Apollonius of Myndus differs in his view from Epigenes. He asserts 1 that a comet is not one star made up of many planets, but that many comets are planetary. A comet, he goes on, is not an illusion nor a trail of fire produced on the borders of two stars, but is a distinctive heavenly body, just as the sun or the moon is. Its shape is not limited to the round, but is somewhat extended and produced lengthwise. On the other hand its orbit is not visible. It cuts 2 (‍=‍intersects) the upper part of the universe, but only emerges when at length it reaches the lowest portion of its course. There is no reason to suppose that the same comet reappears; for instance that the one seen in the reign of Claudius was the same as the one we saw in the reign of Augustus; or that the recent one which appeared during the reign of Nero Caesar--which has redeemed comets from their bad character--was similar to the one which burst out after the death of the late Emperor Julius Caesar, about sunset on the day of the games to Venus Genetrix. Comets are as varied as they are numerous. They are 3 unequal in size, unlike in colour. Some are ruddy without any light; others are bright with a pure clear light; others are flame-coloured, but the flame is not a pure thin flame, but is enveloped in a mass of smoky fire. Some are blood-stained and threatening, bringing prognostication of bloodshed to follow in their train. They wax and wane like other planets. They are brighter when they come down toward us, and show larger from a nearer point, smaller when they depart from us, and dimmer when they retire to a greater distance. XVIII The reply is ready to this last statement, that the same thing does 1 _not_ happen in comets as in the other stars. Some comets attain their maximum on the very first day of their appearance. But, according to the argument, they ought to increase the nearer they approach. As it is, their first aspect remains until they begin to fade. Besides, what has been said in reply to former authorities applies here too: If the comet had an erratic orbit, and were a true planet, it would move within the limits of the zodiac, within which all the planets confine their orbits. Again, a star is never seen through another star. 2 Our sight cannot pierce through the centre of a planet so as to view through it what lies beyond. But through a comet the further regions are discerned as through a cloud. Whence it is evident that it is no planet but an insubstantial, irregular fire. XIX