THE EARTH A MAGNET. 29 



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. 



For so remarkable a phenomenon as this, none but 

 a cosmical cause can suffice. We can neither say 

 that the spots cause the magnetic storms nor that the 

 magnetic storms cause the spots. We must seek for 

 a cause producing at once both sets of phenomena. 

 There is as yet no certainty in this matter, but it 

 seems as if philosophers would soon be able to trace 

 in the disturbing action of the planets upon the solar 

 atmosphere the cause as well of the marked period of 

 eleven years as of other less distinctly marked periods 

 which a diligent observation of solar phenomena is 

 beginning to educe. 



(From the CornUll Magazine, June 1868.) 



