The English experimentalist William Crookes, b. June 17, 1832, d. Apr. 4, 1919, contributed to many of the new fields of physics and chemistry that emerged in the late 19th century. His investigations of the photographic process in the 1850s motivated his work in the new science of spectroscopy. Using its techniques, Crookes discovered (1861) the element thallium, which won him election to the Royal Society. His efforts in determining the weight of thallium in an evacuated chamber led to his research in vacuum physics.
Crookes invented the radiometer in 1875 and, beginning in 1878, investigated electrical discharges through highly evacuated "Crookes tubes." These studies laid the foundation for J. J. Thomson's research in the late 1890s concerning discharge-tube phenomena. At the age of 68, Crookes began investigating the phenomenon of radioactivity, which had been discovered in 1896, and invented a device that detected alpha particles emitted from radioactive material. Crookes maintained an interest in agriculture and warned in 1898 that the world's population would face starvation unless new fertilizer sources were discovered. He was also interested in psychic phenomena. He was knighted in 1897.
Richard Hirsh
