he dial being moved from its normal position until the
hook is in its raised position. This interlocking function involves also
the pivoted dog _4_. Normally the lower end of this dog lies in the path
of the pin _5_ carried on the lever _2_, and thus the shaft, dial, and
segment are prevented from any considerable movement when the receiver
is on the hook. However, when the receiver is removed from its hook, the
upwardly projecting arm from the hook engages a projection on the dog
_4_ and moves the dog out of the path of the pin _5_. Thus the dial is
free to be rotated by the subscriber. The pin _6_ is mounted in a
stationary position and serves to limit the backward movement of the
dial by the lever _2_ striking against it.

Ground Springs:--Five groups of contact springs must be considered, some
of which are controlled wholly by the position of the switch hook,
others jointly by the position of the switch hook and the dial, others
by the movement of the dial itself, and still others by the pressure of
the subscriber's finger on a button. The first of these groups consists
of the springs _7_ and _8_, the function of which is to control the
continuity of the ground connection at the subscriber's station. The
arrangement of these two springs is such that the ground connection will
be broken until the subscriber's receiver is removed from its hook. As
soon as the receiver is raised, these springs come together in an
obvious manner, the dog _4_ being lifted out of the way by the action of
the hook. The ledge on the lower portion of the spring _7_ serves as a
rest for the insulated arm of the dog _4_ to prevent this dog, which is
spring actuated, from returning and locking the dial until after the
receiver has been hung up.

Bell and Transmitter Springs:--The second group is that embracing the
springs _9_, _10_, _11_, and _12_. The springs _10_ and _11_ are
controlled by the lower projection from the switch hook, the spring
_11_ engaging the spring _12_ only when the hook is down. The spring
_10_ engages the spring _9_ only when the hook lever is up and not then
unless the dial is in its normal position. While the hook is raised,
therefore, the springs _9_ and _10_ break contact whenever the dial is
moved and make contact again when it returns to its normal position. The
springs _11_ and _12_ control the circuit through the subscriber's bell
while the springs _9_ and _10_ control the continuity of the circuit
from one side