274 Mr. R. P. Greg on the Periodicity of the Solar Spots. 



helion again ; now, he passed his perihelion in June last, and 

 there was an extraordinary number of spots at that time ; since 

 then the sun has been comparatively free from spots. Mercury 

 is in perihelion now ; and I was observing the sun] on Friday, 

 and the spots had increased very much both in number and 

 size. " I remain, dear Sir, 



" Quarry Bank, near Wihuslow, " Yours tru ty> 



Sept. 8th, I860." "J. Henshall." 



Should future investigation prove that this peculiar conjunc- 

 tion of Mercury and Venus is something more than a mere co- 

 incidence, taken in connexion with the interval of 11*1 years 

 between the solar-spot maxima, it will not fail, I think, to create 

 surprise that two such small planets should produce apparently 

 so strong an influence upon the sun, as that required to regulate 

 the periodicity of his spot- energy; it would have been more 

 natural to suppose that the intensity of the planetary disturbance 

 or effect would at least have been to some extent proportional 

 to the masses, and inversely as the squares of the distance. One 

 can only suppose that Mercury (and probably Venus similarly, 

 though to a minor extent), owing to his extreme density, possesses 

 a metallic constitution highly favourable to electro-magnetic 

 action ; he may indeed intrinsically be a more powerful magnet 

 than all the rest of the planets put together. His proximity to 

 the sun, great eccentricity of orbit, as well as considerable incli- 

 nation of orbit to the ecliptic, may help to favour his magnetic 

 energy upon the sun, direct or reflex ; while generally it may 

 perhaps be found that whatever magnetic action may exist between 

 a planet and the sun, it will be most powerful when the planet is 

 in one of its nodes, in a line with the sun's equator. This, at 

 least, we should be inclined to imagine would be the case, should 

 the solar magnetic poles coincide with his poles of axial rotation, 

 and consequently in a direction perpendicular to the supposed lines 

 of planetary magnetic force. It is worthy of remark that Jupiter 

 passed his ascending node about the 1st of September last year, 

 about the time of the great magnetic auroral disturbance, at a 

 time likewise when the spots and markings on his own surface 

 were remarkably numerous and distinct, and also near the time 

 of solar-spot maximum. 



Manchester, Yours respectfully, 

 Sept. 18, 1860. R. P. Greg. 



Note. — Since writing the above, I have received a short note 

 from Mr. Carrington, to whom I wrote respecting the peculiar 

 conjunction of Mercury and Venus, mentioned by Mr. Henshall ; 

 and I am inclined to agree with him, that it would be natural to 

 expect nearly as decided solar effects from the ordinary and more 

 frequent conjunctions of Venus and Mercury, There is likewise 



