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Now that great rivers never freeze downwards is but consentaneous to reason. For those parts which are frozen above transmit no exhalation outward; for this, being penned up within and forced downward, affords heat to the moisture at the bottom. A clear demonstration of which is this, that when the ice is dissolved, you may observe a steam arising out of the water upwards in a very great quantity. And therefore the bodies of living creatures are warmest within in the winter, for that the heat is driven inward by the ambient cold. Now those upward exhalations and ascensions of the vapors deprive the waters not only of their heat but of their coolness. And therefore they that vehemently desire their drink to be cold never move the snow nor the moisture that is pressed out of it; for motion would deprive them both of the virtue which is required from them.
