ONYX, a variety of agate or chalcedony, in which occur even layers of white and black or white and brown, sharply defined in good specimens; they come from India, and are highly valued for cameo-cutting.

OOSTERZEE, JAN JAKOB VAN, a theologian of the Dutch Church, born at Rotterdam; became professor at Utrecht, wrote several theological and exegetical works on evangelical lines (1817-1882).

OPAL, a variety of quartz, of which the finest kind, precious opal, is translucent, with blue or yellow tint, and when polished with a convex surface shows an admirable play of colours; it is found chiefly at Cerwenitza, Austria.

OPEN SECRET, THE, the secret that lies open to all, but is seen into and understood by only few, applied especially to the mystery of the life, the spiritual life, which is the possession of all.

OPEN, SESAME, the magic formula the pronunciation of which opened the robbers’ stronghold in the “Arabian Nights.”

OPERA, a drama set to music and acted and sung to the accompaniment of a full orchestra, of which there are several kinds according as they are grave, comic, or romantic.

OPERA BOUFFE, an opera in an extravagant burlesque style, with characters, music, and other accompaniments to match; is the creation of OFFENBACH (q. v.), his more distinguished successors in the production of which have been Lecocq, Herve, and Strauss.

OPHELIA, the daughter of Polonius in “Hamlet” and in love with the lord, but whose heart, from the succession of shocks it receives, is shattered and broken.

OPHICLEIDE, a keyed brass wind instrument of recent invention, of great compass and power, and of which there are two kinds in use.

OPHIR, a region in the East of uncertain situation, frequently referred to in Scripture as a region from which gold and precious stones were imported.

OPHITES, a sect of Gnostics who regarded the serpent as a benefactor of the race in having persuaded Eve to eat of the tree of the knowledge of good and evil in disregard, or rather in defiance, of the warning of the God of the Jews.

OPIE, JOHN, English artist, born near Truro, Cornwall; began to learn his father’s trade of carpenter, but turning to art went with Dr. Wolcott to London in 1780; for a year he had phenomenal success as a portrait-painter; on the wane of his popularity he turned to scriptural and historical painting and to illustration; after being Associate for a year he was elected Academician in 1787; besides some lectures on art, he wrote a Life of Reynolds and other works (1761-1807).

OPINICUS, a fabulous winged creature with the head of a griffin, the body of a lion, and the tail of a camel; a heraldic symbol.

OPITZ, MARTIN VON, a German poet, born in Silesia; was much patronised by the princes of Germany; was crowned with laurel, and ennobled by Ferdinand II.; his poetry was agreeable to classic models, but at the expense of soul, though, to his credit it must be said, the German language and German poetry owe him a deep debt (1597-1639).