of the fixed stars round the axis of the ecliptic, which
is called the Precession of the Equinoxes,--one of the greatest
discoveries in astronomy. He maintained that the precession was not
greater than fifty-nine seconds, and not less than thirty-six seconds.
Hipparchus also framed a catalogue of the stars, and determined their
places with reference to the ecliptic by their latitudes and longitudes.
Altogether he seems to have been one of the greatest geniuses of
antiquity, and his works imply a prodigious amount of calculation.

Astronomy made no progress for three hundred years, although it was
expounded by improved methods. Posidonius constructed an orrery, which
exhibited the diurnal motions of the sun, moon, and five planets.
Posidonius calculated the circumference of the earth to be two hundred
and forty thousand stadia, by a different method from Eratosthenes. The
barrenness of discovery from Hipparchus to Ptolemy,--the Alexandrian
mathematician, astronomer, and geographer in the second century of the
Christian era,--in spite of the patronage of the royal Ptolemies of
Egypt, was owing to the want of instruments for the accurate measure of
time (like our clocks), to the imperfection of astronomical tables, and
to the want of telescopes. Hence the great Greek astronomers were unable
to realize their theories. Their theories however were magnificent, and
evinced great power of mathematical combination; but what could they do
without that wondrous instrument by which the human eye indefinitely
multiplies its power? Moreover, the ancients had no accurate almanacs,
since the care of the calendar belonged not so much to the astronomers
as to the priests, who tampered with the computation of time for
sacerdotal objects. The calendars of different communities differed.
Hence Julius Caesar rendered a great service to science by the reform of
the Roman calendar, which was exclusively under the control of the
college of pontiffs, or general religious overseers. The Roman year
consisted of three hundred and fifty-five days; and in the time of
Caesar the calendar was in great confusion, being ninety days in
advance, so that January was an autumn month. He inserted the regular
intercalary month of twenty-three days, and two additional ones of
sixty-seven days. These, together with ninety days, were added to three
hundred and sixty-five days, making a year of transition of four hundred
and forty-five days, by which January was b