Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 3 - By Alexander Von Humboldt And Aime Bonpland.
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However Unequal
May Be The Quantity Of Rain That Falls During Several Successive
Years, In Such Or Such A Valley, The Swellings Of Rivers That Have A
Very Long Course Are Little Affected By These Local Variations.
The
swellings represent the average of the humidity that reigns in the
whole basin; they follow annually the same
Progression because their
commencement and their duration depend also on the mean of the
periods, apparently extremely variable, of the beginning and end of
the rains in the different latitudes through which the principal trunk
and its various tributary streams flow. Hence it follows that the
periodical oscillations of rivers are, like the equality of
temperature of caverns and springs, a sensible indication of the
regular distribution of humidity and heat, which takes place from year
to year on a considerable extent of land. They strike the imagination
of the vulgar; as order everywhere astonishes, when we cannot easily
ascend to first causes. Rivers that belong entirely to the torrid zone
display in their periodical movements that wonderful regularity which
is peculiar to a region where the same wind brings almost always
strata of air of the same temperature; and where the change of the sun
in its declination causes every year at the same period a rupture of
equilibrium in the electric intensity, in the cessation of the
breezes, and the commencement of the season of rains. The Orinoco, the
Rio Magdalena, and the Congo or Zaire are the only great rivers of the
equinoctial region of the globe, which, rising near the equator, have
their mouths in a much higher latitude, though still within the
tropics.
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