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edge at that date. We have no evidence be-
yond his own statement that he was a prac-
tical observer. He theorised on the plan-
etary motions, and held that the earth is
fixed in the centre of the universe. He adopted
the excentric and equant of Hipparchus to
explain the unequal motions of the sun and
moon. He adopted the epicycles and def-
erents which had been used by Apollonius
112
