fixed, this is an actual revolution;
but if it moves the anomalistic revolution is greater or less than a
complete circumference.

An _Anomalistic year_ is the time (365 days, 6 hours, 13 minutes, 48
seconds) in which the earth (and similarly for any other planet) passes
from perihelion to perihelion, or from any given value of the anomaly to
the same again. Owing to the precession of the equinoxes it is longer
than a tropical or sidereal year by 25 minutes and 2.3 seconds. An
_Anomalistic month_ is the time in which the moon passes from perigee to
perigee, &c.

For the mathematics of Kepler's problem see E.W. Brown, _Lunar Theory_
(Cambridge 1896), or the work of Watson or of Bauschinger on
Theoretical Astronomy.

ANORTHITE, an important mineral of the felspar group, being one of the
end members of the plagioclase (q.v.) series. It is a calcium and
aluminium silicate, CaAl2Si2O3, and crystallizes in the anorthic system.
Like all the felspars, it possesses two cleavages, one perfect and the
other less so, here inclined to one another at an angle of 85 deg. 50'.
The colour is white, greyish or reddish, and the crystals are
transparent to translucent. The hardness is 6-6-1/2, and the specific
gravity 2.75.

[Illustration: Anorthite]

Anorthite is an essential constituent of many basic igneous rocks, such
as gabbro and basalt, also of some meteoric stones. The best developed
crystals are those which accompany mica, augite, sanidine, &c., in the
ejected blocks of metamorphosed limestone from Monte Somma, the ancient
portion of Mount Vesuvius; these are perfectly colourless and
transparent, and are bounded by numerous brilliant faces. Distinctly
developed crystals are also met with in the basalts of Japan, but are
usually rare at other localities.

The name anorthite was given to the Vesuvian mineral by G. Rose in 1823,
on account of its anorthic crystallization. The species had, however,
been earlier described by the comte de Bournon under the name indianite,
this name being applied to a greyish or reddish granular mineral forming
the matrix of corundum from the Carnatic in India. Several unimportant
varieties have been distinguished. (L. J. S.)

ANQUETIL, LOUIS PIERRE (1723-1808), French historian, was born in Paris,
on the 21st of February 1723. He entered the congregation of
Sainte-Genevieve, where he took holy orders and became professor of
theology and literature. Later, he became direct