VIII
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How, then, is a blast of this kind, which is called by the Greeks a gulf breeze (ἐγκολπίας), formed? This is the theory of them: All the exhalations of marshes and rivers—and they are abundant and constant—form by day the sun’s nourishment. By night, however, there is no drain on them, and they are enclosed by the mountains and accumulate in one quarter. When they have filled up this quarter and can no longer find accommodation in it, but are squeezed out on one side and move in a particular direction, then you have the wind. It inclines, of course, toward the side to which it is invited by the freer exit, and by the openness of the place toward which the accumulated elements can rush. A proof of this is that a wind of this kind does not blow in the early part of the night. At that time the gathering only begins, but by daybreak it has reached the full, and seeks relief by flowing off. It chooses its exit by preference where there is the largest empty space and a great expanse of open. It is stimulated by the rays of the rising sun striking on the chilly air. Even before he makes his appearance his light of itself has an influence. The sun does not at that stage, it is true, drive away the atmosphere with his beams; still, he already attacks and harasses it by the shafts of light he sends before him. When he comes out himself in his power, part of the gathering is carried off to a greater altitude, part is dissipated by his heat. Wherefore power is not granted to these winds to continue longer than the morning. All their strength collapses at sight of the sun. Even if their blast is somewhat violent, yet they begin to subside as mid-day approaches; in fact, the breeze73 never lasts as long as noon. Any other variety of the breeze is weaker and shorter in duration; they vary according as the causes to which they owe their origin are more or less powerful.