Plutarch De primo frigido 17

[17] Now you must pursue the subject by comparing these arguments with those of my opponents. For Chrysippus, ¹ thinking that the air is primordially cold because it is also dark, merely mentioned those who affirm that water is at a greater distance from the aether ² than is air; and, wishing to make them some answer, he said, If so, we might as well declare that even earth is primordially cold because it is at the greatest distance from the aether - tossing off this argument as if it were utterly inadmissible and absurd. But I have a mind to maintain the thesis that earth too is not destitute of probable and convincing arguments, and I shall start with the one that Chrysippus has found most serviceable for air. And what is this ? Why, that it is primordially dark and cold. For if he takes these two pairs of opposing forces and assumes that one must of necessity accompany the other, there are, surely, innumerable oppositions and antipathies between the aether and the earth with which one might suppose this to be consistent. For it is not only opposed as heavy to light and as moving by gravity downwards, not upwards, or as dense to rare or as slow and stable to mobile and active, but as heaviest to lightest and as densest to rarest and, finally, as immovable of itself to self-moving, and as occupying the central position in the universe to revolving forever around a centre. It is not absurd, then, if oppositions so numerous and important carry with them the opposition of cold and heat as well. Yes, Chrysippus may say, but fire is bright. Is not the earth, then, dark ? Why, it is the darkest and most unilluminated of all things. Certainly air is first of all to participate in light; it is instantly altered and when it is saturated, it distributes illumination everywhere, lending itself to light as a body in which to reside. For when the sun arises, as one of the dithyrambic writers ³ has said, Next the air, moving downward, infuses a part of its brightness into the lakes and the sea, and the depths of the rivers flash brightly, ⁴ to the extent that air is able to penetrate them. Of all bodies only the earth remains constantly without light, impenetrable to the illumination of sun or moon; yet it is warmed by them and permits the heat to sink in and warm it up to a slight depth. But because it is solid, earth does not give passage to light, but is encircled by light on its surface only, while the inner parts are called Darkness and Chaos and Hades ⁵ - so that Erebus ⁶ turns out to be the subterranean and interior darkness. Then, too, the poets tell us that Night was born of Earth ⁷ and mathematicians demonstrate that night is the shadow of Earth blocking the light of the sun. The air, indeed, is saturated with darkness by the earth, just as it is with light by the sun. The unlighted portion of the air is the area of night, amounting to the space occupied by the earth’s shadow. This is the reason why men make use of the air out of doors even when it is night, as well as many beasts which do their pasturing in the darkness, since it retains some vestiges of light and dispersed glimmerings of radiance; but the house-bound man who is under a roof is utterly blind and without light inasmuch as there the earth envelops him from all directions. Whole skins, furthermore, and horns of animals do not let light pass through them because of their solidity; yet if sections are sawed off and polished, they become translucent when once the air has been mixed with them. It is also my opinion that the earth is called black by the poets, ⁸ whenever they have occasion to do so, because of its murky and lightless characteristics. The result, then, of these considerations is that the much-prized antithesis of light and darkness belongs to earth rather than to air.