72 Book of Engineering 



rather opal, but some appear bloodshot, 

 these latter indicate a public service such 

 as a call office. Each wire from the cables 

 or from the overhead lines is led into the 

 exchange, and here it ends at the back of 

 the switchboard. Connected to each wire 

 is an indicator which signals the operator 

 when the person at the other end of the 

 line desires to make a call. One thing in 

 particular strikes us in the exchange that 

 is the absence of bells. At our end we get 

 the thrilling sound of the telephone bell 

 too often, and we talk glibly of ringing up 

 the exchange. If we did, those poor girls 

 would be driven to sheer desperation; it 

 is quite bad enough to have a succession 

 of eyes winking at one. When we need to 

 make a connection, we lift our receiver 

 from its usual position, and straightway in 

 the distant exchange an opal eye becomes 

 bright, a minute electric bulb being ignited 

 by the lifting of the receiver. 



The actual termination of the caller's 

 wire is termed a jack, and several hundreds 

 of them will confront the telephonist. She 



