332 
Agricultural Meteorology. 
wet until so late a period of the season for vegetation, we find 
then that on practically impervious soils, where this measure of 
humidity is retained within a short distance of their surface until 
the commencement of June, the power of the soil and heat of 
the sun are neutralized until that period by the attempt to free it 
from the effects of the winter's rain. Thus much of the season 
is in point of fact lost ; to say nothing of the advantage of fully 
replenishing those lower recesses of the soil by which moisture 
may be retained in reserve, at a proper distance beneath, against 
the parching droughts of the summer, in even these northern 
countries. 
Some recent observations have aided in increasing the appre- 
hensions long felt by scientific men in France and Italy with 
regard to the progressive stripping of the mountainous districts 
of their woody clothing : thinking that the earth, when deprived 
of the natural reserve of moisture which these forests preserve 
among the heights in which they grow, devastated by the un- 
checked torrents which descend from them in the season of rains 
and thaws, parched by the torrid action of the summer sun, will 
not only cease to produce, but be the means of visiting with deso- 
lation (by the rapid whirling down of the materials that compose 
them) the fertile plains below. 
Berghaus collected a series of observations on the two rivers 
the Elbe and the Oder. On the latter, from 1/78 to 1835, the 
volume of water has been gradually diminishing. On the Elbe 
the same thing has been remarked from 1728 dow-n to 1836. 
Judging from the rate of decrease, Berghaus predicted that if it 
continued as it had done since 1781, it would be necessary to 
change the form of the boats on the Elbe for others drawing less 
water. The same thing had been remarked on the Volga. At 
the beginning of the last century the boats that carried salt could 
ship 300,000 kilograms of that commodity; they can now, as we 
are told, only transport 180 000. It w-as at first supposed that 
the decrease might be due to the stripping of the mountain sides, 
and the gradual disappearance of the forests from their slopes; 
but Merian observed that every succeeding mean of ten years on 
the Rhine exhibited a decrease of volume, and yet, on its upper 
portion, the forests have not been much impaired ; and as the river 
itself is mainly supplied by the melting of glaciers, other causes 
must be sought for. Nor has the increase of the tillage, or the 
destruction of wood on the Ural mountains, been sufficient to 
account for this, when we consider the immense basin which the 
Volga drains. It may then be a question whether the quantity 
of rain has diminished. As far as can be inferred from registers 
kept in different parts of the continent, it is rather the reverse 
of this. For one hundred years, from 1689, the annual fall at 
