Charles Thomson Rees Wilson

Charles Thomson Rees Wilson CH (February 14, 1869 – November 15, 1959) was a Scottish meteorologist and physicist who developed the cloud chamber for visualizing the tracks of electrically charged particles such as the electron. The cloud chamber became an essential instrument for exploration of the realm of subatomic particles and the development of physics in the twentieth century. In 1927, Wilson received the Nobel prize for his method of making the paths of electrically charged particles visible.

Biography

Early years

Wilson was born in the parish of Glencorse, Midlothian, near Edinburgh, Scotland, to a farmer, John Wilson, and his mother Annie Clerk Harper. After his father died in 1873, his family moved to Manchester. Assisted financially by his stepbrother, Wilson enrolled at the Owen's College, where remained from 1884 to 1888, studying biology with the intent of becoming a physician. He then won a scholarship to Sidney Sussex College, Cambridge, where he became interested in physics and chemistry. He remained there from 1888 to 1894, earning a master's degree in 1892.

The cloud chamber

Wilson became particularly interested in meteorology after his admission to Cambridge, and in 1893 he began to study clouds and their properties. He worked for some time at the observatory on Ben Nevis, and was impressed by the beautiful play of colors and effects from the interaction between the sunlight and the cloud cover surrounding the mountain's summit. He tried to reproduce this effect on a smaller scale in the laboratory in Cambridge by expanding humid air within a sealed glass container. The air cooled as it expanded, and, at the lower temperature, became supersaturated with water vapor.

Usually, the nucleus of condensation for water vapor is a piece of dust. But Wilson noticed that, even when he eliminated the dust, condensation still occurred. He suspected that the condensation nuclei were ions, and reported his results to the Cambridge Philosophical Society in May of 1895. He then exposed the chamber to X-rays, and noticed that the degree of condensation was considerably enhanced, thus re-enforcing his original conjecture, since X-rays were known for their quality of ionizing a gas.

Further research

In 1895, Wilson joined the Cavendish Laboratory, and in 1896 was appointed Clerk Maxwell Student at Cambridge, allowing him to devote the next three years to research on the cloud chamber. He continued his experiments, noting that when the enclosed supersaturated air was exposed to an electric field to clear ions, no clouds formed, thus affirming his original conjecture that ions of molecular dimensions caused clouds to form. He reported his results in a series of papers until 1900, when his investigations turned to atmospheric electricity.

In 1900, Wilson became a teaching fellow at Sindey Sussex College, while continuing to lecture in Physics at the Cavendish Labboratory. He married Jessie Fraser in 1908, the daughter of a minister from Glasgow, and the couple had four children.

Tracks of subatomic particles

As his responsibilities increased over the years, he tended to have less time to devote to research. But in 1910, he returned once again to the cloud chamber, and in 1911 he experimented to see if the condensation tracks of charged particles would become visible. Wilson first tried X-rays, and noted that the paths of electrons formed by x-ray exitation immediately became visible. He then introduced radioactive materials, and found that he could identify the paths of the alpha and beta rays they emitted. Wilson reported these effects, including photographs of the same, to the Royal Society. After completing the construction of an improved apparatus, he reported further results to the society in 1912.

Tracks left by alpha rays closely matched diagrams of the paths postulated for these particles and published by William H. Bragg, who later went on to win a Nobel prize for his work in X-ray crystallography. Wilson enhanced the images of the paths of charged particles in his cloud chamber through stereophotography, which presented a three-dimensional image of the phenomena.

Meteorological work

Wilson received an appointment as an observer at the Cambridge Solar Physics Observatory in 1913. He was able to continue his research in this position until the outbreak of World War I.

In 1918, he left his position at the Cavendish laboratory and became a reader in electrical meteorology. One of his conjectures was that thunderclouds were, on average, positively charged, and that, as a result, the earth's surface was negatively charged.

Perfecting the cloud chamber

It was not until 1921 that Wilson fully resumed his work on cloud chamber physics. He published new results in 1923 with the new cloud chamber he had built before the war, including a new series of photographs of the paths of alpha and beta particles. These photographs, and their analysis, vindicated the views of Arthur Holly Compton, who had earlier demonstrated that the frequency of X-rays change in the process of energizing electrons. Sometimes the electrons may change their direction, and the energy and direction of the X-ray can be calculated.

Nobel prize

Compton's result meant that the phenomena associated with X-rays cannot be fully accounted for by the electromagnetic wave model, and that "Compton scattering"—the change in direction of both the electron and the photon after interaction—demonstrates that X-rays have some of the characteristics of a particle.

Wilson shared the Nobel prize in 1927 for his method of making the paths of electrically charged particles visible.

Later work

In 1925, Wilson was appointed Jacksonian Professor of Natural Philosophy at Cambridge University, a position he held until 1934. He retired from Cambridge in 1936, moving to Edinburgh, but remaining active in scientific work. During World War II, he assisted the war effort by conducting research on lightning protection. Much of his later work dealt with the subject of electricity in the atmosphere. In his later years, he moved to Carlops, Scotland, where he died on November 15, 1959.

Legacy

Wilson's major field of interest was meteorology. But when he uncovered unexpected phenomena in his research, he knew enough to realize that he had stumbled upon something of great importance. What is interesting about Wilson's work on the cloud chamber is that he did not develop its true potential until 27 years after his first discovery. The cloud chamber became a major tool for research into the world of subatomic particles, so much so that it would be hard to imagine what the field would have been like without it.

Honors

• Fellow of the Royal Society (1900)
• Hughes Medal (1911), a Royal Medal (1922)
• Copley Medal (1935)
• Hopkins Prize (1920)
• Gunning Prize (1921)
• Howard Potts Medal (1925)

Named after Wilson

• The Wilson crater on the Moon is co-named for him, Alexander Wilson and Ralph Elmer Wilson.
• The Wilson Society, the natural sciences society of Sidney Sussex College, is also named after him.

See also

• Ion
• Subatomic particle

References

ISBN links support NWE through referral fees

• Angelo, Joseph A. 2004. Nuclear technology. Sourcebooks in modern technology. Westport, Conn: Greenwood Press. 106-108. ISBN 1573563366.
• Asimov, Isaac. 1982. Asimov's Biographical Encyclopedia of Science and Technology. Garden City: Doubleday. ISBN 0385177712.
• Lundqvist, Stig. 1992. Physics 1971-1980. Nobel lectures, including presentation speeches and laureates' biographies. Singapore: World Scientific. 167-199. ISBN 9810207263.
• Galison, Peter Louis. 1997. Cloud Chambers: the peculiar genius of British physics in Image and logic: a material culture of microphysics. Chicago: University of Chicago Press. ISBN 0226279162.
• Rakov, Vladimir A., and Martin A. Uman. 2003. Lightning: physics and effects. Cambridge, U.K.: Cambridge University Press. ISBN 052158327673.

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