XIV
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Let me now recall a remark that I had made early in this book, namely, that wind issues from cave or inner recess of earth. The whole earth is not of solid compact constitution down to its lowest foundations, but at many points is hollow,
... hung over dark retreats.
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In some places it contains voids that have no moisture. Though there is no light there to show the distinctions in the air, yet I venture to assert that cloud and mist settle in that gloom. Above ground cloud and mist surely do not exist because they are seen; but, rather, they are seen because they exist. Well, there too rivers none the less exist that they are not seen. You must understand that down there rivers flow equal in size to our own. Some glide gently, others resound as they tumble down headlong over the broken ground. So must not you equally allow that there are some lakes underground and some water in pools without an exit? This being so, it is of necessity that the air be charged with moisture, and that, being charged, it lean in one direction, raising the wind by its propulsion. We must recognise, therefore, that from those subterranean clouds blasts of wind are raised in the dark, what time they have gathered strength sufficient to remove the obstacles presented by the earth, or can seize upon some open path for their exit, and from this cavernous retreat can escape toward the abodes of men. Now it is obvious that underground there are large quantities of sulphur and other substances no less inflammable. When the air in search of a path of escape works its tortuous way through ground of this nature, it necessarily kindles fire by the mere friction. By and by, as the flames spread more widely, any sluggish air there may be is also rarefied and set in motion; a way of escape is sought with great roaring and violence. This point I will elaborate in more detail when I go on to treat of earthquakes.