Mr. R. P. Greg on the Periodicity of the Solar Spots. 271 

 From equation (3), we find 



r= ° 8 =2-16. 



-° 4+ I^5 X l5 ( ' 94 + -° 4 ) 

 From equation (2), taking b = a,we find 11=2*94, or 3 nearly. 

 Hastings, September 4, 1860. 



XXXIII. On the Periodicity of the Solar Spots. 

 By R. P. Greg, F.G.S. 



To the Editors of the Philosophical Magazine and Journal. 

 Gentlemen, 



IN the last Number of this Journal, while briefly suggesting 

 that the recent meteorological disturbances we have expe- 

 rienced might be connected with increased magnetic action in 

 the sun, as apparent in the phenomenon of periodicity in spot- 

 maximum, I at the same time alluded to the possibility of these 

 periodical changes on the sun's surface being likewise a result, 

 more remotely, of planetary influence. I stated that Mr. Car- 

 rington and M. Wolf had likewise entertained the same idea, 

 though without, I believed, arriving at any precise or satisfactory 

 results. In the Comptes Rendus for January 1859, M. Wolf 

 gives a formula which, according to the Rev. Robert Walker*, 

 " expresses the number of years from the mean frequency of the 

 spots in terms of the sines of angles dependent on the revolution 

 of Venus, the Earth, Jupiter, and Saturn, round the Sun. The 

 coefficients of the sines in the terms of this formula are in each 

 case the mass of the planet divided by the square of its mean 

 distance. According to this formula, the spots are determined 

 as to number and frequency by the position of these four planets : 

 Jupiter preponderates and determines the length and height of 

 the undulation of the curve ; the action of Saturn shows itself 

 by small variations ; Venus and the Earth transform the line of 

 simple undulation into a zigzag vibration." The Rev. R. 

 Walker adds that the " form appears to be entirely empirical^ 

 which I believe to be the case. 



The excess of 7 or 8 months in the sidereal period of Jupiter 

 over the supposed solar-spot period of 11*1 years, becomes also 

 a considerable discrepancy in the course of a moderate term of 

 years ; and his most favourable conjunctions with other planets 

 do not seem very constantly to agree with the periods given for 

 solar-spot maximum during the present century. The periods, 

 too, for Jupiter in perihelion, supposing that position naturally 

 to favour an increase of magnetic action or attraction in the sun, 



* See his discourse " On the Physical Constitution of the Sun," read 

 before the late Meeting of the British Association at Oxford. 



