Eight-Year Cycle in Relation to Physical Cause 109 



announced the discovery of the synchronism between 

 the sunspot cycles and the frequency of terrestrial 

 magnetic storms. His findings were quickly confirmed 

 by Wolf and Gautier, and subsequent observations 

 have strengthened the theory of the essential concord- 

 ance of the sunspot cycle and the cycles of terrestrial 

 magnetic variations. But how can the Sun at a dis- 

 tance of 93 millions of miles affect the state of terres- 

 trial magnetism? The investigations which have the 

 solution of this problem in view are among the most 

 stimulating of contemporary inquiries and, as will 

 appear later on, they have a direct bearing upon our 

 meteorological problem. 



After one series of terrestrial phenomena had been 

 showTi to be in direct accord with the sunspot cycle, 

 it was inevitable that a host of alert investigators 

 should set about discovering other agreements. For 

 some time it had been known that the aurora bore- 

 alis and magnetic disturbances were associated phenom- 

 ena, and about 1819 Arago had added materially to the 

 measured e\'idence of their relation. With Sabine's 

 proof of the synchronism of the sunspots and magnetic 

 storms, it was only a corollary that the aurorae should 

 vary with the sunspot cycle. To Wolf, of Zurich, 

 credit is usually given for the detailed proof of the 

 coincidence. 



Economists are familiar with Sir William Herschel's 

 speculation^ in 1801 on the possible relation of sun- 



1 " Observations tending to investigate the Nature of the Sun, 

 in order to find the Causes or Symptoms of its Variable Emission 



