Electric Company. The two electromagnets are mounted side by side, as
shown, by attaching their cores to a yoke piece _1_ of soft iron. This
yoke piece also carries the standards _2_ upon which the gongs are
mounted. The method of mounting is such that the standards may be
adjusted slightly so as to bring the gongs closer _to_ or farther
_from_, the tapper.

The soft iron yoke piece _1_ also carries two brass posts _3_ which,
in turn, carry another yoke _4_ of brass. In this yoke _4_ is pivoted,
by means of trunnion screws, the armature _5_, this extending on each
side of the pivot so that its ends lie opposite the free poles of the
electromagnets. From the center of the armature projects the tapper
rod carrying the ball or striker which plays between the two gongs.

In order that the armature and cores may be normally polarized, a
permanent magnet _6_ is secured to the center of the yoke piece _1_.
This bends around back of the electromagnets and comes into close
proximity to the armature _5_. By this means one end of each of the
electromagnet cores is given one polarity--say north--while the
armature is given the other polarity--say south. The two coils of the
electromagnet are connected together in series in such a way that
current in a given direction will act to produce a north pole in one
of the free poles and a south pole in the other. If it be assumed that
the permanent magnet maintains the armature normally of south polarity
and that the current through the coils is of such direction as to make
the left-hand core north and the right-hand core south, then it is
evident that the left-hand end of the armature will be attracted and
the right-hand end repelled. This will throw the tapper rod to the
right and sound the right-hand bell. A reversal in current will
obviously produce the opposite effect and cause the tapper to strike