http://www.jstor.org/stable/3653092 The Mystery of the Einstein-Poincaré Connection, Olivier Darrigol: "It is clear from the context that Poincaré meant here to apply the postulate [of constancy of the speed of light] only in an ether-bound frame, in which case he could indeed state that it had been "accepted by everybody." In 1900 and in later writings he defined the apparent time of a moving observer in such a way that the velocity of light measured by this observer would be the same as if he were at rest (with respect to the ether). This does not mean, however, that he meant the postulate to apply in any inertial frame. From his point of view, the true velocity of light in a moving frame was not a constant but was given by the Galilean law of addition of velocities."
Et vous, Olivier Darrigol, qu'en pensez-vous?
1. "...the velocity of light measured by this [moving] observer would be the same as if he were at rest (with respect to the ether)": Vrai? Faux? La fréquence mesurée par l'observateur en mouvement varie avec sa vitesse (par rapport à la source lumineuse), et si le mouvement de l'observateur ne peut pas changer la longueur d'onde, alors... en mesurant la variation de la fréquence l'observateur mesure, indirectement, la variation de la vitesse de la lumière, ce qui est évident sur cette vidéo: