ar will not have occupied
a position which would make it possible for any of the lines to
appropriate this trunk during the intervening time.

_Master Switch._ Associated with each master bar there is a master
switch which determines the position in which the master bar shall stop
in order that the idle plungers may be pointed always to the contacts of
an idle trunk. The arm _10_ of this switch is attached to the master bar
and oscillates with it and serves to connect the segment _11_
successively with the contacts _12_, which are connected respectively to
the third, or release wire of each first selector trunk. In the figure
the arm _10_ is shown resting on the sixth contact of the switch and
this sixth contact is connected to a spring _13_ in the line-switch
contact bank that has not yet been referred to. As soon as the plunger
is inserted into the contact bank, the spring _14_ will be pressed into
engagement with the spring _13_, and this spring _14_ is connected with
the live side of the battery through the release magnet winding.

The contact strip _11_ on the master switch is thus connected through
the release magnet to the battery and from this current flows through
the left-hand winding of the master-switch relay. This energizes this
relay and causes the closure of the circuit of the locking magnet which
magnet unlocks the master bar to permit its further rotation. The
unlocking of the master bar brings the spring _15_ into engagement with
_16_ and thus energizes the master magnet, the armature of which
vibrates back and forth after the manner of an electric-bell armature,
and steps the wheel _17_ around. The wheel _17_ is mechanically
connected to the master bar so that each complete revolution of the
wheel will cause one complete oscillation of the master bar. The master
bar will thus be moved so as to cause all the idle plungers to sweep
through an arc and this movement will stop as soon as the master-switch
arm _10_ connects the arc _11_ with one of the contacts _12_ that is not
connected to the live side of the battery through the springs _13_ and
_14_ of some other line switch. It is by this means that the plungers of
the line switches are always kept pointing at the contacts of an idle
trunk. The way in which this feature has been worked out must demand
admiration and accounts for the marvelous quickness of this line switch.
The fact that the plungers are pointed in the right direction before the
time co