226 J. HOPEINSOJS'^ — THE CLIMATE OF ST. ALBAKS. 



Rainfall (Tables XIII-XV, p. 227). — There could scarcely 

 have been a better decade than 1887-96 from which to form an 

 idea of the rainfall of St. Albans, for the mean rainfall throughout 

 the county has been very nearly the average of a long series of 

 years. In the fifty-seven years ending 1896 the mean annual 

 rainfall at all the stations in Hertfordshire was 26 '3 3 inches. In 

 this determination no adjustment has been made for the disparity 

 of distribution of the rainfall-stations. The rainfall increasing 

 from east to west, and there being a larger number of stations for 

 the area in the west than in the east, the mean value derived from 

 all the stations requires a deduction in order to arrive at the true 

 mean for the county, which is probably about 26 inches. How 

 this value has been arrived at will be seen on referring to pp. 37 

 and 38 of the present volume of our ' Transactions.' The mean 

 annual rainfall at all the stations in Hertfordshire for the ten years 

 1887-96 was 25-21 inches. This requires a slight deduction for 

 disparity of distribution of the stations, and we may fairly consider 

 that the true mean was about 25 inches. Whether the values 

 arrived at be thus adjusted or not, the rainfall during the last ten 

 years will be found to have been a little under 4 per cent, below 

 the mean for the last fifty or sixty years. In such a very varying 

 element of climate as rainfall this is a very slight difference, and 

 it may be neglected for all practical purposes. Applying the 

 correction, however, the mean annual rainfall at St. Albans for the 

 last ten years, 26*74 inches, would be raised to 27-81 for the last 

 half-century, but if we wished to arrive at the probable value for 

 the last century a deduction would have to be made, and the true 

 mean value would be between 27 and 27J inches. 



For the last half-century the following was probably the ap- 

 proximate mean monthly and seasonal rainfall : — 



March 2-15 June 1-86 Sept. 2-25 Dec. 2-23 



April 1-37 July 3-27 Oct. 3-44 Jan. 1-88 



May 1-98 Aug. 3-03 Nov. 3-09 Feb. 1-26 



Spring 5-50 Summer 8-16 Autumn 8-78 Winter o-37 



"Winter and spring have each 20 per cent, of the year's rainfall, 

 summer has 29 per cent., and autumn has 31 per cent. Spring 

 has 23 per cent, of the year's wet days, summer has 24 per cent., 

 autumn has 26 per cent., and winter has 27 per cent. 



The fall of rain varies on the average most in summer and least 

 in autumn, and more in winter than in spring, the mean deviation 

 from the average fall for each season having been as follows : — In 

 spring 154 in., in summer 1-78 in., in autumn 1-^9 in., and in 

 winter 1-65 in. The extreme deviation, however, has been greatest 

 in spring and least in winter, the wettest spring (1889) having had 

 five times as much rain as the driest (1893), and the wettest winter 

 (1892-93) only twice as much rain as the driest (1887-88); and 

 it has been rather greater in summer than in autumn. 



February and April are much the driest months; July and 

 October are the wettest, followed closely by August and j^ovember. 



