This mythical phase of thought terminated in Greece with the rise of the Ionian School of Philosophy. Immemorial legends, discredited by the advent of a new wisdom, took out a fresh lease of life under the guise of folk-lore; Orphic fables were left to the poets and the people; and the sage of Miletus set on foot a speculative tradition, maintained by a long succession of metaphysicians down to the very threshold of the recent scientific epoch. All were what we should call evolutionists--Thales of Miletus no less than Descartes and Swedenborg; their main object, in other words, was to find a practicable mode of evoking a systematic arrangement of related parts from the monotony of undifferentiated confusion. Now, in essaying this enterprise they encountered two distinct problems. One was concerned with the nature of the primeval world-stuff; the other with the operations to which it had been submitted. Modern theorists have made it their primary object to expound the mechanism of cosmic growth--the play of forces involved in it, the transformations and progressive redistribution of energy attending it. But questions of this kind could only in the scantiest measure be formulated by early thinkers, who accordingly devoted their chief attention to selecting an appropriate material for the exercise of their constructive ingenuity. Thales asserted all things to have been derived from water, and water is still among unsophisticated tribes the favourite 'Urstoff.' Anaximenes substituted air. Heracleitus gave the preference to the mobile and vital element (as he thought it) of fire. Anaximander, on the other hand, might put forward a colourable claim to priority over Sir William Crookes in the invention of 'protyle.' He imagined as the matrix of the world a boundless expanse of generalized matter, containing potentially all the chemical species, which, separating out by degrees through the affinity of like for like, formed, by their contrasts and conjunctions, the infinitely varied sum of things. The successors of Anaximander had recourse to spontaneously arising condensations and rarefactions as the mainspring of development; but all these vague principles were quickly crowded into oblivion by the definite and intelligible doctrine of the 'four elements' enunciated by Empedocles, which, guaranteed by the imprimatur of Plato, took a place unchallenged for nearly two millenniums among the fundamentals of science. Erroneous and misleading though it was, it yet served as a means of regulating appearances and guiding vagrant ideas--it was a track to follow in the absence of any better method of orientation.