LEAD LINES. 107 



a depth of two feet, but even the railways preferred 

 to lay such underground lines, although the indications 

 of the speedy destruction of these lines increased 

 daily. In particular the destructive action of rats 

 and mice became more evident - - especially on the 

 first lines , which were laid in the sandy railway 

 embankments one and a half to two feet deep. The 

 wires laid over two feet deep were indeed at first 

 exposed to no such destruction, but subsequently it 

 occurred even in them. 



I then believed that a coating of lead would 

 completely cope with this evil. To coat the wires 

 with lead I proceeded at first in the following manner. 

 Leaden tubes were straightened out, then a hempen 

 band was blown through them by means of a bellows, 

 and with its help the conducting wire insulated by 

 gutta-percha was drawn into the tube. Thereupon 

 the tube was passed through a draw-plate, in order 

 to effect a firm attachment to the insulated layer of 

 the conductor. We afterwards succeeded in pressing 

 the leaden tube directly round the insulated wire, 

 when the lead had exactly acquired a certain tempe- 

 rature and permanently retained it. The difficulty of 

 continually controlling this temperature I overcame by 

 a thermo-electric arrangement. 



o 



Such conductors, surrounded by lead casing, were 

 frequently furnished by Halske and me in the beginning 

 of the fifties. So among others in the telegraphic 

 system, which we set up for the police service and 

 the fire-brigade of Berlin. These lead lines acted quite 



