[Illustration:  Fig. 244.  Subscribers Connected for Conversation.]

Subscribers Conversing. The only other thing necessary to establish a complete set of talking conditions between the two subscribers is for the called subscriber to remove his receiver from its hook, which he does as soon as he responds to the call.  The conditions for conversation between the two subscribers are shown in Fig. 244.  It is seen that the two limbs of the calling line are connected respectively to the two limbs of the called line by the two strands of the cord circuit, both the operator’s receiver and the central-office generator being cut out by the listening and ringing keys, respectively.  Likewise the two line drops are cut out of circuit and the only thing left associated with the circuit at the central office is the clearing-out drop C.  O., which remains bridged across the cord circuit.  This, like the two ringers at the respective connected stations, which also remain bridged across the circuit when bridging instruments are used, is of such high resistance and impedance that it offers practically no path to the rapidly fluctuating voice currents to leak from one side of the line circuit to the other.  Fluctuating currents generated by the transmitter at the calling station, for instance, are converted by means of the induction coil into alternating currents flowing in the secondary of the induction coil at that station.  Considering a momentary current as passing up through the secondary winding of the induction coil at the calling station, it passes through the receiver of that station through the upper limb of the line to the spring 1 of the line jack belonging to that line at the central office; thence through the tip 4 of the answering plug to the conductor 6 of the cord; thence through the pair of contacts 14 and 12 forming one side of the ringing key to the tip 4 of the calling plug; thence to the tip spring 1 of the jack of the called subscriber’s line; thence over the upper limb of his line through his receiver and through the secondary of the induction to one of the upper switch-hook contacts; thence through the hook lever to the lower side of the line, back to the central office and through the sleeve contact 2 of the jack and the sleeve contact 5 of the plug; thence through the other ringing key contacts 13 and 15; thence through the strand 7 of the cord to the sleeve contact 5 and the sleeve contact 2 of the answering plug and jack, respectively; thence through the lower limb of the calling subscriber’s line to the hook lever at his station; thence through one of the upper contacts of this hook to the secondary of the induction coil, from which point the current started.

[Illustration:  Fig. 245.  Clearing-Out Signal]

Obviously, when the called subscriber is talking to the calling subscriber the same path is followed.  It will be seen that at any time the operator may press her listening key L.K., bridge her telephone set across the circuit of the two connected lines, and listen to the conversation or converse with either of the subscribers in case of necessity.