‹‹‹ Vitr. 8.1.7 | Table of Contents | Vitr. 8.2.2 ›››
2Water collected from showers possesses wholesome qualities, because it consists of the lightest and most subtle particles of all springs, which, cleansed by the action of the air, and loosened by the tempests, descend upon the earth: and the reason why showers do not fall so often upon plains as they do on mountains or their vicinity is, because the vapours ascending from the earth at sunrise, to whatever part of the heavens they incline, drive the air before them, and, being in motion, receive an impetus from the air which rushes after them.
2Rainwater has, therefore, more wholesome qualities, because it is drawn from the lightest and most delicately pure parts of all the springs, and then, after being filtered through the agitated air, it is liquefied by storms and so returns to the earth. And rainfall is not abundant in the plains, but rather on the mountains or close to mountains, for the reason that the vapour which is set in motion at sunrise in the morning, leaves the earth, and drives the air before it through the heaven in whatever direction it inclines; then, when once in motion, it has currents of air rushing after it, on account of the void which it leaves behind.