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In this paper, the authors have detected a new effect in
the area of geomagnetism, related to the behavior of a magnetic
dipole freely floating on water surface. An experiment is
described in the present paper in which a magnetic dipole
fixed upon a float placed on non-magnetized water surface
undergoes displacement along with reorientation caused by
fine structure of the earth's magnetic field. This fact
can probably be explained by secular decrease of the earth's
major dipole moment. Further, a detailed study of the phenomenon
may create interesting premises for its practical use, particularly
for the analysis of fine structure of geomagnetic field
and its time-dependent anomalies. A strange behavior of
some sea fish species prior to strong earthquakes may be
explained if the fish are assumed as `live magnetic dipoles'.
The history of human familiarity with the magnetic field
of the earth goes down to such ancient times that one is
even unable to determine the epoch when the people learned
to use the magnetic needle properties for orientation. However,
the birth of geomagnetism as the earth science is assumed
to occur in the year 1600, when William Gilbert published
his book, De Magnete. Although the magnetic inclination
phenomenon was discovered by Robert Norman 20 years before
that book appeared, it was Gilbert who generalized all the
effects related with magnetic needle known by that time
and explained them by the presence of the earth's magnetic
field, in which case the earth appeared as a `big magnet'.
Norman invented a needle which could turn in a vertical
plane, and thus discovered the magnetic inclination phenomenon.
He also suggested that the earth's action on the needle
represents a rotation moment, rather than an attraction
force. His second idea on that special point should exist
on the earth's surface around which the compass needle turns,
however, was rejected by Gilbert who represented the earth
as a magnet having two opposite polarities. But the Norman's
first concept is preserved until now. Particularly, Borgman
wrote (Borgman 1914-1916): "A magnet attached to a
float freely swimming on water surface, away from iron masses
or other magnets, does not undergo any displacement. Thus,
only directional force acts on the magnet, as a result of
which its magnetic axis assumes a certain orientation in
space".
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