France 165 



form a cable. From the size of the beads it will be seen that the 

 Fortin- Hermann system conduces to a very bulky cable ; six pairs, 

 which is the size commonly used in Paris, occupying a space of 

 over an inch. For this reason, and in 'spite of its electrical 

 qualities, which are excellent, its use is not being materially ex- 

 tended. The insulation obtained is never less than 200 megohms 

 per kilometer, while the capacity does not exceed '05 microfarad 

 per kilometer. The cable now chiefly employed is insulated with 

 paper, and made in the workshops of M. Georges Aboilard, 

 Avenue de Breteuil. While possessing (with No. 20 wire) a 

 capacity of '055 mf. per kilometer, fifty-two twisted pairs occupy 

 a diameter of only forty-three millimeters, including the leaden 

 protection. An insulation resistance of 6,000 megohms per kilo- 

 meter is easily attained. The paper employed is of French 

 manufacture, and before being used is severely tested for strength, 

 a strip fifteen millimeters wide and one meter long being required 

 to support a weight of seven kilogrammes and to resist twisting 

 round eight times. The paper strip is very rapidly wound 

 spirally on the conductor by special machinery in such a way 

 that an air space is left between the wire and its covering. A 

 second spiral in the reverse direction is then added, the process 

 resulting in the formation of an almost perfect paper tube, round 

 which a light cotton thread is wound to keep it in position. The 

 conductors are then twisted in pairs, and made up into cores 

 containing two, seven, twenty- eight, or fifty-six pairs, which are 

 kept together by a spiralling of cotton threads. The core is 

 wound on iron drums and dried in an oven at a temperature of 

 no Centigrade for twenty-four hours before receiving its coating 

 of pure lead. This it does by means of an hydraulic press, through 

 which the cable passes, the molten lead which is fed to the press 

 being somewhat cooled by water. The finished cable emerges 

 cased in a leaden tube three millimeters thick, which lies directly 

 on the core, the intervening layers of jute, &c., employed by 

 British and German makers being dispensed with, as is also the 

 usual steel armour. But then it must be remembered that this 

 French cable is laid in troughs or trenches, and not drawn into 

 conduits. The different-sized cores are employed according to 

 the distance from the switch-room : thus a 5 6 -pair cable leaves 



