408 Telephone Systems of the Continent of Europe 



from that over a corresponding length of overhead metallic 

 circuit. The only criticism that need be offered in respect to this 

 underground work is that, when a mass of cables has been laid in 

 an iron pipe, the weight of the upper ones will render it impos- 

 sible to safely withdraw any of the lower ones that need replace- 

 ment. The engineers expect that as many as 3,000 metallic 

 circuits, say fifty-seven 52-pair cables, can be placed in the 

 6o-centimeter pipes. Perhaps so ; but once there they are fixtures. 

 The cables used at Zurich were supplied by Messrs. Felten & 

 Guilleaume. These underground routes are carried to convenient 

 spots, where are erected handsome and substantial iron-lattice 

 columns set in concrete (fig. 147), from thirty to seventy-five feet 

 in height. They carry from 256 to 400 insulators on iron arms 

 arranged in the form of a cage, one face 

 to each point of the compass, of similar 

 construction to that shown in fig. 150. 

 The base of the lattice column is enclosed 

 in a hollow plinth of cast iron, which 

 forms a commodious house for the junc- 

 tions of the underground with the aerial 

 wires. These houses contain test-terminals 

 and lightning-guards for each pair of wires, 

 FlG 6 together with a set of speaking instru- 



ments in connection with the exchange. 

 The underground wires terminate at the test-board, and are 

 carried up the column by lighter cables disposed in the corners, 

 where they are out of sight. These lighter cables end at the level 

 of the different arms, where soldered connections are made with 

 the overhead wires. At present, as the exchange continues to be 

 worked on the single-wire plan, the second wire of each under- 

 ground metallic circuit is earthed at the distributing columns, 

 the subscriber's current going to the exchange by one wire and 

 returning to earth at the column by the other, the indicator being 

 looped in between the two wires, and cut off from earth at the 

 exchange. The officials at Zurich appear to think that this plan 

 of doubling back to earth helps to reduce disturbance materially. 

 It no doubt assists in reducing disagreeable inductive effects, 

 but, except to subscribers doubling back to the same column and 



