indeed, it is now understood that no submarine telegraph can be fished up at so great a depth as 400 fathoms. The nature of the bottom on which a cable rests has a great deal to do with its preservation or destruction. It has been observed that wherever a cable rests upon iron-stone rocks, a galvanic action is set up which speedily oxidises its iron wires. Sometimes zoophytes attach themselves to the wires and do serious mischief. When the Hague cable was lifted it was found that, in one place, it was loaded with “ten miles of rare and fine zoophytes.” Where could Mr. Gosse have been on this momentous occasion? These creatures seem to attach themselves to the oxide of the iron wire, which they further corrode by the secretion of an acrid juice from their footstalks. An immense mass of mussels was found attached to the Channel Islands cables; in some instances such an agglomeration of marine creatures is found sticking to the telegraph lines that they measure a foot in diameter.
A very singular accident happened to the cable laid in Bass’s Straits, Tasmania. This line, which weighed ten tons per mile, was absolutely floated by the immense quantities of kelp or sea-weed which became attached to it. Again, it often happens that fatal injury to a cable is produced by seaweed attaching itself to a line situated in a great tideway. The cable is swayed about and speedily becomes abraded, especially if there happens to be a rocky bottom. The Channel Islands cable once suffered in this way, and gave a singular example of the slight pathway along which the electric current will find its way. The cable had been completely destroyed as regards one side of the hemp, gutta-percha envelope, and wire, and no conducting material remained for three inches but an oxide of copper resting on the other half of the insulating sheath. Nevertheless, along this oxide the current was found to flow. Lightning in one instance struck a cable and ran along under the sea for sixteen miles, when it forced its way out and produced a destructive fault in the insulating envelope.
The ocean bed and its inhabitants, however, are not always the enemies of telegraphy. For instance, it is found that, when the cables have worked themselves into the sand or mud, they are well preserved. The coral insect of warm latitudes appears also to be friendly to telegraphic cables. When the Malta and Cagliari line was taken up, in 1858, after having lain in the water for three years, a most lovely sight presented itself. Mr. Webb, the engineer, who recovered it, says that about Cape Spartivento, “The cable appeared to have been suspended free from the ground, for the young clean coral completely enveloped it, and appeared to grow out from it equally in every part of the circumference and in a radiating direction. In some places it was so completely covered that not a particle of the cable was visible for forty or fifty fathoms consecutively, and as it came out of the water it had the appearance of a huge but beautiful coral necklace.”
The cable had indeed
Into somethiSuffered a sea change
Into something rich and strange,
but it had been perfectly protected from rust.
Besides the causes of destruction which have to be provided against or avoided when the cable is submerged, it has to contend against microscopic mischiefs in the course of manufacture, which speedily enlarge into fatal faults. Thus whilst the copper wire is being insulated with its sheath of gutta-percha, which is laid on in a fluid state, minute air bubbles, scarcely perceptible to the naked eye, create fine punctures in it. When the cable is laid the electric current finds its way out by these channels, and gradually burns the hole until the whole electric fluid is enabled to escape into the surrounding water. It is hoped that the use of india-rubber as an insulator will in future obviate the difficulty. But there are wilful accidents against which science is indeed helpless. Thus in laying the Ostend cable, one of the persons engaged in paying it out, in spite or from some other bad motive, furtively drove a nail through the core, so as to bring into contact the copper conducting wire, and the outside protecting wire. The consequence was that the current ceased to flow. Had such a piece of spite been perpetrated upon a cable as long as that crossing the Atlantic, a third of a million would have been cast into the sea at once: the “Koh-i-Noor” thrown overboard would not have been so great a loss.
Our belief in the practical application of submarine telegraphy to any length, thanks to our advanced knowledge upon the subject, need not be in the least shaken by the mishaps that have already taken place. Our knowledge, gained by a bold tentative process, has solved many difficulties that before seemed insurmountable; and it is also cheering to know that nearly every failure that has taken place is attributable to defined and preventable causes. Numerous advances have been made in the manufacture of the cables themselves. Difficulties of insulation have been entirely overcome, and the application of india-rubber in this service will eliminate in deep sea cables frequent sources of danger arising from the use of indifferent gutta-percha. A frequent cause of the retardation and the weakening of electric currents was of old owing to the imperfect plan on which the copper wire was selected. It is now known that the coppers of commerce vary immensely in their power of transmitting the electric fluid. Thus taking 100 as the mean of the pure metal, it is found that copper from Lake Superior has a conducting power represented by 92-57, whilst Spanish or Rio Tinto copper has only a conducting power of 14-24, or not greater than that of iron. So essential is the good transmitting power of the metal along which our messages fly considered, that contractors have now to supply it for electric purposes according to its conductivity rather than by weight, a regular standard being always referred to. With regard to the mishaps of paying out deep sea cables, the Submarine Telegraph Committee of the House of Commons attribute them mainly to the employment of ships not fitted for the duty, and they recommend that special vessels should be constructed with a capacity to admit of cables being coiled easily without injury, and with holds isolated from the engine-rooms. Power and steadiness are other essentials required in vessels employed