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 double that of the other, no increase in current will cause the
device to ring any louder. This makes obvious the importance of a
proper permanent magnetism and displays the fallacy of some effort to
increase the output of various devices depending upon these
principles. This discussion of magneto-electric signaling is
introduced here because of a belief in its being fundamental. Chapter
VIII treats of such a signaling in further detail.