all of the apparatus there.

For the purpose of convenience the simplified diagram of Fig. 398 has
been prepared, which shows the complete connection from a calling
subscriber to a called subscriber in a multi-office exchange, wherein
the first movement of the dial is employed to establish the connection
to the proper office and the four succeeding movements to make a
selection among ten thousand lines in that office. This circuit,
therefore, employs at the first office the line switch, the first
selector, and the trunk repeater; and at the second office the second
selector, third selector, connector, and line switch.

The third selector is omitted from Fig. 398, but this will cause no
confusion, since it is exactly like the second selector. The circuits
shown are exactly like those previously described but in drawing them
the main idea has been to simplify the connections to the greatest
possible extent at a sacrifice in the clearness with which the
mechanical inter-relation of parts is shown. No correct understanding of
the circuits of an automatic system is possible without a clear idea of
the mechanical functions performed by the different parts, and,
therefore, we have described what are apparently the more complex
circuit drawings first. It is believed that the student, in attempting
to gain an understanding of this marvel of mechanical and electrical
intricacy, will find his task less burdensome if he will refer freely to
both the simplified circuit drawing of Fig. 398 and the more complex
ones preceding it. By doing so he will often be enabled to clear up a
doubtful circuit point from the simpler diagram and a doubtful
mechanical point from those diagrams which represent more clearly the
mechanical relation of parts.

[Illustration: Fig. 398. Connection between a Calling and a Called
Subscriber in an Automatic System]

=Automatic Sub-Offices.= Obviously, the system of trunking employed in
automatic exchanges lends itself with great facility to the subdivision
of an exchange into a large number of comparatively small office
districts and the establishment of branch offices or sub-offices at the
centers of these districts.

The trunking between large offices has already been described. An
attractive feature of the automatic system is the establishment of
so-called sub-stations or sub-offices. Where there is, in an outlying
district, a distinct group of subscribers whose lines may readily be
centered at a co