148 BELL SYSTEM TECHNICAL JOURNAL 



proper limits. It is one of the obligations of the one who " picks up " 

 the program to hold his range of volume between proper limits. At 

 the central distributing point those in charge of the wire circuits 

 usually find it desirable to make checks from time to time to insure 

 that the proper range of volume is maintained. This checkup is 

 made by means of a device known as a "volume indicator" similar 

 to the one which the program supplier uses for purposes of regulating 

 his volume range. Other volume indicators are provided at various 

 strategic points in the wire network in order to insure that the proper 

 range of volume is reaching these points. In addition to regularly 

 making these observations by means of volume indicators, loud- 

 speaker monitoring observations are continually made at practically 

 all repeater points. 



The results of these observations are transmitted back to the con- 

 trol points periodically by means of telegraph order wires so that the 

 control operator knows at all times the condition of transmission at 

 every point in his territory. 



With the network chains grown to such vast proportions as indi- 

 cated in Figs. 1 and 4, it is essential that the system for controlling 

 the networks be such that all points involved be in instant commu- 

 nication with certain designated control points. To accomplish this, 

 the United States has been divided into four areas, each area of which 

 is under the control of a distributing center or control station. The 

 four control stations in the United States at present (January 15, 

 1929) are. New York covering the eastern section, Chicago the western 

 section, Cincinnati the southern section, and San Francisco the Pacific 

 Coast section. Each of these control points is connected to ever>- 

 repeater point in its area by means of telegraph order wires and in 

 addition is connected to every radio station in the area served by 

 the networks under its control. The various control points are also 

 connected together by means of order wires and arrangements are 

 provided so that New York can be placed in communication with any 

 of the radio stations in the United States which are served by the 

 chains. The total telegraph wire mileage employed for this service 

 is now approximately 43,000 miles (70,000 kilometers). 



A large corps of specially trained telephone men is needed to properly 

 supervise the transmission performance of the chains as well as to 

 take care of the switching and general coordination work involved. 

 At present, about 300 men are employed in the United States for 

 this service, these men, of course, being in addition to those who care 

 for the regular wire and equipment maintenance. 



