Masterpieces of Science 



the air into the sea. In the main the causes 

 which hinder a pulse committed to a cable are 

 two: induction, and the electrostatic capacity of 

 the wire, that is, the capacity of the wire to take 

 up a charge of its own, just as if it were the 

 metal of a Ley den jar. 



Let us first consider induction. As a current 

 takes its way through the copper core it induces 

 in its surroundings a second and opposing cur- 

 rent. For this the remedy is one too costly to 

 be applied. Were a cable manufactured in a 

 double line, as in the best telephonic circuits, 

 induction, with its retarding and quenching 

 effects, would be neutralized. Here the steel 

 wire armour which encircles the cable plays an 

 unwelcome part. Induction is always pro- 

 portioned to the conductivity of the mass in 

 which it appears; as steel is an excellent con- 

 ductor, the armour of an ocean cable, close as it is 

 to the copper core, has induced in it a current 

 much stronger, and therefore more retarding, 

 than if the steel wire were absent. 



A word now as to the second difficulty in work- 

 ing beneath the sea that due to the absorbing 

 power of the line itself. An Atlantic cable, like 

 any other extended conductor, is virtually a long, 

 cylindrical Ley den jar, the copper wire forming 

 the inner coat, and its surroundings the outer 

 coat. Before a signal can be received at the 

 distant terminus the wire must first be charged. 

 The effect is somewhat like transmitting a signal 

 through water which fills a rubber tube; first of 

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