AITKEN, JOHN (1839–1919), British physicist, was born at Falkirk Sept. 18 1839. He was educated at Falkirk grammar school and Glasgow University, and trained as marine engineer at R. Napier & Sons, Glasgow. He lived at Falkirk, where he carried out his great experiments on atmospheric dust in relation to the formation of clouds and mists (1882), on the formation of dew (1885, see 8.136) and on the laws of cyclones (1891). His instrument for counting the dust particles in the air (see 8.714, 18.279) has been utilized in principle by many later workers. He also invented new forms of thermometer screens and powerfully aided the development of meteorology. He was elected F.R.S. in 1889 and was awarded the Royal medal in 1917. He also received the Keith medal (1886) and Gunning prize (1897) from the Royal Society of Edinburgh, in whose Transactions and Proceedings most of his valuable contributions were published. He died at Falkirk Nov. 14 1919.