BOOK II. L. 133-LI. 136 



typlioon does not occur with a northerly wind, nor a 

 cloudburst with snow or when snow is lying. If it 

 flared up as soon as it burst the cloud, and had fire in 

 it, did not catch fire afterwards, it is a thunder- 

 bolt. It differs from a fiery pillar in the way in which 

 a flame differs from a fire : a fiery pillar spreads out 

 its blast widely, whereas a thunderbolt masses 

 together its onrush. On the other hand a tornado 

 differs from a whirlwind by returning, and as a whizz 

 differs from a crash ; a storm is different from either 

 in its extent — it is caused by the scattering rather 

 than the bursting of a cloud. There also occurs a 

 darkness caused by a cloud shaped Uke a wild 

 monster — this is direful to sailors. There is also what 

 is called a column, when densified and stiffened 

 moisture raises itself aloft ; in the same class also is 

 a waterspout, when a cloud draws up water Hke a pipe. 



LI. Thunderbolts are rare in winter and in Thunder- 

 summer, from opposite causes. In winter, owing to ^f^^}^.^^ 

 the thicker envelope of cloud, the air is rendered 

 extremely dense, and all the earth's exhalation being 

 stiff and cold extinguishes whatever fiery vapour it 

 receives. This reason renders Scythia and the 

 frozen regions round it immune from the fall of 

 thunderbolts, wliile conversely the excessive heat 

 does the same for Egypt, inasmuch as the hot and 

 dry exhalations from the earth condense very rarely, 

 and only form thin and feeble clouds. But in spring 

 and autumn thunderbolts are more frequent, their 

 summer and winter causes being combined in each 

 of ihose seasons ; this explains why they are fre- 

 quent in Italy, where the milder winter and stormy 

 summer make the air more mobile, and it is always 

 somewhat vernal or autumnal. Also in the parts of 



273 



