165 
A brown fertile soil and a cold barren clay 
were each artificially heated to 88°, having been 
previously dried : they were then exposed in a 
temperature of 57° ; in half an hour the dark soil 
was found to have lost 9° of heat ; the clay had 
lost only 6°. An equal portion of the clay con- 
taining moisture, after being heated to 88°, was 
exposed in a temperature of 55° ; in less than a 
quarter of an hour, it was found to have gained 
the temperature of the room. The soils in all 
these experiments were placed in small tin plate 
trays two inches square, and half an inch in depth, 
and the temperature ascertained by a delicate 
thermometer. 
Nothing can be 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 prevented : so that the tem- 
perature 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 sometimes a useful instrument to the pur- 
chaser 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 dried, in the day 
or the night, in sunshine or in shade. The soil 
that radiates most heat acquires the greatest in- 
crease of weight, and of course the radiating 
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