Crookes, Sir William, 1832–1919, English chemist and physicist. After serving at the Radcliffe Observatory, Oxford, and teaching chemistry at Chester Training College, he retired to work in his own laboratory in London. He discovered the element thallium and made special studies of radioactive substances in the course of which he invented the spinthariscope, used to make visible the flashes produced by bombarding a screen with the alpha rays of a particle of radium, and he devised the radiometer, which measures the intensity of radiant energy. He also intensively studied the rare earths and diamonds. Crookes devised spectacles to protect the eyes of glassworkers from damaging rays. One of his chief inventions is the Crookes tube, with which J. J. Thomson, W. C. Roentgen, R. A. Millikan, and others conducted important research. He founded the Chemical News in 1859 and was the author of numerous scientific papers and of Select Methods in Chemical Analysis (1871). Crookes was also interested in psychical research.
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