John Sealy Townsend

John Sealy Edward Townsend (June 7, 1868 - February 16, 1957) was a mathematical physicist who conducted various studies concerning the electrical conduction of gases (concerning the kinetics of electrons and ions) and directly measured the electrical charge.

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Biography

He was born in Galway, County Galway, Ireland. He studied at Trinity College, Dublin. He was a research student at Cambridge University together with Ernest Rutherford. At the Cavendish laboratory, he studied under Joseph John Thomson. He developed the "Townsend's collision theory". Townsend supplied important work to the electrical conductivity of gases ("Townsend discharge" circa 1897). This work determined the elementary electrical charge with the droplet method developed. This method was improved later by Robert Andrews Millikan.

In 1900, he became a professor at Oxford. In 1901, he discovered the ionization of molecules by ion impact and the dependence of the mean free path on electrons (in gases) of the energy (and his independent studies concerning the collisions between atoms and low-energy electrons in the 1920s would later be called the Ramsauer-Townsend effect). On June 11, 1903, he was elected to Fellow of the Royal Society (FRS). He was awarded the Hughes Medal in 1914. During World War I, he researched (at Woolwich, London, England) wireless methods for the Royal Navy Air Service. He was knighted in 1941. He died in Oxford, England.

Works

• The Theory of Ionisation of Gases by Collision (1910)
• Motion of Electrons in Gases (1925)
• Electricity and Radio Transmission (1943)
• Electromagnetic Waves (1951)

References

• Top 1000 Scientists: From the Beginning of Time to 2000 AD Philip Barker ISBN 81-7371-210-7
• A. von Engel "John Sealy Edward Townsend. 1868-1957," Biographical Memoirs of Fellows of the Royal Society, Vol. 3, Nov., 1957, pp. 256-272.