ed_ by the roots of the
trees, would become gradually covered with a vegetable earth, and be
thus changed from dry to wet? Again, the complication and conflict of
effects arises, not only from the soil, vegetation, and geographical
position of the place of the experiment itself, but from the
distribution of similar or different conditions in its immediate
neighbourhood, and probably to great distances on every side. A forest,
for example, as we know from Herr Rivoli's comparison, would exercise a
perfectly different influence in a cold country subject to warm winds,
and in a warm country subject to cold winds; so that our question might
meet with different solutions even on the east and west coasts of Great
Britain.

The consideration of such a complexity points more and more to the
plantation of Malta as an occasion of special importance; its insular
position and the unity of its geological structure both tend to simplify
the question. There are certain points about the existing climate,
moreover, which seem specially calculated to throw the influence of
woods into a strong relief. Thus, during four summer months, there is
practically no rainfall. Thus, again, the northerly winds when stormy,
and especially in winter, tend to depress the temperature very suddenly;
and thus, too, the southerly and south-westerly winds, which raise the
temperature during their prevalence to from eighty-eight to ninety-eight
degrees, seldom last longer than a few hours; insomuch that "their
disagreeable heat and dryness may be escaped by carefully closing the
windows and doors of apartments at their onset."[58] Such sudden and
short variations seem just what is wanted to accentuate the differences
in question. Accordingly, the opportunity seems one not lightly to be
lost, and the British Association or this Society itself might take the
matter up and establish a series of observations, to be continued during
the next few years. Such a combination of favourable circumstances may
not occur again for years; and when the whole subject is at a standstill
for want of facts, the present occasion ought not to go past unimproved.

Such observations might include the following:--

The observation of maximum and minimum thermometers in three different
classes of situation--_videlicet_, in the areas selected for plantation
themselves, at places in the immediate neighbourhood of those areas
where the external influence might be expected to reach its