Flourished Circa 545 B.C.E.
Philosopher

Universal Building Block. No information survives about the life of Anaximenes, the last of the Milesians, except that he is said to have been the pupil of Anaxagoras. His theory that aer (air, mist, or vapor) is the fundamental element of the universe marks a genuine advance over earlier theories because it provides a dynamic mechanism to account for physical changes in the world. According to Anaximenes, cycles of condensation and rarefaction and contraction and expansion determine the transformation of "thin" air into increasingly denser air: "Clouds occur when air gets thickened; when compressed further, rain is squeezed out; and hail occurs when the falling water condenses." In the case of snow, a lower temperature and some wind would cause the water to get frothy and white.

Source:

G. E. R. Lloyd, Early Greek Science: Thales to Aristotle (New York: Norton...