C. T. R. Wilson

Charles Thomson Rees Wilson (1869–1959) was a Scottish physicist who invented the cloud chamber, a detector that makes charged-particle tracks visible as droplets.

John Aitken: A Scottish meteorologist who studied atmospheric dust and the formation of cloud droplets. Aitken’s dust experiments shaped the questions Wilson pursued about condensation.
Cloud chamber: A particle detector in which supersaturated vapor condenses into droplets along paths of ionization. Wilson’s invention made the particles’ ionized trails visible.
Cosmic ray: A high-energy particle arriving at Earth from space, usually a proton or atomic nucleus. Cloud chambers revealed the tracks of cosmic-ray particles entering the atmosphere.
Ben Nevis Observatory: A meteorological observatory that operated near the summit of Ben Nevis in Scotland from 1883 to 1904. Wilson’s observations of cloud and optical effects there helped inspire his chamber experiments.
Particle detector: An instrument that detects, measures, or records particles such as electrons, protons, or photons. Wilson’s chamber became an early foundational detector for subatomic particles.
Ernest Rutherford: A physicist who established the nuclear model of the atom and pioneered experimental nuclear physics. Rutherford’s laboratory used Wilson’s chamber to reveal particle tracks.
Supersaturation: A state in which vapor pressure exceeds the equilibrium value for condensation at a given temperature. Rapid expansion drove the chamber’s vapor into the state needed for droplet formation.
Positron: The positively charged antiparticle of the electron, with the same mass as an electron. A cloud-chamber track curved like an electron’s but indicated positive charge, revealing the positron.
Cloud: A visible mass of water droplets or ice crystals suspended in the atmosphere. Wilson sought to reproduce cloud formation in a controlled laboratory apparatus.
Track reconstruction: The process of inferring a particle’s trajectory and properties from detector measurements. Photographed chamber trails let physicists reconstruct paths, charge, and momentum.

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BKS theoryRelated: Cloud-chamber observations of recoil electrons helped test whether scattering events obeyed individual conservation laws.