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30 NATURAL HISTORY OF PRECIOUS STONES, &c.
the
influence, where such matter is found ready for its operation. The
which virtue is indeed designated by some ' the Virtue of the Heavens.'
And this is what Plato means by saying that 'the virtues of the heavens
are infused in proportion to the worthiness of the subject matter.'
"
In Physics also it is granted that all formative or efficient virtue
has some proper instrument in some particular species, through the
means of which it effects or produces its own operation. For this
reason we must adopt the opinion of Aristotle put forth in his treatise
' On Minerals,' and maintain that ' the peculiar efficient or
generative virtue of stones, existing in the material of stones, which
is termed mineral matter, is made up of two things; or, as it were,
instruments, which instruments are diversified according to the
difference of the nature or the species of the stones. Of which
instruments, the one is Heat digestive, extractive or desiccative of Moisture, inducing
form in the stone through the medium of the coagulation of its earthy
particles, to which it is subjected by the unctuous moisture; and this
heat is directed by the formative or mineral virtue of the stones
themselves, which last is termed by Aristotle ' the Hot, Desiccative
Cause.' Nor is it doubtful that such heat, if it were not regulated by
some other condition, would be in excess above the nature of the stone,
and would reduce it to ashes; and, on the 'other hand, if the heat were
lessened, it would not digest the matter properly, and so not bring the
material of the stone to its best and perfect form, because it was
insufficient to produce that effect. The second instrument is Cold subsisting
in the matter of the aqueous moisture, which aqueous moisture is
affected by the dryness of its earth, and this is the ' Cold
constrictive of moisture,' which moisture by means of such constriction
is forced out, and does not remain in the matter except in such a
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