the same station are not disturbed by the ringing of
the bell when a call is being made by that station.

A difficulty encountered on non-selective bridging party lines, which
at first seems amusing rather than serious, but which nevertheless is
often a vexatious trouble, is that due to the propensity of some
people to "listen in" on the line on hearing calls intended for other
than their own stations. People whose ethical standards would not
permit them to listen at, or peep through, a keyhole, often engage in
this telephonic eavesdropping.

Frequently, not only one but many subscribers will respond to a call
intended for others and will listen to the ensuing conversation. This
is disadvantageous in several respects: It destroys the privacy of
conversation between any two parties; it subjects the local batteries
to an unnecessary and useless drain; and it greatly impairs the
ringing efficiency of the line. The reason for this interference with
ringing is that the presence of the low-resistance receivers across
the line allows the current sent out by any of the generators to pass
in large measure through the receivers, thus depriving the ringers,
which are of comparatively high resistance and impedance, of the
energy necessary to operate them. As a result of this it is frequently
impossible for one party to repeat the call for another because,
during the interval between the first and second call, a number of
parties remove their receivers from their hooks in order to listen.
Ring-off or clearing-out signals are likewise interfered with.

[Illustration: Fig. 169. Circuits of Bridging Station]

A partial remedy for this interference with ringing, due to
eavesdropping, is to introduce a low-capacity condenser into the
receiver circuit at each station, as shown in Fig. 169. This does not
seriously interfere with the speech transmission since the condensers
will readily transmit the high-frequency voice currents. Such
condensers, however, have not sufficient capacity to enable them
readily to transmit the low-frequency ringing currents and hence
these are forced, in large measure, to pass through the bells for
which they are intended rather than leaking through the low-resistance
receiver paths.

The best condenser for this use is of about 1/2-microfarad capacity,
which is ample for voice-transmitting purposes, while it serves to
effectively bar the major portion of the generator currents. A higher
capacity condenser