From Thales to Plato, a century and a half intervened.[5] During this period there arose, according to Mr. Grote, twelve distinct schemes of philosophy, the authors of which that learned Englishman has enumerated, together with an admirable summary of their respective systems. From this summary certain things are apparent. All these philosophers, from Thales to Democritus, while each speculated upon Nature in an original vein of his own, endeavored to find an explanation or hypothesis on which to account for the production and generation of the universe by some physical agency apart from the mythical personifications which were believed in by the populace and assumed in the poetical theologies. Some of them, without blending ethics and theology in their speculations, adopted, as the universal and sufficient agents, the common, familiar, and pervading material substances, such as water, fire, air, etc.; others, as Pythagoras and his sect, united with ethical and theological speculations the idea of geometrical and arithmetical combinations as the primal scientific basis of the phenomena of Nature. But what was common to all these speculations was the attempt to find a scientific basis on which to explain, by physical generation, by transmutation and motion from place to place, the generation of the Kosmos, to take the place of generation by a divine personal agency or agencies. But while these speculations were of course unsuccessful, their abundance and variety, the inventive genius which they exhibit, the effort to find a scientific basis apart from the popular and poetic belief in a multitude of personal and divine agencies, constitute, as Mr. Grote has well said, "one of the most memorable facts in the history of the Hellenic mind"; and "the mental effort required to select some known agency and to connect it by a chain of reasoning with the result, all this is a new phenomenon in the history of the human mind." Such an amount of philosophical speculations could not go on for a century and a half without enlarging the means for dealing with questions of natural theology; for they very nearly exhausted the "causings and beginnings" which could be assigned to regular knowable and predictable agencies; and these they carried through almost every conceivable form of action by which such agencies could be supposed to operate. While the authors of these systems of philosophy were constantly hampered by the popular and poetic conceptions of a diversified and omnipresent polytheistic agency, a belief which, as Mr. Grote has said, was "eminently captivating and impressive," and which pervaded all the literature of their time, their speculations accumulated a vast fund of ideas in the sphere of scientific explanations, which, although unsatisfactory to modern science, became, when we reach Plato, the principal influence which led him to revert to the former idea of a divine agency, intentionally and