One of the essential features of a submarine cable is the speed of signaling. In operating long cables delicate instruments are required, and the currents arriving at the receiving end are feeble in comparison with those employed in land-line signaling. The longer the cable, naturally, the feebler the impulses arriving at the receiving end.

A short cable, a cable of under 1,000 miles being generally considered a short cable, gives a speed of signaling amply sufficient for all purposes, with a conductor weighing about 100 pounds to the mile, surrounded by an insulating envelope of gutta-percha weighing about an equal amount, says Scribner’s Magazine. When we come to a cable of about twice this length it is found necessary, In order to get a practically unlimited speed — that is, a speed as high as the most expert operator can read at — to employ a core of 650 pounds of copper to the mile, insulated with 400 pounds of gutta-percha to the mile.