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.