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Meteorology By Aristotle

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Author Topic: Meteorology By Aristotle  (Read 1439 times)
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« Reply #15 on: August 30, 2009, 11:39:42 pm »

These views involve impossibilities, some of which are common to all
of them, while others are peculiar to some only.

This is the case, first, with those who say that the comet is one
of the planets. For all the planets appear in the circle of the zodiac,
whereas many comets have been seen outside that circle. Again more
comets than one have often appeared simultaneously. Besides, if their
tail is due to reflection, as Aeschylus and Hippocrates say, this
planet ought sometimes to be visible without a tail since, as they
it does not possess a tail in every place in which it appears. But,
as a matter of fact, no planet has been observed besides the five.
And all of them are often visible above the horizon together at the
same time. Further, comets are often found to appear, as well when
all the planets are visible as when some are not, but are obscured
by the neighbourhood of the sun. Moreover the statement that a comet
only appears in the north, with the sun at the summer solstice, is
not true either. The great comet which appeared at the time of the
earthquake in Achaea and the tidal wave rose due west; and many have
been known to appear in the south. Again in the archonship of Euclees,
son of Molon, at Athens there appeared a comet in the north in the
month Gamelion, the sun being about the winter solstice. Yet they
themselves admit that reflection over so great a space is an impossibility.
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« Reply #16 on: August 30, 2009, 11:39:56 pm »

An objection that tells equally against those who hold this theory
and those who say that comets are a coalescence of the planets is,
first, the fact that some of the fixed stars too get a tail. For this
we must not only accept the authority of the Egyptians who assert
it, but we have ourselves observed the fact. For a star in the thigh
of the Dog had a tail, though a faint one. If you fixed your sight
on it its light was dim, but if you just glanced at it, it appeared
brighter. Besides, all the comets that have been seen in our day have
vanished without setting, gradually fading away above the horizon;
and they have not left behind them either one or more stars. For instance
the great comet we mentioned before appeared to the west in winter
in frosty weather when the sky was clear, in the archonship of Asteius.
On the first day it set before the sun and was then not seen. On the
next day it was seen, being ever so little behind the sun and immediately
setting. But its light extended over a third part of the sky like
a leap, so that people called it a 'path'. This comet receded as far
as Orion's belt and there dissolved. Democritus however, insists upon
the truth of his view and affirms that certain stars have been seen
when comets dissolve. But on his theory this ought not to occur occasionally
but always. Besides, the Egyptians affirm that conjunctions of the
planets with one another, and with the fixed stars, take place, and
we have ourselves observed Jupiter coinciding with one of the stars
in the Twins and hiding it, and yet no comet was formed. Further,
we can also give a rational proof of our point. It is true that some
stars seem to be bigger than others, yet each one by itself looks
indivisible. Consequently, just as, if they really had been indivisible,
their conjunction could not have created any greater magnitude, so
now that they are not in fact indivisible but look as if they were,
their conjunction will not make them look any bigger.

Enough has been said, without further argument, to show that the causes
brought forward to explain comets are false.
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« Reply #17 on: August 30, 2009, 11:40:06 pm »

Part 7

We consider a satisfactory explanation of phenomena inaccessible to
observation to have been given when our account of them is free from
impossibilities. The observations before us suggest the following
account of the phenomena we are now considering. We know that the
dry and warm exhalation is the outermost part of the terrestrial world
which falls below the circular motion. It, and a great part of the
air that is continuous with it below, is carried round the earth by
the motion of the circular revolution. In the course of this motion
it often ignites wherever it may happen to be of the right consistency,
and this we maintain to be the cause of the 'shooting' of scattered
'stars'. We may say, then, that a comet is formed when the upper motion
introduces into a gathering of this kind a fiery principle not of
such excessive strength as to burn up much of the material quickly,
nor so weak as soon to be extinguished, but stronger and capable of
burning up much material, and when exhalation of the right consistency
rises from below and meets it. The kind of comet varies according
to the shape which the exhalation happens to take. If it is diffused
equally on every side the star is said to be fringed, if it stretches
out in one direction it is called bearded. We have seen that when
a fiery principle of this kind moves we seem to have a shooting-star:
similarly when it stands still we seem to have a star standing still.
We may compare these phenomena to a heap or mass of chaff into which
a torch is thrust, or a spark thrown. That is what a shooting-star
is like. The fuel is so inflammable that the fire runs through it
quickly in a line. Now if this fire were to persist instead of running
through the fuel and perishing away, its course through the fuel would
stop at the point where the latter was densest, and then the whole
might begin to move. Such is a comet-like a shooting-star that contains
its beginning and end in itself.
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« Reply #18 on: August 30, 2009, 11:40:18 pm »

When the matter begins to gather in the lower region independently
the comet appears by itself. But when the exhalation is constituted
by one of the fixed stars or the planets, owing to their motion, one
of them becomes a comet. The fringe is not close to the stars themselves.
Just as haloes appear to follow the sun and the moon as they move,
and encircle them, when the air is dense enough for them to form along
under the sun's course, so too the fringe. It stands in the relation
of a halo to the stars, except that the colour of the halo is due
to reflection, whereas in the case of comets the colour is something
that appears actually on them.

Now when this matter gathers in relation to a star the comet necessarily
appears to follow the same course as the star. But when the comet
is formed independently it falls behind the motion of the universe,
like the rest of the terrestrial world. It is this fact, that a comet
often forms independently, indeed oftener than round one of the regular
stars, that makes it impossible to maintain that a comet is a sort
of reflection, not indeed, as Hippocrates and his school say, to the
sun, but to the very star it is alleged to accompany-in fact, a kind
of halo in the pure fuel of fire.
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« Reply #19 on: August 30, 2009, 11:40:30 pm »

As for the halo we shall explain its cause later.
The fact that comets when frequent foreshadow wind and drought must
be taken as an indication of their fiery constitution. For their origin
is plainly due to the plentiful supply of that secretion. Hence the
air is necessarily drier and the moist evaporation is so dissolved
and dissipated by the quantity of the hot exhalation as not readily
to condense into water.-But this phenomenon too shall be explained
more clearly later when the time comes to speak of the winds.-So when
there are many comets and they are dense, it is as we say, and the
years are clearly dry and windy. When they are fewer and fainter this
effect does not appear in the same degree, though as a rule the is
found to be excessive either in duration or strength. For instance
when the stone at Aegospotami fell out of the air-it had been carried
up by a wind and fell down in the daytime-then too a comet happened
to have appeared in the west. And at the time of the great comet the
winter was dry and north winds prevailed, and the wave was due to
an opposition of winds. For in the gulf a north wind blew and outside
it a violent south wind. Again in the archonship of Nicomachus a comet
appeared for a few days about the equinoctial circle (this one had
not risen in the west), and simultaneously with it there happened
the storm at Corinth.

That there are few comets and that they appear rarely and outside
the tropic circles more than within them is due to the motion of the
sun and the stars. For this motion does not only cause the hot principle
to be secreted but also dissolves it when it is gathering. But the
chief reason is that most of this stuff collects in the region of
the milky way.
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« Reply #20 on: August 30, 2009, 11:41:17 pm »

Part 8

Let us now explain the origin, cause, and nature of the milky way.
And here too let us begin by discussing the statements of others on
the subject.

(1) Of the so-called Pythagoreans some say that this is the path of
one of the stars that fell from heaven at the time of Phaethon's downfall.
Others say that the sun used once to move in this circle and that
this region was scorched or met with some other affection of this
kind, because of the sun and its motion.

But it is absurd not to see that if this were the reason the circle
of the Zodiac ought to be affected in the same way, and indeed more
so than that of the milky way, since not the sun only but all the
planets move in it. We can see the whole of this circle (half of it
being visible at any time of the night), but it shows no signs of
any such affection except where a part of it touches the circle of
the milky way.

(2) Anaxagoras, Democritus, and their schools say that the milky way
is the light of certain stars. For, they say, when the sun passes
below the earth some of the stars are hidden from it. Now the light
of those on which the sun shines is invisible, being obscured by the
of the sun. But the milky way is the peculiar light of those stars
which are shaded by the earth from the sun's rays.

This, too, is obviously impossible. The milky way is always unchanged
and among the same constellations (for it is clearly a greatest circle),
whereas, since the sun does not remain in the same place, what is
hidden from it differs at different times. Consequently with the change
of the sun's position the milky way ought to change its position too:
but we find that this does not happen. Besides, if astronomical demonstrations
are correct and the size of the sun is greater than that of the earth
and the distance of the stars from the earth many times greater than
that of the sun (just as the sun is further from the earth than the
moon), then the cone made by the rays of the sun would terminate at
no great distance from the earth, and the shadow of the earth (what
we call night) would not reach the stars. On the contrary, the sun
shines on all the stars and the earth screens none of them.

(3) There is a third theory about the milky way. Some say that it
is a reflection of our sight to the sun, just as they say that the
comet is.
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« Reply #21 on: August 30, 2009, 11:41:35 pm »

But this too is impossible. For if the eye and the mirror and the
whole of the object were severally at rest, then the same part of
the image would appear at the same point in the mirror. But if the
mirror and the object move, keeping the same distance from the eye
which is at rest, but at different rates of speed and so not always
at the same interval from one another, then it is impossible for the
same image always to appear in the same part of the mirror. Now the
constellations included in the circle of the milky way move; and so
does the sun, the object to which our sight is reflected; but we stand
still. And the distance of those two from us is constant and uniform,
but their distance from one another varies. For the Dolphin sometimes
rises at midnight, sometimes in the morning. But in each case the
same parts of the milky way are found near it. But if it were a reflection
and not a genuine affection of these this ought not to be the case.

Again, we can see the milky way reflected at night in water and similar
mirrors. But under these circumstances it is impossible for our sight
to be reflected to the sun.

These considerations show that the milky way is not the path of one
of the planets, nor the light of imperceptible stars, nor a reflection.
And those are the chief theories handed down by others hitherto.
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« Reply #22 on: August 30, 2009, 11:41:49 pm »

Let us recall our fundamental principle and then explain our views.
We have already laid down that the outermost part of what is called
the air is potentially fire and that therefore when the air is dissolved
by motion, there is separated off a kind of matter-and of this matter
we assert that comets consist. We must suppose that what happens is
the same as in the case of the comets when the matter does not form
independently but is formed by one of the fixed stars or the planets.
Then these stars appear to be fringed, because matter of this kind
follows their course. In the same way, a certain kind of matter follows
the sun, and we explain the halo as a reflection from it when the
air is of the right constitution. Now we must assume that what happens
in the case of the stars severally happens in the case of the whole
of the heavens and all the upper motion. For it is natural to suppose
that, if the motion of a single star excites a flame, that of all
the stars should have a similar result, and especially in that region
in which the stars are biggest and most numerous and nearest to one
another. Now the circle of the zodiac dissolves this kind of matter
because of the motion of the sun and the planets, and for this reason
most comets are found outside the tropic circles. Again, no fringe
appears round the sun or moon: for they dissolve such matter too quickly
to admit of its formation. But this circle in which the milky way
appears to our sight is the greatest circle, and its position is such
that it extends far outside the tropic circles. Besides the region
is full of the biggest and brightest constellations and also of what
called 'scattered' stars (you have only to look to see this clearly).
So for these reasons all this matter is continually and ceaselessly
collecting there. A proof of the theory is this: In the circle itself
the light is stronger in that half where the milky way is divided,
and in it the constellations are more numerous and closer to one another
than in the other half; which shows that the cause of the light is
the motion of the constellations and nothing else. For if it is found
in the circle in which there are most constellations and at that point
in the circle at which they are densest and contain the biggest and
the most stars, it is natural to suppose that they are the true cause
of the affection in question. The circle and the constellations in
it may be seen in the diagram. The so-called 'scattered' stars it
is not possible to set down in the same way on the sphere because
none of them have an evident permanent position; but if you look up
to the sky the point is clear. For in this circle alone are the intervals
full of these stars: in the other circles there are obvious gaps.
Hence if we accept the cause assigned for the appearance of comets
as plausible we must assume that the same kind of thing holds good
of the milky way. For the fringe which in the former case is an affection
of a single star here forms in the same way in relation to a whole
circle. So if we are to define the milky way we may call it 'a fringe
attaching to the greatest circle, and due to the matter secreted'.
This, as we said before, explains why there are few comets and why
they appear rarely; it is because at each revolution of the heavens
this matter has always been and is always being separated off and
gathered into this region.

We have now explained the phenomena that occur in that part of the
terrestrial world which is continuous with the motions of the heavens,
namely, shooting-stars and the burning flame, comets and the milky
way, these being the chief affections that appear in that region.
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« Reply #23 on: August 30, 2009, 11:42:03 pm »

Part 9

Let us go on to treat of the region which follows next in order after
this and which immediately surrounds the earth. It is the region common
to water and air, and the processes attending the formation of water
above take place in it. We must consider the principles and causes
of all these phenomena too as before. The efficient and chief and
first cause is the circle in which the sun moves. For the sun as it
approaches or recedes, obviously causes dissipation and condensation
and so gives rise to generation and destruction. Now the earth remains
but the moisture surrounding it is made to evaporate by the sun's
rays and the other heat from above, and rises. But when the heat which
was raising it leaves it, in part dispersing to the higher region,
in part quenched through rising so far into the upper air, then the
vapour cools because its heat is gone and because the place is cold,
and condenses again and turns from air into water. And after the water
has formed it falls down again to the earth.

The exhalation of water is vapour: air condensing into water is cloud.
Mist is what is left over when a cloud condenses into water, and is
therefore rather a sign of fine weather than of rain; for mist might
be called a barren cloud. So we get a circular process that follows
the course of the sun. For according as the sun moves to this side
or that, the moisture in this process rises or falls. We must think
of it as a river flowing up and down in a circle and made up partly
of air, partly of water. When the sun is near, the stream of vapour
flows upwards; when it recedes, the stream of water flows down: and
the order of sequence, at all events, in this process always remains
the same. So if 'Oceanus' had some secret meaning in early writers,
perhaps they may have meant this river that flows in a circle about
the earth.

So the moisture is always raised by the heat and descends to the earth
again when it gets cold. These processes and, in some cases, their
varieties are distinguished by special names. When the water falls
in small drops it is called a drizzle; when the drops are larger it
is rain.
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« Reply #24 on: August 30, 2009, 11:42:17 pm »

Part 10

Some of the vapour that is formed by day does not rise high because
the ratio of the fire that is raising it to the water that is being
raised is small. When this cools and descends at night it is called
dew and hoar-frost. When the vapour is frozen before it has condensed
to water again it is hoar-frost; and this appears in winter and is
commoner in cold places. It is dew when the vapour has condensed into
water and the heat is not so great as to dry up the moisture that
has been raised nor the cold sufficient (owing to the warmth of the
climate or season) for the vapour itself to freeze. For dew is more
commonly found when the season or the place is warm, whereas the opposite,
as has been said, is the case with hoar-frost. For obviously vapour
is warmer than water, having still the fire that raised it: consequently
more cold is needed to freeze it.

Both dew and hoar-frost are found when the sky is clear and there
is no wind. For the vapour could not be raised unless the sky were
clear, and if a wind were blowing it could not condense.

The fact that hoar-frost is not found on mountains contributes to
prove that these phenomena occur because the vapour does not rise
high. One reason for this is that it rises from hollow and watery
places, so that the heat that is raising it, bearing as it were too
heavy a burden cannot lift it to a great height but soon lets it fall
again. A second reason is that the motion of the air is more pronounced
at a height, and this dissolves a gathering of this kind.

Everywhere, except in Pontus, dew is found with south winds and not
with north winds. There the opposite is the case and it is found with
north winds and not with south. The reason is the same as that which
explains why dew is found in warm weather and not in cold. For the
south wind brings warm, and the north, wintry weather. For the north
wind is cold and so quenches the heat of the evaporation. But in Pontus
the south wind does not bring warmth enough to cause evaporation,
whereas the coldness of the north wind concentrates the heat by a
sort of recoil, so that there is more evaporation and not less. This
is a thing which we can often observe in other places too. Wells,
for instance, give off more vapour in a north than in a south wind.
Only the north winds quench the heat before any considerable quantity
of vapour has gathered, while in a south wind the evaporation is allowed
to accumulate.

Water, once formed, does not freeze on the surface of the earth, in
the way that it does in the region of the clouds.
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« Reply #25 on: August 30, 2009, 11:42:34 pm »

Part 11

From the latter there fall three bodies condensed by cold, namely
rain, snow, hail. Two of these correspond to the phenomena on the
lower level and are due to the same causes, differing from them only
in degree and quantity.

Snow and hoar-frost are one and the same thing, and so are rain and
dew: only there is a great deal of the former and little of the latter.
For rain is due to the cooling of a great amount of vapour, for the
region from which and the time during which the vapour is collected
are considerable. But of dew there is little: for the vapour collects
for it in a single day and from a small area, as its quick formation
and scanty quantity show.

The relation of hoar-frost and snow is the same: when cloud freezes
there is snow, when vapour freezes there is hoar-frost. Hence snow
is a sign of a cold season or country. For a great deal of heat is
still present and unless the cold were overpowering it the cloud would
not freeze. For there still survives in it a great deal of the heat
which caused the moisture to rise as vapour from the earth.

Hail on the other hand is found in the upper region, but the corresponding
phenomenon in the vaporous region near the earth is lacking. For,
as we said, to snow in the upper region corresponds hoar-frost in
the lower, and to rain in the upper region, dew in the lower. But
there is nothing here to correspond to hail in the upper region. Why
this is so will be clear when we have explained the nature of hail.
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« Reply #26 on: August 30, 2009, 11:42:53 pm »

Part 12

But we must go on to collect the facts bearing on the origin of it,
both those which raise no difficulties and those which seem paradoxical.

Hail is ice, and water freezes in winter; yet hailstorms occur chiefly
in spring and autumn and less often in the late summer, but rarely
in winter and then only when the cold is less intense. And in general
hailstorms occur in warmer, and snow in colder places. Again, there
is a difficulty about water freezing in the upper region. It cannot
have frozen before becoming water: and water cannot remain suspended
in the air for any space of time. Nor can we say that the case is
like that of particles of moisture which are carried up owing to their
small size and rest on the iar (the water swimming on the air just
as small particles of earth and gold often swim on water). In that
case large drops are formed by the union of many small, and so fall
down. This cannot take place in the case of hail, since solid bodies
cannot coalesce like liquid ones. Clearly then drops of that size
were suspended in the air or else they could not have been so large
when frozen.
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« Reply #27 on: August 30, 2009, 11:43:10 pm »

Some think that the cause and origin of hail is this. The cloud is
thrust up into the upper atmosphere, which is colder because the reflection
of the sun's rays from the earth ceases there, and upon its arrival
there the water freezes. They think that this explains why hailstorms
are commoner in summer and in warm countries; the heat is greater
and it thrusts the clouds further up from the earth. But the fact
is that hail does not occur at all at a great height: yet it ought
to do so, on their theory, just as we see that snow falls most on
high mountains. Again clouds have often been observed moving with
a great noise close to the earth, terrifying those who heard and saw
them as portents of some catastrophe. Sometimes, too, when such clouds
have been seen, without any noise, there follows a violent hailstorm,
and the stones are of incredible size, and angular in shape. This
shows that they have not been falling for long and that they were
frozen near to the earth, and not as that theory would have it. Moreover,
where the hailstones are large, the cause of their freezing must be
present in the highest degree: for hail is ice as every one can see.
Now those hailstones are large which are angular in shape. And this
shows that they froze close to the earth, for those that fall far
are worn away by the length of their fall and become round and smaller
in size.

It clearly follows that the congelation does not take place because
the cloud is thrust up into the cold upper region.
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« Reply #28 on: August 30, 2009, 11:43:25 pm »

Now we see that warm and cold react upon one another by recoil. Hence
in warm weather the lower parts of the earth are cold and in a frost
they are warm. The same thing, we must suppose, happens in the air,
so that in the warmer seasons the cold is concentrated by the surrounding
heat and causes the cloud to go over into water suddenly. (For this
reason rain-drops are much larger on warm days than in winter, and
showers more violent. A shower is said to be more violent in proportion
as the water comes down in a body, and this happens when the condensation
takes place quickly,-though this is just the opposite of what Anaxagoras
says. He says that this happens when the cloud has risen into the
cold air; whereas we say that it happens when the cloud has descended
into the warm air, and that the more the further the cloud has descended).
But when the cold has been concentrated within still more by the outer
heat, it freezes the water it has formed and there is hail. We get
hail when the process of freezing is quicker than the descent of the
water. For if the water falls in a certain time and the cold is sufficient
to freeze it in less, there is no difficulty about its having frozen
in the air, provided that the freezing takes place in a shorter time
than its fall. The nearer to the earth, and the more suddenly, this
process takes place, the more violent is the rain that results and
the larger the raindrops and the hailstones because of the shortness
of their fall. For the same reason large raindrops do not fall thickly.
Hail is rarer in summer than in spring and autumn, though commoner
than in winter, because the air is drier in summer, whereas in spring
it is still moist, and in autumn it is beginning to grow moist. It
is for the same reason that hailstorms sometimes occur in the late
summer as we have said.

The fact that the water has previously been warmed contributes to
its freezing quickly: for so it cools sooner. Hence many people, when
they want to cool hot water quickly, begin by putting it in the sun.
So the inhabitants of Pontus when they encamp on the ice to fish (they
cut a hole in the ice and then fish) pour warm water round their reeds
that it may freeze the quicker, for they use the ice like lead to
fix the reeds. Now it is in hot countries and seasons that the water
which forms soon grows warm.
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« Reply #29 on: August 30, 2009, 11:43:38 pm »

It is for the same reason that rain falls in summer and not in winter
in Arabia and Ethiopia too, and that in torrents and repeatedly on
the same day. For the concentration or recoil due to the extreme heat
of the country cools the clouds quickly.

So much for an account of the nature and causes of rain, dew, snow,
hoar-frost, and hail.

Part 13

Let us explain the nature of winds, and all windy vapours, also of
rivers and of the sea. But here, too, we must first discuss the difficulties
involved: for, as in other matters, so in this no theory has been
handed down to us that the most ordinary man could not have thought

Some say that what is called air, when it is in motion and flows,
is wind, and that this same air when it condenses again becomes cloud
and water, implying that the nature of wind and water is the same.
So they define wind as a motion of the air. Hence some, wishing to
say a clever thing, assert that all the winds are one wind, because
the air that moves is in fact all of it one and the same; they maintain
that the winds appear to differ owing to the region from which the
air may happen to flow on each occasion, but really do not differ
at all. This is just like thinking that all rivers are one and the
same river, and the ordinary unscientific view is better than a scientific
theory like this. If all rivers flow from one source, and the same
is true in the case of the winds, there might be some truth in this
theory; but if it is no more true in the one case than in the other,
this ingenious idea is plainly false. What requires investigation
is this: the nature of wind and how it originates, its efficient cause
and whence they derive their source; whether one ought to think of
the wind as issuing from a sort of vessel and flowing until the vessel
is empty, as if let out of a wineskin, or, as painters represent the
winds, as drawing their source from themselves.
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