This Solar Radiometer is made by traditional Thuringian hand-blowing in Germany, of Lauschaer bottle glass - amber-colored for the globe, clear for the top and foot. 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.
Height: ca. 15cm. (6 in) Globe diameter: ca. 8cm. (3.25 in)
The Crookes radiometer, also known as the light mill or solar engine, consists of an airtight glass bulb, containing a partial vacuum. Inside are a set of vanes which are mounted on a spindle. The vanes rotate when exposed to light. The reason for the rotation has been the cause of much scientific debate. It 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.