The operation of a lightning rod, which is designed to protect a building from lightning strikes, is demonstrated in today’s Cabinet of Physics video. A wooden model house is equipped with a metal rod projecting above its roof.
“Lightning” is provided by a group of Leyden jars, those high-voltage capacitors which have been faithful workhorses of electrostatic demonstrations for most of three centuries. The jars are charged by a wheel-like electrostatic generator; I’m not a connoisseur of such devices, but this one resembles a Wimshurst Machine I’ve played with.
To add drama to the Thunder House demonstration, a firecracker is connected to its lightning rod. No doubt this flourish made the lesson more memorable–and probably more enjoyable–to students. Enthusiasts of electrostatics love to quote the 18th-Century experimenter Georg Christoph Lichtenberg, who said:
“A physical experiment which makes a bang
is always worth more than a quiet one.
Therefore a man cannot strongly enough ask of Heaven:
if it wants to let him discover something,
may it be something that makes a bang.
It will resound into eternity.”
The Foundation for Science and Technics, or Fondazione Scienza e Tecnica, of Florence, Italy, has made available many videos exploring the Cabinet of Physics, a large collection of antique scientific demonstration instruments. The Foundation’s homepage may be found here, and its Youtube channel, florencefst, here.