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: Vereins for 1873 
1876.] Are We Drying Up? 519 
forty-two years ; but the observations for shorter periods of from 
fifty to seventy years, which in the case of the other streams are 
all that are available, seem to leave no doubt as to the character 
of the result. : 
The probable causes of this diminution in the quantity of water 
in the Middle European streams are discussed at some length by 
Mr. Wex,! as also by a committee of the Vienna Academy of 
Sciences, appointed to report on his communication, and among 
whom were several eminent meteorologists. The general im- 
pression, both of Mr. Wex and the committee, seems to be that 
the cutting down of the forests is the essential cause of the desic- 
cation. But the number of facts which can be given in support 
of this hypothesis is quite small. It is, as Mr. Marsh has stated, 
not so much facts as the general opinion on which reliance is 
placed in citing the destruction of the forests as the probable 
principal cause of the difficulty. It is easy to see that stripping 
the woods from the surface increases the rapidity of the evapora- 
tion, and that in consequence of this less water must flow in the 
streams unless the deficiency is made up by a larger precipitation. 
It is extremely difficult to prove anything in this connection in 
a region where so many small patches of forest are mixed up 
with the cleared land, as is the case in Germany. But it is fair 
to presume that the moisture taken up in one part of a great 
river basin must be let fall again in the form of rain somewhere 
within the limits of the same basin. Hence we should have no 
difficulty in understanding that stripping the surface of its trees 
Would cause increased and irregular precipitation, which would 
have injurious and even disastrous effects in mountain regions, 
where the soil was thus laid bare to be washed away by torrential 
flows of the streams following on sudden and heavy falls of rain. 
That this is really the case is well known from experience in the 
Swiss and French Alps, and elsewhere. But that a positive 
diminution in the average quantity of water carried down in the 
streams would necessarily ensue on removing a portion of the 
forests in any region, we do not consider to have been proved as 
yet. The commission, in reporting on Mr. Wex’s paper, are 
this subject, 
This paper was published in the Zeitschrift des Ost. Ingenieur and Architekten 
