xx CO MB IN A TION OF CA USES 2 5 1 



to pronounce anything as certain in matters in 

 which conjecture must be resorted to. As he says, 5 

 then, water is capable of producing earthquake 

 by washing and rubbing off certain portions, the 

 weakening of which removes the support of what 

 was upborne by them when unimpaired. The 

 force of air is also capable of moving the earth. 

 Perhaps the air within the earth is set in violent 

 agitation by other air entering from without. Or, 

 perchance, it may be that the earth receives an 

 internal blow from the sudden fall of some portion 

 of it, and derives thence the shock. Or, perchance, 

 some portion of the earth is upheld, as it were, by 

 certain pillars and stakes, the injury or withdrawal 

 of which causes a tremor to run through the mass 

 they support. Or, perchance, a quantity of hot air 6 

 turning to fire and assuming the character of light- 

 ning courses along to the widespread destruction 

 of all obstacles it encounters. Or, perchance, some 

 wind stirs the sluggish marshy waters, whose stroke 

 in consequence shakes the earth ; or the tossing 

 of the air, increasing to violence through the mere 

 movement, is carried from the lowest depths right 

 up to the surface of the earth. Still, Epicurus is 

 satisfied that there is no more potent cause of earth- 

 quake than air. 



XXI 



WE Stoics also are convinced that it is only air that 

 can attempt such a feat as the production of an 

 earthquake, for than it nothing in the whole realm 

 of nature is more powerful, more energetic ; in 

 absence of it even the elements that are most violent 

 lose their force. It is by air that fire is kindled ; 



