52 BELL SYSTEM TECHNICAL JOURNAL 



has deferred the cable somewhat longer than was originally expected 

 as the growth of traffic has not been quite as rapid as was expected 

 at the time of the war emergency. 



Another example of line congestion enabling the carrier to be 

 proved in on somewhat shorter than the ordinary economical length 

 is in case a considerable amount of line reconstruction is involved if 

 open-wire circuits are added to an existing lead. A case of this 

 kind was the Boston-Burlington system where a very considerable 

 amount of line reconstruction work would have been involved if an 

 effort had been made to add a phantom group to the existing lead. 

 The use of the carrier system on the existing 104 mil circuits enabled 

 this work to be eliminated from consideration and it is possible that 

 the work will not need to be done until this section of the line is re- 

 lieved by cable or other means. 



There are many cases in which the use of carrier can be considered 

 a stop-gap to take care of the transient period between open wire 

 and cable facilities. This has been true in the case of the former 

 Baltimore-Pittsburgh system where the original apparatus has been 

 removed from service as cable facilities are now available between 

 these points via Philadelphia, Reading and Harrisburgh. This does 

 not mean that the equipment is no longer of value, since it usually 

 can be used again on some other location. Even the experimental 

 panels which were used in the Pittsburgh-Baltimore system will 

 probably be reinstalled within the next year. It is now thought that 

 this apparatus will be used between Chicago and Minneapolis in 

 connection with some additional panels to provide for new telephone 

 circuits there. 



Expected Development 



Looking forward for the next ten years, it is expected that carrier 

 telephone facilities will be installed at the rate of about 5,000 to 10,000 

 channel miles and telegraph facilities at the rate of from 20,000 to 

 30,000 channel miles per year. In the meantime development work 

 may produce cheaper systems which will prove in on shorter circuits, 

 thereby extending the field of use so that the rate of application may 

 possibly be doubled or trebled. Even now the number of channel 

 miles in service constitutes an important part of the total facilities 

 of the Bell System and present a very interesting picture of rapid 

 growth when compared with the beginning between Baltimore and 

 Pittsburgh in 1918. 



