DEVELOPMENT OF THE TELEPHONE 



installed wherever the lamp-signal equipment is em- 

 ployed. Briefly, it may be described as follows: 



"A subscriber, upon lifting his receiver from the 

 hook, operates in the main office a line-relay similar 

 to that used in the modern lamp-signal board, but this, 

 instead of lighting a line-lamp, energizes a simple 

 selector-switch which selects an operator who is not 

 busy and, in turn, selects a connecting cord which is 

 not busy, and lights the lamp associated with this 

 cord. The current lighting this lamp passes through 

 a low-wound relay, which connects the operator with 

 the subscriber. Upon receiving the number of the 

 instrument wanted, the operator inserts the plug in 

 the multiple, and rings. Upon inserting the plug in 

 the jack, the cord-lamp is automatically extinguished 

 and the operator's listening-set is disconnected at the 

 same time, leaving the two subscribers to converse 

 in privacy." 



Automatic telephone systems, which dispense with 

 manually operated central exchanges, are installed 

 and working satisfactorily in many places throughout 

 the United States at the present time. They are par- 

 ticularly popular in the Middle West, Chicago having 

 such a system with over ten thousand subscribers. 

 The system works perfectly for short-distance messages 

 such, for example, as in the urban service or be- 

 tween a large city and its suburbs but it is not adapted 

 to long-distance communications. 



The telephone instrument itself resembles the or- 

 dinary wall-piece, with bells, receivers, and trans- 

 mitters, but in addition has what is known as a 



