INFLUENCE OF FOREST ON HUMIDITY. 181 
atmosphere by exhalation ;* while in heavier rains, the large 
drops which fall upon the leaves and branches are broken into 
smaller ones, and consequently strike the ground with less 
mechanical force, or are perhaps even dispersed into vapor 
without reaching it.t 
* Mangotti had observed and described, in his usual picturesque way, the 
retention of rain-water by the foliage and bark of trees, but I do not know 
that any attempts were made to measure the quantity thus intercepted before 
the experiments of Becquerel, communicated to the Academy of Sciences in 
1866. These experiments embraced three series of observations continued 
respectively for periods of a year, a month, and two days. According to 
Becquerel’s measurements, the quantity falling on bare and on wooded soil re- 
spectively was as 1 to 0.67; 1 to 0.5; and 1 to 0.6, or, in other words, he 
found that only from five-tenths to sixty-seven hundredths of the precipitation 
reached the ground. —Comptes Rendus de? Académie des Sciences, 1866. 
It seemed, indeed, improbable that in rain-storms which last not hours but 
whole days in succession, so large a proportion of the downfall should continue 
to be intercepted by forest vegetation after the leaves, the bark, and the whole 
framework of the trees were thoroughly wet, but the conclusions of this 
eminent physicist appear to have been generally accepted until the very careful 
experiments of Mathieu at the Forest-School of Nancy were made known. The 
observations of Mathieu were made in a plantation of deciduous trees forty- 
two years old, and were continued through the entire years 1866, 1867, and 
1868. The result was that the precipitation in the wood was to that in an 
open glade of several acres near the forest station as 943 to 1,000, and the 
proportion in each of the three years was nearly identical. According to 
Mathieu, then, only 57 thousandths or 5.7 per cent. of the precipitation is in- 
tercepted by trees.—SuRELL, Etude sur les Torrents, 2d ed., ii., p. 98. 
By order of the Direction of the Forests of the Canton of Berne, a series of 
experiments on this subject was commenced at the beginning of the year 
1869. During the first seven months of the year (the reports for which alone 
I have seen), including, of course, the season when the foliage is most 
abundant, as well as that when it is thinnest, the pluviometers in the woods 
received only fifteen per cent. less than those in the open grounds in the 
vicinity.—RISLER, in Revue des Haux et Foréts, of 10th January, 1870. 
+ We are not, indeed, to suppose that the condensation of vapor and the 
evaporation of water are going on in the same stratum of air at the same time, 
or, in other words, that vapor is condensed into rain-drops, and rain-drops 
evaporated, under the same conditions; but rain formed in one stratum may 
fall through another, where vapor would not be condensed. Two saturated 
strata of different temperatures may be brought into contact in the hicher 
regions, and discharge large rain-drops, which, if not divided by some obstruc- 
