rought back to the first
month in the year after the winter solstice; and to prevent the
repetition of the error, he directed that in future the year should
consist of three hundred and sixty-five and one-quarter days, which he
effected by adding one day to the months of April, June, September, and
November, and two days to the months of January, Sextilis, and
December, making an addition of ten days to the old year of three
hundred and fifty-five. And he provided for a uniform intercalation of
one day in every fourth year, which accounted for the remaining
quarter of a day.

Caesar was a student of astronomy, and always found time for its
contemplation. He is said even to have written a treatise on the motion
of the stars. He was assisted in his reform of the calendar by
Sosigines, an Alexandrian astronomer. He took it out of the hands of the
priests, and made it a matter of pure civil regulation. The year was
defined by the sun, and not as before by the moon.

Thus the Romans were the first to bring the scientific knowledge of the
Greeks into practical use; but while they measured the year with a great
approximation to accuracy, they still used sun-dials and water-clocks to
measure diurnal time. Yet even these were not constructed as they should
have been. The hour-marks on the sun-dial were all made equal, instead
of varying with the periods of the day,--so that the length of the hour
varied with the length of the day. The illuminated interval was divided
into twelve equal parts; so that if the sun rose at five A.M., and set
at eight P.M., each hour was equal to eighty minutes. And this rude
method of measurement of diurnal time remained in use till the sixth
century. Clocks, with wheels and weights, were not invented till the
twelfth century.

The last great light among the ancients in astronomical science was
Ptolemy, who lived from 100 to 170 A.D., in Alexandria. He was
acquainted with the writings of all the previous astronomers, but
accepted Hipparchus as his guide. He held that the heaven is spherical
and revolves upon its axis; that the earth is a sphere, and is situated
within the celestial sphere, and nearly at its centre; that it is a mere
point in reference to the distance and magnitude of the fixed stars, and
that it has no motion. He adopted the views of the ancient astronomers,
who placed Saturn, Jupiter, and Mars next under the sphere of the fixed
stars, then the sun above Venus and Mercury, and las