Physics Photo of the Week
Italian Lightning Rods
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
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
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.
Photo of the
published weekly during the academic year on Fridays by the Warren
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