the line is already “busy” a slight buzz is heard, not only by “central,” but by the subscriber also if he listens; “central” notifies and then disconnects you.  If the line is clear the twin plug is thrust into the opening, and at the same time “central” presses a button, which either rings a bell or causes a drop to fall in the private exchange station of the party you wish to talk to.  The moment the new connection is made and the party you wish to talk to takes off the receiver from his hook, a second light glows beside yours, and continues to glow as long as the receiver remains off.  The two little lamps are a signal to “central” that the connection is properly made and she can then attend to some other call.  When your conversation is finished and your receivers are hung up the little lights go out.  That signals “central” again, and she withdraws the plug from both holes and pushes another button, which connects with a meter made like a bicycle cyclometer.  This little instrument records your call (a meter is provided for each subscriber) and at the same time lights the two tiny lamps again—­a signal to the inspector, if one happens to be watching, that the call is properly recorded.  All this takes long to read, but it is done in the twinkling of an eye.  “Central’s” hands are both free, and by long practice and close attention she is able to make and break connections with marvellous rapidity, it being quite an ordinary thing for an operator in a busy section to make ten connections a minute, while in an emergency this rate is greatly increased.

[Illustration:  “CENTRAL” MAKING CONNECTIONS The front of a small section of a central-station switchboard.  Each dot on the face of the blackboard is a subscriber’s connection.  The cords connect one subscriber with another.  The switches throwing in the operator’s “phone”, and the pilot lamps showing when a subscriber wishes a connection, are set in the table or shelf before her.]

The call of one subscriber for another number in the same section, as described above—­for instance, the call of 4341 Eighteenth Street for 2165 Eighteenth Street—­is the easiest connection that “central” has to make.

As it is impossible for each branch exchange to be connected with every individual line in a great city, when a subscriber of one exchange wishes to talk with a subscriber of another, two central operators are required to make the connection.  If No. 4341 Eighteenth Street wants to talk to 1748 Cortlandt Street, for instance, the Eighteenth Street central who gets the 4341 call makes a connection with the operator at Cortlandt Street and asks for No. 1748.  The Cortlandt Street operator goes through the operation of testing to see if 1748 is busy, and if not she assigns a wire connecting the two exchanges, whereupon in Eighteenth Street one plug is put in 4341 switch hole; the twin plug is put into the switch hole connecting with the wire to Cortlandt Street; at Cortlandt Street the same thing is done with No. 1748 pair of plugs.  The lights glow in both exchanges, notifying the operators when the conversation is begun and ended, and the operator of Eighteenth Street “central” makes the record in the same way as she does when both numbers are in her own district.