Telegraphy 189 



by an alphabet of signs introduced by the American inventor 

 Morse, but an alternative one-wire system of Cooke and 

 Wheatstone in which the letters are directly indicated on a dial, 

 though much slower in its working, continued to be employed 

 in the British Telegraph Service at stations where it was 

 difficult to obtain operators sufficiently practised in the 

 Morse code. Subsequent improvements in telegraphy over 

 land lines are mainly of technical interest. 



An entirely new set of problems arose when submarine 

 cables had to be laid across the oceans. As water is not an 

 insulator like air, the conductor which serves for the trans- 

 mission of the message has to be surrounded by a non- 

 conducting material like guttapercha. The copper wire inside 

 and the water outside separated by an insulating substance 

 then act like a condenser which must be charged up before a 

 steady electric current can flow through the wire. This 

 retards the transmission, and otherwise complicates the 

 effects, so that the ordinary telegraphic apparatus become 

 useless. Lord Kelvin's inventive genius soon supplied a 

 suitable instrument, but there were other dangers ahead, such 

 as the enormous mechanical stresses to which the cables are 

 exposed, and the destructive effects of submarine boring 

 animals. The credit of overcoming these difficulties is largely 

 due to Robert Newall, whose name has already been 

 referred to in connexion with Astronomy. As a practical 

 engineer, Newall had improved the manufacture of wire 

 rope to such an extent that quite a new industry may be 

 said to have originated through his efforts. He used the 

 experience gained by introducing wires to strengthen the 

 cables and inventing suitable appliances for paying them out. 

 The first commercially successful cable was laid across the 

 Straits of Dover in 1857, and the possibility of telegraphic 

 communication between Europe and America was then 

 opened out. In July, 1857, a cable was ready, and the shore 

 end was fixed at Valentia ; but the cable snapped when 

 380 miles had been laid. In the following year, after a further 

 failure, a cable was finally stretched across the Atlantic ; but, 

 unfortunately, Kelvin's instructions were ignored and high 

 potential currents were used to transmit the messages, 

 with the result .that the insulation was completely ruined. 



