1914] on Improvements in Long-Distance Telephony 



107 



now over 30,000 miles of loaded telephone circuits, aerial and cable, 

 using 12,448 loading coils. There are also 45,645 miles of circuits 

 being loaded with 17,767 coils. Hence the G.P.O. will soon have over 

 75,000 miles of loaded telephone lines in Great Britain containing 

 30,000 loading coils, not including the submarine cables above 

 mentioned. The longest British aerial loaded lines are the two 

 Trunk circuits running from London to Leeds, the details of which 

 are given in Table III, and taken by permission from a recent paper 

 by Mr. J. G. Hill,* one of the Post Office Engineers, who has given 

 in that paper full information of the experiments conducted by the 

 G.P.O. on these lines. 



The details of the loading of these long aerial lines, including 

 the BerKn-Frankfurt line in Germany, are given in Table III. 



As regards loaded underground cables, Mr. Slingo informs me 

 that the longest workin^r underground loaded cable in Great Britain 

 is that from Hull to Newcastle via Leeds, which is 154 miles long. 

 The conductors of the Hull-Leeds and Leeds-Stockton sections weigh 

 70 lb. per mile. They are laid up in multiple twin formation. 



The inductance added is 54 millihenries per mile, and wire-to- 

 wire capacity is 0*065 microfarads per mile. The loading coils are 

 spaced 2 • 5 miles apart. The conductors of the Stockton-Newcastle 

 section (34 miles) weigh 100 lb. per mile. The total attenuation 

 over the whole length is 2 * 32. 



TABLE III. — Loaded Aerial Land Lines. 

 All values are per mile or per kilometre at 800 frequency. 



* Mr. J. G. Hill, " The Loading of Aerial Lines and the Constants of 

 Loaded Circuits." The Electrician, vol. Ixxii., p. 602, January 16, 1914. 



