TELEPHONE SYSTEM OF THE UNITED STATES 71 



the remainder is used by commercial, financial and other organiza- 

 tions. Between New York and Chicago, a distance of approximately 

 1,400 kilometers, there are slightly over 300 such circuits now in 

 operation. 



Figure 54 shows the system of telegraph circuits furnished by the 

 Bell Companies to one of the press associations. An indication of 

 the importance of private communication systems to commercial and 

 financial institutions is given in Fig. 55 which shows the telegraph 

 circuits furnished by the Bell Companies to a single brokerage com- 

 pany. 



The greater part of such telegraph circuits have in the past been 

 operated by hand-speed Morse telegraph. At the present time, how- 

 ever, nearly a third of the mileage is operated with telegraph printers 

 and this method of operation is rapidly increasing. Two speeds of 

 service employing printers are offered, one operating at 40 words 

 per minute and the other operating at 60 words per minute. At the 

 present time, in view of the use to which this service is put, no demand 

 has arisen for multiplex operation, but this method of operation is 

 possible and will be used if it should become desirable. 



The telegraph circuits were originally all obtained as a by-product 

 of the telephone business by compositing or otherwise superposing 

 them on the telephone wires, using direct current for the telegraph 

 circuits. At the present time approximately two-thirds are obtained 

 in this way. The remaining third are obtained by " carrier current " 

 methods. The carrier current system of open-wire lines uses fre- 

 quencies above the voice range and provides ten duplex telegraph 

 circuits on each pair of wires. The carrier current system used on 

 cable circuits employs frequencies within the voice range, the currents 

 being transmitted over an ordinary telephone four-wire cable circuit. 

 This system gives twelve duplex telegraph circuits on each such 

 circuit. 



Telephone Circuits Provided for Private Use 



In addition to the usual telephone message business, the Bell 

 Companies furnish telephone circuits for the private use of individuals 

 and organizations. 



So-called " special contract " telephone circuits are set up between 

 particular parties for their private use at definite times specified in 

 the contract. Approximately 2,000,000 circuit km. hours of such 

 facilities are now in use during each complete business day. This is 

 the sum of the figures obtained by multiplying the length of each such 

 special circuit by the number of hours per day it is continued in use. 



