

Natural History, fyc. 415 



$ 3. NATURAL HISTORY. 

 1. FORMATION OF HAIL. 



M. de Perevoschtchikoff has endeavoured to support experimentally 

 the objections made by Bellani against Volta's theory of hail, and 

 to develope the influence of evaporation on the temperature of liquids. 

 He used a thermometer with the tube bent, so that the ball was 

 turned upwards, and the upper part of the ball was dished, so as to 

 form a receptacle for fluid ; in this way the temperature of any fluid 

 evaporating from the part could be ascertained. From his experi- 

 ments with water, he found that a prompt evaporation produced cold, 

 even under the direct influence of the sun. From experiments with 

 spirit of wine, he concluded that the temperature of an evaporating 

 liquid could not rise, except when the evaporation was feeble ; and 

 he ultimately concludes, that the cause of the first formation of hail 

 exists in a prompt evaporation of the vesicles constituting clouds. 

 According to him, Volta lost sight of the principal cause of the 

 cooling of clouds, and also of the concentric structure of hail-stones. 

 The correct account of the phenomenon he conceives to be the 

 following : When the clouds consist of many thick strata, which 

 gradually rise, they become an obstacle to the free distribution of the 

 radiant heat from the earth, which being reflected back again, 

 produces that suffocating sensation which usually precedes the storm. 

 Above the clouds, however, the heavens are serene, and consequently 

 radiation goes on freely from their upper surface. Hence the prin- 

 cipal cause of the refrigeration upon which depends the formation of 

 the nucleus of the hailstone. The specific gravity of these nuclei 

 being too great to allow of their remaining suspended in the cloud, 

 they fall ; and traversing different strata of clouds, they become 

 covered at each, by a fresh opaque coat of the liquid, congealed at 

 their surface, the number of layers in the hailstone corresponding to 

 the number of strata it has passed through. The hailstones, by con- 

 cussion against each other, are supposed to have a rotatory motion 

 given to them, tending to produce the spherical form. The author 

 concludes that paragreles, or hailrods, are not only useless, but 

 even dangerous*. 



2. GEORGIA METEOR AND AEROLITE. 



The following is a very circumstantial account of the descent of the 

 stone which fell in May, 1829, at Forsyth, in Georgia, United States. 

 Between three and four o'clock on the 8th instant, on that day a 

 small black cloud appeared south from Forsyth, from which two dis- 

 tinct explosions were heard, following in immediate succession, suc- 

 ceeded by a tremendous rumbling or whizzing noise passing through 

 the air, which lasted, from the best account, from two to four minutes. 

 This extraordinary noise was on the same evening accounted for by 



* Bib. Univ. 1830, p. 410, 



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