The Sun 



ceptible difference in the two positions, and by 

 measuring the distance separating them we shall 

 be able to determine the speed with which the 

 sun's eastern edge is approaching us and the 

 other edge is receding, owing to the rotation of 

 the orb on itself. The results obtained by this 

 method agree with those deduced from the 

 displacement of the sun spots. 



The fact that the sun rotates, though of great 

 intrinsic interest, would not have claimed so 

 much of our attention if it did not lead to 

 another fact of the highest interest. Astronomers 

 have observed thousands of spots and have 

 invariably noted that equatorial spots move 

 with greater rapidity than those nearer the 

 poles; the period of rotation being 24 days 

 9 hours at the equator, 25 days 7 hours at a 

 latitude of 20, and 26 days 7 hours at a latitude 

 of 35. Thus the surface of the sun does not 

 rotate as a coherent whole, as would be the case 

 if the surface consisted of a solid crust. To 

 realise the full meaning of this well-ascertained 

 fact we must adduce another. The study of 

 the variations of the magnetic needle on the 



earth's surface has revealed a periodicity of 



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