The Botany of Iceland - 01.12.1930, Page 182
172
H. M0LHOLM HANSEN
42.3 and 14.2. A comparison between the daily temperature amp-
litudes for rock and sandy soil shows, for the same depths, apart
from the uppermost layers, a greater amplitude for the solid than
for the loose soil. All these figures show that sandy soil is a better
isolator than rocky soil.
Table 36. Average Diurnal Variation of Temperature
in different Soils with differing Vegetation. After Th. Homén.
Nos. 1-3 (1897, p. 48); 4-14 (1894, p. 231).
Granite Sandy heath Bog Sunny open heath Forest-clad heath
10_l3/8 10_13/8 10-13/8 12-13/s °-8/9 ls-ls/8 6-s/9
1893 1893 1893 1892 1892 1892 1892
1 2 3 4 5 6 7
0 cm depth.. 20.2° 34.0° 21.4° 18.4° 22.0° 7.1° 6.3°
2 » » 10 1 19.3 9.6 13.0 13 2 4.3 3.6
5 » » 13.8 11.8 2.8 9 4 9.2 2.7 2.1
10 » » 11.7 7.8 1.5 64 6.2 1.5 1.3
20 » » . . 7.9 3.9 0.4 2.9 2.7 0.7 0.6
40 » » 3.4 0.7 0.05 0.0 0:4 0.2 0.1
Sunny open bog Forest-clad moor Boggy fleld Clayey field
ls-l3/s 6-8/o l9-ls/s 6-8/9 preserv. harvest. ri-is/^
1892 1892 1892 1892 12-is/sl892 6*8/9 1892 1892
» 9 10 11 12 13 14
0 cm depth. . 18.1° 14.7° 8.2° 7.4° 12.0° 18.6° 8.5°
2 » » 11.1 9.5 4.8 4.1 7.4 9.9 6.9
5 » » 4.4 3.9 1.9 1.7 3.0 4.7 4.0
10 » » .. 2.1 1.8 0.8 0.7 1 1 1.2 2.4
‘20 » » 0.5 0.5 0 2 02 0.3 0.3 1.0
40 » » 0.04 0.04 0.02 0.02 0.03 0.03 0.3
If, next, the dry soil, the sandy heath, is compared with the
damp soil, the bog, the above-mentioned deviations are seen to be con-
tinual. The surface of the bog only attains a temperature maximum of
27.7°, owing to a great deal of heat becoming latent by evaporation
of the water present in the bog. At a depth of 60 cm the maximum
temperature is only 11.70. The minimum temperature of the sur-
face is no less than 6.3° and is thus the lowest of the temperatures