Radiometer!

Experience the sphere powered by the sun! Measuring just 5 inches high, this is the perfect addition to the classroom or any window sill. The vanes, or wings, in the Radiometer are alternately dark and light in color. When the light strikes these vanes it transfers heat to each one - but not to the same degree. The lighter wing reflects the rays and the darker wing absorbs the rays. Now, when the freely moving particles of air inside the radiometer strike the light-colored reflective wings, they take on very little energy and do not bounce off very fast. However, when the the atoms strike the dark wings, they "kick" away at terrific speed. The result is the vane begins to spin and continues to spin as the bits of air continue to "kick" away from the dark-sided vane. The stronger the light, the more energy there is to "heat up" the dark side of the wing....causing the vanes to spin faster...faster....faster! The "bulb" is made of glass, be careful around children.