William Crookes (1832–1919)
Born 1832 CE, died 1919 CE.
Sir William Crookes (; 17 June 1832 – 4 April 1919) was an English chemist and physicist who attended the Royal College of Chemistry, now part of Imperial College London, and worked on spectroscopy. He was a pioneer of vacuum tubes, inventing the Crookes tube, which was made in 1875. Observing cathode rays generated in these tubes, Crookes posited that "radiant matter" was a unique fourth state of matter, a foundational contribution to plasma physics. He is credited with discovering the element thallium, announced in 1861, with the help of spectroscopy. He was also the first to describe the spectrum of terrestrial helium, in 1865. Crookes was the inventor of the Crookes radiometer, but did not discern the true explanation of the phenomenon he detected. According to historian William H. Brock, Crookes's later work on ultraviolet eye protection arose from 1907 Royal Society investigations into cataracts among furnace and glass workers.
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