SUBMARINE TELEGRAPHY 243 



Atlantic Cable, it is well to avoid so powerful a decomposing 

 agent as is furnished by a large voltaic battery. 400 cells were 

 used in 1858. For the signals sent in 1866, 12 cells are suf- 

 ficient, but 20 or 30 is the number in daily use. Mr. Latimer 

 Clark sent signals through the two cables joined in one, being a 

 circuit of 3,754 geographical miles, with one small cell formed in 

 a thimble. In connection with the subject of signalling, it is 

 interesting to remark that perhaps Sir William Thomson's 

 connection with the Atlantic Telegraph Cables was due to a con- 

 troversy between him and Mr. Whitehouse on the subject of 

 signalling ; the letters are published in the Athenaeum ' from 

 August to November 1856, and are extremely curious. Mr. 

 Whitehouse misinterpreted some careful experiments, and re- 

 marks in one place that to lay such a cable as he thought Sir 

 William Thomson's theory demanded would require Mr. Scott 

 Russell's ' Leviathan.' It is needless to add that subsequent 

 experiment has confirmed every part of Sir W. Thomson's theory, 

 although the constants he used have been somewhat modified by 

 experience. 



Attention has so far been chiefly directed to the Atlantic 

 Cables, because in connection with these almost every late im- 

 provement has been adopted or invented. Lines in shallow 

 water remain much what they were in general construction ten 

 years since. Those of later design are heavier on the average 

 than the earlier cables, for experience has shown that a saving 

 of weight and strength results in great ultimate loss. The 

 average life of a shallow-water cable, weighing less than two 

 tons per mile, is about five years, whereas no limit can as 

 yet be assigned to the life of cables weighing eight or ten tons 

 to the mile. The iron wires are now almost always galvanised, 

 and frequently covered with hemp, and Bright and Clark's 

 silicated bituminous compound, which seems very efficiently to 

 protect the cables from rust, and to prevent broken wires, 

 during submersion, from fouling any part of the machinery, a 

 frequent occurrence some years since, producing what was called 

 a brush, formed by the one broken wire remaining on board in a 

 constantly increasing coil or tangle round the axis of the rope, 

 while the rest of the cable went overboard. The Persian Gulf 

 Cable made by Mr. Henley, and tested and laid by Messrs. 



B 2 



