Kennelly-Heaviside Layer: Layer of the Earth's ionosphere

It is a region which is between 90 km and 150 km from the earth’s surface. It is named after the American engineer Arthur Edwin Kennelly and the British scientist Oliver Heaviside. These two scientists both predicted that this area existed, although it was not until some years later that it was proved.

In the Kennelly-Heaviside layer neutral molecules are split into electrons and positively charged molecules. Radio waves can be bounced off this region so that long-distance radio messages can be sent over long distances around the curved surface of the earth. This was why Marconi had been able to send radio messages across the Atlantic in 1902, although it was not understood at the time.

• The New Encyclopædia Britannica vol 4, 15th edition, 1986, ISBN 0-85229-434-4

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