182 
INUNDATIONS. 
that it is safer to regard it as a historical problem, or at least 
as what lawyers call a mixed question of law and fact, than to 
attempt to decide it upon d priori grounds. Unfortunately the 
evidence is conflicting in tendency, and sometimes equivocal in 
interpretation, but I believe that a majority of the foresters 
and physicists who have studied the question are of opinion 
that in many, if not in all cases, the destruction of the woods 
has been followed by a diminution in the annual quantity of 
rain and dew. Indeed, it has long been a popularly settled 
belief that vegetation and the condensation and fall of atmos* 
pheric moisture are reciprocally necessary to each other, and 
even the poets sing of 
Afric’s barren sand, 
Where nought can grow, because it raineth not, 
And where no rain can fall to bless the land, 
Because nought grows there.* 
Before stating the evidence on the general question and 
citing the judgments of the learned upon it, however, it is w T ell 
to remark that the comparative variety or frequency of inun¬ 
dations in earlier and later centuries is not necessarily, in most 
cases not probably, entitled to any weight whatever, as a proof 
that more or less rain fell formerly than now; because the 
accumulation of water in the channel of a river depends far 
less upon the quantity of precipitation in its valley, than upon 
the rapidity with which it is conducted, on or under the sur¬ 
face of the ground, to the central artery that drains the basin. 
But this point will be more fully discussed in a subsequent 
chapter. 
There is another important observation which may prop¬ 
erly be introduced here. It is not universally, or even gener¬ 
ally true, that the atmosphere returns its humidity to the local 
* -Bet golde Strog i Afrika, 
Ber Intet voxe kan, da ei det regner, 
Og, omvendt, ingen Regn kan falde, da 
Ber Intet voxer. 
Paludan-Mullek, Admn Homo , ii, 408. 
