language leaves it doubtful
whether the observations made at this station are logically comparable
with those made at the other two. If the end in view were to compare
the progression of temperatures above the earth, above a tree, and in
free air, removed from all such radiative and absorptive influences, it
is plain that all three should have been equally exposed to the sun or
kept equally in shadow. As the observations were made, they give us no
notion of the relative action of earth-surface and forest-surface upon
the temperature of the contiguous atmosphere; and this, as it seems to
me, was just the _crux_ of the problem. So far, however, as they go,
they seem to justify the view that all these actions are the same in
kind, however they may differ in degree. We find the forest heating the
air during the day, and heating it more or less according as there has
been more or less sunshine for it to absorb, and we find it also
chilling it during the night; both of which are actions common to any
radiating surface, and would be produced, if with differences of amount
and time, by any other such surface raised to the mean level of the
exposed foliage.

To recapitulate:

1st. We find that single trees appear to act simply as bad conductors.

2nd. We find that woods, regarded as solids, are, on the whole, slightly
lower in temperature than the free air which they have displaced, and
that they tend slowly to adapt themselves to the various thermal changes
that take place without them.

3rd. We find forests regarded as surfaces acting like any other part of
the earth's surface, probably with more or less difference in amount and
progression, which we still lack the information necessary to estimate.

All this done, I am afraid that there can be little doubt that the more
general climatic investigations will be long and vexatious. Even in
South America, with extremely favourable conditions, the result is far
from being definite. Glancing over the table published by M. Becquerel
in his book on climates, from the observations of Humboldt, Hall,
Boussingault, and others, it becomes evident, I think, that nothing can
be founded upon the comparisons therein instituted; that all reasoning,
in the present state of our information, is premature and unreliable.
Strong statements have certainly been made; and particular cases lend
themselves to the formation of hasty judgments. "From the Bay of Cupica
to the Gulf of Guayaquil," says