On Friday, January 13, 2023 at 6:08:24 PM UTC-3, patdolan wrote:
> On Thursday, January 12, 2023 at 4:02:34 PM UTC-8, Richard Hertz wrote:
> > On Thursday, January 12, 2023 at 6:40:49 PM UTC-3, Pentcho Valev wrote:
> > > "How do Maxwell's equations predict that the speed of light is constant" https://twitter.com/fermatslibrary/status/1613538798750646273
> > >
> > > The derivation says nothing about whether or not the speed of light relative to an observer varies with the speed of that observer. Maxwell believed that it did vary:
> > >
> > > John Norton: "[Maxwell's] theory allows light to slow and be frozen in the frame of reference of a sufficiently rapidly moving observer." http://www.pitt.edu/~jdnorton/papers/Chasing.pdf
> > >
> > > The speed of light relative to an observer OBVIOUSLY varies with the speed of the observer. Consider Doppler effect (moving observer):
> > >
> > > https://www.youtube.com/watch?v=bg7O4rtlwEE
> > >
> > > The speed of the light pulses relative to the stationary observer is
> > >
> > > c = df
> > >
> > > where d is the distance between subsequent pulses and f is the frequency at the stationary observer. The speed of the pulses relative to the moving observer is
> > >
> > > c' = df' = c+v
> > >
> > > where f' = (c+v)/d is the frequency at the moving observer.
> > >
> > > See more here: https://twitter.com/pentcho_valev
> > >
> > > Pentcho Valev
> > NO, PENTCHO. MAXWELL NEVER HAD A SINGLE THOUGHT ABOUT SUCH A THING.
> >
> > I TOOK THE LIBERTY TO COMPRESS PART OF THE EXCELLENT BOOK:
> >
> > The MAN Who CHANGED EVERYTHING
> > The Life of James Clerk Maxwell
> >
> > Basil Mahon
> > Published in the UK in 2003 by John Wiley & Sons Ltd
> >
> > ENJOY THOSE WHO APPRECIATE, DIRECTLY FROM MAXWELL'S MEMOIRS, SOME EXCERPTS:
> >
> > ////////////////////////////////////////////////////////////////////////////////
> >
> > The difficulty lay deep in the scientific thinking of the time.
> > People believed that all physical phenomena resulted from
> > mechanical action and that all would be clear to us if, and only if,
> > we could discover the true mechanisms. With a century and a half
> > of hindsight we can see the spinning cell model as a crucial bridge
> > between old and new ideas built from old materials but paving
> > the way for a completely new type of theory, one which admits
> > that we may never understand the detailed workings of nature.
> >
> > James himself was not entirely content with the model, but for
> > different reasons. He wanted to free the theory if possible from all
> > speculative assumptions about the actual mechanism by which
> > electromagnetism works. He was to achieve this wish 2 years
> > later by taking an entirely new approach. Scientific historians
> > now look upon his spinning cells paper as one of the most
> > remarkable ever written but hold the one that followed to be
> > greater still.
> > ......
> > It was at this time, busy as he was with experiments and
> > College business, that Maxwell produced a paper which will remain
> > forever one of the finest of all man’s scientific accomplishments,
> > A Dynamical Theory of the Electromagnetic Field. Its boldness,
> > originality and vision are breathtaking.
> > ......
> > Much of the mathematics he had developed in earlier papers
> > was still applicable, in particular the way of representing electric
> > and magnetic fields at any point in space at any time. But
> > to derive the equations of the combined electromagnetic field
> > independently of his spinning cell model he needed something else.
> > ......
> > James enlisted a method that had been created in the mid-eighteenth
> > century by Joseph-Louis Lagrange.
> > .....
> > For James, the keynote of Lagrange’s method was that it
> > treated the system being analysed like a ‘black box’ if you knew
> > the inputs and could specify the system’s general characteristics
> > you could calculate the outputs without knowledge of the internal
> > mechanism.
> > ......
> > This was just what he needed. Nature’s detailed mechanism could
> > remain secret, like the machinery in the belfry. As long as it obeyed
> > the laws of dynamics, he should be able to derive the equations of
> > the electromagnetic field without the need for any kind of model.
> > ......
> > The task was formidable; James had to extend Lagrange’s
> > method from mechanical to electromagnetic systems. This was
> > new and hazardous ground, but he was well prepared.
> >
> > His cardinal principle was that electromagnetic fields, even in
> > empty space, hold energy which is in every way equivalent to
> > mechanical energy. Electric currents and the magnetic fields
> > associated with them carry kinetic energy, like the moving
> > parts in a mechanical system. Electric fields hold potential
> > energy, like mechanical springs. Faraday’s electrotonic state is a
> > form of momentum. Electromotive and magnetomotive forces
> > are not forces in the mechanical sense but behave somewhat
> > similarly.
> > ......
> > Most of these quantities were vectors, having a direction as well
> > as a numerical value. The five main vectors were the electric and
> > magnetic field intensities, which resembled forces, the electric
> > and magnetic flux densities, which resembled strains, and the
> > electric current density, which was a kind of flow. One important
> > quantity, electric charge density, was a scalar, having only a
> > numerical value. These six quantities were like the ropes and
> > bells connected by the invisible machinery inside the belfry.
> > ......
> > The essence of the theory is embodied in four equations which
> > connect the six main quantities. They are now known to every
> > physicist and electrical engineer as Maxwell’s equations.
> >
> > They are majestic mathematical statements, deep and subtle
> > yet startlingly simple. So eloquent are they that one can get a
> > sense of their beauty and power even without advanced
> > mathematical training.
> > When the equations are applied to a point in empty space,
> > the terms which represent the effects of electric charges and
> > conduction currents are not needed.
> > ......
> > His system of equations worked with jewelled precision. Its
> > construction had been an immense feat of sustained creative
> > effort in three stages spread over 9 years. The whole route was
> > paved with inspired innovations but from a historical perspective
> > one crucial step stands out the idea that electric currents exist
> > in empty space. It is these displacement currents that give the
> > equations their symmetry and make the waves possible.
> > ......
> > James published A Dynamical Theory of the Electromagnetic Field
> > in seven parts and introduced it at a presentation to the Royal
> > Society in December 1864.
> > ......
> > One can understand these reactions. Not only was the theory
> > ahead of its time but James was no evangelist and hedged his
> > presentation with philosophical caution. He thought that his
> > theory was probably right but could not be sure. No-one could
> > until Heinrich Hertz produced and detected electromagnetic
> > waves over 20 years later. The ‘great guns’ had been paraded
> > but it would be a long while before they sounded.
> >
> > It is almost impossible to overstate the importance of James’
> > achievement. The fact that its significance was but dimly
> > recognised at the time makes it all the more remarkable. The
> > theory encapsulated some of the most fundamental characteristics
> > of the universe. Not only did it explain all known electromagnetic
> > phenomena, it explained light and pointed to the existence of
> > kinds of radiation not then dreamt of.
> >
> > Professor R. V. Jones was doing no more than representing the common
> > opinion of later scientists when he described the theory as one of the greatest
> > leaps ever achieved in human thought.
> > ......
> > The work of the British Association’s committee on electrical
> > standards had not stopped with the production of a standard of
> > resistance. The next task on their agenda stemmed from James’
> > prediction of electromagnetic waves which travelled at a speed
> > equal to the ratio of the electromagnetic and electrostatic units of charge.
> >
> > As we have seen, an earlier measurement of this ratio by
> > Kohlrausch and Weber, once converted to the appropriate units,
> > was very close to Fizeau’s measurement of the speed of light,
> > thus supporting James’ theory that light itself was composed of
> > electromagnetic waves. This result was so important that the
> > evidence needed to be checked; a new experiment was urgently
> > needed to corroborate Kohlrausch and Weber’s result. It would
> > be a difficult experiment and at best the range of possible error
> > would be a few percent, but it had to be done.
> >
> > This time James’ chief collaborator was Charles Hockin, of St
> > John’s College, Cambridge. They decided to try to balance the
> > electrostatic attraction between two charged metal plates against
> > the magnetic repulsion between two current-carrying coils, and
> > built a balance arm apparatus to do this. For this method to work
> > they needed a very high voltage source. The biggest batteries in
> > Britain were owned by a Clapham wine merchant, John Peter
> > Gassiot, who had acquired them for his private laboratory.
> >
> > Gassiot was delighted to act as host for the experiment and furnished his
> > guests with a battery of 2600 cells, giving about 3000 volts.
> > James arranged to do the experiment during his 1868 spring
> > visit to London. It was not easy work. First they had to take
> > precautions to stop electricity leaking from the great battery
> > through the laboratory floor. Then they had to become expert
> > at taking readings at speed because the batteries ran down so
> > quickly. When these problems had been overcome, the experiment
> > gave a value for the ratio of the two units of charge, and hence for
> > the speed of James’ waves, of 288,000 kilometres per second.
> >
> > This was about 7% below the value which Kohlrausch and
> > Weber had obtained for the electromagnetic=electrostatic units
> > ratio and 8% below the speed of light as measured by Fizeau (the
> > two results James had quoted in his paper). And it was 3% below a
> > new measurement of the speed of light by Fizeau’s compatriot Foucault.
> >
> > We now know that the true speed of light is about mid-way between that
> > predicted by James’ experiment and that predicted by Weber’s.
> Fascinating read. You are a wonderful aggregator of scientific literature, Richard. Please continue in this endeavor. Worth far more than the paltry 21 views it has garnered so far.

Thanks, Pat. I recommend to read (free download) the tribute biography written by two friends, two years after James death. It's full
with Maxwell's correspondece with Faraday and many others, original drawings of his inventions (many), drawings about many other
non-technical things and lot of poetry. He even wrote as poems scientific theories.

I can't even grasp the magnitude of his incredible genius. For me, he's far greater than Newton and heirs (like Euler, Laplace, Lagrange).
It's hard to believe how vast were his interests: natural philosopher, mathematician, astronomer, biochemist, biophysicist, atomicist,
poet, teacher, inventor, chief coordinator of difficult projects, devote christian and husband, dog lover, wonderkind geometer, so well
informed of everything that happened in the scientific world in Europe and other parts of the world, generous with friends and alumns,
humble, great sense of humor, an incredible lust for life.

I can't stand even the slightest comparison with the cretin.

This is the ONLY BIOGRAPHY EXISTENT, PUBLISHED IN 1882.

THE LIFE OF JAMES CLERK MAXWELL
WITH A SELECTION FROM HIS CORRESPONDENCE AND OCCASIONAL WRITINGS
AND A SKETCH OF HIS CONTRIBUTIONS TO SCIENCE

BY
LEWIS CAMPBELL, M.A., LL.D.
PROFESSOR OF GREEK IN THE UNIVERSITY OF ST. ANDREWS
AND
WILLIAM GARNETT, M.A.
LATE FELLOW OF ST. JOHN S COLLEGE, CAMBRIDGE
PROFESSOR OF NATURAL PHILOSOPHY IN UNIVERSITY COLLEGE, NOTTINGHAM

WITH THREE STEEL PORTRAITS, COLOURED PLATES, ETC.

London, MACMILLAN AND CO., 1882