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In optics, an optical medium is material through which light and other electromagnetic waves propagate. It is a form of transmission medium . The permittivity and permeability of the medium define how electromagnetic waves propagate in it.
Luminiferous aether or ether [1] (luminiferous meaning 'light-bearing') was the postulated medium for the propagation of light. [2] It was invoked to explain the ability of the apparently wave -based light to propagate through empty space (a vacuum ), something that waves should not be able to do.
In the 19th century, luminiferous aether (or ether), meaning light-bearing aether, was a theorized medium for the propagation of light. James Clerk Maxwell developed a model to explain electric and magnetic phenomena using the aether, a model that led to what are now called Maxwell's equations and the understanding that light is an ...
When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not orthogonal (or rather normal) to the boundary, the change in wavelength results in a change in the direction of the beam.
The medium mentally "hears" (clairaudience), "sees" (clairvoyance), and/or feels (clairsentience) messages from spirits. Directly or with the help of a spirit guide, the medium passes the information on to the message's recipient(s). When a medium is doing a "reading" for a particular person, that person is known as the "sitter".
A medium having this common property may be termed a dispersive medium. Although the term is used in the field of optics to describe light and other electromagnetic waves, dispersion in the same sense can apply to any sort of wave motion such as acoustic dispersion in the case of sound and seismic waves, and in gravity waves (ocean waves
McLuhan understood "medium" as a medium of communication in the broadest sense. In Understanding Media he wrote: "The instance of the electric light may prove illuminating in this connection. The electric light is pure information. It is a medium without a message, as it were, unless it is used to spell out some verbal ad or name."
This slowing applies to any medium such as air, water, or glass, and is responsible for phenomena such as refraction. When light leaves the medium and returns to a vacuum, and ignoring any effects of gravity, its speed returns to the usual speed of light in vacuum, c. A correct explanation rests on light's nature as an electromagnetic wave. [5]