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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Its Summit Was Discovered Under An Angle
Considerable Enough To Lead The Observer, Don Manual Baruti, To
Conclude That The Volcano Might Have Been Visible At Nine Miles
Farther.
It was in September, towards evening, and in very damp
weather.
Reckoning fifteen feet for the elevation of the eye, I
find, that to render an account of this phenomenon, we must suppose
a refraction equal to 0.158 of the arch, which is not very
extraordinary for the temperate zone. According to the observations
of General Roy, the refractions vary in England from one-twentieth
to one-third; and if it be true that they reach these extreme
limits on the coast of Africa, (which I much doubt,) the peak, in
certain circumstances, may be seen on the deck of a vessel as far
off as 61 leagues.
Navigators who have much frequented these latitudes, and who can
reflect on the physical causes of the phenomena, are surprised that
the peaks of Teyde and of the Azores* (* The height of this peak of
the Azores, according to Fleurieu, is 1100 toises; to Ferrer, 1238
toises; and to Tofino, 1260 toises: but these measures are only
approximative estimates. The captain of the Pizarro, Don Manuel
Cagigal, proved to me, by his journal, that he observed the peak of
the Azores at the distance of 37 leagues, when he was sure of his
latitude within two minutes. The volcano was seen at 4 degrees
south-east, so that the error in longitude must have an almost
imperceptible influence in the estimation of the distance.
Nevertheless, the angle which the peak of the Azores subtended was
so great, that the captain of the Pizarro was of opinion this
volcano must be visible at more than 40 or 42 leagues.
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