Knowing that by torsion we can rotate or diminish magnetism, I was
anxious to obtain by its means a complete rotation from north polarity
to neutrality, and from neutrality to south polarity, or to completely
reverse magnetic polarity by a slight right or left torsion.
I have succeeded in doing this, and in obtaining strong reversal of
polarities, by superposing one polarity given while the rod is under a
right elastic torsion, with another of the opposite polarity given under
a left elastic torsion, the neutral point then being reached when the
rod is free from torsion. The rod should be very strongly magnetized
under its first or right-hand torsion, so that its interior molecules
are rotated, or, in other words, magnetized to saturation; the second
magnetization in the contrary sense and torsion should be feebler, so
as only to magnetize the surface, or not more than one-half its depth;
these can be easily adjusted to each other so as to form a complete
polar balance of force, producing, when the rod is free from torsion,
the neutrality as shown at B, Fig. 1.
The apparatus needed is simply a good compound horseshoe permanent
magnet, 15 centimeters long, having six or more plates, giving it a
total thickness of at least 3 centimeters. We need a sufficiently
powerful magnet, as I find that I obtain a more equal distribution of
magnetism upon a rod or strip of iron by drawing it lengthwise over a
single pole in a direction from that pole, as shown in Fig. 2; we can
then obtain saturation by repeated drawings, keeping the same molecular
symmetry in each experiment.
In order to apply a slight elastic torsion when magnetizing rods or
wires, I have found it convenient to attach two brass clamp keys to the
extremities of the rods, or simply turn the ends at right angles, as
shown in the following diagram, by which means we can apply an elastic
twist or torsion while drawing the rod over the pole of the permanent
magnet. We can thus superpose several and opposite symmetrical
structures, producing a polar north or south as desired, greatly in
excess of that possible under a single or even double magnetization, and
by carefully adjusting the proportion of opposing magnetisms, so that
both polarities have the same external force, the rod will be at perfect
external neutrality when free from torsion.
[Illustration: FIG. 2.]
If we now hold one end of this rod at a few centimeters distance from
a magnetic directive needle, we find it perfectly neutral when free
of torsion, but the slightest torsion right or left at once produces
violent repulsion or attraction, according to the direction of the
torsion given to the rod, the iron rod or strips of hoop-iron which
I use for this experiment being able, when at the distance of five
centimeters from the needle, to turn it instantly 90° on either side of
its zero.
The external neutrality that we can now produce at will is absolute, as
it crosses the line of two contrary polarities, being similar to the
zero of my electric sonometer, whose zero is obtained by the crossing of
two opposing electric forces.
This rod of iron retains its peculiar powers of reversal in a remarkable
degree, a condition quite different to that of ordinary magnetization,
for the same rod, when magnetized to saturation under a single ordinary
magnetism, loses its evident magnetism by a few elastic torsions, as I
have already shown; but when it is magnetized under the double torsion
with its superposed magnetism, it is but slightly reduced by variations
or numerous torsions, and I have found it impossible to render this
rod again free from its double polar effects, except by strongly
remagnetizing it to saturation with a single polarity. The superposed
magnetism then becomes a single directive force, and we can then by a
few vibrations or torsions reduce the rod to its ordinary condition.
The effects of superposed magnetism and its double polarity I have
produced in a variety of ways, such as by the electro-magnetic influence
of coils, or in very soft iron simply by the directive influence of
the earth's magnetism, reversing the rod and torsions when held in
the magnetic meridian, these rods when placed magnetic west showing
distinctly the double polar effects.
It is remarkable, also, that we are enabled to superpose and obtain
the maximum effects on thin strips of iron from ¼ to ½ millimeter in
thickness, while in thicker rods we have far less effect, being masked
by the comparatively neutral state of the interior, the exterior
molecules then reaching upon those of the interior, allowing them to
complete in the interior their circle of attractions.
I was anxious to obtain wires which would preserve this structure
against the destructive influence of torsion and vibrations, so that I
could constantly employ the same wires without the comparatively long
and tedious process of preparation. Soft iron soon loses the structure,
or becomes enfeebled, under the constant to and fro torsions requisite
where we desire a constant change of polarity, as described later in the
magnetic bells. Hard steel preserves its structure, but its molecular
rigidity is so great that we obtain but mere traces of any change of
polarity by torsion. I have found, however, that fine cast drill steel,
untempered, of the kind employed by watchmakers, is most suitable;
these are generally sold in straight lengths of 30 centimeters. Wires
1 millimeter in diameter should be used, and when it is desired to
increase the force, several of these wires, say, nine or ten, should be
formed into a single rod or bunch.
The wire as sold is too rigid to give its maximum of molecular rotation
effect. We must therefore give it two entire turns or twists to the
right, and strongly magnetize it on the north pole of the magnet while
under torsion. We must again repeat this operation in the contrary
direction, after restoring the wire to its previous position, giving now
two entire turns to the left and magnetizing it on the south pole. On
restoring the wire to its original place, it will be extremely flexible,
and we may now superpose several contrary polarities under contrary
torsions, as already described.
The power of these wires, if properly prepared, is most remarkable,
being able to reverse their polarity under torsion, as if they were
completely saturated; and they preserve this power indefinitely if not
touched by a magnet. It would be extremely difficult to explain the
action of the rotative effects obtained in these wires under any other
theory than that which I have advanced; and the absolute external
neutrality that we obtain in them when the polarities are changing, we
know, from their structure, to be perfectly symmetrical.
I was anxious to show, upon the reading of this paper, some mechanical
movement produced by molecular rotation, consequently I have arranged
two bells that are struck alternately by a polarized armature put in
motion by the double polarized rod I have already described, but whose
position, at three centimeters distant from the axis of the armature,
remains invariably the same. The magnetic armature consists of a
horizontal light steel bar suspended by its central axle; the bells are
thin wine glasses, giving a clear musical tone loud enough, by the force
with which they are struck, to be clearly heard at some distance. The
armature does not strike these alternately by a pendulous movement, as
we may easily strike only one continuously, the friction and inertia of
the armature causing its movements to be perfectly dead beat when not
driven by some external force, and it is kept in its zero position by a
strong directive magnet placed beneath its axle.
The mechanical power obtained is extremely evident, and is sufficient to
put the sluggish armature in rapid motion, striking the bells six times
per second, and with a power sufficient to produce tones loud enough to
be clearly heard in all parts of the hall of the Society. As this is
the first direct transformation of molecular motion into mechanical
movement, I am happy to show it on this occasion.
There is nothing remarkable in the bells themselves, as they evidently
could be rung if the armature was surrounded by a coil, and worked by an
electric current from a few cells. The marvel, however, is in the small
steel superposed magnetic wire producing by slight elastic torsions from
a single wire, one millimeter in diameter, sufficient force from mere
molecular rotation to entirely replace the coil and electric current.