amiliar
transmitter, receiver, and hook switch, and in the wall set, the call
bell. The portion of these telephone sets which is unfamiliar at present
is the part which is enclosed in the enlarged base of the desk stand and
the protruding device below the speech transmitter in the wall set--the
signal transmitter referred to earlier in the chapter. The small push
button and small plate through which the number may be seen directly
below the transmitter in Fig. 402, are for the purpose of registering
calls.

[Illustration: Fig. 401. Lorimer Automatic Desk Stand]

The signal transmitter is a device whose function is to record
mechanically the number of the subscriber's station with which
connection is desired, and to transmit that record to the central office
by a system of electrical impulses over the line conductors. Instead of
operating by its own initiative, the signal transmitter is adapted to
respond to central-office control in transmitting electrically the
number which has been recorded mechanically upon it.

The signal transmitter shown removed from the base of the desk stand at
the left in Fig. 403 comprises in part four sets of contact pins having
ten pins in each set, one set for each of the digits of a four-digit
number. There are also several additional contact pins for signaling and
auxiliary controlling purposes. All of these contact pins are arranged
upon the circumference of a circle and a movable brush mounted upon a
shaft at the center of the circle is adapted to be rotated by a clock
spring and to make contact with each of the pins successively. The call
is started, after the number desired has been set on the dial, by giving
the crank at the right of the signal transmitter a complete turn and
thus winding the spring. The shaft carrying the signal transmitter brush
carries also an escapement wheel, the pallet of which is directly
controlled by an electromagnet.

[Illustration: Fig. 402. Lorimer Automatic Wall Set]

The four dials with the numerals printed on them are attached to four
levers, respectively, and are moved by their levers opposite windows,
near the top of the casing. Through each of these windows a single
numeral may be seen on the corresponding one of the dials. The dials may
be adjusted so that the four numerals seen will read from left to right
to correspond to the number of the line with which connection is
desired.

The setting of the dials so that the number desired shows at