Radiometer with Two Mills, c. 1890

This radiometer with two sets of light vanes works in the same way as a conventional radiometer. The airtight glass bulb forms a vacuum which allows the vanes to rotate when a light is shone onto them. The two sets of light vanes are blacked on opposite sides which causes them to rotate in opposing directions. The glass bulb stands on a turned blackened wooden base, which is weighted down by a lead ring.