[16]The results were made public at the meeting of the Royal Society on the 6th Nov., 1919.—H. L. B.
[APPENDIX]
[Note 1] (p. 4). So long as the universal significance of the velocity of light remained unknown, two conjectures were possible in the question as to whether, under certain circumstances, the motion of the source of light would make itself observable in the velocity of propagation of light. It might be surmised that the velocity of the source simply added itself to that velocity of light which is characteristic for the propagation of the light from a source at rest. Or, it might be conceived that the motion of the source has no influence at all on the velocity of the light emitted by it. In the second case it was imagined that the source of light only excites the periodically changing states of the luminiferous ether, which is at rest, that is, which does not share in the motion of the matter (source of light), and that these states then propagate themselves with a velocity that is characteristic of the ether, and with a velocity that makes these states perceptible to us as light waves. This view had finally apparently won the day. It was the advent of the special theory of relativity and the quantum hypothesis that made this view impossible. For the special theory of relativity, in robbing the assertion: "the ether is at rest" of its significance, since we may arbitrarily define any system as being at rest in the ether, as far as uniform translations are concerned, and in depriving the luminiferous ether of its existence, deprived light-waves of their carrying or transmitting medium. The quantum hypothesis, in raising light-quanta to the rank of self-supporting individuals, deprived the velocity of light of its character as a constant that is characteristic of the ether. Thus, our view of light-quanta again leads to a kind of emission theory of light. According to classical mechanics it would have been typical of a theory of emission for the velocity of the source in motion to have added itself to the velocity of the light from the source at rest. We thus revert to the conjecture which we quoted first above. Now, such a superposition of velocities would necessarily cause quite remarkable phenomena in the case of spectroscopic binary stars (de Sitter, "Phys. Zeitschrift," 14, 429). For if two stars move in circular Kepler orbits around each other, and if our line of sight lies in the common plane of the orbits, then we should necessarily perceive the following: if
is the time of revolution of the system,
the orbital velocity of the one (bright) component,
the distance of the whole system from the earth, and, finally,
