128 
On the Influence of Water 
" 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 containing moisture, after being heated to 88°, was exposed in a 
temperature of 55°. In less than a quarter of an hour it was fouud to 
have gained the temperature of the room.* The soils, in all these expe- 
riments, were placed in small tin-plate trays, two inches square, and half 
an inch in depth ; and the temperature ascertained by a delicate ther- 
mometer. 
" 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 temperature of the sur- 
face, 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 purchaser or improver of lands, 
&c." — Agricultural Chemistry. 
The chapter containing these experiments and opinions of Sir 
Humphry Davy will supply many other useful hints for the 
guidance of the experimentalist in his inquiry into the causes of 
the varying temperature of soils. I will select only one other 
short extract from the well known lectures of this eminent man, 
as it records information touching the affinity of some particular 
soils to moisture, the fertility and rent-value of which he quotes 
as being pretty nearly in the ratio of their hygrometric powers.f 
The soils were first dried at a temperature of 212°, and then 
exposed to air saturated w ith moisture at G2° : — 
• A remarkable confirmation of what has been before stated of the chill- 
ing effect of evaporation. — J. P. 
•j- Schiiblerhas criticised this opinion of Davy's (Journal, vol. i. p. 197). He 
observes, "The assumption of Davy that this capacity ol'absorption possessed 
by a soil was to be received as a conclusive proof of its fertihty, is liable, 
therefore, to many exceptions; and, if applied without modification, might 
easily mislead." Excepting in one nistance, Schiibler's experiments appear 
to confirm, very closely, Davy"s observation, — " I have compared tlie ab- 
sorbent powers of many soils with respect to atmospheric moisture, and I 
have always found it greatest in the most fertile soils: so that it affords one 
method of judging of the ])roductiveness of land.'' I have not noticed that 
Davy has anywhere spoken of it as a conclusive method. Dav}-, Leslie, and 
Schiibler all agree on the fact of garden mould being the most absorbent 
of all soils. Davy specially excepted the case of a pure clay : and Schiibler 
also instances that earth, as an exception to the general law deduced by 
both philosophers, that the fertility of soils is pretty much in the ratio of 
their powers of absorbing and retaining moisture. Schiibler has made a 
step in advance of Davy, by his elaborate experiments tending to establish 
the fact that moisture in earth is a preparation for its absorption of oxygen, 
and con-secpicntly that the attraction of soils for moisture is a property of 
lirst-rate importance to agriculture. 
