2 90 PHYSICAL SCIENCE BK. vn 



which it was broken up, since they must have been 

 some of the five planets ? 



XVII 



1 APOLLONIUS of Myndus differs in his view from 

 Epigenes. He asserts 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. 



2 On the other hand its orbit is not visible. It cuts 

 ( == 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 



3 Venus Genetrix. Comets are as varied as they 

 are numerous. They are 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 prognosti- 

 cation of bloodshed to follow in their train. They 

 wax and wane like other planets. They are brighter 



