Born June 17, 1832, in London; died there Apr. 4, 1919. British physicist and chemist. Member (1863) and president (1913–15) of the Royal Society of London.

Crookes studied at the Royal College of Chemistry in London (1848–50) and was an assistant there under A. W. von Hofmann from 1850 to 1854. He was a professor of chemistry at Chester from 1855 to 1859. Subsequently, he worked in his private laboratory in London.

Crookes discovered the element thallium in 1861 with the aid of spectral analysis and isolated it in pure form in 1862. He investigated the radiometric effect and designed a radiometer (1873–74). He also studied electrical discharges in gases and discovered a number of phenomena in gas-discharge tubes (Crookes dark space, for example). In 1904 he invented the spinthariscope, a device for registering alpha particles. Many of his works were devoted to problems in applied chemistry (for example, textile dyeing, beet sugar production) and metallurgy. Crookes was a staunch supporter of spiritualism. A criticism of Crookes’ spiritual “research” is given by F. Engels in the article “Natural Science in the World of Spirits” (see K. Marx and F. Engels, Soch., 2nd ed., vol. 20, pp. 373–83).