Читать книгу The Story of the Atlantic Cable - Sir Charles Bright - Страница 8

Table of Contents

Design and Construction—Ships—Testing, Shipment, and Stowage—Paying-out Machinery—Staff—Preparations for the Expedition.

THE construction of the cable was taken in hand the following February (1857).

The distance from Valentia, on the western Irish coast, to Trinity Bay, Newfoundland—the two landing-points selected[14]—being 1,640 nautical miles, it was estimated that a length of 2,500 N.M.[15] would be sufficient to meet all requirements. This would provide sufficient margin for a considerable amount of “slack” cable for accommodating the irregularities of the bottom. The Gutta-Percha Company of London were entrusted with the manufacture of the “core,” consisting of a strand of seven No. 22 B.W.G. copper wires (total diameter No. 14 gage) weighing 107 pounds per N.M. insulated, with three coatings of gutta-percha (to ⅜-inch diameter) weighing 261 pounds per N.M., the conductor being, in fact, covered to No. 00 B.W.G.

This formed a far heavier core than had been previously adopted, and on this account the difficulties of manufacture were proportionately increased.{47} The enormous pressure of the ocean at such depths involved also a much severer test for the core.

On the other hand, as we now know, the conductor—and consequently also the insulator—should have been still larger, to a material degree. The engineer of the line strongly urged a conductor weighing 392 pounds per N.M., with the same weight for the insulator;[16] but his fellow projectors (the business element of the undertaking) were all for getting the work done, while the weather permitted, that year; and they were perhaps overquick to recognize the difference in the capital required. Moreover, they were here supported technically by the views of the responsible electrician, as well as by such high authorities as Michael Faraday and Morse. The latter reported that “large coated wires used beneath the water or the earth are worse conductors—so far as velocity of transmission is concerned—than small ones; and, therefore, are not so well suited as small ones for the purposes of submarine transmission of telegraphic signals.” Faraday had stated: “The larger the wire, the more electricity was required to charge it; and the greater was the retardation of that electric impulse which should be occupied in sending that charge forward.”[17]

Thus it will be seen that although Faraday laid the foundations of a large proportion of the electrical engineering of to-day, his views in this instance did not prove to be correct. The theoretical{48} resemblance of a cable to a Leyden jar—in reference to the effect of charging either—seems to have been prominently in mind, without proper regard to the resistance offered by the wire to the electric current—a resistance which becomes less the greater the bulk of the wire. Besides the engineer being overridden in this matter, the word of the electrical adviser on the Board (Professor Thomson) regarding the carrying capacity or working speed that would be obtained with such a core as that decided on—in view of the length involved—was also unavailing.

While no one can fail to appreciate the businesslike manner in which this undertaking was pushed through from the moment of inception—comparing only too favorably with some experiences of to-day—it was, without doubt, a vast pity that more time was not devoted to a fuller consideration of some of the problems, such as that involved over the dimensions of the conductor and insulator. No serious fault could, however, be detected with its actual manufacture, though the methods of those days were primitive as compared with present practise, and a system of efficient electrical testing altogether wanting.

After various experiments had been made with sample lengths of different iron wires made up into cable, the contract for the outer sheathings was, in order to get through the work quickly, divided equally between Messrs. Glass, Elliot & Co., of Greenwich, and Messrs. R. S. Newall & Co., of Birkenhead—both originally pit-rope makers.

The insulated core was first surrounded with{49} a serving of hemp saturated with a mixture of tar, pitch, linseed-oil, and wax; and then sheathed spirally with an armor of eighteen strands, each containing seven iron wires of No. 22 B.W.G., the completed strand being No. 14 gage in diameter.

Fig. 5.—Manufacture of the Core.

The cable (Fig. 8) was then finally drawn through another mixture of tar. Its weight in air was 1 ton per N.M., and in water only 13.4 hundredweight, bearing a strain of 3 tons 5 hundredweight before breaking—equivalent to nearly five miles of its weight in water.

For each end approaching the shore, the sheathing (see Fig. 9) consisted of twelve wires of No. 0 gauge, making a total weight of about nine tons to the mile. This type was adopted for the first ten miles from the Irish coast, and for fifteen miles from the landing at Newfoundland,{50} at both of which localities rocks had been found to abound plentifully—so much so that the armor was insufficient, and present practise provides double the weight under similar conditions.

Fig. 6.—Serving the Core with Hemp-Yarn.

Fig. 7.—Applying the Iron Sheathing.

Fig. 8.—The Deep Sea Cable.

Fig. 9.—The Shore-End Cable.

Only four months was allowed for the manufacture of this 2,500 miles of cable, which had to be delivered in June of that year (1857). This involved the preparation and drawing of 20,500 miles of copper wire (providing for the lay) and stranding into the 2,500 miles of conductor. For the insulation nearly 300 tons of gutta-percha required to be prepared, and the three separate layers of gutta-percha required to be applied to the wire, subsequently followed by the spiral serving of yarn. Finally—and with a due allowance for lay—367,500 miles of wire had to be drawn, from 1,687 tons of charcoal iron, and laid up into{51} 50,000 miles of strand for the outer sheathing. The entire length of copper and iron wire employed was, therefore, 340,500 miles—enough to engirdle the earth thirteen times, and considerably more than enough to extend from the earth to the moon. The work was enormously increased, of course, on account of the sheathing being composed of a number of strands instead of several single wires. While having certain mechanical advantages at the outset, this stranded sheathing is not a durable type of cable—besides being somewhat costly—and is never adopted nowadays. The contract price for the{53} entire cable was £225,000, the core costing £40 and the armor £50 per mile.[18]

As fast as the cable was made at the respective factories, it was coiled into iron tanks ready for shipment.

Fig. 10.—Coiling the Finished Cable into the Factory Tanks.

Ships and Paying-out Machinery.—The race against time—resulting from an unfortunate arrangement with American interests—was truly appalling; for, besides the manufacture of the line itself, ships had to be selected and prepared for receiving the cable, and machinery for paying out the line had to be designed and made. So far as the manufacture went, the machinery for that was already in existence, in view of the cables that had previously been laid—apart from the fact that the sheathing machinery was practically the same as had already been used for making ropes with. But this being the first ocean line, special apparatus had to be worked out for submerging a cable satisfactorily in deep water. So far as ships were concerned, the British and United States Governments had already expressed willingness to furnish these. The former undertaking took shape by the Admiralty placing H.M.S. Agamemnon (a screw-propelled line-of-battle ship and one of the finest in the British navy) at the company’s disposal for the expedition. She had been Admiral Lyons’s flagship during the bombardment of Sebastopol a couple of years before; but, in her coming mission,{54} was to do more to bring about the reign of peace—by drawing together in closer commune the several nations of the earth—than any man-of-war was ever called to do, before or after. With a somewhat peculiar construction, she was admirably adapted for her work. Her engines were quite near the stern, while amidships she had a magnificent hold, forty-five feet square and about twenty feet deep. In this capacious receptacle nearly half the cable was stowed from the works at Greenwich. The American Government sent over the largest and finest ship of their navy, the U.S. frigate Niagara (Fig. 11), a screw-corvette of 5,200 tons. As a consort, the U.S. paddle frigate Susquehanna was also de{55}tailed for the expedition, while H.M.S. Leopard and H.M. sounding-vessel Cyclops were similarly provided by the British Government. The latter was to precede the fleet—nicknamed the Wire Squadron—to show the way.

Fig. 11.—U.S.N.S. Niagara.

The paying-out apparatus for the two laying vessels H.M.S. Agamemnon and U.S.N.S. Niagara had to be somewhat hurriedly put together; consequently not as much attention was paid to its design as the novelty of the undertaking really demanded. The previous, and somewhat primitive, gear hitherto used had proved to possess too little strength, the cable—when being laid in anything but quite shallow water—having more than once obtained the mastery, through meeting insufficient restraining force. In the new machine (Fig. 12) there was certainly no lack of holding-back power. It erred, indeed, the other way, being so heavy and powerful that it was liable to break the cable under any material strain. The degree of retardation was regulated by a hand-wheel actuating a frame-clutch surrounding the outside of a brake-wheel. The details of this machine were worked out by Messrs. C. de Bergue & Co., the manufacturers. The engineer-in-chief also furnished external guards to the propelling screws of each laying vessel to prevent a foul with the cable in the case of going “astern.” This cage was nicknamed a “crinoline” (then in fashion with ladies), which, indeed, it somewhat resembled. The above screw-guard may be seen in several of the illustrations of either ships farther on. Were it not for the necessity of sounding operations, it would be applied to all telegraph-ships to-day.{57}

Preparations for Starting.—By the third week in July (within the course of as many weeks) the great ships had absorbed all their precious cargo—the Agamemnon in the Thames and the Niagara in the Mersey. The process of coiling the cable on board the Agamemnon is illustrated in Fig. 13.

Fig. 12.—The Paying-out Machine, 1857.

Staff.—For such an undertaking the staff had, of course, to be considerable. Besides the engineer-in-chief (Mr. Bright), the engineering department was composed as follows: Mr. (afterward Sir Samuel) Canning, formerly a railway engineer, who had laid the Gulf of St. Lawrence and other cables; Mr. William Henry Woodhouse, who had laid some of the cables in the Mediterranean; Mr. F. C. Webb, with much experience in early cable work; and, finally, Mr. Henry Clifford, a mechanical engineer, destined to be responsibly associated with a large proportion of the cables since laid.

Besides Mr. Whitehouse (whose health, however, did not permit him to accompany the expedition) there were on the electrical staff Mr. C. V. de Sauty, Mr. J. C. Laws, Mr. F. Lambert, Mr. H. A. C. Saunders, Mr. Benjamin Smith, Mr. Richard Collett, and Mr. Charles Gerhardi, all of whom were afterward prominently connected with subsequent submarine cable under{58}takings. Their respective energies were divided up between the two laying ships.[19] The expedition was to be further strengthened by a representative of The Times, as well as of the Daily News and New York Herald.

Fig. 13.—Coiling the Cable on Board.

On the vessels being fully loaded ready for the start, “send-off” festivities occurred, in which all classes of those engaged on the work took part. The Times recounted the function on board the Agamemnon as follows: