I. The philosophical system expounded in the poem is the atomic theory of Democritus[377], in the form in which it was accepted by Epicurus, and made the basis of his moral and religious doctrines. Lucretius lays no claim to original discovery as a philosopher: he professes only to explain, in his native language, 'Graiorum obscura reperta.' His originality consists, not in any expansion or modification of the Epicurean doctrine, but in the new life which he has imparted to its exposition, and in the poetical power with which he has applied it to reveal the secret of the life of Nature and of man's true position in the world. After enunciating the first principles of the atomic philosophy, he discusses in the last four books of the poem some special applications of that doctrine, which formed part of the physical system of Epicurus. But the extent to which he carries these discussions is limited by the practical purpose which he has in view. The impelling motive of all his labour is the impulse to purify human life, and, especially, to emancipate it from the terrors of superstition. The source of these terrors is traced to the general ignorance of certain facts in Nature,--ignorance, namely, of the constitution and condition of our souls and bodies, of the means by which the world came into existence and is still maintained, and lastly, of the causes of many natural phenomena, which are attributed to the direct agency of the gods. With the view of establishing knowledge in the room of ignorance on these questions, it is necessary, in the first place, to give a full account of the original principles of being: and to this enquiry the two first books of the poem are devoted. Had his purpose been merely speculative, the subject of the fifth book,--viz. the origin of the world, of life, and of human society,--would naturally have been treated immediately after the exposition of these first principles. But the order of treatment is determined by the immediate object of attacking the chief stronghold of superstition: and, accordingly, the third and fourth books contain an examination of the nature of the soul, a proof of its non-existence after death, and an explanation of the origin of the belief in a future state. In the fifth and sixth books an attempt is made to show that the creation and preservation of the world, the origin and progress of human society, and the phenomena of thunder, tempests, volcanoes, and the like, are the results of natural laws, without Divine intervention. Although he sometimes carries his argument into greater detail than is necessary for his purpose, and addresses himself to the reform of other evils to which the human heart is liable, yet his whole treatment of his subject is determined by the thought of the irreconcilable opposition between the truths of Nature and the falsehood of the ancient religions. The key-note to the argument is contained in the