324 MEMOIRS OF THE AMERICAN ACADEMY. 



vious year of the series, or during the twelve following years. In Franeker more 

 auroras were seen in 1775 than at the following spot-maximum of 1779. In 1776 there 

 was a minimum at New Haven and Cambridge, but an equal minimum at New Haven 

 in 1771. 15. Now arrives the spot-maximum of 1779. In the same year are indica- 

 tions of an aurora-maximum in Spain, Switzerland, France, Austria ; also in St. Peters- 

 burg, Copenhagen, Berlin, Jena, Carlsruhe, Boningen, and Montmorenci. In Brussels 

 a large number of auroras were seen in 1778 and 1779, but none in 1780 and 1781. 

 A large number were also seen at Franeker in 1779 and the two preceding years, but 

 few in the three following years. While twenty-four were seen at Berlin in 1779, 

 only two were seen in 1780. In Jena, Boningen, Montmorenci. and St. Petersburg, 

 the number was small for 1780. At Abo not so many were seen in 177'.' as at the 

 spot-minimum of 1775, and none whatever in 1780 and 1781. In New Haven and 

 Cambridge there is as good evidence of a minimum in 1779 as in 1775. A compari- 

 son of the series observed at Cambridge with that observed at New Haven will, how- 

 ever, justify the opinion that the Cambridge series is defective about this period. 

 16. The spot-minimum of 17S4 comes next under consideration. In Brussels, Mann- 

 heim, St. Petersburg, and Abo, an aurora-minimum falls upon the same year. In Italy, 

 France, and Germany, in Montmorenci, Ratisbon, Carlsruhe, Prague, Sagan, Berlin, 

 Copenhagen, and Spydberg, it comes in 1785. Only one aurora was seen at Jena in 

 1785, but none were seen in 1782. None were seen in Great Britain in 1781 or 1779. 

 In Cambridge and New Haven the minimum belongs to 1784. 17. Another spot- 

 maximum appears in 1787. In Switzerland. France, Germany, in Montmorenci. Paris, 

 Ratisbon, Prague, Mannheim, Copenhagen, Spydberg, and Abo, an aurora-maximum is 

 in the same year. In Berlin, St. Petersburg, and perhaps Brussels, it comes one year 

 earlier ; and in Sagan, Jena, and Great Britain, one year later. There were none 

 at Prague in 1788 and 1789, and thirteen in 1787. No auroras were recorded 

 at Carlsruhe in 1785, 1787, and 1788. In New Haven, Cambridge, and perhaps 

 Salem, the year 1786 claims the aurora-maximum. How far the great number of 

 auroras, generally observed at this epoch, was caused by the secular maximum, and 

 how far by a subordinate maximum, it may not be easy to decide. 18. After a long 

 interval comes the spot-minimum of 1798. This year contains, decidedly, an aurora- 

 minimum, only two having been observed the whole earth over. 19. The year 1804 

 brings with it another spot-maximum. A feeble aurora-maximum can be traced in . 

 the observations made in Great Britain, France, Germany, St. Petersburg, and Abo, 

 for the year 1804. The same remark will apply to Salem, and perhaps to New Haven. 

 20. The year 1810 is another in which the solar spots reach a minimum. Only two 



