Company horizontal spring key is shown in Fig. 266. In this particular
key, as illustrated, there are two cam levers operating upon three
sets of springs. The cam lever at the left operates the ordinary
ringing and listening set of springs according to whether it is pushed
one way or the other. In ringing on single-party lines the cam lever
at the left is the one to be used; while on two-party lines the lever
at the left serves to ring the first party and the ringing key at the
right the second party.

In order that the operator may have an indication as to which station
on a two-party line she has called, a small target _1_ carried on a
lever _2_ is provided. This target may display a black or a white
field, according to which of its positions it occupies. The lever _2_
is connected by the links _3_ and _4_ with the two key levers and the
target is thus moved into one position or the other, according to
which lever was last thrown into ringing position.

It will be noticed that the springs are mounted horizontally and on
edge. This on-edge feature has the advantage of permitting ready
inspection of the contacts and of avoiding the liability of dust
gathering between the contacts. As will be seen, at the lower end of
each switch lever there is a roller of insulating material which
serves as a wedge, when forced between the two long springs of any
set, to force them apart and into engagement with their respective
outer springs.

[Illustration: Fig. 267. Vertical-Spring Listening and Ringing Key]

_Vertical Spring Type._ The other type of ringing and listening key
employing vertical springs is almost universally used by the various
independent manufacturing companies. A good example of this is shown
in Fig. 267, which shows partly in elevation and partly in section a
double key of the Monarch Company. The operation of this is obvious
from its mode of construction. The right-hand set of springs of the
right-hand key in this cut are the springs of the listening key, while
the left-hand set of the right-hand key are those of the calling-plug
ringing key. The left-hand set of the left-hand key may be those of a
ring-back key on the answering plug, while the right-hand set of the
left-hand key may be for any special purpose. It is obvious that these
groups of springs may be grouped in different combinations or omitted
in part, as required. This same general form of key is also
manufactured by the Kellogg Company and the