1874.] 



. Sun-spot Period and the Rainfall. 



471 



Differences of Rainfall for Great Britain and of Sun-spot area for 

 1832 to 1867. 



If we seek the value of / for the mean of the three periods of eleven 

 years commencing 1832 and 1835, we find the following equations : 



1832 to 1864 . AE= +0-0019 AA ; 



1835 to 1867 AE=+ 0-0011 AA. 



These results, then, are, as we expected, in conformity with Mr. Mel- 

 drum's conclusion ; so that if we compare the year of largest with that of 

 smallest spot-area, the difference of rainfall should amount to 2-61 in. by 

 the first and to 1-51 in. by the second value of/. If we take the mean 

 spot-area for the years 1834, 1844, 1856, and 1866, and for 1836, 1848, 

 and 1861, we find that the mean difference of rainfall for these years 

 should be 2-06 in. by the first and 1-20 in. by the second value of /, in- 

 stead of 8'45 in. as found by Mr. Meldrum. 



It will be seen also that the greatest mean difference of rainfall is that 

 for the years 1841, 1852, and 1863, and this was an excess of rain for 

 years of spot-area deficiency ; were another such opposite difference to 

 present itself, it would neutralize the conclusion derived from these 

 means. It should also be observed that while the first and third periods 

 of eleven years are in favour of the connexion, the second (1843 to 1853) 

 is opposed to it (this is also the case for the eleven years 1857 to 1867). 



It will be seen, then,, that from this discussion a probable difference of 

 about 2 inches of rain may be expected betwixt years of greatest and 

 least spot-area. 



This result is derived from observations at ten stations, distributed 

 over a very small patch of the earth's surface ; and it is evident that for 

 any serious investigation a much larger series of observations represent- 

 ing the rainfall over a great extent of country would be essential. 



* Indicates opposite signs of AA and AR. 

 VOL. XXII. 2 X 



