be
operated whenever the plug is withdrawn from or replaced in its seat.
The operation of this arrangement is as follows: Whenever an operator at
the right-hand end of this trunk receives a call for a subscriber whose
line terminates within the reach of the operator at the left-hand end of
the trunk, she inserts the calling plug of the pair used in answering
the calling subscriber into the jack of the trunk, and thus lights both
of the trunk lamps. The operator at the other end of the trunk, seeing
the trunk lamp lighted, raises the plug from its seat and, having
learned the wishes of the calling subscriber, inserts this plug into the
jack of the called subscriber without using one of her regular pairs.
When she raised the trunk plug from its seat, she permitted the long
spring _1_ of the plug seat switch to rise, thus extinguishing both
lamps and giving the signal to the originating operator that the trunk
connection has received attention. On taking down the connection, the
withdrawal of the plug from the right hand of the trunk lights both
lamps, and the restoring of the trunk plug to its normal seat again
extinguishes both lamps.

=Plug-Seat Switch.= The plug-seat switch is a device that has received a
good deal of attention not only for use with transfer systems, but also
for use in a great variety of ways with other kinds of manual switching
systems. The placing of a plug in its seat or withdrawing it therefrom
offers a ready means of accomplishing some switching or signaling
operation automatically. The plug-seat switch has, however, in spite of
its possibilities, never come into wide use, and so far as we are aware
the Monarch Telephone Manufacturing Company is the only company of
prominence which incorporates it in its regular output. The Monarch
plug-switch mechanism is shown in Fig. 333, and its operation is
obvious. It may be stated at this point that one of the reasons why the
plug-seat switch has not been more widely adopted for use, is the
difficulty that has been experienced due to lint from the switchboard
cords collecting on or about the contact points. In the construction
given in the detailed cut, upper part, Fig. 333, is shown the means
adopted by the Monarch Company for obviating this difficulty. The
contact points are carried in the upper portion of an inverted cup
mounted on the under side of the switchboard shelf, and are thus
protected, in large measure, from the damaging influence of dust and