10 Phenomena and Causes of Hail Storms. 



France is so peculiarly exposed to hail storms, on account of its 

 situation between the Alps and the Pyrennees. The country lying 

 between these high mountains being heated by the summer's sun, the 

 cold blasts from the regions of snow and ice, mingling with the hot ' 

 and humid air over the intervening country, ought, in conformity 

 with our principles, to produce frequent hail storms. 



The most violent hail storms occur in the warmer season of the 

 year, and usually in the hottest month, because it is then that the 

 heat of the sun contributes most to set the opposite currents in mo- 

 tion. Hail stones are smaller on the tops of mountains than in 

 the neighboring plains, because not falling so far, they have less op- 

 portunity to accumulate by the congelation of successive layers of 

 watery vapor. The white, snowy nucleus which large hail stones 

 frequently exhibit in the centre, indicates that the congelation began 

 in highly rarefied air, such being precisely the appearance of a drop 

 of water frozen under the exhausted receiver of an air pump.* And 

 finally, the sudden and severe cold weather which often immedi- 

 ately follows a hail storm, only indicates that the cold blast which 

 produced the hail, extends something of its influence even to the sur- 

 face of the earth itself. 



What is the cause of the small momentum of hail stones ? Although 

 hail stones, when large, do great damage to tender crops, and occa- 

 sionally kill small animals, yet, it is on the whole, surprising that they 

 fall with no greater force than they do. A pebble of the same size 

 falling from the mouth of a well, upon the head of a man at the bot- 

 tom, would kill him ; and the meteoric stones which fall from the 

 sky, many of which do not exceed the size of some hail stones, bury 

 themselves deep in the ground, and sometimes even penetrate through 

 the entire body of a house, and bury themselves in the cellar. f The 

 small momentum of hail stones is partly to be ascribed to their low 

 specific gravity, which is a little less than that of water ; but still 

 they are heavy enough to fall with a hundred times the momentum 

 which they actually exhibit, descending as they do through many 

 thousand feet. Their velocity is in fact very small, whereas we 

 should expect to find it immensely great : the true reason of this I 



* Leslie, Encyc. Ed. Meteorology. 



t See an amusing account of the force of falling hail stones hy Fairfax, in the first 

 volume of the Phil. Transactions. 



