CHAJPTER IL 



THE philosophical principles upon which the phenomena of 

 rain are immediately dependent, are not yet well settled : rain. 

 is supposed, however, by many of the best writers, to depend 

 upon the action of electricity for its origin. All causes which 

 have a tendency to reduce the temperature of the air, cause a 

 precipitation of moisture. When the aqueous vapor which is 

 held in suspension by the air becomes condensed by cold, the 

 minute vesicles coalesce and form drops, which by their gravity 

 descend through the air, which is no longer capable of sus- 

 taining them. 



The drops of rain are said to be from one twenty fifth to 

 one third of an inch in diameter : when they descend through 

 a stratum of dry air, they are partly dissipated by evaporation. 

 This accounts in part for the fact that there is less rain on 

 plains than on mountains. 



The same latitudes have not the same quantity of rain! 

 this, like climate, is modified by various local circumstances, 

 as altitude, proximity to the sea, direction and prevalence of 

 winds, agricultural condition, forests, &c. The quantity of 

 rain which falls during the year is greatest at the equator, and 

 diminishes as we leave this point and approach the poles. 



The quantity also which falls during the night and during 

 the day, varies at different places : in Europe more rain falls 

 during the day than during the night time; while in South 



