toward which it has urged the gathering of the waters. Sometimes, again, the air is driven into passages through the earth, and in its 4 search for a way of escape causes a general movement. The earth, as we know, is pervious to wind; air is too subtle to be excluded, too violent to be resisted when excited to rapid movement. Turning from Democritus to Epicurus, we find the latter to assert that all the foregoing may be causes of earthquake, but he tries to introduce some additional ones. He criticises other authors for affirming too positively that some particular one of the causes is responsible, as it is difficult to pronounce anything as certain in matters in which conjecture must be resorted to. As he says, then, 5 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 lightning 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 earthquake than air. XXI We Stoics also are convinced that it is only air that can attempt 1 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; if you withdraw wind, water is sluggish. Water becomes impetuous only when the blast tosses it with violence. This force it is that has power to scatter vast spaces of earth, to raise from the depths new mountains, and to set in mid-ocean islands hitherto unseen. Can any one doubt that There and Therasia and this 2 island which in our days under our very eyes rose out of the Aegean Sea, were carried up to the light by the force of air?