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Appleton, Sir Edward (Victor)

layer radio physics ionosphere

(1892–1965) British physicist: pioneer of ionospheric physics; discovered reflective layers within the ionosphere.

Appleton studied physics at Cambridge, but it was service in the First World War as a signals officer which led to his interest in radio. In 1924 he was appointed professor of experimental physics at King’s College, London. In 1939 he was appointed secretary of the Department of Scientific and Industrial Research, and later became vice-chancellor of Edinburgh University.
In 1901 had transmitted radio signals across the Atlantic, to the astonishment of many in the scientific community who believed that, since electromagnetic radiation travels in straight lines and the Earth’s surface is curved, this was not possible. Shortly afterward, A E Kennelly (1861–1939) and proposed a reflecting layer of charged particles in the atmosphere as the explanation. In a classic experiment in 1925, Appleton became the first to demonstrate beyond doubt the existence of such a reflecting layer within the ionosphere. He transmitted signals between Bournemouth and Cambridge (a distance of 170 km); and by slowly Page 10  varying the frequency and studying the received signal he showed that interference was occurring between the part of the signal that travelled in a straight line from transmitter to receiver (the direct, or ground, wave) and another part that was reflected by the ionosphere (the sky wave). Measurement of the interference caused by the different path lengths enabled him to measure the height of the reflecting layer, about 70 km. This was the first radio distance measurement. This layer is now known as the Heaviside layer or E layer. Further work revealed a second layer above the first, which is now called the Appleton layer or F layer. The E layer is more effective after dark, since the Sun’s ultraviolet rays interact with the ionosphere, which is why distant radio stations are more readily picked up at night. For his achievements Appleton received the Nobel Prize for physics in 1947.

Appleton, Steven - Overview, Personal Life, Career Details, Social and Economic Impact, Chronology: Steven Appleton [next] [back] Appleton, Jon (Howard)

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