CONFLICTING INFLUENCES. 
177 
water that falls upon the surface, and also by spreading over 
the earth a spongy mantle which sucks up and retains the 
humidity it receives from the atmosphere, while, at the same 
time, this covering acts in the contrary direction by accumu¬ 
lating, in a reservoir, not wholly inaccessible to vaporizing 
influences, the water of precipitation which might otherwise 
suddenly sink deep into the bowels of the earth, or flow by 
superficial channels to other climatic regions. We now see 
that, as a living organism, it tends, on the one hand, to dimin¬ 
ish the humidity of the air by absorbing moisture from it, and, 
on the other, to increase that humidity by pouring out into the 
atmosphere, in a vaporous form, the water it draws up through 
its roots. This last operation, at the same time, lowers the 
temperature of the air in contact with or proximity to the 
wood, by the same law as in other cases of the conversion of 
water into vapor. 
As I have repeatedly said, we cannot measure the value of 
any one of these elements of climatic disturbance, raising or 
lowering of temperature, increase or diminution of humidity, 
nor can we say that in any one season, any one year, or any 
one fixed cycle, however long or short, they balance and com¬ 
pensate each other. They are sometimes, but certainly not 
always, contemporaneous in their action, whether their tend¬ 
ency is in the same or in opposite directions, and, therefore, 
their influence is sometimes cumulative, sometimes conflicting ; 
but, upon the whole, their general effect seems to be to miti¬ 
gate extremes of atmospheric heat and cold, moisture and 
drought. They serve as equalizers of temperature and hu¬ 
midity, and it is highly probable that, in analogy with most 
other works and workings of nature, they, at certain or uncer¬ 
tain periods, restore the equilibrium which, whether as lifeless 
masses or as living organisms, they may have temporarily 
disturbed. 
it was wished to punish the brigandage of the unsubdued tribes, it was im¬ 
possible to set their grain fields on fire until a late hour of the day; for 
the plants were so wet with the night dew that it was necessary to wait 
until the sun had dried them .”—Etudes et Lectures , ii, p. 212. 
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