do
not think it unlikely that Nero's emerald was an aqnamarina cut for the
purpose of a magnifying glass. In corroboration of the above, we bring
to the notice of the reader the fact that Nicola de Cusa, Bishop of
Brixen, who died in 1454, gave the name of Beryllus to one of his works
for this reason, that " by means of its assistance, people could
understand things otherwise incomprehensible ;" and in the second
chapter he expressly says : " The beryl is a bright, transparent,
colourless stone, to which a concave or convex form is given by art,
and by means of which whoever looks through it sees things otherwise
invisible to the naked eye."
XVI.
BOORT (KNOTTY DIAMOND).
This particular
species of adamantine carbon, which seems placed by nature between
crystallized carbon and the pure diamond, bears a name of unknown
etymology, but certainly of Dutch origin.
Most
frequently it is of spherical form, and its crystallization is so
irregular that it resembles the most complicated knots in certain woods.
It
is a mixture of molecules without order or continuity, and these,
adhering solely by the force of cohesion, are the cause of its
wonderful hardness. It has not any regular cleavage.
The boort is externally more rough than some
