194 INFLUENCE OF THE FOREST ON PRECIPITATION. 
to say convincing, their opinions are rather d priori conclusions 
from general meteorological laws, than deductions from facts 
of observation, and it is remarkable that there is so little direct 
evidence on the subject. 
On the other hand, Foissac expresses the opinion that 
forests have no influence on precipitation, beyond that of pro¬ 
moting the deposit of dew in their vicinity, and he states, as a 
fact of experience, that the planting of large vegetables, and 
especially of trees, is a very efficient means of drying morasses, 
because the plants draw from the earth a quantity of water 
larger than the average annual fall of rain.* Kloden, admit¬ 
ting that the rivers Oder and Elbe have diminished in quan¬ 
tity of water, the former since 1778, the latter since 1828, 
denies that the diminution of volume is to be ascribed to a 
decrease of precipitation in consequence of the felling of the 
forests, and states, what other physicists confirm, that, during 
the same period, meteorological records in various parts of 
Europe show rather an augmentation than a reduction of 
rain.f 
The observations of Belgrand tend to show, contrary to the 
general opinion, that less rain falls in wooded than in denuded 
districts. He compared the precipitation for the year 1852, at 
Yezelay in the valley of the Bouchat, and at Avallon in the 
valley of the Grenetiere. At the first of these places it w r as 
881 millimetres, at the latter 581 millimetres. The two cities 
are not more than eight miles apart. They are at the same 
altitude, and it is stated that the only difference in their geo¬ 
graphical conditions consists in the different proportions of 
forest and cultivated country around them, the basin of the 
Bouchat being entirely bare, while that of the Grenetiere is 
well wooded.^: Observations in the same valleys, considered 
* Meteorologies German translation by Emsmann, p. 605. 
t Handbuch der Physischen Geographies p. 658. 
X Annales des Fonts et Chaussees , 1854, 1st semestre, pp. 21 et seqq. 
See the comments of Valles on these observations, in his fitudes sur les 
InondationSs pp. 441 et seqq. 
