Magnificent glass radiometer, an excellent gift for the person who has everything. Made entirely of glass. The globe is 3.5 inches in diameter and stands 8 inches tall. This physical and engineering marvel clearly shows you how sunlight is converted into energy. Place near a window or under incandescent light and watch the vanes rotate. Invented in 1873 by chemist Sir William Crookes as a byproduct of chemical research. The radiometer is made of a glass bulb from which much of the air has been removed to form a partial vacuum. Inside the bulb, on a low-friction spindle, is a rotor with several (usually four) vertical metal vanes evenly spaced around the axis. The vanes are polished or white on one side and black on the other. When exposed to sunlight, artificial light, or infrared radiation (even the heat of a nearby hand can be enough), the vanes rotate without any apparent motive power, the dark sides receding from the radiation source and the light sides advancing. Simply place near a window or under a direct incandescent light as the vanes only rotate in light (sunlight or incandescent light). The more light on the globe, the faster the vanes rotate. Color: Photo Color Material: Glass Type: C: Green Base Package Contents: 1x 4 Blades Rotating Glass Windmill Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.