[PLATE XX., Fig. 2.], and belonging to the twelfth century before our era, is not perhaps, strictly speaking, a zodiac, but it is almost certainly an arrangement of constellations according to the forms assigned them in Babylonian uranography. [PLATE XXI.] The Ram, the Bull, the Scorpion, the Serpent, the Dog, the Arrow, the Eagle or Vulture may all be detected on the stone in question, as may similar forms variously 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.