THE ELECTRIC TELEGRAPH. 



78. The earliest attempt to transmit a voltaic current under 

 water for telegraphic purposes, is attributed to Dr. O'Shaughnessy, 

 who is so well known for his successful exertions to establish 

 the electric telegraph in India. He succeeded in 1839 in de- 

 positing an insulated conducting wire, attached to a chain cable, 

 in the river Hoogly, by which the electric current was transmitted 

 from one bank of that river to the other. 



The first important project of this kind which was executed in 

 Europe, was the connection of the coasts of England and France 

 by the submarine cable, deposited in the bed of the channel 

 between Dover and Calais. A concession being obtained from the 

 French government on certain conditions, a single conducting 

 wire, invested with a thick coating of gutta-percha, was sunk by 

 means of leaden weights across the channel, and the extremities 

 being put into connection with telegraphic instruments, messages 

 were transmitted from coast to coast. One of the conditions of the 

 French concession being that this should be effected before 

 September, 1850, this object was attained, but nothing more ; for 

 the action of the waves near the shore constantly rubbing the 

 rope against the rocky bottom, soon wore off the insulating 

 envelope and rendered the cable useless. 



79. It is right to state that the projectors themselves did not 

 expect from this first trial permanent success, and regarded it 

 merely as the experimental test of the practicability of the 

 enterprise. It was, therefore, immediately resolved to resort to 

 means for the effectual protection of the conducting wires 

 from the effects of all the vicissitudes to which they would be 

 exposed. With this view, Messrs. Newall and Co., the eminent 

 wire-rope makers of Gateshead, were charged with the difficult 

 and unprecedented task of discovering expedients, by which a 

 cable of gutta-percha containing the conducting wires could be 

 invested with an armour of iron, at the same time so strong as to 

 resist the action of the forces to which it wouli L be exposed, and 

 yet not too ponderous or too rigid to allow of being deposited in 

 the bed of the channel. The result was the invention of the form 

 of submarine cable, which has since been successfully adopted 

 upon the various lines of international electric communication 

 which will be presently described. 



The conducting wires inclosed in the'se cables are usually 

 copper wires, having a diameter of the sixteenth of an inch. 

 Each wire is first separately covered with two coatings of gutta- 

 percha. Each successive coating increases the thickness by 

 a certain fraction of an inch. The object of laying on this 

 succession of coats of the gum, is to guard against accidental 

 defects which might render the insulation imperfect. If such a 

 152 



