A lightning rod

A lightning rod (US, AUS) or lightning conductor (UK) is a metal rod or metallic object mounted on top of a building, electrically bonded using a wire or electrical conductor to interface with ground or "earth" through an electrode, engineered to protect the building in the event of lightning strike. If lightning hits the building it will preferentially strike the rod and be conducted to ground through the wire, instead of passing through the building, where it could start a fire or cause electrocution.

A lightning rod is a single component in a lightning protection system. Lightning rods are also called finials, air terminals or strike termination devices. The lightning rod requires a connection to earth to perform its protective function. Lightning rods come in many different forms, including hollow, solid, pointed, rounded, flat strips or even bristle brush-like. The main attribute of all lightning rods is they are conductive.

Copper and its alloys are the most common materials used in lightning protection.[1]

History

The lightning rod was invented by Benjamin Franklin in the Americas in 1749,[2] and in Europe, probably independently and as the first grounded lightning rod ever, by the Czech priest Prokop Diviš in Bohemia (now Czech Republic), in 1754.[3]

Nevyansk Tower crowned with a metallic rod grounded through a complex system of rebars (some are seen at the basement)

"Machina meteorologica" invented by Diviš worked like a lightning rod

Franklin’s earliest papers on electricity[4]

As buildings become taller, lightning becomes more of a threat. Lightning can damage structures made of most materials (masonry, wood, concrete and steel) as the huge currents involved can heat materials to high temperature, causing a potential for fire.

Asia

Some of the most ancient lightning conductors can be found in Sri Lanka in places like the Anuradhapura Kingdom that dates back thousands of years. The Sinhalese kings, who mastered construction of stupas and advanced building structures, installed a metal tip made of silver or copper on the highest point of every building to conduct any lightning charge. In many parts of the world, ancient Buddhist monuments have been destroyed by lightning strikes, but not in Sri Lanka.[citation needed]

Russia

A lightning conductor may have been intentionally used in the Leaning Tower of Nevyansk. The spire of the tower is crowned with a metallic rod in the shape of a gilded sphere with spikes. This lightning rod is grounded through the rebar carcass, which pierces the entire building.

The Nevyansk Tower was built between 1725 and 1732, on the orders of industrialist Akinfiy Demidov. The Nevyansk Tower was built 25 years before Benjamin Franklin's experiment and scientific explanation.[5] However, the true intent behind the metal rooftop and rebars remains unknown.[6]

Europe

The church tower of many European cities, which was usually the highest structure in the city, was likely to be hit by lightning. Early on, Christian churches tried to prevent the occurrence of the damaging effects of lightning by prayers. Peter Ahlwardts ("Reasonable and Theological Considerations about Thunder and Lightning", 1745) advised individuals seeking cover from lightning to go anywhere except in or around a church.[7] In Europe, the lightning rod may have been independently invented by Czech Premonstratensian priest Prokop Diviš between 1750 to 1754. Diviš then placed the first grounded lightning rod ever in his garden in Přímětice near Znojmo in 1754.

United States

In what later became the United States, the pointed lightning rod conductor, also called a "lightning attractor" or "Franklin rod," was invented by Benjamin Franklin in 1749 as part of his groundbreaking exploration of electricity. Although not the first to suggest a correlation between electricity and lightning, Franklin was the first to propose a workable system for testing his hypothesis.[8] Franklin speculated that, with an iron rod sharpened to a point,

"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.[citation needed]

In the 19th century, the lightning rod became a decorative motif. Lightning rods were embellished with ornamental glass balls[9] (now prized by collectors). The ornamental appeal of these glass balls has been used in weather vanes. The main purpose of these balls, however, is to provide evidence of a lightning strike by shattering or falling off. If after a storm a ball is discovered missing or broken, the property owner should then check the building, rod, and grounding wire for damage.

Balls of solid glass occasionally were used in a method purported to prevent lightning strikes to ships and other objects. The idea was that glass objects, being non-conductors, 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 combined with observers' confirmation bias 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.

The first lightning conductors on ships were supposed to be hoisted when lightning was anticipated, and had a low success rate. In 1820 William Snow Harris invented a successful system for fitting lightning protection to the wooden sailing ships of the day, but despite successful trials which began in 1830, the British Royal Navy did not adopt the system until 1842, by which time the Imperial Russian Navy had already adopted the system.

Nikola Tesla's

"Lightning-Protector"

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