h thus flow
through the rotary magnet occur at a frequency dependent upon the
battery interrupter and this is at a rate of approximately fifteen
impulses per second. The rotary magnet will step the selector shaft
rapidly around until something occurs to stop these impulses. This
something is the finding by the private wiper of an ungrounded private
contact in the bank, since all of the contacts corresponding to busy
trunks are grounded, as will be explained.

The action of the private magnet enters into this operation in the
following way: A circuit may be traced from the battery through the
private magnet to the third side switch wiper when in its second
position, thence through the back release relay to the private wiper. If
the wiper is at the time on the private bank contact of a busy trunk, it
will find that contact grounded and the private magnet will be
energized. The energizing of this magnet will not, however, cause the
release of the side switch. It must be energized and de-energized. The
private magnet armature will, therefore, be operated by the finger of
the rotary magnet armature on the first rotary step. The private magnet
will be energized and hold its armature operated if the private wiper
finds a ground on the first bank contact and will stay energized as long
as the private wiper is passing over private contacts of busy trunks.
Its armature will not be allowed to fall back during the passage of the
wiper from one trunk to another, because during that interval the finger
of the rotary magnet will hold it operated. As soon, however, as the
private wiper reaches the private bank contact of an idle trunk, no
ground will be found and the circuit of the private magnet will be left
open. When the impulse through the rotary magnet ceases, the private
magnet armature will fall back and the side switch will be released to
its third position.

_Third Position of Side Switch._ The first thing to be noted in this
position is that the calling line is cut straight through to the second
selector trunk, the connection being clean with no magnets bridged
across or tapped off. The third wiper of the side switch, when in its
third position, is grounded and this connects the release wire of the
second selector trunk, on which the switch wipers rest, through the
private wiper, the winding of the back release magnet, and the third
wiper of the side switch to ground. This establishes a path for the
subsequent release curre