166 



BELL SYSTEM TECHNICAL JOURNAL 



Toll Cable. — The change in methods c^f designuig and constructing 

 toll circuits which is of greatest importance from the standpoint of 

 general development of telephone plant is the great increase in use of 

 cables for those circuits, including both the very long distance circuits 

 and the sliorter interurban circuits. This increase is shown by Fig. 5. 



o 5 

 in 



z 

 o 



Z 3 



1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 

 YEAR 



Fig. 5^Toll telephone circuit growth by classifications. 



A single cable may provide for from 250 to 500 telephone circuits and 

 several hundred telegraph circuits, that is, as many circuits as would be 

 provided by five to ten heavily loaded pole lines of aerial wire construc- 

 tion. This concentration of circuits in a single cable, a number of 

 which can be placed on a single route, is in itself of great assistance in 

 coordination problems by greatly reducing the number of routes for 

 which coordination arrangement nmst be made, l^^urthermore, the 



