We have seen how and why Thales deemed water to be the _Welt-stoff_. His immediate successors, while adhering to his principles and aims, were not content with his choice. They successively sought for something less material. One of them, Anaximenes, was attracted by the qualities and functions of the atmosphere, and his speculations will serve as an introduction to the mysticism of winds and storms and clouds. Only a single statement of his is preserved in its original form; but fortunately it is full of significance. "As our soul" (said the sage), "which is air, holds us together, so wind and air encompass the whole world." This, interpreted in the light of ancient comments, shows that Anaximenes compared the breath of life to the air, and regarded the two as essentially related--indeed as identical. For the breath, he thought, holds together both animal and human life; and so the air holds together the whole world in a complex unity. He reached the wider doctrine by observing that the air is, to all appearance, infinitely extended, and that earth, water, and fire seem to be but islands in an ocean which spreads around them on all sides, penetrating their inmost pores, and bathing their smallest atoms. It was on such facts and appearances that he based his main doctrine. If we think of the modern theory of the luminiferous ether, we shall not be far from his view-point. But the simpler and more obvious qualities of the air would of course not be without their influence--its mobility and incessant motion; its immateriality; its inexhaustibility; its seeming eternity. It is, therefore, not astonishing that with his attention thus focussed on a group of truly wonderful phenomena, the old nature-philosopher should have selected air as his primary substance--as the universal vehicle of vital and psychic force.