How can light itself make something move? This phenomenon has been explained a zillion times but still it seems unfathomable, which is why we like to offer it here as a tantalizing object that is not exactly a toy, but is definitely fun. The vanes, or wings, of the Radiometer are alternately dark and light in color. When light strikes these surfaces heat is transferred, but since the dark wings absorb light and the light wings reflect the light, the Radiometer spins. The stronger the light, the more energy there is to heat up the darker side of the wing, causing the wings to spin faster as the light gets brighter. Note that the Radiometer is made of thin light absorbing glass and so should not be left where it could be knocked over by young children. Information on how to place your order by fax or by telephone. Grades K-3. Product Number: TS79723