Give the disk a spin and observe the hypnotic display of light and continually changing sound. The movement seems to go forever, spinning and precessing as it slowly transforms gravitational potential energy into kinetic. The concave mirror base provides an ideal reflective surface to see the visual effects. Amazing to use in a darkened room with a flashlight or laser. Includes magnetic holographic film. 7.5 cm dia. disk, 20 cm dia. mirror.