ON SUNSPOTS AND RAINFALL. 



233 



The range of variation is about 3"7 inches. 



The epoch of maximum rainfall occurs about one year after th& 

 epoch of maximum sunspots. 



The spot variation has been derived from Table I. 



15. An important advantage of the above arrangement is that th& 

 columns of " means " enable us to compare directly the mean of the sun- 

 spot numbers for the maximum years with the mean rainfall for the same 



Table III. — Great Britain. — Maximum years in 6th line. 



years, and also the sunspots with the rainfall for two years on either side 

 of the maximum years, with very little risk of distortion from the mini- 

 mum years not being all in the same horizontal line. 



16. With regard to the way in which the " mean cycle " is formed, it 



may be remarked that b in the expression 



a +2 b + c 



(see par. 8) gets 



double weight, and that the quotient is put down as the rainfall of the 

 first year of the " mean cycle," which year corresponds with the^second of 

 the thirteen terms or series of years, that is, with b. This is somewhat 

 similar to the common practice of tracing with the hand an approximate 

 average curve through the peaks and hollows of a jagged or serrated 

 curve. 



17. An example of the converse process, namely, that of placing the 

 minimum years in the eighth line or term, is given in the following 

 Table, which has been constructed from the annual mean rainfalls of ten 

 stations, " widely separated," as given by Mr. Symons, in the ' Report of 

 the British Association for 1865.' 



Table IV. has been constructed in the same way as Table II. (Sun- 

 spots). 



Now it would appear that on the whole the rainfall attained its mini- 

 mum a year or two after the epoch of minimum sunspots. 



In fact, both this table and Table III. show that the rainfall lags 

 behind the sunspots in respect of time. 



The mean of the mean cycle is 28 - l inches, and the mean for the- 

 whole period (1816-61) is 283 inches. 



From the column of " means " we see that although the rainfall was 



