Abstract

The most recent attempt at factually establishing a "true" value for the one-way velocity of light is shown to be faulty. The proposal consists of two round-trip photons travelling first in vacuo and then through a medium of refractive index n before returning to their common point of origin. It is shown that this proposal, as well as a similar one considered by Salmon (1977), presupposes that the one-way velocities of light are equal to the round-trip value. Furthermore, experiments of this type, involving regions of space with varying refractive indices, cannot "single out" any factual value for the Reichenbach-Grünbaum ε factor thus posing no threat to the conventionalist thesis