Euclid

Euclid. 1. Of Megara, one of the founders of the Megarian school of philosophy (about 400 B.C.). His doctrines probably influenced those of Plato.

2. A famous geometrician who lived and taught in Alexandria at about 300 B.C., in the time of Ptolemy I. Besides his Elements he wrote the Phenomena, on astronomy, and the Data, a collection of geometrical theorems, and possibly also various books on Harmony, Optics, etc. Euclid's Elements have been used as a text-book for centuries, though abroad various systems of modern geometry have taken its place. It is in thirteen books; the first four are on plane geometry involving only figures built up of straight lines and circles; the fifth is on proportion generally; the sixth on proportion as applied to similar plane figures; the seventh, eighth, and ninth are on numbers; the tenth on incommensurable quantities; and the last three on solid geometry. The first printed edition of the Elements was published at Venice in 1482. The only full edition is that of Gregory, published at Oxford in 1703.