456 PHILOSOPHY OF STORMS. 



the superior warmth of the inferior strata be occasioned by 

 clouds arresting the radiant heat passing downwards to- 

 wards the surface of the ground during day, or passing 

 upwards from that surface during night; or whether it be 

 occasioned by the evolution of heat which attends the con- 

 densation of invisible vapor into clouds during the trans- 

 portation of air from a warm to a comparatively cold local- 

 ity, or any other cause. 



The causes before mentioned are also assisted, 2d. By 

 the more rapid diminution of the elasticity of aqueous va- 

 por than that of air, as the temperature of both is reduced 

 in ascending perpendicularly. This is unquestionably the 

 chief cause of clouds forming at a considerable altitude in 

 the atmosphere, rather than nearer the level of the sea. 

 Indeed when the ocean to the north is warmer during the 

 depth of winter than the incumbent atmosphere, and much 

 warmer than the land, evaporation may, and frequently 

 does, go on from the ocean to such an extent as to produce 

 long continued rainy and cloudy weather, when the wind 

 blows from a northerly and cold direction. Our snow storms 

 from the north east or north west, and I apprehend your 

 snow storms from the north east, during the coldest season 

 of the year, are produced in this manner. The moisture 

 evaporated from the then warm surface of the ocean is con- 

 densed into clouds as it rises in the cold atmosphere. And 

 this condensation is promoted by the farther reduction of 

 temperature which it undergoes, in being transported over 

 the cold winter surface of the land by aerial currents. In 

 the climate in which I reside, the principal cause of the 

 formation of clouds undoubtedly is, the transportation of 

 air from a warm towards a comparatively cold locality by 

 means of aerial currents. But whatever causes clouds to 



one time one fourth as much vapor as would be required to make thirty-one 

 inches of rain, yet the great ocean of vapor surrounding the region in ques- 

 tion, by flowing in, and ascending with the up-moving current of air, might 

 easily furnish a supply to any amount. 



