Crookes Maltese cros tube (left) and radiometer (right), 1879-1888.
© Science Museum / Science & Society Picture Library
Sir William Crookes (1832- 1919), an experimental chemist and physicist, discovered a new element in 1861 which he called thallium. Whilst weighing samples he noticed that there were inconsistencies which led him to devise the light-mill or radiometer in 1875. The Maltese cros tube is still used to demonstrate properties of cathode rays (rays which cause minerals such as ruby to phosphoresce emit light without combustion or perceptible heat).