THE ELECTRIC TELEGRAPH. 



interfere more or less with the practical working of all telegraphs 

 having underground conducting wires ; and I have been informed 

 by the agents engaged in bureaux of the Paris telegraph, that 

 they are sensible of its effects in all direct communications between 

 that capital and London. 



On the other hand the Magneto-Electric Telegraph Company, who 

 at the present time (May, 1S54), have nearly 900 miles of under- 

 ground wire in operation, report that they sometimes pass their 

 signals without any difficulty through 500 miles of underground 

 wire without any break or delay in the circuit, and that they have 

 in constant operation continuous underground lines connecting 

 towns above 300 miles apart. 



The only defect complained of in the underground wires is that 

 which proceeds from accidental failures of complete insulation, 

 produced by defects in the gutta percha or other coating which 

 allow moisture to penetrate in wet weather and to reach the con- 

 ducting wire, or it may arise from accidental fracture of the wire. 

 In any such cases the flow of the current to its destination is 

 interrupted, and the telegraph conveys no signal. 



The use of underground wires, and the discovery of the 

 phenomenon of inductive action above described, are too recent to 

 justify any certain inference as to their effects on telegraphic 

 operations. Time and enlarged experience alone can settle the 

 questions which have been thus raised. 



98. Although as a general rule the overground lines of 

 telegraphic wire are sustained by supports at intervals of about 

 sixty yards, many exceptional cases are presented in* which they 

 are extended between supports at much greater distances asunder. 

 Every recent visitor to Paris may have observed the long lines of 

 wire which are in several cases extended along the boulevards 

 and across the river. 



But the most surprising examples of long lines of wires 

 without intermediate support, are presented on the telegraphic 

 line passing north and south through Piedmont between Turin and 

 Genoa. There, according to a report published in the "Pied- 

 niontese Gazette," in the course of the line passing through the 

 district intersected by the chain of the Bochetta, the engineer, 

 M. Bonelli, had the boldness to carry the wires from summit to 

 summit across extensive valleys and ravines at immense heights 

 above the level of the ground. In many cases the distance 

 between these summits amounted to more than half a mile, and 

 in some to nearly three-quarters of a mile. In passing through 

 towns, this line is carried underground, emerging from which 

 it is again stretched through the air from crest to crest of the 

 Maritime Apennines, after which it finally sinks into the earth, 

 172 



