106 Professor J. A. Fleming [March 27, 



loading coils each having an effective resistance of 6 ' 5 ohms and an 

 inductance of 0-2G5 henry. 



The average effective resistance per mile thus becomes 5 ohms 

 and the inductance 0'0365 henry. 



A simple calculation then shows that the attenuation constant of 

 this circuit therefore is 0" 00125, or about -^l^. In other words, 

 the wave runs 80( » miles before its amplitude is reduced to 36*7 per 

 cent of its initial value. 



The total attenuation for 2000 miles is therefore about 2 * 5, which 

 admits of excellent speech transmission. In fact, so good is the 

 speech transmitted from New York to Denver that on first trying it 

 many persons could not believe they were speaking to correspondents 

 2000 miles away. 



I am indebted for the above information to Mr. J. J. Carty, 

 the able Chief Engineer of the American Telephone and Telegraph 

 Company, under whom the work has been carried out. This 

 remarkable achievement has brought within reach of possibility. an 

 additional feat which is a carefully cherished ambition of Mr. Vail, the 

 President of the above company, and of his technical staff, viz. to 

 connect by a loaded telephone line New York and San Francisco, a 

 distance of over 30U0 miles, and establish direct speecli transmission 

 between the two cities. Another very long loaded aerial line second 

 only in length to the New York and Denver hue is that now just 

 completed between Berlin and Rome, a distance of about 2080 kilo- 

 metres, or 1300 miles. This line runs from Berlin to Frankfort, thence 

 10 Bale, and to Brieg at the entrance of the Simplon tunnel. A short 

 length of uniformly loaded telephone cable is laid through the tunnel 

 to Iselle on the Italian side, and an aerial line then proceeds from 

 Iselle to Milan and thence to Rome. The conductor consists of a 

 pair of phosphor bronze wires 4 '5 mm. m diameter, weighing about 

 500 lb. per mile. The lead and return wires are kept 42 cm. apart, 

 and loading coils inserted every 10 kilometres or 6^ miles. These 

 coils have an effective resistance of 5 ohms and an inductance of 

 0"2 heniy. The line has thus an effective resistance of 2 '9 ohms, 

 inductance ()-022 henry, and capacity of O'Or.56 microfarad per kilo- 

 metre. The attenuation constant is thus about ' 0011 per kilometre, 

 and the whole line has a total attenuation of about 2 "2. There is 

 no doubt excellent speech transmission will therefore be obtained. I 

 am indebted for the above information to Dr. G. di Pirro, who has 

 been in control of the scientific side of the work for the Italian 

 Government, and to Dr. F. Breisig, who in like manner is the chief 

 of the telegraphic and telephonic research department of the Imperial 

 German Post Office. 



Then, turning to our own country, it is possible by the kindness of 

 Mr. W. Slingo, the present Engineer-in-Chief of the British General 

 Post Office, to put you in possession of information as to the present 

 state of loaded telephone lines in Great Britain. The Post Office has 



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