800 GENERAL FUNCTIONS OF FORESTS. 
a protection against the diffusion of miasmatic exhalations and 
malarious poisons; that it performs a most important fune- 
tion as a mechanical shelter from blasting winds to grounds 
and crops in the lee of it; that, as a conductor of heat, it tends to 
equalize the temperature of the earth and the air; that its dead © 
products form a mantle over the surface, which protects the 
earth from excessive heat and cold; that the evaporation from 
the leaves of living trees, while it cools the air around them, 
diffuses through the atmosphere a medium which resists the 
escape of warmth from the earth by radiation, and hence that 
its general effect is to equilibrate caloric influences and mode- 
rate extremes of temperature. 
We have seen, further, that the forest is equally useful as a re- 
gulator of terrestrial and of atmospheric humidity, preventing by 
its shade the drying up of the surface by parching winds and 
the scorching rays of the sun, intercepting a part of the pre- 
cipitation, and pouring out a vast quantity of aqueous vapor 
into the atmosphere ; that if it does not increase the amount of 
rain, it tends to equalize its distribution both in time and in 
place; that it preserves a hygrometric equilibrium in the 
superior strata of the earth’s surface; that it maintains and 
regulates the flow of springs and rivulets; that it checks the 
superficial discharge of the waters of precipitation and conse- 
quently tends to prevent the sudden rise of rivers, the violence 
of floods, the formation of destructive torrents, and the abrasion 
of the surface by the action of running water ; that it impedes 
the fall of avalanches and of rocks, and destructive slides of the 
superficial strata of mountains; that it is a safeguard against 
the breeding of locusts, and finally that it furnishes nutriment 
and shelter to many tribes of animal and of vegetable life 
which, if not necessary to man’s existence, are conducive to his 
rational enjoyment. In fine, in well-wooded regions, and in 
inhabited countries where a due proportion of soil is devoted to 
the growth of judiciously distributed forests, natural destrue- 
tive tendencies of all sorts are arrested or compensated, and 
man, bird, beast, fish, and vegetable alike find a constant uni- 
