mes for their use, leaves only the simple thrusting motion of the
plunger to accomplish the desired connection immediately upon the
initiation of a call by the subscriber.

_Locking Segment._ It will be understood that the locking segment _18_
and the master-switch contact finger _10_ are both rigidly connected
with the master bar _8_ and move with it, the locking segment _18_
serving always to determine accurately the angular position at which the
master bar and the master-switch arm are brought to rest.

_Bridge Cut-Off._ One important feature of automatic switching,
particularly as exemplified in the system of the Automatic Electric
Company, is the disconnection, after its use, of each operating magnet
of each piece of apparatus involved in making a connection. Since these
operating magnets are always bridged across the line at the time of
their operation and then cut off after they have performed their
function, this feature may be referred to as the _bridge cut-off_.

_Guarding Functions._ Still another feature of importance is the means
for guarding a line or a piece of apparatus that has already been
appropriated or made busy, so that it will not be appropriated or
connected with for use in some other connection. For this latter purpose
contacts and wires are associated with each piece of apparatus, which
are multipled to similar contacts on other pieces of apparatus in much
the same way and for a similar purpose that the test thimbles in a
multiple switchboard are multipled together. Such wires and contacts in
the Automatic Electric Company's apparatus are called _private wires_
and _contacts_.

The bridge cut-off and guarding functions are provided for in the line
switch by a bridge cut-off relay shown in Fig. 389 and also in Fig. 385,
it being the upper one of the individual line relays in each of those
figures. This bridge cut-off relay is operated as soon as the plunger of
the line is thrust into the bank; the contacts _19_ and _20_, closed by
the plunger, serving to complete the circuit of this relay. To make
clear the bridge cut-off feature it will be noted that the trip magnet
of a line switch is connected in a circuit traced from the rotary side
of the line through the contacts _21_ and _22_ of the bridge cut-off
relay, thence through the coil of the trip magnet to the common wire
leading to the spring _23_ of the master-bar locking device and thence
to the live side of the battery. Obviously, therefo