RAIN. 453 



amount of rain; it increases in proportion as we approach toward 

 them, and the higher and steeper they are. The reason is obvious 

 here also: the strata of air over the mountains are colder than those 

 over plains, and a constant reaction takes place between these differ- 

 ent strata. Sometimes the warm air of the plains rises up the sides 

 of the mountains, or through the valleys, sometimes the masses of 

 cold air flow down from the mountains into the plains ; these strata, 

 possessing different temperatures, meet above and below ; cooling is 

 thus caused, and the vapors are precipitated as rain. When we in- 

 quire into the amounts of rain upon the great plain which is bounded 

 on the north by the xVlps, and toward the south by the Apennines, 

 we find that they increase toward the Alps. Southward of the Po, 

 the annual quantity of rain amounts, on an average, to twenty-six 

 inches; northward of the river, to thirty-eight inches ; immediately 

 at the foot of the Alps to sixty inches. There are particular places 

 in the southern part of the plain where the quantity of rain amounts 

 only to twenty-one inches, and isolated points in the Alps where it 

 amounts to one hundred inches. We meet with similar conditions 

 when we follow the Rhine or the Rhone upward, or when we compare 

 the quantities of rain in the mountains of Germany and France with 

 those presented by the plains." 



Again, he observes, that the 



" Influence of mountain chains, in the increase of rain, is greater 

 than that of the ocean ; where, however, a range sinks down pre- 

 cipitously toward the sea, the increase of the rain is especially strik- 

 ing. This is seen on the east and west side of Scandinavia, on the 

 mountains on the west side of England, and of the south side of the 

 Northern Apennines, which extend down to the Mediterranean, where 

 there is sometimes a hundred inches of rain. The relation of the 

 various winds to rain is just as simply and readily explained. In 

 North America the east wind is the principal source of rain ; it comes 

 from the Atlantic Ocean." 



From which last opinion, and some others, many Ameri- 

 can meteorologists entirely dissent. 



On the subject of the amount of rain which falls on the 

 summits of the Alleghany Mountains, there have been but 

 few observations made by actual measurement of the aggre- 

 gate of precipitation.* The observations made would point 



* It is with extreme regret that the statement must be made, that the Observatory 

 of the Alleghany Mountain Health Institute has not yet been completed and furnished 



