2 BELL SYSTEM TECHXICAL JOURNAL 



In present day systems the relay is as essential to a telephone 

 conversation as the transmitter or receiver. Some idea of our de- 

 pendence on the device may be had from a consideration of the num- 

 bers of simple relays involved in a typical connection. A circuit 

 established between two subscribers served by manual exchanges 

 in a multi-office district will involve 21 relays. When these sub- 

 scribers arc stT\e(l b\' machine switrhiiii; olTires tlif number of relays 



Fig. 1 — Relays in a Inc.il mamial (ilTiie 



