292 PHYSICAL SCIENCE BK. vn 



of neighbouring stars or the union of stars that 

 2 stick together. Some, again, say that comets are 

 true stars, but with orbits of their own, and that after 

 certain periods they come out into the view of man- 

 kind. Some allow their existence but refuse them 

 the title of stars, because they glide out of sight 

 without long duration, and within a brief space are 

 scattered to the winds. 



XX 



1 MOST of our Stoic brethren entertain another view, 

 which they do not regard as inconsistent with fact. 

 Let me explain it. We observe many species of 

 fire engendered on high, now the heavens ablaze, 

 now 



Long glistening trains of flame behind, 



now huge torches of fire being hurried along. 

 The lightning itself, whose velocity is so marvel- 

 lous that it at once blinds, and at the same instant 

 restores, the sight, is fire arising from the friction 

 of air that suffers more violent internal pressure 



2 than usual. That is why it does not remain long, 

 but glides off once it issues from the cloud, forth- 

 with perishing. But other fiery appearances remain 

 for a considerable time, and do not break up until all 

 the fuel on which they fed has been used up. Here 

 belong the strange sights recorded by Posidonius 

 pillars and shields all ablaze, and other flames 

 of marvellous strangeness. They would attract no 

 attention if they ran their course after customary 

 laws ; but now the sight of them sends all men agape. 



3 They bring down sudden fire from the heights of 

 heaven, sometimes producing a flash which is gone 



