on the Temperature of Soils. 
143 
I have now to invite your attention to a few deductions from 
the tabulated results which we may be authorised to draw, not- 
withstanding the restriction of the observations to the short space 
of twelve days. 
Firstly. The constant temperature of the natural bog, from 
12 inches to 30 feet deep, was 46°; and the thermometer planted 
in the same substance at 7 inches deep, constantly indicated 47"' 
during the term of the experiments. 
Now, the thermometer at 31 inches deep in the worked bed 
exhibited a maximum heat of 48^°, having gradually gained 2i° ; 
and it was, apparently, still rising. The thermometer at 7 inches 
below the surface reached 66°, after a thunderstorm, showing a 
maximum increase of 19°, and, on a mean of the thirty-five 
observations, of 10° over its fellow, at the same depth, in the 
natural bog. 
We have here satisfactory evidence that the accession of heat 
was solely derived from meteorological agency, i. e. from action 
on the surface and not from the substratum, as the latter pos- 
sessed, invariably, a lower temperature, which must have tended 
to diminish, rather than to increase, the heat finally acquired by 
the worked bed. And, we may safely deduce from these facts, 
that the origin of the increased tempeiature is attributable to the 
change induced on the mechanical condition of the soil by drain- 
age and pulverization, as no other changes were effected in it than 
those of comminution of its texture and the withdrawal of free 
water. 
Secondly. The inference may be permitted, even from these 
few experiments, that, in the month of June, rain-water carries 
down heat, and raises the temperature of the subsoil ; whilst the 
loss of heat by the strata nearer the surface is quickly restored 
by the sun's rays. By an inspection of the Table no doubt 
will be left on the mind as to the truth of these inferences. It 
appears that, at 7 inches deep, the temperature of the soil was 
subject to considerable diurnal increase and decrease, as well as 
from day to day, according to the state of the weather; that these 
variations became of less amount at lower depths ; and that, at 
31 inches, increase alone, for the time, was felt. Heat is con- 
ducted downwards so slowly by all bodies, and by moist sub- 
stances particularly, that rain-water would appear, when allowed 
to permeate the bed, to be the most active agent in the propaga- 
tion of heat to the subsoil. Accordingly, we find the lower ther- 
mometers to indicate accession of heat more quickly after rain 
than in dry weather ; and had a rain of longer continuance fallen, 
instead of short showers, it is probable that the lower thermo- 
meters would have been affected much more rapidly, and have 
