Solar Prominences and Terrestrial Magnetism. 249 



The facts in this paper explain why it is that magnetic storms some- 

 times take place when there are no spots, or no very large spots, on 

 the surface of the sun. Since the occurrence of magnetic storms is 



shown to be very closely connected with the solar prominences, there 

 may be prominences and magnetic storms when there are no spots. 

 Prominences may also sometimes be associated with large spots, and as. 

 the latter can be seen while the former can not, the resulting magnetic 

 storm is generally attributed to the spots. 



