_Heraclitus of Ephesus_(B.C. 503-420) comes next in the order of speculative thought. In his philosophy, _fire_ is the ἀρχή, or first principle; but not fire in the usual acceptation of that term. The Heraclitean "fire" is not flame, which is only an intensity of fire, but a warm, dry vapor--an _ether_, which may be illustrated, perhaps, by the "caloric" of modern chemistry. This "_ether_" was the primal element out of which the universe was formed; it was also a vital power or principle which animated the universe, and, in fact, the _cause_ of all its successive phenomenal changes. "The world," he said, "was neither made by the gods nor men, and it was, and is, and ever shall be, an _ever-living fire_, in due proportion self-enkindled, and in due measure self-extinguished."[416] The universe is thus reduced to "an eternal fire," whose ceaseless energy is manifested openly in the work of dissolution, and yet secretly, but universally, in the work of renovation. The phenomena of the universe are explained by Heraclitus as "the concurrence of opposite tendencies and efforts in the motions of this ever-living fire, out of which results the most beautiful harmony. This harmony of the world is one of conflicting impulses, like the lyre and the bow. The strife between opposite tendencies is the parent of all things. All life is change, and change is strife."[417] [Footnote 416: Ritter's "History of Ancient Philosophy," vol. i. p. 235.] [Footnote 417: Lewes's "Biographical History of Philosophy," p. 70; Ritter's "History of Ancient Philosophy," vol. i. p. 244.] Heraclitus was the first to proclaim the doctrine of the perpetual fluxion of the universe (τὸ ῥέον, τὸ γιγνόμενον--Unrest and Development), the endless changes of matter, and the mutability and perishability of all individual things. This restless, changing flow of things, which never _are_, but always are _becoming_, he pronounced to be the _One_ and the _All_.