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 Tints Of Reflected Light Are
Generally Very Different From The Tints Of Transmitted Light;
Particularly When The Transmission Takes Place Through A Great Portion
Of Fluid.
If there were no absorption of rays, the transmitted light
would be of a colour corresponding with that of the reflected light;
and in general we judge imperfectly of transmitted light, by filling
with water a shallow glass with a narrow aperture.
In a river, the
colour of the reflected light comes to us always from the interior
strata of the fluid, and not from the upper stratum.
Some celebrated naturalists, who have examined the purest waters of
the glaciers, and those which flow from mountains covered with
perpetual snow, where the earth is destitute of the relics of
vegetation, have thought that the proper colour of water might be
blue, or green. Nothing, in fact, proves, that water is by nature
white; and we must always admit the presence of a colouring principle,
when water viewed by reflection is coloured. In the rivers that
contain a colouring principle, that principle is generally so little
in quantity, that it eludes all chemical research. The tints of the
ocean seem often to depend neither on the nature of the bottom, nor on
the reflection of the sky on the clouds. Sir Humphrey Davy was of
opinion that the tints of different seas may very likely be owing to
different proportions of iodine.
On consulting the geographers of antiquity, we find that the Greeks
had noticed the blue waters of Thermopylae, the red waters of Joppa,
and the black waters of the hot-baths of Astyra, opposite Lesbos.
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