shown at the bottom of the dial in Fig. 192. The dial is then
allowed to return by the action of a spring to its normal position,
and in doing so it operates a switch within the box to make and break
the battery circuit the proper number of times.

_Operation._ A complete description of the operation may now be had in
connection with Fig. 193, which is similar to Fig. 189, but contains
the details of the calling arrangement at the central office and also
of the talking circuits at the various subscribers' stations.

[Illustration: Fig. 191. K.B. Lock-Out Station]

Referring to the central-office apparatus the usual ringing key is
shown, the inside contacts of which lead to the listening key and to
the operator's telephone set as in ordinary switchboard practice.
Between the outside contact of this ringing key and the ringing
generator there is interposed a pair of contact springs _8-8_ and
another pair _9-9_. The contact springs _8_ are adapted to be moved
backward and forward by the impulse wheel which is directly controlled
by the dial under the manipulation of the operator. When these springs
_8_ are in their normal position, the ringing circuit is continued
through the release-key springs _9_ to the ringing generator. These
springs _8_ occupy their normal position only when the dial is in its
normal position, this being due to the notch _10_ in the contact wheel.
At all other times, _i.e._, while the impulse wheel is out of its
normal position, the springs _8-8_ are either depressed so as to engage
the lower battery contacts, or else held in an intermediate position so
as to engage neither the battery contacts nor the generator contacts.

[Illustration: Fig. 192. Calling Apparatus K.B. System]

When it is desired to call a given station, the operator pulls the
subscriber's number on the dial and holds the ringing key closed,
allowing the dial to return to normal. This connects the impulse
battery to the subscriber's line as many times as is required to move
the subscriber's sectors to the proper position, and in such direction
as to cause the stepping movement of the various relays. As the
impulse wheel comes to its normal position, the springs _8_,
associated with it, again engage their upper contacts, by virtue of
the notch _10_ in the impulse wheel, and this establishes the
connection between the ringing generator and the subscriber's line,
the ringing key being still held closed. The pulling of the
transmit