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Callais, Turquois

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60                   NATURAL HISTORY OF GEMS.
Sapphirine Calcedony (jaspis). On the other hand, there are many points of analogy to induce a belief that our ; Turquois was the Hermean or Persian Smaragdus of De-mocritus, " protuberant, not transparent, of an agreeable and '. even colour, like the eye of a leopard or cat ; losing their beauty in the sunshine, but lustrous in the shade, and con-spicuous from a greater distance than any other precious stone :" one grand distinction of the Turquois being that its colour is improved by artificial light, in which, even though greenish, it becomes a perfect celestial blue. A strong confirmation of this view is to be found in the war so hotly waged between the mediaeval doctors as to whether that great oracle of the science, the Arabian Mesues, meant the Emerald or the Turquois by his "Firuzegi,"* that essen­tial ingredient in his highly-esteemed electuary.
The "Fossil Ivory "of Theophrastus (37) "dark blue ; mottled with white," can hardly be other than the Occi­dental Turquois, or petrified bone, tinged by copper oxide, in which the osseous structure is plainly discernible under the microscope, and which, besides, is much softer than the true Persian Turquois ("de la vieille roche" in jewellers' parlance), which is sufficiently hard to strike fire with steel. According to Hill, the blue that mottles the surface of the former species can, by the judicious application ot heat, be evenly diffused throughout its mass, thus greatly improving its appearance, and often enabling it to pass muster for the actual and precious stone. Its Greek appel­lation, so much more correct than the modern, may be set down amongst the proofs that continually strike us of the sagacity of the primitive naturalists in discovering by observation and induction alone the true origin of many substances. Barbot found by experiment that the teeth of
* " The Victor," an epithet attesting its reputation amongst the Persians.
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