reached our times could have been ascertained. Thus the
Babylonians had fixed the length of a tropical year within
twenty-five seconds of the truth; their estimate of the sidereal
year was barely two minutes in excess. They had detected the
precession of the equinoxes. They knew the causes of eclipses,
and, by the aid of their cycle called Saros, could predict them.
Their estimate of the value of that cycle, which is more than
6,585 days, was within nineteen and a half minutes of the truth.

INTELLECTUAL CONDITION OF PERSIA. Such facts furnish
incontrovertible proof of the patience and skill with which
astronomy had been cultivated in Mesopotamia, and that, with very
inadequate instrumental means, it had reached no inconsiderable
perfection. These old observers had made a catalogue of the
stars, had divided the zodiac into twelve signs; they had parted
the day into twelve hours, the night into twelve. They had, as
Alistotle says, for a long time devoted themselves to
observations of star-occultations by the moon. They had correct
views of the structure of the solar system, and knew the order of
the emplacement of the planets. They constructed sundials,
clepsydras, astrolabes, gnomons.

Not without interest do we still look on specimens of their
method of printing. Upon a revolving roller they engraved, in
cuneiform letters, their records, and, running this over plastic
clay formed into blocks, produced ineffaceable proofs. From their
tile-libraries we are still to reap a literary and historical
harvest. They were not without some knowledge of optics. The
convex lens found at Nimroud shows that they were not
unacquainted with magnifying instruments. In arithmetic they had