In
the twelfth century a "Book on Precious Stones" was written by Mohammed
Ben Mansur, of great value on account of it being of a much more exact
nature than any of its forerunners, though much of his information
would appear to have been derived from the same source. In spite of the
forward step which the appearance of this work marks, it was followed
by a number of other books which, from the point of view of the present
day mineralogist, entirely forsook the subject, as they dealt almost
wholly with the supernatural, ascribing to gem stones all sorts of
powers against evil spirits, diseases, and the mighty manifestations
of Nature. These ideas were still further modified by a growth in the
belief that various symbols and inscriptions engraved on the stones
were able to enhance their already supernatural powers. King (op. cit.) ascribes
these new forms of thought to the influence of the Crusades upon the
learning of the country, in bringing back magic-lore gleaned from the
Arabic philosophers.
No
further work of any great value appeared till that of Bcetius de Boot,
physician to the Emperor Budolf II., which was entitled " De Gemmis et
Lapidibus," and which was published in 1609. At the same time De Boot,
while decrying the magical powers ascribed to gems, goes on to give
recipes for the making of various pharmacopoeial preparations of
precious stones. In 1672, again, we find Robert Boyle, one of the early
Fellows of the Boyal Society, in his "Essay About the Origin and
Virtues of Gems," after making most careful reservations in his preface
as to what his opinions were about the virtues of gems, and stating
that "not only some of the writers of Natural Magick, but men of note,
who should be more cautious and sober, have
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