APPLICATION OF THE ELECTKIC TELEGRAPH. 363 



108,900 miles per second.* MM. Fiseau and Gounelle 

 deduced a velocity of 112,680 miles per second in copper 

 wire one tenth of an inch in diameter, and 62,600 miles 

 in iron wire one sixth of an inch in diameter.f 



All these results differ materially from that obtained in 

 1836 by Professor Wheatstone, who determined the 

 velocity of frictional electricity to be 288,000 miles per 

 second. Professor Faraday is of opinion that the veloc- 

 ity of discharge through the same wire must vary with 

 the tension or intensity of the first urging force ; and on 

 account of the lateral induction of the current, he con- 

 siders that the velocity must be different if the wires be 

 turned round a frame in small space, or be spread through 

 the air through a large space, or adhere to walls, or be 

 laid upon the ground. 



The telegraph wires from London to Manchester are 

 covered with gutta-percha inclosed in metallic tubes, and 

 buried in the earth ; and when they are all connected so 

 as to make one series, form a length of over 1500 miles. 

 Professor Faraday placed one galvanometer at the be- 

 ginning of the wire ; a second galvanometer in the 

 middle ; and a third at the end ; the three galvanometers 

 being side by side in the same room, and the third per- 

 fectly connected with the earth. On bringing the pole 

 of a battery into contact with the wire through the gal- 

 vanometers, the first galvanometer was instantly affected; 

 after about a second the next was affected; and it re- 

 quired two seconds for the electric stream to reach the 



* Comptes Kendus, Aug. 14, 1854. f Ibid., April 15, 1850. 



