mirror acts as a new source of light and the reflected light has the same velocity c with respect to the mirror as has original light with respect to its source. (Proposed by Richard Chase Tolman in 1910, although he was a supporter of special relativity). Light reflected from a mirror acquires a component of velocity equal to the velocity of the mirror image of the original source (Proposed by Oscar M. Stewart in 1911). A modification of the Ritz–Tolman theory was introduced by J. G. Fox (1965). He argued that the extinction theorem (i.e., the regeneration of light within the traversed medium) must be considered. In air, the extinction distance would be only 0.2 cm, that is, after traversing this distance the speed of light would be constant with respect to the medium, not to the initial light source. (Fox himself was, however, a supporter of special relativity.) Albert Einstein is supposed to have worked on his own emission theory before abandoning it in favor of his special theory of relativity. Many years later R.S. Shankland reports Einstein as saying that Ritz's theory had been "very bad" in places and that he himself had eventually discarded emission theory because he could think of no form of differential equations that described it, since it leads to the waves of light becoming "all mixed up". Refutations of emission theory The following scheme was introduced by de Sitter to test emission theories: where c is the speed of light, v that of the source, c' the resultant speed of light, and k a constant denoting the extent of source dependence which can attain values between 0 and 1. According to special relativity and the stationary aether, k=0, while emission theories allow values up to 1. Numerous terrestrial experiments have been performed, over very short distances, where no "light dragging" or extinction effects could come into play, and again the results confirm that light speed is independent of the speed of the source, conclusively ruling out emission theories. Astronomical sources In 1910 Daniel Frost Comstock and in 1913 Willem de Sitter wrote that for the case of a double-star system seen edge-on, light from the approaching star might be expected to travel faster than light from its receding companion, and overtake it. If the distance was great enough for an approaching star's "fast" signal to catch up with and overtake the "slow" light