TOTAL INFLUENCE OF THE FOREST ON TEMPERATURE. 177 
though sensible, is less than it would be if water in the gaseous 
state were as impervious to heat given out by the sun as to that 
emitted by terrestrial objects. 
Total Influence of the Forest on Temperature. 
It has not yet been found practicable to measure, sum up, 
and equate the total influence of the forest, its processes and 
its products, dead and living, upon temperature, and investiga- 
tors differ much in their conclusions on this subject. It seems 
probable that in every particular case the result is, if not deter- 
mined, at least so much modified by local conditions which are 
infinitely varied, that no general formula is applicable to the 
question. 
In the report to which I referred on page 163, Gay-Lussac 
says: “In my opinion we have not yet any positive proof that 
the forest has, in itself, any real influence on the climate of a 
great country, or of a particular locality. By closely examin- 
ing the effects of clearing off the woods, we should perhaps 
find that, far from being an evil, it is an advantage; but these 
questions are so complicated when they are examined in a 
climatological point of view, that the solution of them is very 
difficult, not to say impossible.” 
Becquerel, on the other hand, considers it certain that in 
tropical climates the destruction of the forests is accompanied 
with an elevation of the mean temperature, and he thinks it 
highly probable that it has the same effect in the temperate 
zones. ‘The following is the substance of his remarks on this 
subject: 
“ Forests act as frigorific causes in three ways : 
“1. They shelter the ground against solar irradiation and 
maintain a greater humidity. 
“2. They produce a cutaneous transpiration by the leayes. 
“3, They multiply, by the expansion of their branches, the 
surfaces which are cooled by radiation. 
“These three causes acting with greater or less force, we 
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