Charles Thomson Rees Wilson
Born: 14 February 1869, Glencorse, Scotland
Died: 15 November 1959, Carlops, Scotland
Affiliation at the time of the award: University of Cambridge, Cambridge, United Kingdom
Prize motivation: "for his method of making the paths of electrically charged particles visible by condensation of vapour"
Prize share: 1/2
If the volume of a mixture of air and water vapor increases, small water drops form. If the air contains electrically charged particles - ions - then droplet formation occurs around these especially. C.T.R. Wilson exploited this phenomenon when he constructed his cloud chamber in 1911 - a glass container with air and water vapor and ingenious devices that allow traces left by ionizing radiation and particles that pass through the chamber to become visible and be photographed. The cloud chamber became an important tool in physics.