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Spinning Radiometer

Just as much fun to examine now as when first designed in the 1870's

Made in the USA

First made almost 140 years ago by the British inventor who first developed the vacuum tube later adapted by Edison into a light bulb.

The Radiometer demonstrates energy transfer from natural radiation (light). It consists of a set of four vanes (shiny on one side and black on the other) sensitively balanced on a spindle in a partial vacuum. When exposed to light, the vanes revolve. The blackened vane becomes hotter than its opposite shiny side and repels residual air molecules from its warm surface. This tiny difference in air pressure is what causes the vanes to rotate-the brighter the light, the faster the rotation.

Heat energy is being converted into mechanical energy. And it will go on like this forever, so long as the light is on. Delight your children, delight yourself, and impress clients. It's old-fashioned fun and a good lesson in basic physics.

Note: the Radiometer absorbs light; it does not give it off.


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  • Spinning Radiometer


    Spinning Radiometer

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