[Illustration:  Fig. 240.  Normal Condition of Line]

The drop or line signal is permanently connected between the jack sleeve and the anvil 3.  As a result, the drop is normally bridged across the circuit of the line so as to be in a receptive condition to signaling current sent out by the subscriber.  It is evident, however, that when the plug is inserted into the jack this connection between the line and the drop will be broken.

In this normal condition of the line, therefore, the drop stands ready at the central office to receive the signal from the subscriber and the generator at the sub-station stands ready to be bridged across the circuit of the line as soon as the subscriber turns its handle.  Similarly the ringer—­the call-receiving device at the sub-station—­is permanently bridged across the line so as to be responsive to any signal that may be sent out from the central office in order to call the subscriber.  The subscriber’s talking apparatus is, in this normal condition of the line, cut out of the circuit by the switch hook.

Subscriber Calling. Fig. 241 shows the condition of the line when the subscriber at the sub-station is making a call.  In turning his generator the two springs which control the connection of the generator with the line are brought into engagement with each other so that the generator currents may pass out over the line.  The condition at the central office is the same as that of Fig. 240 except that the drop is shown with its shutter fallen so as to indicate a call.

[Illustration:  Fig. 241.  Subscriber Calling]

[Illustration:  A SPECIALLY FORMED CABLE FOR KEY SHELF OF MONARCH SWITCHBOARD]

Operator Answering. The next step is for the operator to answer the call and this is shown in Fig. 242.  The subscriber has released the handle of his generator and the generator has, therefore, been automatically cut out of the circuit.  He also has removed his receiver from its hook, thus bringing his talking apparatus into the line circuit.  The operator on the other hand has inserted one of the plugs P_{a} into the jack.  This action has resulted in the breaking of the circuit through the drop by the raising of the spring 1 from the anvil 3, and also in the continuance of the line circuit through the conductors of the cord circuits.  Thus, the upper limb of the line is continued by means of the engagement of the tip spring 1 with the tip 4 of the plug to the conducting strand 6 of the cord circuit; likewise the lower limb of the line is continued by the engagement of the thimble 2 of the jack with the sleeve contact 5 of the plug P_{a} to the strand 7 of the cord circuit.  The operator has also closed her listening key L.K. In doing so she has brought the springs 8 and 9 into engagement with the anvils 10 and 11 and has thus bridged her head telephone receiver with