To those few weeks spent on the highest point of my native land I owe many happy years of work...”
C. T. R. Wilson, on receiving the Nobel Prize in 1927
In September 1894, Charles Thomson Rees Wilson (1869-1959) climbed to the summit of the Scottish mountain, Ben Nevis. He was so impressed by the effects of sunlight upon the clouds that he decided to try to reproduce them in his laboratory. His work was based on that done by John Aitken, the engineer who had created artificial clouds in a laboratory container. Aitken had found that if you put water vapor into a glass jar, a cloud would form if the air was unfiltered— that is, dusty. The water molecules in the air were treating the dust particles as tiny nucleation points onto which they could condense, forming a cloud.
Air pressure inside the container could be reduced by expanding the volume, which forced water vapor to condense onto dust. Wilson also discovered that he was able to make airborne water droplets even when the dust had been removed. He theorized that condensation was occurring due to the presence of charged particles. To test this, he fired X-rays into his cloud chamber and also exposed it to uranium. In both cases he was able to form clouds from the radiation.
Wilson perfected his cloud chamber in 1912. He was able to track the movements of ionizing particles, which leave a track of ions through the chamber. This formed tracks of water droplets that he would photograph, allowing scientists to study the properties of the electrons and helium nuclei that formed them.
