XXIII
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Perchance, too, when the wind only blows softly and exerts no great force, the clouds, wafted against each other, will emit fire strong enough to show a gleam, though not to issue from them. Less force is required for lightning than for the thunderbolt. We found above what a glow the friction of certain woods caused. Now when the air, which is interchangeable with fire, [has been changed in full force into fire and]45 undergoes friction, it is credible and even probable that fire is struck out, but of an evanescent and transitory character, as it arises from no solid material and has no fuel in which it can lodge. It therefore quickly passes; its duration is no longer than its route and course; it has nothing to support it when hurled forth into space.