"What are you, where did you come from, and whither are you bound?"--the question which from Homer's days has been put to the wayfarer in strange lands--is likewise the all-absorbing question which man is ever asking of the universe of which he is himself so tiny yet so wondrous a part. From the earliest times the ultimate purpose of all scientific research has been to elicit fragmentary or partial responses to this question, and philosophy has ever busied itself in piecing together these several bits of information according to the best methods at its disposal, in order to make up something like a satisfactory answer. In old times the best methods which philosophy had at its disposal for this purpose were such as now seem very crude, and accordingly ancient philosophers bungled considerably in their task, though now and then they came surprisingly near what would to-day be called the truth. It was natural that their methods should be crude, for scientific inquiry had as yet supplied but scanty materials for them to work with, and it was only after a very long course of speculation and criticism that men could find out what ways of going to work are likely to prove successful and what are not.