1864.] Dr. Wolf on the Magnetic Variations at Greenwich, 89 



sent them from my Sun-spot-ratios r in the same way that I had succeeded 

 in doing with those obtained at numerous other stations (see different Nos. 

 of my Mittheilungen iiber die Sonnenflecken*'), and I obtained the for- 

 mula 



?;^ = 9'-95 + 0-056.r (I) 



The comparison contained in the Table between the observed values and 

 the values computed by formula (I) gave me, however, a strikingly less good 

 accord than I had obtained for Munich, Prague, Christiania, &e. ; and this 

 induced me to try how it would be if I formed groups of the years "rich," 

 medium," and "poor" in sun-spots, and compared for each group the 

 mean variation with the mean ratio. Thus 





Sun-spots. 





Calculated by (II). 



Years. 





Mean. 



A- 





Number. 



Mean r. 





Wi- 



DifF. 



1841-1842 



Medium 



24*60 



11-70 



ll -28 



+0*42 



I 843-1 844 



Poor ... 



Io-8o 



11*60 



10-44 



+ i'i6 



1845-1846 



Medium 



40*00 



12*85 



I2'22 



+0-63 



I 847-1 849 



Rich ... 



91-80 



15-80 



15-38 



+0-42 



1850-1852 



Medium 



59"53 



12-50 



13*41 



— 0-91 



1853-1854 



Medium 



28-45 



11*30 



11*52 



— 0-22 



1855-1857 



Poor ... 



10*90 



9"43 



10-44 



— 1*01 









Sum of squares 



3"99i9 



And I then obtained the formula 



v=9^'7S + 0'QQ\.r, (II) 



the comparison of which with the values derived from the observations 

 shows a much better accord, without the individual years being much 

 worse represented than by (I) . It follows that the Greenwich observations 

 also give on the whole a march corresponding to that of the sun-spots, but 

 at the same time with materially greater deviations than appear in the con- 

 tinental stations which I have previously treated. 



When I communicated to Professor Airy the unexpected result of my 

 calculations, he called my attention to the circumstance that his varia- 

 tions were absolute ones, i. e. the means of the differences between the 

 daily extremes, while the variations at other stations which I had employed 

 were probably obtained from observations at definite hours ; and on my in- 

 forming him that such was really the case, he gave me in addition the 

 Means of the Declinations which corresponded at Greenwich to the pre- 

 scribed hours of Gottingen time. It is from these subsequently commu- 

 nicated values that I have derived the maxima and minima and their 

 differences entered in the Table under v.^. The calculation of the quan- 

 tities in ^2 then led me to make the formula 



^?^=6'•67 + 0•039.r; ...... (Ill) 



