160 
TOTAL INFLUENCE OF THE FOREST. 
probable tliat 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 149, 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 leaves. 
“ 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 
must, in the study of the climatology of a country, take into 
account the proportion between the area of the forests and the 
surface which is bared of trees and covered with herbs and 
grasses. 
“We should be inclined to believe d priori, according to 
the foregoing considerations, that the clearing of the woods, 
by raising the temperature and increasing the dryness of the 
air, ought to react on climate. There is no doubt that, if the 
vast desert of the Sahara were to become wooded in the course 
of ages, the sands would cease to be heated as much as at the 
present epoch, when the mean temperature is twenty-nine 
