It is a misfortune that an apparently full history of Greek geometry and sstronomy, covering the period prior to B.c., written by Eudemus, B pupil Aristotle, has been lost. A brief account of this history was given(ca. A.D.) by Proclus, in his commentary on Euclid. This abstract, known as the Eudemian Sum information for the very constitutes our most reliable source of cussion. early period of Greek mathematies now under dis- in the The account of the achievements of Thales, sketched preceding section, was furnished by the Eudemian Summary