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Meteorology By Aristotle

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Author Topic: Meteorology By Aristotle  (Read 1169 times)
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« Reply #45 on: August 30, 2009, 11:47:51 pm »

To return to the saltness of the sea: those who create the sea once
for all, or indeed generate it at all, cannot account for its saltness.
It makes no difference whether the sea is the residue of all the moisture
that is about the earth and has been drawn up by the sun, or whether
all the flavour existing in the whole mass of sweet water is due to
the admixture of a certain kind of earth. Since the total volume of
the sea is the same once the water that evaporated has returned, it
follows that it must either have been salt at first too, or, if not
at first, then not now either. If it was salt from the very beginning,
then we want to know why that was so; and why, if salt water was drawn
up then, that is not the case now.

Again, if it is maintained that an admixture of earth makes the sea
salt (for they say that earth has many flavours and is washed down
by the rivers and so makes the sea salt by its admixture), it is strange
that rivers should not be salt too. How can the admixture of this
earth have such a striking effect in a great quantity of water and
not in each river singly? For the sea, differing in nothing from rivers
but in being salt, is evidently simply the totality of river water,
and the rivers are the vehicle in which that earth is carried to their
common destination.

It is equally absurd to suppose that anything has been explained by
calling the sea 'the sweat of the earth', like Empedicles. Metaphors
are poetical and so that expression of his may satisfy the requirements
of a poem, but as a scientific theory it is unsatisfactory. Even in
the case of the body it is a question how the sweet liquid drunk becomes
salt sweat whether it is merely by the departure of some element in
it which is sweetest, or by the admixture of something, as when water
is strained through ashes. Actually the saltness seems to be due to
the same cause as in the case of the residual liquid that gathers
in the bladder. That, too, becomes bitter and salt though the liquid
we drink and that contained in our food is sweet. If then the bitterness
is due in these cases (as with the water strained through lye) to
the presence of a certain sort of stuff that is carried along by the
urine (as indeed we actually find a salt deposit settling in chamber-pots)
and is secreted from the flesh in sweat (as if the departing moisture
were washing the stuff out of the body), then no doubt the admixture
of something earthy with the water is what makes the sea salt.
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« Reply #46 on: August 30, 2009, 11:48:05 pm »

Now in the body stuff of this kind, viz. the sediment of food, is
due to failure to digest: but how there came to be any such thing
in the earth requires explanation. Besides, how can the drying and
warming of the earth cause the secretion such a great quantity of
water; especially as that must be a mere fragment of what is left
in the earth? Again, waiving the question of quantity, why does not
the earth sweat now when it happens to be in process of drying? If
it did so then, it ought to do so now. But it does not: on the contrary,
when it is dry it graws moist, but when it is moist it does not secrete
anything at all. How then was it possible for the earth at the beginning
when it was moist to sweat as it grew dry? Indeed, the theory that
maintains that most of the moisture departed and was drawn up by the
sun and that what was left over is the sea is more reasonable; but
for the earth to sweat when it is moist is impossible.

Since all the attempts to account for the saltness of the sea seem
unsuccessful let us explain it by the help of the principle we have
used already.

Since we recognize two kinds of evaporation, one moist, the other
dry, it is clear that the latter must be recognized as the source
of phenomena like those we are concerned with.

But there is a question which we must discuss first. Does the sea
always remain numerically one and consisting of the same parts, or
is it, too, one in form and volume while its parts are in continual
change, like air and sweet water and fire? All of these are in a constant
state of change, but the form and the quantity of each of them are
fixed, just as they are in the case of a flowing river or a burning
flame. The answer is clear, and there is no doubt that the same account
holds good of all these things alike. They differ in that some of
them change more rapidly or more slowly than others; and they all
are involved in a process of perishing and becoming which yet affects
them all in a regular course.
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« Reply #47 on: August 30, 2009, 11:48:31 pm »

This being so we must go on to try to explain why the sea is salt.
There are many facts which make it clear that this taste is due to
the admixture of something. First, in animal bodies what is least
digested, the residue of liquid food, is salt and bitter, as we said
before. All animal excreta are undigested, but especially that which
gathers in the bladder (its extreme lightness proves this; for everything
that is digested is condensed), and also sweat; in these then is excreted
(along with other matter) an identical substance to which this flavour
is due. The case of things burnt is analogous. What heat fails to
assimilate becomes the excrementary residue in animal bodies, and,
in things burnt, ashes. That is why some people say that it was burnt
earth that made the sea salt. To say that it was burnt earth is absurd;
but to say that it was something like burnt earth is true. We must
suppose that just as in the cases we have described, so in the world
as a whole, everything that grows and is naturally generated always
leaves an undigested residue, like that of things burnt, consisting
of this sort of earth. All the earthy stuff in the dry exhalation
is of this nature, and it is the dry exhalation which accounts for
its great quantity. Now since, as we have said, the moist and the
dry evaporations are mixed, some quantity of this stuff must always
be included in the clouds and the water that are formed by condensation,
and must redescend to the earth in rain. This process must always
go on with such regularity as the sublunary world admits of. and it
is the answer to the question how the sea comes to be salt.

It also explains why rain that comes from the south, and the first
rains of autumn, are brackish. The south is the warmest of winds and
it blows from dry and hot regions. Hence it carries little moist vapour
and that is why it is hot. (It makes no difference even if this is
not its true character and it is originally a cold wind, for it becomes
warm on its way by incorporating with itself a great quantity of dry
evaporation from the places it passes over.) The north wind, on the
other hand, comb ing from moist regions, is full of vapour and therefore
cold. It is dry in our part of the world because it drives the clouds
away before it, but in the south it is rainy; just as the south is
a dry wind in Libya. So the south wind charges the rain that falls
with a great quantity of this stuff. Autumn rain is brackish because
the heaviest water must fall first; so that that which contains the
greatest quantity of this kind of earth descends quickest.
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« Reply #48 on: August 30, 2009, 11:48:45 pm »

This, too, is why the sea is warm. Everything that has been exposed
to fire contains heat potentially, as we see in the case of lye and
ashes and the dry and liquid excreta of animals. Indeed those animals
which are hottest in the belly have the hottest excreta.

The action of this cause is continually making the sea more salt,
but some part of its saltness is always being drawn up with the sweet
water. This is less than the sweet water in the same ratio in which
the salt and brackish element in rain is less than the sweet, and
so the saltness of the sea remains constant on the whole. Salt water
when it turns into vapour becomes sweet, and the vapour does not form
salt water when it condenses again. This I know by experiment. The
same thing is true in every case of the kind: wine and all fluids
that evaporate and condense back into a liquid state become water.
They all are water modified by a certain admixture, the nature of
which determines their flavour. But this subject must be considered
on another more suitable occasion.

For the present let us say this. The sea is there and some of it is
continually being drawn up and becoming sweet; this returns from above
with the rain. But it is now different from what it was when it was
drawn up, and its weight makes it sink below the sweet water. This
process prevents the sea, as it does rivers, from drying up except
from local causes (this must happen to sea and rivers alike). On the
other hand the parts neither of the earth nor of the sea remain constant
but only their whole bulk. For the same thing is true of the earth
as of the sea: some of it is carried up and some comes down with the
rain, and both that which remains on the surface and that which comes
down again change their situations.
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« Reply #49 on: August 30, 2009, 11:48:57 pm »

There is more evidence to prove that saltness is due to the admixture
of some substance, besides that which we have adduced. Make a vessel
of wax and put it in the sea, fastening its mouth in such a way as
to prevent any water getting in. Then the water that percolates through
the wax sides of the vessel is sweet, the earthy stuff, the admixture
of which makes the water salt, being separated off as it were by a
filter. It is this stuff which make salt water heavy (it weighs more
than fresh water) and thick. The difference in consistency is such
that ships with the same cargo very nearly sink in a river when they
are quite fit to navigate in the sea. This circumstance has before
now caused loss to shippers freighting their ships in a river. That
the thicker consistency is due to an admixture of something is proved
by the fact that if you make strong brine by the admixture of salt,
eggs, even when they are full, float in it. It almost becomes like
mud; such a quantity of earthy matter is there in the sea. The same
thing is done in salting fish.

Again if, as is fabled, there is a lake in Palestine, such that if
you bind a man or beast and throw it in it floats and does not sink,
this would bear out what we have said. They say that this lake is
so bitter and salt that no fish live in it and that if you soak clothes
in it and shake them it cleans them. The following facts all of them
support our theory that it is some earthy stuff in the water which
makes it salt. In Chaonia there is a spring of brackish water that
flows into a neighbouring river which is sweet but contains no fish.
The local story is that when Heracles came from Erytheia driving the
oxen and gave the inhabitants the choice, they chose salt in preference
to fish. They get the salt from the spring. They boil off some of
the water and let the rest stand; when it has cooled and the heat
and moisture have evaporated together it gives them salt, not in lumps
but loose and light like snow. It is weaker than ordinary salt and
added freely gives a sweet taste, and it is not as white as salt generally
is. Another instance of this is found in Umbria. There is a place
there where reeds and rushes grow. They burn some of these, put the
ashes into water and boil it off. When a little water is left and
has cooled it gives a quantity of salt.
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« Reply #50 on: August 30, 2009, 11:49:10 pm »

Most salt rivers and springs must once have been hot. Then the original
fire in them was extinguished but the earth through which they percolate
preserves the character of lye or ashes. Springs and rivers with all
kinds of flavours are found in many places. These flavours must in
every case be due to the fire that is or was in them, for if you expose
earth to different degrees of heat it assumes various kinds and shades
of flavour. It becomes full of alum and lye and other things of the
kind, and the fresh water percolates through these and changes its
character. Sometimes it becomes acid as in Sicania, a part of Sicily.
There they get a salt and acid water which they use as vinegar to
season some of their dishes. In the neighbourhood of Lyncus, too,
there is a spring of acid water, and in Scythia a bitter spring. The
water from this makes the whole of the river into which it flows bitter.
These differences are explained by a knowledge of the particular mixtures
that determine different savours. But these have been explained in
another treatise.

We have now given an account of waters and the sea, why they persist,
how they change, what their nature is, and have explained most of
their natural operations and affections.

Part 4

Let us proceed to the theory of winds. Its basis is a distinction
we have already made. We recognize two kinds of evaporation, one moist,
the other dry. The former is called vapour: for the other there is
no general name but we must call it a sort of smoke, applying to the
whole of it a word that is proper to one of its forms. The moist cannot
exist without the dry nor the dry without the moist: whenever we speak
of either we mean that it predominates. Now when the sun in its circular
course approaches, it draws up by its heat the moist evaporation:
when it recedes the cold makes the vapour that had been raised condense
back into water which falls and is distributed through the earth.
(This explains why there is more rain in winter and more by night
than by day: though the fact is not recognized because rain by night
is more apt to escape observation than by day.) But there is a great
quantity of fire and heat in the earth, and the sun not only draws
up the moisture that lies on the surface of it, but warms and dries
the earth itself. Consequently, since there are two kinds of evaporation,
as we have said, one like vapour, the other like smoke, both of them
are necessarily generated. That in which moisture predominates is
the source of rain, as we explained before, while the dry evaporation
is the source and substance of all winds. That things must necessarily
take this course is clear from the resulting phenomena themselves,
for the evaporation that is to produce them must necessarily differ;
and the sun and the warmth in the earth not only can but must produce
these evaporations.
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« Reply #51 on: August 30, 2009, 11:49:21 pm »

Since the two evaporations are specifically distinct, wind and rain
obviously differ and their substance is not the same, as those say
who maintain that one and the same air when in motion is wind, but
when it condenses again is water. Air, as we have explained in an
earlier book, is made up of these as constituents. Vapour is moist
and cold (for its fluidity is due to its moistness, and because it
derives from water it is naturally cold, like water that has not been
warmed): whereas the smoky evaporation is hot and dry. Hence each
contributes a part, and air is moist and hot. It is absurd that this
air that surrounds us should become wind when in motion, whatever
be the source of its motion on the contrary the case of winds is like
that of rivers. We do not call water that flows anyhow a river, even
if there is a great quantity of it, but only if the flow comes from
a spring. So too with the winds; a great quantity of air might be
moved by the fall of some large object without flowing from any source
or spring.

The facts bear out our theory. It is because the evaporation takes
place uninterruptedly but differs in degree and quantity that clouds
and winds appear in their natural proportion according to the season;
and it is because there is now a great excess of the vaporous, now
of the dry and smoky exhalation, that some years are rainy and wet,
others windy and dry. Sometimes there is much drought or rain, and
it prevails over a great and continuous stretch of country. At other
times it is local; the surrounding country often getting seasonable
or even excessive rains while there is drought in a certain part;
or, contrariwise, all the surrounding country gets little or even
no rain while a certain part gets rain in abundance. The reason for
all this is that while the same affection is generally apt to prevail
over a considerable district because adjacent places (unless there
is something special to differentiate them) stand in the same relation
to the sun, yet on occasion the dry evaporation will prevail in one
part and the moist in another, or conversely. Again the reason for
this latter is that each evaporation goes over to that of the neighbouring
district: for instance, the dry evaporation circulates in its own
place while the moist migrates to the next district or is even driven
by winds to some distant place: or else the moist evaporation remains
and the dry moves away. Just as in the case of the body when the stomach
is dry the lower belly is often in the contrary state, and when it
is dry the stomach is moist and cold, so it often happens that the
evaporations reciprocally take one another's place and interchange.
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« Reply #52 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

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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« Reply #53 on: August 30, 2009, 11:49:50 pm »

Part 5

The sun both checks the formation of winds and stimulates it. When
the evaporation is small in amount and faint the sun wastes it and
dissipates by its greater heat the lesser heat contained in the evaporation.
It also dries up the earth, the source of the evaporation, before
the latter has appeared in bulk: just as, when you throw a little
fuel into a great fire, it is often burnt up before giving off any
smoke. In these ways the sun checks winds and prevents them from rising
at all: it checks them by wasting the evaporation, and prevents their
rising by drying up the earth quickly. Hence calm is very apt to prevail
about the rising of Orion and lasts until the coming of the Etesiae
and their 'forerunners'.

Calm is due to two causes. Either cold quenches the evaporation, for
instance a sharp frost: or excessive heat wastes it. In the intermediate
periods, too, the causes are generally either that the evaporation
has not had time to develop or that it has passed away and there is
none as yet to replace it.

Both the setting and the rising of Orion are considered to be treacherous
and stormy, because they place at a change of season (namely of summer
or winter; and because the size of the constellation makes its rise
last over many days) and a state of change is always indefinite and
therefore liable to disturbance.
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« Reply #54 on: August 30, 2009, 11:50:05 pm »

The Etesiae blow after the summer solstice and the rising of the dog-star:
not at the time when the sun is closest nor when it is distant; and
they blow by day and cease at night. The reason is that when the sun
is near it dries up the earth before evaporation has taken place,
but when it has receded a little its heat and the evaporation are
present in the right proportion; so the ice melts and the earth, dried
by its own heat and that of the sun, smokes and vapours. They abate
at night because the cold pf the nights checks the melting of the
ice. What is frozen gives off no evaporation, nor does that which
contains no dryness at all: it is only where something dry contains
moisture that it gives off evaporation under the influence of heat.

The question is sometimes asked: why do the north winds which we call
the Etesiae blow continuously after the summer solstice, when there
are no corresponding south winds after the winter solstice? The facts
are reasonable enough: for the so-called 'white south winds' do blow
at the corresponding season, though they are not equally continuous
and so escape observation and give rise to this inquiry. The reason
for this is that the north wind I from the arctic regions which are
full of water and snow. The sun thaws them and so the Etesiae blow:
after rather than at the summer solstice. (For the greatest heat is
developed not when the sun is nearest to the north, but when its heat
has been felt for a considerable period and it has not yet receded
far. The 'bird winds' blow in the same way after the winter solstice.
They, too, are weak Etesiae, but they blow less and later than the
Etesiae. They begin to blow only on the seventieth day because the
sun is distant and therefore weaker. They do not blow so continuously
because only things on the surface of the earth and offering little
resistance evaporate then, the thoroughly frozen parts requiring greater
heat to melt them. So they blow intermittently till the true Etesiae
come on again at the summer solstice: for from that time onwards the
wind tends to blow continuously.) But the south wind blows from the
tropic of Cancer and not from the antarctic region.
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« Reply #55 on: August 30, 2009, 11:50:22 pm »

There are two inhabitable sections of the earth: one near our upper,
or nothern pole, the other near the other or southern pole; and their
shape is like that of a tambourine. If you draw lines from the centre
of the earth they cut out a drum-shaped figure. The lines form two
cones; the base of the one is the tropic, of the other the ever visible
circle, their vertex is at the centre of the earth. Two other cones
towards the south pole give corresponding segments of the earth. These
sections alone are habitable. Beyond the tropics no one can live:
for there the shade would not fall to the north, whereas the earth
is known to be uninhabitable before the sun is in the zenith or the
shade is thrown to the south: and the regions below the Bear are uninhabitable
because of the cold.

(The Crown, too, moves over this region: for it is in the zenith when
it is on our meridian.)

So we see that the way in which they now describe the geography of
the earth is ridiculous. They depict the inhabited earth as round,
but both ascertained facts and general considerations show this to
be impossible. If we reflect we see that the inhabited region is limited
in breadth, while the climate admits of its extending all round the
earth. For we meet with no excessive heat or cold in the direction
of its length but only in that of its breadth; so that there is nothing
to prevent our travelling round the earth unless the extent of the
sea presents an obstacle anywhere. The records of journeys by sea
and land bear this out. They make the length far greater than the
breadth. If we compute these voyages and journeys the distance from
the Pillars of Heracles to India exceeds that from Aethiopia to Maeotis
and the northernmost Scythians by a ratio of more than 5 to 3, as
far as such matters admit of accurate statement. Yet we know the whole
breadth of the region we dwell in up to the uninhabited parts: in
one direction no one lives because of the cold, in the other because
of the heat.
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« Reply #56 on: August 30, 2009, 11:50:37 pm »

But it is the sea which divides as it seems the parts beyond India
from those beyond the Pillars of Heracles and prevents the earth from
being inhabited all round.

Now since there must be a region bearing the same relation to the
southern pole as the place we live in bears to our pole, it will clearly
correspond in the ordering of its winds as well as in other things.
So just as we have a north wind here, they must have a corresponding
wind from the antarctic. This wind cannot reach us since our own north
wind is like a land breeze and does not even reach the limits of the
region we live in. The prevalence of north winds here is due to our
lying near the north. Yet even here they give out and fail to penetrate
far: in the southern sea beyond Libya east and west winds are always
blowing alternately, like north and south winds with us. So it is
clear that the south wind is not the wind that blows from the south
pole. It is neither that nor the wind from the winter tropic. For
symmetry would require another wind blowing from the summer tropic,
which there is not, since we know that only one wind blows from that
quarter. So the south wind clearly blows from the torrid region. Now
the sun is so near to that region that it has no water, or snow which
might melt and cause Etesiae. But because that place is far more extensive
and open the south wind is greater and stronger and warmer than the
north and penetrates farther to the north than the north wind does
to the south.

The origin of these winds and their relation to one another has now
been explained.
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« Reply #57 on: August 30, 2009, 11:50:53 pm »

Part 6

Let us now explain the position of the winds, their oppositions, which
can blow simultaneously with which, and which cannot, their names
and number, and any other of their affections that have not been treated
in the 'particular questions'. What we say about their position must
be followed with the help of the figure. For clearness' sake we have
drawn the circle of the horizon, which is round, but it represents
the zone in which we live; for that can be divided in the same way.
Let us also begin by laying down that those things are locally contrary
which are locally most distant from one another, just as things specifically
most remote from one another are specific contraries. Now things that
face one another from opposite ends of a diameter are locally most
distant from one another. (See diagram.)

Let A be the point where the sun sets at the equinox and B, the point
opposite, the place where it rises at the equinox. Let there be another
diameter cutting this at right angles, and let the point H on it be
the north and its diametrical opposite O the south. Let Z be the rising
of the sun at the summer solstice and E its setting at the summer
solstice; D its rising at the winter solstice, and G its setting at
the winter solstice. Draw a diameter from Z to G from D to E. Then
since those things are locally contrary which are most distant from
one another in space, and points diametrically opposite are most distant
from one another, those winds must necessarily be contrary to one
another that blow from opposite ends of a diameter.

The names of the winds according to their position are these. Zephyrus
is the wind that blows from A, this being the point where the sun
sets at the equinox. Its contrary is Apeliotes blowing from B the
point where the sun rises at the equinox. The wind blowing from H,
the north, is the true north wind, called Aparctias: while Notus blowing
from O is its contrary; for this point is the south and O is contrary
to H, being diametrically opposite to it. Caecias blows from Z, where
the sun rises at the summer solstice. Its contrary is not the wind
blowing from E but Lips blowing from G. For Lips blows from the point
where the sun sets at the winter solstice and is diametrically opposite
to Caecias: so it is its contrary. Eurus blows from D, coming from
the point where the sun rises at the winter solstice. It borders on
Notus, and so we often find that people speak of 'Euro-Noti'. Its
contrary is not Lips blowing from G but the wind that blows from E
which some call Argestes, some Olympias, and some Sciron. This blows
from the point where the sun sets at the summer solstice, and is the
only wind that is diametrically opposite to Eurus. These are the winds
that are diametrically opposite to one another and their contraries.
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« Reply #58 on: August 30, 2009, 11:51:09 pm »

There are other winds which have no contraries. The wind they call
Thrascias, which lies between Argestes and Aparctias, blows from I;
and the wind called Meses, which lies between Caecias and Aparctias,
from K. (The line IK nearly coincides with the ever visible circle,
but not quite.) These winds have no contraries. Meses has not, or
else there would be a wind blowing from the point M which is diametrically
opposite. Thrascias corresponding to the point I has not, for then
there would be a wind blowing from N, the point which is diametrically
opposite. (But perhaps a local wind which the inhabitants of those
parts call Phoenicias blows from that point.)

These are the most important and definite winds and these their places.

There are more winds from the north than from the south. The reason
for this is that the region in which we live lies nearer to the north.
Also, much more water and snow is pushed aside into this quarter because
the other lies under the sun and its course. When this thaws and soaks
into the earth and is exposed to the heat of the sun and the earth
it necessarily causes evaporation to rise in greater quantities and
over a greater space.

Of the winds we have described Aparctias is the north wind in the
strict sense. Thrascias and Meses are north winds too. (Caecias is
half north and half east.) South are that which blows from due south
and Lips. East, the wind from the rising of the sun at the equinox
and Eurus. Phoenicias is half south and half east. West, the wind
from the true west and that called Argestes. More generally these
winds are classified as northerly or southerly. The west winds are
counted as northerly, for they blow from the place of sunset and are
therefore colder; the east winds as southerly, for they are warmer
because they blow from the place of sunrise. So the distinction of
cold and hot or warm is the basis for the division of the winds into
northerly and southerly. East winds are warmer than west winds because
the sun shines on the east longer, whereas it leaves the west sooner
and reaches it later.
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« Reply #59 on: August 30, 2009, 11:51:21 pm »

Since this is the distribution of the winds it is clear that contrary
winds cannot blow simultaneously. They are diametrically opposite
to one another and one of the two must be overpowered and cease. Winds
that are not diametrically opposite to one another may blow simultaneously:
for instance the winds from Z and from D. Hence it sometimes happens
that both of them, though different winds and blowing from different
quarters, are favourable to sailors making for the same point.

Contrary winds commonly blow at opposite seasons. Thus Caecias and
in general the winds north of the summer solstice blow about the time
of the spring equinox, but about the autumn equinox Lips; and Zephyrus
about the summer solstice, but about the winter solstice Eurus.

Aparctias, Thrascias, and Argestes are the winds that fall on others
most and stop them. Their source is so close to us that they are greater
and stronger than other winds. They bring fair weather most of all
winds for the same reason, for, blowing as they do, from close at
hand, they overpower the other winds and stop them; they also blow
away the clouds that are forming and leave a clear sky-unless they
happen to be very cold. Then they do not bring fair weather, but being
colder than they are strong they condense the clouds before driving
them away.

Caecias does not bring fair weather because it returns upon itself.
Hence the saying: 'Bringing it on himself as Caecias does clouds.'

When they cease, winds are succeeded by their neighbours in the direction
of the movement of the sun. For an effect is most apt to be produced
in the neighbourhood of its cause, and the cause of winds moves with
the sun.

Contrary winds have either the same or contrary effects. Thus Lips
and Caecias, sometimes called Hellespontias, are both rainy gestes
and Eurus are dry: the latter being dry at first and rainy afterwards.
Meses and Aparctias are coldest and bring most snow. Aparctias, Thrascias,
and Argestes bring hail. Notus, Zephyrus, and Eurus are hot. Caecias
covers the sky with heavy clouds, Lips with lighter ones. Caecias
does this because it returns upon itself and combines the qualities
of Boreas and Eurus. By being cold it condenses and gathers the vaporous
air, and because it is easterly it carries with it and drives before
it a great quantity of such matter. Aparctias, Thrascias, and Argestes
bring fair weather for the reason we have explained before. These
winds and Meses are most commonly accompanied by lightning. They are
cold because they blow from the north, and lightning is due to cold,
being ejected when the clouds contract. Some of these same bring hail
with them for the same reason; namely, that they cause a sudden condensation.
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