iously arranged on other similar monuments.

[Illustration: PLATE XXI.]

The Babylonians called the Zodiacal constellations the "Houses of the
Sun," and distinguished from them another set of asterisms, which they
denominated the "Houses of the Moon." As the Sun and Moon both move
through the sky in nearly the same plane, the path of the Moon merely
crossing and recrossing that of the Sun, but never diverging from it
further than a few degrees, it would seem that these "Houses of the
Moon," or lunar asterisms, must have been a division of the Zodiacal
stars different from that employed with respect to the sun, either
in the number of the "Houses," or in the point of separation between
"House" and "House."

The Babylonians observed and calculated eclipses; but their power of
calculation does not seem to have been based on scientific knowledge,
nor to have necessarily implied sound views as to the nature of eclipses
or as to the size, distance, and real motions of the heavenly bodies.
The knowledge which they possessed was empirical. Their habits of
observation led them to discover the period of 223 lunations or 18 years
10 days, after which eclipses--especially those of the the moon--recur
again in the same order. Their acquaintance with this cycle would enable
them to predict lunar eclipses with accuracy for many ages, and solar
eclipses without much inaccuracy for the next cycle or two.

That the Babylonians carefully noted and recorded eclipses is witnessed
by Ptolemy, who had access to a continuous series of such observations
reaching back from his own time to B.C. 747. Five of these--all eclipses
of the moon--were described by Hipparchus from Babylonian sources, and
are found to answer all the requirements of modern science. They belong
to the years B.C. 721, 720, 621, and 523. One of them, that of B.C. 721,
was total at Babylon. The others were partial, the portion of the moon
obscured varying from one digit to seven.

There is no reason to think that the observation of eclipses by the
Babylonians commenced with Nabonassar. Ptolemy indeed implies that the
series extant in his day went no higher; but this is to be accounted for
by the fact, which Berosus mentioned, that Nabonassar destroyed, as
far as he was able, the previously existing observations, in order that
exact chronology might commence with his own reign.

Other astronomical achievements of the Babylonians were the following.
They accomplished a