220 APPLIED SCIENCE 



There are some popular fallacies connected with cable-laying 

 which are exceedingly tenacious of life one is, that inasmuch 

 as the wires are laid round a cable like a corkscrew, they will 

 stretch a great deal before supporting the cable, and so the 

 core will be injured by having to support a considerable part of 

 the strain. In point of fact, nothing of this kind occurs. The 

 iron wires abut one against the other, and form a tube which 

 cannot diminish in diameter as a corkscrew does, or would do, 

 if made of soft wire ; and experiment shows that an iron- 

 covered cable stretches very little more than a simple straight 

 iron wire. Cables of the Atlantic class stretch a little more, for 

 the soft strands are compressible ; but even in this class of cable 

 the elongation, with half their breaking strain, is quite insignifi- 

 cant, and with the strain actually used it is insensible. Then 

 some people say these cables untwist, and they certainly do a 

 little, but the cables recovered from great depths prove that the 

 number of turns which are thus taken out of a cable is quite 

 insignificant, producing no sensible elongation or change in the 

 lay. Others think the rise and fall of the ship must cause 

 sudden jerks and great changes in the strain on the cable as 

 paid out, and quite a small army of patents stand ready to 

 defend the right of inserting some elastic contrivance by which 

 the cable is to have a certain play. Probably the see-saw which 

 these contrivances might introduce would be far more dangerous 

 than the evil they are designed to remedy, for in truth the strain 

 changes very little even in heavy weather, so long as the ship 

 is going fast enough to let the cable lie at a small angle with 

 the horizon. When the cable hangs vertically the case is 

 different, though even then the change of strain is much less 



0-028 in. diameter ; total diameter of cable 0'62 in. ; weight of cable in air per 

 knot 21'7 cwt. ; in water 16'3 cwt. 



Second, or 1865 Atlantic. Length when complete in 1866, 1,896 knots ; 

 copper conductor 7-wire strand weighing 300 Ibs. per knot, diameter 0'114 in. ; 

 covered with gutta-percha and Chatterton's Compound, weighing 400 Ibs. 

 per knot, diameter C'464 in. ; served with wet tanned hemp covered with 

 ten bright steel wires, each enclosed in five tarred manilla hemp strands, dia- 

 meter of each wire - 095 in. ; diameter of strand 0'28 in. ; diameter of cable 

 1125 in. ; weight of cable per knot in air, 35 cwt. ; in water, 14 cwt. 



Third, or 1866 Cable. Length as laid, 1,858 knots ; similar to 1865 cable, 

 except that the steel wires were galvanised nnd the manilla strands were not 

 tanned but left white. Weight in air 31 cwt., in water 14f cwt. ; breaking 

 strain, 8 tons. 



