Sun-spot Frequencies Contrasted. 163 



From the 33-year periods. From 10x3 rears of Sr.ru. & S min. 

 Tables I. and III. Tables I. aud V. 



! Sun-spot ratio. Auroral ratio. Sun-spot ratio. ! Auroral ratio. 





Scandinavian data .. 3:1 2:1 7:1 T6 : 1 



Iiove ring's data 3:1 5"5:1 7:1 1-5:1 



3 successive years of largest aud 3 successive years of least 

 auroral frequency. One of the groups for New York State 

 was made up of the last and the two earliest years of the 

 period of observation. The differences between the mean 

 sun-spot frequencies for the contrasted groups of years in 

 Table VI. are really much less than in the corresponding 

 cases in Table V., but the opposite is true of the mean 

 auroral frequencies. For the ratio between the auroral 

 frequencies in the contrasted groups of years we have 

 21 : 10 in Table VI., both for Scandinavia aud New York 

 State, whereas in Table V. the corresponding ratios are 

 respectively only 16 : 10 and 15 : 10. 



As to annual variation in Table VI., the group of years 

 of few auroras shows, as compared to that of many auroras, 

 an enhanced maximum at one or both equinoxes, and a lower 

 minimum both in winter and summer. 



Lovering's general catalogue is not considered in Table VI. 

 owing to the erratic way in which the auroral frequencies in 

 it vary from year to year. In some of the 11-year cycles 

 years of many and few auroras seem to occur almost pro- 

 miscuously, and the selection of 3 successive years as repre- 

 sentative of either high or low frequency presented difficulties. 

 Even in the comparatively homogeneous Scandinavian data. 

 the same phenomenon occurred to a certain extent. 



§ 12, The difference between the results in Tables V. and 

 VI., and the great irregularity in the variations from year 

 to year of auroral as compared to sun-spot frequency, point 

 to one of two conclusions, — either 



(1) Auroral data are so heterogeneous, or so intrinsi- 



cally defective, that consecutive years' results are 

 affected by large differential errors when treated as 

 measures of the same quantity; or 



( 2) Auroral frequency depend.-, and to no small extent, 



on something more than the contemporaneous value 

 of sun-spot frequency. 

 M 2 



