Scientific American/Series 1/Volume 1/Issue 1/Cause of Sound in Thunder

Cause of Sound in Thunder.—Thunder is one of the consequences resulting from lightning, and lightning appears to be occasioned by the combustion of some of the inflammable particles of air; or according to more recent opinions, of a condensation of aerial matter conducing to electricity, by which in either case, a vacuum is created. The surrounding atoms which remain uninfluenced by this change, being forced together, by the whole weight of the atmosphere, greatly constrict each other; but their elastic nature causes them immediately to expand, and by this enlargement their sonorous property is acquired. A centrifugal force being thus established, it acts in all directions alike; but as the circle extends, its propulsive power becomes gradually diminished, till at last its pressure is no longer felt, nor sound created. The fumbling noise of thunder is produced by that portion of the sonorous circle which strikes upon the earth, whence it becomes condensed; and, being intercepted in its upward course by dense masses of vapor, it is again reflected, and this alternate motion and reverberation continue, until the interruption ceases, or the original force is exhausted. Echo is occasioned also by reverbration from one cloud to another.—Webster's Principles of Sound.