* This is believed to have been much larger before cutting; original size not known.
are said to have been stones such as the Great Mogul, weighing 787.5
carats, the Mattan, 367 carats, and the Braganza, 1680 carats, but
these have not been authenticated.
from hardness, the special qualities of a diamond depend upon its
optical characters, under which we group such related subjects as
refraction, reflection, and color dispersion. Light, of all colors and
all wave lengths, travels with a velocity of about 186,000 miles per
second, a little less in air than in a vacuum. But when it enters a
denser medium, such as a crystal, the velocity receives a check
proportional to the index of refraction of the medium. In diamonds the
velocity of red light is about 77,000 miles per second and of violet
light about 75,000 miles per second. It takes longer for a violet ray
to get 'round inside a brilliant-cut diamond, before flashing out from
the front of the gem, than it does for a red ray traveling along the
same path. As a result of this check in the velocity, the path of the
ray is deflected when it enters the stone. This is known as the
refraction of light, and the amount of refraction of light, or
bending, gives a measure of the index of refraction.