ON SOME RECENT SUN SPOTS. 



159 



aurora and kindred phenomena, there probably is an indirect 

 connection between Sun Spots and the condition of our skies. 



NORTH. 



THE GREAT SUN SPOT OF 1903, OCTOBER 9th. 



Photographed with the Greenwich Photoheliograph. 

 By kiucl permission of the Editor of " Knowledge." 



Periodicity of Sun Spots. In 1851 Schwabe, of Dessau, by 

 the comparison of an extensive series of observations running 

 over nearly thirty years, showed that the Sun Spots are periodic, 

 being at times vastly more numerous than at others, with a 

 roughly regular recurrence every ten or eleven years. This had 

 been surmised by Horrebow more than a century before, though 

 not proved. Subsequent study fully confirmed this remarkable 

 result of Schwabe. Wolf, of Zurich, has collected all the 

 observations discoverable, and finds a pretty complete record 

 as far back as 1610. The cause of this periodicity is not known. 

 The influence of some of the planets has been conjectured. 

 Jupiter especially, as its vast mass and attractive power would 



