Subject: Physics Inside the bulb, on a low friction spindle, is a rotor with several (usually four) vertical metal vanes spaced equally 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 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.