What We Learn from the Sun 



reached its greatest extent, and thence returned 

 to its first value, no less than eleven years elapsed, 

 and a much longer time passed before the per- 

 iodic character of the change was satisfactorily 

 determined. 



The reader will at once see what these observa- 

 tions tend to. The sun-spots vary in frequency 

 within a period of eleven years, and the magnetic 

 diurnal observations vary within a period of the 

 same duration. It might seem fanciful to 

 associate the two periodic series of changes to- 

 gether, and doubtless when the idea first 

 occurred to Sabine, it was not with any great 

 expectation of finding it confirmed, that he 

 examined the evidence bearing on the point. 

 Judging from known facts, we may see reasons 

 for such an expectation in the correspondence of 

 the needle's diurnal vibration, with the sun's 

 apparent motion, and also in the law which 

 associates the annual variations of the magnet's 

 power with the sun's distance. But undoubtedly 

 when the idea occurred to Sabine, it was an 

 exceedingly bold one, and the ridicule with which 

 the first announcement of the supposed law was 

 received, even in scientific circles, suffices to show 

 how unexpected that relation was which is now 

 so thoroughly established. For a careful com- 

 parison between the two periods has demon- 

 strated that they agree most perfectly, not merely 

 in length, but maximum for maximum and 

 minimum for minimum. When the sun-spots 

 are most numerous, then the daily vibration of 

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