M. De la Rive on the Formation of Hail 297 



atmosphere, on account of the moisture with which the air is 

 then almost always saturated. 



Should the atmosphere cease to be serene, or should a mass oF 

 air loaded with humidity, and carried by the wind, happen by its 

 mixture with another mass of air to produce clouds, immediate- 

 ly a new distribution of temperature, and consequently of the 

 electrical condition of the column of air, would be effected. To 

 comprehend this result, we must remember that the solar rays 

 which heat the surface of the earth traverse the atmosphere 

 without sensibly heating it ; and that it is the heat emanating 

 from the earth which essentially determines the calorific state of 

 the atmosphere. Now, when a vertical column of atmospheric 

 air is divided into two sections by a layer of vapours, or by a 

 cloud more or less thick, the terrestrial heat, not being able at 

 least wholly to traverse this layer or this cloud, is sent back to- 

 wards the earth whence it came, instead of penetrating through 

 and beyond it. The portion of the column comprehended be- 

 tween the cloud and the soil preserves, therefore, this heat, 

 whilst the portion included between the cloud and the limit 

 of the atmosphere receives little or no heat; and the more 

 the former of these two portions becomes hot, the more the second 

 must be cold. Thus the column, instead of exhibiting a gra- 

 dual decrease of temperature from its base to its summit, is 

 found to be divided into two portions, having each a uniform 

 but very different temperature. The cloud, more or less thick 

 (or there may be many of them superposed on each other) 

 which separates the two portions, is then very warm on its infe- 

 rior surface, and very cold on its upper surface. It must of 

 course, be very strongly electrified, negatively on the one side 

 and positively on the other ; and this electrical condition may 

 be constantly destroyed by the neutralization of the two op- 

 posite electricities, which operate across the cloud itself, without 

 however ceasing to exist, since the cause which produces it con- 

 tinues to act, and is ready to reproduce it as rapidly as it dis- 

 appears. Here, then, we perceive the two strata of clouds of 

 which M. Lecoq speaks ; the wind ere long separates them ; 

 the atmosphere is speedily filled with clouds, some of which are 

 negatively electrified, and the others positively, without includ- 

 ing those which are electrical through the influence of others. 



