SUBMARINE TELEGRAPHY z\i 



Bright and Clark. Other tests of a similar nature have been 

 proposed, but have been found less convenient. The first test for 

 a joint, distinct from that of the whole cable, was, it is believed, 

 proposed by Mr. Whitehouse. No instance has yet occurred of 

 failure in a joint which has successfully passed the accumula- 

 tion test above described. There are about two thousand joints 

 in each Atlantic Cable. 



Any further description of the various tests would only ba 

 wearisome. There are tests of charge, of discharge, of the 

 effects of electrification, of the effects of positive and negative 

 currents, tests with statical electricity as well as voltaic cur- 

 rents ; but enough has been said to show that the examination 

 of a submarine cable, as now conducted, is not guess-work, or 

 even a matter of experience and skill ; it consists simply of a 

 long and laborious series of exact measurements, so expressed 

 in figures that all electricians can understand the results, and 

 compare them with those obtained from other cables, or by other 

 observers. In this lies our safety. 



Granting that the production of a perfectly insulated con- 

 ductor 2,000 miles long is no longer a matter of chance, can we 

 protect and lay this wire with equal certainty in such depths 

 as the Atlantic presents ? or do we here fall back into a region 

 of mere good or bad luck ? As to shallow water, the question 

 need not be asked. No serious strains occur, and the sub- 

 mersion of the cable depends on a few simple mechanical 

 arrangements which have long since been perfected. Even in 

 deep water cables have not broken during the laying nearly 

 so often as is supposed. Some very early Mediterranean expedi-* 

 tions, a later attempt to join Candia with Alexandria, and the 

 experimental trip of the first Atlantic expedition, give almost the 

 only instances where a cable parted suddenly during submersion ; 

 but it must be allowed that the strains endured in passing over 

 depths of 2,000 fathoms approached far too nearly to the break- 

 ing strain of the cables, and it is by no means impossible that 

 some cables may have been injuriously stretched, although they 

 were not broken. 



In order to lay a cable of any construction taut along the 

 bottom of the sea, it is necessary to restrain its free exit from 

 the ship by applying a retarding force, nearly equal to the weight 



