opticians
for making the lenses of spectacles, on account of its superior
hardness and durability to glass, and its coldness,—as it, in common
with all precious stones, feels cool to the touch. The lenses, however,
must be cut at right angles to the axis of the crystal, in order to
avoid the effect of the double refraction of the mineral, which is not
only unpleasant, but prejudicial to the eyesight ; colourless quartz is
also used in the polariscope, in sections cut across the prism. Lately
it has been much used in jewellery, stones and enarpel being in-crusted
in it. In India the natives hollow it out into cups, goblets, and vases
of a surprising thinness and frequently cover them with the most
elaborate ornamentation. The Chinese also use this substance largely,
and attach great value to it, although the forms into which they cut it
are less graceful, and the ornamentation far inferior to that of the
Indian workmen. In Japan it is cut into large round balls, which are
said to be used for the purpose of cooling the hands. The Eastern
nations frequently make it into beads for necklaces. The natives of
India believe the crystal to be the mother, or external husk, of the
diamond, and call the diamond the ripe, and the crystal the unripe,
diamond. The ancient Egyptians used the crystal for making cylinders,
scarabei, etc., some specimens being elaborately engraved. The Greeks
supposed it to be water congealed by intense cold, as the name (κρύσταλλος, ice) signifies ; and it was thought to be procurable only in the frozen regions. In the Middle Ages it was be-
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