Kennelly, Arthur Edwin, 1861-1939, American electrical engineer, b. Bombay (now Mumbai), India, educated at University College School, London. He was Edison's chief electrical assistant (1887-94) and was later professor at Harvard (1902-30) and at the Massachusetts Institute of Technology (1913-24). Much of his research was on electromagnetism and alternating currents. In 1902 he advanced the theory, also proposed by Oliver Heaviside, that a layer of ionized air in the upper atmosphere might deflect downward electromagnetic waves. The theory was demonstrated as fact, and the deflecting layer is known as the Heaviside-Kennelly layer (see ionosphere).
The Kennelly-Heaviside layer, also known as the E region or simply the Heaviside layer, is a layer of ionised gas occurring at 90–150 km above the ground — one of several layers in the Earth's ionosphere. It reflects medium-frequency radio waves, and because of this reflection radio waves can be propagated beyond the horizon.

Propagation is affected by time of day. During the daytime the solar wind presses this layer closer to the Earth, thereby limiting how far it can reflect radio waves. On the night side of the Earth, the solar wind drags the ionosphere further away, thereby greatly increasing the range which radio waves can travel by reflection, called skywave. The extent of the effect is further influenced by the season (because of the differing distance between Earth and the Sun), and the amount of sunspot activity.


Its existence was predicted in 1902 independently and almost simultaneously by the American electrical engineer Arthur Edwin Kennelly (1861-1939) and the British physicist Oliver Heaviside (1850-1925). However, it was not until 1924 that its existence was detected by Edward V. Appleton.

In 1899, Nikola Tesla, in his Colorado Springs experiments, transmitted extremely low frequency electromagnetic waves between the earth and ionosphere, up to the Kennelly-Heaviside layer (Grotz, 1997). Tesla made mathematical calculations and computations based on his experiments. He predicted the resonance frequency of this area within 15% of modern accepted experimental value. (Corum, 1986) In the 1950s, researchers confirmed the resonance frequency was at the low range 6.8 Hz.


  • Corum, J. F., and Corum, K. L., "A Physical Interpretation of the Colorado Springs Data". Proceedings of the Second International Tesla Symposium. Colorado Springs, Colorado, 1986.
  • Grotz, Toby, "The True Meaning of Wireless Transmission of power". Tesla : A Journal of Modern Science, 1997.

Cultural impact

The "Heaviside layer" is used as a symbol for heaven (in the afterlife sense) in Andrew Lloyd Webber's musical Cats. This reference is based on a quote found in a letter written by T. S. Eliot, whose book Old Possum's Book of Practical Cats forms the basis of the musical. In the musical, one cat is chosen each year by Old Deuteronomy to go to the Heaviside Layer and begin a new life. In the song "The Journey to the Heaviside Layer", it is stated that the Heaviside Layer is "past the Russell Hotel" and "past the Jellicle moon", indicating that it is very far away and difficult to access.

In the end of the musical, Grizabella is chosen to go the Heaviside Layer. She does so by ascending on a flying tyre until she reaches a structure resembling clouds, into which she disappears.

The "Heaviside Layer" is another name for the Ionosphere. There are two kinds of ions, anions and cations. This reference may be a scientific pun by T. S. Eliot.

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