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 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.