they do arise. VIII Let us now refute this other explanation of Epigenes, for he employs 1 two. He believes that when all the moist and dry exhalations of the earth unite, the mere discord of the different bodies turns the air into whirlwind. Then the force of that wind as it revolves sets fire by its rapid motion to all that it embraces in itself, and raises it on high. The gleam of the fire that is thus extracted remains as long as there is sufficient nutriment; when the fuel fails, the fire subsides too. Now, one who talks thus pays no attention to the nature of the 2 course of whirlwinds as compared with that of comets. The career of the former is swift and violent, more rapid than the winds themselves. But a comet’s movement is so gradual as to render imperceptible the space traversed during a day and a night. Besides, whirlwinds have an erratic, disorderly, and, to use a word of Sallust’s, eddying, motion. Comets have a regular course, which observes the appointed track. Surely none of us will believe that either the moon or the five planets are carried by the wind or spun round by the whirlwind. I trow not. And why? Just because they have not an irregular and 3 unrestrained motion. Let us apply the principle to comets. They do not move in confusion or irregularity so as to justify the belief that they are impelled by unruly and fickle forces. Besides, even if those eddies could enclose moist earthy elements, and had power to raise them from the depths to the heights, still they could not carry them up higher than the moon. All their force is spent when they reach the region of clouds. But as for the comets, we see them sailing through the upper regions, mingling with the very stars. It is, therefore, improbable that a whirlwind could persist over such a long distance, for the greater it is, the more rapidly is it spent. IX