The forces which brought philosophy, properly so called, to the birth at the beginning of the sixth century were three in number. First, the poetry then extant, which had cast into artless shape a number of speculative observations on the subject of the Cosmos--such as the conceptions of Oceanus encircling the earth, of Zeus dwelling in ether above it, of Tartarus beneath it, and so forth. Nothing but a cool head and a turn for systematisation was needed to convert these images into “ideas” and to combine the latter into a homogeneous and coherent conception. Another service was rendered by the study of geography, mathematics, and astronomy, developed as it had been by the long voyages of Milesians and Phocæans in the Mediterranean after they had supplanted the Phœnicians. A school of navigation came into being at Miletus, which city had successfully opened up the Euxine in the seventh century; and both Thales and Anaximander were trained in it. Miletus, where the trade with Egypt was started about the same time and the establishment of permanent factories like Naucratis taken in hand, likewise constituted the meeting-place of the geometry and astronomy of the Egyptians, whose learning was formerly much over estimated, with the far superior astronomical science of the Babylonians. The reports of mariners, charts, the catalogue of the stars, all combined with Oriental tradition and the unbiassed perspicacity of the Greeks to give the world the first science, _i.e._, research built upon a basis of empiricism, tested by the methods of mathematics and logic, and aiming at a harmonious interpretation of the Cosmos. To give a name to this study the Ionians evolved the idea of _Historia_, which in the sixth century took the place of _Philosophia_; the latter not coming into use until the fifth century. In this place I must mention the third element, although it is not in evidence in the earliest exponents of Ionian philosophy. It is the tendency to mysticism, to abstraction from the world, then beginning to develop in the Orphic school, which has left traces of its influence with ever-increasing distinctness in Anaximander, Pythagoras, Heraclitus, and Empedocles. It favoured the rise of a transcendental idealism which, although we do not find it matured into immaterial conceptions in these first natural philosophers, yet contains the germ of Plato’s dualistic idea of the universe. Not that the curve of development runs in smooth ascent from Thales to Plato; it exhibits the spiral windings inseparable from historic processes, since every new tendency calls forth the antagonistic principle to that which has spent its force, and thus brings about the necessity of reaction in a retrospective sense.