Phenomena and Causes of Hail Storms. 253 



and ordinary kind, which is formed near the earth, before de- 

 scribed as being common in the polar regions. 



This will become obvious by inspecting the following figure. 



90 80 70 60 50 40 30 20 10 10 20 30 40 50 60 VO 80 90 



The curve B, C, D, represents the litie of perpetual congelation, as given in 

 the Edinburgh Encyclopaedia, under the article " Physical Geography," and 

 is beKeve J to be a very accurate delineation of it. Let then, a a' denote the 

 path described by the opposite winds that are supposed to meet at the latitude 

 of 40' ; b h', that of similar winds meeting at the equator, each being at the 

 height of 10,000 feet above the earth ; and c c', the path of two currents at the 

 lieight of 2000 feet, meeting at the latitude of 70°. These heights are taken 

 arbitrarily, as atfording a favourable view of the nature of our reasoning. 

 The same mode of reasoning, however, may be applied to other points of ele- 

 vation, at which any particular hail-storm may be supposed to be generated. 



France is peculiarly exposed to hail storms, on account of 

 its situation between the Alps and the Pyrenees. The country 

 lying between these high mountains being heated by the sura- 

 "mer's sun, the cold blasts from the regions of snow, and ice, 

 mingling with the hot and humid air over the intervening coun- 

 try, ought, in conformity with our principles, to produce fre- 

 quent hail-storms. 



Tile most violent liail-slorms occur in the warmer season of 

 the year, and usually in the hottest months, because it is then 

 that the heat of the sun contributes most to set the opposite 

 currents in motion. Hailstones are smaller on the tops of 

 mountains than in tlie neighbouring plains, because not falling 

 so far, they have less opportunity to accumulate l)y the congela- 

 tion of successive layers of watery vapour. The white, snowy 

 nucleus which large hailstones fre(iucntly exhibit in the centre. 



