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Well, first of all, the fire which is thus produced is, as it is found in the clouds, not water, but thick air, adapted for the generating of water; it is not yet changed into it, but is already inclined toward, and ready for, the change. There is no ground for supposing that water is first gathered in the clouds and afterwards shed from them. It falls simultaneously with its formation. But in the second place, though I grant that the cloud is moist and charged with fully formed water, still there is nothing to prevent fire being drawn from what is moist, yes—and what will surprise you more to learn—out of pure moisture. Some authorities have actually affirmed that nothing can be converted into fire without a prior change into water. A cloud, then, without prejudice to the water it may contain, may emit fire at some part of it, just as often one end of a log is blazing while the other exudes moisture. I do not deny that fire and water are opposing elements and that the one destroys the other. But where the fire is stronger than the water it wins the day. On the other hand, where there is a superabundant supply of moisture, then fire is powerless. That is why green wood won’t burn. The result depends, therefore, on the quantity of water present. If it is small, no effectual resistance is offered, the fire is not prevented. Why, according to Posidonius’ account, when an island rose in the Aegean Sea long ago in our forefathers’ days, the sea was lashed into foam for a long time previously and sent up smoke from its depths. At last fire was emitted, not continuously, but in flames shooting out at intervals, after the fashion of thunderbolts, just as often as the fervent heat of what lay below had overcome the weight of water above it. By and by boulders were thrown up and rocks, part of them still unimpaired, which the air had thrust out before their calcination, part of them corroded by the fire and changed to light pumice; at last the cone of a blasted mountain issued from the waves. Subsequently, there was an addition to its height, and the rock grew in extent into an island. The same thing happened within our own recollection during the second consulship of Valerius Asiaticus.
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Why have I narrated these incidents? My purpose was to make it evident that neither is fire necessarily extinguished by having the whole sea poured over it, nor its violence prevented from bursting out by the weight of huge waves. Asclepiodotus, a pupil of Posidonius, has left it on record that the height to which the fire mounted, after overcoming the resistance of the waves, was a hundred fathoms. Now, if such a huge mass of water was unable to overcome the force of the flames that rose from its depths, how much less can the thin, dewy moisture in the clouds extinguish fire in the atmosphere? In short, the moisture of the clouds is so far from presenting any obstacle to the formation of fire that lightning is never seen to flash except when the sky threatens rain. A clear sky has no bolts to hurl. No terror of that sort proceeds from a bright day, nor for the matter of that from a night that is not enveloped in cloud. But what! I hear some one say. Does it not sometimes lighten in a calm night when the stars are visible? It does, but you must remember that there are clouds all the same in that quarter whence issues the flash; only, the earth’s hump does not allow them to be seen by us. Add, too, what is quite possible, that low clouds near the earth may produce fire through friction. This fire when forced up to the upper regions becomes visible in the clear bright part of the sky, but none the less its place of origin was in the dark vicinity of earth.