MACHINE SWITCHING TELEPHONE SYSTEM 



57 



today in so-called manual operation. It is worthy of note in this con- 

 nection that the attainment of these ends was made possible by the 

 extensive introduction of automatic features. 



A very brief description at this point of the type of manual switch- 

 board more commonly employed will be helpful. 



In this switchboard the subscriber's line terminates at the central 

 office in so-called "jacks." Associated with each line is a lamp, 

 individual to it, which automatically lights when the subscriber 

 removes his receiver from the hook. This serves as a signal to the 

 operator that a connection is desired. 



The operator answers this call by inserting one end of a cord in the 

 jack associated with the calling subscriber's line, operates a listening 

 key which connects her telephone set to the subscriber's line, and asks 

 for the number desired. When this is obtained the operator com- 

 pletes the connection by inserting the other end of the cord in the 

 jack of the desired subscriber's line, and the subscriber's bell is rung. 

 Suitable lamp signals are provided so that the operator may know 

 when the called subscriber answers, when either subscriber desires 

 further attention, or when either or both of them have finished talking 

 and have hung up their receivers. 



If the subscriber desired is connected to a distant office, the operator 

 receiving the call would, instead of plugging directly into the subscrib- 

 er's line, directly connect the subscriber's line to a trunk terminating 

 in the desired office, where the connection would be completed by a 

 second operator, known as the "B" operator, as shown in Fig. 4. 



Answering Jack - 



(O) Line Lamp 



ailing Subscriber 



_Ca_ll_Cireuit_ 

 A BOARD B BOARD 



Fig. -1 — Diagram Showing Manual Interoffice Connection 



Such communication between the two operators as is necessary to 

 establish this connection takes place over a special pair of wires known 

 as a "call circuit." 



