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 deg. 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