Note 14 — Chapter I · The Development of Astronomical Thought to 1400 A.D. A Preliminary Sketch of Early Theories as a Background.

This is the only account of his system. Even the age in which he flourished is so little known that there have been many disputes whether he was the original inventor of this system or followed some other. He was probably a contemporary of Cleanthes the Stoic in the 3rd century B.C. He is mentioned also by Ptolemy, Diogenes Laërtius and Vitruvius. (Schiaparelli: Die Vorlaufer des Copernicus im Alterthum, 75. See also Heath: Op. cit.)