Among the causes which tend to 'lower' the mean annual temperature I include
the following: elevation above the level of the sea, when not forming part
of an extended plain; the
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vicinity of an eastern coast in high and middle latitudes; the compact
configuration of a continent having no littoral curvatures or bays; the
extension of land toward the poles into the region of perpetual ice, without
the intervention of a sea remaining open in the winter; a geographical
position, in which the equatorial and tropical regions are occupied by the
sea, and consequently, the absence, under the same meridian, of a
continental tropical land having a strong capacity for the absorption and
radiation of heat; mountain chains, whose mural form and direction impede
the access of warm winds, the vicinity of isolated peaks, occasioning the
descent of cold currents of air down their declivities; extensive woods,
which hinder the isolation of the soil by the vital activity of their
foliage, which produces great evaporation, owing to the extension of these
organs, and increases the surface that is cooled by radiation, acting
consequently in a three-fold manner, by shade, evaporation, and radiation;
the frequency of swamps or marshes, which in the north form a kind of
subterranean glacier in the plains, lasting till the middle of the summer; a
cloudy summer sky, which weakens the action of the solar rays; and, finally,
a very clear winter sky, favoring the radiation of heat.
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