 At the beginning of his treatise of Meteorology, Aristotle summarizes his preceding research: he has established the four causes of nature and dealt with all natural motion in Physics. He has investigated the ordered movement of the stars in the heavens in De caelo, and changes of the four elements into one another, growth, and perishing in De generatione et corruptione. What still has to be investigated is that which takes place “in the region nearest to the motion of the stars such as the Milky Way” (Meteo. 338b 3–4).