There are, Epigenes goes on to say, two classes of comets. One kind 1 sheds its light on all sides without changing its position; the other extends a loose kind of fire in one direction, after the fashion of hair, and passes through among the stars; of the latter kind were the two seen in our own days. The former variety, with hair on all sides, that do not move, are usually low down, and arise from the same causes as beams and torches, that is, from a distempered thick atmosphere that carries in it many of the earth’s exhalations, both dry and moist. Air driven out through narrow apertures is capable of setting on fire 2 the atmosphere situated over it, which is full of elements suitable for feeding a fire; and it is able after that to drive it forward from the clear space, lest from any cause it should fall back and relax its force. After that, it can rise again on the next and following days and set fire to the same spot. As presumptive proof of this, we see winds return during several days at their set time. Rain, too, and storms in other forms recur according to appointment. His opinion may be briefly expressed by saying that he supposes comets to be formed 3 pretty much in the same way as fires excited by whirlwind. There is this one difference, that those whirlwinds are pressed down to earth from a higher region, while these others are raised from earth to the upper regions. VII A great deal can be urged against this view. First of all, if wind 1 were responsible, a comet would never make its appearance without wind. As a matter of fact, it appears when the air is perfectly still. In the next place, if it were due to wind, it would fall with the wind; and if it began through wind, would increase with increase of wind, and would be the brighter the more furious the wind was. This point, too, has to be added to the foregoing: while the wind impels many parts of the atmosphere, a comet appears in one spot. The wind does not mount up high, but comets are seen higher up than the winds are permitted to go. Epigenes afterwards goes on to speak of the comets that, he 2 says, have a more definite resemblance to stars, traversing an orbit and passing through the zodiacal signs. He attributes their origin to the same causes as produce those that he called lower comets, the only difference being that the earth’s exhalations in this case contain many dry elements, and therefore seek the higher region, and are driven by the north wind toward the more exalted portions of the heavens. But, surely, if the north wind urged them, they would always be borne toward the south, whither this wind urges its course. And yet, as a fact, they 3 have had different movements, some to east, others to west, all in a curved path, a direction which the wind could not impart. Besides, if the impulse which produced the comet carried up on high those north winds from the earth, comets would not arise when other winds blew; yet