sensitiveness is rapidly diminished. Changing either of these but
little will generally stop the rotation. The sensitiveness is likewise
affected by the variations of temperature. To attain great
sensitiveness it is necessary to have the small sphere s in the centre
of the globe L, as otherwise the electrostatic action of the glass of
the globe will tend to stop the rotation. The sphere s should be small
and of uniform thickness; any dissymmetry of course has the effect to
diminish the sensitiveness.
The fact that the brush rotates in a definite direction in a permanent
magnetic field seems to show that in alternating currents of very high
frequency the positive and negative impulses are not equal, but that
one always preponderates over the other.
Of course, this rotation in one direction may be due to the action of
two elements of the same current upon each other, or to the action of
the field produced by one of the elements upon the other, as in a
series motor, without necessarily one impulse being stronger than the
other. The fact that the brush turns, as far as I could observe, in
any position, would speak for this view. In such case it would turn
at any point of the earth's surface. But, on the other hand, it is
then hard to explain why a permanent magnet should reverse the
rotation, and one must assume the preponderance of impulses of one
kind.
As to the causes of the formation of the brush or stream, I think it
is due to the electrostatic action of the globe and the dissymmetry of
the parts. If the small bulb s and the globe L were perfect concentric
spheres, and the glass throughout of the same thickness and quality, I
think the brush would not form, as the tendency to pass would be equal
on all sides. That the formation of the stream is due to an
irregularity is apparent from the fact that it has the tendency to
remain in one position, and rotation occurs most generally only when
it is brought out of this position by electrostatic or magnetic
influence. When in an extremely sensitive state it rests in one
position, most curious experiments may be performed with it. For
instance, the experimenter may, by selecting a proper position,
approach the hand at a certain considerable distance to the bulb, and
he may cause the brush to pass off by merely stiffening the muscles of
the arm. When it begins to rotate slowly, and the hands are held at a
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