Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 2 - By Alexander Von Humboldt And Aime Bonpland.
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The Illusion Was Augmented When
The Disk Of The Sun Appearing On The Horizon, Repeated Its Image By
The Effects Of Refraction, And, Soon Losing Its Flattened Form,
Ascended Rapidly And Straight Towards The Zenith.
Sunrise in the plains is the coolest moment of the day; but this
change of temperature does not make a very lively impression on the
organs.
We did not find the thermometer in general sink below 27.5;
while near Acapulco, at Mexico, and in places equally low, the
temperature at noon is often 32, and at sunrise only 17 or 18 degrees.
The level surface of the ground in the Llanos, which, during the day,
is never in the shade, absorbs so much heat that, notwithstanding the
nocturnal radiation toward a sky without clouds, the earth and air
have not time to cool very sensibly from midnight to sunrise.
In proportion as the sun rose towards the zenith, and the earth and
the strata of superincumbent air took different temperatures, the
phenomenon of the mirage displayed itself in its numerous
modifications. This phenomenon is so common in every zone, that I
mention it only because we stopped to measure with some precision the
breadth of the aerial distance between the horizon and the suspended
object. There was a constant suspension, without inversion. The little
currents of air that swept the surface of the soil had so variable a
temperature that, in a drove of wild oxen, one part appeared with the
legs raised above the surface of the ground, while the other rested on
it.
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