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.

_Clearing Out_. At the close of the conversation, either one or both
of the subscribers may send a clearing-out signal by turning their
generators after hanging up their receivers. This condition is shown
in Fig. 245