PEECOLATIOX, AlfD EVAPORATION". 



35 



The whole of the stations being represented for tlie List twenty 

 years, the arithmetical mean of the values in these ten tables is 

 given for these years without any adjustment. Some one or more 

 of the stations not being represented for the first thirty years, 

 an adjustment has been made, where it is required, to the arith- 

 metical mean in accordance with, the ratio, during the last twenty 

 years, the rainfall at the stations represented bears to the mean 

 rainfall at the whole of the ten stations during the same period. 

 The mean annual rainfall at these ten stations for the twenty years 

 1872 to 1892 (April to March) being 27-71 inches, the adjustments 

 are as follows : — For the eight years 1842-50, minus 4f per cent., 

 Kash trills being the only station represented, and its mean annual 

 rainfall for 1872-92 being 29-01 ins. ; for the year 1850-51, plus 

 2 per cent., Xasli Mills and Hitehin being the stations represented, 

 and their mean annual rainfall for 1872-92 being 27-32 ins. ; for 

 the two years 1851-53, phis 5i per cent., Nasb Mills, Hitehin, 

 and Royston being the stations I'epresented, and their mean annual 

 rainfall for 1872-92 being 26-18 ins. ; and for tbe three years 

 1853-56, plus 2 per cent., Nash Mills, Hitehin, Royston, and 

 Rothamsted being the stations represented, and their mean annual 

 rainfall for 1872-92 being 27-19 ins. No adjustment has been 

 made for the sixteen years 1856-72, the rainfall at the stations 

 represented during this period being, during the twenty years 

 187-2-92, sufficiently near the mean at the whole of the ten 

 stations, viz., in 1856-60 (five stations), 27-77 ins. ; in 1860-66 

 (seven stations), also 27-77 ins. ; in 1866-70 (eight stations), 

 27-61 ins. ; and in 1870-72 (nine stations), 27-78 ins. 



The mean annual rainfall in Hertfordshire, as shown by this 

 table, for the half-century ending 31st March, 1892, is 26-33 ins., 

 the mean summer rainfall being 13-24 ins., and the mean winter 

 rainfall 13-09 ins. 



Dividing the half -century into two equal periods of twenty -five 

 years each, we have the following result : — 



The rainfall during the first quarter-century was thus 3 per 

 cent, below the mean for the half-centuiy, and the rainfall during 

 the last quarter-century was 3 per cent, above it, the winter 

 rainfall deviating -\ per cent, more from the mean. 



