no reason for moving in one direction rather than another. If this were valid, he said, a man placed
at the centre of a circle with food at various points of the circumference would starve to death for
lack of reason to choose one portion of food rather than another. This argument reappears in
scholastic philosophy, not in connection with astronomy, but with free will. It reappears in the
form of "Buridan's ass," which was unable to choose between two bundles of hay placed at equal
distances to right and left, and therefore died of hunger.
Pythagoras, in all probability, was the first to think the earth spherical, but his reasons were (one
must suppose) aesthetic rather than scientific. Scientific reasons, however, were soon found.
Anaxagoras discovered that the moon shines by reflected light, and gave the right theory of
eclipses. He himself still thought the earth flat, but the shape of the earth's shadow in lunar
eclipses gave the Pythagoreans conclusive arguments in favour of its being spherical. They went
further, and regarded the earth as one of the planets. They knew-from Pythagoras himself, it is
said--that the morning star and the evening star are identical, and they thought that all the planets,
including the earth, move in circles, not round the sun, but round the "central fire." They had
discovered that the moon always turns the same face to the earth, and they thought that the earth
always turns the same face to the "central fire." The Mediterranean regions were on the side turned
away from the central fire, which was therefore always invisible. The central fire was called "the
house of Zeus," or "the Mother of the gods." The sun was supposed to shine by light reflected
from the central fire. In addition to the earth, there was another body, the counter-earth, at the
same distance from the central fire. For this, they had two reasons, one scientific, one derived
from their arithmetical mysticism. The scientific reason was the correct observation that an eclipse
of the moon sometimes occurs when both sun and moon are above the horizon. Refraction, which
is the cause of this phenomenon, was unknown to them, and they thought that, in such cases, the
eclipse must be due to the shadow of a body other than the earth. The other reason was that the
sun and moon, the five planets, the earth and counter-earth, and the central fire, made ten heavenly
bodies, and ten was the mystic number of the Pythagoreans.
This Pythagorean theory is attributed to Philolaus, a Theban, who