144 
On the Influence of Water 
indicated higher temperatures, as no water was observed to have 
passed through the soil into the drain. 
On the 11th of June I was able to devote an entire day to the 
observation of the thermometers. The results are interesting, by 
showing the steadiness of the increments and decrements of heat 
during a cloudless day, and by denoting the period of maximum 
temperature attained by the thermometer at 7 inches, which was 
about 2 P.M. 
On the 16th, I had foreseen the probability of a thunderstorm, 
and hastened to my thermometers to observe its effect. It is well 
worthy of remark, that after the temperature of the soil at 7 
inches deep had attained its maximum, under the previous cir- 
cumstances of the day, it was subsequently raised 3^° by the de- 
scent of the rain. It is also notable, that in half an hour after 
the cessation of the storm, the sun again shining brightly, and 
evaporation being visibly great from the surface, the earth at the 
same depth had lost 3° of its highest temperature ; showing the 
rapidity with which heat is carried off by water in iis transfor- 
mation into vapour. It would have been highly interesting to 
have known, by other thermometers, the temperature of the sur- 
face when this storm fell, as the transition was almost instanta- 
neous from bright sunshine to heavy rain ; but I was unprovided 
with a sufficiency of these instruments. 
An effect of importance — which might be predicated of all 
soils properly prepared to receive heat and water, and permit 
their descent — is traceable to the preparation of the bed : viz., — 
that the transmission of accessions of heat downwards continues 
during the afternoon of the day, and throughout the night, whilst 
the superstrata (but chiefly from 7 inches upwards) are losing 
some amount of their heat by conduction upwards, and radiation 
into space. The reverse may be expected to occur during the 
cold seasons of the year, when the heat accumulated and stored 
up in the subsoil will be drawn as from a reservoir, and supply 
part of the loss then taking place more freely near the surface. 
As I have criticized the labours and experiments of others in 
this branch of science, it is right I should point out the defi- 
ciencies of my own, which are also numerous. The experiments 
related can, indeed, only be regarded as a slight contribution to 
our stock of knowledge on the subject — the investigation of which 
deserves to be commenced de novo ; to be carried on simultane- 
ously, if possible, by different observers, and with appliances of 
all the instrumental means which the existing state of science can 
furnish. The enumeration of the phenomena which demand 
attention — of the methods we possess, or still need, for ascer- 
taining their force, or measuring their amount — will, perhaps, be 
