Magnificent Glass Radiometer, makes a great gift for who have everything. All made of glass. Globe is 3.5 inch in diameter and stands 8 inch tall. This physical and technical miracle shows you in a clear way how sunlight is converted to energy. Place near a window or under incandescent light and watch as the vanes rotate. Invented in 1873 by the chemist Sir William Crookes as the by-product of some chemical research, the radiometer is made from 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 spaced equally around the . 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 hand nearby can be enough), the vanes turn with no apparent motive power, the dark sides retreating from the radiation source and the light sides advancing. Just place near a window or under a direct incandescent light as the vanes only rotates in light (sunlight or incandescent light). The shine on the globe the faster the vanes rotates. Colour:Photo Color Material:Glass Type: A: Blue 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.