MAGIC STONES AND ELECTRIC GEMS 55
furnished
him by Lehmann, a fellow-member of the Berlin Academy, who, as Aepinus
frankly admits, first drew his attention to the electric action of the
stone. That not only friction but heat also should develop the electric
energy, both positive and negative, of the tourmaline, serves to
differentiate it from many other potentially electric substances, in
the case of which friction alone is effective.
The
specimen shown by M. Lémery to the French Academy of Sciences in 1717
is stated to have come from "a river in the Island of Ceylon," and is
described as being of small size, flat, orbicular, quite thin, of a
brown color, and smooth brilliant surface.98 Its peculiar
property of attracting and then repelling ashes or iron filings as well
as bits of paper, was duly noted. This specimen had cost M. Lémery 15
livres. After reciting the constant repulsion and attraction exercised
by a magnet upon the needle, the attraction by the opposite pole, and
repulsion by the same pole, he proceeds to remark that this Cinghalese
stone acted quite differently, since it first attracted and then
repulsed the same object presented in the same way. This intermittent
or irregular action was in his opinion to be explained by the theory
that a vortex was intermittently developed in the substance. As it
begins the small bodies are attracted, when it ceases they remain
stationary, but when it is renewed "and there emanates from the stone
a material analogous to the magnetic emanation" then the bodies are
repulsed. Another peculiarity was that the body which had been
repulsed could not again be attracted, whence the conclusion was
arrived at that the stone's repellent force was superior to its
attractive power. These necessarily somewhat inexact observations are
interesting as marking one of the earliest attempts to
" See Historie de l'Académie Royale dea Sciences Année mdcccxvii Paris, 1719, pp. 7, 8.
