120 ANNUAL OF SCIENTIFIC DISCOVERY. 



of the cable, at regular intervals, suitable coils of copper wire, the 

 resistance of which, for a long series of temperatures, had been deter- 

 mined beforehand. The ends of these copper coils issued into the 

 air, so that they could be connected at any time with a suitable 

 apparatus for determining their resistance. Now, Mr. Siernans found 

 that although the outer portion of the coil of cable had a temperature 

 not sensibly higher than that of air, the wires which he had placed 

 within the coil showed a steady augmentation of resistance, from 

 which he inferred that the cable was heating within. He waited 

 until the augmented resistance indicated an increase of temperature 

 from sixty to eighty-six degrees. Had he waited much longer, the 

 cable would probably have been destroyed. Some of those to whom 

 he communicated his conclusions regarded them for a time as the 

 mere refinements of theory ; but all their doubts were dissipated when 

 a quantity of water, at a temperature of forty-two degrees, thrown 

 upon the top of the cable, after passing through the inner portions 

 of the coil, issued from its bottom raised to seventy-two degrees ! 

 The precise cause of this generation of heat has not, we believe, been 

 yet determined. It may be due to some chemical action in the gutta- 

 percha ; but it may also be due to the gradual rusting of the iron 

 which encases the cable. The rusting of iron is really the burning 

 of iron ; but this burning, under ordinary circumstances, is so slow 

 that the heat generated is all dissipated in the air. But if this dis- 

 sipation be prevented, it is easy to see that such an accumulation 

 may take place as would produce the effects observed by Mr. Sie- 

 mans, and still worse effects, if not guarded against in time. Were 

 the human skin, for example, an envelope impervious to heat, which 

 prevented the escape of the warmth generated by respiration, each 

 of us would very soon act the part of a Pepin's digester upon his own 

 bones, and boil them into jelly. Who can say what injury was 

 done to the gutta-percha covering of the Atlantic cable through 

 ignorance of the fact, observed so opportunely in the case of that 

 of Rangoon and Singapore ? 



SUBMARINE TELEGRAPHS. 



From a report on the condition of submarine telegraphs, recently 

 issued by the London Board of Trade, we derive the following infor- 

 mation : 



Up to the present time, 11,364 miles of submarine telegraphic 

 cable have been laid; but only about 3,000 are actually working. 

 The lines not working include the Atlantic, 2,200 miles ; the Red Sea 

 and India, 3,499 miles; the Sardinia, Malta and Corfu, 700 miles; 

 and the Singapore and Batavia, 550 miles. The committee give a 

 succinct history of these, as well as of all the others, and state their 

 conclusions. The failure of the Atlantic is attributed to " the cable 

 having been faulty, owing to the absence of experimental data, to 

 the manufacture having been conducted without proper supervision, 

 and to the cable not having been handled after manufacture with 

 sufficient care;" and they add that "practical men ought to have 

 known that the cable was defective, and to have been aware of the 

 locality of the defects before it was laid." The Red Sea and India 



