470 Mr. J. A. Broun on the [June 18, 



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 011 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 + 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 1853t. Applying the above equation to 

 these observations, the following results were obtained : 



Greenwich AR= -0-00092 AA ; 



Makerstoun AR= 0-00020 A A ; 



Carbeth AB= +0-00158 AA ; 



Aberdeen AE= +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 

 1 2 inches less than the mean, while at the other three stations the defi- 

 ciency is only from 0-6 in. at Greenwich 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 J. 



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

 Britain, and for this end have employed the quantities deduced by Mr. 

 Symons from ten stations (British Association Report, 1865, p. 203 ; 

 1871, p. 102). The differences of spot-area from the mean, in millionths 

 of the sun's surface, and of the rainfall for each year are given in the 

 following Table : 







* Phil. Trans. 1870, p. 399. 



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

 Eoy. 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 E and the 

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



Greenwich. Makerstoun. Carbeth. Aberdeen. 



Mean fall 244 in. 26-2 in. 43-6 in. 24-2 in. 



Sums of AE 100-1 in. G7'8 in. 924 in. 94'3irr. 



It will be sesn that the sums of differences have no relation to the mean fall of rain. 



