if
they have a sufficiently firm hardness, if rubbed after they have been
polished and when they remain bright with the friction--towards those
substances everything, if presented to them in the air, turns, if its too
heavy weight does not prevent it. For amber has been compacted of moisture,
and jet also. Lucid gems are made of water; just as Crystal[132], which has
been concreted from clear water, not {52} always by a very great cold, as
some used to judge, and by very hard frost, but sometimes by a less severe
one, the nature of the soil fashioning it, the humour or juices being shut
up in definite cavities, in the way in which spars are produced in mines.
So clear glass is fused out of sand, and from other substances, which have
their origin in humid juices. But the dross of metals, as also metals,
stones, rocks, woods, contain earth rather, or are mixed with a good deal
of earth; * and therefore they do not attract. Crystal, mica, glass, and
all electricks do not attract if they are burnt or roasted; for their
primordial supplies of moisture perish by heat, and are changed and
exhaled. All things therefore which have sprung from a predominant moisture
and are firmly concreted, and retain the appearance of spar and its
resplendent nature in a firm and compact body, allure all bodies, whether
humid or dry. Those, however, which partake of the true earth-substance or
are very little different from it, are seen to attract also, but from a far
different reason, and (so to say) magnetically; concerning these we intend
to speak afterwards. But those substances which are more mixed of water and
earth, and are produced by the equal degradation of each element (in which
the magnetick force of the earth is deformed and remains buried; while the
watery humour, being fouled by joining with a more plentiful supply of
earth, has not concreted in itself but is mingled with earthy matter), can
in no way of themselves attract or move from its place anything which they
do not touch. On this account metals, marbles, flints, woods, herbs, flesh,
and very many other things can neither allure nor solicit any body either
magnetically or electrically. (For it pleases us to call that an electrick
force, which hath * its origin from the humour.) But substances consisting
mostly of humour, and which are not very firmly compacted by nature
(whereby do they neither bear rubbing, but either melt down and become
soft, or are not levigable, such as