ents. This defect in the series party line is
fundamental, as it is obvious that the ringers must be left in the
circuit of the stations which are not in use, in order that those
stations may always be in such condition as to be able to receive a
call.

This defect may in some measure be reduced by making the ringers of
low impedance. This is the general practice with series telephones,
the ringers ordinarily having short cores and a comparatively small
number of turns, the resistance being as a rule about 80 ohms.

Bridging Systems. Very much better than the series plan of
party-line connections, is the arrangement by which the instruments
are placed in bridges across the line, such lines being commonly known
as bridged or bridging lines. This was first strongly advocated and
put into wide practical use by J.J. Carty, now the Chief Engineer of
the American Telephone and Telegraph Company.

A simple illustration of a bridging telephone line is shown in Fig.
166, where the three telephones shown are each connected in a bridge
path from the line wire to ground, a type known as a "grounded
bridging line." Its use is very common in rural districts.

A better arrangement is shown in Fig. 167, which represents a
metallic-circuit bridging line, three telephone instruments being
shown in parallel or bridge paths across the two line wires.

The actual circuit arrangements of a bridging party line are better
shown in Fig. 168. There are three stations and it will be seen that
at each station there are three possible bridges, or bridge paths,
across the two limbs of the line. The first of these bridges is
controlled by the hook switch and is normally open. When the hook is
raised, however, this path is closed through the receiver and
secondary of the induction coil, the primary circuit being also closed
so as to include the battery and transmitter. This constitutes an
ordinary local-battery talking set.

[Illustration: Fig. 166. Grounded Bridging Line]

[Illustration: Fig. 167. Metallic Bridging Line]

[Illustration: Fig. 168. Metallic Bridging Line]

A second bridge at each station is led through the ringer or
call-bell, and this, in most bridging telephones, is permanently
closed, the continuity of this path between the two limbs of the line
not being affected either by the hook switch or by the automatic
switch in connection with the generator.

A third bridge path at each station is led through the generator.
This