Page:Physical Geography of the Sea and its Meteorology.djvu/46

20 time, and the line to Algiers has been suspended, if not abandoned, for the present.

61. Their iron wrappings.— All these lines had cables encased in a wrapping of iron wire;—and it is a question whether the difficulty with them all be not owing to that circumstance. The wire wrapping of the Atlantic cable has been found in a state almost of complete disintegration, like the iron fastenings of coppered ships. This evidence of galvanic action excites suspicions as to the proper insulation of that cable. Iron, sea-water, and copper, will make a battery of no inconsiderable power; and the decayed state of the iron wire in this instance encourages the belief as to defective insulation.

62. Imperfect insulation.—Such are the facts. But the facts do not prove that gutta-percha is an imperfect insulator. With regard to the Atlantic cable, they suggest that the insulation of that cable, though perfect at first, might have been injured by the handling to which the cable was afterwards subjected, and above all by the heavy strains which were brought upon it by the "brakes" during the operation of laying it along the plateau.

63. The Red Sea and Mediterranean cables.—These facts, however, do not suggest the same for the Red Sea and Mediterranean cables, for these cables had all been down for some time, and had been working more or less satisfactorily; nevertheless, we are reminded by these failures now, and that too from a fresh quarter, that iron wrappings about a telegraphic wire are of no use in the deep sea.

64. A galvanic battery in the sea.—Two metals, as a copper conductor and an iron wrapper, would seem not to be desirable for the same cord, for in case of leakage a galvanic battery is at once formed in the sea, and brought into play upon the cable. not only so, the cable itself is a long and powerful Leyden jar; the iron wrapping assists to make it so. This circumstance may also assist to excite the two metals still more, and so hasten the destruction of the cable as an electrical conductor.

65. Two metals should not be used about a submarine cable.—But