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Summary: Describes the ionosphere's reflection of signals.
If we were limited to line-of-sight communications, long
distance wireless communication, like ship-to-shore
communication, would be impossible. At the turn of the century,
Marconi, the inventor of wireless telegraphy, boldly tried such
long distance communication without any evidence — either
empirical or theoretical — that it was possible. When the
experiment worked, but only at night, physicists scrambled to
determine why (using Maxwell's equations, of course). It was
Oliver Heaviside, a mathematical physicist with strong
engineering interests, who hypothesized that an invisible
electromagnetic "mirror" surrounded the earth. What he meant was
that at optical frequencies (and others as it turned out), the
mirror was transparent, but at the frequencies Marconi used, it
reflected electromagnetic radiation back to earth. He had
predicted the existence of the ionosphere, a plasma that
encompasses the earth at altitudes
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This work is licensed by Don Johnson under a Creative Commons Attribution License (CC-BY 1.0), and is an Open Educational Resource.
Last edited by Charlet Reedstrom on Apr 25, 2005 8:42 pm -0500.
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