MACHINE SWITCHING TELEPHONE SYSTEM 



81 



of numbered lamps located on this operator's keyboard. The oper- 

 ator picks up the plug, tests the called line and, if it is found idle, 

 plugs in; or, if it is found busy, she plugs into a special jack which is 

 arranged to send the intermittent busy tone back to the calling 

 subscriber. 



The called subscriber's number is displayed in the following manner. 

 Associated with the operator's position, and with her call indicator, is 

 a group of relays. When the display key is depressed, this group of 

 relays is attached to the trunk. The sender which has meanwhile 

 been waiting on the connection, is thereby given a signal, and sends the 

 number called by means of code pulses which are received by the 

 group of relays. These relays, in turn, Might the set of lamps on the 

 call indicator corresponding to the digits of the called number, as 

 shown in Figs. 22 and 23. The code pulses employed for sending 



Fig. 22 — Incoming Trunk Position in a Manual Office Arranged for Call Indicator 



Operation 



this called number are positive and negative, strong and weak, and 

 are translated by the sender from the decimal dial pulses to this type 

 of pulse to reduce the time required and to simplify the receiving 

 apparatus. 



