Description: Educational Science Toy: The solar power Crookes radiometer is a nice physics teaching toy, under sunlight or strong irradiation, the vanes inside will automatically rotatePrinciple: Sun light energy spinning vanes, when the sun shines, the black vane surface absorbs heat energy, and the white vane surface releases heat energy, that drives the vanes to rotatePremium Material: The solar Crookes radiometer windmill is made of premium high boron glass, sturdy, not easy to break and crack, and ensures a long time to useDesktop Ornament: The solar power Crookes radiometer is a nice addition to your home decoration, suitable for decorating the desk, table, shelf, cabinet, entrance, fireplace, office, bedroom, living room, etcNice Gift: The Crookes radiometer is a nice gift choice for kids, family and friends on Christmas, birthdays, parties, festivals, housewarmings, etc Specification: Material: high boron glass Size Chart: Height 21cm/8.27inchBall diameter 9cm/3.54inchBase diameter 8cm/3.15inch Package Includes: 1Solar Crookes Radiometer Note: Please allow slightly errors 1-2cm/0.39-0.79inch 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.