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25 NATURAL HISTORY OF PRECIOUS STONES, &c,
My object
has therefore been, as a primary consideration, to establish a sound
system of nomenclature for rendering the antique into our own; to
define each species with pre cision, employing so much (and no more) of
modern science as was necessary for the purpose; to consider the whole
subject as thoroughly as my materials allowed in its bearings upon
History and Art (as intimately connected with which I have introduced
the two essays upon the Precious Metals) ; and whilst doing this, to
supply accurate guidance to the purchaser, or admirer, in our own days,
of these the choicest of Nature's treasures.
STONES, THEIR ORIGIN.
The
secret process whereby Precious Stones are produced in the laboratory
of Nature early engaged the attention of the philosophers of Greece, as
doubtless similar speculations had long before employed the subtile
ingenuity of their forerunners, the wise men of India and of Chaldea.
Of such investigations the most elaborate preserved to us is that of
Plato in his 'Timaeus' (60 C), where, after describing the origin of
metals, and of the Adamas (as quoted under that head), he thus
accounts for the composition and for the various species of stones:—"
With respect to the different kinds of earth, one sort being filtered
through water in the aforesaid manner becomes a stony substance: as the
water originally mingled with it, in the case where it is the weaker of
the two in the mixture, is transformed into the shape of air. Now this
air, on returning into its natural place, mounts upwards, for no vacuum
surrounded it. "Consequently it impels the air nearest to itself; this
latter therefore, inasmuch as it is ponderous, being impelled, and
enveloping the mass of earthy matter, forcibly squeezes and drives the
same into those receptacles out of which the
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