

 towards her destination. Now, similarly, the wave of 

 voltaic current meets that of the induced cable-current, 

 and the effect is tliat which we have described. 



The question next arises as to what means can be 

 adopted to overcome this difficulty ; and the leading 

 doctrine of Homoeopathy " similia slmilibus curantur" 

 (Anglvce " Like cures like") was called in to the aid of 

 the telegrapher. It was considered that, if an iuten.se 

 current were opposed to an intense current, although 

 produced from different sources, the strongest would 

 gain the advantage, and more speedy signals would re- 

 sult. This plan was accordingly adopted on the Atlantic 

 cable soon after it gave the first sign of defect. Power- 

 ful voltaic batteries, magneto-electric machines, and 

 Rhumkorf's coil, or its modifications, were successively 

 tried ; but, alas ! with no effect : and it is certain, that 

 if the slightest break in the cable had existed, and a 

 current had been transmitted, even for a few moments, 

 from a Rhumkorf in good action, the fate of the cable 

 would be for ever sealed by the combustion of the two 

 edges of the fractured parts. The reason of this will be 

 at once perceived by reference to our remarks on that 

 coil, at a previous page.f 



One effect of a fresh intense current, besides that of 

 overcoming the resistance of a long conducting wire, is 

 to neutralise the induction of the wire current, produced 

 by a previously passing current ; hence the employment 

 of such means in the way we have just mentioned. 

 Their want of success, in the case of the Atlantic tele- 

 graph, must not be ascribed to a defect in the principle 

 of the doctrine, but rather to the peculiar circumstances 

 in which it was applied. A section of the map of tlio 

 bottom of the Atlantic, as prepared by Captain Maury 

 and others, exhibited, as near as can be, just such a bed 

 as would be found for a cable, if one wero laid from 

 Lombardy over the Alps, at the top of Mont Blanc 

 then into the valleys and plains of France, across the 

 English channel, and so continued over the hilly parts 

 of England and Scotland concluding its career on the 

 north side of Ben Nevis. For 500 miles from the Irish 

 and American coasts, the cable was suspended on the 

 tops of marine mountains, and hung in the deep hollow 

 which intervened. Between these two localities, a level 

 bed of sand, and the remains of shells, of nearly 1,200 

 miles in length, existed, on which the cable might have 

 rested in undisturbed repose. The depth of the ocean 

 there, was sufficient to prevent the least risk of injury 

 from any cause whatever. 



See 0'itf, p HO. t Ante, p. 253; Experiment 12. 



2 M 



