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I am surprised, nevertheless, when those who maintain that the air is cold because it is dark do not perceive that others think it must be hot because it is light. For darkness is not so closely connected and akin to cold as heaviness and stability are; many things, in fact, which have no heat are bright, but nothing cold is buoyant, light, and soaring. Why, the very clouds, as long as they are akin to the substance of air, float aloft; but as soon as they change to moisture, they fall at once and lose their lightness no less than their warmth as coldness grows within them. Contrariwise, when heat supervenes, they reverse the movement again, for their substance begins to soar as soon as it has changed to air.