is not
encumbered by any bridge circuits at any of the instruments that are
not engaged in the conversation. Furthermore, in the selecting of a
subscriber or the ringing of his bell there is no splitting up of
current among the magnets at the various stations as in ordinary
practice, but the operating current goes straight to the station
desired and to that station alone where its entire strength is
available for performing its proper work.

In order to make the system clear it may be stated at the outset that
one side of the metallic circuit line is continued as in ordinary
practice, passing through all of the stations as a continuous
conductor. The other side of the line, however, is divided into
sections, its continuity being broken at each of the subscriber's
stations. Fig. 186 is intended to show in the simplest possible way
how the circuit of the line may be extended from station to station in
such manner that only the ringer of one station is in circuit at a
time. The two sides of the line are shown in this figure, and it will
be seen that limb _L_ extends from the central office on the left to
the last station on the right without a break. The limb _R_, however,
extends to the first station, at which point it is cut off from the
extension _R_{x}_ by the open contacts of a switch. For the purpose of
simplicity this switch is shown as an ordinary hand switch, but as a
matter of fact it is a part of a relay, the operating coil of which is
shown at _6_, just above it, in series with the ringer.

[Illustration: Fig. 186. Principle of Broken-Line System]

Obviously, if a proper ringing current is sent over the metallic
circuit from the central office, only the bell at Station A will
operate, since the bells at the other stations are not in the circuit.
If by any means the switch lever _2_ at Station A were moved out of
engagement with contact _1_ and into engagement with contact _3_, it
is obvious that the bell of Station A would no longer be in circuit,
but the limb _R_ of the line would be continued to the extension
_R_{x}_ and the bell of Station B would be in circuit. Any current
then sent over the circuit of the line from the central office would
ring the bell of this station. In Fig. 187 the switches of both
Station A and Station B have been thus operated, and Station C is thus
placed in circuit. Inspection of this figure will show that the bells
of Station A, Station B, and Station D are all cut out of circu