few subscribers, is prohibitive.

Non-selective telephone party lines most often employ magneto
telephones. The early forms of party lines employed the ordinary
series magneto telephone, the bells being of low resistance and
comparatively low impedance, while the generators were provided with
automatic shunting devices, so that their resistance would normally be
removed from the circuit of the line.

Series Systems. The general arrangement of a series party line
employing a ground return is shown in Fig. 163. In this three ordinary
series instruments are connected together in series, the end stations
being grounded, in order to afford a return path for the ringing and
voice currents.

[Illustration: Fig. 164. Metallic-Circuit Series Line]

In Fig. 164 there is shown a metallic-circuit series line on which
five ordinary series telephones are placed in series. In this no
ground is employed, the return being through a line wire, thus making
the circuit entirely metallic.

[Illustration: Fig. 165. Series Party Line]

The limitations of the ordinary series party line may be best
understood by reference to Fig. 165, in which the circuits of three
series telephones are shown connected with a single line. The receiver
of Station A is represented as being on its hook, while the receivers
of Stations B and C are removed from their hooks, as when the
subscribers at those two stations are carrying on a conversation. The
hook switches of Stations B and C being in raised positions, the
generators and ringers of those stations are cut out of the circuit,
and only the telephone apparatus proper is included, but the hook
switch of Station A being depressed by the weight of its receiver,
includes the ringer of that station in circuit, and through this
ringer, therefore, the voice currents of Stations B and C must pass.

The generator of Station A is not in the circuit of voice currents,
however, because of the automatic shunt with which the generator is
provided, as described in Chapter VIII.

A slight consideration of the series system as shown in this figure,
indicates that the voice currents of any two stations that are in use,
must pass (as indicated by the heavy lines) through the ringers of all
the stations that are not in use; and when a great number of stations
are placed upon a single line, as has been frequently the case, the
impedance offered by these ringers becomes a serious barrier to the
passage of the voice curr