calling line of a pair of connected
lines and the other in all cases with the called line. As shown in
Fig. 132, the left-hand battery is connected with the line leading to
Station A through the impedance coils _1_ and _2_. Likewise, the
right-hand battery is connected to the line of Station B through the
impedance coils _3_ and _4_. These four impedance coils are wound on
separate cores and do not have any inductive relation whatsoever with
each other. Condensers _5_ and _6_ are employed to completely isolate
the lines conductively. Current from the left-hand battery, therefore,
passes only to Station A, and current from the right-hand battery to
Station B. Whenever the transmitter at Station A is actuated the
undulations of current which it produces in the line cause a varying
difference of potential across the outside terminals of the two
impedance coils _1_ and _2_. This means that the two left-hand
terminals of condensers _5_ and _6_ are subjected to a varying
difference of potential and these, of course, by electrostatic
induction, cause the right-hand terminals of these condensers to be
subject to a correspondingly varying difference of potential. From
this it follows that alternating currents will be impressed upon the
right-hand line and these will affect the receiver at Station B.

A rough way of expressing the action of this circuit is to consider it
in the same light as that of the impedance-coil circuit shown in Fig.
131, and to consider that the voice currents originating in one line
are prevented from passing through the bridge paths at the central
office on account of the impedance, and are, therefore, forced to
continue on the line, being allowed to pass readily by the condensers
in series between the two lines.

_Kellogg Substation Arrangement._ An interesting form of substation
circuit which is employed by the Kellogg Company in all of its
common-battery telephones is shown in Fig. 132. In passing, it may be
well to state that almost any of the substation circuits shown in this
chapter are capable of working with any of the central-office
circuits. The different ones are shown for the purpose of giving a
knowledge of the various substation circuits that are employed, and,
as far as possible, to associate them with the particular
central-office arrangements with which they are commonly used.

In this Kellogg substation arrangement the line circuit passes first
through the transmitter and then divide