52 H. I. JENSEN. 



simultaneously, and disturbances of the earth's magnetic 

 condition are accompanied by Aurora Borealis displays." 1 



Wolf and Fritz suggested that in addition to the eleven 

 year period there was also a period of longer duration 

 (which they thought to be fifty-five years) in the sunspot 

 and magnetic curves. Later researches by Bruckner, 

 Lockyer and others show this period to have a duration of 

 thirty-five years. In this connection it is important to 

 notice that Wolf found a secular variation in climatic con- 

 ditions in Europe with a period of about thirty-five years. 



On looking at the diagram (Plate II.) we also observe 

 traces of a thirty-five year period. Thus violent outbursts 

 of volcanic energy after a considerable lull occurred in 1867 

 and the present year. The groups centered around 1822, 

 1855 and 1889, are less well defined than the others. Mount 

 Redoubt in Alaska, was in eruption in 1867 and again in 1902. 



Before proceeding it will be as well to point out that Mr. 

 Meldrum found the number of severe cyclones in the West 

 Indies, in years of sunspot maxima, to exceed the number 

 in minima. Blanford's observations in India (1848 — 1876) 

 show that the maximum pressure occurs in minimum sun- 

 spot years. These two facts seem to show that anticyclonal 

 conditions in the earth's atmosphere are most prevalent 

 with a sunspot minimum, and cyclonal conditions with a 

 maximum. Mr. H. O. Russell points out in " Periodicity 

 of Good and Bad Seasons " that violent hurricanes come in 

 droughts. Now these facts are quite in accord, for anti- 

 cyclonal conditions would lead to droughts, and when anti- 

 cyclone follows anticyclone, cols would be frequent, and the 

 breaking of these cols would give rise to violent hurricanes. 



Finally we come to the possible causes of the dependence 

 of earthquakes on sunspots. 



1 Milne observes that particularly fine auroral displays have on a few 

 occasions been accompanied by earthquakes — " Earthquakes,"p.264). This 

 however seems only to be exceptional. 



