Memoir, Correspondence, and Miscellanies, From the Papers of Thomas Jefferson, Volume 2Jefferson, Thomas
History
Memoir, Correspondence, and Miscellanies, From the Papers of Thomas Jefferson, Volume 2
Jefferson, Thomas
United States -- Politics and government -- 1775-1783; United States -- Politics and government -- 1783-1865
To apply these observations to the phenomena under consideration. The
first settlements of Virginia were made along the sea coast, bearing
from the south, towards the north, a little eastwardly. These
settlements formed a zone, in which, though every point was not cleared
of its forest, yet a good proportion was cleared and cultivated. The
cultivated earth, as the sun advances above the horizon in the morning,
acquires from it an intense heat, which is retained and increased
through the warm parts of the day. The air resting on it becomes warm
in proportion, and rises. On one side is a country still covered with
forest: on the other is the ocean. The colder air from both of these,
then rushes towards the heated zone, to supply the place left vacant
there by the ascent of its warm air. The breeze from the west is light
and feeble; because it traverses a country covered with mountains and
forests, which retard its current. That from the east is strong; as
passing over the ocean, wherein there is no obstacle to its motion.
It is probable, therefore, that this easterly breeze forces itself far
into, or perhaps beyond, the zone which produces it. This zone is,
by the increase of population, continually widening into the interior
country. The line of equilibrium between the easterly and westerly
breezes is, therefore, progressive.
Did no foreign causes intervene, the sea breezes would be a little
southwardly of the east, that direction being perpendicular to our
coast. But within the tropics, there are winds which blow continually
and strongly from the east. This current affects the course of the air,
even without the tropics. The same cause, too, which produces a strong
motion of the air, from east to west, between the tropics, to wit, the
sun, exercises its influence without those limits, but more feebly, in
proportion as the surface of the globe is there more obliquely presented
to its rays. This effect, though not great, is not to be neglected when
the sun is in or near our summer solstice, which is the season of these
easterly breezes. The northern air, too, flowing towards the equatorial
parts, to supply the vacuum made there by the ascent of their heated
air, has only the small rotary motion of the polar latitudes from which
it comes. Nor does it suddenly acquire the swifter rotation of the parts
into which it enters. This gives it the effect of a motion opposed to
that of the earth, that is to say, of an easterly one. And all these
causes together are known to produce currents of air in the Atlantic,
varying from east to northeast, as far as the fortieth degree of
latitude. It is this current which presses our sea breeze out of its
natural southeasterly direction, to an easterly, and sometimes almost a
northeasterly one.
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