Royal Society. 475 



Should there be any connexion betwixt the rainfall and spot- 

 area, we may always in the first instance represent it approxi- 

 mately by an equation of this form, 



AK=/AA, 



where A!R is the excess or deficiency of the rainfall from the 

 mean, AA is the excess or defect of spot-area for the same period 

 of time, and /is a constant to be deduced from the observations. 



Having obtained the mean spot-area for each year from 1832 to 

 1867, from Table VII. of the paper on this subject by Messrs. 

 De La Rue, Stewart, and Loewy*, the mean for three periods of 

 11 years (1832 to 1864) was found equal to 643 millionths of the 

 sun's visible surface ; with this quantity the values of jt AA (in 

 millionths of the sun's surface) for each year were obtained. 



Mr. Meldrum's conclusion depends chiefly on observations 

 during these periods in Great Britain ; and as he has deduced the 

 rainfall for the first period of minimum spots from observations at 

 three stations, Greenwich, Carbeth (near Glasgow), and Aberdeen, 

 I first examined the observations at these places together with 

 simultaneous observations at Makerstoun for the two periods 

 1832 to 1853f . Applying the above equation to these observa- 

 tions, the following results were obtained : — 



Greenwich . . AE= -0-00092 AA 



Makerstoun AE= —0*00020 AA 



Carbeth AE= +0-00158 A A 



Aberdeen AR= +0-00128 AA. 



Greenwich and Makerstoun are thus opposed to the conclusion, 

 and Carbeth and Aberdeen are more strongly in its favour. It 

 should be remarked, however, that the result for Aberdeen depends 

 wholly on the rainfall given for that place in 1834 (12-3 in.) 

 being exact. As it is 12 inches less than the mean, while at the 

 other three stations the deficiency is only from 0*6 in. at Green- 

 wich and Makerstoun to 1*2 in. at Carbeth, this may be due to a 

 leaky rain-gauge or to a clerical error of 10 inches. In any case 

 no great weight can be given to the conclusion from these four 

 stations %. 



I now sought for an approximation to the mean fall of rain for 

 Great Britain, and for this end have employed the quantities de- 



* Phil. Trans. 1870, p. 399. 



t The means for Makerstoun during the years 1832 to 1849 will be found in 

 Trans. Roy. Soc. Edinb. vol. xix. pt. ii. p. 108 ; the falls for the other years 

 are— 1850, 21-49 in. ; 1851, 25-57 in. ; 1852, 32-20 in. ; 1853, 23-54 in. 



\ It may here be noted that the sum of the plus and minus differences of R 

 and the mean rainfall for the four stations during the twenty-two years were — 



Greenwich. Makerstoun. Carbeth. Aberdeen.] 



Mean fall 24-4 in. 26-2 in. 43-6 in. 24-2 in. 



Sums of AR 100-1 in. 67'8in. 92-4in. 94-3 in. 



It will be seen that the sums of differences have no relation to the mean fall of 

 rain. 



