Quaestiones Convivales
Plutarch
Plutarch. Plutarch's Morals, Vol. III. Goodwin, William W., editor; Creech, Thomas, translator. Boston: Little, Brown, and Company; Cambridge: Press of John Wilson and Son, 1874.
Whereupon we began to commend the man very highly for his happy memory; but we called in question the pretended reason. For if the air wherein the vessel hangs be cold, how, I pray, does it heat the water? If hot, how does it afterwards make it cold? For it is absurd to say, that the same thing is affected by the same thing with contrary qualities, no difference at all intervening. While the gentleman held his peace, as not knowing what to say; there is no cause, said I, that we should raise any scruple concerning the nature of the air, forasmuch as we are ascertained by sense that it is cold, especially in the bottom of a well; and therefore we can never imagine that it should make the water hot. But I should rather judge this to be the reason: the cold air, though it cannot cool the great quantity of water which is in the well, yet can easily cool each part of it, separate from the whole.
I SUPPOSE you may remember what Aristotle says in his problems, of little stones and pieces of iron, how it hath been observed by some that being thrown into the water
they temper and cool it. This is no more than barely asserted by him; but we will go farther and enquire into the reason of it, the discovery of which will be a matter of difficulty. Yes, says I, it will so, and it is much if we hit upon it; for do but consider, first of all, do not you suppose that the air which comes in from without cools the water? But now air has a great deal more power and force, when it beats against stones and pieces of iron. For they do not, like brazen and earthen vessels, suffer it to pass through; but, by reason of their solid bulk, beat it back and reflect it into the water, so that upon all parts the cold works very strongly. And hence it comes to pass that rivers in the winter are colder than the sea, because the cold air has a power over them, which by reason of its depth it has not over the sea, where it is scattered without any reflection. But it is probable that for another reason thinner waters may be made colder by the air than thicker, because they are not so strong to resist its force. Now whetstones and pebbles make the water thinner by drawing to them all the mud and other grosser substances that be mixed with it, that so by taking the ’strength from it it may the more easily be wrought upon by the cold. But besides, lead is naturally cold, as that which, being dissolved in vinegar, makes the coldest of all poisons, called white-lead; and stones, by reason of their density, raise cold in the bottom of the water. For every stone is nothing else but a congealed lump of frozen earth, though some more or less than others; and therefore it is no absurdity to say that stones and lead, by reflecting the air, increase the coldness of the water.