Loe raamatut: «Triumphs of Invention and Discovery in Art and Science», lehekülg 10
The Electric Telegraph
"Speak the word and think the thought,
Quick 'tis as with lightning caught —
Over, under lands or seas,
To the far antipodes;
Here again, as soon as gone,
Making all the earth as one;
Moscow speaks at twelve o'clock, —
London reads ere noon the shock."
I. – MR. COOKE
Of all the marvels of our time, the most marvellous is the subjugation of the electric fluid, that potent elemental force, – twin brother of the fatal lightning, – to be our submissive courier, to bear our messages from land to land, and "put a girdle round about the earth in forty minutes." The Prospero that tamed this Ariel was no individual genius, but "two single gentlemen rolled into one." The idea of employing the electric current for the conveyance of signals between distant points, can be traced pretty far back in date; but to Mr. Cooke and Professor Wheatstone is undoubtedly due the credit of having made the electric telegraph an actual and accomplished fact, and rendered it practicable for everyday uses.
Having served for a number of years as an officer in our Indian army, Mr. Cooke came back to Europe to recruit his health in the beginning of 1836, and took up his abode at Heidelberg. He found agreeable occupation for his leisure in the study of anatomy, and in the construction of anatomical models for his father's museum at Durham, where he was a professor in the university. Entirely self-taught in this delicate art, Mr. Cooke applied himself to it with characteristic ardour, and attained remarkable skill. One day he happened to witness some experiments which were made by Professor Möncke, to illustrate the feasibility of electric signalling. A current of electricity was passed through a long wire, and set a magnetic needle at the end quivering under its influence. The experiment was a very simple one, and not at all novel; but Cooke had never paid any attention to the subject before, and was much struck with what he saw. He became strongly impressed with the possibility of employing electricity in the transmission of telegraphic intelligence between distant places. From the day he witnessed the experiments in Professor Möncke's classroom, he forsook the dissecting knife, threw aside his modelling tools, and applied himself to the realization of his conception. With such ardour and devotion did he labour, and such skill and ingenuity did he bring to the work, that within three weeks he had constructed a telegraph with six wires, forming three complete metallic currents, and influencing three needles, by the varied inclination of which twenty-six different signals were designated. In that short time he had also invented the detector, by which injuries to the wires, whether from water, fracture, or contact with substances capable of diverting the current, were readily traced, and the alarum, by which notice is given at one end of the wire that a message is coming from the other. Both these contrivances were of the utmost value, – indeed, without them electric telegraphy would be impracticable, – and are still in use. Possessing more of a mechanical than a scientific genius, Mr. Cooke bestowed more of his time and ingenuity on the perfection of a telegraph to be worked by clock mechanism, set in action by the withdrawal of a detent by an electro magnet than in the completion of the electric telegraph pure and simple.
Soon after having invented his telegraph, he came over to London, and spent the rest of the year in making a variety of instruments, and in efforts to get his telegraph introduced on the Liverpool and Manchester Railway. He found an obstacle to the complete success of his mechanical telegraph, in the difficulty of transmitting to a distance sufficient electric power to work the electro magnet upon which its action depended. A friend advised him to consult Professor Wheatstone, then known to be deeply engaged in electrical experiments, with a view to telegraphy; and accordingly, an interview between them took place in February 1837.
II. – PROFESSOR WHEATSTONE
Mr. Charles Wheatstone, F.R.S., and Professor of Experimental Philosophy in King's College at the time of that interview, had made considerable advances in the scientific part of the enterprise. At the commencement of his career as a maker and seller of musical instruments in London, he was led to investigate the science of sound; and from his researches in that direction, he was led – much as Herschel was led – to devote himself to optics, and to study the philosophy of light. He was the first to point out the peculiarity of binocular vision, and to describe the stereoscope, which has since become so popular an instrument. Gradually, however, his thoughts and researches came to be steadfastly directed to the application of electricity to the communication of signals. In determining the rate at which the electric current travels through a wire he had laid down, he made an important stride towards the end in view. He proved by a series of most ingenious experiments, that one spark of electricity leaps on before another, and that its progress is a question of time. He found that electricity travels through a copper wire as fast as, if not faster, than light, that is, at the rate of 200,000 miles in a second; but through an iron wire, electricity moves at the rate of only 15,400 miles in a second. In 1836 Mr. Wheatstone had begun experiments in the vaults of King's College, with four miles of wire, properly insulated, and was working out the details of a telegraph, the scientific principles of which he had already laid down. He had discovered an original method of converting a few wires into a considerable number of circuits, so that the greatest number of signals could be transmitted by a limited number of wires, by the deflection of magnetic needles. Mr. Wheatstone, however, was somewhat backward in the mechanical parts of the scheme, and the meeting between him and Cooke was therefore of the greatest benefit to both, and an admirable illustration of the old proverb, that two heads are better than one. Had they never been brought together, – had they kept on working out their own ideas apart – each would, no doubt, have been able to produce an electric telegraph; but a great deal of time would have been lost, and their respective efforts less complete and valuable than the one they effected in conjunction. Cooke wanted sound, scientific knowledge; Wheatstone wanted mechanical ingenuity; and their union supplied mutual deficiencies. A partnership was immediately formed between them. Before their combined genius all difficulties vanished; and in the June of the same year they were able to take out a patent for a telegraph with five wires and five needles. Their respective shares in its invention are clearly marked out by Sir J. Brunel and Professor Daniell, who, as arbiters between the two upon that delicate question, gave the following award in 1841: —
"Whilst Mr. Cooke is entitled to stand alone as the gentleman to whom this country is indebted for having practically introduced and carried out the electric telegraph as a useful undertaking, promising to be a work of national importance; and Professor Wheatstone is acknowledged as the scientific man whose profound and successful researches had already prepared the public to receive it as a project capable of practical application, – it is to the united labours of two gentlemen so well qualified for mutual assistance, that we must attribute the rapid progress which this important invention has made during the five years since they have been associated."
Shortly after the taking out of a patent, wires were laid down between Euston Square Terminus and Camden Town Station, on the North-Western Railway; and the new telegraph was subjected to trial. Late in the evening of the 25th July 1837, in a dingy little room in one of the Euston Square offices, Professor Wheatstone sat alone, with a hand on each handle of the signal instrument, and an anxious eye upon the dial, with its needles as yet in motionless repose. In another little room at the Camden Town Station, Mr. Cooke was seated in a similar position before the instrument at the other end of the wires, along with Mr., now Sir Charles Fox, Robert Stephenson, and some other gentlemen. It was a trying, agitating moment for the two inventors, – how Wheatstone's pulse must have throbbed, and his heart beat, as he jerked the handle, broke the electric current, and sent the needles quivering on the dial; in what suspense he must have spent the next few minutes, holding his breath as though to hear his fellow's voice, and almost afraid to look at the dial lest no answer should be made; with what a thrill of joy must each have seen the needles wag knowingly and spell out their precious message, – the "All's well; thank God," that flashed from heart to heart, along the line of senseless wire. "Never," said Wheatstone, "did I feel such a tumultuous sensation before, as when all alone in the still room I heard the needles click; and as I spelled the words, I felt all the magnitude of the invention now proved to be practicable beyond cavil or dispute."
A few days before this trial of the telegraph in London, Steinheil, of Munich, is said to have had one of his own invention at work there; and it is a difficult question to decide whether he or Cooke and Wheatstone were the first inventors. It is, however, a question of no consequence, as each worked independently. Since the first English electric telegraph was patented, there have been a thousand and one other contrivances of a similar kind taken out; but it may be doubted whether, for practical purposes, the original apparatus, with the improvements which its own inventors have made on it, is not still the best of them all.
From being used merely to carry railway messages, the telegraph was brought into the service of the general public; the advantages of such almost instantaneous communication were readily appreciated; and eight years after Messrs. Cooke and Wheatstone took out their patent, lines of telegraph to the extent of 500 miles were in operation in England upon the original plan. In 1855 telegraphic correspondence had become so general, that the Electric Telegraph Company was started to supply the demand. In that establishment the Needle Telegraph of Wheatstone and Cooke is the one generally used, with the Chemical Recording Telegraph of Bain for special occasions. By means of the latter, blue lines of various lengths, according to an alphabet, are drawn upon a ribbon of paper, and as many as 20,000 words can be sent in an hour, though the ordinary rate is 100 per minute. In the purchase of patent rights alone, the Company have spent £170,000, and they are every year adding to the length of their wires. In June 1850 they had 6730 miles of wires, and despatched 29,245 messages a year. In December 1853 they had 24,340 miles of wires, and despatched 212,440 messages a-year. Their lines now extend over a much larger mileage, and convey a greatly increased number of messages. The Magnetic Telegraph Company have also a large extent of wires, and do a considerable business.
III. – THE SUBMARINE TELEGRAPH
The land telegraph having had such success, the next step was to carry the wires across the deep, and link continent to continent, – an all-important step for an island kingdom such as ours, with its legion of distant colonies. The success of a submerged cable between Gosport and Portsmouth, and of one across the docks at Hull, proved the feasibility of a water telegraph, at least on a small scale, and it was not long before more ambitious attempts were made. On the 28th of August 1850, a cable, 30 miles long, in a gutta percha sheathing, was stretched at the bottom of the straits between Dover and Cape Grisnez, near Calais. Messages of congratulation sped along this wire between England and France; and although a ridge of rocks filed the cable asunder on the French coast, the suspension of communication was only temporary. The link has once more been established, and is in daily use. The first news sent by the wire to England was of the celebrated coup d'etat of the 2d December, which cleared the way for Louis Napoleon's ascent of the throne. Numerous other cables have since been sunk beneath the waters; complete telegraphic communication has just been established between England and India, and will, no doubt, before long be extended to Australia.
The greatest enterprise of this kind, however, still remains unaccomplished – that is, the laying of the Atlantic cable. A company was started in 1856 to carry out this great enterprise, the governments of Great Britain and the United States engaging to assist them, not only with an annual subsidy of £10,000 a-year for twenty-five years, but to furnish the men and ships required for laying the cable from one side of the Atlantic to the other. The chief difficulty which engaged the attention of Mr. Wildman Whitehouse and the other agents of the notable enterprise was the enormous size of the cable which, it was thought, would be necessary. The general belief at that time was, that the greater the distance to be traversed, the larger must be the wire along which the electric current was to pass, and that the rate of speed would be in proportion to the size of the conductor. Mr. Whitehouse, however, thought it would be as well to begin by making sure that this was really the case, and that a monster cable was essential; and after some three thousand separate observations and experiments, was delighted to find that the difficulty which stared them in the face was imaginary. Instead of a large cable transmitting the current faster than a small one, he ascertained beyond a doubt, that the bigger the wire, the slower was the passage of the electricity. It would be needful, therefore, to make the cable only strong enough to stand the strain of its own weight, and heavy enough to sink to the bottom. A single wire would have been quite sufficient, but a strand of seven wires of the finest copper was used for the cable, so that the fracture of one of them might not interfere with the communication, – as long as one wire was left intact the current would proceed. A triple coating of gutta percha, to keep the sea from sucking out the electricity, and a thick coating of iron wire, to sink the cable to the bottom and give it strength, were added to the copper rope, and then the cable was complete. No less than 325,000 miles of iron and copper wire were woven into this great cable, – as much as might be wound thirteen times round the globe; and its weight was about a ton per mile. The length of the cable was 18,947 miles – some 600 miles being allowed to come and go upon, in case of accidents.
The end of July 1857 was selected for the sailing of the ships that were to lay the cable, as fogs and gales were then out of season, and no icebergs to be met with. On the 8th of August, the Agamemnon (English) and Niagara (American), with four smaller steamers to attend them, and each with half of the mighty cable in her hold, got up their steam and left Valentia Harbour. One end of the cable was carried by a number of boats from the Niagara on shore, where the Lord-Lieutenant was in waiting to receive it, and place it in contact with the batteries, which were arranged in a little tent upon the beach. A slight accident to the cable for a little while delayed the departure of the ships; but by the 10th they had got 200 miles out to sea, and so far the cable had been laid successfully. Messages passed and repassed between the ships and the shore. The next day the engineer discovering that too much cable was being paid out, telegraphed to the people on board to put a greater grip on it; the operation was clumsily managed, and the cable snapped, sinking to a depth of 12,000 feet.
Not disheartened, however, the Company replaced the lost portion of the cable; the Government again furnished ships and men, and the cable was actually laid at the bottom of the Atlantic from Valentia Bay to Trinity Harbour.
Addresses of congratulation passed between the Queen and the President of the States, and numerous messages were transmitted. But gradually the signals grew fainter and more faint, till they ceased altogether. The cable was stricken dumb. A little to the north of the fiftieth parallel of latitude, at the bottom of the Atlantic, where the plateau is unbroken by any great depression, some 1500 miles of the disabled cable were lying, on a soft bed of mud, which was constantly thickening, at a depth of from 10,000 to 15,000 feet.
The importance of telegraphic communication between England and the United States was, however, so obvious that its projectors were not to be daunted by the failure they had sustained. Nor was it altogether a failure. They had proved that a cable could be laid, and messages flashed through it. What was wanted was evidently a stronger cable, which should be less liable to injury, and more perfect in its insulation of the telegraphic wires.
From 1858 to 1864, the Company were engaged in the difficult task of raising fresh funds, and in endeavouring to secure grants from the British and American Governments. Their men of science, meanwhile, were devising improvements in the form of cable, and contriving fresh apparatus to facilitate its submersion. Eventually the Telegraph Construction and Maintenance Company, an union of the Gutta Percha Company with the celebrated firm of Glass and Elliott, constructed an entirely new cable, which was not only costlier, but thicker and stronger than the preceding one. The conductor, three hundred pounds per mile, and one-seventh of an inch thick, consisted of seven No. 18 copper wires, each one-twentieth of an inch in thickness. The core or heart of the cable, says a writer in "Chambers's Encyclopædia," was formed of four layers of gutta percha alternating with four of Chatterton's compound (a solution of gutta percha in Stockholm tar); the wire and conductor being seven hundred pounds per mile, and nine-twentieths of an inch thick. Outside this was a coating of hemp or jute yarn, saturated with a preservative composition; while the sheath consisted of ten iron wires, each previously covered with five tarred Manilla yarns. The whole cable was an inch and one eighth thick, weighed thirty-five and three-quarter hundredweights per mile, and was strong enough to endure a breaking strain of seven tons and three-quarters. During the various processes of manufacture, the electrical quality of the cable was tested to an unusual extent. The portions of finished core were tested by immersion in water at various temperatures; next submitted to a pressure of six hundred pounds to the square inch, to imitate the ocean pressure at so great depth; then the conducting power of the copper wire was tested by a galvanometer; and various experiments were also made on the insulating property of the gutta percha. The various pieces having been thus severely put to the proof, they were spliced end to end, and the joints or splicings tested. In a word, nothing was left undone that could insure the success or guarantee the stability of the new cable.
When completed, the cable measured two thousand three hundred miles, and weighed upwards of four thousand tons. It was felt that such a burden could only be intrusted to Brunel's "big ship," the Great Eastern. For this purpose three huge iron tanks were built, in the fore, middle, and aft holds of the vessel, each from fifty to sixty feet in diameter, and each twenty and a half feet in depth; and in these the cable was deposited in three vast coils.
On the 23rd of July 1865, the Great Eastern left Valentia, the submarine cable being joined end to end to a more massive shore cable, which was hauled up the cliff at Foilhummerum Bay, to a telegraph-house at the top. The electric condition of the cable was continually tested during the ship's voyage across the Atlantic; and more than once its efficiency was disturbed by fragments of wire piercing the gutta percha and destroying the insulation. At length on August 2nd, the cable snapped by overstraining, and the end sank to the bottom in two thousand fathoms water, at a distance of one thousand and sixty-four miles from the Irish coast. Attempts were made to recover it by dredging. A five-armed grapnel, suspended to the end of a stout iron-wire rope five miles long, was flung overboard; and when it reached the bottom, the Great Eastern steamed to and fro in the direction where the lost cable was supposed to be lying; but failure followed upon failure, and the cable was never once hooked. There remained nothing to be done but for the Great Eastern to return to England with the news of her non-success, and leaving (including the failure of 1857-8) nearly four thousand tons of electric cable at the bottom of the ocean.
The promoters of ocean telegraphy, however, were determined to be resolute to the end. A new Company was formed, new capital was raised, and a third cable manufactured, differing in some respects from the former. The outside jacket was made of hemp instead of jute; the iron wires of the sheath were galvanized, and the Manilla hemp which covered them was not tarred. Chiefly through the absence of the tar, the weight of the cable was diminished five hundred pounds per mile; while its strength or breaking strain was increased. A sufficient quantity of this improved cable was made to cross the Atlantic, with all due allowance for slack; and also a sufficient quantity of the 1865 cable to remedy the disaster of that year.
On July 13th, 1866, the Great Eastern once more set forth on her interesting voyage, accompanied by the steamers Terrible, Medway, and Albany, to assist in the submersion of the cable, and to act as auxiliaries whenever needed. The line of route chosen lay about midway between those of the 1858 and 1865 cables, but at no great distance from either. The Great Eastern exchanged telegrams almost continuously with Valentia as she steamed towards the American continent; and great were the congratulations when she safely arrived in the harbour of Heart's Content, Newfoundland, on the 27th.
Operations were next commenced to recover the end of the 1865 cable, and complete its submergence. The Albany, Medway, and Terrible were despatched on the 1st of August, to the point where, "deep down beneath the darkling waves," the cable was supposed to be lying, and on the 9th or 10th they were joined by the Great Eastern, when grappling was commenced, and carried on through the remainder of the month. The cable was repeatedly caught, and raised to a greater or less height from the ocean bed; but something or other snapped or slipped every time, and down went the cable again. At last, after much trial of patience, the end of the cable was safely fished up on September 1st; and electric messages were at once sent through to Valentia, just as well as if the cable had not had twelve months' soaking in the Atlantic. An additional length having been spliced to it, the laying recommenced; and on the 8th the squadron entered Heart's Content, having thus succeeded in laying a second line of cable from Ireland to America.
The two cables, the old and the new, continued to work very smoothly during the winter of 1866 and 1867; but in May 1867, the new cable was damaged by an iceberg, which drifted across it at a distance of about three miles from the Newfoundland shore. The injury was soon repaired; but again, in July 1867, the same cable broke at about fifty miles from Newfoundland.
The earlier cable continued to work for several years, but both cables gave way towards the close of the autumn of 1870. No special inconvenience was felt, however, as two years ago a French line of cable was laid down between Europe and America; the Great Eastern being again employed, and the operations being conducted under the superintendence of English electricians. The two British cables will probably be repaired in the spring of the present year (1871).
Submarine cables have multiplied recently, and almost every ocean flows over the mysterious wires which flash intelligence beneath the rolling waters from point to point of the civilized world. By a telegraph-cable, which is partly submarine, the India Office in Westminster is united with the Governor-General and his Council at Calcutta. There is also communication between Singapore and Australia, and the network of ocean telegraphy is being so rapidly extended that, before long, the British Government in the metropolis will be enabled to convey its instructions in a few hours to the administrative authorities in every British colony. And thus the words which the poet puts into the mouth of "Puck" will be nearly realized in a sense the poet never dreamed of – "I'll put a girdle round about the world in forty minutes."
