he condenser results in a click in the operator's ear.

[Illustration: Fig. 355. Dean Party Line Ringing Key]

[Illustration: Fig. 356. Dean Party Line Ringing Key]

=Stromberg-Carlson Multiple Board.= _Line Circuit._ In Fig. 357 is shown
the multiple common-battery switchboard circuits employed by the
Stromberg-Carlson Telephone Manufacturing Company. The subscriber's line
circuits shown in this drawing are of the three-wire type and, with the
exception of the subscriber's station, are the same as already described
for the Western Electric Company's system.

_Cord Circuit._ The cord circuit employed is of the two-conductor type,
the plugs being so constructed as to connect the ring and thimble
contacts of the jack when inserted. This cord circuit is somewhat
similar to that employed by the Kellogg Switchboard and Supply Company,
shown in Fig. 352, except that only one battery is employed, and that
certain functions of this circuit are performed mechanically by the
inter-action of the armatures of the relays.

_Supervisory Signals._ When the answering plug is inserted in a jack, in
response to a call, the current passing to the subscriber's station and
also through the cut-off relay must flow through the relay _1_, thus
energizing it. As the calling subscriber's receiver is at this time
removed from the hook switch, the path for current will be completed
through the tip of the jack, thence through the tip of the plug, through
relay _2_ to ground, causing relay _2_ to be operated and to break the
circuit of the answering supervisory lamp. The two relays _1_ and _2_
are so associated mechanically that the armature of _1_ controls the
armature of _2_ in such a manner as to normally hold the circuit of the
answering supervisory lamp open. But, however, when the plug is inserted
in a jack, relay _1_ is operated and allows the operation of relay _2_
to be controlled by the hook switch at the subscriber's station. The
supervisory relay _3_ associated with the calling cord is operated when
the calling plug is placed in a jack, and this relay normally holds the
armature of relay _4_ in an operated position in a similar manner as the
armature of relay _1_ controlled that of relay _2_. Supervisory relay
_4_ is under the control of the hook switch at the called subscriber's
station.

_Test._ In this circuit, as in several previously described, when a plug
is inserted in a jack of a line, the thimble contacts of the jacks
asso