INFLUENCE OF THE FOREST ON PRECIPITATION. 
193 
might reach. Boussingault admits that extensive clearing 
beloiv an alpine lake, even at a considerable distance, might 
affect the level of its waters. How it would produce this 
influence he does not inform us, but, as he says nothing of the 
natural subterranean drainage of surface waters, it is to be 
presumed that he refers to the supposed diminution of the 
quantity of rain from the removal of the forest, which might 
manifest itself at a point more elevated than the cause which 
occasioned it. The elevation or depression of the level of nat¬ 
ural lakes, then, cannot be relied upon as a proof, still less as a 
measure of an increase or diminution in the fall of rain within 
their geographical basins, resulting from the felling of the 
woods which covered them; though such phenomena afford 
very strong presumptive evidence that the supply of water is 
somehow augmented or lessened. The supply is, in most 
cases, derived much less from the precipitation which falls 
directly upon the surface of lakes, than from waters which 
flow above or under the ground around them, and which, in 
the latter case, often come from districts not comprised within 
what superficial geography would regard as belonging to the 
lake basins. 
It is, upon the whole, evident that the question can hardly 
be determined except by the comparison of pluviometrical 
observations made at a given station before and after the de¬ 
struction of the woods. Such observations, unhappily, are 
scarcely to be found, and the opportunity for making them is 
rapidly passing away, except so far as a converse series might 
be collected in countries—France, for example—where forest 
plantation is now going on upon a large scale. The Smith¬ 
sonian Institution at Washington is well situated for directing 
the attention of observers in the newer territory of the United 
States to this subject, and it is to be hoped that it will not fail 
to avail itself of its facilities for this purpose. 
Numerous other authorities might be cited in support of 
the proposition that forests tend, at least in certain latitudes 
and at certain seasons, to produce rain ; but though the argu¬ 
ments of the advocates of this doctrine are very plausible, not 
13 
