lines, which recur as a kind of prelude to the successive stages on which it enters, in the first, second, third, and sixth books:-- Hunc igitur terrorem animi tenebrasque necessest Non radii solis neque lucida tela diei Discutiant, sed naturae species ratioque.[378] The action of the poem might be described as the gradual defeat of the ancient dominion of superstition by the new knowledge of Nature. This meaning seems to be symbolised in its magnificent introduction, where the genial, all-pervading Power--the source of order, beauty, and delight in the world and in the heart of man,--and the grim phantom of superstition-- Horribili super aspectu mortalibus instans,-- the cause of ignorance, degradation, and misery,--are vividly personified and presented in close contrast with one another. The thought, thus symbolised, pervades the poem. The processes of Nature are explained not chiefly for the purpose of satisfying the love of knowledge (although this end is incidentally attained), but as the means of establishing light in the room of darkness, peace in the room of terror, faith in the laws and the facts of the universe in the room of a base dependence on capricious and tyrannical Powers. What then was this philosophy which supplied to Lucretius an answer to the perplexities of existence? The object contemplated by all the early systems of ontology was the discovery of the original substance or substances out of which all existing things were created, and which alone remained permanent amid the changing aspects of the visible world. Various systems, of a semi-physical, semi-metaphysical character, were founded on the answers given by the earliest enquirers to this question. In the first book of the poem several of these theories are discussed. Lucretius following Epicurus, adopts the answer given by Democritus to this question, that the original substances were the 'atoms and the void'--ἄτομα καὶ κενόν. After the invocation and the address to Memmius, and the representation of the universal tyranny exercised by superstition until its power was overcome by Epicurus, and after a summary of the various topics to be treated in order to banish this influence from the world, he lays down this principle as the starting-point of his argument,--that no existing thing is formed out of nothing by divine agency-- Nullam rem e nilo gigni divinitus unquam. The apprehension of this principle--a principle common to all the ontological systems of antiquity--is the first step in the enquiry, as to what are the original substances out of which all creation comes into being and is maintained. The proof of this principle is the manifest order and causation recognisable in the world. If things could arise out of nothing, all existence would be confused and capricious. The regularity of Nature subsists-- Materies quia rebus reddita certast Gignundis e qua constat quid possit oriri.