174 H. MØLHOLM HANSEN 
monthly mean temperatures. The table confirms the rule previously 
laid down that the amplitude decreases with the distance from the 
surface, and further that it is greatest for the sunny open soil, less 
for the wooded soil. This applies in still greater degree to the mean 
temperature of the warmest month and to the annual mean tempera- 
ture. The sequence is as follows: grassfield — birchwood — firwood. 
From a knowledge of the daily and annual variations in tempe- 
rature it is possible to determine the heat-conducting power of a 
rock, this quantity being the less the slower the maximum and 
minimum spread in the soil, or the quicker the amplitude decreases 
downwards. 
After Hann (1926, p. 800) we give the following values for a 
series of natural rocks (minute, cm.). 
Sandston eee a een 1.39 
Clay with an admixture of sand ........ 0.82 
SANT SUISSE EEE RP 0.52 
Beas We sranite LE oem cp accrue 1.14 
BAUM RE DENDE SEE SEE SES SEERE sub ve Dee 0.32 
POON SOME Sohn. ern vite eek e 0.13 
IEGOSE SHOW 4..2.....2.% Han bases CRUE 0.16 
POMPACE SON 235.5) us Ru nel rer 0.24 
|S vgs ae ea Re 0.68 
LR EAST earth 5,87 a alc. cys 6, ods eats Re 0.56 
EOL EOZEM «sis IEEE ee 0.32 
However, the heat-conducting power is not only different for 
the different rocks, it also varies in the same rock according to the 
air and water-content. The more solid and moist a rock is, the 
better is its heat-conducting power. 
