Lightning rod

From the Simple English Wikipedia, the free encyclopedia that anyone can change

A lightning rod or lightning conductor is a metal rod that is used to make lightning strike it, rather than something else. It is part of a lightning protection system. Such a system is made of many such rods. These rods are usually placed at high points of buildings and structures. In addition, paths are made the electricity can take from the rooftop to the ground.

[change] History

Lightning can damage structures made of most materials (masonry, wood, concrete and even steel). The huge currents involved can heat materials, and especially water to high temperatures. This will cause fire, loss of strength and explosions from superheated steam and air.

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The church tower was usually the highest structure or building in medieval European towns and villages. It was also the building very often hit by lightning. Early on, Christian churches tried to prevent the damage of lightning by prayers. Priests prayed,

"temper the destruction of hail and cyclones and the force of tempests and lightning; check hostile thunders and great winds; and cast down the spirits of storms and the powers of the air."

Peter Ahlwardts ("Reasonable and Theological Considerations about Thunder and Lightning", 1745) said people who sought to protect themselves from lightning should go anywhere except in or around a church.^[1] In Europe, the lightning rod was invented by Václav Prokop Diviš between 1750 and 1754.

[change] United States

In the United States, the pointed lightning rod conductor, often incorrectly referred to as the "lightning attractor," was invented by Benjamin Franklin as part of his groundbreaking explorations of electricity. Franklin thought that, with an iron rod sharpened to a point at the end,

"The electrical fire would, I think, be drawn out of a cloud silently, before it could come near enough to strike [...]."

Franklin speculated about lightning rods for several years before his reported kite experiment. This experiment, in fact, took place because he was tired of waiting for Christ Church in Philadelphia to be completed so he could place a lightning rod on top of it. There was some resistance from churches who felt that it was defying divine will to install these rods. Franklin countered that there is no religious objection to roofs on buildings to resist precipitation, so lightning, which he proved to be simply a giant electrical spark, should be no different. As an act of philanthropy, Franklin decided against patenting the invention.

In the 19th century the lightning rod became a symbol of American ingenuity and a decorative motif. Lightning rods were often embellished with ornamental glass balls^[2] (now prized by collectors). The ornamental appeal of these glass balls has also been incorporated into weather vanes.

Balls of solid glass occasionally were used in a method thought to prevent lightning strikes to ships. It is worth noting here not because it worked, which it didn't, but because it reveals a lot about pre-scientific thought. Glass objects do not conduct electricity well. They are seldom struck by lightning. Therefore, goes the theory, there must be something about glass that repels lightning. Hence the best method for preventing a lightning strike to a wooden ship was to bury a small solid glass ball in the tip of the highest mast. The random behavior of lightning ensured that the method gained a good bit of credence even after the development of the marine lightning rod soon after Franklin's initial work.

Nikola Tesla's U.S. Patent 1,266,175  was an improvement in lightning protectors. The patent was granted due to a fault in Franklin's original theory of operation; the pointed lightning rod actually ionizes the air around itself. This makes the air conductive, which in turn raises the probability of a strike. Many years after receiving his patent, in 1919 Dr. Tesla wrote an article for The Electrical Experimenter entitled "Famous Scientific Illusions", in which he explains the logic of Franklin's pointed lightning rod and discloses his improved method and apparatus.