SCIENCE AND PRACTICE. 341 



ness, and, secondly, because ft has 110 pretensions whatever 

 to simplicity. One of the two systems the mercury or the 

 alloy must therefore be chosen, or both, for security. 

 Indeed, why it should be necessary at all to exclude a 

 single method by which truth may with great probability 

 be attained or truth controlled, is to us incomprehensible. 



VI. SUBMARINE TELEGRAPH LINES. 



66. The greatest achievement of the electric telegraph is 

 unquestionably the instantaneous transmission of intelligence 

 across the seas. To whom the credit of the first idea of a 

 submarine cable is due, is matter of secondary importance. 

 It has been claimed for several, with, perhaps, equal justice. 



The first cable, however, which was intended to be of any 

 real use, was the gutta-percha covered copper wire paid out 

 in 1850, between Dover and Calais, by Mr. Brett, but which, 

 unhappily, lived only a single day just sufficient to save the 

 concession. 



The next cable made consisted of four copper wires No. 

 10, B.W.Gr., each twenty-seven miles long, separately insu- 

 lated with gutta-percha to a thickness of 0,284" diameter, 

 and the whole spun up in the form of a rope with tarred 

 hemp, with an outer protection of ten No. 1 galvanised iron 

 wires, as shown in natural size in Fig. 154. This cable 

 weighed, when completed, seven tons per mile. It was laid 

 successfully in the year 1851, and is still at work. The 

 partial success of the first wire, and the brilliant success of 

 the second, decided the practicability of submarine telegraphy, 

 and, after a little line of three miles had been laid down 

 between Keyhaven and Hurst Castle, and one of eighteen 

 miles across the Belt, both of which succeeded, and are still 

 in working order, faith expanded, and the length of the ropes 

 grew proportionally. In 1853, Messrs. Newall made a line, 

 which they laid down between Dover and Ostend, seventy miles 

 long, weighing seven tons per mile. In this cable the number 

 of conducting wires was increased to six ; they were of copper, 



