140 
J. HOPXINSON-WATER AND WATER SUPPLY 
the Hertfordshire observations the record at Sunbury in Middlesex, 
compiled from observations taken continuously from Sept. 1796 to 
Sept. 1839.* For the 6 years, Oct. 1833 to Sept. 1839, the rainfall 
in Hertfordshire, deduced from the observations taken at Nash 
Mills during this period, was 10£ per cent, greater than at Sun¬ 
bury, and therefore, in order to arrive approximately at the mean 
rainfall in Hertfordshire from Oct. 1800 to Sept. 1833, the Sunbury 
record has been increased 10| per cent. By this method the earlier 
portion of the following table, showing approximately the mean 
annual rainfall in Hertfordshire in decades for the last 90 years, 
has been compiled. 
Computed Mean Rainfall in Hertfordshire for the present Century. 
Decade. 
Winter. 
Oct.-March. 
Summer. 
April-Sept. 
Year. 
Oct-Sept. 
Inches. 
Ratio. 
Inches. 
Ratio. 
Inches. 
Ratio. 
1800-10 
1 1 '417 
93 
12-139 
96 
23-556 
95 
1810-20 
n ‘359 
93 
11 *359 
90 
22-718 
91 
1820-30 
ii’567 
94 
13726 
I09 
25-293 
102 
1830-40 
10-876 
88 
10-549 
84 
21-425 
86 
1840-50 
12-695 
103 
ii*8io 
93 
24*505 
98 
1850-60 
12*094 
99 
14-454 
ii 5 
26-548 
107 
1860-70 
12-993 
106 
11-748 
93 
24-741 
99 
1870-80 
13-470 
no 
15-132 
120 
28*602 
US 
1880-90 
I 3-995 
114 
12-628 
100 
26-623 
io 7 
Mean 
12-274 
100 
12-616 
100 
24*890 
100 
Assuming that 25 inches is our approximate mean annual rainfall, 
although the secular decrease in the rainfall of the globe should not 
be totally ignored, we may for all practical purposes accept with 
confidence the conclusions which Mr. Symons has arrived at with 
regard to the probable extreme variation. “ There are now,” he 
said a few years ago,f ‘ 4 hundreds of records of rainfall in this 
country of thirty or more years each, and in a very large proportion 
of them it will be found that the following proportions will be 
within 7 per cent, of the truth :■— 
Wettest year, 45 per cent, more than the average. 
Driest year, 33 per cent, less than the average. 
Driest two consecutive years, 26 per cent, less than the average. 
Driest three consecutive years, 21 per cent, less than the 
average.” 
* 4 Meteorological Register kept at Sunbury Yicarage, Middlesex, by the Rev. 
James Cowe, M.A., 1795 to 1839.’ London, 1889. I have examined several 
old records of the rainfall in the neighbourhood of London, and all show a less 
amount of rain in the earlier than in the latter part of this century, and in general 
corroborate Mr. Cowe’s observations. 
t ‘ Water-Supply and Distribution,’ pp. 41, 42. (International Health Exhi¬ 
bition. Conferences.) 
