Appleton Layer

The Appleton layer was discovered in 1924 by British physicist Edward Appleton*. It exists as the highest layer of the ionosphere (so-called because the sun’s ultraviolet energy breaks up air molecules, ‘ionizing’ them, and this releases ‘free electrons.’) The amount of free electrons in the ionosphere is highest in the Appleton layer, which extends from about 120 to about 400 kilometers above the Earth’s surface.

High-frequency radio waves hitting the free electrons in the Appleton layer are bounced back to Earth. This was the phenomenon discovered by Appleton when he was testing the theory, of Kennelly* and Heaviside* , that some kind of ionized layer (causing radio-wave ‘bounce-back’) would explain why Marconi’s first radio messages were going around the curvature of the Earth and reaching from Europe to the North American continent (and vice versa).

OTHER CONNECTIONS: None

ONELINER: The Appleton layer

BIBLIOGRAPHY:

Dictionary of Scientific Biography

Wikipedia