The method of operation is as follows:  When a subscriber on a certain line desires to get connection through the switchboard he turns his generator and throws the drop.  The operator in order to communicate with him inserts the plug in which her telephone terminates into the jack, and removes her receiver from its hook.  Having learned that it is for a certain subscriber on another line, she withdraws her plug from the jack of the calling line and inserts it into the jack of the called line, then, hanging up her receiver, she turns the generator crank in accordance with the proper code to call that subscriber.  When that subscriber responds she connects the two lines by inserting the two plugs of a pair into their respective jacks, and the subscribers are thus placed in communication.  The extra jack associated with each line is merely an open jack having its terminals connected respectively with the two sides of the line.  Whenever an operator desires to listen in on two connected lines she does so by inserting the operator’s plug into one of these extra jacks of the connected lines, and she may thus find out whether the subscribers are through talking or whether either one of them desires another connection.  The drops in such switchboards are commonly high wound and left permanently bridged across the line so as to serve as clearing-out drops.  The usual night-alarm attachment is provided, the buzzer being shown at the upper right-hand portion of the cabinet.

[Illustration:  Fig. 293.  Combined Telephone and Switchboard]

Another type of switchboard commonly employed for this kind of service is shown in Fig. 293, in which the telephone and the switchboard cabinet are combined.  The operation of this board is practically the same as that of Fig. 292, although it has manually-restored drops instead of self-restoring drops; the difference between these two types, however, is not material for this class of service.  For such work the operator has ample time to attend to the restoring of the drop and the only possible advantage in the combined drop-and-jack for this class of work is that it prevents the operator from forgetting to restore the drops.  However, she is not likely to do this with the night-alarm circuit in operation, since the buzzer or bell would continue to ring as long as the drop was down.

[Illustration:  Fig. 294.  Upright Magneto Switchboard]

[Illustration:  Fig. 295.  Upright Magneto Switchboard—­Rear View]

Upright Type Switchboard. By far the most common type of magneto switchboard is the so-called upright type, wherein the drops and jacks are mounted on the face of upright panels rising from a horizontal shelf, which shelf contains the plugs, the keys, and any other apparatus which the operator must manipulate.  Front and rear views of such a switchboard, as manufactured by the Kellogg Company, are shown in Figs. 294 and 295.  This particular board is provided with fifty