Physics Photo of the Week

November 16, 2007

Italian Lightning Rods
Most tourists visit Florence, Italy to view the  magnificent rennaissance art and architecture.  Perhaps the most impressive building is the Duomo of Florence - The Basilica di Santa Maria del Fiore.  The massive dome or cupula towers over all other impressive buildings in the city.  The dome was designed and completed in the early 15th century by Filippo Brunelleschi.  The structure is most noted for its being built (40 meters wide, 90 meters high) without any temporary supporting structure
for the building process by means of ingeneous design of interlocking bricks of the masonry.

High structures, however, are prone to lightning strikes.  Major damage had been done to the lantern on top of the cupula in 1600 as well as numerous other strikes.
With all the architectural, engineering, and artistic achievements, the Italians of the times had no better lightning protection then by placing relics of saints in the ball on top of the lantern on top of the cupula. (

An American inventor - Benjamin Franklin - through his early experiments in electricity, developed lightning rods.  The lightning soon proved to provide substantial protection of countless buildings from lightning damage.  Each rib on the dome is covered by numerous lightning rods connected with a substantial grounding wire.

Considerable controversy exists on how lightning rods work.  Franklin  at first believed that lightning rods dissipated the charged cloud by means of corona discharge around the points.  He didn't understand the principles, but electrostatic experiments in the laboratory easily demonstrate the dissipation effect.  The other theory is that lightning rods are struck by lightning, but the tremendous current is diverted safely to the ground through the heavy conductors attached to the points.  Some manufacturers claim that blunted rods are better than pointed rods. (Geophysical Research Letters,
May 15. 2000).  It is still a controversy exactly which theory is correct.

Due to Thanksgiving break, there will be no Physics Photo of the Week next week.  The next Physics Photo of the Week will be published November 30, 2007.

All photos created by Donald Collins.

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department.  These photos feature an interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation.  Atmospheric phenomena are especially welcome.  Please send any photos to

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