British physicist, who discovered and investigated the properties of the ionosphere. He was knighted in 1941 and awarded the Nobel Prize for Physics in 1947.
Born in Bradford, he studied physics at Cambridge (1910–13) and spent World War I in the Royal Engineers. Much concerned with the persistent problem of the fading of radio signals during the war, Appleton turned after the war to the study of the propagation of electromagnetic waves. It had been proposed by Oliver Heaviside and Arthur Kennelly in 1902 that some waves (known as sky waves) were reflected back to earth by an electrified layer in the upper atmosphere. Appleton set out to confirm this suggestion experimentally and to explore the nature of the layer, which eventually became known as the ionosphere. Suspecting that fading was caused by interference, Appleton arranged for the BBC to vary the frequency of their transmitter while he recorded the strength of the signal received some miles away in Cambridge. He found a strengthening of the signal when the ground waves interfered constructively with the sky waves. Appleton calculated the height of the reflecting layer to be about 95 km and went on to show that it had a complex structure. The top layer (F-region) of the ionosphere is often known as the Appleton layer. This work had enormous practical and theoretical implications for radio transmission.
From 1924 to 1936 Appleton was Wheatstone Professor of Experimental Physics at King's College, London. After a spell as Jacksonian Professor of Natural Philosophy at Cambridge, he was appointed secretary to the Department of Scientific and Industrial Research (1939–49). During his period with the DSIR Appleton was one of the key figures in the development of the British nuclear programme, both for military and industrial applications. In 1944 he moved to Edinburgh University, where he was vice chancellor until his death.
Subjects: Science and technology