Kirkwood.] 



96 



[April 2, 



1847, has discussed all accessible recorded observations, botli solar and 

 magnetic, bearing on the subject. He has thus ascertained a number of 

 epochs of maxima and minima anterior to those observed by Schwabe, — 

 from all of which he has determined the period of the spots to be 

 11.11 years. He undertakes to show, moreover, that this period coincides 

 more exactly with that of the magnetic variation than the 10-year cycle 

 of Lamont. 



(5.) The 5(i-Year Period. — Besides Schwabe's period of 11 years. Wolf 

 finds a larger cycle of 55 years, in which the solar activity passes through 

 a sei-ies of changes. It is not, however, so distinctly marked as the cycle 

 of Schwabe. Its last maximum was about 1837, and that preceding, 

 about 1780. The relative number of spots in different years, from 1749 to 

 1826, when Schwabe commenced his systematic observations, are given 

 (according to Wolf) in Table II. 



TABLE II. 

 Solar Spots, from 1749 to 1825. 



(6.) The 233-Z>a?/ Period.— FroL Wolf, after carefully discussing his 

 own and Schwabe's observations, claims to have discovered two or three 

 minor periods of solar activity. ''By projecting all the results in a con- 



