This story, however, is discredited by the writers who mention it insofar as they say he wrote books and dissected animals, neither of which could be done well without eyes. Democritus expanded the atomic theory of Leucippus. He maintained the impossibility of dividing things ad infinitum . From the difficulty of assigning a beginning of time, he argued the eternity of existing nature, of void space, and of motion. He supposed the atoms, which are originally similar, to be impenetrable and have a density proportionate to their volume.
All motions are the result of active and passive affection.
He drew a distinction between primary motion and its secondary effects, that is, impulse and reaction. This is the basis of the law of necessity, by which all things in nature are ruled. The human soul consists of globular atoms of fire, which impart movement to the body. He distinguished between a rude, imperfect, and therefore false perception and a true one. We know these from dreams and the causes of divination.