Editing Luminiferous aether (section)

===Electromagnetism===
In 1856, [[Wilhelm Eduard Weber]] and [[Rudolf Kohlrausch]] measured the numerical value of the ratio of the electrostatic unit of charge to the electromagnetic unit of charge. They found that the ratio between the [[electrostatic unit of charge]] and the [[Abcoulomb|electromagnetic unit of charge]] is the speed of light ''c''.<ref>{{Cite book |last=Schwartz |first=Melvin |title=Principles of Electrodynamics |publisher=Dover Publications, Inc. |year=1987 |isbn=978-0-486-65493-5 |edition=Revised |pages=106–107}}</ref> The following year, [[Gustav Kirchhoff]] wrote a paper in which he showed that the speed of a signal along an electric wire was equal to the speed of light. These are the first recorded historical links between the speed of light and electromagnetic phenomena.

[[James Clerk Maxwell]] began working on [[Michael Faraday]]'s [[lines of force]]. In his 1861 paper ''[[:Image:On Physical Lines of Force.pdf|On Physical Lines of Force]]'' he modelled these magnetic lines of force using a sea of molecular vortices that he considered to be partly made of aether and partly made of ordinary matter. He derived expressions for the dielectric constant and the magnetic permeability in terms of the transverse elasticity and the density of this elastic medium. He then equated the ratio of the dielectric constant to the magnetic permeability with a suitably adapted version of Weber and Kohlrausch's result of 1856, and he substituted this result into Newton's equation for the speed of sound. On obtaining a value that was close to the speed of light as measured by [[Hippolyte Fizeau]], Maxwell concluded that light consists in undulations of the same medium that is the cause of electric and magnetic phenomena.<ref group=B name=whitt /><ref group=B name=janb /><ref group=B name=darrigol /><ref group=B name=schaffner />

Maxwell had, however, expressed some uncertainties surrounding the precise nature of his molecular vortices and so he began to embark on a purely dynamical approach to the problem. He wrote another paper in 1864, entitled "[[A Dynamical Theory of the Electromagnetic Field]]", in which the details of the luminiferous medium were less explicit.<ref group=A name=maxb /> Although Maxwell did not explicitly mention the sea of molecular vortices, his derivation of [[Ampère's circuital law]] was carried over from the 1861 paper and he used a dynamical approach involving rotational motion within the electromagnetic field which he likened to the action of flywheels. Using this approach to justify the electromotive force equation (the precursor of the [[Lorentz force]] equation), he derived a wave equation from a set of eight equations which appeared in the paper and which included the electromotive force equation and [[Ampère's circuital law]].<ref group=A name=maxb /> Maxwell once again used the experimental results of Weber and Kohlrausch to show that this wave equation represented an electromagnetic wave that propagates at the speed of light, hence supporting the view that light is a form of electromagnetic radiation.

In 1887–1889, [[Heinrich Rudolf Hertz|Heinrich Hertz]] experimentally demonstrated the electric magnetic waves are identical to light waves. This unification of electromagnetic wave and optics indicated that there was a single luminiferous aether instead of many different kinds of aether media.<ref>{{Cite journal |url=https://en.wikisource.org/wiki/Popular_Science_Monthly/Volume_66/November_1904/The_Fundamental_Concepts_of_Physical_Science |first=Edward L. |last=Nichols |title=The Fundamental Concepts of Physical Science |journal=Popular Science Monthly |volume=66 |date=November 1904}}</ref>

The apparent need for a propagation medium for such [[Heinrich Rudolf Hertz|Hertzian waves]] (later called [[Radio wave|radio waves]]) can be seen by the fact that they consist of orthogonal electric (E) and magnetic (B or H) waves. The E waves consist of undulating dipolar electric fields, and all such dipoles appeared to require separated and opposite electric charges. Electric charge is an inextricable property of [[matter]], so it appeared that some form of matter was required to provide the alternating current that would seem to have to exist at any point along the propagation path of the wave. Propagation of waves in a true vacuum would imply the existence of [[electric field]]s without associated [[electric charge]], or of electric charge without associated matter. Albeit compatible with Maxwell's equations, [[electromagnetic induction]] of electric fields could not be demonstrated in vacuum, because all methods of detecting electric fields required electrically charged matter.

In addition, Maxwell's equations required that all electromagnetic waves in [[vacuum]] propagate at a fixed speed, ''[[speed of light|c]]''. As this can only occur in one [[frame of reference|reference frame]] in Newtonian physics (see [[Galilean invariance|Galilean relativity]]), the aether was hypothesized as the absolute and unique frame of reference in which Maxwell's equations hold. That is, the aether must be "still" universally, otherwise ''c'' would vary along with any variations that might occur in its supportive medium. Maxwell himself proposed several mechanical models of aether based on wheels and gears, and [[George Francis FitzGerald]] even constructed a working model of one of them. These models had to agree with the fact that the electromagnetic waves are transverse but never longitudinal.