Engineering Wonders of the World
Volume III

362 ENGINEERING WONDERS OF THE WORLD. very special precautions. They are, however, best avoided altogether, provided a more suit- able route can be found. Fig. 7.—CABLE LAYING OVER AN IRREGULAR BOTTOM. Fig. 8 represents the sort of bed that cables are laid on under normal conditions. Even then it is advisable to take soundings in ad- Fig. 8.—CONTOURS OF THE SEA BOTTOM. vance at intervals of about ten miles, lest there should be a submarine mountain—or, on the other hand, a valley—on the route, such as must be avoided, or allowed for, in laying. All deep-water soundings are nowadays effected by means of very fine but intensely strong steel wire of the type employed in the treble notes of a piano, bearing a strain equivalent to 130 tons per square inch. With such a wire, and a suitable weight attached thereto, the depth is ascertained by noting the length which runs out before bottom is struck, the wire being afterwards recovered by means of a steam or other engine.* Be- sides measuring the depth, it is customary, by means of small metallic tubes f attached to the line, to secure a specimen of the bottom ; and occasionally, with the aid of a suitable thermometer, to ascertain the tem- perature—also a matter of some importance— which at great depths is almost down to freezing point. Having dealt with the construction of a cable and the survey of the route preparatory to laying, we now come to the shipment of the line. There are, at the present time, no less than Telegraph fifty-seven telegraph ships in active service in various parts of the world. Most of these, however, merely have to do with the maintenance of cables already laid ; for there are less than a dozen large vessels employed for the original laying of ocean cables by the contractors, by far the largest of which are the Tele- graph Construction and Maintenance Com- pany’s T.S. Colonia; the India-rubber, Gutta-percha, and Telegraph Works Company’s T.S. Silvertown ; and Messrs. Siemens Bros, and Co.’s T.S. Faraday. The Colonia is the latest of the big telegraph ships, and has entirely out- stripped all others of the present day in size and every other respect. With a length of 500 feet and a carrying capacity of 11,000 tons, she is capable of laying an entire Atlantic cable with the assistance of a smaller vessel for landing the shoal-water shore ends. The Silvertown (p. 365) comes next in point of size. Her beam is as much as 56 feet, and she can carry 8,000 tons, though her length is comparatively inconsiderable. * The apparatus and routine associated with deep-sea soundings has been fully described in Mr. H. D. Wilkinson’s treatise on this subject, as well as by the present author in “ Engineering” of January 13, January 27, and February 10 1899. f On the principle of the Brooke sounder already de- scribed (vol. ii., p. 279) in tho chapter on “ Early Atlantic Cables.”