THUNDER AND LIGHTNING
Reading edition
The lightning flash is merely a huge electric spark, such as may be seen between the terminals of any electric machine. In cases of flashes, or forked lightning, this “spark” is seen directly. Sheet lightning is observed when the original flash is hidden behind clouds, and only its reflection or effects are seen. The rumbling of thunder is due to the reverberations and echoes of the original “peal.” The peal is thought to be due to the sudden rushing together of the molecules of the upper atmosphere, which have been rent asunder by the flash—a sort of vacuum created. Camille Flammarion has written an interesting book on “Thunder and Lightning,” which may be consulted for further details.