Plutarch's Natural Questions (7-9)

WHETHER, because the river-air, which is at all times heavy and slow, being in winter more condensed by the cold, does more resist sailing? Or is it long of the water rather than the air? For the piercing cold makes the water heavy and thick, as one may perceive in a water-clock; for the water passes more slowly in winter than in summer. Theophrastus talks of a well about Pangaeum in Thrace, how that a vessel filled with the water of it weighs twice as much in winter as it does in summer. Besides, hence it is apparent that the grossness of the water makes ships sail slower, because in winter river-vessels carry greater burthens. For the water, being made more dense and heavy, makes the more renitency; but the heat hinders the sea from being condensed or frozen.

WHETHER that motion expels and dissipates the heat of other liquors as a thing adscititious, and the winds do rather excite and increase the innate heat of the sea? Its transparentness is an argument of heat; and so is its not being frozen, though it is terrene and heavy.

Is it that the bitterness of the sea is not devoid of all sweetness, as receiving so many rivers into it; but, since the sun exhales the sweet and potable water thereof, arising to the top by reason of its levity, and since this is done in summer more than in winter, when it affects the sea more weakly by reason of the debility of its heat, that so in winter a great deal of sweetness is left, which tempers and mitigates its excessive poisonous bitterness? And the same thing befalls potable waters; for in summer they are worse, the sun wasting the lightest and sweetest part of them. And a fresh sweetness returns in winter, of which the sea must needs participate, since it moves, and is carried with the rivers into the sea.