ter dial and holding the ringing key closed, therefore, not
only sends the stepping impulses to line, but also follows it by the
ringing current. The sending of five impulses to line moves all of the
sectors to the sixth notch, and this corresponds to the position
necessary to make the fourth station operative. Such a condition is
shown in Fig. 193, it being assumed that the subscriber at Station C
originated the call and pressed his own button so as to prevent his
sector from being moved out of its normal position. As a result of
this, the talking circuit at Station C is left closed, and the talking
and the ringing circuit of Station D, the called station, are closed,
while both the talking and the ringing circuits of all the other
stations are left open. Station D may, therefore, be rung and may
communicate with Station C, while all of the other stations on the
line are locked out, because of the fact that both their talking and
ringing circuits are left open.

[Illustration: Fig. 193. Circuit K.B. System]

When conversation is ended, the operator is notified by the usual
clearing-out signal, and she then depresses the release button, which
brings the springs _9_ out of engagement with the generator contact
but into engagement with the battery contact in such relation as to
send a battery current on the line in the reverse direction from that
sent out by the impulse wheel. This sends current through all of the
relays in such direction as to withdraw both the moving and the
holding pawls from the segments and thus allow all of the segments to
return to their normal positions. Of course, in thus establishing the
release current, it is necessary for the operator to depress the
ringing key as well as the release key.

A one-half microfarad condenser is placed in the receiver circuit at
each station so that the line will not be tied up should some
subscriber inadvertently leave his receiver off its hook. This permits
the passage of voice currents, but not of the direct currents used in
stepping the relays or in releasing them.

The circuit of Fig. 193 is somewhat simplified from that in actual
practice, and it should be remembered that the hook switch, which is
not shown in this figure, controls in the usual way the continuity of
the receiver and the transmitter circuits as well as of the generator
circuits, the generator being attached to the line as in an ordinary
telephone.

Broken-Line System. The broken-line met