M4 



UNDULATORY FORCEa ELECTRO-MAGNETISM. [SCBKAKINB CABLM. 



information on the subject Thcro is, perhaps, hardly 

 any other substance in nature with which wo are ac- 

 quainted, so suitable to telegraphic purposes as those wo 

 have named ; and the only advantage which has arisen, 

 hitherto, in the search after substitutes for them, has 

 accrued to the patent offices, in the shape of fees paid 

 by inventors, who started forth in legions as soon as any 

 defect in a submarine cable was discovered. On this 

 point we may remark, that it would be a most merciful 

 provision, on the part of the government, if a kind of 

 committee were appointed, whose duty it would be to 

 investigate and report on the various projects which are 

 continually being patented. An immense amount of 

 money and litigation would be saved; really good in- 

 ventions would oe reported as of value; and our insol- 

 vent courts and lunatic asylums cut off from a supply 

 of broken-down and disappointed, but too sanguine 

 inventors, who unwittingly, but surely, flock thither. 



We next arrive at the conducting wires which always 

 form the centre of a cable, and on which its value 

 entirely depends. They are always made of copper, 

 which combines elasticity, cheapness, and high conduct- 

 ing power. Various sizes are employed ; but, generally 

 speaking, that of No. 14 or 1C gauge is preferred, and is 

 about equal to the tenth part of an inch in diameter. 

 Occasionally, as in the Atlantic cable, a number of fine 

 wires are twisted together, so as, electrically speaking, 

 to form one; but we ore not aware that anything is 

 gained thereby, except, perhaps, a slight additional 

 strength. We may hero mention a circumstance which, 

 we believe, often causes the failure in submarine cables. 

 We have already noticed the fact, that copper wire 

 becomes hardened, and eventually " rotten," after having 

 long conveyed an electric current.* If it be enclosed in 

 gutta-percha, the fact that the wire is broken cannot be 

 discovered externally; and hence, during the laying of 

 a cable, it is essential that its conducting power should 

 bo constantly tested. But the defect to which we allude 

 does not occur until the cable has been some time in use, 

 and its wire injured by the electric current passing by 

 it. Our attention was first directed towards this point 

 in 1856, when attempting to illustrate the explosion of 

 the Russian infernal machines by means of the voltaic 

 batteries, t After a few times of using the gutta-percha 

 covered wires, which were the same as those employed 

 for submarine telegraphs, they invariably broke on being 

 bent to the least degree. The explosion of the powder 

 would, of course, be prevented. But, strange to say, a 

 broken wire would at times convey the current perfectly. 

 This, however, is easily explained ; for if, by accident, 

 the broken wire were so bent whilst in use, as that the 

 fractured edges were again brought into contact, the 

 current would, for the moment, find a complete con- 

 ductor, and so the explosion would take place. Now 

 this is what frequently occurs in submarine cables. 

 At times the current affords no indication of its passage : 

 and we would suggest, that the cause which so con- 

 tinually hindered the success of our experiment, may 

 just as likely be active in the cose of submarine cables, 

 more especially as far more intense currents are sent 

 through their wires than those we employed. We ob- 

 served, that, on submitting the edges of the fractured 

 wires to a microscope, the metal had a decided crystalline 

 appearance proving that it had undergone a molecular 

 change* 



To those of our readers who may be engaged in 

 practical telegraphy, we may state, that the "rottenness" 

 of copper wire is produced the more rapidly as the 

 intensity of current is increased ; and, from our experi- 

 ments, we do not consider that it matters of what 

 thickness the wire is. We have employed copper wire, 

 of a quarter of an inch in thickness, for conveying the 

 current of from 60 to 100 cells (large size) of Grove's 

 batteries ; and the action on any portion of the wire 

 may easily be noticed after they have been constantly in 

 use for twenty or thirty hours. The readiest way of 

 trying the experiment, is that of making some No. 22 

 gauge copper wire the terminals of a common .or 



Be* <*., p. WO. 1 Ante, p. 193 ; Fig. 53. 



Khumkorf coil. They will soon become as brittle as a 

 piece of zinc or lead wire ; and we have, in rare cases, 

 seen a piece, ten inches long, break by its own weight 

 after having been so employed. 



The iiumluT of wires placed in any one cable, is regu- 

 lated according to the amount of business expected to 

 occur between any two stations. That hud between 

 Ireland and Scotland, contains six wires: the Dover 

 and Ostend cable, laid i 1853, has also six. The cable 

 hud between the coast of Suffolk and Holland, has 

 seven ; which, however, have each an external coat of 

 iron wire the whole being twisted together to form 

 one cable ; whilst the temporary cable laid between 

 Varna and Balaclava during the Russian war, ami 

 which served so many valuable purposes, was of small 

 size, and contained but one wire, without any external 

 covering. It will be unnecessary for us to enter into 

 any special description of those we have na:m-d above; 

 but we may hero more fully describe the Atlantic cable, 

 because so intense an interest has been attached t 

 As wo have already stated, it consisted of an external 

 covering of iron wire, and a coating of gutta-percha ; and, 

 in the centre, seven fine copper wires, twisted together, 

 formed the conducting medium. Its appearance is in- 

 dicated in the annexed cut, both in section and in 

 length. 



Fig. 29. 



Our readers will, doubtless, be surprised to find that 

 such a comparatively slender cable (its actual size is repre- 

 sented in the cut) should have been employed. It n 

 however, be borne in mind, that, at great depths. 

 ocean is not liable to disturbance, as is observed on its 

 surface. A dead and imperturbable calm always ex 

 so, if the cable stand the trial it has to undergo durin : 

 submersion, it is liable to little subsequent injury fivm 

 causes external to it. 



The following table may bo of value to many of our 

 readers who take a general interest in the subject of 

 submarine telegraphy. We have selected our informa- 

 tion from various sources ; and have chosen the lea 

 cables now at work between different stations, or which 

 have been worked and have failed. 



In the above table, the Red Sea and Mediterranean 

 cables have not been included. The former has lately 

 failed to work ; and those laid in the Mediterranean nro 

 of various lengths and sizes. The cable between Malta 

 and Alexandria is but just completed. 



\\'o may remark, in reference to the comparative 

 weight of the different cables, that, in ninny cases, ron- 



:l>lo material has been saved by laying a light < 

 in deep water, and attaching to it a stronger one i 

 the shores where it terminates. The reason of this is 

 obvious from our previous remarks; but wo may odd, 

 that occasionally, cables are liable to accident from 

 vessels anchoring near them. As the anchor is weighed, 

 its fluke may catch the cable ; indeed, some time ago, 

 one of the Channel cables was tints accidentally fished 

 up. The caotoin of the vessel whose anchor had caught 



