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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

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