Lucretius’ great poem, _On Nature_, was apparently being written during the middle decade of the last pre-Christian century. It was not quite complete when the poet died; the preface addresses Memmius as one who is in the midst of danger and apparently in arms,[5] a reference perhaps to Memmius’ governorship of Bithynia in 57. But the preface assumes the present arrangement of books, which was not established till books 1, 2 and 4 had been written. Perhaps this foreword was thrown in for an incomplete presentation copy to accompany Memmius when he sailed to Bithynia in the spring of 57. Of the legend that the poet experienced intervals of insanity I need only repeat the judgment of the noted physician Dr. Osler:[6] “Of love-philtres that produce insanity we may read the truth in a chapter of that most pleasant manual of erotology, the _Anatomy of Melancholy_. Of insanity of any type that leaves a mind capable in lucid intervals of writing such verses as _De Rerum Natura_ we know nothing. The sole value of the myth is its casual association with the poem of Tennyson.” This of course does not preclude the possibility that Lucretius committed suicide in a fit of madness, though what a father of the church reports about a member of the Epicurean sect must not be taken too seriously. Wishful thinking often ends in the misjudging of sources. The poem of Lucretius may be classed with Milton’s _Paradise Lost_ as a purposive work of art. Milton set out to “justify the ways of God to man” in verses that should carry the reader by their sheer emotional beauty; Lucretius, while equally aware of the demands of art, proclaimed his chief purpose to be to remove fear of the gods by describing creation as natural and independent of divine intervention. Milton is one of the last of the didactic poets; Lucretius wrote while the didactic tradition was still generally accepted. He wrote in verse because his predecessors, the earlier philosophers had done so, had indeed composed wholly in verse at a time when reading and writing were not general, when teaching was by word of mouth, and rhythm seemed a legitimate aid to memory. Didactic verse, at first a necessity, had established itself by its very bulk, and was accepted as a customary form by Ennius and Vergil as well as by Lucretius. The effort that the modern reader finds in adapting himself to imaginative and highly colored phraseology employed in scientific arguments need not be strenuous if one accepts the tradition as then vital and unquestioned.