e relay _14_, already referred to as forming a shunt for the trunk
disconnect lamp, has for its function the keeping of the talking circuit
through the trunk open until such time as the relay _13_ operates, this
being purely an insurance against unnecessary ringing of a subscriber in
case the _A_-operator should by mistake plug into the wrong trunk. It is
not, therefore, until the _A_-operator has plugged into the trunk and
the relay _13_ has been operated to cause the energization of the relay
_14_ that the ringing of the called subscriber can occur, regardless of
what the _B_-operator may have done.

The relay _9_ has an additional function to that of helping to control
the circuit of the ringing-key holding magnet. This is the holding of
the test circuit complete until the operator has tested and made a
connection and then automatically opening it. The test circuit of the
_B_-operator's trunk may be traced, at the time of testing, from the
thimble of the multiple jack under test, through the tip of the cord,
thence through the uppermost pair of contacts of the relay _9_ to ground
through a winding of the _B_-operator's induction coil. After the test
has been made and the plug inserted, the relay _9_, which is operated by
the insertion of the plug, acts to open this test circuit and at the
same time complete the tip side of the cord circuit.

In the upper portion of Fig. 371 the order-wire connections, by which
the _A_-operator and the _B_-operator communicate, are indicated. It
must be remembered in connection with these that the _A_-operator only
has control of this connection, the _B_-operator being compelled
necessarily to hear whatever the _A_-operators have to say when the
_A_-operators come in on the circuit.

[Illustration: Fig. 372. Incoming Trunk Circuit]

The incoming trunk circuit employed by the Western Electric Company for
four-party line ringing is shown in Fig. 372, it being necessarily
somewhat modified from that shown in Fig. 371, which is adapted for
two-party line ringing only. In addition to the provision of the
four-party line ringing keys, by which positive or negative pulsating
current is received over either limb of the line, and to the provision
of the regular alternating current ringing key for ringing on single
party lines, it is necessary in the ringing cut-off relay to provide for
keeping the alternating and the pulsating ringing currents entirely
separate. For this reason, the ringing