ven, in which case it is used in establishing connection with
the called subscriber.

[Illustration: Fig. 243. Operator Calling]

_Operator Calling._ We may now consider how the operator calls the
called subscriber. The condition existing for this operation is shown
in Fig. 243. The operator after receiving the order from the calling
subscriber inserts the calling plug _P__{c} into the jack of the line
of the called station. This act at once connects the limbs of the line
with the strands _6_ and _7_ of the cord circuit, and also cuts out the
line drop of the called station, as already explained. The operator is
shown in this figure as having opened her listening key _L.K._ and
closed her ringing key _R.K._ As a result, ringing current from the
central-office generator will flow out over the two ringing key springs
_12_ and _13_ to the tip and sleeve contacts of the calling plug
_P__{c}, then to the tip spring _1_ and the sleeve or thimble _2_ of
the jack, and then to the two sides of the metallic-circuit line to the
sub-station and through the bell there. This causes the ringing of the
called subscriber's bell, after which the operator releases the ringing
key and thereby allows the two springs _12_ and _13_ of that key to
again engage their normal contacts _14_ and _15_, thus making the two
strands _6_ and _7_ of the cord circuit continuous from the contacts of
the answering plug _P__{a} to the contacts of the calling plug
_P__{c}. This establishes the condition at the central office for
conversation between the two subscribers.

[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