THE INDIAN SUMMER. 317 



moisture it draws from the earth, cools the atmosphere in 

 proportion to the amount of its foliage, while at the same 

 time it shades the ground from the sun. Anything that 

 should check this vegetable perspiration would in the 

 same ratio preserve the heat of the atmosphere by di- 

 minishing the radiation of heat that takes place more 

 slowly in dry than in moist air. 



This is precisely what happens soon after the first severe 

 frosts of November, when the whole extent of the forest 

 over thousands of miles is laid bare in the brief space of 

 two or three days. There is a sudden and universal 

 diminution of the moisture that was given out from the 

 leaves of trees and other plants before the frost had de- 

 stroyed them ; for the evaporation caused by the drying 

 of fallen leaves and herbage is comparatively slight, and 

 ceases after a few hours' exposure to the sun. The at- 

 mosphere being dry, and the radiation of heat proportion- 

 ally small in quantity, all these circumstances, if no un- 

 usual atmospheric disturbances occur from any other 

 hidden cause, unite in producing a sudden and universal 

 accumulation of heat. The warm period that follows is 

 the Indian Summer. 



A writer in " Silliman's Journal " of 1833, who advances 

 a very different theory to explain this phenomenon, makes 

 a statement that favors my view : " It appears to us that 

 the existence and duration of the Indian Summer in this 

 country has an important connection with the extensive 

 forests and uncultivated lands peculiar to America. And 

 it is worthy of remark, that, according to the recollection 

 of the oldest of our inhabitants, its former duration was 

 often three or four weeks ; whereas its present continu- 

 ance is short and uncertain, seldom exceeding ten or fif- 

 teen days. It appears also that this decline has been some- 

 what regular, keeping pace with, and evidently influenced 

 by, the gradual uncovering of the country." 



