William Crookes (17.06.1832-4.04.1919) was an English chemist and physicist and a Fellow of the Royal Society (1863), and its president in 1913-15. He was born in London. He graduated from the Royal College of Chemistry (1850), where he worked until 1854; in 1855-59 he was a lecturer at the college in Chester, after which he worked in his own laboratory, and from 1885 he lived in Oxford.
His research in physics concerned mainly electric discharges in gases, cathode rays and atomic physics. He proved that an electric discharge in a vacuum rests on a stream of charged particles coming from the negative electrode. He introduced (1879) the concept of a fourth state of matter. He constructed the radiometer (1873). He studied cathode rays in the so-called Crookes tubes, to which he gave various shapes, and discovered a number of properties of these rays. In particular, he proved that cathode rays carry energy and momentum (1879). He observed the luminescence of certain oxides and salts caused by cathode rays (1886). In 1903 he discovered the effect produced by alpha rays falling on a plate of zinc sulfide (the scintillation effect), and on that basis he constructed an instrument (the Crookes spinthariscope) for recording individual alpha particles by the flashes they cause. He put forward ideas about the evolution of the chemical elements, about isotopy and about the existence of a charged microparticle (1886). In 1892 he showed that radio communication was possible and described its principles.
He was a convinced supporter of spiritualism, for which F. Engels criticised him. A member of a number of academies of sciences and scientific societies.