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Meteorology   


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

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