Subject: Physics 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. Magnificent Glass Radiometer, makes a great gift for who have everything. All made of glass.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. colour:Transparent Material:glass size:Base Size: 80mm/3.1 inch Height: 205mm/8.1 inch Sphere diameter: 90mm/3.5 inch Package Contents: 1*Crookes Radiometer 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.