131 
1918-19.] The Cooling of the Soil at Night. 
In so short a period one could not expect to arrive at any definite 
conclusions, but the observations so taken clearly point to the fact that 
the difficulties of forecasting the minimum surface soil temperature may 
be overcome successfully in the near future. 
V. The Thermal Effect of a Layer of Poor Conducting 
Material on the Surface of The Soil. 
To obtain a measure of the efficiency of various poor conductors in 
checking the loss of heat from the surface of the soil on clear nights, I 
Table IV. 
Date. 
Open 
firmed 
soil 
minimum. 
Minimum 
under 
| in. loose 
raked soil. 
Minimum 
under 
\ in. ashes. 
Minimum 
under \ in. 
manure. 
Air just 
over soil 
minimum. 
Weather. 
1918. 
September 6 
40-0 
46'0 
46-5 
Clear 
» 8 . 
38-5 
44-0 
45-0 
55 
„ 29 . 
33 5 
36-0 
36*5 
55 
„ 30 . 
36*0 
39-0 
39-0 
55 
October 13 
33-5 
34*5 
365 
37*0 
55 
„ 16 . 
34’5 
35-5 
38*5 
39-0 
55 
November 8 
36*0 
375 
39-0 
39-5 
3*6*0 
55 
„ 9 . 
325 
34-0 
36-5 
37*5 
33-0 
55 
„ 11 . 
34-5 
35-5 
38 ’0 
39-0 
34-0 
.55 
„ 12 . 
28'0 
31-0 
33-0 
34*0 
24-0 
55 
„ 13 . 
28-5 
30-0 
330 
34*0 
27-0 
55 
„ 15 . 
29-0 
31-0 
33*0 
34-0 
27-0 
55 
Average increase in tempera- 
1-5 
4-0 
4-7 
ture over open firmed 
soil 
Greatest increase on any 
3-0 
6'0 
6*5 
night 
have made a series of observations during the past winter on the minimum 
temperature of the surface when covered with layers (J in. thick) of — 
(1) Loose soil, well raked, 
(2) Ashes, 
(3) Manure, 
(4) Fallen leaves, 
(5) Grass and moss growing naturally, 
as compared with the minimum temperature of open firmed soil. These 
results are given in Tables IV and V. Three very suitable periods for 
such observations occurred from December 15-22, December 23-26, 
