Glass crafts: Radiometer, Floral Pattern German-made glass craft: Radiometer, Lichtmühle Radiometer Lichtmühle "Blade Stem" This is a glass craft interior object that converts light energy into kinetic energy. The blades inside the vacuum glass container react to light (infrared) and rotate beautifully. Placing it near a window or a light bulb, it moves at varying speeds depending on the intensity of the light. It's a soothing scientific novelty item. The reaction to light may be diminished. The movement in response to light feels sluggish. Please be aware of this before considering a purchase. There are black spots that appear to be from the manufacturing process. Please check the 10th photo. Approximate size: Height: 13cm Ball diameter: 5.5cm Base diameter: 5.5cm 7423-750