326 MEMOIRS OF THE AMERICAN ACADEMY. 



an aurora-minimum in 1823. The Boston series of observations notices only the more 

 brilliant auroras. More are recorded for 1830 than for any other year since 1819. 

 But for two years before 1830, and for four years afterwards, there were none. 

 24. After a very brief interval, the spot-minimum of 1833 approaches. The European 

 observations are consistent with the supposition of an aurora-minimum in 1833, as com- 

 pared with 1830. However, thirteen auroras were observed at Wasa in 1833. The 

 American observations, with the exception of those made at New Haven, agree with 

 the European observations in the conclusion to which they point. 25. A spot-maxi- 

 mum comes again in 1837. In the low latitudes of Europe, in France, and in Germany, 

 at St. Petersburg and at Abo, there is a slight aurora-maximum in 1837, as contrasted 

 with 1833. In Great Britain there is no indication of such a maximum. In Maine 

 and New York, in Boston, Providence, and New Haven, the number of auroras has in- 

 creased since 1833, although the increase has not always reached its limit in the year 

 1837. 26. A spot-minimum arrives in 1843. In France and Russia an aurora-minimum 

 is possible in the same year. In Dunse and Christiania an aurora-minimum in 1844 or 

 1845 is more probable. In Germany and Great Britain there is nothing to justify the 

 suspicion of an aurora-minimum in 1843. The observations made in New Haven, 

 Providence, Cambridge, Boston, Newberry, New York State, Toronto, and possibly 

 Worcester, permit the assumption of an aurora-minimum in 1843 as compared with 

 1837. 27. In 1848 is another spot-maximum. More than the usual number of 

 auroras were counted this year in the low latitudes of Europe. In 1847, 1848, and 

 1849, more auroras were seen in France than in 1842, 1843, and 1844. In Germany, 

 Great Britain, Russia, and perhaps Christiania, there is an apparent maximum about 

 1848. In America, at most of the places where regular observations were made, the 

 year 1848 represents a period of greater activity in the aurora than the year 1843. 

 The observations at Worcester and Jakobshavn are not clear in their utterance, on this 

 point; and in New York State the number of auroras observed in 1847, 1848, and 

 1849 was not so large as the number observed in 1839, 1840, and 1841. The secular 

 maximum, which occurred some time between 1840 and 1850, would have some influ- 

 ence upon the subordinate maxima and minima of this period. 28. A spot-minimum 

 is found in the year 1856. In the low latitudes of Europe, in France, Germany, Great 

 Britain, Russia, Christiania, the observations accord well with the supposition of an 

 aurora-minimum in 1856. The observations at Providence, Cambridge, Worcester, 

 Newberry, and Toronto agree with the European observations in their silent testi- 

 mony. In New York State the great reduction in the number of observed auroras is 

 partly due to other causes than the infrequency of the phenomenon. 



