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To explain, however, more at length, the case is this. The sun,
in his passage across the upper parts of Libya, affects them in the
following way. As the air in those regions is constantly clear, and
the country warm through the absence of cold winds, the sun in his
passage across them acts upon them exactly as he wont to act elsewhere
in summer, when his path is in the middle of heaven - that is, he
attracts the water. After attracting it, he again repels it into the
upper regions, where the winds lay hold of it, scatter it, and reduce
it to a vapour, whence it naturally enough comes to pass that the winds
which blow from this quarter - the south and south-west - are of all
winds the most rainy. And my own opinion is that the sun does not get
rid of all the water which he draws year by year from the Nile, but
retains some about him. When the winter begins to soften, the sun
goes back again to his old place in the middle of the heaven, and
proceeds to attract water equally from all countries. Till then the
other rivers run big, from the quantity of rain-water which they bring
down from countries where so much moisture falls that all the land is
cut into gullies; but in summer, when the showers fail, and the sun
attracts their water, they become low. The Nile, on the contrary,
not deriving any of its bulk from rains, and being in winter subject to
the attraction of the sun, naturally runs at that season, unlike all
other streams, with a less burthen of water than in the summer time.
For in summer it is exposed to attraction equally with all other
rivers, but in winter it suffers alone. The sun, therefore, I
regard as the sole cause of the phenomenon.
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