Greek natural philosopher, believed everything was composed of air
Background
Anaximenes was the third in a line of Philosopher from Miletus, after Thales and Anaximander. He is reported that Anaximenes was a student of Anaximander and tried to give a scientific explanation of the world rather than religious. He maintained that the basic substance was not water or apeiron but air. All other things could be created in the process of air cooling down air or warming it up.
Natural Change
“Air differs in essence in accordance with its rarity or density. When it is thinned it becomes fire, while when it is condensed it becomes wind, then cloud, when still more condensed it becomes water, then earth, then stones. Everything else comes from these.” A quote from Diels-Kranz collection of Presocratic sources.
Model of the Earth
The earth floats on a cushion of air. The heavenly bodies, or at least the sun and the moon, seem also be flat bodies that float on streams of air. On one account the heaven is like a felt cap that turns around the head. The stars may be fixed to this surface like nails. In another account the stars are like fiery leaves floating on air. The sun does not travel under the earth but circles around it, and is hidden by the higher parts of the earth at night.
Rainbows and Hailstones
Anaximenes, like Anaximander uses scientific reasoning to account for various natural phenomena. Lightning and thunder result from wind breaking out of clouds, rainbows are the result of the rays of the sun falling on clouds; earthquakes are caused by the cracking of the earth when it dries out after being moistened by rains. He gives a correct account of hail as frozen rainwater.