SUBTERRANEAN LINES. 
143 
other 011 the left bank of the river, receive several cables which 
pass from the sea through the Huveaune, the mouth of which 
is about 150 yards lower down. 
Where submarine lines are connected with subterranean 
lines, lightning-rods (which we shall describe on another page) 
are placed. Some subterranean lines are laid in sewers, others 
in trenches. In both cases these lines are constituted of sub¬ 
marine deep-water cables. In the sewers they are fixed to the 
arch by cramps, such as we have already described. Sub¬ 
terranean lines are buried in the ground, to the depth of a 
yard, and the connections are made by joints on Willoughby 
Smith’s system, enclosed in earthenware pipes made water¬ 
tight with Portland cement. The lines of the Eastern Tele¬ 
graph Company, however, have only three or four such junc¬ 
tions in a length of 2| miles. The ground in which these 
lines have been laid (the Prado at Marseilles) possesses very 
favourable conditions for the preservation of the cables, as 
regards moisture. In other stations of the Eastern Telegraph 
Company, at Aden, for instance, it has been necessary, on 
account of the dryness of the ground through which the line 
passes, to enclose it in cast-iron pipes kept constantly full of 
water. The duplex system of telegraphy, which has generally 
been adopted on this company’s lines, requires a perfect insu¬ 
lation of the subterranean line. Now variations of tempera¬ 
ture, or the escape from the gas-pipes of a town, causes the 
gutta-percha to crack in a few months, and this would occasion 
a loss of current such as it would be impossible to compensate 
in the delicate electrical equilibrium required by the duplex 
arrangement. 
