STUDIES ON THE VEGETATION OF ICELAND 171 
TABLE 35. Average Maxima, Minima, and Amplitudes 
of various Soils. After Homen. 1897, pp. 47—48. The investigations 
cover the period 10—13 August 1893. 
Granite Sandy heath Bog 
Diff. | Max. | Min. | Diff. | Max. Min. Diff. 
Max. | Min. 
Air temperature C°... | 22.7 | - 9.6 | 13.1 » » » > » » 
Vegetable covering ... | 32.5 | 12.6 | 19.9 | 37.7 | 6.4 | 31.3 | 328 22 30.7 
sr nr. 34.8 | 14.5 | 20.3 | 42.3 | 7.8 | 34.6 | 27.7 | 63 | 214 
Sk. aes | 33.1 | 15.2 | 17.9 | 35.9 | 9.7 | 26.2 | 23.9 | 8.9 | 15.3 
ne | 31.9 | 15.8 | 16.1 || 30.6 | 11.3 | 19.3 | 20.6 | 111 | 9.6 
| + | 304 166 138 247 128 118 167 139 2.8 
ee | 28.9 | 17.2 | 11.7 | 22.2 | 14.4 | 7.8 | 16.2 | 148 | 15 
eee | 26.1-| 182 | 7.9 | 19.4 | 15.5 | 3.9 | 153 | 149 | 04 
er: | 243 | 19.1) 5.2) 17-7 | 15.9 | 1.8 | 143 | 142 0.1 
ee... 29|195| 3.4 | 162 | 15.5 | 0.7 | 13.5 | 134 | 0.05 
en ne | 21.7 | 19.6 | 2.1 | 15.0 | 148 | 03 | 124 | 124 » 
N. 200 | 20.9 | 19.6 | 14] 142 | 141! 01|117 16| » 
clothing of vegetation have been made in Finland by Th. Homén 
and described in a series of works (1894, 1896, and 1897). Tables 
35, 36, and 37 give the chief data of these works. Table 35 com- 
prises the daily heat maximum, heat minimum, and amplitude for 
granite, sandy soil, and boggy soil, respectively a solid, a loose, and 
a damp rock. The figures are the mean values of a series of in- 
vesligations. Table 36 shows the daily amplitude for various kinds 
of soil, sandy soil, clayey soil, and boggy soil with or without wood 
or a covering of cultivated plants (cereals). Table 37 shows the 
annual mean temperature, the annual variation in temperature, i. e. 
the difference between the mean temperatures of the coldest and 
warmest months and the mean temperature of each month at different 
depths in soils with a different clothing of vegetation, thus at 0.5, 
1.0, and 2.0 m for open grassfield, birchwood, and firwood. 
A comparison between the temperature conditions of solid rock 
and loose sandy soil shows a much greater current of heat in the 
solid than in the loose soil. Taking the average of 4 days, the 
surface of a granite rock will be heated to 34.8° by day. The heat 
accumulated at the surface will comparatively rapidly spread down- 
wards so as to make the temperature maximum at a depth of 60 cm 
no less than 20.9; for sandy soil the same figures are respectively 
