Masterpieces of Science 



stances of interest connected with the sun, that 

 the variable condition of his photosphere must 

 cause him to change in brilliancy as seen from 

 vast distances. If Herr Schwabe, for instance, 

 instead of observing the sun's spots from his 

 watch-tower at Dessau, could have removed 

 himself to a distance so enormous that the sun's 

 disk would have been reduced, even in the most 

 powerful telescope, to a mere point of light, there 

 can be no doubt that the only effect which he 

 would have been able to perceive would have 

 been a gradual increase and diminution of 

 brightness, having a period of about eleven years. 



Our sun, therefore, if viewed from the neigh- 

 bourhood of any of the stars, whence undoubtedly 

 he would simply appear as one among many 

 fixed stars, would be a "variable," having a 

 period of about eleven years and a very limited 

 range of variation. Further, if an observer, 

 viewing the sun from so enormous a distance, 

 had the means of very accurately measuring its 

 light, he would undoubtedly discover that while 

 the chief variation of the sun takes place in a 

 period of about eleven years, its light is sub- 

 jected to minor variations, having shorter periods. 



The discovery that the periodic changes of the 

 sun's appearance are associated with the periodic 

 changes in the character of the earth's magnetism 

 is the next thing that we have to consider. 



It had long been noticed that during the 

 course of a single day the magnetic needle ex- 

 hibits a minute change of direction, taking place 

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