During the early days of telegraphy, overhead lines were a source of considerable danger when thunderstorms were taking place. Lightning flashes often completely wrecked the instruments, giving severe shocks to those in the vicinity, and in a few cases operators were killed at their posts. Danger of this kind is now obviated by the use of contrivances known as lightning arresters. There are several forms of these, but only one need be mentioned. The main features of this are two metal plates separated slightly from one another, so that there is a small air gap between them. One plate is connected to the line wire, and the other to earth. Almost all lightning flashes consist of an oscillatory discharge, that is one which passes a number of times backwards and forwards between a cloud and the earth. A very rapidly alternating discharge of this kind finds difficulty in passing along the line wire, being greatly impeded by the coils of wire in the various pieces of apparatus; and although the resistance of this air gap is very high, the lightning discharge will cross the gap sooner than struggle along the line wire. In this way, when a flash affects the line, the discharge jumps the gap between the plates of the arrester and passes away harmlessly to earth, without entering the telegraph office at all. As was mentioned in [Chapter III]., the prevalence of magnetic storms sometimes renders telegraph lines quite unworkable for a time, but although such disturbances cause great delay and general inconvenience, they are not likely to be at all dangerous. It is often possible to maintain telegraphic communication during magnetic disturbances by using two lines to form a complete metallic loop, so that there is no earth return.
CHAPTER XVII
SUBMARINE TELEGRAPHY
The story of submarine telegraphy is a wonderful record of dogged perseverance in the face of tremendous obstacles and disastrous failures. It would be of no interest to trace the story to its very beginning, and so we will commence with the laying of the first cable across the English Channel from Dover to Calais, in 1850. A single copper wire covered with a layer of gutta-percha half an inch thick was used, and leaden weights were attached to it at intervals of one hundred yards, the fixing of each weight necessitating the stoppage of the cable-laying ship. The line was laid successfully, but it failed after working for a single day, and it afterwards turned out that a Boulogne fisherman had hauled up the cable with his trawl. This line proved that telegraphic communication between England and France was possible, but the enterprise was assailed with every imaginable kind of abuse and ridicule. It is said that some people really believed that the cable was worked in the style of the old-fashioned house bell, and that the signals were given by pulling the wire! In the next year another attempt was made by Mr. T. R. Crampton, a prominent railway engineer, who himself contributed half of the £15,000 required. The form of cable adopted by him consisted of four copper wires, each covered with two layers of gutta-percha, and the four enclosed in a covering formed of ten galvanized iron wires wound spirally round them. The line proved a permanent success, and this type of cable, with certain modifications, is still in use. In 1852 three attempts were made to connect England and Ireland, but the first two failed owing to the employment of cables too light to withstand the strong tidal currents, and the third was somehow mismanaged as regards the paying-out, so that there was not enough cable to reach across. A heavier cable was tried in the next year, and this was a lasting success.
The success of these two cables led to the laying of many other European cables over similar distances, but we must now pass on to a very much bigger undertaking, the laying of the Atlantic cable. In 1856 the Atlantic Telegraph Company was formed, with the object of establishing and working telegraphic communication between Ireland and Newfoundland, the three projectors being Messrs. J. W. Brett, C. T. Bright, and C. W. Field. The British and the United States Governments granted a subsidy, in return for which Government messages were to have priority over all others, and were to be transmitted free. The objections launched against the scheme were of course many, some of them making very amusing reading. It is however very strange to find so eminent a scientist as Professor Airy, then Astronomer Royal, seriously stating that it was a mathematical impossibility to submerge a cable safely to such depths, and that even if this could be done, messages could not be transmitted through such a great length of cable.
It was estimated that a length of about 2500 nautical miles would be enough to allow for all contingencies, and the construction of the cable was commenced in February 1857, and completed in June of that year. It is difficult to realize the gigantic nature of the task of making a cable of such dimensions. The length of copper wire used in making the conductor was 20,500 miles, while the outer sheathing took 367,500 miles of iron wire; the total length of wire used being enough to go round the Earth thirteen times. The cable was finally stowed away on board two warships, one British and the other American.
The real troubles began with the laying of the cable. After landing the shore end in Valentia Bay, the paying-out commenced, but scarcely had five miles been laid when the cable caught in the paying-out machinery and parted. By tracing it from the shore the lost end was picked up and spliced, and the paying-out began again. Everything went well for two or three days, and then, after 380 miles had been laid, the cable snapped again, owing to some mismanagement of the brakes, and was lost at a depth of 2000 fathoms. The cable had to be abandoned, and the ships returned to Plymouth.
In the next year, 1858, another attempt was made, with new and improved machinery and 3000 miles of cable, and this time it was decided that the two ships should start paying-out from mid-ocean, proceeding in opposite directions towards the two shores after splicing their cables. On the voyage out the expedition encountered one of the most fearful storms on record, which lasted over a week, and the British man-of-war, encumbered with the dead weight of the cable, came near to disaster. Part of the cable shifted, and those on board feared that the whole of the huge mass would break away and crash through the vessel’s side. Sixteen days after leaving Plymouth the rendezvous was reached, the cables were spliced and the ships started. After the British ship had paid out 40 miles it was discovered that the cable had parted at some distance from the ship, and the vessels once more sought each other, and spliced again ready for another effort. This time the cable parted after each vessel had paid out a little more than 100 miles, and the ships were forced to abandon the attempt.
The failure of this second expedition naturally caused great discouragement, and the general feeling was that the whole enterprise would have to be given up. The chairman of the company recommended that in order to make the best of a bad job the remainder of the cable should be sold, and the proceeds divided amongst the shareholders, but after great efforts on the part of a dauntless few who refused to admit defeat, it was finally decided to make one more effort. No time was lost, and on 17th July 1858 the vessels again sailed from Queenstown. As before, the cables were spliced in mid-ocean, and this time, after many anxious days, many false alarms, and one or two narrow escapes from disaster through faulty pieces of cable discovered almost too late, the cable was landed successfully on both shores of the Atlantic early in August.
The Atlantic cable was now an accomplished fact, and dismal forebodings were turned into expressions of extravagant joy. The first messages passed between Queen Victoria and the President of the United States, and amongst the more important communications was one which prevented the sailing from Canada of two British regiments which had been ordered to India during the Mutiny. In the meantime the Indian Mutiny had been suppressed, and therefore these regiments were not required. The dispatch of this message saved a sum of about £50,000. The prospects of the cable company seemed bright, but after a short time the signals began to grow weaker and weaker, and finally, after about seven hundred messages had been transmitted, the cable failed altogether. This was a great blow to the general public, and we can imagine the bitter disappointment of the engineers and electricians who had laboured so hard and so long to bring the cable into being. It was a favourable opportunity for the croakers, and amongst a certain section of the public doubts were expressed as to whether any messages had been transmitted at all.
A great consultation of experts took place with the object of determining the cause of the failure, and the unanimous opinion was that the cable had been injured by the use of currents of too great intensity. Some years elapsed before another attempt could be made, but the idea was never abandoned, and a great deal of study was given to the problems involved. Mr. Field, the most energetic of the original projectors, never relaxed his determination that the cable should be made a success, and he worked incessantly to achieve his ambition. It is said that in pursuance of his object he made sixty-four crossings of the Atlantic, and considering that he suffered greatly from sea-sickness every time this shows remarkable pluck and endurance.