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But why, again, are winds of this nature stronger in spring and summer? For during the remainder of the year they are very light, never rising sufficiently to fill the sails of a boat. The reason is that spring is a wetter season. There is at that time more evaporation going on, both from the abundance of water lying about, and from the saturation of the ground to overflowing through the moist character of the sky. And the reason why this wind is equally prevalent in summer is that the heat of the day remaining after sundown and lasting during a great part of the night draws out exhalations, and attracts more forcibly any of them that are wont to be given off spontaneously by the ground. But subsequently the heat has not sufficient strength to use up what it drew out. This is the reason, I say, why the soil and its moisture give off for a longer period [at certain seasons] the particles derived from the earth’s wonted emanations and exhalations. The sunrise produces wind by its stroke as well as by its warmth. For, as I have already said, the light which precedes the sun does not as yet heat up the atmosphere, but merely smites upon it; being smitten the air retires to one side. And yet I cannot go so far as to admit that the light is quite devoid of heat, inasmuch as it is derived from heat. Probably it does not contain as great an amount as would appear from its effect. Still, it accomplishes its own task by separating and rarefying the dense exhalations. Moreover, places which through some disservice of nature are so shut in that they cannot receive the direct rays of the sun, even they, I say, are heated somewhat by the dull cloudy light that can pierce to them and are less rigid during the day than by night. Furthermore, all heat naturally dispels cloud and drives it off from itself. Therefore the sun likewise has the same effect. For that reason some people suppose that the blast must come from the direction in which the sun lies. But this opinion is manifestly false, seeing that the breeze sets in any direction, and one can sometimes sail right toward the sunrise with all canvas set. That could not happen if the wind were always coming from the direction of the sun.