Description: 【Automatic rotating】:The glass Radiometer will rotate automatically under the sunlight or strong irradiation. 【Table decoration】:Rotating Vanes Desk Toy can be used for decoration in offices, living rooms, bedrooms, classrooms, study rooms, parties, etc. 【Educational】: Glass Windmill with an internal vacuum. It can rotate by itself through light, and can also rotate in the opposite direction through cold wind. 【Principle】: When the light black fan absorbs heat energy, white fan releases heat energy, it can promote the four fans rotation. 【Material】:Solar Power Crookes is made of glass, great for Physics teaching tool. Size Chart: Diameter of ball:7.5cm/2.95inch Diameter:6.5cm/2.56inch Height:13.8cm/5.43inch Package Includes: 1 Solar Power Crookes Note: Please allow slightly errors 1-2cm differences due to manual measurement.Customer satisfaction is our primary concern. If the product is somehow cracked or broken during shipping, please feel free to contact us. We will try our best to give you a satisfactory solution.