By looking at the original publications, rather than only at the articles and books talking of them, one finds
Galileo Galilei (1564-1642).
Dialogo sopra i due massimi sistemi del mondo, Tolemaico e Copernicano (1632)
Galilei states the relativity principle, without using the term, as a consequence of the experimental evidence, by stating that all possible experiments, with bodies interacting in any possible ways, performed inside a ship cannot show whether the ship is moving or not, provided the motion is uniform. The principle is stated to be valid for all the phenomena.
After having performed a number of experiments inside a ship standing in the harbour,
“... have the ship moving with whatever velocity, then (provided that the motion be uniform and not fluctuating in one or the other direction) you will not recognise any variation in any of the just mentioned effects, neither you will be able to recognise from any of them whether the ship is moving or standing.”
Jules Henri Poincaré (1854-1912)
L’état actuel et l’avenir de la Physique Mathématique (1904)
For the first time the term “Relativity Principle” is introduced and stated, on the basis of all the experiments performed at the time, including Michelson Morley, as
“According to the “Relativity Principle” the laws of the physical phenomena must be the same for a standing observer and for one in uniform translation motion; so that we have no means, neither we can have any, to chose whether we are or not transported in such a motion”
Albert Einstein (1879-1955)
Ist die Trägheit eines Körpers von seinen Energiehalt abhänging?, Ann. d. Phys, 18 (1905), 639
Principle of Relativity: “The laws by which the states of physical systems undergo change are not affected, whether these changes of state be referred to the one or the other of two systems of co-ordinates in uniform translatory motion.”
Hendrik Antoon Lorentz (1853-1928)
Deux mémoires de Henri Poincaré dans la physique mathématique, Acta mathematica 38 (1921), 293-308 (written in 1914)
“It was not me to establish the Relativity Principle as rigorously and universally valid. Poincaré on the contrary obtained the perfect invariance of the electrodynamic equations and formulated the “Relativity Principle”, a term that was first to use.”
Does anybody understand why usually only the last one, Einstein, is quoted, and the other forgotten?
Strictly speaking, the first concept of Relativity, as recorded in history, was discovered by Galileo.
The recent discussion has nothing to do with physics. Several statements are simply wrong. Maxwel equations are covariant under Lorentz transformations. This means that their form does not vary. However the quantities that appear in the equation, electric and magnetic field, current and charge densities, are different in different frames. All of them are physical meaning measureble objects. Their relationships are given by Lorentz transformations. The velocity of electromagnetic waves in vacuum is however the same in all the inertial frames. It does not depend on frequency.
The wave velocity c has a well known physical meaning is the speed at which energy associated with light moves. Is something we do measure in our laboratories
In a medium the speed is still c at microscopic level. In a macroscopic description one must model the behaviour of matter, something that can be done approximately with the dielectric and magnetic permettivity. The wave equation is not the same as in vacuum.
Before saying that Poincare, or other, do not understand physics, Akira, you should go back and study electromagnetism in any elementary textbook
Akira,
I fully agree with Charles. There is no point to respond to your posts that contain so many mistakes to show that you do not know physics and need to go back to learn it