nergized,
and the lamp _5_ will be lighted.

In a nutshell, the sleeve supervisory relay normally prevents the
lighting of the corresponding supervisory lamp, but as soon as the
operator inserts a plug into the jack of the line, the relay _2_
establishes such a condition as to make possible the lighting of the
supervisory lamp, and the lighting of this lamp is then controlled
entirely by the relay _1_, which is, in turn, controlled by the position
of the subscriber's switch hook.

_Battery Feed._ A 2-microfarad condenser is included in each strand of
the cord, and battery is fed through the relay windings to the calling
and called subscribers on opposite sides of these condensers, in
accordance with the combined impedance coil and condenser method
described in Chapter XIII. Here the relay windings do double duty,
serving as magnets for operating the relays and as retardation coils in
the system of battery supply.

_Complete Cord and Line Circuits._ The complete cord and line circuits
of the Kellogg two-wire system are shown in Fig. 352. In the more recent
installations of the Kellogg Company the cord and line circuits have
been slightly changed from those shown in Figs. 350 and 351, and these
changes have been incorporated in Fig. 352. The principles of operation
described in connection with the simplified figures remain, however,
exactly the same. One of the changes is, that the tip side of the lines
is permanently connected to the tips of the jacks instead of being
normally cut off by the cut-off relay, as was done in the system as
originally developed. Another change is, that the line relay is
associated with the tip side of the line, rather than with the sleeve
side, as was formerly done. The cord circuit shown in Fig. 352 shows
exactly the same arrangement of supervisory relays and exactly the same
method of battery feed as in the simplified cord circuit of Fig. 351,
but in addition to this the detailed connections of the operator's
talking set and of her order-wire keys are indicated, and also the
ringing equipment is indicated as being adapted for four-party harmonic
work.

[Illustration: Fig. 352. Kellogg Two-Wire Board]

In connection with this ringing key it may be stated that the springs
_7_, _8_, _9_, and _10_ are individually operated by the pressure of one
of the ringing key buttons, while the spring _17_, connected with the
sleeve side of the calling plug, is always operated simultaneously with
the