"But you will say, according to the opinion of Epicurus, that successions of atoms coming in a ceaseless course, and mixing with one another, and conglomerating through unlimited and endless periods of time, are made solid bodies. I do not treat this opinion as a pure fiction, and that, too, a badly contrived one; but let us examine it, whatever be its character, and see if what is said can stand. For they say that those corpuscles, which they call atoms, are of different qualities: that some are moist, and therefore heavy, and tending downwards; others dry and earthy, and therefore still heavy; but others fiery, and therefore always pushing upwards; others cold and inert, and always remaining in the middle. Since then some, as being fiery, always tend upward, and others, as being moist and dry, always downwards, and others keep a middle and unequal course, how could they meet together and form one body? For if any one throw down from a height small pieces of straw, for example, and pieces of lead of the same size, will the light straws be able to keep up with the pieces of lead, though they be equal in size? Nay; the heavier reach the bottom far more quickly. So also atoms, though they be equal in size, yet, being unequal in weight, the lighter will never be able to keep pace with the heavier; but if they cannot keep pace, certainly neither can they be mixed or form one body.