12 BELL SYSTEM TECHNICAL JOURNAL 



million of such stations. This number is rapidly increasing particu- 

 larly for residence use as people appreciate further the advantages 

 of having telephones in a number of convenient locations. The best 

 residences are more and more being equipped to have telephones 

 available in all parts of the house. 



In order to make telephone service possible for those people whose 

 sense of hearing is more or less deficient, special sets are installed. 

 By means of a vacuum tube amplifier which the user can adjust, 

 the receiving may be amplified so as to bring the range up to the 

 point giving best results, this point depending on the degree of im- 

 pairment of his hearing. 



Public telephone stations constitute an important part of telephone 

 development in the United States, there being at present more than 

 275,000 of such stations in service. Whereas residence and business 

 service is largely given by contract, the customers contracting to 

 pay a definite amount per month or a certain amount per call, a great 

 many of the public pay stations are supplied with coin boxes by means 

 of which the money is collected at the time the call is made. 



These installations are also for the most part in booths to insure 

 quiet and privacy. Fig. 4 shows a form of booth furnished by the 

 telephone companies, provided with a seat and with lighting and 

 ventilation as well as a convenient location for the necessary telephone 

 directories. 



Private Branch Exchange 



For customers who use a large amount of telephone service, one 

 of several types of private branch exchange is provided which not 

 only permits distribution of the incoming calls to the particular 

 station desired but also makes it possible for one extension to call 

 another without going through the central office. In the Bell System 



Private Branch Exchange Stations 2,740,000 



Per Cent of Total Bell Stations 19.0 



Private Branch Exchange Boards 



Cordless '. 53,300 



Cord 60,900 



Total 114,200 



Private Branch Exchange Cord Positions 



Manual 68,600 



Dial 1,700 



Total * 70,300 



Private Branch Exchange Attendants 



Cord Board Attendants 75,000 



Cordless Board Attendants 53,000 



Total 128.000 



Fig. 5^Private Branch Exchange Statistics for the Bell 

 System as of Feb. 1, 1929. 



