ceiver from its hook who is enabled to
successfully establish a connection with the line, all subsequent
efforts, by other subscribers, failing to do so because of the fact
that the line is short-circuited by the path through the
low-resistance winding and the transmitter of the station that is
already connected with the line.

A little target is moved by the action of the relay so that a visual
indication is given to the subscriber in making a call to show whether
or not he is successful in getting the use of the line. If the relay
operates and he secures control of the line, the target indicates the
fact by its movement, while if someone else is using the line and the
relay does not operate, the target, by its failure to move, indicates
that fact.

When one party desires to converse with another on the same line, he
depresses the button _3_ at his station until after the called party
has been rung and has responded. This holds the circuit of his
low-resistance winding open, and thus prevents the lock-out from
becoming effective until the called party is connected with the line.
The relay armature of the calling party does not fall back with the
establishment of the low-resistance path at the called station,
because, even though shunted, it still receives sufficient current to
hold its armature in its attracted position. After the called party
has responded, the button at the calling station is released and both
low-resistance holding coils act in multiple.

[Illustration: ONE WING OF OPERATING ROOM, BERLIN, GERMANY Ultimate
Capacity 24,000 Subscribers' Lines and 2,100 Trunk Lines.
Siemens-Halske Equipment. Note Horizontal Disposal of Multiple Jack
Field.]

No induction coil is used in this system and the impedance of the
holding coil is such that incoming voice currents flow through the
condenser and the receiver, which, by reference to the figure, will be
seen to be in shunt with the holding coil. The holding coil is in
series with the local transmitter, thus making a circuit similar to
that of the Kellogg common-battery talking circuit already discussed.

A possible defect in the use of this system is one that has been common
to a great many other lock-out systems, depending for their operation
on the same general plan of action. This appears when the instruments
are used on a comparatively long line. Since the locking-out of all the
instruments that are not in use by the one that is in use depends on
the low