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Some authors, including Asclepiodotus, are convinced that thunder and lightning may also be produced by the collision of certain solid bodies. Once Etna was in violent eruption and cast up a huge quantity of burning sand. The daylight was veiled with the cloud of dust, and sudden night terrified the world. On that occasion, they allege, there was much thunder and lightning, produced, they maintain, by the concourse of dry bodies, not of clouds: with such a glow in the firmament there probably were no clouds at all. Cambyses once sent an army to the temple of Jupiter Ammon in the desert. The sand raised by the south wind fell on it like snowflakes, first covering and finally overwhelming it. Probably on that occasion also there was thunder and lightning, caused by the mutual friction of the particles of sand. Such a view is not inconsistent with my contention above. I have said that the earth’s exhalations contain bodies of two kinds, dry and moist, portions of which roam through the whole expanse of the atmosphere. So if any heavy element be introduced, it makes a cloud thicker and more solid than if its texture were of pure air exclusively. Such a [solid] cloud may burst with a loud report. The elements I have mentioned, whether they have charged the atmosphere with moist fires or with earth-sweeping winds, must produce a cloud before they produce a report. Dry elements no less than moist may make up a cloud. For cloud, as we have already said, is just a condensation of thick air.