seurs the most notable work of the kind during the Gothic
period.
Some of the best known engravings on this stone are,
probably, a head of Jupiter, in Greek style, set in the handle
of a Turkish dagger ; a head of Medusa, and another of Caracalla, in the Marlborough collection ; the head of Julius Cassar
and of Apollo, formerly belonging to the Herz ; a portrait of
Pope Paul III., in the Pulsky, one of Henry IV. of France, and
a cameo representing Hebe and the eagle, cut on a stone of this
kind, measuring one inch and one-half by one and one-fourth.
The collection of the late Duke of Brunswick comprised a
sapphire engraved with the arms of England, which formerly
belonged to Mary Queen of Scots ; a specimen bearing a
female figure, and conspicuous for its dichroism, is found
among the imperial jewels of Russia, and the French cabinet
contains an intaglio in this gem with the portrait of the
Emperor Pertinax.
Asteria. — This name was applied by the ancients to a
variety of certain species of precious stones, more especially
the corundum and the quartz, which, on account of a peculiar
structure, displays divergent rays of light, like those of a star.
This singular phenomenon is exhibited only in certain translucent or semi-opaque stones, cut en cabochon, or in hexagonal
prisms, with the top rounded off. These rays are white or
only slightly tinged, though the gem may be of various colors,
and are most distinctly seen in sunlight or by the bright flame
of a candle. The cause of this appearance is the numerous
minute crystals arranged in different angles within the stone,
which reflect the light so as to produce the stellar rays.
The corundums yielding this variety are called star-sapphires and star-rubies; when they assume a fibrous texture,
they are called cat's-eye.
