b Moors, gave loose to all the warmth of
imagination. And several of the Christian fathers applied to it the
descriptions of heaven which are found in the Holy Scripture.

[628] _Hence motion darts its force._--This is the tenth sphere, the
_Primum Mobile_ of the ancient system. To account for the appearances of
the heavens, the Peripatetics ascribed a double motion to it. While its
influence drew the other orbs from east to west, they supposed it had a
motion of its own from west to east. To effect this, the ponderous
weight and interposition of the ninth sphere, or crystalline heaven, was
necessary. The ancient astronomers observed that the stars shifted their
places. This they called the motion of the crystalline heaven, expressed
by our poet at the rate of one pace during two hundred solar years. The
famous Arab astronomer, Abulhasan, in his Meadows of Gold, calculates
the revolution of this sphere to consist of 49,000 of our years. But
modern discoveries have not only corrected the calculation,{*} but have
also ascertained the reason of the apparent motion of the fixed stars.
The earth is not a perfect sphere; the quantity of matter is greater at
the equator; hence the earth turns on her axis in a rocking motion,
revolving round the axis of the ecliptic, which is called the procession
of the equinoxes, and makes the stars seem to shift their places at
about the rate of a degree in 72 years; according to which all the stars
seem to perform one revolution in the space of 25,920 years, after which
they return exactly to the same situation as at the beginning of this
period. However imperfect in their calculations, the Chaldean
astronomers perceived that the motions of the heavens composed one great
revolution. This they called the _annus magnus_, which those who did not
understand them mistook for a restoration of all things to their first
originals.

{*} However deficient the astronomy of Abulhasan may be, it is nothing
to the calculation of his prophet Mohammed, who tells his disciples,
that the stars were each about the bigness of a house, and hung from the
sky on chains of gold.

[629] _And binds the starry sphere._--This was called the firmament, or
eighth heaven. Saturn, Jupiter, Mars, Apollo, Venus, Mercury, and Diana,
were the planets which gave name to, and whose orbits composed, the
other spheres or heavens.

[630] _In shining frost the Northern Chariot rides._--Commonly called
Charles' Wain. Andromeda w