that it had emitted earlier when it was receding, then the image of the star system should appear completely scrambled. De Sitter argued that none of the star systems he had studied showed the extreme optical effect behavior, and this was considered the death knell for Ritzian theory and emission theory in general, with . The effect of extinction on de Sitter's experiment has been considered in detail by Fox, and it arguably undermines the cogency of de Sitter type evidence based on binary stars. However, similar observations have been made more recently in the x-ray spectrum by Brecher (1977), which have a long enough extinction distance that it should not affect the results. The observations confirm that the speed of light is independent of the speed of the source, with . Hans Thirring argued in 1924, that an atom which is accelerated during the emission process by thermal collisions in the sun, is emitting light rays having different velocities at their start- and endpoints. So one end of the light ray would overtake the preceding parts, and consequently the distance between the ends would be elongated up to 500 km until they reach Earth, so that the mere existence of sharp spectral lines in the sun's radiation, disproves the ballistic model. Terrestrial sources Such experiments include that of Sadeh (1963) who used a time-of-flight technique to measure velocity differences of photons traveling in opposite direction, which were produced by positron annihilation. Another experiment was conducted by Alväger et al. (1963), who compared the time of flight of gamma rays from moving and resting sources. Both experiments found no difference, in accordance with relativity. Filippas and Fox (1964) did not consider Sadeh (1963) and Alväger (1963) to have sufficiently controlled for the effects of extinction. So they conducted an experiment using a setup specifically designed to account for extinction. Data collected from various detector-target distances were consistent with there being no dependence of the speed of light on the velocity of the source, and were inconsistent with modeled behavior assuming c ± v both with and without extinction. Continuing their previous investigations, Alväger et al. (1964) observed π0-mesons which decay into photons at 99.9% light speed. The experiment showed that the photons didn't attain the velocity of their sources and still traveled at the speed of light, with . The investigation of the media which were crossed by the photons