derived from position and arrangement of particles, but that all quality whatever is founded upon position and arrangement. All becoming is explained by Empedocles as the result of motion of material particles. To bring this mechanical philosophy to its logical conclusion, all qualitativeness of things must be explained in the same way. Hence it was impossible that the philosophy of mechanism and materialism should stand still in the position in which Empedocles left it. It had to advance to the position of Atomism. The Atomists, therefore, maintain the essential position of Empedocles, after eliminating the inconsistencies which we have just noted. The philosophy of Empedocles is therefore to be considered as merely transitional in character. First, the Atomists developed the theory of particles. According to Leucippus and Democritus, if matter were divided far enough, we should ultimately come to indivisible units. These indivisible units are called atoms, and atoms are therefore the ultimate constituents of matter. They are infinite in number, and are too small to be perceptible to the senses. Empedocles had assumed four different kinds of matter. But, for the Atomists, there is only one kind. All the atoms are composed of exactly the same kind of matter. With certain exceptions, which I will mention in a moment, they possess no quality. They are entirely non-qualitative, the only differences between them being differences of quantity. They differ in size, some being larger, some smaller. And they likewise differ in shape. Since the ultimate particles of things thus possess no quality, all the actual qualities of objects must be due to the {89} arrangement and position of the atoms. This is the logical development of the tentative mechanism of Empedocles. I said that the atoms possess no qualities. They must, however, be admitted to possess the quality of solidity, or impenetrability, since they are defined as being indivisible. Moreover it is a question whether the atoms of Democritus and Leucippus were thought to possess weight, or whether the weight of objects is to be explained, like other qualities, by the position and movement of the atoms. There is no doubt that the Epicureans of a later date considered the atoms to have weight. The Epicureans took over the atomism of Democritus and Leucippus, with few modifications, and made it the basis of their own teaching. They ascribed weight to the atoms, and the only question is whether this was a modification introduced by them, or whether it was part of the original doctrine of Democritus and Leucippus.