TOTAL INFLUENCE OF THE FOREST ON TEMPERATURE. 179 
forests in Northern America exert a refrigerating influence 
equally powerful. But the conditions of the soil are so differ- 
ent in the two regions compared, that I think we cannot, 
with entire confidence, reason from the one to the other, and 
it is much to be desired that observations be made on the 
summer and winter temperature of both the air and the ground 
in the depths of the North American forests, before it is too 
late. 
Recent inquiries have introduced a new element into the 
problem of the influence of the forest on temperature, or 
rather into the question of the thermometrical effects of its 
destruction. I refer to the composition of the soil in respect 
to its hygroscopicity or aptitude to absorb humidity, whether 
in a liquid or a gaseous form, and to the conducting power of 
the particles of which it is composed. * 
* Composition, texture, and color of soil are important elements to be con- 
sidered in estimating the effects of the removal of the forest upon its thermo- 
scopic action. ‘‘Hxperience has proved,” says Becquerel, ‘‘ that when the soil 
is hared, it becomes more or less heated [by the rays of the sun] according to 
the nature and the color of the particles which compose it, and according to 
its humidity, and that, in the refrigeration resulting from radiation, we 
must take into the account the conducting power of those particles also. 
Other things being equal, siliceous and calcareous sands, compared in equal 
volumes with different argillaceous earths, with calcareous powder or dust, 
with humus, with arable and with garden earth, are the soils which least 
conduct heat. It is for this reason that sandy ground, in summer, maintains 
a high temperature even during the night. We may hence conclude that 
when a sandy soil is stripped of wood, the local temperature will be raised. 
After the sands follow successively argillaceous, arable, and garden ground, 
then humus, which occupies the lowest rank. 
‘“ The retentive power of humus is but half as great as that of calcareous 
sand. We will add that the power of retaining heat is proportional to the 
density. It has also a relation to the magnitude of the particles. It is for 
this reason that ground covered with siliceous pebbles cools more slowly than 
siliceous sand, and that pebbly soils are best suited to the cultivation of the 
vine, because they advance the ripening of the grape more rapidly than chalky 
and clayey earths, which cool quickly. Hence we see that in examining the 
calorific effects of clearing forests, it is important to take into account the 
properties of the soil laid bare.”—BECQUEREL, Des Climats et des Sols boisés, 
p. 187. 
