XI
Some attribute these earthquakes to fire, but give different explanations of its action. When fire causes intense heat at various points beneath the earth, it must roll up a great cloud of vapour, which can find no exit, and which dilates the air by its high temperature. If the pressure of the vapour is excessive, it scatters all obstructions; but if it is comparatively moderate, it merely causes movement of the earth. We observe water smoke when fire is applied. What the fire does to this water in a narrow pot, one may suppose is done on a much greater scale when a violent and wide-spreading fire causes immense extents of water to boil. It then by evaporation from the overflowing waters shakes violently whatever it strikes.