Approx Size: 3.74 inches diameter, 6 inches long The Radiometer is an invention of the English Physicist Crookes and shows vividly the conversion of light into kinetic energy. The black surface of the solar wing-wheel (a circle of elements which are sensitive to light) absorbs much more light energy than the bright one. Because of the stronger heating of the air molecules on the black surface, a higher pressure arises there that leads to a rotary motion of the solar wings. The rotary force on the solar wing-wheel must be higher than the resistance of the air molecules, a partial vacuum is generated in the ball. This rotary motion is the result of the light incidence and as well as possible in a lit room (except for cold neon light). The more intensive the light is, the faster the solar wheel moves. This demonstration model shows how light is transformed into kinetic energy.