As a necessary result of a system of natural philosophy based on assumptions, largely illustrated indeed, but not corroborated by the observation of phenomena, with no verification of experiment or ascertainment of special laws, there is throughout the poem the utmost hardihood of assertion and inference on many points, on which modern science clearly proves this system to have been as much in error as it was possible to be. It is strange to note how inadequate an idea Lucretius had of the vastness and complexity of the problem which he professed to solve. He has no real conception of the progressive advance of knowledge, and of the necessity of patiently building on humble foundations. The striking lines-- Namque alid ex alio clarescet nec tibi caeca Nox iter eripiet quin ultima naturai Pervideas: ita res accendent lumina rebus[26], look rather like an unconscious prophecy of the future progress of science than an account of the process of enquiry exhibited in the book. A few out of many erroneous assertions about physical facts, in regard to some of which the opinions of Lucretius are behind the science even of his own time, may be noticed. Thus, at i. 1025, the existence of the Antipodes is denied. Again, in Book iii. the mind is stated to be a material substance, seated in the centre of the breast, composed of very minute particles, the relative proportions of which determine the characters both of men and animals. Lucretius shows a close and subtle observation of facts that establish the interdependence of mind and body, but no suspicion of that interdependence being connected with the functions of the brain and nervous system. His whole account of the _mundus_, of the earth at rest in the centre, and of the rolling vault of heaven, with its sun and moon and stars--'trembling fires in the vault'--all no larger than they appear to our eyes, is given without any notion of the inadequacy of his data to bear out his conclusions. The science which satisfied Epicurus was on astronomical and meteorological questions behind that attained by the mathematicians of Alexandria: and thus some of the conclusions enunciated by Virgil in the Georgics are nearer the truth than those accepted by Lucretius. While enlarging on the variety and subtlety in the combinations of his imaginary atoms, he has no adequate idea of the variety and subtlety in the real forces of Nature. His observation of the outward and visible appearances of things is accurate and vivid: there is often great ingenuity as well as a true apprehension of logical conditions in his processes of reasoning both from ideas and from phenomena: yet most of his conclusions as to the facts of Nature, which are not immediately perceptible to the senses, are mere fanciful explanations, indicating, indeed, a lively curiosity, but no real understanding of the true conditions of the enquiry. The root of his error lies in his not feeling how little can be known of the