Summary
Sir Edward Appleton's "The Appleton Layer: A Study of the Upper Atmosphere" (1932) presents the central thesis that the Earth's upper atmosphere contains ionized layers that refract and reflect radio waves, enabling long-distance wireless communication. Appleton details his experiments and findings concerning these reflective strata, which he proposed were responsible for the behavior of short-wave radio signals. The book elucidates the varying properties of these layers, their altitude, and their dependence on time of day and season, establishing the foundation for understanding the ionosphere's role in radio wave propagation.
The work outlines key experimental methods used to probe these atmospheric regions, particularly those involving radio transmissions and reception. Readers gain insight into the scientific process of discovery in atmospheric physics and radio engineering of the early 20th century. The implications of the "Appleton Layer" for predictable and reliable long-distance radio communication are clearly articulated, marking a significant advancement in the field.
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Key concepts
- Ionosphere — A region of Earth's upper atmosphere, about 60 to 1,000 km (37 to 621 miles) above the surface, where atoms and molecules are ionized by solar and cosmic radiation.
- Radio Wave Refraction — The bending of radio waves as they pass through layers of different densities in the atmosphere, causing them to change direction.
- Radio Wave Reflection — The bouncing of radio waves off ionized layers in the upper atmosphere, allowing them to travel beyond the horizon.
- Kennelly-Heaviside Layer — An earlier proposed name for the ionized layer responsible for reflecting radio waves, later distinguished by Appleton into multiple layers.