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Meteorology By Aristotle

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Author Topic: Meteorology By Aristotle  (Read 1316 times)
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« Reply #75 on: August 31, 2009, 12:03:31 am »

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.
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« Reply #76 on: August 31, 2009, 12:03:47 am »

Part 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.
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« Reply #77 on: August 31, 2009, 12:04:03 am »

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.

Part 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.
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« Reply #78 on: August 31, 2009, 12:04:24 am »

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.
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« Reply #79 on: August 31, 2009, 12:04:43 am »

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.
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« Reply #80 on: August 31, 2009, 12:04:53 am »

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.
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« Reply #81 on: August 31, 2009, 12:05:12 am »

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.)

Part 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.)
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« Reply #82 on: August 31, 2009, 12:05:24 am »

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.
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« Reply #83 on: August 31, 2009, 12:05:47 am »

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.)
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« Reply #84 on: August 31, 2009, 12:06:05 am »

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.
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« Reply #85 on: August 31, 2009, 12:06:20 am »

Part 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.
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« Reply #86 on: August 31, 2009, 12:06:38 am »

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.

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« Reply #87 on: August 31, 2009, 12:06:48 am »


Part 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.
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« Reply #88 on: August 31, 2009, 12:07:03 am »

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.
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« Reply #89 on: August 31, 2009, 12:07:19 am »

Part 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.
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