538 



If it form at an equal height over plains and 

 table-lands, we must suppose, that it melts as 

 it falls, in passing through the lowest strata of 

 the atmosphere, the mean temperature of which 

 (between 0 l andSOO 1 ) is from 27*5° to 24° of the 

 centigrade thermometer. I acknowledge it is 

 very difficult to explain, in the present state of 

 meteorology, why it hails at Philadelphia, at 

 Rome, and at Montpellier, during the hottest 

 months, the mean temperature of which attains 

 25° or 26° ; while the same phenomenon is not 

 observed at Cumana, at La Guayra, and, in 

 general, in the equatorial plains. In the United 

 States, and in the South of Europe, the heat of 

 the plains (from 40° to 43° of latitude) is nearly 

 the same as within the tropics ; and according 

 to my researches, the decrement of caloric 

 equally varies but little. If then the absence of 

 hail within the torrid zone, at the level of the 

 sea, be produced by the melting of the hail- 

 stones in crossing the lower strata of the air, we 



zone, Thibault de Chanvalon puts the question, why, above 

 the plains in the temperate zone only, storms are attended 

 with hail. " The heat of the plains," he says, *' can be no 

 obstacle to the formation of hail $ in Europe it is never more 

 common than in the hot seasons." He asserts, that at Mar- 

 tinico hail has been seen to fall once in the plains, in 1721. 

 (Voyage d, la Martinique, p. 135, No. 40). This assertion 

 appears questionable. (Moreau de Jonnes sur le Climat des 

 Antilles, p. 49). 



