The British scientist Sir Edward Victor Appleton (1892-1965) was a pioneer in radio physics who gained fame through his study of the ionosphere— the upper reaches of the atmosphere.
Edward Victor Appleton was born on September 6, 1892, in Bradford, Yorkshire, England. He was a brilliant student who excelled in the study of literature and language as well as science and mathematics. At age 16 he entered the University of London and two years later was awarded a scholarship for study at Cambridge University. Appleton left Cambridge in 1913, graduating with first-class honors in physics. He immediately began postgraduate work in crystallography with the distinguished physicist Sir Lawrence Bragg.
The advent of World War I interrupted this research effort. Appleton enlisted in the Royal Engineers and was assigned to signal duty as a commissioned officer. It was here that he was first introduced to radio, a means of communication then in its infancy in the military. The study of the theory and practice of radio wave propagation and reception, begun during the war, stimulated a life-long interest in the subject and brought Appleton renown as a scientist.
At the end of the war Appleton returned to the Cavendish Laboratory at Cambridge where, in collaboration with Balthazar van der Pol, he began an investigation of the operation of radio vacuum tubes. His original research in this area eventually led to the publication Thermionic Vacuum Tubes (1932), a scholarly monograph that long served as an introduction to the physical principles underlying these important electronic components.
In 1924 Appleton, at age 32, was made Wheatstone Professor of Physics at King's College, University of London. While at London (1924-1936) he made his most significant contributions to physics by studying radio transmission and the upper atmosphere. He was aided in this research by Miles Barnett, a young graduate student from New Zealand.
Guglielmo Marconi had succeeded in transmitting radio waves across the Atlantic Ocean for the first time in 1901. English physicist Oliver Heaviside and American physicist Arthur E. Kennelly postulated that this transmission was made possible by the presence of a layer of ionized gases in the upper atmosphere. These gases were believed to reflect radio waves back toward the earth. The Heaviside-Kennelly layer, which later came to be called the ionoshpere, remained an hypothetical entity until its existence was experimentally verified by Appleton.
Appleton's critical experiments were made using the British Broadcasting Corporation's transmitter at Bournemouth and recording the strength of its signal when received at Cambridge. By varying the frequency of the transmitted signal and noting the interference between the direct (ground) waves and the reflected (sky) waves Appleton was able to prove that the Heaviside-Kennelly layer was located at a height of 60 miles above the surface of the earth. In subsequent experiments Appleton and his coworkers discovered the so-called "Appleton layers," one of which was situated at a height twice that of the Heaviside-Kennelly layer and the other somewhat lower than the Heaviside-Kennelly layer. The electron densities of these layers were calculated, and the daily and seasonal variations of the Appleton layers were determined. The experimental techniques that led to these discoveries were later used by Sir Robert Watson-Watt in the development of radar.
Appleton's scientific achievements were recognized through the bestowal of a number of distinctions. In 1927 he was voted a fellow of the prestigious Royal Society of London; in 1941 he was knighted; and in 1947 he was awarded the Nobel Prize in Physics.
Appleton returned to Cambridge University as Jacksonian Professor of Natural Philosophy in 1936. He continued his ionospheric researches there in a field laboratory built for him by the university. With the coming of World War II Appleton left academic life in order to become a government scientist (1939). In his new role he served as secretary of the Department of Scientific and Industrial Research, a position which ultimately involved him with the organization and management of Britain's nuclear and radar programs.
In 1949 Appleton left government service to accept the post of chancellor at the University of Edinburgh. In addition to his administrative duties he maintained his interest in ionospheric physics and founded the influential Journal of Atmospheric and Terrestrial Physics, serving as its editor until his death. During his later years Appleton's international reputation led to his participation in a number of world-wide scientific activities including the International Geophysical Year of 1957. By the time of his death in 1965 Appleton had published 140 scientific papers, the majority dealing with the physics of the upper atmosphere.
For a full-length biographical study of Appleton see Ronald Clark, Sir Edward Appleton (1971). His scientific work had been evaluated in two excellent shorter pieces: Charles Süsskind, "Appleton, Edward Victor" in the Dictionary of Scientific Biography, edited by C. C. Gillispie (1970) and J. A. Ratliffe, Biographical Memoirs of the Fellows of the Royal Society, volume 12 (1966). On the ionosphere, see H. S. W. Massey and R. L. F. Boyd, The Upper Atmosphere (1958).