THE ELECTRIC TELEGRAPH. 



connection with, a portable battery. The current will fail at the 

 particular mile within which, the fault has taken place. 



72. In passing through tunnels the overground wires have 

 been subject to great inconvenience, owing to the quantity of 

 water percolating through the roof, constantly falling on the wires 

 and their supports, and thus injuring their insulation. It has 

 been found that from this cause the current transmitted along one 

 wire has been subject to leakages, a part of it passing by the 

 moisture which surrounds the supports to an adjacent wire, so 

 that being thus divided, part either returns to the station from 

 which it has been transmitted, or goes on to a station for which 

 it is not intended. 



73. This inconvenience would be removed by adopting for 

 tunnels the under-ground system. Mr. "Walker, to whom great 

 experience in the practical business of electric telegraphy, and 

 considerable scientific knowledge must give much authority on 

 such a subject, has adopted apparently with very favourable 

 results a method of covering the wires, which pass through 

 tunnels, with a coating of gutta-percha. The conducting wire 

 thus treated is copper wire No. 16. The gum being well cleaned 

 and macerated by steam, is put upon the wire by means of 

 grooved rollers. The diameter of the covered wire is a quarter of 

 an inch. Mr. "Walker states that in all the wet tunnels under his 

 superintendence he has substituted this gutta-percha-covered wire 

 for the common line wire, and has thus " accomplished telegraphic 

 feats which could not have been attempted on the old plan." 



74. In France and in the United States the wires, even in the 

 cities and towns, are conducted on rollers at an elevation, as on 

 other parts of the lines. In Paris, for example, the telegraphic 

 wires proceeding from the several railway stations are carried 

 round the external boulevards and along the quays, the rollers 

 being attached either to posts or to the walls of houses or 

 buildings, and are thus carried to the central station at the 

 Ministry of the Interior. 



75. In Europe, the telegraphic wires have until very lately 

 invariably followed the course of railways ; and this circumstance 

 has led some to conclude that, but for the railways, the electric 

 telegraph would be an unprofitable project. 



76. This is however a mistake. Independently of the case of the 

 Magnetic Telegraph Company already mentioned, the wires in the 

 United States, where a much greater extent of electric telegraph 

 has been erected and brought into operation than in Europe, do not 

 follow the course of the railways. They are conducted, generally, 

 along the sides of the common coach-roads, and sometimes even 

 through tracts of country where no roads have been made. 



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