sensitive stage. When it begins to turn around principally, but also
before, it is affected by a magnet, and at a certain stage it is
susceptible to magnetic influence to an astonishing degree. A small
permanent magnet, with its poles at a distance of no more than two
centimetres, will affect it visibly at a distance of two metres,
slowing down or accelerating the rotation according to how it is held
relatively to the brush. I think I have observed that at the stage
when it is most sensitive to magnetic, it is not most sensitive to
electrostatic, influence. My explanation is, that the electrostatic
attraction between the brush and the glass of the bulb, which retards
the rotation, grows much quicker than the magnetic influence when the
intensity of the stream is increased.

When the bulb hangs with the globe L down, the rotation is always
clockwise. In the southern hemisphere it would occur in the opposite
direction and on the equator the brush should not turn at all. The
rotation may be reversed by a magnet kept at some distance. The brush
rotates best, seemingly, when it is at right angles to the lines of
force of the earth. It very likely rotates, when at its maximum speed,
in synchronism with the alternations, say 10,000 times a second. The
rotation can be slowed down or accelerated by the approach or receding
of the observer, or any conducting body, but it cannot be reversed by
putting the bulb in any position. When it is in the state of the
highest sensitiveness and the potential or frequency be varied the
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