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134 NATURAL HISTORY OF GEMS.
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The
last notice is very curious, referring as it does to some method used
by the ancient astronomers in making solar observations, for it must be
borne in mind that the chief authorities upon the properties of gems
quoted in Pliny's Alphabetical List (in which the Heliotrope
stands) were the Magi, the fathers of astronomy. It is, however,
difficult to conceive how a tablet of Heliotrope could have been used
as a mirror ; but, on the other hand, a thin slice of a green
transparent stone would admirably protect the eye of an observer
looking through it. Perhaps here, as in the case of Nero's Emerald (Smaragdus), there may lurk a confusion of ideas, between the looking into a mirror, and the looking through a transparent medium.
Pliny
hereupon quotes, as a most glaring example of the impudence of the
Magi, their assertion that the wearer of this gem coupled with the
plant of the same name was enabled, by means of certain spells known to
them, to make himself invisible. To this notion Dante alludes where he
sees the damned running about under a hail of fire,—
" Senza sperar pertugio ï eliotropio "— " No hope of hiding-hole or Heliotrope."
Pliny goes on to add that the Hephaestites (Vulcan-stone) found near Corinth might similarly be used for a mirror, though fiery-red in
colour. The test of its genuineness was if boiling water immediately
became cold upon the stone's being thrown into the caldron ; or if the
same, being placed in the sunshine, forthwith kindled dry fuel. It is
impossible to divine what mineral is here intended. Orpheus, however
(264), ascribes exactly the same two antagonistic qualities to his
Lychnis or Balais-ruby. The name therefore may only be an epithet for
the latter, or the Garnet, whose hue the description " rutila " will
perfectly suit. In fact,
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