138 THE EARLIEST GREEK GEOMETRY. THALES
this period was doubtless known to Thales, either directly or sun’s
through the Egyptians as intermediaries. Thales, however, of Sa
cannot have known the cause of eclipses; he could not have
given the true explanation of lunar eclipses (as the Doxo-
graphi say he did) because he held that the earth is a circular
disc floating on the water like a log; and, if he had correctly betwe
accounted for solar eclipses, it is impossible that all the (born
succeeding Ionian philosophers should, one after another, have hypol
put forward the fanciful explanations which we find recorded. a s } 10
Thales’s other achievements in astronomy can be very 0 f c j e
shortly stated. Eudemus attributed to him the discovery of ]q | 8 i
‘ the fact that the period of the sun with reference to the suppc
solstices is not always the same’ 1 ; the vague phrase seems equid
to mean that he discovered the inequality of the length of bodie
the four astronomical seasons, that is, the four parts of the opaqi
‘ tropical ’ year as divided by the solstices and equinoxes. filled
Eudemus presumably referred to the written works by Thales (like <
On the Solstice and On the Equinoxes mentioned by Diogenes moon
Laertius. 2 He knew of the division of the year into 365 days, a nd
which he probably learnt from Egypt. suppc
Thales observed of the Hyades that there were two of fixed
them, one north and the other south. He used the Little the s
Bear as a means of finding the pole, and advised the Greeks about
to sail by the Little Bear, as the Phoenicians did, in preference introc
to their own practice of sailing by the Great Bear. This into (
instruction was probably noted in the handbook under the the s<
title of Nautical Astronomy, attributed by some to Thales Greet
and by others to Phocus of Samos. He ii
It became the habit of the Doxographi to assign to Thales, const]
in common with other astronomers in each case, a number mand
of discoveries not made till later. The following is the list, first
with the names of the astronomers to whom the respective The I
discoveries may with most certainty be attributed: (1) the distri
fact that the moon takes its light from the sun (Anaxagoras with
and possibly Parmenides); (2) the sphericity of the earth invob
(Pythagoras); (3) the division of the heavenly sphere into the e
five zones (Pythagoras and Parmenides); (4) the obliquity It is
of the ecliptic (Oenopides of Chios); (5) the estimate of the
m.
1 See Theon of Smyrna, p. 198. 17,
2 Diog. L. i. 23.
