368 AURORA BOREALIS. 



formed in much lower latitudes than during 

 summer. 



It is also an important corroboration of this 

 theory, that they are seen in lower latitudes in 

 the middle and eastern portions of America and 

 Europe, than on their western coasts ; while the 

 former are known to be much colder than the 

 latter in the same latitudes; which is owing to 

 the prevalence of west winds, that blow from 

 the Pacific and Atlantic oceans, and thus tem- 

 per the middle latitudes of western coasts, by 

 giving them an oceanic or insular climate.* 



The northern lights are seen much oftener 

 in Vermont, which is a cold mountainous state, 

 between latitude 42 and 44 IV . than in France 

 or England; though they are much farther 

 north. This is evidently owing to the excessive 



* The effect is increased by the condensation of aqueous va- 

 pour which is brought from the ocean by westerly winds, and 

 which gives out caloric during its condensation and precipitation 

 on the western coasts. Hence, the greater amount of rain which 

 falls on the western coasts of N. America and Europe, than on the 

 interior and eastern portions. Hence also, the dryness of west 

 winds in the United States, east of the rocky mountains, which 

 deposit their vapour on the western slope, before reaching the 

 interior. In the great Mississippi valley, the east wind is dry, 

 while in the Atlantic States it is often moist during winter and 

 spring. On moving westward, it deposits most of its vapour on 

 the eastern slope of the Alleghany mountains. These facts 

 enable us to understand why in the vast regions drained by the 

 Mississippi, west winds are dry; while in Britain and France 

 they are wet, and east winds dry. 



