Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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Without Derogating From The
Respect I Entertain For The Opinion Of That Celebrated Navigator, I
May Be Permitted To Consider This Important Object In A Far More
General Point Of View.
When we cast our eyes over the Atlantic, or that deep valley which
divides the western coasts of Europe and Africa from the eastern
coasts of the new world, we distinguish a contrary direction in the
motion of the waters.
Within the tropics, especially from the coast
of Senegal to the Caribbean Sea, the general current, that which
was earliest known to mariners, flows constantly from east to west.
This is called the equinoctial current. Its mean rapidity,
corresponding to different latitudes, is nearly the same in the
Atlantic and in the Pacific, and may be estimated at nine or ten
miles in twenty-four hours, consequently from 0.59 to 0.65 of a
foot every second! In those latitudes the waters run towards the
west with a velocity equal to a fourth of the rapidity of the
greater part of the larger rivers of Europe. The movement of the
ocean in a direction contrary to that of the rotation of the globe,
is probably connected with this last phenomenon only as far as the
rotation converts into trade winds* (* The limits of the trade
winds were, for the first time, determined by Dampier in 1666.) the
polar winds, which, in the low regions of the atmosphere bring back
the cold air of the high latitudes toward the equator. To the
general impulsion which these trade-winds give the surface of the
sea, we must attribute the equinoctial current, the force and
rapidity of which are not sensibly modified by the local variations
of the atmosphere.
In the channel which the Atlantic has dug between Guiana and
Guinea, on the meridian of 20 or 23 degrees, and from the 8th or
9th to the 2nd or 3rd degrees of northern latitude, where the
trade-winds are often interrupted by winds blowing from the south
and south-south-west, the equinoctial current is more inconstant in
its direction. Towards the coasts of Africa, vessels are drawn in
the direction of south-east; whilst towards the Bay of All Saints
and Cape St. Augustin, the coasts of which are dreaded by
navigators sailing towards the mouth of the Plata, the general
motion of the waters is masked by a particular current (the effects
of which extend from Cape St. Roche to the Isle of Trinidad)
running north-west with a mean velocity of a foot and a half every
second.
The equinoctial current is felt, though feebly, even beyond the
tropic of Cancer, in the 26th and 28th degrees of latitude. In the
vast basin of the Atlantic, at six or seven hundred leagues from
the coasts of Africa, vessels from Europe bound to the West Indies,
find their sailing accelerated before they reach the torrid zone.
More to the north, in 28 and 35 degrees, between the parallels of
Teneriffe and Ceuta, in 46 and 48 degrees of longitude, no constant
motion is observed:
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