XVII
A certain number of writers are of opinion that the air of itself emits a report as it traverses the cold and moist regions. Iron, they point out, when heated cannot be dipped in moisture without noise. A mass of heated metal when plunged in water causes a loud sputtering as it is cooled; so, according to Anaximenes, air meeting cloud produces peals of thunder; then as it rushes struggling through the obstructions that bar its way it kindles the flame of lightning merely by its escape.