catalogue of the fixed stars, of which the Greeks
made use in compiling their stellar tables. They observed and recorded
their observations upon occultations of the planets by the sun and moon.
They invented the _gnomon_ and the _polos_, two kinds of sundial, by
means of which they were able to measure time during the day, and to
fix the true length of the solar day, with sufficient accuracy. They
determined correctly within a small fraction the length of the synodic
revolution of the moon. They knew that the true length of the solar
year was 365 days and a quarter, nearly. They noticed comets, which they
believed to be permanent bodies, revolving in orbits like those of
the planets, only greater. They ascribed eclipses of the sun to the
interposition of the moon between the sun and the earth. They had
notions not far from the truth with respect to the relative distance
from the earth of the sun, moon, and planets. Adopting, as was natural,
a geocentric system, they decided that the Moon occupied the position
nearest to the earth; that beyond the Moon was Mercury, beyond Mercury
Venus, beyond Venus Mars, beyond Mars Jupiter, and beyond Jupiter, in
the remotest position of all, Saturn. This arrangement was probably
based upon a knowledge, more or less exact, of the periodic times which
the several bodies occupy in their (real or apparent) revolutions. From
the difference in the times the Babylonians assumed a corresponding
difference in the size of the orbits, and consequently a greater or less
distance from the common centre.

Thus far the astronomical achievements of the Babylonians rest upon
the express testimony of ancient writers--a testimony confirmed in many
respects by the monuments already deciphered. It is suspected that, when
the astronomical tablets which exist by hundreds in the British Museum
come to be thoroughly understood, it will be found that the acquaintance
of the Chaldaean sages with astronomical phenomena, if not also with
astronomical laws, went considerably beyond the point at which we should
place it upon the testimony of the Greek and Roman writers. There is
said to be distinct evidence that they observed the four satellites of
Jupiter, and strong reason to believe that they were acquainted likewise
with the seven satellites of Saturn. Moreover, the general laws of the
movements of the heavenly bodies seem to have been so far known to
them that they could state by anticipation the position of t