Dean Company, that of the
Kellogg Company being illustrated in perspective, Fig. 268. The keys
of this general type have the same advantages as those of the
horizontal on-edge arrangement with respect to the gathering of dust,
and while perhaps the contacts are not so readily get-at-able for
inspection, yet they have the advantage of being somewhat more simple,
and of taking up less horizontal space on the key shelf.

[Illustration: Fig. 268. Vertical Listening and Ringing Key]

[Illustration: Fig. 269. Four-Party Listening and Ringing Key]

_Party-Line Ringing Keys._ For party-line ringing the key matter
becomes somewhat more complicated. Usually the arrangement is such
that in connection with each calling plug there are a number of keys,
each arranged with respect to the circuits of the plug so as to send
out the proper combination and direction of current, if the polarity
system is used; or the proper frequency of current if the harmonic
system is used; or the proper number of impulses if the step-by-step
or broken-line system is used. The number of different kinds of
arrangements and combinations is legion, and we will here illustrate
only an example of a four-party line ringing key adapted for harmonic
ringing. A Kellogg party-line listening and ringing key is shown in
Fig. 269. In this, besides the regular listening key, are shown four
push-button keys, each adapted, when depressed, to break the
connection back of the key, and at the same time connect the proper
calling generator with the calling plug.

_Self-Indicating Keys._ A complication that has given a good deal of
trouble in the matter of party-line ringing is due to the fact that it
is sometimes necessary to ring a second or a third time on a
party-line connection, because the party called may not respond the
first time. The operator is not always able to remember which one of
the four keys associated with the plug connected with the desired
party she has pressed on the first occasion and, therefore, when it
becomes necessary to ring again, she may ring the wrong party. This is
provided for in a very ingenious way in the key shown in Fig. 269, by
making the arrangement such that after a given key has been depressed
to its full extent in ringing, and then released, it does not come
quite back to its normal position but remains slightly depressed. This
always serves as an indication to the operator, therefore, as to which
key she depressed last, and in t