,907] AND CONTRACTION OF THE EARTH. 249 



collected mass of the cloud, and gives rise to a great noise and clashing, 

 called thunder, just as in water (when heated) a blast of steam breaks forth 

 violently. During the outbreak from the cloud the blast becomes fiery and 

 brilliant, and is called lightning; it strikes before the thunder because it 

 develops before it. . . . 



" Now just as the earth includes within it a large amount of water, so 

 likewise it contains also blasts of vapor, and streams of fire. And of these, 

 those which are beneath the earth are obviously invisible; but many have 

 vents, and eruptions, just as Lapari and Aetna and places in the islands of 

 vEolus; which indeed often produce flows as in rivers and belch forth red 

 hot streams of fire; some coming from beneath the earth, near springs of 

 water, heat them, while others arise from springs of lukewarm character; 

 the former being extremely hot, the latter agreeably tempered." 



" And similarly many blasts of vapor break out from cavities every- 

 where in the earth ; some of these communicate great enthusiasm to those 

 who approach them, while others cause a languishing effect ; and again others 

 are made to sing oracles, as those in Delphi, and in Lebadia, and finally there 

 are some which wholly destroy one another, just as those in Phrygia. 



" And quite often also a blast of vapor conveniently tempered in the 

 earth issues forth into its innermost passages, making strange sounds from 

 familar places, and a large part of the blast flows out. Very often also a 

 strong blast of vapor arises from without, and is absorbed in the cavities of 

 the earth, shutting off the escape, and with force shaking it, seeking to break 

 open its own orifice, and producing the phenomena which we are accustomed 

 to call an earthquake. 



" And of earthquakes there are some which shake sidewise, at acute 

 angles (obliquely), called epiclintae; those shaking upward and downward, 

 at right angles, brastae, those in which the ground collapses, making hollows, 

 chasmatiae, those opening chasms and breaking the ground all to pieces, 

 called rhectae. And of all these, there are some which permit the escape of 

 a blast of vapor; others which throw up stones; others which eject earth, 

 some which disclose sources not suspected before; and still others returning 

 to equilibrium after a single shock, which they call ostae ; those which re- 

 bound, the disturbed body oscillating to and fro, so as always to restore the 

 .equilibrium, such shaking is called palmaticB, which produces a phenomenon 

 like a trembling. 



" There arises also earthquakes with subterranean thunder, shaking the 

 earth with a roaring noise. Very often apart from an earthquake there 

 arises a roaring of the earth, whenever the vapor is not strong enough to 

 shake it, but nevertheless circulates within, endowed with a powerful rota- 

 tory motion. 



" There are likewise blasts of vapor which enter the earth's interior, and 

 are absorbed by the waters hidden within the earth. These phenomena are 

 analogous to those which occur in the sea; for there are also chasms where 

 the sea opens out and again when it withdraws, and there is an inundation 

 of waves, and they have a recoil ; and occasionally there is only a single 

 pushing away of the sea {npouot;-) , just as is related indeed of Helike and 

 of Boura. 



