in CAUSES OF COMETS 275 



ing horoscopes, who say that they studied among 

 the Chaldaeans, are at variance in their accounts. 

 The latter asserts that comets are placed by the 3 

 Chaldaeans among the number of the wandering 

 stars (i.e. planets), and that their orbits have been 

 determined. Epigenes, on the contrary, asserts that 

 the Chaldaeans have ascertained nothing regarding 

 comets, which are thought by them to be fires 

 produced by a kind of eddy of violently rotating 

 air. 



IV 



IN the first place, if it like you, let us set down i 

 the views of the last-mentioned author and refute 

 them. He supposes that the planet Saturn has 

 most influence in determining all motions of the 

 heavenly bodies. When it presses upon the con- 

 stellations next Mars, or crosses to the neighbour- 

 hood of the moon, or encounters the rays of the 

 sun, being naturally cold and windy, it contracts 

 and masses the atmosphere at more than one place. 

 By and by, if Saturn absorb all the sun's rays, there 2 

 is thunder and lightning. If he has Mars in 

 agreement, the lightning is forked. Moreover, he 

 continues, forked and sheet lightning contain 

 different materials. Evaporation from water or 

 other moisture produces only gleams that threaten 

 but stop short of striking. The hotter and drier 

 exhalation of the earth forges the bolts of forked 

 lightning. Beam meteors and torches, which differ 3 

 from one another only in size, are produced in this 

 same way. When any ball of air what we call a 

 whirlwind encloses moist earthy matter, wherever 

 it rushes it presents the appearance of an extended 



