156 
SPECIFIC TEMPERATURE OF TREES. 
heat, and increases the radiating and reflecting area in the 
same proportion. It is impossible to measure the relative 
value of these two elements—increase of absorbing and in¬ 
crease of emitting surface—as tliermometrical influences, 
because they exert themselves under infinitely varied condi¬ 
tions ; and it is equally impossible to make a quantitative esti¬ 
mate of any partial, still more of the total effect of the forest, 
considered as dead matter, on the temperature of the atmos¬ 
phere, and of the portion of the earth’s surface acted on by it. 
But it seems probable that its greatest influence in this respect 
is due to its character of a screen, or mechanical obstacle to 
the transmission of heat between the earth and the air; and 
this is equally true of the standing tree and of the dead 
foliage which it deposits in successive layers at its foot. 
The complicated action of trees and their products, as dead 
absorbents, radiators, reflectors, and conductors of heat, and as 
intercepters of its transmission, is so intimately connected with 
their effects upon the humidity of the air and the earth, and 
with all their living processes, that it is difficult to separate 
the former from the latter class of influences; but upon the 
whole, the forest must thus far be regarded as tending to miti¬ 
gate extremes, and, therefore, as an equalizer of temperature. 
TREES AS ORGANISMS. 
Specific Ileat. 
Trees, considered as organisms, produce in themselves, or 
in the air, a certain amount of heat, by absorbing and con¬ 
densing atmospheric vapor, and they exert an opposite influ¬ 
ence by absorbing water and exhaling it in the form of vapor ; 
but there is still another mode by which their living processes 
may warm the air around them, independently of the ther¬ 
mometric effects of condensation and evaporation. The vital 
heat of a dozen persons raises the temperature of a room. If 
trees possess a specific temperature of their own, an organic 
power of generating heat, like that with which the warm¬ 
blooded animals are gifted, though by a different process, a 
