MOVEMENT OF HUMID AIR. 
183 
source from which it receives it. The air is constantly in 
motion, 
-howling tempests scour amain 
From sea to land, from land to sea ; * 
and, therefore, it is always probable that the evaporation 
drawn up by the atmosphere from a given river, or sea, or 
forest, or meadow, will be discharged by precipitation, not at 
or near the point where it rose, but at a distance of miles, 
leagues, or even degrees. The currents of the upper air are 
invisible, and they leave behind them no landmark to record 
their track. We know not whence they come, or whither 
they go. We have a certain rapidly increasing acquaintance 
with the laws of general atmospheric motion, but of the origin 
and limits, the beginning and end of that motion, as it mani¬ 
fests itself at any particular time and place, we know nothing. 
We cannot say where or when the vapor, exhaled to-day from 
the lake on which we float, will be condensed and fall; 
whether it will waste itself on a barren desert, refresh upland 
pastures, descend in snow on Alpine heights, or contribute to 
swell a distant torrent which shall lay waste square miles of 
fertile corn land; nor do we know whether the rain which 
feeds our brooklets is due to the transpiration from a neigh¬ 
boring forest, or to the evaporation from a far-off sea. If, 
therefore, it were proved that the annual quantity of rain and 
dew is now as great on the plains of Castile, for example, as it 
was when they were covered with the native forest, it would 
by no means follow that those woods did not augment the 
amount of precipitation elsewhere. 
But I return to the question. Beginning with the latest 
authorities, I cite a passage from Clave, f After arguing that 
we cannot reason from the climatic effects of the forest in trop¬ 
ical and sub-tropical countries as to its influence in temperate 
* Und Stiirme brausen um die Wette 
Yom Meer aufs Land, vom Land aufs Meer. 
Goethe, Faust, Song of the Archangels. 
f Etudes sur Vtconomie Forestiere , pp. 45, 46. 
