, as indicated, is normally open, but the automatic cut-in switch
of the generator serves, when the generator is operated, to close its
path across the line, so that it may send its currents to the line and
ring the bells of all the stations.

When any generator is operated, its current divides and passes over
the line wires and through all of the ringers in multiple. It is seen,
therefore, that the requirements for a bridging generator are that it
shall be capable of generating a large current, sufficient when
divided up amongst all the bells to ring each of them; and that it
shall be capable of producing a sufficient voltage to send the
required current not only to the near-by stations, but to the stations
at the distant end of the line.

It might seem at first that the bridging system avoided one difficulty
only to encounter another. It clearly avoids the difficulty of the
series system in that the voice currents, in order to reach distant
stations, do not have to pass through all of the bells of the idle
stations in series. There is, however, presented at each station a
leakage path through the bell bridged across the line, through which
it would appear the voice currents might leak uselessly from one side
of the line to the other and not pass on in sufficient volume to the
distant station. This difficulty is, however, more apparent than real.
It is found that, by making the ringers of high impedance, the leakage
of voice currents through them from one side of the line to the other
is practically negligible.

It is obvious that in a heavily loaded bridged line, the bell at the
home station, that is at the station from which the call is being sent,
will take slightly more than its share of the current, and it is also
obvious that the ringing of the home bell performs no useful function.
The plan is frequently adopted, therefore, of having the operation of
the generator serve to cut its own bell out of the circuit. The
arrangement by which this is done is clearly shown in Fig. 169. The
circuit of the bell is normally complete across the line, while the
circuit of the generator is normally open. When, however, the generator
crank is turned these conditions are reversed, the bell circuit being
broken and the generator circuit closed, so as to allow its current all
to pass the line. This feature of having the local bell remain silent
upon the operation of its own generator is also of advantage because
other parties at