textfiles/etext/AUTHORS/ARISTOTLE/aristotle-meteorology-80.txt

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

  We have now explained earthquakes, their nature and cause, and the
most important of the circumstances attendant on their appearance.

                                 9

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

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

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

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

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

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

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

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

  So much for thunder and lightning.

                              Book III

                                 1

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

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

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

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

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

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

  We have now explained thunder and lightning and hurricane, and
further firewinds, whirlwinds, and thunderbolts, and shown that they
are all of them forms of the same thing and wherein they all differ.

                                 2

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

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

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

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

  These are the facts about each of these phenomena: the cause of them
all is the same, for they are all reflections. But they are
different varieties, and are distinguished by the surface from which
and the way in which the reflection to the sun or some other bright
object takes place.

  The rainbow is seen by day, and it was formerly thought that it
never appeared by night as a moon rainbow. This opinion was due to the
rarity of the occurrence: it was not observed, for though it does
happen it does so rarely. The reason is that the colours are not so
easy to see in the dark and that many other conditions must
coincide, and all that in a single day in the month. For if there is
to be one it must be at full moon, and then as the moon is either
rising or setting. So we have only met with two instances of a moon
rainbow in more than fifty years.

  We must accept from the theory of optics the fact that sight is
reflected from air and any object with a smooth surface just as it
is from water; also that in some mirrors the forms of things are
reflected, in others only their colours. Of the latter kind are
those mirrors which are so small as to be indivisible for sense. It is
impossible that the figure of a thing should be reflected in them, for
if it is the mirror will be sensibly divisible since divisibility is
involved in the notion of figure. But since something must be
reflected in them and figure cannot be, it remains that colour alone
should be reflected. The colour of a bright object sometimes appears
bright in the reflection, but it sometimes, either owing to the
admixture of the colour of the mirror or to weakness of sight, gives
rise to the appearance of another colour.

  However, we must accept the account we have given of these things in
the theory of sensation, and take some things for granted while we
explain others.

                                 3

  Let us begin by explaining the shape of the halo; why it is a circle
and why it appears round the sun or the moon or one of the other
stars: the explanation being in all these cases the same.

  Sight is reflected in this way when air and vapour are condensed
into a cloud and the condensed matter is uniform and consists of small
parts. Hence in itself it is a sign of rain, but if it fades away,
of fine weather, if it is broken up, of wind. For if it does not
fade away and is not broken up but is allowed to attain its normal
state, it is naturally a sign of rain since it shows that a process of
condensation is proceeding which must, when it is carried to an end,
result in rain. For the same reason these haloes are the darkest. It
is a sign of wind when it is broken up because its breaking up is
due to a wind which exists there but has not reached us. This view
finds support in the fact that the wind blows from the quarter in
which the main division appears in the halo. Its fading away is a sign
of fine weather because if the air is not yet in a state to get the
better of the heat it contains and proceed to condense into water,
this shows that the moist vapour has not yet separated from the dry
and firelike exhalation: and this is the cause of fine weather.

  So much for the atmospheric conditions under which the reflection
takes place. The reflection is from the mist that forms round the
sun or the moon, and that is why the halo is not seen opposite the sun
like the rainbow.

  Since the reflection takes place in the same way from every point
the result is necessarily a circle or a segment of a circle: for if
the lines start from the same point and end at the same point and
are equal, the points where they form an angle will always lie on a
circle.

  Let AGB and AZB and ADB be lines each of which goes from the point A
to the point B and forms an angle. Let the lines AG, AZ, AD be equal
and those at B, GB, ZB, DB equal too. (See diagram.)

  Draw the line AEB. Then the triangles are equal; for their base
AEB is equal. Draw perpendiculars to AEB from the angles; GE from G,
ZE from Z, DE from D. Then these perpendiculars are equal, being in
equal triangles. And they are all in one plane, being all at right
angles to AEB and meeting at a single point E. So if you draw the line
it will be a circle and E its centre. Now B is the sun, A the eye, and
the circumference passing through the points GZD the cloud from
which the line of sight is reflected to the sun.

  The mirrors must be thought of as contiguous: each of them is too
small to be visible, but their contiguity makes the whole made up of
them all to seem one. The bright band is the sun, which is seen as a
circle, appearing successively in each of the mirrors as a point
indivisible to sense. The band of cloud next to it is black, its
colour being intensified by contrast with the brightness of the
halo. The halo is formed rather near the earth because that is calmer:
for where there is wind it is clear that no halo can maintain its
position.

  Haloes are commoner round the moon because the greater heat of the
sun dissolves the condensations of the air more rapidly.

  Haloes are formed round stars for the same reasons, but they are not
prognostic in the same way because the condensation they imply is so
insignificant as to be barren.

                                 4

  We have already stated that the rainbow is a reflection: we have now
to explain what sort of reflection it is, to describe its various
concomitants, and to assign their causes.

  Sight is reflected from all smooth surfaces, such as are air and
water among others. Air must be condensed if it is to act as a mirror,
though it often gives a reflection even uncondensed when the sight
is weak. Such was the case of a man whose sight was faint and
indistinct. He always saw an image in front of him and facing him as
he walked. This was because his sight was reflected back to him. Its
morbid condition made it so weak and delicate that the air close by
acted as a mirror, just as distant and condensed air normally does,
and his sight could not push it back. So promontories in the sea
'loom' when there is a south-east wind, and everything seems bigger,
and in a mist, too, things seem bigger: so, too, the sun and the stars
seem bigger when rising and setting than on the meridian. But things
are best reflected from water, and even in process of formation it
is a better mirror than air, for each of the particles, the union of
which constitutes a raindrop, is necessarily a better mirror than
mist. Now it is obvious and has already been stated that a mirror of
this kind renders the colour of an object only, but not its shape.
Hence it follows that when it is on the point of raining and the air
in the clouds is in process of forming into raindrops but the rain
is not yet actually there, if the sun is opposite, or any other object
bright enough to make the cloud a mirror and cause the sight to be
reflected to the object then the reflection must render the colour
of the object without its shape. Since each of the mirrors is so small
as to be invisible and what we see is the continuous magnitude made up
of them all, the reflection necessarily gives us a continuous
magnitude made up of one colour; each of the mirrors contributing
the same colour to the whole. We may deduce that since these
conditions are realizable there will be an appearance due to
reflection whenever the sun and the cloud are related in the way
described and we are between them. But these are just the conditions
under which the rainbow appears. So it is clear that the rainbow is
a reflection of sight to the sun.

  So the rainbow always appears opposite the sun whereas the halo is
round it. They are both reflections, but the rainbow is
distinguished by the variety of its colours. The reflection in the one
case is from water which is dark and from a distance; in the other
from air which is nearer and lighter in colour. White light through
a dark medium or on a dark surface (it makes no difference) looks red.
We know how red the flame of green wood is: this is because so much
smoke is mixed with the bright white firelight: so, too, the sun
appears red through smoke and mist. That is why in the rainbow
reflection the outer circumference is red (the reflection being from
small particles of water), but not in the case of the halo. The
other colours shall be explained later. Again, a condensation of
this kind cannot persist in the neighbourhood of the sun: it must
either turn to rain or be dissolved, but opposite to the sun there
is an interval during which the water is formed. If there were not
this distinction haloes would be coloured like the rainbow. Actually
no complete or circular halo presents this colour, only small and
fragmentary appearances called 'rods'. But if a haze due to water or
any other dark substance formed there we should have had, as we
maintain, a complete rainbow like that which we do find lamps. A
rainbow appears round these in winter, generally with southerly winds.
Persons whose eyes are moist see it most clearly because their sight
is weak and easily reflected. It is due to the moistness of the air
and the soot which the flame gives off and which mixes with the air
and makes it a mirror, and to the blackness which that mirror
derives from the smoky nature of the soot. The light of the lamp
appears as a circle which is not white but purple. It shows the
colours of the rainbow; but because the sight that is reflected is too
weak and the mirror too dark, red is absent. The rainbow that is
seen when oars are raised out of the sea involves the same relative
positions as that in the sky, but its colour is more like that round
the lamps, being purple rather than red. The reflection is from very
small particles continuous with one another, and in this case the
particles are fully formed water. We get a rainbow, too, if a man
sprinkles fine drops in a room turned to the sun so that the sun is
shining in part of the room and throwing a shadow in the rest. Then if
one man sprinkles in the room, another, standing outside, sees a
rainbow where the sun's rays cease and make the shadow. Its nature and
colour is like that from the oars and its cause is the same, for the
sprinkling hand corresponds to the oar.

  That the colours of the rainbow are those we described and how the
other colours come to appear in it will be clear from the following
considerations. We must recognize, as we have said, and lay down:
first, that white colour on a black surface or seen through a black
medium gives red; second, that sight when strained to a distance
becomes weaker and less; third, that black is in a sort the negation
of sight: an object is black because sight fails; so everything at a
distance looks blacker, because sight does not reach it. The theory of
these matters belongs to the account of the senses, which are the
proper subjects of such an inquiry; we need only state about them what
is necessary for us. At all events, that is the reason why distant
objects and objects seen in a mirror look darker and smaller and
smoother, why the reflection of clouds in water is darker than the
clouds themselves. This latter is clearly the case: the reflection
diminishes the sight that reaches them. It makes no difference whether
the change is in the object seen or. in the sight, the result being in
either case the same. The following fact further is worth noticing.
When there is a cloud near the sun and we look at it does not look
coloured at all but white, but when we look at the same cloud in water
it shows a trace of rainbow colouring. Clearly, then, when sight is
reflected it is weakened and, as it makes dark look darker, so it
makes white look less white, changing it and bringing it nearer to
black. When the sight is relatively strong the change is to red; the
next stage is green, and a further degree of weakness gives violet. No
further change is visible, but three completes the series of colours
(as we find three does in most other things), and the change into
the rest is imperceptible to sense. Hence also the rainbow appears
with three colours; this is true of each of the two, but in a contrary
way. The outer band of the primary rainbow is red: for the largest
band reflects most sight to the sun, and the outer band is largest.
The middle band and the third go on the same principle. So if the
principles we laid down about the appearance of colours are true the
rainbow necessarily has three colours, and these three and no
others. The appearance of yellow is due to contrast, for the red is
whitened by its juxtaposition with green. We can see this from the
fact that the rainbow is purest when the cloud is blackest; and then
the red shows most yellow. (Yellow in the rainbow comes between red
and green.) So the whole of the red shows white by contrast with the
blackness of the cloud around: for it is white compared to the cloud
and the green. Again, when the rainbow is fading away and the red is
dissolving, the white cloud is brought into contact with the green and
becomes yellow. But the moon rainbow affords the best instance of this
colour contrast. It looks quite white: this is because it appears on
the dark cloud and at night. So, just as fire is intensified by
added fire, black beside black makes that which is in some degree
white look quite white. Bright dyes too show the effect of contrast.
In woven and embroidered stuffs the appearance of colours is
profoundly affected by their juxtaposition with one another (purple,
for instance, appears different on white and on black wool), and
also by differences of illumination. Thus embroiderers say that they
often make mistakes in their colours when they work by lamplight,
and use the wrong ones.

  We have now shown why the rainbow has three colours and that these
are its only colours. The same cause explains the double rainbow and
the faintness of the colours in the outer one and their inverted
order. When sight is strained to a great distance the appearance of
the distant object is affected in a certain way: and the same thing
holds good here. So the reflection from the outer rainbow is weaker
because it takes place from a greater distance and less of it
reaches the sun, and so the colours seen are fainter. Their order is
reversed because more reflection reaches the sun from the smaller,
inner band. For that reflection is nearer to our sight which is
reflected from the band which is nearest to the primary rainbow. Now
the smallest band in the outer rainbow is that which is nearest, and
so it will be red; and the second and the third will follow the same
principle. Let B be the outer rainbow, A the inner one; let R stand
for the red colour, G for green, V for violet; yellow appears at the
point Y. Three rainbows or more are not found because even the
second is fainter, so that the third reflection can have no strength
whatever and cannot reach the sun at all. (See diagram.)

                                 5

  The rainbow can never be a circle nor a segment of a circle
greater than a semicircle. The consideration of the diagram will prove
this and the other properties of the rainbow. (See diagram.)

  Let A be a hemisphere resting on the circle of the horizon, let
its centre be K and let H be another point appearing on the horizon.
Then, if the lines that fall in a cone from K have HK as their axis,
and, K and M being joined, the lines KM are reflected from the
hemisphere to H over the greater angle, the lines from K will fall
on the circumference of a circle. If the reflection takes place when
the luminous body is rising or setting the segment of the circle above
the earth which is cut off by the horizon will be a semi-circle; if
the luminous body is above the horizon it will always be less than a
semicircle, and it will be smallest when the luminous body culminates.
First let the luminous body be appearing on the horizon at the point
H, and let KM be reflected to H, and let the plane in which A is,
determined by the triangle HKM, be produced. Then the section of the
sphere will be a great circle. Let it be A (for it makes no difference
which of the planes passing through the line HK and determined by
the triangle KMH is produced). Now the lines drawn from H and K to a
point on the semicircle A are in a certain ratio to one another, and
no lines drawn from the same points to another point on that
semicircle can have the same ratio. For since both the points H and
K and the line KH are given, the line MH will be given too;
consequently the ratio of the line MH to the line MK will be given
too. So M will touch a given circumference. Let this be NM. Then the
intersection of the circumferences is given, and the same ratio cannot
hold between lines in the same plane drawn from the same points to any
other circumference but MN.

  Draw a line DB outside of the figure and divide it so that
D:B=MH:MK. But MH is greater than MK since the reflection of the
cone is over the greater angle (for it subtends the greater angle of
the triangle KMH). Therefore D is greater than B. Then add to B a line
Z such that B+Z:D=D:B. Then make another line having the same ratio to
B as KH has to Z, and join MI.

  Then I is the pole of the circle on which the lines from K fall. For
the ratio of D to IM is the same as that of Z to KH and of B to KI. If
not, let D be in the same ratio to a line indifferently lesser or
greater than IM, and let this line be IP. Then HK and KI and IP will
have the same ratios to one another as Z, B, and D. But the ratios
between Z, B, and D were such that Z+B:D=D: B. Therefore
IH:IP=IP:IK. Now, if the points K, H be joined with the point P by the
lines HP, KP, these lines will be to one another as IH is to IP, for
the sides of the triangles HIP, KPI about the angle I are
homologous. Therefore, HP too will be to KP as HI is to IP. But this
is also the ratio of MH to MK, for the ratio both of HI to IP and of
MH to MK is the same as that of D to B. Therefore, from the points
H, K there will have been drawn lines with the same ratio to one
another, not only to the circumference MN but to another point as
well, which is impossible. Since then D cannot bear that ratio to
any line either lesser or greater than IM (the proof being in either
case the same), it follows that it must stand in that ratio to MI
itself. Therefore as MI is to IK so IH will be to MI and finally MH to
MK.

  If, then, a circle be described with I as pole at the distance MI it
will touch all the angles which the lines from H and K make by their
reflection. If not, it can be shown, as before, that lines drawn to
different points in the semicircle will have the same ratio to one
another, which was impossible. If, then, the semicircle A be
revolved about the diameter HKI, the lines reflected from the points
H, K at the point M will have the same ratio, and will make the
angle KMH equal, in every plane. Further, the angle which HM and MI
make with HI will always be the same. So there are a number of
triangles on HI and KI equal to the triangles HMI and KMI. Their
perpendiculars will fall on HI at the same point and will be equal.
Let O be the point on which they fall. Then O is the centre of the
circle, half of which, MN, is cut off by the horizon. (See diagram.)

  Next let the horizon be ABG but let H have risen above the
horizon. Let the axis now be HI. The proof will be the same for the
rest as before, but the pole I of the circle will be below the horizon
AG since the point H has risen above the horizon. But the pole, and
the centre of the circle, and the centre of that circle (namely HI)
which now determines the position of the sun are on the same line. But
since KH lies above the diameter AG, the centre will be at O on the
line KI below the plane of the circle AG determined the position of
the sun before. So the segment YX which is above the horizon will be
less than a semicircle. For YXM was a semicircle and it has now been
cut off by the horizon AG. So part of it, YM, will be invisible when
the sun has risen above the horizon, and the segment visible will be
smallest when the sun is on the meridian; for the higher H is the
lower the pole and the centre of the circle will be.

  In the shorter days after the autumn equinox there may be a
rainbow at any time of the day, but in the longer days from the spring
to the autumn equinox there cannot be a rainbow about midday. The
reason for this is that when the sun is north of the equator the
visible arcs of its course are all greater than a semicircle, and go
on increasing, while the invisible arc is small, but when the sun is
south of the equator the visible arc is small and the invisible arc
great, and the farther the sun moves south of the equator the
greater is the invisible arc. Consequently, in the days near the
summer solstice, the size of the visible arc is such that before the
point H reaches the middle of that arc, that is its point of
culmination, the point is well below the horizon; the reason for
this being the great size of the visible arc, and the consequent
distance of the point of culmination from the earth. But in the days
near the winter solstice the visible arcs are small, and the
contrary is necessarily the case: for the sun is on the meridian
before the point H has risen far.

                                 6

  Mock suns, and rods too, are due to the causes we have described.
A mock sun is caused by the reflection of sight to the sun. Rods are
seen when sight reaches the sun under circumstances like those which
we described, when there are clouds near the sun and sight is
reflected from some liquid surface to the cloud. Here the clouds
themselves are colourless when you look at them directly, but in the
water they are full of rods. The only difference is that in this
latter case the colour of the cloud seems to reside in the water,
but in the case of rods on the cloud itself. Rods appear when the
composition of the cloud is uneven, dense in part and in part rare,
and more and less watery in different parts. Then the sight is
reflected to the sun: the mirrors are too small for the shape of the
sun to appear, but, the bright white light of the sun, to which the
sight is reflected, being seen on the uneven mirror, its colour
appears partly red, partly green or yellow. It makes no difference
whether sight passes through or is reflected from a medium of that
kind; the colour is the same in both cases; if it is red in the
first case it must be the same in the other.

  Rods then are occasioned by the unevenness of the mirror-as
regards colour, not form. The mock sun, on the contrary, appears
when the air is very uniform, and of the same density throughout. This
is why it is white: the uniform character of the mirror gives the
reflection in it a single colour, while the fact that the sight is
reflected in a body and is thrown on the sun all together by the mist,
which is dense and watery though not yet quite water, causes the sun's
true colour to appear just as it does when the reflection is from
the dense, smooth surface of copper. So the sun's colour being
white, the mock sun is white too. This, too, is the reason why the
mock sun is a surer sign of rain than the rods; it indicates, more
than they do, that the air is ripe for the production of water.
Further a mock sun to the south is a surer sign of rain than one to
the north, for the air in the south is readier to turn into water than
that in the north.

  Mock suns and rods are found, as we stated, about sunset and
sunrise, not above the sun nor below it, but beside it. They are not
found very close to the sun, nor very far from it, for the sun
dissolves the cloud if it is near, but if it is far off the reflection
cannot take place, since sight weakens when it is reflected from a
small mirror to a very distant object. (This is why a halo is never
found opposite to the sun.) If the cloud is above the sun and close to
it the sun will dissolve it; if it is above the sun but at a
distance the sight is too weak for the reflection to take place, and
so it will not reach the sun. But at the side of the sun, it is
possible for the mirror to be at such an interval that the sun does
not dissolve the cloud, and yet sight reaches it undiminished
because it moves close to the earth and is not dissipated in the
immensity of space. It cannot subsist below the sun because close to
the earth the sun's rays would dissolve it, but if it were high up and
the sun in the middle of the heavens, sight would be dissipated.
Indeed, even by the side of the sun, it is not found when the sun is
in the middle of the sky, for then the line of vision is not close
to the earth, and so but little sight reaches the mirror and the
reflection from it is altogether feeble.

  Some account has now been given of the effects of the secretion
above the surface of the earth; we must go on to describe its
operations below, when it is shut up in the parts of the earth.

  Just as its twofold nature gives rise to various effects in the
upper region, so here it causes two varieties of bodies. We maintain
that there are two exhalations, one vaporous the other smoky, and
there correspond two kinds of bodies that originate in the earth,
'fossiles' and metals. The heat of the dry exhalation is the cause
of all 'fossiles'. Such are the kinds of stones that cannot be melted,
and realgar, and ochre, and ruddle, and sulphur, and the other
things of that kind, most 'fossiles' being either coloured lye or,
like cinnabar, a stone compounded of it. The vaporous exhalation is
the cause of all metals, those bodies which are either fusible or
malleable such as iron, copper, gold. All these originate from the
imprisonment of the vaporous exhalation in the earth, and especially
in stones. Their dryness compresses it, and it congeals just as dew or
hoar-frost does when it has been separated off, though in the
present case the metals are generated before that segregation
occurs. Hence, they are water in a sense, and in a sense not. Their
matter was that which might have become water, but it can no longer do
so: nor are they, like savours, due to a qualitative change in
actual water. Copper and gold are not formed like that, but in every
case the evaporation congealed before water was formed. Hence, they
all (except gold) are affected by fire, and they possess an
admixture of earth; for they still contain the dry exhalation.

  This is the general theory of all these bodies, but we must take
up each kind of them and discuss it separately.

                              Book IV

                                 1

  WE have explained that the qualities that constitute the elements
are four, and that their combinations determine the number of the
elements to be four.

  Two of the qualities, the hot and the cold, are active; two, the dry
and the moist, passive. We can satisfy ourselves of this by looking at
instances. In every case heat and cold determine, conjoin, and
change things of the same kind and things of different kinds,
moistening, drying, hardening, and softening them. Things dry and
moist, on the other hand, both in isolation and when present
together in the same body are the subjects of that determination and
of the other affections enumerated. The account we give of the
qualities when we define their character shows this too. Hot and
cold we describe as active, for 'congregating' is essentially a
species of 'being active': moist and dry are passive, for it is in
virtue of its being acted upon in a certain way that a thing is said
to be 'easy to determine' or 'difficult to determine'. So it is
clear that some of the qualities are active and some passive.

  Next we must describe the operations of the active qualities and the
forms taken by the passive. First of all, true becoming, that is,
natural change, is always the work of these powers and so is the
corresponding natural destruction; and this becoming and this
destruction are found in plants and animals and their parts. True
natural becoming is a change introduced by these powers into the
matter underlying a given thing when they are in a certain ratio to
that matter, which is the passive qualities we have mentioned. When
the hot and the cold are masters of the matter they generate a
thing: if they are not, and the failure is partial, the object is
imperfectly boiled or otherwise unconcocted. But the strictest general
opposite of true becoming is putrefaction. All natural destruction
is on the way to it, as are, for instance, growing old or growing dry.
Putrescence is the end of all these things, that is of all natural
objects, except such as are destroyed by violence: you can burn, for
instance, flesh, bone, or anything else, but the natural course of
their destruction ends in putrefaction. Hence things that putrefy
begin by being moist and end by being dry. For the moist and the dry
were their matter, and the operation of the active qualities caused
the dry to be determined by the moist.

  Destruction supervenes when the determined gets the better of the
determining by the help of the environment (though in a special
sense the word putrefaction is applied to partial destruction, when
a thing's nature is perverted). Hence everything, except fire, is
liable to putrefy; for earth, water, and air putrefy, being all of
them matter relatively to fire. The definition of putrefaction is: the
destruction of the peculiar and natural heat in any moist subject by
external heat, that is, by the heat of the environment. So since
lack of heat is the ground of this affection and everything in as
far as it lacks heat is cold, both heat and cold will be the causes of
putrefaction, which will be due indifferently to cold in the
putrefying subject or to heat in the environment.

  This explains why everything that putrefies grows drier and ends
by becoming earth or dung. The subject's own heat departs and causes
the natural moisture to evaporate with it, and then there is nothing
left to draw in moisture, for it is a thing's peculiar heat that
attracts moisture and draws it in. Again, putrefaction takes place
less in cold that in hot seasons, for in winter the surrounding air
and water contain but little heat and it has no power, but in summer
there is more. Again, what is frozen does not putrefy, for its cold is
greater that the heat of the air and so is not mastered, whereas
what affects a thing does master it. Nor does that which is boiling or
hot putrefy, for the heat in the air being less than that in the
object does not prevail over it or set up any change. So too
anything that is flowing or in motion is less apt to putrefy than a
thing at rest, for the motion set up by the heat in the air is
weaker than that pre-existing in the object, and so it causes no
change. For the same reason a great quantity of a thing putrefies less
readily than a little, for the greater quantity contains too much
proper fire and cold for the corresponding qualities in the
environment to get the better of. Hence, the sea putrefies quickly
when broken up into parts, but not as a whole; and all other waters
likewise. Animals too are generated in putrefying bodies, because
the heat that has been secreted, being natural, organizes the
particles secreted with it.

  So much for the nature of becoming and of destruction.

                                 2

  We must now describe the next kinds of processes which the qualities
already mentioned set up in actually existing natural objects as
matter.

  Of these concoction is due to heat; its species are ripening,
boiling, broiling. Inconcoction is due to cold and its species are
rawness, imperfect boiling, imperfect broiling. (We must recognize
that the things are not properly denoted by these words: the various
classes of similar objects have no names universally applicable to
them; consequently we must think of the species enumerated as being
not what those words denote but something like it.) Let us say what
each of them is. Concoction is a process in which the natural and
proper heat of an object perfects the corresponding passive qualities,
which are the proper matter of any given object. For when concoction
has taken place we say that a thing has been perfected and has come to
be itself. It is the proper heat of a thing that sets up this
perfecting, though external influences may contribute in some
degrees to its fulfilment. Baths, for instance, and other things of
the kind contribute to the digestion of food, but the primary cause is
the proper heat of the body. In some cases of concoction the end of
the process is the nature of the thing-nature, that is, in the sense
of the formal cause and essence. In other cases it leads to some
presupposed state which is attained when the moisture has acquired
certain properties or a certain magnitude in the process of being
broiled or boiled or of putrefying, or however else it is being
heated. This state is the end, for when it has been reached the
thing has some use and we say that concoction has taken place. Must is
an instance of this, and the matter in boils when it becomes purulent,
and tears when they become rheum, and so with the rest.

    Concoction ensues whenever the matter, the moisture, is
mastered. For the matter is what is determined by the heat
connatural to the object, and as long as the ratio between them exists
in it a thing maintains its nature. Hence things like the liquid and
solid excreta and ejecta in general are signs of health, and
concoction is said to have taken place in them, for they show that the
proper heat has got the better of the indeterminate matter.

  Things that undergo a process of concoction necessarily become
thicker and hotter, for the action of heat is to make things more
compact, thicker, and drier.

  This then is the nature of concoction: but inconcoction is an
imperfect state due to lack of proper heat, that is, to cold. That
of which the imperfect state is, is the corresponding passive
qualities which are the natural matter of anything.

  So much for the definition of concoction and inconcoction.

                                 3

  Ripening is a sort of concoction; for we call it ripening when there
is a concoction of the nutriment in fruit. And since concoction is a
sort of perfecting, the process of ripening is perfect when the
seeds in fruit are able to reproduce the fruit in which they are
found; for in all other cases as well this is what we mean by
'perfect'. This is what 'ripening' means when the word is applied to
fruit. However, many other things that have undergone concoction are
said to be 'ripe', the general character of the process being the
same, though the word is applied by an extension of meaning. The
reason for this extension is, as we explained before, that the various
modes in which natural heat and cold perfect the matter they determine
have not special names appropriated to them. In the case of boils
and phlegm, and the like, the process of ripening is the concoction of
the moisture in them by their natural heat, for only that which gets
the better of matter can determine it. So everything that ripens is
condensed from a spirituous into a watery state, and from a watery
into an earthy state, and in general from being rare becomes dense. In
this process the nature of the thing that is ripening incorporates
some of the matter in itself, and some it rejects. So much for the
definition of ripening.

  Rawness is its opposite and is therefore an imperfect concoction
of the nutriment in the fruit, namely, of the undetermined moisture.
Consequently a raw thing is either spirituous or watery or contains
both spirit and water. Ripening being a kind of perfecting, rawness
will be an imperfect state, and this state is due to a lack of natural
heat and its disproportion to the moisture that is undergoing the
process of ripening. (Nothing moist ripens without the admixture of
some dry matter: water alone of liquids does not thicken.) This
disproportion may be due either to defect of heat or to excess of
the matter to be determined: hence the juice of raw things is thin,
cold rather than hot, and unfit for food or drink. Rawness, like
ripening, is used to denote a variety of states. Thus the liquid and
solid excreta and catarrhs are called raw for the same reason, for
in every case the word is applied to things because their heat has not
got the mastery in them and compacted them. If we go further, brick is
called raw and so is milk and many other things too when they are such
as to admit of being changed and compacted by heat but have remained
unaffected. Hence, while we speak of 'boiled' water, we cannot speak
of raw water, since it does not thicken. We have now defined
ripening and rawness and assigned their causes.

  Boiling is, in general, a concoction by moist heat of the
indeterminate matter contained in the moisture of the thing boiled,
and the word is strictly applicable only to things boiled in the way
of cooking. The indeterminate matter, as we said, will be either
spirituous or watery. The cause of the concoction is the fire
contained in the moisture; for what is cooked in a frying-pan is
broiled: it is the heat outside that affects it and, as for the
moisture in which it is contained, it dries this up and draws it
into itself. But a thing that is being boiled behaves in the
opposite way: the moisture contained in it is drawn out of it by the
heat in the liquid outside. Hence boiled meats are drier than broiled;
for, in boiling, things do not draw the moisture into themselves,
since the external heat gets the better of the internal: if the
internal heat had got the better it would have drawn the moisture to
itself. Not every body admits of the process of boiling: if there is
no moisture in it, it does not (for instance, stones), nor does it
if there is moisture in it but the density of the body is too great
for it-to-be mastered, as in the case of wood. But only those bodies
can be boiled that contain moisture which can be acted on by the
heat contained in the liquid outside. It is true that gold and wood
and many other things are said to be 'boiled': but this is a stretch
of the meaning of the word, though the kind of thing intended is the
same, the reason for the usage being that the various cases have no
names appropriated to them. Liquids too, like milk and must, are
said to undergo a process of 'boiling' when the external fire that
surrounds and heats them changes the savour in the liquid into a given
form, the process being thus in a way like what we have called
boiling.

  The end of the things that undergo boiling, or indeed any form of
concoction, is not always the same: some are meant to be eaten, some
drunk, and some are intended for other uses; for instance dyes, too,
are said to be 'boiled'.

  All those things then admit of 'boiling' which can grow denser,
smaller, or heavier; also those which do that with a part of
themselves and with a part do the opposite, dividing in such a way
that one portion thickens while the other grows thinner, like milk
when it divides into whey and curd. Oil by itself is affected in
none of these ways, and therefore cannot be said to admit of
'boiling'. Such then is the pfcies of concoction known as 'boiling',
and the process is the same in an artificial and in a natural
instrument, for the cause will be the same in every case.

  Imperfect boiling is the form of inconcoction opposed to boiling.
Now the opposite of boiling properly so called is an inconcoction of
the undetermined matter in a body due to lack of heat in the
surrounding liquid. (Lack of heat implies, as we have pointed out, the
presence of cold.) The motion which causes imperfect boiling is
different from that which causes boiling, for the heat which
operates the concoction is driven out. The lack of heat is due
either to the amount of cold in the liquid or to the quantity of
moisture in the object undergoing the process of boiling. Where either
of these conditions is realized the heat in the surrounding liquid
is too great to have no effect at all, but too small to carry out
the process of concocting uniformly and thoroughly. Hence things are
harder when they are imperfectly boiled than when they are boiled, and
the moisture in them more distinct from the solid parts. So much for
the definition and causes of boiling and imperfect boiling.

  Broiling is concoction by dry foreign heat. Hence if a man were to
boil a thing but the change and concoction in it were due, not to
the heat of the liquid but to that of the fire, the thing will have
been broiled and not boiled when the process has been carried to
completion: if the process has gone too far we use the word 'scorched'
to describe it. If the process leaves the thing drier at the end the
agent has been dry heat. Hence the outside is drier than the inside,
the opposite being true of things boiled. Where the process is
artificial, broiling is more difficult than boiling, for it is
difficult to heat the inside and the outside uniformly, since the
parts nearer to the fire are the first to get dry and consequently get
more intensely dry. In this way the outer pores contract and the
moisture in the thing cannot be secreted but is shut in by the closing
of the pores. Now broiling and boiling are artificial processes, but
the same general kind of thing, as we said, is found in nature too.
The affections produced are similar though they lack a name; for art
imitates nature. For instance, the concoction of food in the body is
like boiling, for it takes place in a hot and moist medium and the
agent is the heat of the body. So, too, certain forms of indigestion
are like imperfect boiling. And it is not true that animals are
generated in the concoction of food, as some say. Really they are
generated in the excretion which putrefies in the lower belly, and
they ascend afterwards. For concoction goes on in the upper belly
but the excretion putrefies in the lower: the reason for this has been
explained elsewhere.

  We have seen that the opposite of boiling is imperfect boiling:
now there is something correspondingly opposed to the species of
concoction called broiling, but it is more difficult to find a name
for it. It would be the kind of thing that would happen if there
were imperfect broiling instead of broiling proper through lack of
heat due to deficiency in the external fire or to the quantity of
water in the thing undergoing the process. For then we should get
too much heat for no effect to be produced, but too little for
concoction to take place.

  We have now explained concoction and inconcoction, ripening and
rawness, boiling and broiling, and their opposites.

                                 4

  We must now describe the forms taken by the passive qualities the
moist and the dry. The elements of bodies, that is, the passive
ones, are the moist and the dry; the bodies themselves are
compounded of them and whichever predominates determines the nature of
the body; thus some bodies partake more of the dry, others of the
moist. All the forms to be described will exist either actually, or
potentially and in their opposite: for instance, there is actual
melting and on the other hand that which admits of being melted.

  Since the moist is easily determined and the dry determined with
difficulty, their relation to one another is like that of a dish and
its condiments. The moist is what makes the dry determinable, and each
serves as a sort of glue to the other-as Empedocles said in his poem
on Nature, 'glueing meal together by means of water.' Thus the
determined body involves them both. Of the elements earth is
especially representative of the dry, water of the moist, and
therefore all determinate bodies in our world involve earth and water.
Every body shows the quality of that element which predominates in it.
It is because earth and water are the material elements of all
bodies that animals live in them alone and not in air or fire.

  Of the qualities of bodies hardness and softness are those which
must primarily belong to a determined thing, for anything made up of
the dry and the moist is necessarily either hard or soft. Hard is that
the surface of which does not yield into itself; soft that which
does yield but not by interchange of place: water, for instance, is
not soft, for its surface does not yield to pressure or sink in but
there is an interchange of place. Those things are absolutely hard and
soft which satisfy the definition absolutely, and those things
relatively so which do so compared with another thing. Now
relatively to one another hard and soft are indefinable, because it is
a matter of degree, but since all the objects of sense are
determined by reference to the faculty of sense it is clearly the
relation to touch which determines that which is hard and soft
absolutely, and touch is that which we use as a standard or mean. So
we call that which exceeds it hard and that which falls short of it
soft.

                                 5

  A body determined by its own boundary must be either hard or soft;
for it either yields or does not.

  It must also be concrete: or it could not be so determined. So since
everything that is determined and solid is either hard or soft and
these qualities are due to concretion, all composite and determined
bodies must involve concretion. Concretion therefore must be
discussed.

  Now there are two causes besides matter, the agent and the quality
brought about, the agent being the efficient cause, the quality the
formal cause. Hence concretion and disaggregation, drying and
moistening, must have these two causes.

  But since concretion is a form of drying let us speak of the
latter first.

  As we have explained, the agent operates by means of two qualities
and the patient is acted on in virtue of two qualities: action takes
place by means of heat or cold, and the quality is produced either
by the presence or by the absence of heat or cold; but that which is
acted upon is moist or dry or a compound of both. Water is the element
characterized by the moist, earth that characterized by the dry, for
these among the elements that admit the qualities moist and dry are
passive. Therefore cold, too, being found in water and earth (both
of which we recognize to be cold), must be reckoned rather as a
passive quality. It is active only as contributing to destruction or
incidentally in the manner described before; for cold is sometimes
actually said to burn and to warm, but not in the same way as heat
does, but by collecting and concentrating heat.

  The subjects of drying are water and the various watery fluids and
those bodies which contain water either foreign or connatural. By
foreign I mean like the water in wool, by connatural, like that in
milk. The watery fluids are wine, urine, whey, and in general those
fluids which have no sediment or only a little, except where this
absence of sediment is due to viscosity. For in some cases, in oil and
pitch for instance, it is the viscosity which prevents any sediment
from appearing.

  It is always a process of heating or cooling that dries things,
but the agent in both cases is heat, either internal or external.
For even when things are dried by cooling, like a garment, where the
moisture exists separately it is the internal heat that dries them. It
carries off the moisture in the shape of vapour (if there is not too
much of it), being itself driven out by the surrounding cold. So
everything is dried, as we have said, by a process either of heating
or cooling, but the agent is always heat, either internal or external,
carrying off the moisture in vapour. By external heat I mean as
where things are boiled: by internal where the heat breathes out and
takes away and uses up its moisture. So much for drying.

                                 6

  Liquefaction is, first, condensation into water; second, the melting
of a solidified body. The first, condensation, is due to the cooling
of vapour: what melting is will appear from the account of
solidification.

  Whatever solidifies is either water or a mixture of earth and water,
and the agent is either dry heat or cold. Hence those of the bodies
solidified by heat or cold which are soluble at all are dissolved by
their opposites. Bodies solidified by the dry-hot are dissolved by
water, which is the moist-cold, while bodies solidified by cold are
dissolved by fire, which is hot. Some things seem to be solidified
by water, e.g. boiled honey, but really it is not the water but the
cold in the water which effects the solidification. Aqueous bodies are
not solidified by fire: for it is fire that dissolves them, and the
same cause in the same relation cannot have opposite effects upon
the same thing. Again, water solidifies owing to the departure of
heat; so it will clearly be dissolved by the entry into it of heat:
cold, therefore, must be the agent in solidifying it.

  Hence aqueous bodies do not thicken when they solidify; for
thickening occurs when the moisture goes off and the dry matter
comes together, but water is the only liquid that does not thicken.
Those bodies that are made up of both earth and water are solidified
both by fire and by cold and in either case are thickened. The
operation of the two is in a way the same and in a way different. Heat
acts by drawing off the moisture, and as the moisture goes off in
vapour the dry matter thickens and collects. Cold acts by driving
out the heat, which is accompanied by the moisture as this goes off in
vapour with it. Bodies that are soft but not liquid do not thicken but
solidify when the moisture leaves them, e.g. potter's clay in
process of baking: but those mixed bodies that are liquid thicken
besides solidifying, like milk. Those bodies which have first been
thickened or hardened by cold often begin by becoming moist: thus
potter's clay at first in the process of baking steams and grows
softer, and is liable to distortion in the ovens for that reason.

  Now of the bodies solidified by cold which are made up both of earth
and water but in which the earth preponderates, those which solidify
by the departure of heat melt by heat when it enters into them
again; this is the case with frozen mud. But those which solidify by
refrigeration, where all the moisture has gone off in vapour with
the heat, like iron and horn, cannot be dissolved except by
excessive heat, but they can be softened-though manufactured iron does
melt, to the point of becoming fluid and then solidifying again.
This is how steel is made. The dross sinks to the bottom and is
purged away: when this has been done often and the metal is pure we
have steel. The process is not repeated often because the purification
of the metal involves great waste and loss of weight. But the iron
that has less dross is the better iron. The stone pyrimachus, too,
melts and forms into drops and becomes fluid; after having been in a
fluid state it solidifies and becomes hard again. Millstones, too,
melt and become fluid: when the fluid mass begins to solidify it is
black but its consistency comes to be like that of lime. and earth,
too

  Of the bodies which are solidified by dry heat some are insoluble,
others are dissolved by liquid. Pottery and some kinds of stone that
are formed out of earth burnt up by fire, such as millstones, cannot
be dissolved. Natron and salt are soluble by liquid, but not all
liquid but only such as is cold. Hence water and any of its
varieties melt them, but oil does not. For the opposite of the dry-hot
is the cold-moist and what the one solidified the other will dissolve,
and so opposites will have opposite effects.

                                 7

  If a body contains more water than earth fire only thickens it: if
it contains more earth fire solidifies it. Hence natron and salt and
stone and potter's clay must contain more earth.

  The nature of oil presents the greatest problem. If water
preponderated in it, cold ought to solidify it; if earth
preponderated, then fire ought to do so. Actually neither
solidifies, but both thicken it. The reason is that it is full of
air (hence it floats on the top of water, since air tends to rise).
Cold thickens it by turning the air in it into water, for any
mixture of oil and water is thicker than either. Fire and the lapse of
time thicken and whiten it. The whitening follows on the evaporation
of any water that may have been in it; the is due to the change of the
air into water as the heat in the oil is dissipated. The effect in
both cases is the same and the cause is the same, but the manner of
its operation is different. Both heat and cold thicken it, but neither
dries it (neither the sun nor cold dries oil), not only because it
is glutinous but because it contains air. Its glutinous nature
prevents it from giving off vapour and so fire does not dry it or boil
it off.

  Those bodies which are made up of earth and water may be
classified according to the preponderance of either. There is a kind
of wine, for instance, which both solidifies and thickens by boiling-I
mean, must. All bodies of this kind lose their water as they That it
is their water may be seen from the fact that the vapour from them
condenses into water when collected. So wherever some sediment is left
this is of the nature of earth. Some of these bodies, as we have said,
are also thickened and dried by cold. For cold not only solidifies but
also dries water, and thickens things by turning air into water.
(Solidifying, as we have said, is a form of drying.) Now those
things that are not thickened by cold, but solidified, belong rather
to water, e.g.. wine, urine, vinegar, lye, whey. But those things that
are thickened (not by evaporation due to fire) are made up either of
earth or of water and air: honey of earth, while oil contains air.
Milk and blood, too, are made up of both water and earth, though earth
generally predominates in them. So, too, are the liquids out of
which natron and salt are formed; and stones are also formed from some
mixtures of this kind. Hence, if the whey has not been separated, it
burns away if you boil it over a fire. But the earthy element in
milk can also be coagulated by the help of fig-juice, if you boil it
in a certain way as doctors do when they treat it with fig-juice,
and this is how the whey and the cheese are commonly separated.
Whey, once separated, does not thicken, as the milk did, but boils
away like water. Sometimes, however, there is little or no cheese in
milk, and such milk is not nutritive and is more like water. The
case of blood is similar: cold dries and so solidifies it. Those kinds
of blood that do not solidify, like that of the stag, belong rather to
water and are very cold. Hence they contain no fibres: for the
fibres are of earth and solid, and blood from which they have been
removed does not solidify. This is because it cannot dry; for what
remains is water, just as what remains of milk when cheese has been
removed is water. The fact that diseased blood will not solidify is
evidence of the same thing, for such blood is of the nature of serum
and that is phlegm and water, the nature of the animal having failed
to get the better of it and digest it.

  Some of these bodies are soluble, e.g. natron, some insoluble,
e.g. pottery: of the latter, some, like horn, can be softened by heat,
others, like pottery and stone, cannot. The reason is that opposite
causes have opposite effects: consequently, if solidification is due
to two causes, the cold and the dry, solution must be due to the hot
and the moist, that is, to fire and to water (these being
opposites): water dissolving what was solidified by fire alone, fire
what was solidified by cold alone. Consequently, if any things
happen to be solidified by the action of both, these are least apt
to be soluble. Such a case we find where things have been heated and
are then solidified by cold. When the heat in leaving them has
caused most of the moisture to evaporate, the cold so compacts these
bodies together again as to leave no entrance even for moisture.
Therefore heat does not dissolve them (for it only dissolves those
bodies that are solidified by cold alone), nor does water (for it does
not dissolve what cold solidifies, but only what is solidified by
dry heat). But iron is melted by heat and solidified by cold. Wood
consists of earth and air and is therefore combustible but cannot be
melted or softened by heat. (For the same reason it floats in
water-all except ebony. This does not, for other kinds of wood contain
a preponderance of air, but in black ebony the air has escaped and
so earth preponderates in it.) Pottery consists of earth alone because
it solidified gradually in the process of drying. Water cannot get
into it, for the pores were only large enough to admit of vapour
escaping: and seeing that fire solidified it, that cannot dissolve
it either.

  So solidification and melting, their causes, and the kinds of
subjects in which they occur have been described.

                                 8

  All this makes it clear that bodies are formed by heat and cold
and that these agents operate by thickening and solidifying. It is
because these qualities fashion bodies that we find heat in all of
them, and in some cold in so far as heat is absent. These qualities,
then, are present as active, and the moist and the dry as passive, and
consequently all four are found in mixed bodies. So water and earth
are the constituents of homogeneous bodies both in plants and in
animals and of metals such as gold, silver, and the rest-water and
earth and their respective exhalations shut up in the compound bodies,
as we have explained elsewhere.

  All these mixed bodies are distinguished from one another, firstly
by the qualities special to the various senses, that is, by their
capacities of action. (For a thing is white, fragrant, sonant,
sweet, hot, cold in virtue of a power of acting on sense). Secondly by
other more characteristic affections which express their aptitude to
be affected: I mean, for instance, the aptitude to melt or solidify or
bend and so forth, all these qualities, like moist and dry, being
passive. These are the qualities that differentiate bone, flesh,
sinew, wood, bark, stone and all other homogeneous natural bodies. Let
us begin by enumerating these qualities expressing the aptitude or
inaptitude of a thing to be affected in a certain way. They are as
follows: to be apt or inapt to solidify, melt, be softened by heat, be
softened by water, bend, break, be comminuted, impressed, moulded,
squeezed; to be tractile or non-tractile, malleable or
non-malleable, to be fissile or non-fissile, apt or inapt to be cut;
to be viscous or friable, compressible or incompressible,
combustible or incombustible; to be apt or inapt to give off fumes.
These affections differentiate most bodies from one another. Let us go
on to explain the nature of each of them. We have already given a
general account of that which is apt or inapt to solidify or to
melt, but let us return to them again now. Of all the bodies that
admit of solidification and hardening, some are brought into this
state by heat, others by cold. Heat does this by drying up their
moisture, cold by driving out their heat. Consequently some bodies are
affected in this way by defect of moisture, some by defect of heat:
watery bodies by defect of heat, earthy bodies of moisture. Now
those bodies that are so affected by defect of moisture are
dissolved by water, unless like pottery they have so contracted that
their pores are too small for the particles of water to enter. All
those bodies in which this is not the case are dissolved by water,
e.g. natron, salt, dry mud. Those bodies that solidified through
defect of heat are melted by heat, e.g. ice, lead, copper. So much for
the bodies that admit of solidification and of melting, and those that
do not admit of melting.

  The bodies which do not admit of solidification are those which
contain no aqueous moisture and are not watery, but in which heat
and earth preponderate, like honey and must (for these are in a sort
of state of effervescence), and those which do possess some water
but have a preponderance of air, like oil and quicksilver, and all
viscous substances such as pitch and birdlime.

                                 9

  Those bodies admit of softening which are not (like ice) made up
of water, but in which earth predominates. All their moisture must not
have left them (as in the case of natron and salt), nor must the
relation of dry to moist in them be incongruous (as in the case of
pottery). They must be tractile (without admitting water) or malleable
(without consisting of water), and the agent in softening them is
fire. Such are iron and horn.

  Both of bodies that can melt and of bodies that cannot, some do
and some do not admit of softening in water. Copper, for instance,
which can be melted, cannot be softened in water, whereas wool and
earth can be softened in water, for they can be soaked. (It is true
that though copper can be melted the agent in its case is not water,
but some of the bodies that can be melted by water too such as
natron and salt cannot be softened in water: for nothing is said to be
so affected unless the water soaks into it and makes it softer.)
Some things, on the other hand, such as wool and grain, can be
softened by water though they cannot be melted. Any body that is to be
softened by water must be of earth and must have its pores larger than
the particles of water, and the pores themselves must be able to
resist the action of water, whereas bodies that can be 'melted' by
water must have pores throughout.

  (Why is it that earth is both 'melted' and softened by moisture,
while natron is 'melted' but not softened? Because natron is
pervaded throughout by pores so that the parts are immediately divided
by the water, but earth has also pores which do not connect and is
therefore differently affected according as the water enters by one or
the other set of pores.)

  Some bodies can be bent or straightened, like the reed or the withy,
some cannot, like pottery and stone. Those bodies are apt to be bent
and straightened which can change from being curved to being
straight and from being straight to being curved, and bending and
straightening consist in the change or motion to the straight or to
a curve, for a thing is said to be in process of being bent whether it
is being made to assume a convex or a concave shape. So bending is
defined as motion to the convex or the concave without a change of
length. For if we added 'or to the straight', we should have a thing
bent and straight at once, and it is impossible for that which is
straight to be bent. And if all bending is a bending back or a bending
down, the former being a change to the convex, the latter to the
concave, a motion that leads to the straight cannot be called bending,
but bending and straightening are two different things. These, then,
are the things that can, and those that cannot be bent, and be
straightened.

  Some things can be both broken and comminuted, others admit only one
or the other. Wood, for instance, can be broken but not comminuted,
ice and stone can be comminuted but not broken, while pottery may
either be comminuted or broken. The distinction is this: breaking is a
division and separation into large parts, comminution into parts of
any size, but there must be more of them than two. Now those solids
that have many pores not communicating with one another are
comminuible (for the limit to their subdivision is set by the
pores), but those whose pores stretch continuously for a long way
are breakable, while those which have pores of both kinds are both
comminuible and breakable.

  Some things, e.g. copper and wax, are impressible, others, e.g.
pottery and water, are not. The process of being impressed is the
sinking of a part of the surface of a thing in response to pressure or
a blow, in general to contact. Such bodies are either soft, like
wax, where part of the surface is depressed while the rest remains, or
hard, like copper. Non-impressible bodies are either hard, like
pottery (its surface does not give way and sink in), or liquid, like
water (for though water does give way it is not in a part of it, for
there is a reciprocal change of place of all its parts). Those
impressibles that retain the shape impressed on them and are easily
moulded by the hand are called 'plastic'; those that are not easily
moulded, such as stone or wood, or are easily moulded but do not
retain the shape impressed, like wool or a sponge, are not plastic.
The last group are said to be 'squeezable'. Things are 'squeezable'
when they can contract into themselves under pressure, their surface
sinking in without being broken and without the parts interchanging
position as happens in the case of water. (We speak of pressure when
there is movement and the motor remains in contact with the thing
moved, of impact when the movement is due to the local movement of the
motor.) Those bodies are subject to squeezing which have empty
pores-empty, that is, of the stuff of which the body itself
consists-and that can sink upon the void spaces within them, or rather
upon their pores. For sometimes the pores upon which a body sinks in
are not empty (a wet sponge, for instance, has its pores full). But
the pores, if full, must be full of something softer than the body
itself which is to contract. Examples of things squeezable are the
sponge, wax, flesh. Those things are not squeezable which cannot be
made to contract upon their own pores by pressure, either because they
have no pores or because their pores are full of something too hard.
Thus iron, stone, water and all liquids are incapable of being
squeezed.

  Things are tractile when their surface can be made to elongate,
for being drawn out is a movement of the surface, remaining
unbroken, in the direction of the mover. Some things are tractile,
e.g. hair, thongs, sinew, dough, birdlime, and some are not, e.g.
water, stone. Some things are both tractile and squeezable, e.g. wool;
in other cases the two qualities do not coincide; phlegm, for
instance, is tractile but not squeezable, and a sponge squeezable
but not tractile.

  Some things are malleable, like copper. Some are not, like stone and
wood. Things are malleable when their surface can be made to move (but
only in part) both downwards and sideways with one and the same
blow: when this is not possible a body is not malleable. All malleable
bodies are impressible, but not all impressible bodies are
malleable, e.g. wood, though on the whole the two go together. Of
squeezable things some are malleable and some not: wax and mud are
malleable, wool is not. Some things are fissile, e.g. wood, some are
not, e.g. potter's clay. A thing is fissile when it is apt to divide
in advance of the instrument dividing it, for a body is said to
split when it divides to a further point than that to which the
dividing instrument divides it and the act of division advances: which
is not the case with cutting. Those bodies which cannot behave like
this are non-fissile. Nothing soft is fissile (by soft I mean
absolutely soft and not relatively: for iron itself may be
relatively soft); nor are all hard things fissile, but only such as
are neither liquid nor impressible nor comminuible. Such are the
bodies that have the pores along which they cohere lengthwise and
not crosswise.

  Those hard or soft solids are apt to be cut which do not necessarily
either split in advance of the instrument or break into minute
fragments when they are being divided. Those that necessarily do so
and liquids cannot be cut. Some things can be both split and cut, like
wood, though generally it is lengthwise that a thing can be split
and crosswise that it can be cut. For, a body being divided into
many parts fin so far as its unity is made up of many lengths it is
apt to be split, in so far as it is made up of many breadths it is apt
to be cut.

  A thing is viscous when, being moist or soft, it is tractile. Bodies
owe this property to the interlocking of their parts when they are
composed like chains, for then they can be drawn out to a great length
and contracted again. Bodies that are not like this are friable.
Bodies are compressible when they are squeezable and retain the
shape they have been squeezed into; incompressible when they are
either inapt to be squeezed at all or do not retain the shape they
have been squeezed into.

  Some bodies are combustible and some are not. Wood, wool, bone are
combustible; stone, ice are not. Bodies are combustible when their
pores are such as to admit fire and their longitudinal pores contain
moisture weaker than fire. If they have no moisture, or if, as in
ice or very green wood, the moisture is stronger than fire, they are
not combustible.

  Those bodies give off fumes which contain moisture, but in such a
form that it does not go off separately in vapour when they are
exposed to fire. For vapour is a moist secretion tending to the nature
of air produced from a liquid by the agency of burning heat. Bodies
that give off fumes give off secretions of the nature of air by the
lapse of time: as they perish away they dry up or become earth. But
the kind of secretion we are concerned with now differs from others in
that it is not moist nor does it become wind (which is a continuous
flow of air in a given direction). Fumes are common secretion of dry
and moist together caused by the agency of burning heat. Hence they do
not moisten things but rather colour them.

  The fumes of a woody body are called smoke. (I mean to include bones
and hair and everything of this kind in the same class. For there is
no name common to all the objects that I mean, but, for all that,
these things are all in the same class by analogy. Compare what
Empedocles says: They are one and the same, hair and leaves and the
thick wings of birds and scales that grow on stout limbs.) The fumes
of fat are a sooty smoke and those of oily substances a greasy
steam. Oil does not boil away or thicken by evaporation because it
does not give off vapour but fumes. Water on the other hand does not
give off fumes, but vapour. Sweet wine does give off fumes, for it
contains fat and behaves like oil. It does not solidify under the
influence of cold and it is apt to burn. Really it is not wine at
all in spite of its name: for it does not taste like wine and
consequently does not inebriate as ordinary wine does. It contains but
little fumigable stuff and consequently is inflammable.

  All bodies are combustible that dissolve into ashes, and all
bodies do this that solidify under the influence either of heat or
of both heat and cold; for we find that all these bodies are
mastered by fire. Of stones the precious stone called carbuncle is
least amenable to fire.

  Of combustible bodies some are inflammable and some are not, and
some of the former are reduced to coals. Those are called
'inflammable' which produce flame and those which do not are called
'non-inflammable'. Those fumigable bodies that are not liquid are
inflammable, but pitch, oil, wax are inflammable in conjunction with
other bodies rather than by themselves. Most inflammable are those
bodies that give off smoke. Of bodies of this kind those that
contain more earth than smoke are apt to be reduced to coals. Some
bodies that can be melted are not inflammable, e.g. copper; and some
bodies that cannot be melted are inflammable, e.g. wood; and some
bodies can be melted and are also inflammable, e.g. frankincense.
The reason is that wood has its moisture all together and this is
continuous throughout and so it burns up: whereas copper has it in
each part but not continuous, and insufficient in quantity to give
rise to flame. In frankincense it is disposed in both of these ways.
Fumigable bodies are inflammable when earth predominates in them and
they are consequently such as to be unable to melt. These are
inflammable because they are dry like fire. When this dry comes to
be hot there is fire. This is why flame is burning smoke or dry
exhalation. The fumes of wood are smoke, those of wax and frankincense
and such-like, and pitch and whatever contains pitch or such-like
are sooty smoke, while the fumes of oil and oily substances are a
greasy steam; so are those of all substances which are not at all
combustible by themselves because there is too little of the dry in
them (the dry being the means by which the transition to fire is
effected), but burn very readily in conjunction with something else.
(For the fat is just the conjunction of the oily with the dry.) So
those bodies that give off fumes, like oil and pitch, belong rather to
the moist, but those that burn to the dry.

                                10

  Homogeneous bodies differ to touch-by these affections and
differences, as we have said. They also differ in respect of their
smell, taste, and colour.

  By homogeneous bodies I mean, for instance, 'metals', gold,
copper, silver, tin, iron, stone, and everything else of this kind and
the bodies that are extracted from them; also the substances found
in animals and plants, for instance, flesh, bones, sinew, skin,
viscera, hair, fibres, veins (these are the elements of which the
non-homogeneous bodies like the face, a hand, a foot, and everything
of that kind are made up), and in plants, wood, bark, leaves, roots,
and the rest like them.

  The homogeneous bodies, it is true, are constituted by a different
cause, but the matter of which they are composed is the dry and the
moist, that is, water and earth (for these bodies exhibit those
qualities most clearly). The agents are the hot and the cold, for they
constitute and make concrete the homogeneous bodies out of earth and
water as matter. Let us consider, then, which of the homogeneous
bodies are made of earth and which of water, and which of both.

  Of organized bodies some are liquid, some soft, some hard. The
soft and the hard are constituted by a process of solidification, as
we have already explained.

  Those liquids that go off in vapour are made of water, those that do
not are either of the nature of earth, or a mixture either of earth
and water, like milk, or of earth and air, like wood, or of water
and air, like oil. Those liquids which are thickened by heat are a
mixture. (Wine is a liquid which raises a difficulty: for it is both
liable to evaporation and it also thickens; for instance new wine
does. The reason is that the word 'wine' is ambiguous and different
'wines' behave in different ways. New wine is more earthy than old,
and for this reason it is more apt to be thickened by heat and less
apt to be congealed by cold. For it contains much heat and a great
proportion of earth, as in Arcadia, where it is so dried up in its
skins by the smoke that you scrape it to drink. If all wine has some
sediment in it then it will belong to earth or to water according to
the quantity of the sediment it possesses.) The liquids that are
thickened by cold are of the nature of earth; those that are thickened
either by heat or by cold consist of more than one element, like oil
and honey, and 'sweet wine'.

  Of solid bodies those that have been solidified by cold are of
water, e.g. ice, snow, hail, hoar-frost. Those solidified by heat
are of earth, e.g. pottery, cheese, natron, salt. Some bodies are
solidified by both heat and cold. Of this kind are those solidified by
refrigeration, that is by the privation both of heat and of the
moisture which departs with the heat. For salt and the bodies that are
purely of earth solidify by the privation of moisture only, ice by
that of heat only, these bodies by that of both. So both the active
qualities and both kinds of matter were involved in the process. Of
these bodies those from which all the moisture has gone are all of
them of earth, like pottery or amber. (For amber, also, and the bodies
called 'tears' are formed by refrigeration, like myrrh,
frankincense, gum. Amber, too, appears to belong to this class of
things: the animals enclosed in it show that it is formed by
solidification. The heat is driven out of it by the cold of the
river and causes the moisture to evaporate with it, as in the case
of honey when it has been heated and is immersed in water.) Some of
these bodies cannot be melted or softened; for instance, amber and
certain stones, e.g. the stalactites in caves. (For these stalactites,
too, are formed in the same way: the agent is not fire, but cold which
drives out the heat, which, as it leaves the body, draws out the
moisture with it: in the other class of bodies the agent is external
fire.) In those from which the moisture has not wholly gone earth
still preponderates, but they admit of softening by heat, e.g. iron
and horn.

  Now since we must include among 'meltables' those bodies which are
melted by fire, these contain some water: indeed some of them, like
wax, are common to earth and water alike. But those that are melted by
water are of earth. Those that are not melted either by fire or
water are of earth, or of earth and water.

  Since, then, all bodies are either liquid or solid, and since the
things that display the affections we have enumerated belong to
these two classes and there is nothing intermediate, it follows that
we have given a complete account of the criteria for distinguishing
whether a body consists of earth or of water or of more elements
than one, and whether fire was the agent in its formation, or cold, or
both.

  Gold, then, and silver and copper and tin and lead and glass and
many nameless stone are of water: for they are all melted by heat.
Of water, too, are some wines and urine and vinegar and lye and whey
and serum: for they are all congealed by cold. In iron, horn, nails,
bones, sinews, wood, hair, leaves, bark, earth preponderates. So, too,
in amber, myrrh, frankincense, and all the substances called
'tears', and stalactites, and fruits, such as leguminous plants and
corn. For things of this kind are, to a greater or less degree, of
earth. For of all these bodies some admit of softening by heat, the
rest give off fumes and are formed by refrigeration. So again in
natron, salt, and those kinds of stones that are not formed by
refrigeration and cannot be melted. Blood, on the other hand, and
semen, are made up of earth and water and air. If the blood contains
fibres, earth preponderates in it: consequently its solidifies by
refrigeration and is melted by liquids; if not, it is of water and
therefore does not solidify. Semen solidifies by refrigeration, its
moisture leaving it together with its heat.

                                11

  We must investigate in the light of the results we have arrived at
what solid or liquid bodies are hot and what cold.

  Bodies consisting of water are commonly cold, unless (like lye,
urine, wine) they contain foreign heat. Bodies consisting of earth, on
the other hand, are commonly hot because heat was active in forming
them: for instance lime and ashes.

  We must recognize that cold is in a sense the matter of bodies.
For the dry and the moist are matter (being passive) and earth and
water are the elements that primarily embody them, and they are
characterized by cold. Consequently cold must predominate in every
body that consists of one or other of the elements simply, unless such
a body contains foreign heat as water does when it boils or when it
has been strained through ashes. This latter, too, has acquired heat
from the ashes, for everything that has been burnt contains more or
less heat. This explains the generation of animals in putrefying
bodies: the putrefying body contains the heat which destroyed its
proper heat.

  Bodies made up of earth and water are hot, for most of them derive
their existence from concoction and heat, though some, like the
waste products of the body, are products of putrefaction. Thus
blood, semen, marrow, figjuice, and all things of the kinds are hot as
long as they are in their natural state, but when they perish and fall
away from that state they are so no longer. For what is left of them
is their matter and that is earth and water. Hence both views are held
about them, some people maintaining them to be cold and others to be
warm; for they are observed to be hot when they are in their natural
state, but to solidify when they have fallen away from it. That, then,
is the case of mixed bodies. However, the distinction we laid down
holds good: if its matter is predominantly water a body is cold (water
being the complete opposite of fire), but if earth or air it tends
to be warm.

  It sometimes happens that the coldest bodies can be raised to the
highest temperature by foreign heat; for the most solid and the
hardest bodies are coldest when deprived of heat and most burning
after exposure to fire: thus water is more burning than smoke and
stone than water.

                                12

  Having explained all this we must describe the nature of flesh,
bone, and the other homogeneous bodies severally.

  Our account of the formation of the homogeneous bodies has given
us the elements out of which they are compounded and the classes
into which they fall, and has made it clear to which class each of
those bodies belongs. The homogeneous bodies are made up of the
elements, and all the works of nature in turn of the homogeneous
bodies as matter. All the homogeneous bodies consist of the elements
described, as matter, but their essential nature is determined by
their definition. This fact is always clearer in the case of the later
products of those, in fact, that are instruments, as it were, and have
an end: it is clearer, for instance, that a dead man is a man only
in name. And so the hand of a dead man, too, will in the same way be a
hand in name only, just as stone flutes might still be called
flutes: for these members, too, are instruments of a kind. But in
the case of flesh and bone the fact is not so clear to see, and in
that of fire and water even less. For the end is least obvious there
where matter predominates most. If you take the extremes, matter is
pure matter and the essence is pure definition; but the bodies
intermediate between the two are matter or definition in proportion as
they are near to either. For each of those elements has an end and
is not water or fire in any and every condition of itself, just as
flesh is not flesh nor viscera viscera, and the same is true in a
higher degree with face and hand. What a thing is always determined by
its function: a thing really is itself when it can perform its
function; an eye, for instance, when it can see. When a thing cannot
do so it is that thing only in name, like a dead eye or one made of
stone, just as a wooden saw is no more a saw than one in a picture.
The same, then, is true of flesh, except that its function is less
clear than that of the tongue. So, too, with fire; but its function is
perhaps even harder to specify by physical inquiry than that of flesh.
The parts of plants, and inanimate bodies like copper and silver,
are in the same case. They all are what they are in virtue of a
certain power of action or passion-just like flesh and sinew. But we
cannot state their form accurately, and so it is not easy to tell when
they are really there and when they are not unless the body is
thoroughly corrupted and its shape only remains. So ancient corpses
suddenly become ashes in the grave and very old fruit preserves its
shape only but not its taste: so, too, with the solids that form
from milk.

  Now heat and cold and the motions they set up as the bodies are
solidified by the hot and the cold are sufficient to form all such
parts as are the homogeneous bodies, flesh, bone, hair, sinew, and the
rest. For they are all of them differentiated by the various qualities
enumerated above, tension, tractility, comminuibility, hardness,
softness, and the rest of them: all of which are derived from the
hot and the cold and the mixture of their motions. But no one would go
as far as to consider them sufficient in the case of the
non-homogeneous parts (like the head, the hand, or the foot) which
these homogeneous parts go to make up. Cold and heat and their
motion would be admitted to account for the formation of copper or
silver, but not for that of a saw, a bowl, or a box. So here, save
that in the examples given the cause is art, but in the nonhomogeneous
bodies nature or some other cause.

  Since, then, we know to what element each of the homogeneous
bodies belongs, we must now find the definition of each of them, the
answer, that is, to the question, 'what is' flesh, semen, and the
rest? For we know the cause of a thing and its definition when we know
the material or the formal or, better, both the material and the
formal conditions of its generation and destruction, and the efficient
cause of it.

  After the homogeneous bodies have been explained we must consider
the non-homogeneous too, and lastly the bodies made up of these,
such as man, plants, and the rest.

                                   -THE END-
.