Atlantis Online
July 10, 2020, 10:40:43 pm
Welcome, Guest. Please login or register.

Login with username, password and session length
  Home Help Arcade Gallery Links Staff List Calendar Login Register  

Meteorology By Aristotle

Pages: 1 2 3 4 [5] 6 7 8   Go Down
Author Topic: Meteorology By Aristotle  (Read 1439 times)
Hero Member
Posts: 141

« Reply #60 on: August 30, 2009, 11:51:33 pm »

Hurricanes are commonest in autumn, and next in spring: Aparctias,
Thrascias, and Argestes give rise to them most. This is because hurricanes
are generally formed when some winds are blowing and others fall on
them; and these are the winds which are most apt to fall on others
that are blowing; the reason for which, too, we have explained before.

The Etesiae veer round: they begin from the north, and become for
dwellers in the west Thrasciae, Argestae, and Zephyrus (for Zephyrus
belongs to the north). For dwellers in the east they veer round as
far as Apeliotes.

So much for the winds, their origin and nature and the properties
common to them all or peculiar to each.

Part 7

We must go on to discuss earthquakes next, for their cause is akin
to our last subject.

The theories that have been put forward up to the present date are
three, and their authors three men, Anaxagoras of Clazomenae, and
before him Anaximenes of Miletus, and later Democritus of Abdera.

Anaxagoras says that the ether, which naturally moves upwards, is
caught in hollows below the earth and so shakes it, for though the
earth is really all of it equally porous, its surface is clogged up
by rain. This implies that part of the whole sphere is 'above' and
part 'below': 'above' being the part on which we live, 'below' the
Report Spam   Logged
Hero Member
Posts: 141

« Reply #61 on: August 30, 2009, 11:51:51 pm »

This theory is perhaps too primitive to require refutation. It is
absurd to think of up and down otherwise than as meaning that heavy
bodies move to the earth from every quarter, and light ones, such
as fire, away from it; especially as we see that, as far as our knowledge
of the earth goes, the horizon always changes with a change in our
position, which proves that the earth is convex and spherical. It
is absurd, too, to maintain that the earth rests on the air because
of its size, and then to say that impact upwards from below shakes
it right through. Besides he gives no account of the circumstances
attendant on earthquakes: for not every country or every season is
subject to them.

Democritus says that the earth is full of water and that when a quantity
of rain-water is added to this an earthquake is the result. The hollows
in the earth being unable to admit the excess of water it forces its
way in and so causes an earthquake. Or again, the earth as it dries
draws the water from the fuller to the emptier parts, and the inrush
of the water as it changes its place causes the earthquake.

Anaximenes says that the earth breaks up when it grows wet or dry,
and earthquakes are due to the fall of these masses as they break
away. Hence earthquakes take place in times of drought and again of
heavy rain, since, as we have explained, the earth grows dry in time
of drought and breaks up, whereas the rain makes it sodden and destroys
its cohesion.

But if this were the case the earth ought to be found to be sinking
in many places. Again, why do earthquakes frequently occur in places
which are not excessively subject to drought or rain, as they ought
to be on the theory? Besides, on this view, earthquakes ought always
to be getting fewer, and should come to an end entirely some day:
the notion of contraction by packing together implies this. So this
is impossible the theory must be impossible too.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #62 on: August 30, 2009, 11:52:18 pm »

Part 8

We have already shown that wet and dry must both give rise to an evaporation:
earthquakes are a necessary consequence of this fact. The earth is
essentially dry, but rain fills it with moisture. Then the sun and
its own fire warm it and give rise to a quantity of wind both outside
and inside it. This wind sometimes flows outwards in a single body,
sometimes inwards, and sometimes it is divided. All these are necessary
laws. Next we must find out what body has the greatest motive force.
This will certainly be the body that naturally moves farthest and
is most violent. Now that which has the most rapid motion is necessarily
the most violent; for its swiftness gives its impact the greatest
force. Again, the rarest body, that which can most readily pass through
every other body, is that which naturally moves farthest. Wind satisfies
these conditions in the highest degree (fire only becomes flame and
moves rapidly when wind accompanies it): so that not water nor earth
is the cause of earthquakes but wind-that is, the inrush of the external
evaporation into the earth.

Hence, since the evaporation generally follows in a continuous body
in the direction in which it first started, and either all of it flows
inwards or all outwards, most earthquakes and the greatest are accompanied
by calm. It is true that some take place when a wind is blowing, but
this presents no difficulty. We sometimes find several winds blowing
simultaneously. If one of these enters the earth we get an earthquake
attended by wind. Only these earthquakes are less severe because their
source and cause is divided.

Again, most earthquakes and the severest occur at night or, if by
day, about noon, that being generally the calmest part of the day.
For when the sun exerts its full power (as it does about noon) it
shuts the evaporation into the earth. Night, too, is calmer than day.
The absence of the sun makes the evaporation return into the earth
like a sort of ebb tide, corresponding to the outward flow; especially
towards dawn, for the winds, as a rule, begin to blow then, and if
their source changes about like the Euripus and flows inwards the
quantity of wind in the earth is greater and a more violent earthquake
Report Spam   Logged
Hero Member
Posts: 141

« Reply #63 on: August 30, 2009, 11:52:35 pm »

The severest earthquakes take place where the sea is full of currents
or the earth spongy and cavernous: so they occur near the Hellespont
and in Achaea and Sicily, and those parts of Euboea which correspond
to our description-where the sea is supposed to flow in channels below
the earth. The hot springs, too, near Aedepsus are due to a cause
of this kind. It is the confined character of these places that makes
them so liable to earthquakes. A great and therefore violent wind
is developed, which would naturally blow away from the earth: but
the onrush of the sea in a great mass thrusts it back into the earth.
The countries that are spongy below the surface are exposed to earthquakes
because they have room for so much wind.

For the same reason earthquakes usually take place in spring and autumn
and in times of wet and of drought-because these are the windiest
seasons. Summer with its heat and winter with its frost cause calm:
winter is too cold, summer too dry for winds to form. In time of drought
the air is full of wind; drought is just the predominance of the dry
over the moist evaporation. Again, excessive rain causes more of the
evaporation to form in the earth. Then this secretion is shut up in
a narrow compass and forced into a smaller space by the water that
fills the cavities. Thus a great wind is compressed into a smaller
space and so gets the upper hand, and then breaks out and beats against
the earth and shakes it violently.

We must suppose the action of the wind in the earth to be analogous
to the tremors and throbbings caused in us by the force of the wind
contained in our bodies. Thus some earthquakes are a sort of tremor,
others a sort of throbbing. Again, we must think of an earthquake
as something like the tremor that often runs through the body after
passing water as the wind returns inwards from without in one volume.

The force wind can have may be gathered not only from what happens
in the air (where one might suppose that it owed its power to produce
such effects to its volume), but also from what is observed in animal
bodies. Tetanus and spasms are motions of wind, and their force is
such that the united efforts of many men do not succeed in overcoming
the movements of the patients. We must suppose, then (to compare great
things with small), that what happens in the earth is just like that.
Our theory has been verified by actual observation in many places.
It has been known to happen that an earthquake has continued until
the wind that caused it burst through the earth into the air and appeared
visibly like a hurricane. This happened lately near Heracleia in Pontus
and some time past at the island Hiera, one of the group called the
Aeolian islands. Here a portion of the earth swelled up and a lump
like a mound rose with a noise: finally it burst, and a great wind
came out of it and threw up live cinders and ashes which buried the
neighbouring town of Lipara and reached some of the towns in Italy.
The spot where this eruption occurred is still to be seen.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #64 on: August 30, 2009, 11:52:48 pm »

Indeed, this must be recognized as the cause of the fire that is generated
in the earth: the air is first broken up in small particles and then
the wind is beaten about and so catches fire.

A phenomenon in these islands affords further evidence of the fact
that winds move below the surface of the earth. When a south wind
is going to blow there is a premonitory indication: a sound is heard
in the places from which the eruptions issue. This is because the
sea is being pushed on from a distance and its advance thrusts back
into the earth the wind that was issuing from it. The reason why there
is a noise and no earthquake is that the underground spaces are so
extensive in proportion to the quantity of the air that is being driven
on that the wind slips away into the void beyond.

Again, our theory is supported by the facts that the sun appears hazy
and is darkened in the absence of clouds, and that there is sometimes
calm and sharp frost before earthquakes at sunrise. The sun is necessarily
obscured and darkened when the evaporation which dissolves and rarefies
the air begins to withdraw into the earth. The calm, too, and the
cold towards sunrise and dawn follow from the theory. The calm we
have already explained. There must as a rule be calm because the wind
flows back into the earth: again, it must be most marked before the
more violent earthquakes, for when the wind is not part outside earth,
part inside, but moves in a single body, its strength must be greater.
The cold comes because the evaporation which is naturally and essentially
hot enters the earth. (Wind is not recognized to be hot, because it
sets the air in motion, and that is full of a quantity of cold vapour.
It is the same with the breath we blow from our mouth: close by it
is warm, as it is when we breathe out through the mouth, but there
is so little of it that it is scarcely noticed, whereas at a distance
it is cold for the same reason as wind.) Well, when this evaporation
disappears into the earth the vaporous exhalation concentrates and
causes cold in any place in which this disappearance occurs.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #65 on: August 30, 2009, 11:53:04 pm »

A sign which sometimes precedes earthquakes can be explained in the
same way. Either by day or a little after sunset, in fine weather,
a little, light, long-drawn cloud is seen, like a long very straight
line. This is because the wind is leaving the air and dying down.
Something analogous to this happens on the sea-shore. When the sea
breaks in great waves the marks left on the sand are very thick and
crooked, but when the sea is calm they are slight and straight (because
the secretion is small). As the sea is to the shore so the wind is
to the cloudy air; so, when the wind drops, this very straight and
thin cloud is left, a sort of wave-mark in the air.

An earthquake sometimes coincides with an eclipse of the moon for
the same reason. When the earth is on the point of being interposed,
but the light and heat of the sun has not quite vanished from the
air but is dying away, the wind which causes the earthquake before
the eclipse, turns off into the earth, and calm ensues. For there
often are winds before eclipses: at nightfall if the eclipse is at
midnight, and at midnight if the eclipse is at dawn. They are caused
by the lessening of the warmth from the moon when its sphere approaches
the point at which the eclipse is going to take place. So the influence
which restrained and quieted the air weakens and the air moves again
and a wind rises, and does so later, the later the eclipse.

A severe earthquake does not stop at once or after a single shock,
but first the shocks go on, often for about forty days; after that,
for one or even two years it gives premonitory indications in the
same place. The severity of the earthquake is determined by the quantity
of wind and the shape of the passages through which it flows. Where
it is beaten back and cannot easily find its way out the shocks are
most violent, and there it must remain in a cramped space like water
that cannot escape. Any throbbing in the body does not cease suddenly
or quickly, but by degrees according as the affection passes off.
So here the agency which created the evaporation and gave it an impulse
to motion clearly does not at once exhaust the whole of the material
from which it forms the wind which we call an earthquake. So until
the rest of this is exhausted the shocks must continue, though more
gently, and they must go on until there is too little of the evaporation
left to have any perceptible effect on the earth at all.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #66 on: August 30, 2009, 11:53:30 pm »

Subterranean noises, too, are due to the wind; sometimes they portend
earthquakes but sometimes they have been heard without any earthquake
following. Just as the air gives off various sounds when it is struck,
so it does when it strikes other things; for striking involves being
struck and so the two cases are the same. The sound precedes the shock
because sound is thinner and passes through things more readily than
wind. But when the wind is too weak by reason of thinness to cause
an earthquake the absence of a shock is due to its filtering through
readily, though by striking hard and hollow masses of different shapes
it makes various noises, so that the earth sometimes seems to 'bellow'
as the portentmongers say.

Water has been known to burst out during an earthquake. But that does
not make water the cause of the earthquake. The wind is the efficient
cause whether it drives the water along the surface or up from below:
just as winds are the causes of waves and not waves of winds. Else
we might as well say that earth was the cause; for it is upset in
an earthquake, just like water (for effusion is a form of upsetting).
No, earth and water are material causes (being patients, not agents):
the true cause is the wind.

The combination of a tidal wave with an earthquake is due to the presence
of contrary winds. It occurs when the wind which is shaking the earth
does not entirely succeed in driving off the sea which another wind
is bringing on, but pushes it back and heaps it up in a great mass
in one place. Given this situation it follows that when this wind
gives way the whole body of the sea, driven on by the other wind,
will burst out and overwhelm the land. This is what happened in Achaea.
There a south wind was blowing, but outside a north wind; then there
was a calm and the wind entered the earth, and then the tidal wave
came on and simultaneously there was an earthquake. This was the more
violent as the sea allowed no exit to the wind that had entered the
earth, but shut it in. So in their struggle with one another the wind
caused the earthquake, and the wave by its settling down the inundation.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #67 on: August 31, 2009, 12:01:14 am »

Earthquakes are local and often affect a small district only; whereas
winds are not local. Such phenomena are local when the evaporations
at a given place are joined by those from the next and unite; this,
as we explained, is what happens when there is drought or excessive
rain locally. Now earthquakes do come about in this way but winds
do not. For earthquakes, rains, and droughts have their source and
origin inside the earth, so that the sun is not equally able to direct
all the evaporations in one direction. But on the evaporations in
the air the sun has more influence so that, when once they have been
given an impulse by its motion, which is determined by its various
positions, they flow in one direction.

When the wind is present in sufficient quantity there is an earthquake.
The shocks are horizontal like a tremor; except occasionally, in a
few places, where they act vertically, upwards from below, like a
throbbing. It is the vertical direction which makes this kind of earthquake
so rare. The motive force does not easily accumulate in great quantity
in the position required, since the surface of the earth secretes
far more of the evaporation than its depths. Wherever an earthquake
of this kind does occur a quantity of stones comes to the surface
of the earth (as when you throw up things in a winnowing fan), as
we see from Sipylus and the Phlegraean plain and the district in Liguria,
which were devastated by this kind of earthquake.

Islands in the middle of the sea are less exposed to earthquakes than
those near land. First, the volume of the sea cools the evaporations
and overpowers them by its weight and so crushes them. Then, currents
and not shocks are produced in the sea by the action of the winds.
Again, it is so extensive that evaporations do not collect in it but
issue from it, and these draw the evaporations from the earth after
them. Islands near the continent really form part of it: the intervening
sea is not enough to make any difference; but those in the open sea
can only be shaken if the whole of the sea that surrounds them is
shaken too.

We have now explained earthquakes, their nature and cause, and the
most important of the circumstances attendant on their appearance.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #68 on: August 31, 2009, 12:01:33 am »

Part 9

Let us go on to explain lightning and thunder, and further whirlwind,
fire-wind, and thunderbolts: for the cause of them all is the same.

As we have said, there are two kinds of exhalation, moist and dry,
and the atmosphere contains them both potentially. It, as we have
said before, condenses into cloud, and the density of the clouds is
highest at their upper limit. (For they must be denser and colder
on the side where the heat escapes to the upper region and leaves
them. This explains why hurricanes and thunderbolts and all analogous
phenomena move downwards in spite of the fact that everything hot
has a natural tendency upwards. Just as the pips that we squeeze between
our fingers are heavy but often jump upwards: so these things are
necessarily squeezed out away from the densest part of the cloud.)
Now the heat that escapes disperses to the up region. But if any of
the dry exhalation is caught in the process as the air cools, it is
squeezed out as the clouds contract, and collides in its rapid course
with the neighbouring clouds, and the sound of this collision is what
we call thunder. This collision is analogous, to compare small with
great, to the sound we hear in a flame which men call the laughter
or the threat of Hephaestus or of Hestia. This occurs when the wood
dries and cracks and the exhalation rushes on the flame in a body.
So in the clouds, the exhalation is projected and its impact on dense
clouds causes thunder: the variety of the sound is due to the irregularity
of the clouds and the hollows that intervene where their density is
interrupted. This then, is thunder, and this its cause.

It usually happens that the exhalation that is ejected is inflamed
and burns with a thin and faint fire: this is what we call lightning,
where we see as it were the exhalation coloured in the act of its
ejection. It comes into existence after the collision and the thunder,
though we see it earlier because sight is quicker than hearing. The
rowing of triremes illustrates this: the oars are going back again
before the sound of their striking the water reaches us.

However, there are some who maintain that there is actually fire in
the clouds. Empedocles says that it consists of some of the sun's
rays which are intercepted: Anaxagoras that it is part of the upper
ether (which he calls fire) which has descended from above. Lightning,
then, is the gleam of this fire, and thunder the hissing noise of
its extinction in the cloud.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #69 on: August 31, 2009, 12:01:49 am »

But this involves the view that lightning actually is prior to thunder
and does not merely appear to be so. Again, this intercepting of the
fire is impossible on either theory, but especially it is said to
be drawn down from the upper ether. Some reason ought to be given
why that which naturally ascends should descend, and why it should
not always do so, but only when it is cloudy. When the sky is clear
there is no lightning: to say that there is, is altogether wanton.

The view that the heat of the sun's rays intercepted in the clouds
is the cause of these phenomena is equally unattractive: this, too,
is a most careless explanation. Thunder, lightning, and the rest must
have a separate and determinate cause assigned to them on which they
ensue. But this theory does nothing of the sort. It is like supposing
that water, snow, and hail existed all along and were produced when
the time came and not generated at all, as if the atmosphere brought
each to hand out of its stock from time to time. They are concretions
in the same way as thunder and lightning are discretions, so that
if it is true of either that they are not generated but pre-exist,
the same must be true of the other. Again, how can any distinction
be made about the intercepting between this case and that of interception
in denser substances such as water? Water, too, is heated by the sun
and by fire: yet when it contracts again and grows cold and freezes
no such ejection as they describe occurs, though it ought on their
the. to take place on a proportionate scale. Boiling is due to the
exhalation generated by fire: but it is impossible for it to exist
in the water beforehand; and besides they call the noise 'hissing',
not 'boiling'. But hissing is really boiling on a small scale: for
when that which is brought into contact with moisture and is in process
of being extinguished gets the better of it, then it boils and makes
the noise in question. Some-Cleidemus is one of them-say that lightning
is nothing objective but merely an appearance. They compare it to
what happens when you strike the sea with a rod by night and the water
is seen to shine. They say that the moisture in the cloud is beaten
about in the same way, and that lightning is the appearance of brightness
that ensues.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #70 on: August 31, 2009, 12:02:08 am »

This theory is due to ignorance of the theory of reflection, which
is the real cause of that phenomenon. The water appears to shine when
struck because our sight is reflected from it to some bright object:
hence the phenomenon occurs mainly by night: the appearance is not
seen by day because the daylight is too in, tense and obscures it.

These are the theories of others about thunder and lightning: some
maintaining that lightning is a reflection, the others that lightning
is fire shining through the cloud and thunder its extinction, the
fire not being generated in each case but existing beforehand. We
say that the same stuff is wind on the earth, and earthquake under
it, and in the clouds thunder. The essential constituent of all these
phenomena is the same: namely, the dry exhalation. If it flows in
one direction it is wind, in another it causes earthquakes; in the
clouds, when they are in a process of change and contract and condense
into water, it is ejected and causes thunder and lightning and the
other phenomena of the same nature.

So much for thunder and lightning.

Report Spam   Logged
Hero Member
Posts: 141

« Reply #71 on: August 31, 2009, 12:02:22 am »


Part 1

Let us explain the remaining operations of this secretion in the
same way as we have treated the rest. When this exhalation is secreted
in small and scattered quantities and frequently, and is transitory,
and its constitution rare, it gives rise to thunder and lightning.
But if it is secreted in a body and is denser, that is, less rare,
we get a hurricane. The fact that it issues in body explains its violence:
it is due to the rapidity of the secretion. Now when this secretion
issues in a great and continuous current the result corresponds to
what we get when the opposite development takes place and rain and
a quantity of water are produced. As far as the matter from which
they are developed goes both sets of phenomena are the same. As soon
as a stimulus to the development of either potentiality appears, that
of which there is the greater quantity present in the cloud is at
once secreted from it, and there results either rain, or, if the other
exhalation prevails, a hurricane.

Sometimes the exhalation in the cloud, when it is being secreted,
collides with another under circumstances like those found when a
wind is forced from an open into a narrow space in a gateway or a
road. It often happens in such cases that the first part of the moving
body is deflected because of the resistance due either to the narrowness
or to a contrary current, and so the wind forms a circle and eddy.
It is prevented from advancing in a straight line: at the same time
it is pushed on from behind; so it is compelled to move sideways in
the direction of least resistance. The same thing happens to the next
part, and the next, and so on, till the series becomes one, that is,
till a circle is formed: for if a figure is described by a single
motion that figure must itself be one. This is how eddies are generated
on the earth, and the case is the same in the clouds as far as the
beginning of them goes. Only here (as in the case of the hurricane
which shakes off the cloud without cessation and becomes a continuous
wind) the cloud follows the exhalation unbroken, and the exhalation,
failing to break away from the cloud because of its density, first
moves in a circle for the reason given and then descends, because
clouds are always densest on the side where the heat escapes. This
phenomenon is called a whirlwind when it is colourless; and it is
a sort of undigested hurricane. There is never a whirlwind when the
weather is northerly, nor a hurricane when there is snow. The reason
is that all these phenomena are 'wind', and wind is a dry and warm
evaporation. Now frost and cold prevail over this principle and quench
it at its birth: that they do prevail is clear or there could be no
snow or northerly rain, since these occur when the cold does prevail.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #72 on: August 31, 2009, 12:02:48 am »

So the whirlwind originates in the failure of an incipient hurricane
to escape from its cloud: it is due to the resistance which generates
the eddy, and it consists in the spiral which descends to the earth
and drags with it the cloud which it cannot shake off. It moves things
by its wind in the direction in which it is blowing in a straight
line, and whirls round by its circular motion and forcibly snatches
up whatever it meets.

When the cloud burns as it is drawn downwards, that is, when the exhalation
becomes rarer, it is called a fire-wind, for its fire colours the
neighbouring air and inflames it.

When there is a great quantity of exhalation and it is rare and is
squeezed out in the cloud itself we get a thunderbolt. If the exhalation
is exceedingly rare this rareness prevents the thunderbolt from scorching
and the poets call it 'bright': if the rareness is less it does scorch
and they call it 'smoky'. The former moves rapidly because of its
rareness, and because of its rapidity passes through an object before
setting fire to it or dwelling on it so as to blacken it: the slower
one does blacken the object, but passes through it before it can actually
burn it. Further, resisting substances are affected, unresisting ones
are not. For instance, it has happened that the bronze of a shield
has been melted while the woodwork remained intact because its texture
was so loose that the exhalation filtered through without affecting
it. So it has passed through clothes, too, without burning them, and
has merely reduced them to shreds.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #73 on: August 31, 2009, 12:03:02 am »

Such evidence is enough by itself to show that the exhalation is at
work in all these cases, but we sometimes get direct evidence as well,
as in the case of the conflagration of the temple at Ephesus which
we lately witnessed. There independent sheets of flame left the main
fire and were carried bodily in many directions. Now that smoke is
exhalation and that smoke burns is certain, and has been stated in
another place before; but when the flame moves bodily, then we have
ocular proof that smoke is exhalation. On this occasion what is seen
in small fires appeared on a much larger scale because of the quantity
of matter that was burning. The beams which were the source of the
exhalation split, and a quantity of it rushed in a body from the place
from which it issued forth and went up in a blaze: so that the flame
was actually seen moving through the air away and falling on the houses.
For we must recognize that exhalation accompanies and precedes thunderbolts
though it is colourless and so invisible. Hence, where the thunderbolt
is going to strike, the object moves before it is struck, showing
that the exhalation leads the way and falls on the object first. Thunder,
too, splits things not by its noise but because the exhalation that
strikes the object and that which makes the noise are ejected simultaneously.
This exhalation splits the thing it strikes but does not scorch it
at all.

We have now explained thunder and lightning and hurricane, and further
firewinds, whirlwinds, and thunderbolts, and shown that they are all
of them forms of the same thing and wherein they all differ.
Report Spam   Logged
Hero Member
Posts: 141

« Reply #74 on: August 31, 2009, 12:03:16 am »

Part 2

Let us now explain the nature and cause of halo, rainbow, mock suns,
and rods, since the same account applies to them all.

We must first describe the phenomena and the circumstances in which
each of them occurs. The halo often appears as a complete circle:
it is seen round the sun and the moon and bright stars, by night as
well as by day, and at midday or in the afternoon, more rarely about
sunrise or sunset.

The rainbow never forms a full circle, nor any segment greater than
a semicircle. At sunset and sunrise the circle is smallest and the
segment largest: as the sun rises higher the circle is larger and
the segment smaller. After the autumn equinox in the shorter days
it is seen at every hour of the day, in the summer not about midday.
There are never more than two rainbows at one time. Each of them is
three-coloured; the colours are the same in both and their number
is the same, but in the outer rainbow they are fainter and their position
is reversed. In the inner rainbow the first and largest band is red;
in the outer rainbow the band that is nearest to this one and smallest
is of the same colour: the other bands correspond on the same principle.
These are almost the only colours which painters cannot manufacture:
for there are colours which they create by mixing, but no mixing will
give red, green, or purple. These are the colours of the rainbow,
though between the red and the green an orange colour is often seen.

Mock suns and rods are always seen by the side of the sun, not above
or below it nor in the opposite quarter of the sky. They are not seen
at night but always in the neighbourhood of the sun, either as it
is rising or setting but more commonly towards sunset. They have scarcely
ever appeared when the sun was on the meridian, though this once happened
in Bosporus where two mock suns rose with the sun and followed it
all through the day till sunset.

These are the facts about each of these phenomena: the cause of them
all is the same, for they are all reflections. But they are different
varieties, and are distinguished by the surface from which and the
way in which the reflection to the sun or some other bright object
takes place.
Report Spam   Logged
Pages: 1 2 3 4 [5] 6 7 8   Go Up
Jump to:  

Powered by EzPortal
Bookmark this site! | Upgrade This Forum
SMF For Free - Create your own Forum
Powered by SMF | SMF © 2016, Simple Machines
Privacy Policy