Mr. J. N. Heardcr on the Atlantic Cable, 31 



them. In some cases they have been partially counteracted ; but in 

 others they have been so great as to render useless some most 

 valuable instruments commonly used with the atmospheric lines. 



The action may be thus described. Suppose an insulated 

 wire extended for a great length under the sea^ and having its 

 two ends brought on shore and insulated. It is desired to work 

 through this wire in the ordinary way, that is, with the earth for 

 return circuit. The arrangement would be the following : — 



A voltaic battery will have one of its ends connected with the 

 earth, and the other with a key capable of making contact, when 

 desired, with one end of the insulated wire. At the other end 

 of this insulated wire, a telegraphic instrument will be so ar- 

 ranged as to receive the current from it, and transmit it to the 

 ground; so that, according to some theories, the current origi- 

 nated in the galvanic battery, starts from one end, passes into 

 the insulated wire, and tries to get back again to the other end 

 of the galvanic battery ; or what is the same thing, though not 

 quite in accordance with the theory, tries to get at the earth or 

 sea as soon as possible. If the insulation be perfect, the current 

 is constrained to pass to the other end of the wire, and through 

 the telegraphic instrument, before it can get to the earth ; but if 

 there be any fissures in the insulating coating, by which the 

 electricity can find its way to the water, it will rather escape at 

 once through them than force its way onwards through the 

 resistance offered by the remaining length of wire, especially if 

 that length be very great. Hence, if by accident or careless- 

 ness the gutta-percha coating of a submerged telegraph cable 

 be defective, it is easy to understand, from what I have ex- 

 plained before, that although the conducting wire may be per- 

 fect, yet electricity sent in at one end may never reach the 

 other, especially if the wire be disproportionately small in rela- 

 tion to its length, and consequently offer great resistance. But 

 this is not the only difficulty or peculiarity incident to this 

 arrangement. 



The tendency which the electrical current, pervading the wire, 

 has to escape into the sea throughout its whole length, sets 

 up an inductive action between the conductor and the sea by 

 which it is surrounded; and the conditions and actions of the 

 Leyden jar are thus immediately established ; and whenever a 

 current passes through the conductor, that cmrent necessarily 

 charges the internal surface of the gutta pcrcha with an elec- 

 trical state bearing its own character, viz. positive or negative, 

 according to the direction of the current. The amount of this 

 charge will depend greatly upon the thickness of the gutta- 

 percha coating, and the intensity of the current required to 

 overcome the resistance of the wire. 



