And as the sun, which strikes upon concave mirrors and rebounds from them in a pyramidal concurrence, so that that part of the pyramid will be proportionally so much hotter than its base as it is of lesser thickness, so it happens when this humidity draws itself together: that hot vapour which was mixed with it becomes so much more powerful the more it is united, and the smaller the place into which it is reduced, the greater the heat it generates. Whence often it catches fire and multiplies, the cloud making of itself a bombard; and so with ruinous thunderbolts and thunder it breaks the cloud. The little grains of water, when the cloud is compressed by the cold, cling together, and by their weight fall down. And in this way the clouds are undone, and thus they return as rain to the low ground.

This wears away the high summits of the mountains. This lays bare and removes the great rocks. This drives the sea from its ancient shores, for by the soil it carries it raises the bottom. This shatters and ruins the high banks; no stability is ever seen in it that does not at once corrupt its nature. This with its rivers searches every slope of the valleys, and here it carries away and there it lays down new soil. Whence many rivers may be said to be those through which the whole element has passed, and many times the sea has given back to the sea; and no part of the earth is so high that the sea was not once at its foundations, and no depth of sea is so low that most lofty mountains were not once founded there. And so it is now sharp and now strong, now tart and now bitter, now sweet and now thick or thin, now harmful or pestilent, now healthful or poisonous. Whence we may say that it transmutes into as many natures as are the diverse places through which it passes. And as the mirror transmutes itself into the colour of its object, so this transmutes itself into the nature of the place through which it passes: healthful, harmful, laxative, astringent, sulphurous, salt, sanguine, melancholy, phlegmatic, choleric, red, yellow, green, black, blue, oily, fat, lean. Now it takes hold of fire, now it quenches it; hot, cold; now it lifts or lays down, now it hollows or raises, now it ruins or stabilises, now it fills or empties, now it rises up or sinks deep, now it runs or is at rest, now it is the cause of life or death, now of generation or privation, now it nourishes and now the contrary, now salt or insipid, now with great floods it submerges the wide valleys.

With time everything goes changing.