94 



BELL SYSTEM TECHNICAL JOURNAL 



120 



to 



UJ 



\- 

 u 



Q 



U- 



O 

 V) 



z 

 o 



1920 1921 1922 1923 1924 1925 1926 1927 1928 



Fig. 64 — Kilometers of exchange and toll wire in the United States. 



