which trunk to use and the attendant
operator hangs up her receiver, no further attention being necessary on
her part.

The trunk-holding relay is automatically released when the desired party
(with the telephone receiver off the hook) depresses the proper trunk
button, thus clearing the trunk line of all bridged apparatus and making
the talking circuit the same as in the regular type of private
branch-exchange switchboard.

The most convenient way of installing the wires of an intercommunicating
system is to run a cable containing the proper number of pairs to
provide for the ultimate number of stations to all the stations, tapping
off from the conductors in the cable to the jacks or push buttons at
each station. These tap connections are best made by means of junction
boxes which contain terminals for all the conductors.

Such a junction box, with the through cable and the tap cable in place,
is illustrated in Fig. 450. A schematic lay-out of the various parts of
a Dean intercommunicating system, provided with an attendant's station
and with trunks to a city office, is given in Fig. 451.

CHAPTER XXXVI

LONG-DISTANCE SWITCHING

=Definitions.= Telephone messages between communities are called
long-distance messages. They are also called toll messages. Almost all
long-distance traffic is handled by message-rate (measured-service)
methods of charge. All measured-service messages are toll messages,
whether they are completed within a given community or between
communities. The term "long-distance," therefore, is more descriptive
than the term "toll." The subject of local and long-distance measured
service is treated exhaustively in a chapter of its own.

Some telephone-exchange operating companies call their own inter-city
business "toll," and use the term "long-distance" for business carried
between exchanges for them by another company. The distinction seems to
be unwarranted.

=Use of Repeating Coil.= Most long-distance lines are magneto circuits.
If they are switched to grounded circuits, repeating coils need to be
inserted. Toll switching equipments contain means of inserting repeating
coils in the connecting cords when required. Their use reduces the
volume of transmitted speech, but often is essential even in connecting
metallic circuit lines, as a quiet local metallic circuit may have a
ground upon it which will cause excessive noises when a quiet
long-distance line is connected to it.

=Switc