being shunted
across the two sides of the cord circuit. With this circuit a positive
ring-off is assured even though the line connected with the one
sending the clearing-out signal is short-circuited or open. If it is
short-circuited, the shunt around the clearing-out drop will still
have the resistance of two of the non-inductive windings included in
it, and thus the drop will never be short-circuited by a very
low-resistance path. Obviously, an open circuit in the line will not
prevent the clearing-out signal being received. While this is an
ingenious scheme, it is not one to be highly recommended since the
non-inductive windings, in order to be effective so far as signaling
is concerned, must be of considerable resistance and this resistance
is in series in the talking circuit. Even non-inductive resistance is
to be avoided in the talking circuit when it is of considerable
magnitude and where there are other ways of solving the problem.

[Illustration: Fig. 286. Cord Circuit with Differential Windings]

_Double Clearing-out Type. _Some people prefer two clearing-out drops
in each cord circuit, so arranged that the one will be responsive to
currents sent from the line with which the answering plug is connected
and the other responsive only to currents sent from the line with
which the calling plug is connected. Such a scheme, shown in Fig. 287,
is sometimes employed by the Dean, the Monarch, and the Kellogg
companies. Two 500-ohm clearing-out drops of ordinary construction are
bridged across the cord circuit and in each side of the cord circuit
there is included between the drop connections a 1-microfarad
condenser. Ringing currents originating on the line with which the
answering plug is connected will pass through the clearing-out drop,
which is across that side of the cord circuit, without having to pass
through any condensers. In order to reach the other clearing-out drop
the ringing current must pass through the two 1-microfarad condensers
in series, this making in effect only 1/2-microfarad. As is well
known, a 1/2-microfarad condenser not only transmits voice currents
with ease but also offers a very high apparent resistance to ringing
currents. With the double clearing-out drop system the operator is
enabled to tell which subscriber is ringing off. If both shutters fall
she knows that both subscribers have sent clearing-out signals and
she, therefore, pulls down the connection without the usual precaution
of