13 
1919-20.] The Cooling of the Soil at Night. 
of no difficulty as far as the maximum is concerned, since it occurs in 
the afternoon, but a more serious item as regards the minimum readings, 
which must be made in the early morning. 
R 
With a view to obtaining an approximate value for ~ without the 
xv 0 
strain of continuously getting up early enough to read the minima, 1 
R 
have tabulated a number of observed values of ~ under varying con- 
K 0 
ditions of wetness of the soil. These values, given in Tables I, II, III, 
R 
should serve as a guide to obtain an estimate of ~ with a fair degree 
Ro 
of accuracy from the condition of the surface layer of soil and the 
known number of previous fine days. 
(a) Soil Wet just after Rain 
s values of and imm 
xv 0 K 0 
amount of which in the previous 24 hours is given 
R R 
Table I gives the values of and ^ immediately after rain — the 
xv 0 K 0 
Table I. — Values of _ £ and -V 
ri 0 R o 
Date. 
R-2 
R 0 
E 4 
Ro' 
Amount of Rain in 
previous 24 hours. 
Millimetres. 
April 
1919. 
11, 12, 13, 14, 15 
■66 
•42 
1 to 3 mm. daily 
55 
16 . 
•66 
•44 
20 mm 
55 
20 . 
•65 
•40 
2 
5 > 
55 
29 . 
•66 
•43 
7 
55 
55 
30 . 
•66 
•43 
1 
55 
May 
3 . 
*64 
•40 
1 
55 
55 
4 . 
•66 
•42 
2 
55 
55 
6 . 
•65 
•41 
1 
55 
15 
7 
•67 
•43 
9 
55 
55 
18 . 
•66 
•43 
5 
55 
June 
4 
•44 
3 
55 
55 
5 . 
•41 
2 
55 
55 
8 . 
•42 
3 
55 
10 . 
•43 
6 
55 
11 . 
•41 
10 
55 
12 . 
•40 
1 
55 
55 
13 . 
•43 
7 
55 
55 
21, 26, 30 . 
•40 
1 to 2 mm. daily 
Average value 
•66 
•42 
