German Empire 



215 



metal foil for earthing. In some cables the wires have been 

 placed parallel, but in later types 

 twisting in pairs or in fours has been 

 Introduced, together with, in some 

 cases, paper insulation. The under- 

 ground work, so far, is understood 

 not to have been an unalloyed suc- 

 cess, which is not surprising when 

 the plan usually followed has been 

 to suppress one evil overhearing 

 by exaggerating another capacity. 

 The growing importance of the trunk 

 system will eventually force a resort 

 to metallic circuits, and then the 

 want of foresight which has prevailed 

 will be deplored. The cables have 

 been supplied chiefly by Siemens 

 & Halske, Felten & Guilleaume, 

 Western Electric Company, and 

 Franz Clouth ; the workmanship in 

 every case may be pronounced ex- 

 cellent. One of the cables employed 

 has a conductor composed of three 

 tinned copper strands of '5 mm. dia- 

 meter, insulated with one layer of 

 white Para rubber and one layer of 

 vulcanised, then wrapped in prepared 

 tape, and all vulcanised together. 

 Afterwards, each wire is taped with 

 tin-foil. The cable consists of seven 

 bunches of four wires, coloured blue, 

 green, red, and white, each bunch 

 arranged round a bare copper wire 



of i mm. diameter, with which the , ? ? , ? ^ T ? .pro* 

 foil comes in contact. The whole 

 is wrapped in impregnated tape and 



drawn into a leaden tube of i'5 mm. thickness. The copper 

 resistance per kilometer is 31 ohms ; capacity, '25 mf. ; and insula- 



