AURORA BOREALIS. 



227 



The column mnrkcd 9 contains observations from every part of Europe, as 

 reported in Heis'^ Wochenschrift. 



A careful examination of this table will lead to conclusions similar to those 

 already derived from the American observations. We perceive a period of unu- 

 sual abundance, extending from 1 830 to the present time, the maximum occur- 

 ring apparently from 1840 to 1845. This period was preceded by one of great 

 barrenness, extending from 1793 to 1826, and its middle occurred about 1812. 

 This period was preceded by one of great abundance, extending from 1771 to 

 1792, its middle occurring about 1780. This period was preceded also by one 

 of great barrenness except in very high latitudes, and extended from 1742 to 

 1770, its middle occurring about 1755. This period was preceded by another 

 of great abundance, extending from 1716 to 1741, its middle occurring about 

 1728. This period was preceded by another one of barrenness, whose middle 

 was not far from 1697. Combining all these results, we perceive a' considerable 

 degree of uniformity, approximating towards a period of iifty-nine years from 

 one maximum to another. 



At the same time we cannot overlook the considerable exceptions to this 

 rule ; and these exceptions seem to point to a subordinate period of ten years. 

 In each of the preceding lists we notice this alternation of meagre and abundant 

 years, and the intervals do not generally differ much from ten years. The fol- 



