tations, _all of which may be
required to listen upon the line at the same time_.

It will be seen from this that the telephone dispatching circuit
partakes somewhat of the nature of a long-distance commercial circuit in
its length, and it also resembles a rural line in that it has a large
number of telephones upon it. Regarding three other characteristics,
namely, that many of these stations may be required to be in on the
circuit simultaneously, that they must all be signaled selectively, and
that it must also be possible to talk and signal on the circuit
simultaneously, a telephone train-dispatching circuit resembles nothing
in the commercial field. These requirements are the ones which have
necessitated the development of special equipment.

=Transmitting Orders.= The method of giving orders is the same as that
followed with the telegraph, with one important exception. When the
dispatcher transmits a train order by telephone, he writes out the order
as he speaks it into his transmitter. In this way the speed at which the
order is given is regulated so that everyone receiving it can easily get
it all down, and a copy of the transmitted order is retained by the
dispatcher. All figures and proper names are spelled out. Then after an
order has been given, it is repeated to the dispatcher by each man
receiving it, and he underlines each word as it comes in. This is now
done so rapidly that a man can repeat an order more quickly than the
dispatcher can underline. The doubt as to the accuracy with which it is
possible to transmit information by telephone has been dispelled by this
method of procedure, and the safety of telephone dispatching has been
fully established.

=Apparatus.= The apparatus which is employed at waystations may be
divided into two groups--the selector equipment and the telephone
equipment. The selector is an electro-mechanical device for ringing a
bell at a waystation when the dispatcher operates a key corresponding to
that station. At first, as in telegraphy, the selector magnets were
connected in series in the line, but today all systems bridge the
selectors across the telephone circuit in the same way and for the same
reasons that it is done in bridging party-line work. There are at the
present time three types of selectors in general use, and the mileage
operated by means of these is probably considerably over 95 per cent of
the total mileage so operated in the country.

[Illustration: Fig. 475