CHAP, v.j TELEGRA PHIC LINES. 61 i 



a mass of pitch poured into the bottom of a trench a little more 

 than a yard deep. Such, in Paris, are the lines which join the Central 

 Telegraph Office with the Tuileries, the Louvre, the Hotel de Ville, 

 the Bourse, the Prefecture of Police, which are only partly worked; as 

 well as a line of 1,200 metres fixed at Bordeaux. This method has 

 given excellent results, but the trenches must be protected from 

 the infiltrations of gas, which will in time alter the qualities of the 

 pitch. 



In tunnels also, the wires are placed against the side of the 

 arch, and are protected from damp by a layer of gutta-percha, 

 which unites them into one cable; but it has been found that the 

 insulating covering alters very rapidly from the action of the 

 atmosphere. 



II. SUBMARINE AND TRANSOCEANIC TELEGRAPH LINES. 



Can the transmission of electrical currents and of the signals 

 which constitute electric telegraphy, which signals can as we have 

 seen be made by means of metallic wires suitably insulated in the 

 air and the earth, be effected also in water ? 



This interesting question was answered in the beginning 

 of telegraphy. In fact, in 1839, M. O'Shaughnessy joined tele- 

 graphically the two sides of the river Hooghly, in India, by an 

 insulated wire sunk in the river. The following year Professor 

 Wheatstone, whose name is found connected with every progressive 

 phase of electric telegraphy, proposed to join Dover and Calais 

 by a cable. This project was not realized till 1850. About the 

 same time the French engineer Brett, laid a cupper wire insulated 

 by a coating of gutta-percha between Gris-Nez and Dover. The cable 

 was broken, 1 but the possibility of telegraphic communication beneath 

 the sea was demonstrated, and a fresh cable was definitely established 

 across the Straits in 1851. Fifteen more years of trials, and of more 

 or less fortunate attempts to solve the problem, in its generality 



1 A few messages (about 400) were sent, but suddenly the wire was silent. A 

 fisherman had caught it in his nets, and could not resist cutting a piece off, which 

 he brought triumphantly to Boulogne, to show this singular marine production 

 with a centre of gold. W. Huber, The Telegraphic Network of the Globe. 



R 11 2 



