350 BC
 
 METEOROLOGY

 by Aristotle
 
 translated by E. W. Webster
 
 Book I
 
 
 
 1

  WE have already discussed the first causes of nature, and all
natural motion, also the stars ordered in the motion of the heavens,
and the physical element-enumerating and specifying them and showing
how they change into one another-and becoming and perishing in
general. There remains for consideration a part of this inquiry
which all our predecessors called meteorology. It is concerned with
events that are natural, though their order is less perfect than
that of the first of the elements of bodies. They take place in the
region nearest to the motion of the stars. Such are the milky way, and
comets, and the movements of meteors. It studies also all the
affections we may call common to air and water, and the kinds and
parts of the earth and the affections of its parts. These throw
light on the causes of winds and earthquakes and all the
consequences the motions of these kinds and parts involve. Of these
things some puzzle us, while others admit of explanation in some
degree. Further, the inquiry is concerned with the falling of
thunderbolts and with whirlwinds and fire-winds, and further, the
recurrent affections produced in these same bodies by concretion. When
the inquiry into these matters is concluded let us consider what
account we can give, in accordance with the method we have followed,
of animals and plants, both generally and in detail. When that has
been done we may say that the whole of our original undertaking will
have been carried out.

  After this introduction let us begin by discussing our immediate
subject.

                                 2

  We have already laid down that there is one physical element which
makes up the system of the bodies that move in a circle, and besides
this four bodies owing their existence to the four principles, the
motion of these latter bodies being of two kinds: either from the
centre or to the centre. These four bodies are fire, air, water,
earth. Fire occupies the highest place among them all, earth the
lowest, and two elements correspond to these in their relation to
one another, air being nearest to fire, water to earth. The whole
world surrounding the earth, then, the affections of which are our
subject, is made up of these bodies. This world necessarily has a
certain continuity with the upper motions: consequently all its
power and order is derived from them. (For the originating principle
of all motion is the first cause. Besides, that clement is eternal and
its motion has no limit in space, but is always complete; whereas
all these other bodies have separate regions which limit one another.)
So we must treat fire and earth and the elements like them as the
material causes of the events in this world (meaning by material
what is subject and is affected), but must assign causality in the
sense of the originating principle of motion to the influence of the
eternally moving bodies.

                                 3

  Let us first recall our original principles and the distinctions
already drawn and then explain the 'milky way' and comets and the
other phenomena akin to these.

  Fire, air, water, earth, we assert, originate from one another,
and each of them exists potentially in each, as all things do that can
be resolved into a common and ultimate substrate.

  The first difficulty is raised by what is called the air. What are
we to take its nature to be in the world surrounding the earth? And
what is its position relatively to the other physical elements. (For
there is no question as to the relation of the bulk of the earth to
the size of the bodies which exist around it, since astronomical
demonstrations have by this time proved to us that it is actually
far smaller than some individual stars. As for the water, it is not
observed to exist collectively and separately, nor can it do so
apart from that volume of it which has its seat about the earth: the
sea, that is, and rivers, which we can see, and any subterranean water
that may be hidden from our observation.) The question is really about
that which lies between the earth and the nearest stars. Are we to
consider it to be one kind of body or more than one? And if more
than one, how many are there and what are the bounds of their regions?

  We have already described and characterized the first element, and
explained that the whole world of the upper motions is full of that
body.

  This is an opinion we are not alone in holding: it appears to be
an old assumption and one which men have held in the past, for the
word ether has long been used to denote that element. Anaxagoras, it
is true, seems to me to think that the word means the same as fire.
For he thought that the upper regions were full of fire, and that
men referred to those regions when they spoke of ether. In the
latter point he was right, for men seem to have assumed that a body
that was eternally in motion was also divine in nature; and, as such a
body was different from any of the terrestrial elements, they
determined to call it 'ether'.

  For the um opinions appear in cycles among men not once nor twice,
but infinitely often.

  Now there are some who maintain that not only the bodies in motion
but that which contains them is pure fire, and the interval between
the earth and the stars air: but if they had considered what is now
satisfactorily established by mathematics, they might have given up
this puerile opinion. For it is altogether childish to suppose that
the moving bodies are all of them of a small size, because they so
to us, looking at them from the earth.

  This a matter which we have already discussed in our treatment of
the upper region, but we may return to the point now.

  If the intervals were full of fire and the bodies consisted of
fire every one of the other elements would long ago have vanished.

  However, they cannot simply be said to be full of air either; for
even if there were two elements to fill the space between the earth
and the heavens, the air would far exceed the quantitu required to
maintain its proper proportion to the other elements. For the bulk
of the earth (which includes the whole volume of water) is
infinitesimal in comparison with the whole world that surrounds it.
Now we find that the excess in volume is not proportionately great
where water dissolves into air or air into fire. Whereas the
proportion between any given small quantity of water and the air
that is generated from it ought to hold good between the total
amount of air and the total amount of water. Nor does it make any
difference if any one denies that the elements originate from one
another, but asserts that they are equal in power. For on this view it
is certain amounts of each that are equal in power, just as would be
the case if they actually originated from one another.

  So it is clear that neither air nor fire alone fills the
intermediate space.

  It remains to explain, after a preliminary discussion of
difficulties, the relation of the two elements air and fire to the
position of the first element, and the reason why the stars in the
upper region impart heat to the earth and its neighbourhood. Let us
first treat of the air, as we proposed, and then go on to these
questions.

  Since water is generated from air, and air from water, why are
clouds not formed in the upper air? They ought to form there the more,
the further from the earth and the colder that region is. For it is
neither appreciably near to the heat of the stars, nor to the rays
relected from the earth. It is these that dissolve any formation by
their heat and so prevent clouds from forming near the earth. For
clouds gather at the point where the reflected rays disperse in the
infinity of space and are lost. To explain this we must suppose either
that it is not all air which water is generated, or, if it is produced
from all air alike, that what immediately surrounds the earth is not
mere air, but a sort of vapour, and that its vaporous nature is the
reason why it condenses back to water again. But if the whole of
that vast region is vapour, the amount of air and of water will be
disproportionately great. For the spaces left by the heavenly bodies
must be filled by some element. This cannot be fire, for then all
the rest would have been dried up. Consequently, what fills it must be
air and the water that surrounds the whole earth-vapour being water
dissolved.

  After this exposition of the difficulties involved, let us go on
to lay down the truth, with a view at once to what follows and to what
has already been said. The upper region as far as the moon we affirm
to consist of a body distinct both from fire and from air, but varying
degree of purity and in kind, especially towards its limit on the side
of the air, and of the world surrounding the earth. Now the circular
motion of the first element and of the bodies it contains dissolves,
and inflames by its motion, whatever part of the lower world is
nearest to it, and so generates heat. From another point of view we
may look at the motion as follows. The body that lies below the
circular motion of the heavens is, in a sort, matter, and is
potentially hot, cold, dry, moist, and possessed of whatever other
qualities are derived from these. But it actually acquires or
retains one of these in virtue of motion or rest, the cause and
principle of which has already been explained. So at the centre and
round it we get earth and water, the heaviest and coldest elements, by
themselves; round them and contiguous with them, air and what we
commonly call fire. It is not really fire, for fire is an excess of
heat and a sort of ebullition; but in reality, of what we call air,
the part surrounding the earth is moist and warm, because it
contains both vapour and a dry exhalation from the earth. But the next
part, above that, is warm and dry. For vapour is naturally moist and
cold, but the exhalation warm and dry; and vapour is potentially
like water, the exhalation potentially like fire. So we must take
the reason why clouds are not formed in the upper region to be this:
that it is filled not with mere air but rather with a sort of fire.

  However, it may well be that the formation of clouds in that upper
region is also prevented by the circular motion. For the air round the
earth is necessarily all of it in motion, except that which is cut off
inside the circumference which makes the earth a complete sphere. In
the case of winds it is actually observable that they originate in
marshy districts of the earth; and they do not seem to blow above
the level of the highest mountains. It is the revolution of the heaven
which carries the air with it and causes its circular motion, fire
being continuous with the upper element and air with fire. Thus its
motion is a second reason why that air is not condensed into water.

  But whenever a particle of air grows heavy, the warmth in it is
squeezed out into the upper region and it sinks, and other particles
in turn are carried up together with the fiery exhalation. Thus the
one region is always full of air and the other of fire, and each of
them is perpetually in a state of change.

  So much to explain why clouds are not formed and why the air is
not condensed into water, and what account must be given of the
space between the stars and the earth, and what is the body that fills
it.

  As for the heat derived from the sun, the right place for a
special and scientific account of it is in the treatise about sense,
since heat is an affection of sense, but we may now explain how it can
be produced by the heavenly bodies which are not themselves hot.

  We see that motion is able to dissolve and inflame the air;
indeed, moving bodies are often actually found to melt. Now the
sun's motion alone is sufficient to account for the origin of
terrestrial warmth and heat. For a motion that is to have this
effect must be rapid and near, and that of the stars is rapid but
distant, while that of the moon is near but slow, whereas the sun's
motion combines both conditions in a sufficient degree. That most heat
should be generated where the sun is present is easy to understand
if we consider the analogy of terrestrial phenomena, for here, too, it
is the air that is nearest to a thing in rapid motion which is
heated most. This is just what we should expect, as it is the
nearest air that is most dissolved by the motion of a solid body.

  This then is one reason why heat reaches our world. Another is
that the fire surrounding the air is often scattered by the motion
of the heavens and driven downwards in spite of itself.

  Shooting-stars further suffix to prove that the celestial sphere
is not hot or fiery: for they do not occur in that upper region but
below: yet the more and the faster a thing moves, the more apt it is
to take fire. Besides, the sun, which most of all the stars is
considered to be hot, is really white and not fiery in colour.

                                 4

  Having determined these principles let us explain the cause of the
appearance in the sky of burning flames and of shooting-stars, and
of 'torches', and 'goats', as some people call them. All these
phenomena are one and the same thing, and are due to the same cause,
the difference between them being one of degree.

  The explanation of these and many other phenomena is this. When
the sun warms the earth the evaporation which takes place is
necessarily of two kinds, not of one only as some think. One kind is
rather of the nature of vapour, the other of the nature of a windy
exhalation. That which rises from the moisture contained in the
earth and on its surface is vapour, while that rising from the earth
itself, which is dry, is like smoke. Of these the windy exhalation,
being warm, rises above the moister vapour, which is heavy and sinks
below the other. Hence the world surrounding the earth is ordered as
follows. First below the circular motion comes the warm and dry
element, which we call fire, for there is no word fully adequate to
every state of the fumid evaporation: but we must use this terminology
since this element is the most inflammable of all bodies. Below this
comes air. We must think of what we just called fire as being spread
round the terrestrial sphere on the outside like a kind of fuel, so
that a little motion often makes it burst into flame just as smoke
does: for flame is the ebullition of a dry exhalation. So whenever the
circular motion stirs this stuff up in any way, it catches fire at the
point at which it is most inflammable. The result differs according to
the disposition and quantity of the combustible material. If this is
broad and long, we often see a flame burning as in a field of stubble:
if it burns lengthwise only, we see what are called 'torches' and
'goats' and shooting-stars. Now when the inflammable material is
longer than it is broad sometimes it seems to throw off sparks as it
burns. (This happens because matter catches fire at the sides in small
portions but continuously with the main body.) Then it is called a
'goat'. When this does not happen it is a 'torch'. But if the whole
length of the exhalation is scattered in small parts and in many
directions and in breadth and depth alike, we get what are called
shooting-stars.

  The cause of these shooting-stars is sometimes the motion which
ignites the exhalation. At other times the air is condensed by cold
and squeezes out and ejects the hot element; making their motion
look more like that of a thing thrown than like a running fire. For
the question might be raised whether the 'shooting' of a 'star' is the
same thing as when you put an exhalation below a lamp and it lights
the lower lamp from the flame above. For here too the flame passes
wonderfully quickly and looks like a thing thrown, and not as if one
thing after another caught fire. Or is a 'star' when it 'shoots' a
single body that is thrown? Apparently both cases occur: sometimes
it is like the flame from the lamp and sometimes bodies are
projected by being squeezed out (like fruit stones from one's fingers)
and so are seen to fall into the sea and on the dry land, both by
night and by day when the sky is clear. They are thrown downwards
because the condensation which propels them inclines downwards.
Thunderbolts fall downwards for the same reason: their origin is never
combustion but ejection under pressure, since naturally all heat tends
upwards.

  When the phenomenon is formed in the upper region it is due to the
combustion of the exhalation. When it takes place at a lower level
it is due to the ejection of the exhalation by the condensing and
cooling of the moister evaporation: for this latter as it condenses
and inclines downward contracts, and thrusts out the hot element and
causes it to be thrown downwards. The motion is upwards or downwards
or sideways according to the way in which the evaporation lies, and
its disposition in respect of breadth and depth. In most cases the
direction is sideways because two motions are involved, a compulsory
motion downwards and a natural motion upwards, and under these
circumstances an object always moves obliquely. Hence the motion of
'shooting-stars' is generally oblique.

  So the material cause of all these phenomena is the exhalation,
the efficient cause sometimes the upper motion, sometimes the
contraction and condensation of the air. Further, all these things
happen below the moon. This is shown by their apparent speed, which is
equal to that of things thrown by us; for it is because they are close
to us, that these latter seem far to exceed in speed the stars, the
sun, and the moon.

                                 5

  Sometimes on a fine night we see a variety of appearances that
form in the sky: 'chasms' for instance and 'trenches' and blood-red
colours. These, too, have the same cause. For we have seen that the
upper air condenses into an inflammable condition and that the
combustion sometimes takes on the appearance of a burning flame,
sometimes that of moving torches and stars. So it is not surprising
that this same air when condensing should assume a variety of colours.
For a weak light shining through a dense air, and the air when it acts
as a mirror, will cause all kinds of colours to appear, but especially
crimson and purple. For these colours generally appear when
fire-colour and white are combined by superposition. Thus on a hot
day, or through a smoky, medium, the stars when they rise and set look
crimson. The light will also create colours by reflection when the
mirror is such as to reflect colour only and not shape.

  These appearances do not persist long, because the condensation of
the air is transient.

  'Chasms' get their appearance of depth from light breaking out of
a dark blue or black mass of air. When the process of condensation
goes further in such a case we often find 'torches' ejected. When
the 'chasm' contracts it presents the appearance of a 'trench'.

  In general, white in contrast with black creates a variety of
colours; like flame, for instance, through a medium of smoke. But by
day the sun obscures them, and, with the exception of crimson, the
colours are not seen at night because they are dark.

  These then must be taken to be the causes of 'shooting-stars' and
the phenomena of combustion and also of the other transient
appearances of this kind.

                                 6

  Let us go on to explain the nature of comets and the 'milky way',
after a preliminary discussion of the views of others.

  Anaxagoras and Democritus declare that comets are a conjunction of
the planets approaching one another and so appearing to touch one
another.

  Some of the Italians called Pythagoreans say that the comet is one
of the planets, but that it appears at great intervals of time and
only rises a little above the horizon. This is the case with Mercury
too; because it only rises a little above the horizon it often fails
to be seen and consequently appears at great intervals of time.

  A view like theirs was also expressed by Hippocrates of Chios and
his pupil Aeschylus. Only they say that the tail does not belong to
the comet iself, but is occasionally assumed by it on its course in
certain situations, when our sight is reflected to the sun from the
moisture attracted by the comet. It appears at greater intervals
than the other stars because it is slowest to get clear of the sun and
has been left behind by the sun to the extent of the whole of its
circle before it reappears at the same point. It gets clear of the sun
both towards the north and towards the south. In the space between the
tropics it does not draw water to itself because that region is
dried up by the sun on its course. When it moves towards the south
it has no lack of the necessary moisture, but because the segment of
its circle which is above the horizon is small, and that below it many
times as large, it is impossible for the sun to be reflected to our
sight, either when it approaches the southern tropic, or at the summer
solstice. Hence in these regions it does not develop a tail at all.
But when it is visible in the north it assumes a tail because the
arc above the horizon is large and that below it small. For under
these circumstances there is nothing to prevent our vision from
being reflected to the sun.

  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.

  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.

                                 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.

  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.

  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.

                                 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.

  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.

  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.

                                 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.

                                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.

                                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.

                                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.

  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.

  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.

  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.

                                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 of.

  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.

  We find analogous views about the origin of rivers. It is thought
that the water is raised by the sun and descends in rain and gathers
below the earth and so flows from a great reservoir, all the rivers
from one, or each from a different one. No water at all is
generated, but the volume of the rivers consists of the water that
is gathered into such reservoirs in winter. Hence rivers are always
fuller in winter than in summer, and some are perennial, others not.
Rivers are perennial where the reservoir is large and so enough
water has collected in it to last out and not be used up before the
winter rain returns. Where the reservoirs are smaller there is less
water in the rivers, and they are dried up and their vessel empty
before the fresh rain comes on.

  But if any one will picture to himself a reservoir adequate to the
water that is continuously flowing day by day, and consider the amount
of the water, it is obvious that a receptacle that is to contain all
the water that flows in the year would be larger than the earth, or,
at any rate, not much smaller.

  Though it is evident that many reservoirs of this kind do exist in
many parts of the earth, yet it is unreasonable for any one to
refuse to admit that air becomes water in the earth for the same
reason as it does above it. If the cold causes the vaporous air to
condense into water above the earth we must suppose the cold in the
earth to produce this same effect, and recognize that there not only
exists in it and flows out of it actually formed water, but that water
is continually forming in it too.

  Again, even in the case of the water that is not being formed from
day to day but exists as such, we must not suppose as some do that
rivers have their source in definite subterranean lakes. On the
contrary, just as above the earth small drops form and these join
others, till finally the water descends in a body as rain, so too we
must suppose that in the earth the water at first trickles together
little by little, and that the sources of the rivers drip, as it were,
out of the earth and then unite. This is proved by facts. When men
construct an aqueduct they collect the water in pipes and trenches, as
if the earth in the higher ground were sweating the water out.
Hence, too, the head-waters of rivers are found to flow from
mountains, and from the greatest mountains there flow the most
numerous and greatest rivers. Again, most springs are in the
neighbourhood of mountains and of high ground, whereas if we except
rivers, water rarely appears in the plains. For mountains and high
ground, suspended over the country like a saturated sponge, make the
water ooze out and trickle together in minute quantities but in many
places. They receive a great deal of water falling as rain (for it
makes no difference whether a spongy receptacle is concave and
turned up or convex and turned down: in either case it will contain
the same volume of matter) and, they also cool the vapour that rises
and condense it back into water.

  Hence, as we said, we find that the greatest rivers flow from the
greatest mountains. This can be seen by looking at itineraries: what
is recorded in them consists either of things which the writer has
seen himself or of such as he has compiled after inquiry from those
who have seen them.

  In Asia we find that the most numerous and greatest rivers flow from
the mountain called Parnassus, admittedly the greatest of all
mountains towards the south-east. When you have crossed it you see the
outer ocean, the further limit of which is unknown to the dwellers
in our world. Besides other rivers there flow from it the Bactrus, the
Choaspes, the Araxes: from the last a branch separates off and flows
into lake Maeotis as the Tanais. From it, too, flows the Indus, the
volume of whose stream is greatest of all rivers. From the Caucasus
flows the Phasis, and very many other great rivers besides. Now the
Caucasus is the greatest of the mountains that lie to the northeast,
both as regards its extent and its height. A proof of its height is
the fact that it can be seen from the so-called 'deeps' and from the
entrance to the lake. Again, the sun shines on its peaks for a third
part of the night before sunrise and again after sunset. Its extent is
proved by the fact that thought contains many inhabitable regions
which are occupied by many nations and in which there are said to be
great lakes, yet they say that all these regions are visible up to the
last peak. From Pyrene (this is a mountain towards the west in
Celtice) there flow the Istrus and the Tartessus. The latter flows
outside the pillars, while the Istrus flows through all Europe into
the Euxine. Most of the remaining rivers flow northwards from the
Hercynian mountains, which are the greatest in height and extent about
that region. In the extreme north, beyond furthest Scythia, are the
mountains called Rhipae. The stories about their size are altogether
too fabulous: however, they say that the most and (after the Istrus)
the greatest rivers flow from them. So, too, in Libya there flow
from the Aethiopian mountains the Aegon and the Nyses; and from the
so-called Silver Mountain the two greatest of named rivers, the
river called Chremetes that flows into the outer ocean, and the main
source of the Nile. Of the rivers in the Greek world, the Achelous
flows from Pindus, the Inachus from the same mountain; the Strymon,
the Nestus, and the Hebrus all three from Scombrus; many rivers,
too, flow from Rhodope.

  All other rivers would be found to flow in the same way, but we have
mentioned these as examples. Even where rivers flow from marshes,
the marshes in almost every case are found to lie below mountains or
gradually rising ground.

  It is clear then that we must not suppose rivers to originate from
definite reservoirs: for the whole earth, we might almost say, would
not be sufficient (any more than the region of the clouds would be) if
we were to suppose that they were fed by actually existing water
only and it were not the case that as some water passed out of
existence some more came into existence, but rivers always drew
their stream from an existing store. Secondly, the fact that rivers
rise at the foot of mountains proves that a place transmits the
water it contains by gradual percolation of many drops, little by
little, and that this is how the sources of rivers originate. However,
there is nothing impossible about the existence of such places
containing a quantity of water like lakes: only they cannot be big
enough to produce the supposed effect. To think that they are is
just as absurd as if one were to suppose that rivers drew all their
water from the sources we see (for most rivers do flow from
springs). So it is no more reasonable to suppose those lakes to
contain the whole volume of water than these springs.

  That there exist such chasms and cavities in the earth we are taught
by the rivers that are swallowed up. They are found in many parts of
the earth: in the Peloponnesus, for instance, there are many such
rivers in Arcadia. The reason is that Arcadia is mountainous and there
are no channels from its valleys to the sea. So these places get
full of water, and this, having no outlet, under the pressure of the
water that is added above, finds a way out for itself underground.
In Greece this kind of thing happens on quite a small scale, but the
lake at the foot of the Caucasus, which the inhabitants of these parts
call a sea, is considerable. Many great rivers fall into it and it has
no visible outlet but issues below the earth off the land of the
Coraxi about the so-called 'deeps of Pontus'. This is a place of
unfathomable depth in the sea: at any rate no one has yet been able to
find bottom there by sounding. At this spot, about three hundred
stadia from land, there comes up sweet water over a large area, not
all of it together but in three places. And in Liguria a river equal
in size to the Rhodanus is swallowed up and appears again elsewhere:
the Rhodanus being a navigable river.

                                14

  The same parts of the earth are not always moist or dry, but they
change according as rivers come into existence and dry up. And so
the relation of land to sea changes too and a place does not always
remain land or sea throughout all time, but where there was dry land
there comes to be sea, and where there is now sea, there one day comes
to be dry land. But we must suppose these changes to follow some order
and cycle. The principle and cause of these changes is that the
interior of the earth grows and decays, like the bodies of plants
and animals. Only in the case of these latter the process does not
go on by parts, but each of them necessarily grows or decays as a
whole, whereas it does go on by parts in the case of the earth. Here
the causes are cold and heat, which increase and diminish on account
of the sun and its course. It is owing to them that the parts of the
earth come to have a different character, that some parts remain moist
for a certain time, and then dry up and grow old, while other parts in
their turn are filled with life and moisture. Now when places become
drier the springs necessarily give out, and when this happens the
rivers first decrease in size and then finally become dry; and when
rivers change and disappear in one part and come into existence
correspondingly in another, the sea must needs be affected.

  If the sea was once pushed out by rivers and encroached upon the
land anywhere, it necessarily leaves that place dry when it recedes;
again, if the dry land has encroached on the sea at all by a process
of silting set up by the rivers when at their full, the time must come
when this place will be flooded again.

  But the whole vital process of the earth takes place so gradually
and in periods of time which are so immense compared with the length
of our life, that these changes are not observed, and before their
course can be recorded from beginning to end whole nations perish
and are destroyed. Of such destructions the most utter and sudden
are due to wars; but pestilence or famine cause them too. Famines,
again, are either sudden and severe or else gradual. In the latter
case the disappearance of a nation is not noticed because some leave
the country while others remain; and this goes on until the land is
unable to maintain any inhabitants at all. So a long period of time is
likely to elapse from the first departure to the last, and no one
remembers and the lapse of time destroys all record even before the
last inhabitants have disappeared. In the same way a nation must be
supposed to lose account of the time when it first settled in a land
that was changing from a marshy and watery state and becoming dry.
Here, too, the change is gradual and lasts a long time and men do
not remember who came first, or when, or what the land was like when
they came. This has been the case with Egypt. Here it is obvious
that the land is continually getting drier and that the whole
country is a deposit of the river Nile. But because the neighbouring
peoples settled in the land gradually as the marshes dried, the
lapse of time has hidden the beginning of the process. However, all
the mouths of the Nile, with the single exception of that at
Canopus, are obviously artificial and not natural. And Egypt was
nothing more than what is called Thebes, as Homer, too, shows,
modern though he is in relation to such changes. For Thebes is the
place that he mentions; which implies that Memphis did not yet
exist, or at any rate was not as important as it is now. That this
should be so is natural, since the lower land came to be inhabited
later than that which lay higher. For the parts that lie nearer to the
place where the river is depositing the silt are necessarily marshy
for a longer time since the water always lies most in the newly formed
land. But in time this land changes its character, and in its turn
enjoys a period of prosperity. For these places dry up and come to
be in good condition while the places that were formerly well-tempered
some day grow excessively dry and deteriorate. This happened to the
land of Argos and Mycenae in Greece. In the time of the Trojan wars
the Argive land was marshy and could only support a small
population, whereas the land of Mycenae was in good condition (and for
this reason Mycenae was the superior). But now the opposite is the
case, for the reason we have mentioned: the land of Mycenae has become
completely dry and barren, while the Argive land that was formerly
barren owing to the water has now become fruitful. Now the same
process that has taken place in this small district must be supposed
to be going on over whole countries and on a large scale.

  Men whose outlook is narrow suppose the cause of such events to be
change in the universe, in the sense of a coming to be of the world as
a whole. Hence they say that the sea being dried up and is growing
less, because this is observed to have happened in more places now
than formerly. But this is only partially true. It is true that many
places are now dry, that formerly were covered with water. But the
opposite is true too: for if they look they will find that there are
many places where the sea has invaded the land. But we must not
suppose that the cause of this is that the world is in process of
becoming. For it is absurd to make the universe to be in process
because of small and trifling changes, when the bulk and size of the
earth are surely as nothing in comparison with the whole world. Rather
we must take the cause of all these changes to be that, just as winter
occurs in the seasons of the year, so in determined periods there
comes a great winter of a great year and with it excess of rain. But
this excess does not always occur in the same place. The deluge in the
time of Deucalion, for instance, took place chiefly in the Greek world
and in it especially about ancient Hellas, the country about Dodona
and the Achelous, a river which has often changed its course. Here the
Selli dwelt and those who were formerly called Graeci and now
Hellenes. When, therefore, such an excess of rain occurs we must
suppose that it suffices for a long time. We have seen that some say
that the size of the subterranean cavities is what makes some rivers
perennial and others not, whereas we maintain that the size of the
mountains is the cause, and their density and coldness; for great,
dense, and cold mountains catch and keep and create most water:
whereas if the mountains that overhang the sources of rivers are small
or porous and stony and clayey, these rivers run dry earlier. We
must recognize the same kind of thing in this case too. Where such
abundance of rain falls in the great winter it tends to make the
moisture of those places almost everlasting. But as time goes on
places of the latter type dry up more, while those of the former,
moist type, do so less: until at last the beginning of the same
cycle returns.

  Since there is necessarily some change in the whole world, but not
in the way of coming into existence or perishing (for the universe
is permanent), it must be, as we say, that the same places are not for
ever moist through the presence of sea and rivers, nor for ever dry.
And the facts prove this. The whole land of the Egyptians, whom we
take to be the most ancient of men, has evidently gradually come
into existence and been produced by the river. This is clear from an
observation of the country, and the facts about the Red Sea suffice to
prove it too. One of their kings tried to make a canal to it (for it
would have been of no little advantage to them for the whole region to
have become navigable; Sesostris is said to have been the first of the
ancient kings to try), but he found that the sea was higher than the
land. So he first, and Darius afterwards, stopped making the canal,
lest the sea should mix with the river water and spoil it. So it is
clear that all this part was once unbroken sea. For the same reason
Libya-the country of Ammon-is, strangely enough, lower and hollower
than the land to the seaward of it. For it is clear that a barrier
of silt was formed and after it lakes and dry land, but in course of
time the water that was left behind in the lakes dried up and is now
all gone. Again the silting up of the lake Maeotis by the rivers has
advanced so much that the limit to the size of the ships which can now
sail into it to trade is much lower than it was sixty years ago. Hence
it is easy to infer that it, too, like most lakes, was originally
produced by the rivers and that it must end by drying up entirely.

  Again, this process of silting up causes a continuous current
through the Bosporus; and in this case we can directly observe the
nature of the process. Whenever the current from the Asiatic shore
threw up a sandbank, there first formed a small lake behind it.
Later it dried up and a second sandbank formed in front of the first
and a second lake. This process went on uniformly and without
interruption. Now when this has been repeated often enough, in the
course of time the strait must become like a river, and in the end the
river itself must dry up.

  So it is clear, since there will be no end to time and the world
is eternal, that neither the Tanais nor the Nile has always been
flowing, but that the region whence they flow was once dry: for
their effect may be fulfilled, but time cannot. And this will be
equally true of all other rivers. But if rivers come into existence
and perish and the same parts of the earth were not always moist,
the sea must needs change correspondingly. And if the sea is always
advancing in one place and receding in another it is clear that the
same parts of the whole earth are not always either sea or land, but
that all this changes in course of time.

  So we have explained that the same parts of the earth are not always
land or sea and why that is so: and also why some rivers are perennial
and others not.

                              Book II

                                 1

  LET us explain the nature of the sea and the reason why such a large
mass of water is salt and the way in which it originally came to be.

  The old writers who invented theogonies say that the sea has
springs, for they want earth and sea to have foundations and roots
of their own. Presumably they thought that this view was grander and
more impressive as implying that our earth was an important part of
the universe. For they believed that the whole world had been built up
round our earth and for its sake, and that the earth was the most
important and primary part of it. Others, wiser in human knowledge,
give an account of its origin. At first, they say, the earth was
surrounded by moisture. Then the sun began to dry it up, part of it
evaporated and is the cause of winds and the turnings back of the
sun and the moon, while the remainder forms the sea. So the sea is
being dried up and is growing less, and will end by being some day
entirely dried up. Others say that the sea is a kind of sweat exuded
by the earth when the sun heats it, and that this explains its
saltness: for all sweat is salt. Others say that the saltness is due
to the earth. Just as water strained through ashes becomes salt, so
the sea owes its saltness to the admixture of earth with similar
properties.

  We must now consider the facts which prove that the sea cannot
possibly have springs. The waters we find on the earth either flow
or are stationary. All flowing water has springs. (By a spring, as
we have explained above, we must not understand a source from which
waters are ladled as it were from a vessel, but a first point at which
the water which is continually forming and percolating gathers.)
Stationary water is either that which has collected and has been
left standing, marshy pools, for instance, and lakes, which differ
merely in size, or else it comes from springs. In this case it is
always artificial, I mean as in the case of wells, otherwise the
spring would have to be above the outlet. Hence the water from
fountains and rivers flows of itself, whereas wells need to be
worked artificially. All the waters that exist belong to one or
other of these classes.

  On the basis of this division we can sec that the sea cannot have
springs. For it falls under neither of the two classes; it does not
flow and it is not artificial; whereas all water from springs must
belong to one or other of them. Natural standing water from springs is
never found on such a large scale.

  Again, there are several seas that have no communication with one
another at all. The Red Sea, for instance, communicates but slightly
with the ocean outside the straits, and the Hyrcanian and Caspian seas
are distinct from this ocean and people dwell all round them. Hence,
if these seas had had any springs anywhere they must have been
discovered.

  It is true that in straits, where the land on either side
contracts an open sea into a small space, the sea appears to flow. But
this is because it is swinging to and fro. In the open sea this motion
is not observed, but where the land narrows and contracts the sea
the motion that was imperceptible in the open necessarily strikes
the attention.

  The whole of the Mediterranean does actually flow. The direction
of this flow is determined by the depth of the basins and by the
number of rivers. Maeotis flows into Pontus and Pontus into the
Aegean. After that the flow of the remaining seas is not so easy to
observe. The current of Maeotis and Pontus is due to the number of
rivers (more rivers flow into the Euxine and Maeotis than into the
whole Mediterranean with its much larger basin), and to their own
shallowness. For we find the sea getting deeper and deeper. Pontus
is deeper than Maeotis, the Aegean than Pontus, the Sicilian sea
than the Aegean; the Sardinian and Tyrrhenic being the deepest of all.
(Outside the pillars of Heracles the sea is shallow owing to the
mud, but calm, for it lies in a hollow.) We see, then, that just as
single rivers flow from mountains, so it is with the earth as a whole:
the greatest volume of water flows from the higher regions in the
north. Their alluvium makes the northern seas shallow, while the outer
seas are deeper. Some further evidence of the height of the northern
regions of the earth is afforded by the view of many of the ancient
meteorologists. They believed that the sun did not pass below the
earth, but round its northern part, and that it was the height of this
which obscured the sun and caused night.

  So much to prove that there cannot be sources of the sea and to
explain its observed flow.

                                 2

  We must now discuss the origin of the sea, if it has an origin,
and the cause of its salt and bitter taste.

  What made earlier writers consider the sea to be the original and
main body of water is this. It seems reasonable to suppose that to
be the case on the analogy of the other elements. Each of them has a
main bulk which by reason of its mass is the origin of that element,
and any parts which change and mix with the other elements come from
it. Thus the main body of fire is in the upper region; that of air
occupies the place next inside the region of fire; while the mass of
the earth is that round which the rest of the elements are seen to
lie. So we must clearly look for something analogous in the case of
water. But here we can find no such single mass, as in the case of the
other elements, except the sea. River water is not a unity, nor is
it stable, but is seen to be in a continuous process of becoming
from day to day. It was this difficulty which made people regard the
sea as the origin and source of moisture and of all water. And so we
find it maintained that rivers not only flow into the sea but
originate from it, the salt water becoming sweet by filtration.

  But this view involves another difficulty. If this body of water
is the origin and source of all water, why is it salt and not sweet?
The reason for this, besides answering this question, will ensure
our having a right first conception of the nature of the sea.

  The earth is surrounded by water, just as that is by the sphere of
air, and that again by the sphere called that of fire (which is the
outermost both on the common view and on ours). Now the sun, moving as
it does, sets up processes of change and becoming and decay, and by
its agency the finest and sweetest water is every day carried up and
is dissolved into vapour and rises to the upper region, where it is
condensed again by the cold and so returns to the earth. This, as we
have said before, is the regular course of nature.

  Hence all my predecessors who supposed that the sun was nourished by
moisture are absurdly mistaken. Some go on to say that the solstices
are due to this, the reason being that the same places cannot always
supply the sun with nourishment and that without it he must perish.
For the fire we are familiar with lives as long as it is fed, and
the only food for fire is moisture. As if the moisture that is
raised could reach the sun! or this ascent were really like that
performed by flame as it comes into being, and to which they
supposed the case of the sun to be analogous! Really there is no
similarity. A flame is a process of becoming, involving a constant
interchange of moist and dry. It cannot be said to be nourished
since it scarcely persists as one and the same for a moment. This
cannot be true of the sun; for if it were nourished like that, as they
say it is, we should obviously not only have a new sun every day, as
Heraclitus says, but a new sun every moment. Again, when the sun
causes the moisture to rise, this is like fire heating water. So, as
the fire is not fed by the water above it, it is absurd to suppose
that the sun feeds on that moisture, even if its heat made all the
water in the world evaporate. Again, it is absurd, considering the
number and size of the stars, that these thinkers should consider
the sun only and overlook the question how the rest of the heavenly
bodies subsist. Again, they are met by the same difficulty as those
who say that at first the earth itself was moist and the world round
the earth was warmed by the sun, and so air was generated and the
whole firmament grew, and the air caused winds and solstices. The
objection is that we always plainly see the water that has been
carried up coming down again. Even if the same amount does not come
back in a year or in a given country, yet in a certain period all that
has been carried up is returned. This implies that the celestial
bodies do not feed on it, and that we cannot distinguish between
some air which preserves its character once it is generated and some
other which is generated but becomes water again and so perishes; on
the contrary, all the moisture alike is dissolved and all of it
condensed back into water.

  The drinkable, sweet water, then, is light and is all of it drawn
up: the salt water is heavy and remains behind, but not in its natural
place. For this is a question which has been sufficiently discussed (I
mean about the natural place that water, like the other elements, must
in reason have), and the answer is this. The place which we see the
sea filling is not its natural place but that of water. It seems to
belong to the sea because the weight of the salt water makes it remain
there, while the sweet, drinkable water which is light is carried
up. The same thing happens in animal bodies. Here, too, the food
when it enters the body is sweet, yet the residuum and dregs of liquid
food are found to be bitter and salt. This is because the sweet and
drinkable part of it has been drawn away by the natural animal heat
and has passed into the flesh and the other parts of the body
according to their several natures. Now just as here it would be wrong
for any one to refuse to call the belly the place of liquid food
because that disappears from it soon, and to call it the place of
the residuum because this is seen to remain, so in the case of our
present subject. This place, we say, is the place of water. Hence
all rivers and all the water that is generated flow into it: for water
flows into the deepest place, and the deepest part of the earth is
filled by the sea. Only all the light and sweet part of it is
quickly carried off by the sun, while herest remains for the reason we
have explained. It is quite natural that some people should have
been puzzled by the old question why such a mass of water leaves no
trace anywhere (for the sea does not increase though innumerable and
vast rivers are flowing into it every day.) But if one considers the
matter the solution is easy. The same amount of water does not take as
long to dry up when it is spread out as when it is gathered in a body,
and indeed the difference is so great that in the one case it might
persist the whole day long while in the other it might all disappear
in a moment-as for instance if one were to spread out a cup of water
over a large table. This is the case with the rivers: all the time
they are flowing their water forms a compact mass, but when it arrives
at a vast wide place it quickly and imperceptibly evaporates.

  But the theory of the Phaedo about rivers and the sea is impossible.
There it is said that the earth is pierced by intercommunicating
channels and that the original head and source of all waters is what
is called Tartarus-a mass of water about the centre, from which all
waters, flowing and standing, are derived. This primary and original
water is always surging to and fro, and so it causes the rivers to
flow on this side of the earth's centre and on that; for it has no
fixed seat but is always oscillating about the centre. Its motion up
and down is what fills rivers. Many of these form lakes in various
places (our sea is an instance of one of these), but all of them
come round again in a circle to the original source of their flow,
many at the same point, but some at a point opposite to that from
which they issued; for instance, if they started from the other side
of the earth's centre, they might return from this side of it. They
descend only as far as the centre, for after that all motion is
upwards. Water gets its tastes and colours from the kind of earth
the rivers happened to flow through.

  But on this theory rivers do not always flow in the same sense.
For since they flow to the centre from which they issue forth they
will not be flowing down any more than up, but in whatever direction
the surging of Tartarus inclines to. But at this rate we shall get the
proverbial rivers flowing upwards, which is impossible. Again, where
is the water that is generated and what goes up again as vapour to
come from? For this must all of it simply be ignored, since the
quantity of water is always the same and all the water that flows
out from the original source flows back to it again. This itself is
not true, since all rivers are seen to end in the sea except where one
flows into another. Not one of them ends in the earth, but even when
one is swallowed up it comes to the surface again. And those rivers
are large which flow for a long distance through a lowying country,
for by their situation and length they cut off the course of many
others and swallow them up. This is why the Istrus and the Nile are
the greatest of the rivers which flow into our sea. Indeed, so many
rivers fall into them that there is disagreement as to the sources
of them both. All of which is plainly impossible on the theory, and
the more so as it derives the sea from Tartarus.

  Enough has been said to prove that this is the natural place of
water and not of the sea, and to explain why sweet water is only found
in rivers, while salt water is stationary, and to show that the sea is
the end rather than the source of water, analogous to the residual
matter of all food, and especially liquid food, in animal bodies.

                                 3

  We must now explain why the sea is salt, and ask whether it
eternally exists as identically the same body, or whether it did not
exist at all once and some day will exist no longer, but will dry up
as some people think.

  Every one admits this, that if the whole world originated the sea
did too; for they make them come into being at the same time. It
follows that if the universe is eternal the same must be true of the
sea. Any one who thinks like Democritus that the sea is diminishing
and will disappear in the end reminds us of Aesop's tales. His story
was that Charybdis had twice sucked in the sea: the first time she
made the mountains visible; the second time the islands; and when
she sucks it in for the last time she will dry it up entirely. Such
a tale is appropriate enough to Aesop in a rage with the ferryman, but
not to serious inquirers. Whatever made the sea remain at first,
whether it was its weight, as some even of those who hold these
views say (for it is easy to see the cause here), or some other
reason-clearly the same thing must make it persist for ever. They must
either deny that the water raised by the sun will return at all, or,
if it does, they must admit that the sea persists for ever or as
long as this process goes on, and again, that for the same period of
time that sweet water must have been carried up beforehand. So the sea
will never dry up: for before that can happen the water that has
gone up beforehand will return to it: for if you say that this happens
once you must admit its recurrence. If you stop the sun's course there
is no drying agency. If you let it go on it will draw up the sweet
water as we have said whenever it approaches, and let it descend again
when it recedes. This notion about the sea is derived from the fact
that many places are found to be drier now than they once were. Why
this is so we have explained. The phenomenon is due to temporary
excess of rain and not to any process of becoming in which the
universe or its parts are involved. Some day the opposite will take
place and after that the earth will grow dry once again. We must
recognize that this process always goes on thus in a cycle, for that
is more satisfactory than to suppose a change in the whole world in
order to explain these facts. But we have dwelt longer on this point
than it deserves.

  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.

  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.

  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.

  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.

  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.

  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.

                                 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.

  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.

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

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

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

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

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

                                 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.

  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.

  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.

  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.

                                 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.

  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.

  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.

    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.

                                 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 other.

  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.

                                 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 eart