Use the Classic Radiometer to demonstrate the intensity of radiant energy! The radiometer is a light-bulb shaped glass device with a little weather vane in the middle of it. When you put it in the light (sunlight or lamp) it starts to spin, turning the light energy into mechanical energy. Originally developed in the mid-nineteenth century by Sir William Crookes, the radiometer was developed to measure the intensity of radiant solar energy. Inside the glass bulb is a near perfect vacuum with nearly 99% of the air removed. This makes the air molecules move about more easily. The different colors on either side of the "vane blades" create the convection currents and momentum that causes the blades to spin really fast. This radiometer makes a really cool educational science gift for ages 8 and up. Students and Teachers project tip! A great tool in demonstrating the power of solar energy. A fun experiment uses the "sun block" plastic window film you can buy at hardware or building supply stores. This film is designed to block the sun's heat in the summer to keep your house cooler. Build 2 small cardboard "houses" with one having a clear plastic window and the other using the sun blocking window film in the window. When you place the radiometer in the "house", you will see the difference in how fast the radiometer is spinning in the different "houses". You can also add oven and refrigerator thermometers to see the temperature of the "houses".