Place your Solar Radiometer in the sunlight and watch the pinwheels spin! This radiometer is a fun way to demonstrate heat transfer. The pinwheels are alternately dark and light. When the light strikes the wings, it transfers heat to each one, but not at the same degree. The light wings reflect the rays and the dark wings absorb the rays. Also, the atmosphere inside a radiometer is a nearly perfect vacuum. Dimensions - W-4.25" x H-3.25" Brand: Kikkerland *Comes with a wood base.