William Crookes

Sir William Crookes was an English chemist and physicist, born in London in 1832, who attended the Royal College of Chemistry, now part of Imperial College London, and worked on spectroscopy. He is credited with discovering the element thallium, announced in 1861 with the help of the spectroscope, and he was the first to describe the spectrum of terrestrial helium, in 1865. In 1875 he made the Crookes tube, a pioneering vacuum tube, and from the cathode rays in it he proposed radiant matter as a fourth state of matter, a foundation of plasma physics. He also invented the Crookes radiometer, was elected a fellow of the Royal Society in 1863 and later served as president of the Society for Psychical Research.