On the Rain and Drainage - Waters at Rothamstcd. 265 
though a little below the truth, are at least comparable amongst 
themselves, and exliibit some interesting features. 
The range in the amount of chlorides shown by these 
analyses is very considerable. Thus the rain of July 1880 
contained, by the method of analysis here employed, only O'lO 
part of chlorine per million of water, while the rain and snow 
of November 1879 contained 9 "38 parts of chlorine. The latter 
figure is, however, quite exceptional, and suggests a possible 
contamination of the water. The second highest amount 
reached in the forty-three months is much lower, namely, 5 '80 
parts of chlorine. The average proportion of chlorine in the 
rain-water during the whole period is 1"75 per million. The 
quantity of chlorine brought by the rain on to an acre of land 
in the course of a year (average of 3J years) is 13'42 lbs., for a 
rainfall of 34 038 inches, equal to 2242 lbs. of pure common 
salt. All these figures, as already mentioned, are somewhat 
below the truth. 
With the view of throwing light on the cause of variation in 
the proportion of chlorides, we proceed as before to classify the 
analyses according to the amount of rainfall, and according to 
the season of the year. 
Table XVI. — Aveeage proportion of Chlorine in Monthly Rain- 
falls of different Amount, and at different Seasons of the Year, 
in parts per Million. 
Monthly Rainfall. 
Summer. 
Winter. 
AVhole Year. 
3-87 
5-00 
4-67 
Between 1 and 2 inches .. 
1-81 
3-09 
2-51 
Between 2 and 3 „ 
1-46 
2-75 
2'17 
Between 3 and 4 „ 
0-90 
1-77 
1-24 
Between 4 and 5 ,, 
0-86 
1-83 
1-05 
o-es 
2-48 
1-28 
These figures plainly exhibit two facts : first, that the pro- 
portion of chlorides, as of all the other constituents of rain- 
water, rapidly diminishes as the quantity of the rainfall in- 
creases ; and second, that the proportion of chlorides is much 
higher in the winter than in the summer months. The latter 
fact is consistently shown in every part of the comparison 
between summer and winter rainfalls given in the above Table. 
We have already stated that the average proportion of chlorine 
in the rain of the whole year is 1'75 per million ; but the 
