Scientific American Supplement, No. 392, July 7, 1883Various
Science
Scientific American Supplement, No. 392, July 7, 1883
Various
Science -- Periodicals
If we take a flat bar of soft iron, of 30 or more centimeters in
length, and hold it vertically (giving while thus held a few torsions,
vibrations, or, better still, a few slight blows with a wooden mallet,
in order to allow its molecules to rotate with perfect freedom), we find
its lower end to be of strong north polarity, and its upper end south.
On reversing the rod and repeating the vibrations, we find that its
lower end has precisely a similar north polarity. Thus the iron is
homogeneous, and its polarity symmetrical. If we now magnetize this rod
to produce a strong south pole at its lower portion, we can gradually
reverse this polarity, by the influence of earth's magnetism, by
slightly tapping the upper extremity with a small wooden mallet. If
we observe this rod by means of a direction needle at all parts, and
successively during its gradual passage from one polarity to the other,
there will be no sudden break into a haphazard arrangement, but a
gradual and perfectly symmetrical rotation from one direction to that of
the opposite polarity.
If this rod is placed east and west, having first, say, a north polarity
to the right, we can gradually discharge or rotate the molecules to
zero, and as gradually reverse the polarity by simply inclining the rod
so as to be slightly influenced by earth's magnetism; and at no portion
of this passage from one polarity to neutrality, and to that of the
opposite name, will there be found a break of continuity of rotation or
haphazard arrangement. If we rotate this rod slowly, horizontally or
vertically, taking observations at each few degrees of rotation of an
entire revolution, we find still the same gradual symmetrical change
of polarity, and that its symmetry is as complete at neutrality as in
evident polarity.
In all these cases there is no complete neutrality, the longitudinal
polarity simply becoming transversal when the rod is east and west.
F, G, H, I, J, Fig. 1, show this gradual change, H being neutral
longitudinally, but polarized transversely. If, in place of the rod,
we take a small square soft iron plate and allow its molecules freedom
under the sole influence of the earth's magnetism, then we invariably
find the polarity in the direction of the magnetic dip, no matter in
what position it be held, and a sphere of soft iron could only be
polarized in a similar direction Thus we can never obtain complete
external neutrality while the molecules have freedom and do not form an
internal closed circle of mutual attractions; and whatever theory we may
adopt as to the cause of polarity in the molecule, such as Coulomb's,
Poisson's, Ampere's, or Weber's, there can exist no haphazard
arrangement in perfectly soft iron, as long as it is free from all
external causes except the influence of the earth; consequently these
theories are wrong in one of their most essential parts.
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