28 LIGHT SCIENCE FOR LEISURE HOURS. 



and Hodgson were observing the sun, one at Oxford 

 and the other in London. Their scrutiny was directed 

 to certain large spots which, at that time, marked the 

 sun's face. Suddenly a bright light was seen by each 

 observer to break out on the sun's surface, and to 

 travel, slowly in appearance, but in reality at the rate 

 of about 7,000 miles in a minute, across a part of the 

 solar disc. Now it was found afterwards that the self- 

 registering magnetic instruments at Kew had made at 

 that very instant a strongly marked jerk. We learned, 

 also, that at that moment a magnetic storm prevailed 

 at the West Indies, in South America, and in Australia. 

 The signalmen in the telegraph stations at Washington 

 and Philadelphia received strong electric shocks ; the 

 pen of Bain's telegraph was followed by a flame of fire ; 

 and in Norway the telegraphic machinery was set on 

 fire. At night great auroras were seen in both hemi- 

 spheres. It is impossible not to connect these startling 

 magnetic indications with the remarkable appearance 

 observed upon the sun's disc. 



But there is other evidence. Magnetic storms 

 prevail more commonly in some years than in others. 

 In those years in which they occur most frequently, it 

 is found that the ordinary oscillations of the magnetic 

 needle are more extensive than usual. Now when these 

 peculiarities had been noticed for many years, it was 

 found that there was an alternate and systematic 

 increase and diminution in the intensity of magnetic 

 action, and that the period of the variation was about 

 eleven years. But at the same time, a diligent observer 



