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Radiant Light Mill - Solar Radiometer

Invented at ThinkGeek

A spin on "solar power"

  • Looks great on your desk or a windowsill
  • Demonstrates thermal transpiration
  • Works best in direct sunlight
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$24.99

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A spin on "solar power"

Way back in 1873, some guy named Sir William Crookes noticed some weirdness in a scale he built. It appeared as though some samples weighed more or less depending on if sunlight was shining on the scale. He postulated that it was the pressure of the light being exerted on the scale that modified his results.

Of course, he was totally wrong, but it was a cool idea, right?

How do radiometers work? Well, the bulb in which the blades spin is a partial vacuum. Partial being the tricky part - another clever scientist by the name of Lebedev noticed that the effect disappeared in a hard vacuum. Curious, yes? The light side of the blades are slightly warmer than the internal air temperature but cooler than the black side. Basically, the principal is the air that hangs out by the cool side of the blade flows slowly to the warm side of the blade. That process is called thermal transpiration. Science is cool.

This Radiant Light Mill looks awesome sitting on your desk or windowsill. It works best in direct sunlight, but moves pretty well even hit with a flashlight. Of course, in our own highly scientific testing here at ThinkGeek World Domination HQ we discovered that a laser, while intense, was too focused to significantly move the vanes very much at all. Now what if we told you that sunlight, artificial light, and even infrared radiation can cause the blades to spin? What other sources can you come up with to create thermal transpiration? And what happens when you cool it?

Product Specifications
  • Radiant Light Mill - Solar Radiometer
  • A ThinkGeek creation 
  • For people who love science and sunlight
  • Sunlight, artificial light, and even infrared radiation can cause the blades to spin
  • Materials: Metal stand + glass radiometer
  • Dimensions: 9 1/2" tall x 6 1/2" wide x 5" deep (assembled), 6 1/2" tall x 3" diameter radiometer
  • Weight: 7 oz.
  • Includes stand and radiometer

Radiant Light Mill - Solar Radiometer Video:

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