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.
These are the proportions of copper and gutta-percha In the 1894 Anglo-American Atlantic cable, which is considered the record Atlantic cable for speed of working, and has been worked, by automatic transmission, at the rate of some forty-five words a minute. The type of cable proposed for the Vanoouver-Fanning section of the British Pacific, as designed by Lord Kelvin, is to have a core of 562 pounds of copper and 368 pounds of gutta-percha to the mile, and Is calculated to give a speed of twelve words a minute over a length of 3,560 miles.
It is not considered safe to adopt a much heavier core than this, for the reason that the weight of the complete cable with a core that should weigh more than about half a ton to the nautical mile would be so great that picking it up for repairs from a depth of 3,000 fathoms would be an extremely difficult and hazardous operation.
The Age-Herald, Birmingham, AL, February 11, 1900