Is the speed of light in vacuum constant?

The possibility to accept a new gaseous ether model is considered. From the model it follows that speed of light in vacuum is not constant but it changes depending on ether “density”. It is assumed that ether molecules have mass and therefore they are subject to gravitational attraction and their density increases in the vicinity of a celestial body. Consequently speed of light will change. Therefore when a light beam passes close to the Sun it will suffer additional diversion. It has been calculated to amount to 1,60 ″ arc seconds and it is within the limits of the experimental data available until now. It is suggested to carry out Michelson-Morley experiment on a space ship in order to discover the ether wind. Resume On envisage la possibilite de creer un noveau modele gaseux de l’ether. Il en suit que la vitesse de la lumiere en vacuum n’est pas constante mais elle devrait changer et dependre de la “densite ” de l’ether. On accepte que les molecules de l’ether ont une masse, de ce fait elles sont soumises a l’attraction gravitationnelle et leur densite s’agrandirai a proximite d’un corps celeste. Cependant la vitesse de la lumiere changera aussi. Voila pourquoi lorsqu’un rayon de la lumiere passe autur du Soleil, il subira une derivation suplementaire. Il est calcule que cette derivation, egale a 1,60 ″ secondes d’arc, entre dans les limites des donnes experimentales qu’on a jusqu’a ce moment. On propose que l’essai Michelson-Morley soit fait a un vaisseau spatail en vue de decouvrir le vent d’ether