The etheric plane (see also Etheric body) is a term introduced into Theosophy by Charles Webster Leadbeater and Annie Besant to represent the subtle part of the lower plane of existence. It represents the fourth [higher] subplane of the physical plane (a hyperplane), the lower three being the states of solid, liquid, and gaseous matter. The idea was later used by authors such as Alice Bailey, Rudolf Steiner, Walter John Kilner and others.
The term aether (also written as "ether") was adopted from ancient Greek philosophy and science into Victorian physics (see Luminiferous aether) and utilised by Madame Blavatsky to correspond to akasha, the fifth element (quintessence) of Hindu metaphysics.
The Greek word aither derives from an Indo-European root aith- ("burn, shine"). Blavatsky also related the idea to the Hindu Prana principle, the vital, life-sustaining force of living beings, present in all natural processes of the universe. Prana was first expounded in the Upanishads, where it is part of the worldly, physical realm, sustaining the body and the mind. Blavatsky also tended to use the word "astral" indiscrimininately for these supposed subtle physical phenomena.
Leadbeater and Besant (Adyar School of Theosophy) conceived that the etheric plane constituted four higher subplanes of the physical plane. According to the Theosophist Geoffrey A. Farthing, Leadbeater used the term, because of its resonance in the physical sciences, to describe his clairvoyant investigations of sub-atomic physics.
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The majority of modern physicists, in spite of acknowledging the phenomena known as vacuum energy and the existence of other unsolved problems in physics that are unexplained by current standard theories, continue to maintain that there is no need to imagine that a medium for propagation of electromagnetic waves exists (see also aether theories). However, there have been a number of physicists in western countries whose research, currently considered fringe and controversial among the mainstream scientific community, shows evidence of the existence of the dynamic aether possessing a fluid crystal-like structure and permeating all space, in an apparent accordance with recent experiments and as formerly outlined by Theosophical and Rosicrucian esoteric schools; also their work attempts to provide solutions to tap this energy source which regulates quantum activity for the generation of pollution-free power and other technological applications.
Christian Rosicrucians 
Similarly according to Max Heindel Rosicrucian writings; there is - in addition to the solids, liquids, and gases which compose the Chemical Region of the Physical World - a finer grade of matter called ether that permeates the atomic structure of the earth and its atmosphere. It is disposed in four grades of density and is considered to be a kind of physical matter (the blue haze seen in mountain canyons is said to be in fact ether of the kind known to occult investigators as chemical ether). Associated there is also a type of spiritual sight, that man will eventually develop, called etheric vision. Ether is reported to be of four kinds, or grades of density in our planet Earth; their names (from the lowest or most dense to the highest or most subtle one) and their relation to the human being, from the point of view of these Esoteric Christian teachings, is as following:
- the "Chemical Ether": both positive and negative in manifestation and it is related to the assimilation and excretion processes;
- the "Life Ether": has also a positive and negative pole and it is related to the forces of propagation;
- the "Light Ether": the positive pole is related to forces which generate blood heat in the higher species of animal and in the human being and the negative is related to the forces which operate through the senses (passive functions of sight, hearing, feeling, tasting, and smelling);
- the "Reflective Ether": the medium through which thought makes an impression upon the human brain and this ether contains pictures which work as reflexions of the Memory of Nature found at the World of Thought.
See also 
- Ethereal Plane (a concept in Dungeons & Dragons)
- Blavatsky, H.P., The Key to Theosophy, 1889
- Besant, Annie. Man's life in this and other worlds, Theosophical Publishing House, Adyar, 1913
- Farthing, Geoffrey A., The Etheric Double:The Far-Reaching Effects of a false Assumption, from a booklet in private circulation dated June 1995, reprinted from Theosophy World
- Choi, Charles Q., NASA Baffled by Unexplained Force Acting on Space Probes, Space.com, March 2008
- Marquit, Miranda, Current theories can't explain observed spin segregation, Physorg.com, October 2008
- Tulloch, David & Ford, Katrina, Historic Dispute: Is space filled with a medium known as the aether?, Technology Industry, Vol. 3, 2004
- Roberts, Tom, What is the experimental basis of Special Relativity?, October 2007
- Aspden, H., The Crystalline Vacuum, Journal of New Energy, vol. 3, No. 1, pp. 46-53 (1998)
- Kidwell, Dennis, New Physics, FrontierScience.com, 2002-2008
- PVLAS 2007 experiment, Physorg.com, August 2007: "vacuum acting like a crystal"
- European Patent Office, GB Patent 2432463, May 2007
- Aspden, H., Our Energy Future: A Message of Vital Importance, 2006
- Heindel, Max, The Rosicrucian Mysteries (Chapter III: The Visible and the Invisible Worlds), 1911, ISBN 0-911274-86-3
- A Student, Etheric Vision and What It Reveals, ISBN 0-911274-59-6, 110 pages
- Heindel, Max, The Rosicrucian Cosmo-Conception (Chapter I.2, The Etheric Region of the Physical World), 1909, ISBN 0-911274-34-0
- A Physical Model of The Parallel Ethereal World, 2004
- The Physics of Creation: Chapter 7 - Aether Structure by Harold Aspden (British electrical engineer and physicist, PhD. (Cantab) [1950-1953]), 2003