Observe that not one of these Ionic philosophers had yet asserted the great contrast of mind and matter, the still greater contrast of a Divine architect and his work. The phenomena of mind seemed to them but to be the result of a subtle and more impalpable combination of elements not differing in kind from the nature of material substances. So when a wholly different school came to review what the ancients had accomplished, the _Nous_ of Anaxagoras, and the Love and Hate of Empedocles, were hardly felt to be steps in advance. In fact for a while the development seemed to be the other way, for the last great theory we have to notice, before we come to the ideal philosophy of Plato and his followers, is more decidedly materialistic than all its predecessors. That is the famous Atomic theory of Leucippus and Democritus, which maintained that the universe contains no elements but atoms and the void, the atoms being hard physical particles of only one quality but capable of myriad mechanical combinations in and by means of the void, or empty space which existed more or less in every body. As a hypothesis, this is the simplest that has ever been offered to explain the constitution of matter; it has consequently lasted all through the Renascence of learning into the newer age and has formed the very basis of the modern science of chemistry. The original atoms were not conceived as mathematical points, or as having any spiritual quality like the monads of Leibnitz; they were merely very small, impenetrable, and differing in figure. It was the density of their combination and hence the small fraction of void spaces in any body which made the difference of specific gravity, and the difference of their shape produced other qualities.