Fig. 299.—The Instrument-Room at Valentia.
But these disasters did not crush the hopes of the promoters of the great enterprise, and in the following year the Great Eastern again sailed with a new cable, the construction of which is shown of the actual size, in Fig. [301]. In this there is a strand of seven twisted copper wires, as before, forming the electric conductor; round this are four coatings of gutta-percha; and surrounding these is a layer of jute, which is protected by ten iron wires (No 10, B.W.G) of Webster and Horsfall’s homogeneous metal, twisted spirally about the cable; and each wire is enveloped in spiral strands of Manilla hemp. The Great Eastern sailed on the 13th of July, and on the 28th the American end of the cable was spliced to the shore section in Newfoundland, and the two continents were again electrically connected. They have since been even more so, for the cable of 1865 was eventually fished up, and its electrical condition was found to be improved rather than injured by its sojourn at the bottom of the Atlantic. It was spliced to a new length of cable, which was successfully laid by the Great Eastern, and was soon joined to a Newfoundland shore cable. There were now two cables connecting England and America, and one connecting America and France has since been laid. At the present time upwards of 20,000 miles of submerged wires are in constant use in various parts of the world.
Fig. 300.—The Breaking of the Cable.
Certain interesting phenomena have been observed in connection with submarine cables, and some of the notions which were formerly entertained as to the speed of electricity have been abandoned, for it has been ascertained that electricity cannot properly be said to have a velocity, since the same quantity of electricity can be made to traverse the same distance with extremely different speeds. No effect can be perceived in the most delicate instruments in Newfoundland for one-fifth of a second after contact has been made at Valentia; after the lapse of another fifth of a second the received current has attained about seven per cent. of its greatest permanent strength, and in three seconds will have reached it. During the whole of this time the current is flowing into the cable at Valentia with its maximum intensity. Fig. [302] expresses these facts by a mode of representation which is extremely convenient. Along the line O X the regular intervals of time in tenths of seconds are marked, commencing from O, and the intensity of the current at each instant is expressed by the length of the upright line which can be drawn between O X and the curve. The curve therefore exhibits to the eye the state of the current throughout the whole time. If after nearly a second’s contact with the battery the cable be connected with the earth at the distant end, the rising intensity of the current will be checked and then immediately begin to decline somewhat more gradually than it rose, as indicated by the descending branch of the curve in Fig. [302]. A little reflection will show the unsuitability for such currents of instruments which require a fixed strength to work them. We may remark that, supposing a receiving instrument were in connection with the Atlantic Cable which required the maximum strength of the received current to work it, the sending clerk would have to maintain contact for three seconds before this intensity would be reached, and then, after putting the cable to earth, he would have to wait some seconds before the current had flowed out. Several seconds would, therefore, be taken up in the transmission of one signal, whereas by means of the mirror galvanometer about one-fourteenth of this time suffices, and the syphon recorder will write the messages twelve times as fast as the Morse instrument. The cause of the gradual rise of the current at the distant end of a submarine cable must be sought for in the fact that the coated wire plays the part of a Leyden jar, and the electricity which pours into it is partly held by an inductive action in the surrounding water. The importance of Sir W. Thomson’s inventions as regards rapidity of signalling, upon which the commercial success of the Atlantic Cable greatly depends, will now be understood.
Fig. 301.—Atlantic Telegraph Cable, 1866.
Fig. 302.
By furnishing the means of almost instantaneous communication between distant places, the electric telegraph has enabled feats to be performed which appear strangely paradoxical when expressed in ordinary language. When it is mentioned as a sober fact that intelligence of an event may actually reach a place before the time of its occurrence, a very extraordinary and startling statement appears to be made, on account of the ambiguous sense of the word time. Thus it appears very marvellous that details of events which may happen in England in 1876 can be known in America in 1875, but it is certainly true; for, on account of the difference of longitude between London and New York, the hour of the day at the latter place is about six hours behind the time at the former. It might, therefore, well happen that an event occurring in London on the morning of the 1st of January, 1876, might be discussed in New York on the night of the 31st of December, 1875. There are on record many wonderful instances of the celerity with which, thanks to electricity, important speeches delivered at a distant place are placed before the public by the newspapers. And there are stories in circulation concerning incidents of a more romantic character in connection with the telegraph. The American journals not long ago reported that a wealthy Boston merchant, having urged his daughter to marry an unwelcome suitor, the young lady resolved upon at once uniting herself to the man of her choice, who was then in New York, en route for England. The electric wires were put in requisition; she took her place in the telegraph office in Boston, and he in the office in New York, each accompanied by a magistrate; consent was exchanged by electric currents, and the pair were married by telegraph! It is said that the merchant threatened to dispute the validity of the marriage, but he did not carry this threat into execution. The following jeu d’esprit appeared a short time ago in “Nature,” and, we strongly suspect, has been penned by the same hand as the lines quoted from “Blackwood,” on page [508].