Sir William Crookes, English chemist and physicist, c 1875.
© Science Museum / Science & Society Picture Library
Engraving. After studying at the Royal College of Chemistry, London, Crookes (1832-1919) went on to make significant contributions in several fields of science. He invented the radiometer (1873-1876), a device that responds to light or other electromagnetic radiation (which led to research in vacuum physics), and the spinthariscope (1903) which made individual alpha particles visible. He also discovered the element thallium, and was an authority on sanitation and agriculture.