History of Astronomy | Page 7

his system, in which the earth revolves in an orbit, from fantastic first
principles, of which the following are examples: "The circular motion
is the most perfect motion," "Fire is more worthy than earth," "Ten is
the perfect number." He wrote nothing, but is supposed to have said
that the earth, moon, five planets, and fixed stars all revolve round the
sun, which itself revolves round an imaginary central fire called the
Antichthon. Copernicus in the sixteenth century claimed Pythagoras as
the founder of the system which he, Copernicus, revived.
Anaxagoras (born 499 B.C.) studied astronomy in Egypt. He explained
the return of the sun to the east each morning by its going under the flat
earth in the night. He held that in a solar eclipse the moon hides the sun,
and in a lunar eclipse the moon enters the earth's shadow--both
excellent opinions. But he entertained absurd ideas of the vortical
motion of the heavens whisking stones into the sky, there to be ignited
by the fiery firmament to form stars. He was prosecuted for this
unsettling opinion, and for maintaining that the moon is an inhabited

earth. He was defended by Pericles (432 B.C.).
Solon dabbled, like many others, in reforms of the calendar. The
common year of the Greeks originally had 360 days--twelve months of
thirty days. Solon's year was 354 days. It is obvious that these
erroneous years would, before long, remove the summer to January and
the winter to July. To prevent this it was customary at regular intervals
to intercalate days or months. Meton (432 B.C.) introduced a reform
based on the nineteen-year cycle. This is not the same as the Egyptian
and Chaldean eclipse cycle called Saros of 223 lunations, or a little
over eighteen years. The Metonic cycle is 235 lunations or nineteen
years, after which period the sun and moon occupy the same position
relative to the stars. It is still used for fixing the date of Easter, the
number of the year in Melon's cycle being the golden number of our
prayer-books. Melon's system divided the 235 lunations into months of
thirty days and omitted every sixty-third day. Of the nineteen years,
twelve had twelve months and seven had thirteen months.
Callippus (330 B.C.) used a cycle four times as long, 940 lunations, but
one day short of Melon's seventy-six years. This was more correct.
Eudoxus (406-350 B.C.) is said to have travelled with Plato in Egypt.
He made astronomical observations in Asia Minor, Sicily, and Italy,
and described the starry heavens divided into constellations. His name
is connected with a planetary theory which as generally stated sounds
most fanciful. He imagined the fixed stars to be on a vault of heaven;
and the sun, moon, and planets to be upon similar vaults or spheres,
twenty-six revolving spheres in all, the motion of each planet being
resolved into its components, and a separate sphere being assigned for
each component motion. Callippus (330 B.C.) increased the number to
thirty-three. It is now generally accepted that the real existence of these
spheres was not suggested, but the idea was only a mathematical
conception to facilitate the construction of tables for predicting the
places of the heavenly bodies.
Aristotle (384-322 B.C.) summed up the state of astronomical
knowledge in his time, and held the earth to be fixed in the centre of the
world.

Nicetas, Heraclides, and Ecphantes supposed the earth to revolve on its
axis, but to have no orbital motion.
The short epitome so far given illustrates the extraordinary deductive
methods adopted by the ancient Greeks. But they went much farther in
the same direction. They seem to have been in great difficulty to
explain how the earth is supported, just as were those who invented the
myth of Atlas, or the Indians with the tortoise. Thales thought that the
flat earth floated on water. Anaxagoras thought that, being flat, it would
be buoyed up and supported on the air like a kite. Democritus thought it
remained fixed, like the donkey between two bundles of hay, because it
was equidistant from all parts of the containing sphere, and there was
no reason why it should incline one way rather than another.
Empedocles attributed its state of rest to centrifugal force by the rapid
circular movement of the heavens, as water is stationary in a pail when
whirled round by a string. Democritus further supposed that the
inclination of the flat earth to the ecliptic was due to the greater weight
of the southern parts owing to the exuberant vegetation.
For further references to similar efforts of imagination the reader is
referred to Sir George Cornwall Lewis's _Historical Survey of the
Astronomy of the Ancients_; London, 1862. His list of authorities is
very complete, but some of his conclusions are doubtful. At p.