the left-hand bell.

An important feature in polarized bells is the adjustment between the
armature and the pole pieces. This is secured in the Western Electric
bell by means of the nuts _7_, by which the yoke _4_ is secured to the
standards _3_. By moving these nuts up or down on the standards the
armature may be brought closer _to_ or farther _from_ the poles, and
the device affords ready means for clamping the parts into any
position to which they may have been adjusted.

[Illustration: Fig. 79. Polarized Bell]

_Kellogg Ringer._ Another typical ringer is that of the Kellogg
Switchboard and Supply Company, shown in Fig. 80. This differs from
that of the Western Electric Company mainly in the details by which
the armature adjustment is obtained. The armature supporting yoke _1_
is attached directly to the cores of the magnets, no supporting side
rods being employed. Instead of providing means whereby the armature
may be adjusted toward or from the poles, the reverse practice is
employed, that is, of making the poles themselves extensible. This is
done by means of the iron screws _2_ which form extensions of the
cores and which may be made to approach or recede from the armature by
turning them in such direction as to screw them in or out of the core
ends.

[Illustration: Fig. 80. Polarized Bell]

[Illustration: Fig. 81. Biased Bell]

_Biased Bell._ The pulsating-current generator has already been