248 On the Rain and Drainage - Waters at Rotliamsted. 
lie in a different rainfall district, the maximum rainfall occurs 
in August or July, not in October. At Greenwich, however, 
the order of the rainfall agrees with that observed at Rotliamsted, 
St. Albans, and Hemel Hempstead. The rainfall in both dis- 
tricts is very similar in the month of August ; they differ most 
in January. 
According to the rule adopted by many engineers, the driest 
year in a long series will have a rainfall one-third less, and the 
three consecutive driest years an average rainfall one-sixth less 
than the mean ; while the rainfall in the wettest year will be 
one-third greater than the mean. The maximum rainfall is thus 
reckoned as twice as great as the minimum. The extreme rain- 
falls recorded at the eight stations just mentioned occurred as 
follows : — 
Wettest 
Year. 
Driest Year. 
Driest Three 
Years. 
Eothamsted 
St. Albans 
Hemel Hempstead . . 
Stretham, Ely .. .. 
1879 
1872 
1872 
1860 
1879 
1875 
1877 
1860 
1864 
1864 
1864 
1854, 1864 
1864 
1870 
1854 
1804 
1862-64 
1854-56 
1862-64 
1862-64 
1862-64 
18G9-71 
1854-56 
1856-58 
The rainfalls recorded at these extreme periods of excessive 
rain or drought compare as follows with the quantities which 
would be calculated on the above mode of reckoning : — 
Table IV. — The Eainfalls recorded in the Wettest, Driest, and 
Driest Three Consecutive Years during 27 Years, 1853-79, 
compared with the calculated Estimate. 
Wettest Year. 
Driest Year. 
Driest Three 
Consecutive Years. 
Record. 
Estimate. 
Record. 
Estimate. 
Record. 
Estimate. 
Eothamsted 
St. Albans 
Hemel Hempstead . . 
Caidington 
Stretham,*Ely .. .. 
Mean 
36-04 
38-15 
36-28 
30-28 
30- 06 
31- 39 
29-03 
31-90 
37-46 
37-05 
36-08 
32-88 
31- 36 
29-40 
27-92 
32- 89 
18-56 
18-66 
16- 96 
17- 16 
16-67 
14-87 
13-81 
16-38 
18-73 
18-53 
18-04 
16-44 
15- 68 
14-70 
13-96 
16- 45 
23-94 
23-68 
22-25 
19-68 
19- 49 
18-30 
15-87 
20- 71 
23-41 
23-16 
22-55 
20-55 
19- 60 
18-37 
17-45 
20- 56 
32-89 
33-13 
16-63 
16-57 
20-49 
20-71 
