Show the effect of differential absorption of radiation and expansion of residual gas. A rotating shaft inside the 99%-evacuated glass globe has four attached vanes. Each vane has a black face and a white face. Illuminate the bulb with an ordinary incandescent light. Watch the vanes spin as the black sides absorb more heat than the white ones, and thus expand the neighboring gas at a greater rate. The sphere is approximately 7.6cm in dia. Overall height with glass base: 12cm.