429 



NOTES ON THE YORK RAINFALL.* 



J. EDMUND CLARK. 



York rainfall records now cover a total period of eighty-nine 

 years. Prof. J. Phillips has preserved for us a summary of 

 observations by Jonathan Gray from i8xi to 1824. John Ford, 

 of the Friends' Boys School, begfan observations in 1831, the 

 year when this Association was founded. From the next year 

 on, we still have an almost unbroken series of the original 

 daily records. From 1872, the Yorkshire Philosophical Society 

 records have been used by the Meteorological Office. 



The seven decades from 1831 to 1900 give a mean annual fall 

 of 24.766 inches. The whole eighty-nine years work out at 

 24.584 inches. The sixty years, omitting the seventies, only 

 average' 24.222 inches, the mean for that decade reaching the 

 abnormal value of 28.036 inches. The driest decade was that of 

 the fifties (23.265). 



Examining the monthly totals (reduced for comparison to 

 thirty-day values) we find a curve from the March minimum of 

 1.56 inches to the October maximum of 2.54 inches, unbroken 

 save for a peculiar drop in September. There is thus a variation 

 of nearly an inch on a mean thirty-days fall of 2.01 inches. 



The means for July, August and October are 2.48, 2.51, and 

 2.54 inches. This approach to identity makes the September 

 drop the more striking. In the seventies only did it exceed each 

 of the other three months. 



Over long periods, November, August, and July have each been 

 the wettest months of the year. Decade by decade the wettest 

 months have been (i) November, (2) October, (3) August, (4) 

 October, (5) September, (6) July, (7) October ; the September 

 mean for the seventies (3.36) being the highest. 



Suspecting a possible association with solar activity, the 

 annual and monthly values at maxima and minima were com- 

 pared. The three years about each of these extremes were 

 taken for each of the six cycles in the seventy years, 1831 to 

 1900, the first minimum being at 1833.9, ^^^^ the last maximum 

 at 1 894. 1 



This comparison showed an excess aggregate fall for the 

 whole year of the eighteen years at times of maxima over the 



• A paper lead to Section A at the meeting of the British Association, 

 York, 1906. 



1906 December i. 



