In the beginning, then, there was a chaotic mixture of different kinds of matter. The Nous produced a vortex at one point in the middle of this mass. This vortex spread itself outwards in the mass of matter, like rings caused by the fall of a stone in water. It goes on for ever and continually draws more and more matter out of the infinite mass into itself. The movement, therefore, is never-ending. It causes like kinds of matter to come together with like, gold to gold, wood to wood, water to water, and so on. It is to be noted, therefore, that the action of the Nous is apparently confined to the first movement. It acts only at the one central point, and every subsequent movement is caused by the vortex itself, which draws in more and more of the surrounding matter into itself. First are separated out the warm, dry, and light particles, and these form the aether or upper air. Next come the cold, moist, dark, and dense particles which form the lower air. Rotation takes the latter towards the centre, and out of this the earth is formed. The earth, as with Anaximenes, is a flat disc, borne upon the air. The heavenly bodies consist of {103} masses of stone which have been torn from the earth by the force of its rotation, and being projected outwards become incandescent through the rapidity of their movement. The moon is made of earth and reflects the light of the sun. Anaxagoras was thus the first to give the true cause of the moon's light. He was also the first to discover the true theory of eclipses, since he taught that the solar eclipse is due to the intervention of the moon between the sun and the earth, and that lunar eclipses arise from the shadow of the earth falling upon the moon. He believed that there are other worlds besides our own with their own suns and moons. These worlds are inhabited. The sun, according to Anaxagoras, is many times as large as the Peloponnese. The origin of life upon the earth is accounted for by germs which existed in the atmosphere, and which were brought down into the terrestrial slime by rain water, and there fructified. Anaxagoras's theory of perception is the opposite of the theories of Empedocles and the Atomists. Perception takes place by unlike matter meeting unlike.