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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Now At Cumana, Where It Sometimes
Does Not Rain During A Whole Year, And Where I Had The Means Of
Collecting a great number of hygrometric observations made at
different hours of the day and night, the mean humidity of
The air is
86 degrees; corresponding to the mean temperature of 27.7 degrees.
Taking into account the influence of the rainy months, that is to say,
estimating the difference observed in other parts of South America
between the mean humidity of the dry months and that of the whole
year; an annual mean humidity is obtained, for the valleys of Aragua,
at farthest of 74 degrees, the temperature being 25.5 degrees. In this
air, so hot, and at the same time so little humid, the quantity of
water evaporated is enormous. The theory of Dalton estimates, under
the conditions just stated, for the thickness of the sheet of water
evaporated in an hour's time, 0.36 mill., or 3.8 lines in twenty-four
hours. Assuming for the temperate zone, for instance at Paris, the
mean temperature to be 10.6 degrees, and the mean humidity 82 degrees,
we find, according to the same formulae, 0.10 mill., an hour, and 1
line for twenty-four hours. If we prefer substituting for the
uncertainty of these theoretical deductions the direct results of
observation, we may recollect that in Paris, and at Montmorency, the
mean annual evaporation was found by Sedileau and Cotte, to be from 32
in. 1 line to 38 in.
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