Sir Charles Thomson Rees Wilson
- Name : Wilson
- Born : 1869
- Died : 1959
- Category : Scientists and Inventors
- Finest Moment : First photographs of subatomic particle activity in a Cloud Chamber (1911)
Born St Valentine's Day, 1869, the eighth child of a sheep farmer at Glencorse in the Pentland Hills near Edinburgh. His father died when he was four, and the family moved to Manchester to be near his grandparents. At school no science was taught, but he collected beetles and pond life with his brother, and when he was 13 he was given a microscope, starting his scientific career.
He studied as a medical student at Manchester in 1884, before moving to Cambridge where he became a physicist. And it was then that the unlikely combination of Wilson's mind and the cloudy top of Ben Nevis produced a useful scientific discovery leading to the Nobel Prize.
In September 1894, he spent a fortnight working at the summit Meteorological Observatory on Ben Nevis. His original intention was to study by experimental means the optical phenomena of coronas, glories and Brocken Spectres. These are the rainbow-like coloured rings and human-shaped shadows that hillwalkers often see thrown onto a bank of mist by strong, low sunlight. He was impressed by the optical effects. The following year he was watching a mist-covered Nevis when a storm broke out. His hair stood on end, drawing his attention to the massive electrical field associated with the storm. He later said that the whole of his scientific career was determined by these experiences.
In 1895 he was experimenting in the famous Cavendish Laboratory at Cambridge, under J.J. Thomson. He decided to recreate the effects in the lab, and made clouds by expanding moist air in a chamber, with moisture condensing on dust particles (so-called 'condensation nuclei') at a critical saturation point. He was surprised however to find that even with all dust particles removed he could still create clouds, if he expanded the moist air sufficiently. So what was allowing cloud formation to occur'
With careful observation, he found that there were in fact two main sorts of condensation; a rain-like type, with low numbers produced repeatedly, and at higher expansions a cloud-like fog. This fog re-created the optical effects he had observed. He decided that condensation was created in different ways, either on dust, or on rare, spontaneously produced nuclei (actually ions).
Wilson observed that X-rays and 'uranium rays' could cause huge numbers of fog droplets; in other words they must have been producing the same nuclei that occur spontaneously. These he identified as negatively charged ions, partly explaining the electric field in thunder clouds - drops form on negative particles, which fall by gravity to separate charge in the cloud. So, concluded Wilson, condensation can also be caused by an external influence, and he proposed that radiation from outside the Earth's atmosphere could be the cause (thereby predicting cosmic rays).
During this period, in 1908, he married Jessie Fraser Dick; they had three children.
In 1912, his apparatus, the Wilson Cloud Chamber, was perfected. He made possible the viewing of radioactive particles by photographing the drops condensed on the ions in the track, so that his chamber first revealed the behaviour of the elementary particles of nature. Atomic phenomena which had been deduced indirectly by various means, were now clearly visible to the eye, and his apparatus became essential to the study of particle physics.
Charles Wilson had continued to hillwalk. Aged 84 he climbed Caisteal Abhail in Arran, remarking that it was 64 years since he had sat at the summit. Aged 86 he managed to wangle some flights on RAF planes, passing himself off as a student of meterology.
He had become Professor of Natural Philosophy at Cambridge in 1925, and was awarded the Nobel Prize for Physics in 1927. He retired from the chair in 1934, settling at Carlops near Edinburgh. This did not prevent him from research, and he was still publishing papers aged 87. He died at home aged 90, after a brief illness, the only serious illness of his life.