The Writings of Thomas Jefferson, Vol. 2 (of 9): Being His Autobiography, Correspondence, Reports, Messages, Addresses, and Other Writings, Official and PrivateJefferson, Thomas
History
The Writings of Thomas Jefferson, Vol. 2 (of 9): Being His Autobiography, Correspondence, Reports, Messages, Addresses, and Other Writings, Official and Private
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 the 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 breeze 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 freely, 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 rotatory 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 north-east, as far as the fortieth degree
of latitude. It is this current which presses our sea breeze out of its
natural south-easterly direction, to an easterly, and sometimes almost a
north-easterly one.
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