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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.