Radiometer on a Modern Elm Stand
In a vacuum inside a free-standing globe the vanes constantly revolve in sunlight. The simplest possible demonstration of solar power. The Solar Radiometer is made by traditional Thuringian hand-blowing in Germany, of crystal-clear Lauschaer bottle glass. In the glass body is a 4-vane drive assembly, which turns under the influence of light. One side of each vane is black, the other is silver. This version features a modern elm wood stem. The Crookes radiometer was invented by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigating this effect, he devised the device named after him, still manufactured and sold to this day as a curiosity item.