The Solar Radiometer, also as a Light windmill is an instructive and physical object for demonstration that was devised by the english physicist Sir William Crookes (1832-1919) in the year 1873. This physical and technical miracle shows you easily, how sunlight is changing into energy - the Sun as a source of energy in the future ! The Solar Radiometer is an technical interesting and entertaining objekt of the modern living room and it shows you every ray of sunshine if the lightmill stands or hanging at the window.