THEORY of RAIN. 49 



its parts, however faturated with aqueous vapour, and in dif- 

 ferent degrees of heat, the natural cold of the polar regions, and 

 the contingent cold of fnows, accumulated, during winter, up- 

 on the higher countries, however tranfported to warmer re- 

 gions, would be altogether ineffectual for the purpofe of form- 

 ing clouds and condenfing rain. 



THE prefent fyftem of the atmofphere is fo calculated as 

 that every mixture of different portions of that fluid, unequal 

 in their degrees of heat, and faturated with humidity, muft 

 procure a condenfation of water. This fyftem, therefore, of 

 the atmofphere, with this particular law in relation to heat and 

 cold, is calculated to produce rain, by the continual mixture of 

 its parts, which are in different temperatures. 



IN this fyftem, we fhall fee, that the cold regions of the po- 

 lar circles are not ufelefs and inactive in the operations of this 

 world. In like manner, the frozen regions of the Alpine fitua- 

 tions of the Continent, ferve a purpofe, in the conftitution of 

 this earth, by preferving, in the accumulated fnows, a ftore of 

 the winter cold for the fummer feafon ; and thus preparing cold 

 portions of the atmofphere to be mixed with the warmer por- 

 tions, faturated with humidity, and ready to produce rain *. 



WHILE the atmofphere is thus tempered, by tranfporting the 

 heat and cold of diftant regions, the regions of the earth moft 

 diftant from the fea, may be fupplied with mowers of rain at 

 every feafon of the year, or at any feafon, according to the ar- 

 rival of thofe ftreams of the atmofphere which are in the pro- 

 per conditions for producing, by their mixture, a medium de- 

 gree of heat, and a fuperfaturation or condenfation of aqueous 

 vapour. This wife fyftem of things, or this ufeful purpofe in 

 the ceconomy of the world, could not have been accomplifhed 

 without that particular law of nature reflecting aqueous con- 

 denfation ; for, if the mixing together of the atmofpheric 

 ftreams produced no condenfation, the fummer hemifphere of 



G the 



* THE explanation of this propofition depends upon Dr BLACK'S theory of latent heat. 



