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BELL SYSTEM TECHNICAL JOURNAL 



When the subscriber removes his receiver, he closes the circuit of 

 his line, causing a relay at the central office in series with his line, to 

 operate. This^relay causes an idle line finder, having access to his 

 line, to trip the proper brush and then move upward to his line. At 

 the same time a sender selector attached to that line finder is choosing, 



LINE FINDER 

 FRAME 



TO 



OTHER 



OFFICES 



TO INCOMING FR. 



SENDERS 

 Fig. 13 — Diagram of Line Finder, District and Office Frames 



out of a common group, an idle sender. The sender selector is a small 

 selector of a type in which the brushes are driven by a magnet over 

 contacts arranged as shown in Fig. 19. 



The sender having been attached in this manner to the calling line, 

 a low humming sound, known as the dial tone, is heard by the sub- 

 scriber, advising him that the mechanism is ready for him to dial. 

 The entire sequence of events just described takes place in a fraction 

 of a second, so that ordinarily the subscriber finds the dial tone when 

 the receiver reaches his ear. The subscriber now dials the required 

 letters of the office name, and the numerals of the called number. 



The pulses from the dial come over the subscriber's line through the 

 line finder and sender selector to the sender which records and trans- 

 lates them to control the setting up of the connection. As soon as 

 the connection has been established, the sender is released and is 

 ready to be used for a new call, being kept in use only a few seconds 

 for each call. 



