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BELL SYSTEM TECHNICAL JOURNAL 



increased from the equivalent of about 10 miles to about 14^ miles per 

 100 miles of open-wire telephone toll lead; while on the other hand the 

 exposures not as yet adequately coordinated have in the same period 

 decreased from the equivalent of 2.6 miles to 1.5 miles per 100. 



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Fig. 4 — Toll telephone and power transmission circuit growth. 



Note: Values for 1930 are estimates based on best available data. Telephone 

 data refer to Bell System. 



While the trends of practise in the design, construction and main- 

 tenance of the plants have necessarily been largely controlled by the 

 fundamental requirements of service and economy in developing the 

 two systems, and while the trends naturally have not all been in the 

 same direction as regards their effect on the coordination problem, still 

 the general trend of plant practise at the present time is in the direction 

 to facilitate the coordination of the plants of the two utilities. In the 

 following pages brief statements are made, descriptive of the more im- 

 portant of these trends in the respective systems. 



Trends in Telephone System 

 The telephone plant is at the present time rapidly changing in its 

 physical character through the application of important developments 

 and changes in engineering and construction practise. 



