h are nearest to the permanent magnet _1_ are of the
opposite polarity to the end they approach, the free ends being of
opposite polarity. In the figure, these free ends are marked _N_,
meaning they are of a polarity to point north if free to point at all.
English-speaking persons call this _north polarity_. Similarly, as in
Fig. 19, any arrangement of iron near a permanent magnet always will
have free poles of the same polarity as the end of the permanent
magnet nearest them.

A permanent magnet so related to iron forms part of a polarized
ringer. So does an electromagnet composed of windings and iron cores.
Fig. 20 reminds us of the law of electromagnets. If current flows from
the plus towards the minus side, with the windings as drawn,
polarities will be induced as marked.

[Illustration: Fig. 20. Electromagnet]

[Illustration: Fig. 21. Polarized Ringer]

If, now, such an electromagnet, a permanent magnet, and a pivoted
armature be related to a pair of gongs as shown in Fig. 21, a
polarized ringer results. It should be noted that a permanent magnet
has both its poles presented (though one of the poles is not actually
attached) to two parts of the iron of the _electro_-magnet. The result
is that the ends of the armature are of south polarity and those of
the core are of north polarity. All the markings of Fig. 21 relate to
the polarity produced by the permanent magnet. If, now, a current flow
in the ringer winding from plus to minus, obviously the right-hand
pole will be additively magnetized, the current tending to produce
north magnetism there; also the left-hand pole will be subtractively
magnetized, the current tending to produce south magnetism there. If
the current be of a certain strength, relative to the certain ringer
under study, magnetism in the left pole will be neutralized and that
in the right pole doubled. Hence the armature will be attracted more
by the right pole than by the left and will strike the right-hand
gong. A reversal of current produces an opposite action, the left-hand
gong being struck. The current ceasing, the armature remains where
last thrown.

[Illustration: OPERATOR'S EQUIPMENT
Clement Automanual System.]

It is important to note that the strength of action depends upon the
strength of the current up to a certain point only. That depends
upon the strength of the permanent magnet. Whenever the current is
great enough just to neutralize the normal magnetism of one pole and
to d