the secondary of her induction coil across the two strands 6 and 7 of the cord.  Associated with the secondary winding of her receiver is a primary circuit containing a transmitter, battery, and the primary of the induction coil.  It will be seen that the conditions are now such as to permit the subscriber at the calling station to converse with the operator and this conversation consists in the familiar “Number Please” on the part of the operator and the response of the subscriber giving the number of the line that is desired.  Neither the plug P_{c}, nor the ringing key R.K., shown in Fig. 242, is used in this operation.  The clearing-out drop C.O. is bridged permanently across the strands 6-7 of the cord, but is without function at this time; the fact that it is wound to a high resistance and impedance prevents its having a harmful effect on the transmission.

[Illustration:  Fig. 242.  Operator Answering]

It may be stated at this point that the two plugs of an associated pair are commonly referred to as the answering and calling plugs.  The answering plug is the one which the operator always uses in answering a call as just described in connection with Fig. 242.  The calling plug is the one which she next uses in connecting with the line of the called subscriber.  It lies idle during the answering of a call and is only brought into play after the order of the calling subscriber has been given, 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.