r starting current, and this is obviously
conducive to cross-ringing, that is, to the response of bells to other
than the intended frequency.

Again, easy starting is desirable because when the armature is at
rest, or in very slight vibration, it is at a maximum distance from
the poles of the electromagnet, and, therefore, subject to the weakest
influence of the poles. A current, therefore, which is strong enough
to start the vibration, will be strong enough to keep the bell ringing
properly.

[Illustration: Fig. 180. Dean In-Tune Ringer]

When with this "in-tune" mode of operation, the armature is thrown
into sufficiently wide vibration to cause the tapper to strike the
gong, the gong may tend to accelerate the vibration of the reed
tongue, but the current impulses through the electromagnet coils
continue at precisely the same rates as before. Under this condition
of vibration, when the reed tongue has an amplitude of vibration wide
enough to cause the tapper to strike the gongs, the ends of the
armature come closest to the pole pieces, so that the pole pieces have
their maximum magnetic effect on the armature, with the result that
even if the accelerating tendency of the gongs were considerable, the
comparatively large magnetic attractive impulses occurring at the same
rate as the natural rate of vibration of the reed tongue, serve wholly
to prevent any actual acceleration of the reed tongue. The magnetic
attractions upon the ends of the armature, continuing at the initial
rate, serve, therefore, as a check to offset any accelerating
tendency which the striking of the gong may have upon the vibrating
reed tongue.

It is obvious, therefore, that in the "in-tune" system the
electromagnetic effect on the armature should, when the armature is
closest to the pole pieces, be of such an overpowering nature as to
prevent whatever accelerating tendency the gongs may have from
throwing the armature out of its "stride" in step with the current.
For this reason it is usual in this type to so adjust the armature
that its ends will actually strike against the pole pieces of the
electromagnet when thrown into vibration. Sufficient flexibility is
given to the tapper rod to allow it to continue slightly beyond the
point at which it would be brought to rest by the striking of the
armature ends against the pole pieces and thus exert a whipping action
so as to allow the ball to continue in its movement far enough to
strike against