1911 Encyclopædia Britannica/Anaximenes of Miletus
ANAXIMENES, of Miletus, Greek philosopher in the latter half of the 6th century, was probably a younger contemporary of Anaximander, whose pupil or friend he is said to have been. He held that the air, with its variety of contents, its universal presence, its vague associations in popular fancy with the phenomena of life and growth, is the source of all that exists. Everything is air at different degrees of density, and under the influence of heat, which expands, and of cold, which contracts its volume, it gives rise to the several phases of existence. The process is gradual, and takes place in two directions, as heat or cold predominates. In this way was formed a broad disk of earth, floating on the circumambient air. Similar condensations produced the sun and stars; and the flaming state of these bodies is due to the velocity of their motions.
See Schmidt, Dissertatio de Anaximensis psychologia (Jena, 1869); Ritter and Preller, Historia Phil. §§ 23-27; A. Fairbanks, First Philosophers of Greece (1898); Mullach, Fragmenta Phil. Graec. i. 241-243; also Ionian School of Philosophy; Evolution.