CTR Wilson’s cloud chamber
CTR Wilson’s fascination with clouds helped reveal the hidden subatomic world and was responsible for some of the great finds in 20th-century physics.
One man’s fascination with clouds was about to reveal the hidden subatomic world for the first time.
CTR Wilson’s masterpiece, his final cloud chamber of 1911. © Cavendish Laboratory
Greatly excited, Wilson wanted to replicate the beautiful effect back in Cambridge’s Cavendish laboratory. In early 1895, he built a bulb-like glass chamber to artificially create clouds.
‘Almost immediately,’ Wilson recalled, ‘I came across something which promised to be of more interest than the optical phenomena which I had intended to study’.
In previous experiments, it seemed clouds formed when vapour condensed around dust particles. But Wilson found with an almost perfectly clean chamber that it was still possible to produce clouds – given the right level of air expansion. To find out what was causing the condensation of water vapour, he set about improving his apparatus.
Building cloud chambers was an extremely tedious process. It involved some very tricky glass blowing, which Wilson did entirely himself. ‘Many hours of glass grinding had to be done’, Wilson recalled, ‘in the knowledge that the whole apparatus was almost certain to fly to pieces when the final glassblowing was done’.
JJ Thomson, Professor of the Cavendish at the time, revealed that the frequent breakages 'never seemed to disconcert Wilson; he would take up a fresh piece of glass, perhaps say ‘Dear, dear’, but never anything stronger, and begin again’.
Cloud chamber photograph of Rochester and Butler’s discovery of the k-meson, 1946. © Science Museum / SSPL
In 1910 Wilson built his masterpiece and realised his dream: a cloud chamber that could visualise particle tracks – resembling something like the vapour trails left in the wake of an airplane. The next year he took his first photographs of tracks, exclaiming excitedly, ‘they are as fine as little hairs’. For the first time, physicists could see the activity of the subatomic world.
Cloud chambers practically sparked a whole new field of physics – cosmic-ray research – as they were used as a means to detect particles that come from space. Wondering why clouds form in the absence of an obvious radiation source, Wilson even anticipated the existence of cosmic rays 11 years before they were confirmed by Victor Hess in 1911.
One of the first particle detectors, the cloud chamber would be responsible for some of the great finds in 20th-century physics, including the discovery of antimatter. Rutherford described Wilson’s invention as ‘the most original and wonderful instrument in scientific history’.
Written for the Science Museum's Collider exhibition, 2013. © Creative Commons - CC BY