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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As No River Of America Can Cross The Equator From
South To North, On Account Of The General Configuration Of The Ground,
The Risings Of The Orinoco Have An Influence On The Amazon; But Those
Of The Amazon Do Not Alter The Progress Of The Oscillations Of The
Orinoco.
It results from these data, that in the two basins of the
Amazon and the Orinoco, the concave and
Convex summits of the curve of
progressive increase and decrease correspond very regularly with each
other, since they exhibit the difference of six months, which results
from the situation of the rivers in opposite hemispheres. The
commencement of the risings only is less tardy in the Orinoco. This
river increases sensibly as soon as the sun has crossed the equator;
in the Amazon, on the contrary, the risings do not commence till two
months after the equinox. It is known that in the forests north of the
line the rains are earlier than in the less woody plains of the
southern torrid zone. To this local cause is joined another, which
acts perhaps equally on the tardy swellings of the Nile. The Amazon
receives a great part of its waters from the Cordillera of the Andes,
where the seasons, as everywhere among mountains, follow a peculiar
type, most frequently opposite to that of the low regions.
The law of the increase and decrease of the Orinoco is more difficult
to determine with respect to space, or to the magnitude of the
oscillations, than with regard to time, or the period of the maxima
and minima. Having been able to measure but imperfectly the risings of
the river, I report, not without hesitation, estimates that differ
much from each other.* (* Tuckey, Maritime Geogr. volume 4 page 309.
Hippisley, Expedition to the Orinoco page 38. Gumilla volume 1 pages
56 to 59. Depons volume 3 page 301. The greatest height of the rise of
the Mississippi is, at Natchez, fifty-five English feet. This river
(the largest perhaps of the whole temperate zone) is at its maximum
from February to May; at its minimum in August and September.
Ellicott, Journal of an Expedition to the Ohio.) Foreign pilots admit
ninety feet for the ordinary rise in the Lower Orinoco. M. Depons, who
has in general collected very accurate notions during his stay at
Caracas, fixes it at thirteen fathoms. The heights naturally vary
according to the breadth of the bed and the number of tributary
streams which the principal trunk receives.
The people believe that every five years the Orinoco rises three feet
higher than common; but the idea of this cycle does not rest on any
precise measures. We know by the testimony of antiquity, that the
oscillations of the Nile have been sensibly the same with respect to
their height and duration for thousands of years; which is a proof,
well worthy of attention, that the mean state of the humidity and the
temperature does not vary in that vast basin. Will this constancy in
physical phenomena, this equilibrium of the elements, be preserved in
the New World also after some ages of cultivation?
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