112 



Auroral Observations at New Haven and Boston. 



Average number of auroras annually. 



These numbers exhibit a very steady increase from 1742 to 1786-89, with 

 the exception of the years 1784-5. The middle of the period of maximum 

 abundance may be fixed at 1787, the average number of Auroras for four 

 years amounting to 48. From this date, the number declines rapidly and 

 uninterruptedly to near 1820. The middle of the period of minimum fre- 

 quency may be assigned for 1816, when the average number of auroras did 

 not exceed one per year. From 1827 the numbers increase, and after 1837 

 the number is very remarkable, the average for five years from 1837 to 

 1841 being 42 per year. Then for three or four years there is a marked de- 

 cline, and a subsequent revival which is most decided in 1848 and 1852. 

 Regarding this as a single period of maximum abundance, the middle of 

 the period occurred not far from 1845, making thus an interval of 58 years 

 from the maximum in 1787 to that of 1845. 



It is then established beyond question that during the last century, the 

 frequency of Auroras in New England has been subject to an inequality 

 bearing some resemblance to an Astronomical periodicity — the period being 

 about 58 years ; but whether this period is uniform can only be established 

 hj observations continued for a much longer interval of time. 



