20 niYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



time, and the line to Algieis has been suspended, if not aban 

 doned, for the present. 



61. Their iron icrappings. — i\.ll these lines had cables incased 

 in a wrapping of iron wire ; — and it is a question whether tho 

 difficulty with them all be not owing to that circumstance. Tho 

 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 suspi- 

 cions 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 da 

 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 handlings 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. Tlie Bed Sea and Mediterranean cables. — These facts, how- 

 ever, do not suggest the same for the Eed 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 hi the sea. — Two metals, as a copper con- 

 ductor 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. Xot 

 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 



* "Therefore it may now 1)C considered a settled principle iu submarine 

 telegrapliy, tlmt the true character of a cable for the deep sea is not that of an 

 iron rope as large as a man's arm, but of a single copper wire, or a fascicle of 

 yfhes, coated with gutta-percha, pliant and supple, and not larger than a lady's 

 finger." — Letter to Secretary of the Navy, November 8, 1850. 



