Engineering Wonders of the World
Volume III

360 ENGINEERING WONDERS OF THE WORLD. shown, to the sheathing machine on the floor below, whence it is led through apparatus for applying the aforesaid compound—cold first, then a layer of canvas tape or hemp yarns, then hot compound, then another covering of hemp, or canvas tape with the reverse lay, then hot compound once more— the completed cable finally passing under streams of cold water to cool and harden the surface before being led to the storage-tank, where it is neatly coiled down,* after receiv- ing a coating of whitewash to prevent the different turns and flakes of cable sticking together. The splicing together of different lengths of the cable is performed in the same way as in ordinary hempen or iron ropes. Space does not permit of this being de- Jointing and scrj}je(j jn the complete way Splicing. , that would be necessary to be of any real use. It is also impossible to de- scribe here the important operations of mak- ing a joint in the insulated conductor, the secret of which is care, cleanliness, and ex- perience. These operations have been fully recounted in the course of a paper contributed by the author to the Institution of Civil Engineers.! During every process of manufacture the line is kept under searching electrical tests, by instruments similar to those subsequently em- ployed for signalling through Testing. of which have already been described in the chapter on “ Early Atlantic Cables ” (vol. ii., pp. 292, 295). The length of each constituent part of the line as made is measured throughout by revolution- counters fitted to each ma- 35 miles is an average output Rate of Manufacture. chine. About * This operation has already been depicted on page 286 of the chapter on “ Early Atlantic Cables.” f “ Inst.C.E. Minutes of Proceedings.” Vol. clvii. See also the author’s “Submarine Telegraphs.” of cable manufactured at a factory during an ordinary working day. As already mentioned, the type of armour used in a cable varies considerably with th© depth and nature of the bottom. For deep water, tensile strength and Types. lightness being the main con- siderations, a small gauge-wire of mild (Bes- semer) steel is therefore usually employed, such a wire giving a breaking strain up to 100 tons per square inch. For shore ap- proaches, on the other hand, large metallic surfaces are required for withstanding abra- sion by rocks, anchors, etc. Considerable weight is also necessary in these situations for contending with lateral strains due to strong currents. Thus here an ordinary class of iron wire (“Best-best” quality) is employed, but plenty of it. A cable of the present day is constituted by at least three types—namely, “ shore end,” “ intermediate,” and “ deep-sea ” (or “ main ”) cable. The “ shore end ” is employed for some two miles from each terminus; the “ inter- mediate ”—a modified shore-end type as re- gards the class of wipe used—to a depth of 200 fathoms, say ; and the main cable for the remaining portion. Sometimes, however, as many as six different types are necessary for coping with the varying conditions along the route, a distinguishing letter or number being applied to each. The “ shore end ” is, as a rule, furnished with two sheathings, the outer of which is composed of wires of quite large diameter, with bedding of jute between the inner and outer sheaths. The weight of such a cable is often as much as 30 tons to the mile. In the case of the Irish shore end, illus- trated in Fig. 6, the wires of the outer sheath- ing appear elliptical. In reality, however, they are the ordinary circular wires, but being applied with a very short lay, this appearance is produced in true section.