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Meteorology By Aristotle

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Author Topic: Meteorology By Aristotle  (Read 2793 times)
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Bathos
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« Reply #45 on: August 30, 2009, 11:49:37 pm »

Further, after rain wind generally rises in those places where the
rain fell, and when rain has come on the wind ceases. These are necessary
effects of the principles we have explained. After rain the earth
is being dried by its own heat and that from above and gives off the
evaporation which we saw to be the material cause of. wind. Again,
suppose this secretion is present and wind prevails; the heat is continually
being thrown off, rising to the upper region, and so the wind ceases;
then the fall in temperature makes vapour form and condense into water.
Water also forms and cools the dry evaporation when the clouds are
driven together and the cold concentrated in them. These are the causes
that make wind cease on the advent of rain, and rain fall on the cessation
of wind.

The cause of the predominance of winds from the north and from the
south is the same. (Most winds, as a matter of fact, are north winds
or south winds.) These are the only regions which the sun does not
visit: it approaches them and recedes from them, but its course is
always over the-west and the east. Hence clouds collect on either
side, and when the sun approaches it provokes the moist evaporation,
and when it recedes to the opposite side there are storms and rain.
So summer and winter are due to the sun's motion to and from the solstices,
and water ascends and falls again for the same reason. Now since most
rain falls in those regions towards which and from which the sun turns
and these are the north and the south, and since most evaporation
must take place where there is the greatest rainfall, just as green
wood gives most smoke, and since this evaporation is wind, it is natural
that the most and most important winds should come from these quarters.
(The winds from the north are called Boreae, those from the south
Noti.)

The course of winds is oblique: for though the evaporation rises straight
up from the earth, they blow round it because all the surrounding
air follows the motion of the heavens. Hence the question might be
asked whether winds originate from above or from below. The motion
comes from above: before we feel the wind blowing the air betrays
its presence if there are clouds or a mist, for their motion shows
that the wind has begun to blow before it has actually reached us;
and this implies that the source of winds is above. But since wind
is defined as 'a quantity of dry evaporation from the earth moving
round the earth', it is clear that while the origin of the motion
is from above, the matter and the generation of wind come from below.
The oblique movement of the rising evaporation is caused from above:
for the motion of the heavens determines the processes that are at
a distance from the earth, and the motion from below is vertical and
every cause is more active where it is nearest to the effect; but
in its generation and origin wind plainly derives from the earth.

The facts bear out the view that winds are formed by the gradual union
of many evaporations just as rivers derive their sources from the
water that oozes from the earth. Every wind is weakest in the spot
from which it blows; as they proceed and leave their source at a distance
they gather strength. Thus the winter in the north is windless and
calm: that is, in the north itself; but, the breeze that blows from
there so gently as to escape observation becomes a great wind as it
passes on.

We have explained the nature and origin of wind, the occurrence of
drought and rains, the reason why rain stops wind and wind rises after
rain, the prevalence of north and south winds and also why wind moves
in the way it does.
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