What We Learn from the Sun 



sphere, though in what way that influence is 

 exerted is not at present perfectly clear. Some 

 have thought that the mere attraction of the 

 planets tends to produce tides of some sort in 

 the solar envelopes. Then, since the height of 

 a tide so produced varies inversely as the cube 

 or third power of the distance, it has been thought 

 that a planet when in perihelion [nearest the sun] 

 would generate a much larger solar tide than 

 when in aphelion [farthest from the sun]. So 

 that, as Jupiter has a period nearly equal to the 

 sun-spot period, it has been supposed that the 

 attractions of this planet are sufficient to account 

 for the great spot-period. Venus, Mercury, 

 the Earth and Saturn have, in a similar manner, 

 been rendered accountable for the shorter and 

 less distinctly marked periods. 



Without denying that the planets may be, 

 and probably are, the bodies to whose influence 

 the solar-spot periods are to be ascribed, I yet 

 venture to express very strong doubts whether 

 the action of Jupiter is so much greater in peri- 

 helion than in aphelion as to account for the fact 

 that, whereas at one season the face of the sun 

 shows many spots, at another it is wholly free 

 from them. 



However, we are not at present concerned so 

 much with the explanation of facts as with the 

 facts themselves. We have to consider rather 

 what the sun is, and what he does for the solar 

 system, than why these things are so. 



Let us note, before passing to other circum- 

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