TREES ATTRACTORS OF HUMIDITY. 49 
ascending a hill in the month of March. The weather 
had previously been very fine and dry, and the road in 
a dusty state ; but a fog coming on, an ash tree hanging 
over the road was dripping with water so copiously, 
that the road beneath w T as in a puddle, when the other 
parts continued dry, and manifested no appearance of 
humidity. That leaves imbibe moisture by one set of 
vessels and discharge them by another, is well-known ; 
but these imbibings are never discharged in falling 
drops : the real mystery was, the fog in its progress w r as 
impeded by the boughs of the tree, and gradually col- 
lected on the exposed side of them, until it became 
drops of water, whereas the surrounding country had 
only a mist flying over it. Thus in fact the tree was 
no attractor, but a condenser ; the gate of a field will 
in the same manner run dow T n with water on the one 
side, and be dry on the other ; as will a stick, or a post, 
from the same cause. It is upon this principle that 
currents of air will be found under trees in summer, 
when little is perceived in open places ; and the under 
leaves and sprays will be curled and scorched at times, 
when the parts above are uninjured. The air in its 
passage being stopped and condensed against the foliage 
of the tree, it accordingly descends along its surface 
or front, and escapes at the bottom, where there are no 
branches or leaves to interrupt its progress. In winter 
there is little to impede the breeze in its course, and it 
passes through ; consequently at this season the air un- 
der a tree is scarcely more sensibly felt than in the ad- 
joining field. 
It may be observed, that in the spring of the year 
the herbage under trees is generally more vivid and 
luxuriant, than that which is beyond the spread of the 
branches : this may be occasioned, in some instances, 
by cattle having harbored there, and the ground becom- 
ing in consequence more manured ; but it will be found 
likewise manifestly verdant and flourishing where no 
such accessory could have enriched it, and is, I appre- 
hend, in general, chiefly owing to the effects of the 
driving fogs and mists, which cause a frequent drip be- 
neath the tree, not experienced in other places, and 
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