e telephone and back to
it quickly. The Western Electric telephone arm developed for this use is
shown in Fig. 483. In this the transmitter and the receiver are so
disposed as to conform approximately to the shape of the operator's
head. When the arm is thrown back out of the way it opens the
transmitter circuit by means of a commutator in its base.

[Illustration: Fig. 483. Telephone Arm]

_Siding Telephones._ Two types of sets are employed for siding
purposes. The first is an ordinary magneto wall instrument, which
embodies the special apparatus and circuit features employed in the
standard waystation sets. These are used only where it is possible to
locate them indoors or in booths along the line. These sets are
permanently connected to the train wire, and since the chances are small
that more than one of them will be in use at a time, they are rung by
the dispatcher, by means of a regular hand generator, when it is
necessary for him to signal a switching.

[Illustration: Fig. 484. Weather-Proof Telephone Set]

In certain cases it is not feasible to locate these siding telephone
sets indoors, and to meet these conditions an iron weather-proof set is
employed, as shown in Figs. 484 and 485. The apparatus in this set is
treated with a moisture-proofing compound, and the casing itself is
impervious to weather conditions.

[Illustration: Fig. 485. Weather-Proof Telephone Set]

_Portable Train Sets._ Portable telephone sets are being carried
regularly on wrecking trains and their use is coming into more and more
general acceptance on freight and passenger trains. Fig. 486 shows one
of these sets equipped with a five-bar generator for calling the
dispatcher. Fig. 487 shows a small set without generator for conductors'
and inspectors' use on lines where the dispatcher is at all times
connected in the circuit.

[Illustration: Fig. 486. Portable Telephone Set]

[Illustration: Fig. 487. Portable Telephone Set]

These sets are connected to the telephone circuit at any point on the
line by means of a light portable pole arranged with terminals at its
outer extremity for hooking over the line wires, and with flexible
conducting cords leading to the portable set. The use of these sets
among officials on their private cars, among construction and bridge
gangs working on the line, and among telephone inspectors and repairmen
for reporting trouble, is becoming more and more general.

=Western Electric Circuits.= As alread