Résumé
An amazing characteristic of Maxwell equations is their robustness: Discovered several decades before the rise of Einsteinian relativity and quantum mechanics, they nevertheless remain true in almost all contexts. They were initially designed by J. C. Maxwell in around 1865. The description of fields in terms of functions of space-time coordinates with vector values is probably not the best description, from the point of view of neither mathematics nor physics. Indeed, it is not clear to understand why the magnetic field should depend on the orientation of space, why the circulation of the electric fields is an energy and so on. In physics, dispersion most often refers to materials that bring about frequency-dependent effects in wave propagation. To a large extent, all materials are dispersive, except in vacuum. It is clear that the constitutive relations have been obtained roughly: They cannot convey physical properties as important as dispersion and absorption.