When it turns toward the northern parts, gnawing the bottom of its banks; when toward the south the opposite bank falls in ruin; when it turns toward the earth's centre, consuming the bed that sustains it; when toward the sky it leaps up with seething bubbles; when with circular revolution it confounds its course; when on the western side it spreads, stripping the tilled fields from their husbandmen; when on the eastern side it unloads the plundered soil. And so, now it hollows and now it fills, here it takes away and there it lays down. Thus, without any rest, it forever removes or consumes whatever borders upon it. So, now turbulent and ruinous it goes raging; now clear and tranquil, with gentle course among the fresh little grasses, it goes playing. When with rain or snow or hail it falls again from the sky; when with subtle mists it composes the great clouds. Now by itself, and now moved by another's force; when with vital moisture it increases the things that are born; when it shows itself fetid or fragrant. Nothing is found among us without it. When it is infused with the hot element and, vaporising, mixes with the air, and drawn upward by the heat rises on high where, finding the cold region, by the contrary nature it draws itself together, and the minute particles cling one to another. And as the hand under water presses the sponge when it is well soaked, so that the enclosed water pushes in among the rest and, with the surging of its position, drives it out and flees through the openings, so does the cold that compresses the warm humidity; so that when it has reduced it to a denser form, that air which is enclosed within it breaks by force the weaker parts and blows out just as if it issued from a bellows, when it is pressed by excessive weight. And thus through diverse places it drives out the lighter clouds that lie athwart its opposing courses.