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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Unfortunately The
Misty Atmosphere Of A Valley, Where The Surrounding Forests Fill
The Air With An Enormous Quantity Of Vapour, Was Unfavourable To
Astronomical Observations.
I spent a part of the nights waiting to
take advantage of the moment when some star should be visible
between the clouds, near its passage over the meridian.
I often
shivered with cold, though the thermometer only sunk to 16 degrees,
which is the temperature of the day in our climates towards the end
of September. The instruments remained set up in the court of the
convent for several hours, yet I was almost always disappointed in
my expectations. Some good observations of Fomalhaut and of Deneb
have given 10 degrees 10 minutes 14 seconds as the latitude of
Caripe; which proves that the position indicated in the maps of
Caulin is 18 minutes wrong, and in that of Arrowsmith 14 minutes.
Observations of corresponding altitudes of the sun having given me
the true time, within about 2 seconds, I was enabled to determine
the magnetic variation with precision, at noon. It was, on the 20th
of September, 1799, 3 degrees 15 minutes 30 seconds north-east;
consequently 0 degrees 58 minutes 15 seconds less than at Cumana.
If we attend to the influence of the horary variations, which in
these countries do not in general exceed 8 minutes, we shall find,
that at considerable distances the variation changes less rapidly
than is usually supposed. The dip of the needle was 42.75 degrees,
centesimal division, and the number of oscillations, expressing the
intensity of the magnetic forces, rose to 229 in ten minutes.
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