INFLUENCE OF THE FOREST ON TEMPERATURE. 143 
land springs sensibly affect the chemistry of the sea. I may, 
then, properly dismiss the chemical, as I have done the elec¬ 
trical influences of .the forest, and treat them both alike, if not 
as unimportant agencies, at least as quantities of unknown 
value in our meteorological equation.* Our inquiries upon 
this branch of the subject will accordingly be limited to the 
tliermometrical and liygrometrical influences of the woods. 
Influence of the Forest , considered as Inorganic Matter , 
on Temperature. 
The evaporation of fluids, and the condensation and expan¬ 
sion of vapors and gases, are attended with changes of temper¬ 
ature ; and the quantity of moisture which the air is capable 
of containing, and, of course, the evaporation, rise and fall 
with the thermometer. The hygroscopical and the tliermo- 
scopical conditions of the atmosphere are, therefore, insep¬ 
arably connected as reciprocally dependent quantities, and 
neither can be fully discussed without taking notice of the 
other. But the forest, regarded purely as inorganic matter, 
and without reference to its living processes of absorption and 
exhalation of water and gases, has, as an absorbent, a radiator 
and a conductor of heat, and as a mere covering of the ground, 
an influence on the temperature of the air and the earth, which 
may be considered by itself. 
* Schacht ascribes to the forest a specific, if not a measurable, influence 
upon the constitution of the atmosphere. “ Plants imbibe from the air 
carbcnic acid and other gaseous or volatile products exhaled by animals or 
developed by the natural phenomena of decomposition. On the other 
hand, the vegetable pours into the atmosphere oxygen, which is taken up 
by animals and appropriated by them. The tree, by means of its leaves 
and its young herbaceous twigs, presents a considerable surface for absorp¬ 
tion and evaporation; it abstracts the carbon of carbonic acid, and solidifies 
it in wood, fecula, and a multitude of other compounds. The result is that 
a forest withdraws from the air, by its great absorbent surface, much more 
gas than meadows or cultivated fields, and exhales proportionally a con¬ 
siderably greater quantity of oxygen. The influence of the forests on the 
chemical composition of the atmosphere is, in a word, of the highest im¬ 
portance .”—Les ArbreSy p. 111. 
