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.
In 1865, new capital having been raised, preparations were made for another expedition. It was now decided to use only one vessel for laying the cable, and the Great Eastern was chosen for the task. This vessel had been lying idle for close on ten years, owing to her failure as a cargo boat, but her great size and capacity made her most suitable for carrying the enormous weight of the whole cable. In July 1865 the Great Eastern set sail, under the escort of two British warships. When 84 miles had been paid out, a fault occurred, and after drawing up about 10½ miles it was found that a piece of iron wire had pierced the coating of the cable. The trouble was put right, and the paying-out continued successfully until over 700 miles had been laid, when another fault appeared. The cable was again drawn in until the fault was reached, and another piece of iron was found piercing clean through. It was evident that two such pieces of iron could not have got there by accident, and there was no doubt that they had been inserted intentionally by some malicious scoundrel, most likely with the object of affecting the company’s shares. A start was made once more, and all went well until about two-thirds of the distance had been covered, when the cable broke and had to be abandoned after several nearly successful attempts to recover it.
In spite of the loss, which amounted to £600,000, the energetic promoters contrived to raise fresh capital, and in 1866 the Great Eastern started again. This effort was completely successful, and on 28th July 1866 the cable was landed amidst great rejoicing. The following extracts from the diary of the engineer Sir Daniell Gooch, give us some idea of the landing.
“Is it wrong that I should have felt as though my heart would burst when that end of our long line touched the shore amid the booming of cannon, the wild, half-mad cheers and shouts of the men?... I am given a never-dying thought; that I aided in laying the Atlantic cable.... The old cable hands seemed as though they could eat the end; one man actually put it into his mouth and sucked it. They held it up and danced round it, cheering at the top of their voices. It was a strange sight, nay, a sight that filled our eyes with tears.... I did cheer, but I could better have silently cried.”
This time the cable was destined to have a long and useful life, and later in the same year the 1865 cable was recovered, spliced to a new length, and safely brought to land, so that there were now two links between the Old World and the New. It was estimated that the total cost of completing the great undertaking, including the cost of the unsuccessful attempts, was nearly two and a half millions sterling. Since 1866 cable-laying has proceeded very rapidly, and to-day telegraphic communication exists between almost all parts of the civilized world. According to recent statistics, the North Atlantic Ocean is now crossed by no less than 17 cables, the number of cables all over the world being 2937, with a total length of 291,137 nautical miles.
Before describing the actual working of a submarine cable, a few words on cable-laying may be of interest. Before the cable-ship starts, another vessel is sent over the proposed course to make soundings. Galvanized steel pianoforte wire is used for sounding, and it is wound in lengths of 3 or 4 nautical miles on gun-metal drums. The drums are worked by an engine, and the average speed of working is somewhere about 100 fathoms a minute in descending, and 70 fathoms a minute in picking up. Some idea of the time occupied may be gained from a sounding in the Atlantic Ocean which registered a depth of 3233 fathoms, or nearly 3½ miles. The sinker took thirty-three minutes fifty seconds in descending, and forty-five minutes were taken in picking up. The heavy sinker is not brought up with the line, but is detached from the sounder by an ingenious contrivance and left at the bottom. The sounder is fitted with an arrangement to bring up a specimen of the bottom, and also a sample of water; and the temperature at any depth is ascertained by self-registering thermometers.
When the soundings are complete the cable-ship takes up her task. The cable is coiled in tanks on board, and is kept constantly under water to prevent injury to the gutta-percha insulation by overheating. As each section is placed in the tank, the ends of it are led to a test-box, and labelled so that they can be easily recognized. Insulated wires run from the test-box to instruments in the testing-room, so that the electrical condition of the whole cable is constantly under observation. During the whole time the cable is being laid its insulation is tested continuously, and at intervals of five minutes signals are sent from the shore end to the ship, so that a fault is instantly detected. The cable in its tank is eased out by a number of men, and mechanics are posted at the cable drums and brakes, while constant streams of water cool the cable and the bearings and surfaces of the brakes. The tension, as shown by the dynamometer, is at all times under careful observation. When it becomes necessary to wind back the cable on account of some fault, cuts are made at intervals of a quarter or half a mile, tests being made at each cutting until the fault is localized in-board. As soon as the cable out-board is found “O.K.,” the ends are spliced up and the paying-out begins again. If the cable breaks from any cause, a mark-buoy is lowered instantly on the spot, and the cable is grappled for. This may take a day or two in good weather, but a delay of weeks may be caused by bad weather, which makes grappling impossible.
The practical working of a submarine cable differs in many respects from that of a land telegraph line. The currents used in submarine telegraphy are extremely small, contrary to the popular impression. An insulated cable acts like a Leyden jar, in the sense that it accumulates electricity and does not quickly part with it, as does a bare overhead wire. In the case of a very long cable, such as one across the Atlantic, a current continues to flow from it for some time after the battery is disconnected. A second signal cannot be sent until the electricity is dissipated and the cable clear, and if a powerful current were employed the time occupied in this clearing would be considerable, so that the speed of signalling would be slow. Another objection to a powerful current is that if any flaw exists in the insulation of the cable, such a current is apt to increase the flaw, and finally cause the breakdown of the line.
The feebleness of the currents in submarine telegraphy makes it impossible to use the ordinary land telegraph receiver, and a more sensitive instrument known as the “mirror receiver” is used. This consists of a coil of very fine wire, in the centre of which a tiny magnetic needle is suspended by a fibre of unspun silk. A magnet placed close by keeps the needle in one position when no current is flowing. As the deflections of the needle are extremely small, it is necessary to magnify them in some way, and this is done by fixing to the needle a very small mirror, upon which falls a ray of light from a lamp. The mirror reflects this ray on to a sheet of white paper marked with a scale, and as the mirror moves along with the needle the point of light travels over the paper, a very small movement of the needle causing the light to travel some inches. The receiving operator sits in a darkened room and watches the light, which moves to the right or to the left according to the direction of the current. The signals employed are the same as those for the single-needle instrument, a movement to the left indicating a dot, and one to the right a dash. In many instruments the total weight of magnet and mirror is only two or three grains, and the sensitiveness is such that the current from a voltaic cell consisting of a lady’s silver thimble with a few drops of acidulated water and a diminutive rod of zinc, is sufficient to transmit a message across the Atlantic.
The mirror receiver cannot write down its messages, and for recording purposes an instrument invented by Lord Kelvin, and called the “siphon recorder,” is used. In this instrument a coil of wire is suspended between the poles of an electro-magnet, and to it is connected by means of a silk fibre a delicate glass tube or siphon. One end of the siphon dips into an ink-well, and capillary attraction causes the ink to fill the siphon. The other end of the siphon almost touches a moving paper ribbon placed beneath it. The ink and the paper are oppositely electrified, and the attraction between the opposite charges causes the ink to spurt out of the siphon in very minute drops, which fall on to the paper. As long as no current is passing the siphon remains stationary, but when a current flows from the cable through the coil, the latter moves to one side or the other, according to the direction of the current, and makes the siphon move also. Consequently, instead of a straight line along the middle of the paper ribbon, a wavy line with little peaks on each side of the centre is produced by the minute drops of ink. This recorder sometimes refuses to work properly in damp weather, owing to the loss of the opposite charges on ink and paper, but a later inventor, named Cuttriss, has removed this trouble by using a siphon kept constantly in vibration by electro-magnetism. The ordinary single-needle code is used for the siphon recorder.