MAGNETIC AND ELECTRIC INFLUENCES 59
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in a similar manner to the pith ball, the tourmaline will be found to
have become an excellent magnet. By testing this continually as it
cools there will soon be perceived a point which is of extreme delicacy
of temperature, where the magnetic properties are almost in abeyance.
But as the tourmaline cools yet further, though but a fraction of a
degree, the magnetic properties change : the positive pole becomes the
negative, the negative having changed to the positive.
It
is also interesting to note that if the tourmaline is not warmed so
high as to reach a temperature of 50° F., or is heated so strongly as
to exceed more than a few degrees above 300° F., then these magnetic
properties do not appear, as no polarity is present. This polarity, or
the presence of positive and negative electricity in one stone, may be
strikingly illustrated in a very simple manner:—If a little sulphur and
red-lead, both in fine powder, are shaken up together in a paper or
similar bag, the moderate friction of particle against particle
electrifies both : one negatively, the other positively. If. then, a
little of this now golden-coloured mixture is gently dusted over the
surface of the tourmaline or other stone possessing electric polarity,
a most interesting change is at once apparent. The red-lead separates
itself from the sulphur and adheres to the negative portion of the
stone, whilst the separated sulphur is at once attracted to the
positive end, so that the golden-coloured mixture becomes slowly
transformed into its two separate components — the brilliant yellow
sulphur, and the equally brilliant red-lead. These particles form in
lines and waves around the respective poles in beautiful symmetry,
their positions
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