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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