Engineering Wonders of the World
Volume III

BY CHARLES BRIGHT, F.R.S.(Edin.), M.I.E.E. CONSTRUCTION. HE important part played by sub- marine telegraphs throughout the civilized world centres itself in th© electrical conductor, the rest of the cable serving merely to render the The „ . x conductor lastingly effective Conductor. . 0 J in its object at the bottom of the sea. For the conduction of electricity, whether for telegraphic or other purposes, this all- important wire is composed of the purest possible copper. Where considerable distances Fig. 1.—TYPES OF ELECTRICAL CONDUCTORS (ACTUAL size). have to be electrically spanned, a solid wire of the required dimensions is too rigid, so the conductor is made up from a number of comparatively small wires laid up into the form of a strand of the necessary total dimen- sions.* On the other hand, for connecting points over, say, 750 miles apart, the central wire is, as a rule, substantially larger than those surrounding it, with a view to increasing the conducting properties of the line. This is necessary in order to meet speed requirements by compensating for the con- siderable length entailed, seeing that the rate at which electrical signals can be transmitted through a cable varies inversely with the square of the length, in addition to being de- pendent on the type of conductor and its insulating envelope. In the same way, for still greater lengths a conductor with strips of copper outside a large solid wire has recently been resorted to. Stranding the several wires together is effected by a vertical rope-making machine. Motive power is transmitted to this machine * The total diameter of a submarine cable conductor varies from about -069 to -204 of an inch, according to the length and working speed requirements.