Lightning is the dazzling light produced by an electrical discharge
passing between clouds which are oppositely electrified, or between the
clouds and the earth. Lightning flashes have been distinguished as
zigzag or chain lightning, sheet and globular lightning.
The first has the aspect of a sharply defined chain of fire, and moves
at the rate of 250,000 miles per second. Its zigzag course is attributed
to the resistance of the air, condensed in the passage of the electrical
discharge, which is sufficient to turn it aside frequently in the
direction of less resistance.
Sheet lightning includes the expanded flashes which occur during a
storm, and the heat lightning, seen on summer evenings, when no clouds
are visible, which is supposed to be the reflection of a storm taking
place below the horizon.
Globular lightning is seen on rare occasions, when the electrical
discharge takes the form of a ball of fire, and descending with less
rapidity, is visible for several seconds. In certain conditions of the
atmosphere, globes or spires of electrical light, called St. Elmo’s
fire, are seen tipping the extremities of bodies in contact with the
earth, like church spires, or masts of ships.
All the conditions which give rise to electrical excitement in the
atmosphere are much more intense in warm than in cold latitudes; hence
the thunder storms of the tropical regions greatly exceed, both in
frequency and in violence, those of temperate and cold climates.