had
the power of strengthening the eye. It was highly esteemed by them, as
we learn from Pliny, who thought that the play of color originates from
the beautiful colors of the carbuncle, amethyst, and emerald.
The
phenomenon of the play of colors in the precious opal has not yet been
satisfactorily explained. Haiiy attributes it to the fissures of the
interior being filled with films of air, agreeably with the law of
Newton's colored rings, when two pieces of glass are pressed together.
Mohs' con-tradicts this theory upon reasonable grounds, which are, that
the phenomenon would present merely a kind, of iridescence. Brewster
concludes that it is owing to fissures and cracks in the interior of
the mass, not accidental but of a uniform shape, and which reflect the
tints of Newton's scale; but it is, in my opinion, sufficiently
plausible, that the unequal division of smaller and larger cavities,
which are filled with water, produces the prismatic colors, and for the
simple reason that the opal which grows, after a while, dull and
opaque, may be restored to its former beauty if put for a short time in
water or oil.
Although
the precious opal was never found in the East, yet it bears the name of
Oriental opal among jewellers: for in former times opals were carried
by the Grecian and Turkish merchants from Hungary, their native
locality, to the Indies, and brought back by the way of Holland to
Europe, as Oriental opals. Th/3 precious opal is found, in small
irregular gangues, nests of the trachytic porphyry formation and its
conglomerates, in Hungary, particularly in the neighborhood of the
village of Czerwin-ceza; also, in the Faroe Islands, Saxony, and South
America. The Hungarian opal is found of various qualities, and is
obtained from mines which have been wrought for several centuries; and,
according -to the archives of that part of the country, there were, in
the year 1400, more than three
