Engineering Wonders of the World
Volume I

EARLY ATLANTIC CABLES. 283 pulling the wire after the manner of mechanical house-bells, for he was at pains to point out that the bed of the ocean was too rough for that! The Manufacture of the Line. The construction of the cable was in due course taken in hand. The distance from Valencia, on the western Irish coast, to Trinity Bay, Newfoundland— the two landing-points selected—being 1,640 N.M. (= nautical miles), it was estimated that a length of 2,500 n.m. would meet all re- quirements, and would provide enough 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, weighing 107 lbs. per n.m., insulated with three coatings of gutta-percha (to |-inch diameter), weighing 261 lbs. per n.m. This formed a far heavier core than had been previously adopted, and on this account the difficulties of manufacture were pro- portionately increased. The enormous pres- sure 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 in- sulator—of such a length should have been still larger for the purpose of message-carrying capacity. The engineer of the undertaking (Mr. Bright) strongly championed a con- ductor weighing 392 lbs. per n.m., with the same weight for the insulator. Though such a core would have been a great novelty at that time, it closely approximated to subse- quent practice until higher working speeds were rendered possible by the introduction of automatic (machine) transmitting apparatus. But his co-projectors (the business element of the enterprise) were all for getting the work done whilst the weather permitted, attaching, perhaps, too much importance to the difference in the capital required. Moreover, their views were supported on technical grounds by the responsible electrician (Mr. Whitehouse), as well as by such high authorities as Michael Faraday and Morse. Besides the engineer being overridden in this matter, the word of the electrical adviser on the board (Professor Thomson) was also unavailing. More time should undoubtedly have been devoted beforehand to the consideration of some of the problems involved, such as the dimensions of the conductor and insulator. No serious fault was, however, detected during the manufacture, though the methods of those days were primitive as compared with present practice, and a really efficient system of 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 sheathing was, with a view to hastening the work, divided equally between Messrs. Glass, Elliot, and Company of Greenwich, and Messrs. R. S. Newall and Company of Birken- head, both originally pit-rope makers. The insulated core was first surrounded with a serving of hemp saturated with a mixture of tar, pitch, linseed oil, and wax ; and then sheathed spirally with an armour of eighteen strands, each containing seven iron wires of No. 22 B.W.G., the completed strand being No. 14 gauge in diameter. The cable (see illustration, p. 285) 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 cwt. It stood a strain of 3 tons 5 cwt.—equivalent to that of support- ing nearly five miles of its weight in water— before breaking. For each shore end the sheathing (see illustration) consisted of twelve wires of No. 0 gauge, making a total weight of about 9 tons to the mile. This type was adopted for the first 10 miles from the Irish coast,