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Sir Edward Appleton, c. 1935  © Appleton was an English physicist and Nobel prize winner who discovered the ionosphere.

Edward Victor Appleton was born on 6 September 1892 in Bradford. He studied natural sciences at Cambridge University and during World War One served in the Royal Engineers. After the war, he returned to Cambridge to research on atmospheric physics mainly using radio waves. In 1920 he was appointed assistant demonstrator in experimental physics at the Cavendish Laboratory. In 1924, Appleton became professor of physics at London University, returning to Cambridge in 1936 as professor of natural philosophy.

In 1924 Appleton began research into the strength of the radio signals received at Cambridge from the Â鶹Éç station in London. He soon discovered that the strength of the signal was constant during the day but varied during the night, rising and falling in an almost regular manner. He suggested that, at night, the Cambridge apparatus was receiving not one but two waves, one travelling directly and the other being reflected by the atmosphere. The existence of a reflecting layer had first been suggested around forty years earlier by Balfour Stewart. In 1902 Oliver Heaviside and A.E. Kennelly had independently postulated the theory of a conducting layer of the atmosphere: the Kennelly-Heaviside Layer.

Using a Â鶹Éç transmitter, Appleton conducted experiments to prove that this layer existed and its position and height above the ground were determined. However, these experiments produced more questions than answers. In 1926, Appleton discovered another layer 250-350 km high which reflected back shorter wavelengths in daytime as well as at night, and that they were reflected back with greater strength than the Heaviside layer. Appleton realised that this was the layer responsible for reflecting short wave radio round the world - 'the Appleton layer' - that now enables communication with Australia and America.

On the outbreak of war, Appleton was appointed secretary of the department of scientific and industrial research, the senior British government post concerned with physical science. Working on Appleton's findings, Robert Watson-Watt and his colleagues developed radar, a crucial weapon in the war. Appleton was knighted in 1941.

In 1947 Appleton was awarded the Nobel Prize for Physics and, two years later, moved to the University of Edinburgh to become principal and vice-chancellor, a position he held for the rest of his life. He died on 21 April 1965.