MISTS AND FOGS. 359 



more rapid cooling of the land by radiation, 

 than of the surrounding ocean. 



The frost rime of the Polar seas is produced 

 in the same manner as fogs, but by the agency 

 of a lower temperature. 



During summer, mountains are generally 

 covered with fog in the morning, when the 

 weather is serene and clear. Being cooled 

 down at night by radiation below the dew point, 

 they abstract caloric from the transparent aque- 

 ous vapour that is always mixed with the atmos- 

 phere in greater or less quantity, by which it is 

 condensed into huge volumes of mist or fog, that 

 envelope the mountains with giant folds of ma- 

 jestic drapery ; and which are not redissolved by 

 the solar rays before 9 or 10 o'clock in the morn- 

 ing. The greater quantity of rain and snow which 

 fall on mountains than on plains, is also owing 

 to their greater coldness as before explained. 



Indian Summer. 



In all parts of the United States, there is an 

 autumnal period of most delightful weather, 

 which usually commences late in October, and 

 continues with occasional intermissions through 

 the greater part of November some seasons 

 in the Mississippi valley, until Christmas. It is 

 generally attended with a southerly wind, which, 

 being warm, is filled with transparent aqueous 



