SIR — Here we propose a model of ball lightning, a rare and beautiful phenomenon, so far unexplained. Usually, it appears as a flaming ball, most frequently red, orange or bright white, green or blue in some rarer cases, its diameter being typically10-30 cm, although some examples of a few centimetres or of several metres have also been observed. It moves in an unpredictable way and disappears after several seconds, sometimes smoothly, occasionally with an explosion.
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