isolated crystals of borax are frequently found. For example,
crystals up to 7 in. in length and weighing a pound each have been found
in large numbers at Borax Lake in Lake county, and at Borax Lake in San
Bernardino county, both in California.

Borax crystallizes with ten molecules of water, the composition of the
crystals being Na2B4O7 + 10H2O. The crystals belong to the monoclinic
system, and it is a curious fact that in habit and angles they closely
resemble pyroxene (a silicate of calcium, magnesium and iron). There
is a perfect cleavage parallel to the orthopinacoid and less perfect
cleavages parallel to the faces of the prism. The mineral is
transparent to opaque and white, sometimes greyish, bluish or greenish
in colour. Hardness 2-2-1/2; sp. gr. 1.69-1.72.

The optical characters are interesting, because of the striking
crossed dispersion of the optic axes, of which phenomenon borax
affords the best example. The optic figure seen in convergent
polarized light through a section cut parallel to the plane of
symmetry of a borax crystal is symmetrical only with respect to the
central point. The plane of the optic axes for red light is inclined
at 2 deg. to that for blue light, and the angle between the optic axes
themselves is 3 deg. greater for red than for blue light.

BORDA, JEAN CHARLES (1733-1799), French mathematician and nautical
astronomer, was born at Dax on the 4th of May 1733. He studied at La
Fleche, and at an early age obtained a commission in the cavalry. In
1756 he presented a _Memoire sur le mouvement des projectiles_ to the
Academy of Sciences, who elected him a member. He was present at the
battle of Hastembeck, and soon afterwards joined the naval service. He
visited the Azores and the Canary Islands, of which he constructed an
admirable map. In 1782 his frigate was taken by a British squadron; he
himself was carried to England, but was almost immediately released on
parole and returned to France. He died at Paris on the 20th of February
1799. Borda contributed a long series of valuable memoirs to the Academy
of Sciences. His researches in hydrodynamics were highly useful for
marine engineering, while the reflecting and repeating circles, as
improved by him, were of great service in nautical astronomy. He was
associated with J.B.J. Delambre and P.F.A. Mechain in the attempt to
determine an arc of the meridian, and the greater number of the
instruments empl