sensation
than the false stone, because being a better conductor of heat. Various
methods are attempted for testing the genuineness of Diamonds; most of
the same being only feasible by an expert; nevertheless the test by
light is very reliable, and simple enough to be easily applied by an
amateur. The Gem should be held at arm's length, about ten inches from
the light of a candle, or lamp, in a straight line with the eye. If the
Diamond is real it will give out only a single bright ray of refraction.
Diamantino
is the city of the Diamond mines in Brazil. A negro is reported to have
found a diamond there of nine carats among the roots of some vegetables
which he pulled up in his garden.
If
a manufactured diamond contains a flaw, (being thus " off colour,") its
value is diminished. To ascertain if the flaw exists, the gem should
be breathed-on until its lustre is temporarily abolished, when any such
imperfection may be easily detected.
Other
precious Stones besides the Diamond are sensibly affected by mutations
of light, and heat, when telling on their substance. Topazes, when
exposed to a low red heat in a sand bath, become of a fine pink hue ;
but they lose much of their first brilliancy after being exposed to any
bright light for a length of time. Opals, as is well known, are
peculiarly sensitive to extremes of heat, and cold ; whilst at the same
time they are the most brittle stones which occur. The prismatic
reflections to which they owe their beauty are entirely due to the
minute seams, and clefts which are distributed over their surface, and
which emit rays of light in every direction. Rubies, again, are to be
included amongst those Gems which are most
