ishes such a connection as will place the ringing relay under the
control of the vertical relay. This may be seen by tracing from ground
to the vertical relay springs _23_ and _24_, thence through the normally
closed upper pair of contacts on the private magnet, thence through the
fourth wiper on the side switch to its third contact, thence through the
ringing relay magnet, and through the springs _16_ and _17_ of the
calling battery supply relay and to battery. The calling battery supply
relay winding being in series with the vertical relay winding, the two
operate together and close the two normally open points in the ringing
relay circuit. This ringing relay acts as an ordinary ringing key and
connects the generator to the called subscriber's line in an obvious
manner, at the same time opening the talking circuit back of the ringing
relay in order to prevent the ringing current chattering the relays in
the circuit back of it. All that remains now is for the called
subscriber to respond. When he does he closes the metallic circuit of
the line through his talking apparatus.

_Battery Supply to Connected Subscriber._ Throughout the whole process
of building up a connection, it will be remembered that both sides of
the calling line are connected through the respective vertical and
rotary relays involved in building up the connection with the live side
of the battery. At the time when the connection is finally established
and the called subscriber rung, both sides of the calling line are
connected through various relay windings to the live side of the
battery. Such a condition leaves both sides of the line at the same
potential and, therefore, there is no tendency for current to flow
through the calling subscriber's talking apparatus, even though it is
connected across the circuit of the line. It remains, therefore, to be
seen how these conditions are so changed after the building up of a
connection as to supply the calling subscriber with talking current.

The calling subscriber can get no current until the called subscriber
responds. When the connection is first made with the called subscriber's
line, battery connection to his line is made from the live side of
battery through the normally closed contacts of the calling battery
supply relay, thence through the winding _25_ of the called battery
supply relay to the vertical side of the called line. The grounded side
of the battery is connected to the rotary side of his l