170 
than a quarter of an hour, it was found to have gained the tem- 
perature of tlie room. The soils in all these experiments were 
placed in small tin plate ti’ays, two inches square, and half an 
inch in depth, and the temperature ascertained by a delicate 
thermometer. 
Nothing can he more evident than that the genial heat of the 
soil, particularly in spring, must be of the highest importance to 
the rising plant. And when the leaves are fully developed, the 
ground is shaded, and any injurious influence, which in the 
summer might be expected from too great a heat, entirely pre- 
vented ; so that the temperatm’e of the surface, when bare and 
exposed to the rays of the sun, affords at least one indication of 
the degrees of its fertility ; and the thermometer may be some- 
times a useful instrument to the purchaser or improver of lands. 
There is a very simple test of the cooling or radiating powers of 
soils, the formation of dew upon them, or their relative increase 
of weight by exposure to the air, after being diied in the day or 
the night, in sunshine or in shade. The soil that radiates most 
heat acquires the greatest increase of weight ; and of course the 
radiating powers of the soil are not only connected with its 
temperature, but likewise with its relations to moisture The 
moisture in the soil influences its temperature ; and the man- 
ner in which it is distributed through, or combined with, the 
earthy materials, is of great importance in relation to the nutri- 
ment of the plant. If water is too strongly attracted by the 
earths, it will not be absorbed by the roots of the plants ; if it is 
in too great a quantity, or too loosely united to them, it tends to 
injure or destroy the fibrous parts of the roots. 
The power of soils to absorb water from air is much connected 
with fertility. When this power is great, the plant is supplied 
with moisture in dry seasons; and the effect of evaporation in 
the day is counteracted by the absorption of aqueous vapour 
from the atmosphere, by the interior parts of the soil during the 
day, and by both the exterior and interior during the night. The 
stiff clays approaching to pipe clays in their nature, which 
take up the greatest quantity of water when poured upon them 
in a fluid form, are not the soils which absorb most moisture 
from the atmosphere in dry weather. They cake, and present 
only a small surface to the air; and the vegetation on them is 
generally .burnt up almost as readily as on sands. The soils 
