This trio constitutes the Ionian school of philosophy, the earliest of the Greek schools; and one who reads for the first time the few vague statements which seem to constitute the sum of their contributions to human knowledge is impelled to wonder that so much has been made of the men. This wonder disappears, however, when one realizes that the appearance of these thinkers was really a momentous thing. For these men turned their faces away from the poetical and mythologic way of accounting for things, which had obtained up to their time, and set their faces toward Science. Aristotle shows us how Thales may have been led to the formulation of his main thesis by an observation of the phenomena of nature. Anaximander saw in the world in which he lived the result of a process of evolution. Anaximenes explains the coming into being of fire, wind, clouds, water, and earth, as due to a condensation and expansion of the universal principle, air. The boldness of their speculations we may explain as due to a courage born of ignorance, but the explanations they offer are scientific in spirit, at least. Moreover, these men do not stand alone. They are the advance guard of an army whose latest representatives are the men who are enlightening the world at the present day. The evolution of science--taking that word in the broad sense to mean organized and systematized knowledge--must be traced in the works of the Greek philosophers from Thales down. Here we have the source and the rivulet to which we can trace back the mighty stream which is flowing past our own doors. Apparently insignificant in its beginnings, it must still for a while seem insignificant to the man who follows with an unreflective eye the course of the current. It would take me too far afield to give an account of the Greek schools which immediately succeeded the Ionic: to tell of the Pythagoreans, who held that all things were constituted by numbers; of the Eleatics, who held that "only Being is," and denied the possibility of change, thereby reducing the shifting panorama of the things about us to a mere delusive world of appearances; of Heraclitus, who was so impressed by the constant flux of things that he summed up his view of nature in the words: "Everything flows"; of Empedocles, who found his explanation of the world in the combination of the four elements, since become traditional, earth, water, fire, and air; of Democritus, who developed a materialistic atomism which reminds one strongly of the doctrine of atoms as it has appeared in modern science; of Anaxagoras, who traced the system of things to the setting in order of an infinite multiplicity of different elements,--"seeds of things,"--which setting in order was due to the activity of the finest of things, Mind.