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