ating on these principles using wires simultaneously with their use for 

 telephone transmission without mutual interference. 



Development of the Mathematical Theory of Transmission — Loading 



As telephone lines came to be extended over greater distances, it 

 was evident that, even with the best copper telephone circuits, the 

 loudness of speech transmitted over the circuit rapidly became less 

 with distance, and also, particularly when the circuits were in cable, 

 the clearness of the speech was impaired at the greater distances. At 

 first these effects were not clearly understood, there being no adequate 

 quantitative analysis of the effects on telephone transmission of the 

 various electrical characteristics of the telephone circuits. Through- 

 out all the early development period, the continued study of the 



COMPOSITE SET 

 I 1 



COMPOSITE SET 



TO 

 TELEPHONE 

 APPARATUS 



TO 

 TELEPHONE 

 APPARATUS 



TELEGRAPH 

 APPARATUS 



TELEGRAPH 

 APPARATUS 



Fig. 8 — Schematic of a telegraph circuit superposed on a telephone circuit using 



"composite sets." 



mathematical theory of the transmission of currents over wires led 

 to an increasing insight into these problems and into the conditions 

 necessary for transmitting telephone currents over long distances 

 efficiently and without undue distortion. The foundation was laid 

 in the masterful, if sometimes enigmatic, papers of Oliver Heaviside 

 published over a long period of years beginning with 1882. One 

 result of Heaviside's work was an appreciation on his part of the 

 unexpected fact that an improvement in transmission efficiency of 

 telephone circuits would be brought about by an increased inductance 

 of the telephone circuits, and he suggested in his papers that means 



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