XXVII
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Some writers have distinguished different kinds of thunder, saying there was one kind with a deep growl like that which precedes an earthquake, when the wind moans and tries to burst its prison walls, Let me tell you how they suppose this kind of thunder to arise. When the clouds have enclosed air, it rolls through their cavernous depths and emits a hoarse, regular, continuous sound like bellowing. So also when that quarter of the heavens is charged with moisture, its exit is prevented until the thunder begins. Therefore, thunder of this kind is a sure sign that rain is to follow. There is another kind, which is sharp, and it might be described more accurately as a crackling than as a regular sound; it resembles the report one hears when a bladder is burst over some one’s head. Such thunder is the result of the breaking up of a densely massed cloud and the release of the air by which it was inflated. This is appropriately named a peal, sudden and violent. When it occurs, people collapse and are sometimes literally frightened to death by it; others retain life, but are dazed and completely lose their wits: we call them thunder-struck, for that sound in the heavens has quite unhinged their minds. This sound may also be produced by the atmosphere shut up in a hollow cloud being rarefied, merely through motion, and expanded. By and by in seeking more room for itself it resounds against the walls that envelop it. In fact, is it not just similar to the applause given out by the clapping of the hands? only, when the clouds collide, the sounds may be expected to correspond in volume to the greatness of the encountering bodies.