I907 J AND CONTRACTION OF THE EARTH. 247 



not cease of a sudden, nor rapidly, but by gradual giving away, along with the 

 decrease of the symptom, so likewise the cause that produces the exhalation 

 of vapor, and the first shock of the blast, do not at once set free the matter, 

 from which are developed the kind of wind, which we call an earthquake. 

 Until therefore the rest of these vapors has escaped the shaking of the earth 

 necessarily continues. But it acts more and more feebly, till the time when 

 the exhalation is too reduced to make a movement which remains sensible. 



" And the blast of vapor also makes those sounds which arise beneath 

 the earth, and those which precede earthquakes. And even without earth- 

 quakes there are places where these noises are developed under the earth; 

 for just as the air when struck and rent produces all kinds of noises, so like- 

 wise also the ground itself produces noises when shaken; for there is no 

 difference, since in the shock everything which agitates is itself shaken in 

 its entirety. The roaring precedes the commotion, because the sound has 

 parts as tenuous as the wind itself, and it penetrates as easily through all 

 bodies. 



" And whenever it is unable to move the earth on account of its very 

 lightness, it is certain, since it passes through without difficulty, that it does 

 not make it tremble, but according as it strikes against hard substances with 

 cavities, and all manner of shapes, so they give off all kinds of sounds; 

 consequently it sometimes seems, just as the marvel-mongers say, that the 

 earth is made to roar. 



" Occasionally as the result of earthquakes water gushes forth from the 

 ground ; but one is not able to say on this account that it was the water 

 which caused the commotion; on the contrary it is always the blast of wind, 

 whether from the surface, or confined below the earth, that produces the 

 violence; dnd this is the moving power, just as one may say that the winds 

 develop waves in the sea but the waves are not the cause of the winds ; and 

 thus then one may say that this earth itself is the cause of the phenomenon; 

 for having been shaken it oscillates, just as water does, for the wave is 

 a kind of oscillation ; but the cause of the phenomenon is the same in both 

 (the water and the earth) ; it experiences the agitation, yet does not produce 

 it; but the blast of vapor is the real cause. 



" Wherever along with an earthquake an inundation is produced the 

 cause of it is the development of blasts of wind of a contrary nature. This 

 happens whenever the blast of wind which shakes the earth is unable to 

 repel completely the sea, which another blast of wind controls, nevertheless 

 meeting it, opposing it, and confining it, gathering much force at the same 

 point; for then necessarily the blast of wind confined in the earth by the sea 

 cannot be resisted from breaking open a passage against the force of the 

 opposite blast, and making a cataclysm. 



" This is exactly what happened in the region of Achaia ; for above the 

 earth there was the south wind on one side, the north wind on the other. 

 A calm having arisen, and the wind flowing within, there was produced at 

 the same time an inundation and the accompanying earthquake; and the 

 violence arose chiefly because the sea would not give passage to the wind 

 imprisoned under the earth, but on the contrary obstructed it. Then having 

 forced open other passages, the blast of vapor produced the earthquake, and 

 the rising of the great sea wave caused the cataclysm. 



