This term is used in four senses:

(1) in theosophy, it refers to the material of the ASTRAL LIGHT, the lowest level of AKASA (as contrasted to AETHER, which is the higher level of Akasa); in this aspect, it refers also to the material of the LINGA-SARIRA or ETHERIC DOUBLE;

(2) in physics, it is the supposed universal medium needed for the transmission of light;

(3) in Hinduism, the 5th primordial element or TATTVA;

(4) in chemistry, it is an organic compound. It is with the first three that this article is concerned.

Ether in physics. During the nineteenth century many physicists postulated the existence of an intangible substance that permeated all space, including the matter contained therein. Light, it was discovered, had a wave motion and it was thought that ether would provide the medium by which light-waves could be transmitted. Also, it was thought that ether might account for effects operating between objects at a distance from each other in space such as between the planets. Then again it was suggested that magnetism might be an etheric effect. In 1881, this theory became questionable when the Michelson-Morley experiment showed the motion of the earth through the ether which was supposed to affect the speed of light did not have such expected effects. From 1900 the concept of the ether was discarded when Albert Einstein demonstrated that it was unnecessary as space-time could accommodate the properties formerly attributed to ether.

Ether in theosophy. In 1891, H. P. Blavatsky published The Secret Doctrine and stated that this ether is a reality. It is one of the lower principles of Akasa, or primordial substance. It is also called the ASTRAL LIGHT (SD I:326). Aether, on the other hand, is used to refer to Akasa itself. In this sense Aether is identical with the way the Greeks used the word. For example, Virgil calls Jupiter “the great Aether” (SD I:331). Thus, we must distinguish between Aether and Ether, Akasa and the Astral Light (CW I:384).

The word “ether” is also used to refer to the “nerve force” of people, such as that used by John Kelly in running his motor. Blavatsky identifies this as the “etheric (or Astral) Force” (SD I:562). This belongs to the linga-sarira of the human constitution (not the kama-rupa or emotional body).

Ether in Hinduism. In Hinduism, there are five primordial elements (tattvas): akasa (aether), air, fire, water, earth.

P.S.H./V.H.C.

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