Page:DeSitterConstancy1.djvu/1

 In the theory of  light emitted by a source moving with velocity u is propagated through space in the direction of the motion of the source with the velocity c+u, c being the velocity of light emitted by a motionless source. In other theories (,  ) the velocity of light is always c, independent of the motion of the source. Now it is easily seen that the hypothesis of leads to results which are absolutely inadmissible.

Consider one of the components of a double star, and an observer situated at a great distance Δ. Let at the time t, the projection of