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On the Formation of Hail. By M. De la Rive. 



Electricity, whose presence in the formation of hail is ren- 

 dered probable by the thunder and lightning which always 

 accompany and characterize storms, has for long been regarded as 

 playing an important part in this phenomenon, as in almost all 

 other meteorological occurrences. Volta especially, by means of 

 the opposite electricities with which he supposed the clouds which 

 were placed the one over the other were charged, explained 

 the augmentation in the size of the hailstones, which, according 

 to him, passed from one of these clouds to the other, as light 

 bodies situated between two jars filled with opposite electricities, 

 would be alternately attracted and repelled between them. 



In thus frequently traversing the humid atmosphere which 

 separates the two clouds, and in slightly penetrating the clouds 

 themselves, he maintained that each hailstone condenses upon 

 itself an increasing quantity of water, which is congealed, thus 

 forming the concentric layers which are observed in its structure ; 

 till finally becoming too heavy, it could no longer be sustained 

 among the clouds, and fell upon the earth in a more or less in- 

 clined direction, according to the strength of the wind. It is 

 to this tossing to and fro between the two clouds_> and to the 

 dashing of the hailstones against each other, that he ascribed 

 the peculiar noise which is heard in the air some time previous 

 to the descent of hail, and which has been compared to the 

 noise which the quick and violent shaking of a sackful of nuts 

 would produce. As to the formation of the nucleus of the 

 hailstone, Volta attributed it to the great degree of cold pro- 

 duced by the evaporation which takes place at the upper sur- 

 face of a cloud, the rapidity of which is increased by the direct 

 effect of the solar rays which strike upon the cloud, and are 

 absorbed by it. 



The theory of Volta was attacked in^a very powerful man- 

 ner by M. Arago, in a very interesting article, which appeared 

 in the Annuaire of the Board of Longitude for 1828. After 

 confirming some objections which had previously been advanced 

 by M. Bellani, the illustrious Frenchman suggested many others. 

 How, for example, can it be admitted, that the great evapora- 



