His speculations about things, like those of Parmenides before him and of Lucretius after him, are set down in verse. From the remains of his Poem on Nature we learn that he conceived "the four roots of all things" to be FIRE, AIR, EARTH, and WATER. They are "fools, lacking far-reaching thoughts, who deem that what before was not comes into being, or that aught can perish and be utterly destroyed." Therefore the "roots" or elements are eternal and indestructible. They are acted upon by two forces, which are also material, LOVE and STRIFE; the one a uniting agent, the other a disrupting agent. From the four roots, thus operated upon, arise "the colours and forms" of living things; trees first, both male and female, then fragmentary parts of animals, heads without necks, and "eyes that strayed up and down in want of a forehead," which, combined together, produced monstrous forms. These, lacking power to propagate, perished, and were replaced by "whole-natured" but sexless "forms" which "arose from the earth," and which, as Strife gained the upper hand, became male and female. Herein, amidst much fantastic speculation, would appear to be the germ of the modern theory that the unadapted become extinct, and that only the adapted survive. Nature kills off her failures to make room for her successes. Anaxagoras, who was a contemporary of Empedocles, interests us because he was the first philosopher to repair to Athens, and the first sufferer for truth's sake of whom we have record in Greek annals. Because he taught that the sun was a red-hot stone, and that the moon had plains and ravines in it, he was put upon his trial, and but for the influence of his friend, the famous Pericles, might have suffered death. Speculations, however bold they be, pass unheeded till they collide with the popular creed, and in thus attacking the gods, attack a seemingly divinely settled order. Athens then, and long after, while indifferent about natural science, was, under the influence of the revival referred to above, actively hostile to free thinking. The opinions of Anaxagoras struck at the existence of the gods and emptied Olympus. If the sky was but an air-filled space, what became of Zeus? if the sun was only a fiery ball, what became of Apollo? Mr. Grote says (History of Greece, vol. i, p. 466) that "in the view of the early Greek, the description of the sun, as given in a modern astronomical treatise, would have appeared not merely absurd, but repulsive and impious; even in later times, Anaxagoras and other astronomers incurred the charge of blasphemy for dispersonifying Hēlios." Of Socrates, who was himself condemned to death for impiety in denying old gods and introducing new ones, the same authority writes: "Physics and astronomy, in his opinion, belonged to the divine class of phenomena, in which human research was insane, fruitless, and impious." So Demos and his "betters" clung, as the majority still cling, to the myths of their forefathers.