The English chemist and physicist Sir William Crookes discovered the element thallium and invented the radiometer, the spinthariscope, and the Crookes tube.

William Crookes was born in London on June 17, 1832. His education was limited, and despite his father's wish that he become an architect, he chose industrial chemistry as a career. He entered the Royal College of Chemistry in London, where he began his researches in chemistry. In 1859, he founded the Chemical News, which made him widely known, and remained its editor and owner all his life.

Most notable among Crookes's chemical studies is that one which led to his 1861 discovery of thallium. Using spectrographic methods, he had observed a green line in the spectrum of selenium, and he was thus led to announce the existence of a new element, thallium. While determining the atomic weight of thallium, using a delicate vacuum balance, he noticed several irregularities in...