Thunder is the noise which succeeds the rush of the electrical fluid through the air.
615. Why does noise follow the commotion caused by electricity?
Because, by the violence of the electric force, vast fields of air are divided; great volumes of air are rarefied; and vapours are condensed, and thrown down as rain. Thunder is therefore caused by the vibrations of the air, as it collapses, and seeks to restore its own equilibrium.
616. Why is the thunder-peal sometimes loud and continuous?
Because the electrical discharge takes place near the hearer, and therefore the vibrations of the air are heard in their full power.
617. Why is the thunder-peal sometimes broken and unequal?
Because the electrical discharge takes place at a considerable distance, and the vibrations are affected in their course by mountains and valleys. Because, also, the forked arms of the lightning strike out in different directions, causing the sounds of thunder to reach us from varying distances.
"Lo, these are parts of his ways; but how little a portion is heard of him? but the thunder of his power who can understand?"—Job xxv.