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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Sometimes Several Of These Causes Concur To One And The
Same Effect, And Sometimes They Produce Several Contrary Effects.
Winds
That are light, but which, like the trade-winds, are
continually acting on the whole of a zone, cause a
Real movement of
transition, which we do not observe in the heaviest tempests,
because these last are circumscribed within a small space. When, in
a great mass of water, the particles at the surface acquire a
different specific gravity, a superficial current is formed, which
takes its direction towards the point where the water is coldest,
or where it is most saturated with muriate of soda, sulphate of
lime, and muriate or sulphate of magnesia. In the seas of the
tropics we find, that at great depths the thermometer marks 7 or 8
centesimal degrees. Such is the result of the numerous experiments
of commodore Ellis and of M. Peron. The temperature of the air in
those latitudes being never below 19 or 20 degrees, it is not at
the surface that the waters can have acquired a degree of cold so
near the point of congelation, and of the maximum of the density of
water. The existence of this cold stratum in the low latitudes is
an evident proof of the existence of an under-current, which runs
from the poles towards the equator: it also proves that the saline
substances which alter the specific gravity of the water, are
distributed in the ocean, so as not to annihilate the effect
produced by the differences of temperature.
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