44 LIGHT SCIENCE FOR LEISURE HOURS. 



"Washington and Philadelphia received strong electric 

 shocks ; the pen of Bain's telegraph was followed by a 

 flame of tire ; and in Norway the telegraphic machin- 

 ery was set on fire. At night great auroras were seen 

 in both hemispheres. It is impossible not to connect 

 these startling magnetic indications with the remark- 

 able appearance observed upon the sun's disk. 



But there is other evidence. Magnetic storms pre- 

 vail 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. !N\)w, 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 

 had been recording the appearance of the sun's face 

 from day to day and from year to year. He had found 

 that the solar spots are in some years more freely dis- 

 played than in others. And he had determined the 

 period in which the spots are successively presented 

 with maximum frequency to be about eleven years. 

 On a comparison of the two sets of observations, it was 

 found (and has now been placed beyond a doubt by 

 many years of continued observation) that magnetic 

 perturbations are most energetic when the sun is most 

 spotted, and vice versa. 



