From: BillK (bill@wkidston.freeserve.co.uk)
Date: Tue Aug 12 2003 - 06:22:45 MDT
On Tue Aug 12, 2003 04:43 am Eliezer wrote:
>
> I want to know: when Maxwell surprisingly found that the
> already-measured speed of light could astonishingly also be derived
> from the already-measured electric and magnetic constants, what were
> the electric and magnetic constants measured to be at that time? (I'm
> looking for a good, strong, unambiguous historical example of
> Nature's Surprise Consistency; no one realized in advance that these
> constants ought to match when they were measuring them.)
>
Maxwell's paper "On physical lines of force" 1861-62, was mostly later
discarded by him, but this was where he originally made the claim.
http://physics.hallym.ac.kr/reference/physicist/maxwell/maxnew-2.html
describes his discovery. The section I think you want is:
Quote:
The Speed of an Electromagnetic Wave
In 1861 the British Association for the Advancement of Science set up a
committee under William Thomson's chairmanship to establish a set of
electrical and magnetic standards. During the course of their work it
became clear to Maxwell and others that important insight can be
obtained by comparing results expressed in the two sets of units,
electrostatic and electromagnetic, that were being used at the time. The
electrostatic units were particularly appropriate to static electricity,
and related the force of attraction and repulsion between two charged
bodies to the quantities of electricity that they held. The
electromagnetic system of units, on the other hand, related force to
electric currents. The quantity of electricity residing on a wire at a
given time depends on the speed with which the current travels along the
wire. It can be shown that the ratio of an electromagnetic unit of
charge to an electrostatic unit of charge is the speed with which the
current passes along a wire.
During the 1860s Maxwell and various colleagues carried out careful
experiments in which they compared the two units. Maxwell's own
experiments were carried out using equipment made available to him by
John Peter Gassiot (1797-1877), a wealthy wine merchant and amateur
scientist who had already done some remarkable experiments using vast
numbers of electric cells. The conclusion from the experiments comparing
the two sets of units was that the speed of an electric current was
close to 3 x 10 m/s, which is the speed of light.
An alternative approach, used by Maxwell and others, was to compare the
electrical quantity now called the permittivity of a vacuum, o, with the
magnetic quantity now called the permeability, ľo. Maxwell's
mathematical treatment of Faraday's lines of force led to the conclusion
that the speed v of an advancing electromagnetic field was given by
v =1/(o ľo)
Measurements made by various physicists of ľo and o also led to the
result that v obtained in this way was the speed of light. These results
convinced Maxwell and others that light is an electromagnetic wave; in
his own words, emphasized in italics in his 1861-62 papers:
"Light consists in the transverse undulations of the same medium
which is the cause of electric and magnetic oscillations."
In other words, a single electromagnetic theory is needed for light, an
electric field and a magnetic field. The field produced by an electric
current has also a magnetic component, and the field produced by a
magnet has also an electric component; light also has electric and
magnetic components.
End Quote.
It should at least give you lots of words to google on!
Regards, BillK
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