Well, then, I take it, in water there resides some vital principle. In water, did I say? Why, fire, the universal destroyer, has a creative function; it may not seem a likely thing, but all the same it is but the truth that some animals are generated by fire. The atmosphere, then, possesses some power of this kind; and that is why it sometimes grows thick, sometimes expands and throws off impurities, sometimes contracts, at others opens up and disperses. There is thus the same difference between air and wind as between lake and river.[72] There are occasions when the sun is the sole cause of wind, as he rarefies the stiff atmosphere and opens it out from its thick contracted state. [72] This remark would have been more apposite in Chap. I., above; possibly that is its correct place. VII Having spoken of the winds in general, let us now proceed to the discussion of individual winds. Perchance the discovery of the time and place of their origin will conduce to the discovery of their manner of formation. First, then, let us look at breezes before dawn, which are borne either from rivers or hollow valleys or from some bay. None of these winds lasts long, but falls when the sun has got stronger; nor is it carried up out of sight of the earth. This class of wind sets in in spring, and does not last beyond summer. It comes chiefly from a quarter where there are spaces of water and mountains. Plains, for instance, may have abundance of water, and yet they have no breeze; I mean a breeze strong enough to be called wind. VIII