July, 1911. 



KNOWLEDGE. 



269 



began to consider tlie hix'ing of a new telephone cable 

 across the Enghsh Channel, the question of a 

 loaded cable was seriously considered. After man\ 

 experiments and measurements, a type of Pupin- 

 loaded cable was evolved which \vas made and laid 

 for the Post Office by Messrs. Siemens Brothers, in 

 1910. This Anglo-French loaded telephone cable was 

 described to the Institution of Electrical Engineers 

 recentl}' in a paper by Major O'Meara, C.M.G.. 

 the Engineer-in-Chief_|()f the P>ritish Postal Telegrai)h 

 Department. 



senting the British and Prencli Telegraph Ser\-ices, 

 between May 15th and May ISth, 1910. Some 

 special precautions had to be taken in handling the 

 thickened-u[) portions f)f the cable containing the 

 loading coils (see Figure 7). The operations were, 

 however, successfully carried out, and London and 

 Paris are now connected by a new telephone cable of 

 superior type containing two complete circuits. The 

 attenuation constant of the new cable or ratio in which 

 the current is enfeebled in passing along the cable was 

 t(jund to be close to the predicted value, and the 





FiGURH 7. 



Passing over the sheave a loading coil in the Anglo-French telephone (1910) cable laid across the English Ch.inncl. 



The cable contains four-stranded copper con- 

 ductors insulated with gutta percha in the usual waw 

 and every nautical mile, coils are inserted which con- 

 sist of silk-covered wire wound over an iron core so 

 as to form an inductance coil \\liicli is inserted in the 

 run of the cable (see Figure 5). The gutta percha 

 insulation and the steel wire armouring are, of course, 

 continued over the coil, and the result is to produce 

 an enlargement or protuberance on the cable ever\- 

 mile. 



The cable was laid with great skill by the manu- 

 facturers at the bottom of the English Channel 

 between Abbots Cliff, near Doser. and Ca[)e Grisnez, 

 in France. 



The cable was laid h\' the cable ship " Farada\-" 

 by the experienced operators of Messrs. Siemens 

 Brothers, and under the inspection of officials repre- 



speaking qualities of the cable also fully realised 

 expectations. }W the employment of extra thick 

 conductors in the land lines at each end, and 

 w hen the added distances do not exceed seventeen 

 hundred miles, Major O'Meara states in his paper 

 that well maintained conversations bv telephone 

 could be conducted between London and Astrakhan 

 on the Caspian Sea. This important achievement 

 has been watched with great interest by practical 

 telephone engineers on both sides of the .Atlantic. 

 The great improvement in the distances over which 

 it is possible to speak telephonically through cables 

 when loaded in the Pupin manner is a great testi- 

 mony to the value of correct scientific theory in 

 guiding })ractice. The old rule-of-thumb methods 

 are abolished, tekqihonic engineers are everywhere 

 engaged in studying the improved methods of 



