TKI.KUKAl'H. KI.lHTIIlr. 



, I:I.K Tun-. 



lion, in preference to a weak one. because a strung current would 

 force a paaaxge through an imperfection which might be too ilight to 

 allow a weak current to make iU way. During the progress of the 

 work, a plan wai devised which enabled the testing for both con- 

 f the itranil ami insulation of the sheath to be carried on 

 simultaneously. A voltaic current can pas* through a charged Leyden 

 jar without either the current or the charge being in any practical 

 way interfered with. Therefore the entire length of cable under 

 examination was joined up into a loop or endless ring, and a voltaic 

 battery of five hundred pain of plates had one of it* poles connected 

 with the conducting strand of this ring, and the other pole placed in 

 communication with the earth. A small iniiilatrd battery of low 

 tension was also introduced into the circuit of the ring, so that its 

 current flowed round continually, from pole to pole, through the 

 strand. An insulated bell was also so placed in the circuit, that any 

 break of continuity dropped a needle, before held magnetically f;wt, 

 and caused the bell to sound. Another bell instrument wan BO 

 arranged that it was rung whenever the current from the five hundred 

 cell battery began to run, in consequence of electrical leakage, with 

 undesirable speed. The feeble battery iu the circuit rung its bell 

 whenever the circuit was broken. The strong battery out of the 

 circuit rung its bell whenever an outflowing current was Bet up 

 through the strand, in consequence of the insulating sheath being 

 unable to retain the charge. 



During the prosecution of these experiments the discovery was mode, 

 that the insulating power of gutta percha is very materially affected by 

 temperature. A high temperature seems greatly to impair its insula- 

 ting capacity, and the recurrence of alow temperature speedily restores 

 it to its original excellence. An opportunity was taken, when a single 

 flake or tier of the completed cable was lying at the bottom of the 

 receptacle in the yard of the manufactory at Greenwich, to watch the 

 changes which the natural variation of temperature during forty-eight 

 hours produced in its conducting capability. When the thermometer 

 stood at 42, the deflection of the galvanometer needle was barely 3 ; 

 but when the thermometer rose to 59, the deflection of the magnetic 

 needle became 64*. Even passing sunshine and cloud made the tell- 

 tale needle traverse out and in with surprising rapidity. There was 

 reason to conclude, from the soundings taken by Lieutenant Dayman 

 of the Cyclops, that the bottom of the Atlantic would supply the low 

 temperature essential to the good performance of the insulating 

 material. 



The separate lengths of manufactured core were joined into longer 

 extents in the following manner. The gutta percba was scraped from 

 the ends for a short distance, and these were placed in contact. A 

 piece of copper wire was th'in attached by firm brazing to one side of 

 the joint, and \cound round the strand until it reached as far on the 

 other side, being there brazed again. A second binding was then 

 effected outside the first in precisely the same way, and several layers 

 of gutta percha placed over the whole by the aid of hot irons. In case 

 of the core on each side of the joint being at any time so dragged that 

 the ends of the strand were broken asunder, this outer investment of 

 wire would unroll spirally without being detached from the strand. 

 Thus the electric continuity of the strand would be preserved even 

 when the strand iUelf was severed. 



Every two miles of the completed core were wound upon channelled 

 drums with deep flanges, iron shod at the rim, so that they could be 

 rolled about and mode to perform their own locomotion. When the 

 contents of these drums were used in supplying the cable with more 

 core, one of the ends was attached to the outgoing core of the com- 

 prawed cable, and so the contents were unrolled from the drum as the 

 external metallic wires were spun round the core. During the unrol- 

 ling, a serving of hemp, saturated with a mixture of pitch and tar, was 

 compactly wound round the core to act as a bed for the external me- 

 tallic sheath. Then eighteen strands, each of seven wires of charcoal 

 iron, were twisted firmly round the core. The strands aud the cable 

 were made by precisely analogous machinery. A large horizontal 

 table, containing seven bobbins on the circumference in the case of the 

 traod machine, and eighteen in the case of the closing or finishing 

 machine, was whirled round by steam-power with great rapidity. A 

 central wire, or the core, was drawn up through a hole in the middle 

 of the Uble, and so invested with a twisted whorl of wires or strands, 

 given off from the bobbin* as the table revolved. The strands were 

 used in completing the cable, instead of solid wires, because by this 

 mean* greater flexibility and strength, for the material used, were 

 obtained. The external investment of iron was solely designed to pro- 

 toot the coated core from mechanical violence during the act of sub- 

 mergence, and to confer upon it a convenient amount of weight for 

 m~Aitrc it tinting in the sea. 



Each atrand-machine, during the manufacture of the cable, was 

 worked day and night, and in twenty-four hours spun ninety-eight 

 mile* of wire into fourteen miles of strand. The several strand-machines 

 at work simultaneously every twenty-four hours transformed 2058 

 mile* of wire into 294 miles of strand. As much as thirty mil< < nf 

 cable have been made within twenty-four hours. At one time all the 

 wire-drawer* in England proved to bo unable to supply the 

 dumanda of the machinery, and the works hod to panne for a short 

 apace. The entire length of wire, iron and cj,]xr, i-puu into this 

 wonderful structure, amounted to 332,500 miles ; a length sufficient to 



engirdle the earth thirteen times ! The completed cable weighed from 

 nineteen hundredweight to one ton per mile, and proved to be able to 

 bear with impunity a direct strain of five tons. In the salt-water the 

 weight of the cable would, however, not exceed fourteen hundredweight 

 per mile ; and as the greatest depth of the Atlantic in whieh it would 

 have to bo laid is only a little more than two miles, and a certain por- 

 tion of the weight would necessarily be borne by friction against the 

 particles of the water as the rope sank, it was anticipated that the cable 

 would never, under any circumstance*, be required to meet a strain of 

 more than one ton and a half. 



The failure of the Atlantic cable was due, in some respect*, to the 

 haste with whieh it was manufactured. The company had obtained, 

 in 1854, the exclusive right, for fifty years, of lauding cables on the. 

 shores of Newfoundland and Labrador, and in 1856 the British as well 

 as the American government made a grant of 14,0007. a year, con- 

 ditional on success, the company pledging themselves to make the first 

 attempt to lay the cable in 1857. It is now admitted that the con- 

 struction of the cable was hastily commenced, before the experiments 

 necessary to ascertain the proper form and other conditions had been 

 completed. " The manufacture was, however, not fairly commenced 

 till February, 1857, and 2500 miles were completed in June, 1857. 

 Half was made at Messrs. Newall's works at Birkeuhead, and half at 

 Messrs. Glass and Elliot's works at Greenwich. The manufacture was 

 ver* much hurried. The portion made by Messrs. Glass and Elliot, 

 not being under cover, suffered from exposure to heat. The testing of 

 each coat of gutta pervha in water was recommended by Mr. White- 

 house, but this could not be performed on account of the speed at 

 which the cable was required to be made. In the manufacture of the 

 last 400 miles a system of testing the copper wire for its conducting 

 power was introduced, by which an improvement of from 20 to 25 per 

 cent, in the conductivity of the cable was obtained. Messrs. Newall's 

 half of the cable was put on board the United States' ship Niagara, 

 and Messrs. Glass and Elliot's half wasput on board the Agamemnon ; 

 but so backward were the preparations, that the machinery for laying 

 the cable was being put together as the ships went round to Yalentia. 

 The break machinery was novel and cumbrous." (' Edinburgh Review," 

 1861.) 



The object for which all these complicated arrangements are made 

 is for the purpose of indicating at the distant station certain electric 

 signals by visible motions or by sounds, or by marks on a ribbon of 

 paper. In all these cases there must be a contrivance for connecting 

 the voltaic battery or other electro-motor with the line, in such a way 

 as to be able to send along it a positive or a negative current at will, so 

 as to be able to produce variety in the signals at the distant station, 

 and having performed its work there, the current returns back to the 

 battery by way of the earth. In this way, as already explained, the 

 circuit is completed without the necessity of a return wire. Although 

 a line of earth, as a conductor of electricity, is many thousand times infe- 

 rior in power to a line of metal of the same diameter, yet as the conduct- 

 ing power of bodies increases in proportion to the area of the section of 

 the conductor, and the area of the conducting portion of the earth 

 between the two stations may be indefinitely extended, we thus have 

 a return line offering less resistance than the wire which conveys the 

 current. All that is necessary, therefore, instead of the return wire, is 

 to bury a large copper plate in the earth, and to connect with it a w ire 

 from the telegraphic apparatus at the end of the line. Instead of this 

 copper plate, or rarth as it is called, the gas-pipes and water-pipes of 

 towns are used as earths. In the Electric Telegraph Company's Cen- 

 tral Station at Lothbury, au earth was formed by digging a hole in the 

 foundations until moist ground was arrived at, and into this a cylinder 

 of copper, 401bs. in weight, was sunk, and this was covered up with 

 crystals of sulphate of copper. All the earth-wires of the establishment 

 are connected with this earth-plate. The general arrangement w ill be 

 made clearer by means of jiy. 12, in whieh v and L represent two 



telegraphic instruments, one stationed in York, another in London, 

 connected by on insulated air-line, r Q are two earth-plates, connected 

 by means of i<:h instrument. A message, we will Itt] 



is being transmitted from London to York. If cz represent tlie lat- 

 tery at the London Station, the current will pass from c, to a wire 

 connected witli tlio earth-plate cj, thence through -Oil miles of earth ; 

 when at th York earth-plate, P, the current will ]- taken up again, 

 nil, l'\ in.'. HIM of the wire, will act upon the instrument v, from which 

 it will |>as to the line, return back to London, p.i ihrom-li 111. > 

 the inntnniK nt. dellecting the needle, and so back to the cud z of the 

 battery, wharo the ran. nl will be compl' 



Now, iu order that the clerk may have it iu his power to send the 



