64 Telephone Systems of tlie Continent of Europe 



into which cables may be drawn from suitably placed boxes, and 

 partly of iron troughs, access to which can only be had by breaking 

 the streets. The original cables laid were of the anti-induction 

 type single wires wrapped in foil ; but now nothing is used but 

 paper insulation and twisted pairs. The most recent work is that 

 just completed (February 1895) at Landshut, which consists of 

 cables containing twenty-eight pairs. The conductors are wrapped 

 in perforated impregnated paper, one red and one white for each 

 pair, arranged in three concentric circles containing respectively 



500 mm - 



1! 



;;o:: 



FIG. 15 



three, ten, and fifteen pairs. Some of the wires in each circle are 

 tinned to aid identification. The pairs, being cabled and wrapped 

 in impregnated cotton, are covered with lead of 2 mm. thickness^ 

 which is in turn protected by a layer of jute, making up a total 

 diameter of 33 mm. The copper resistance is 22*6 ohms per 

 kilometer, and the capacity 'i microfarad when all other wires 

 are earthed. The insulation resistance is 2,000 megohms per 

 kilometer, and is guaranteed not to fall below 500 megohms for 

 two years. This cable, which has been supplied by Franz Clouth, 



