J95 



SUBMARINE TELEGRAPHY. 1 



AT a time when the first successful submarine cable has been 

 laid across the Atlantic, and a second has been recovered from 

 depths once thought unfathomable, many persons will probably 

 be led to consider how far these great achievements, following on 

 failures almost as great, have been due to mere good fortune, or 

 to a real progress in knowledge. The object of this article is 

 shortlv to explain the advances which have lately been made in 

 theory and practice by those who carry out the manufacture and 

 submersion of telegraph cables. To make this explanation in- 

 telligible to the general reader, it will be well first to describe 

 what a submarine cable is, and what are the functions it has to 

 perform, although probably few who read this article will be so 

 entirely ignorant of the subject as to suppose, with an ingenious 

 correspondent of the ' English [Mechanic and Mirror of Science ' 

 that the copper conductor is a long rope which slips backwards 

 and forwards inside a gutta-percha tube, so as to ring a bell in 

 America when pulled by the clerk in England. 



The electrical conductor in a cable really is a copper rope in 

 almost all cables now made, though a single wire is still some- 

 times used ; when small, three wires generally form the strand ; 

 when larger, seven wires are used. Single wires were first em- 

 ployed, but they sometimes broke at a brittle part, and when 

 large were inconveniently stiff, tending to force their way out 

 through the insulating sheath of gutta-percha. The seven wires 

 of the strand never break all at one point, and the fracture of 

 any one produces no sensible effect on the conductor as a whole ; 

 for although the strength of a chain is limited by that of its 

 weakest link, the conducting power of a wire or strand is in no 

 way limited by that of its smallest section. The large Atlantic 

 1 From the North British Reriew, December 1866. 



o 2 



