http://www.worldnpa.org/pdf/abstracts/abstracts_215.pdf Herbert Dingle: "Either there is an absolute standard of rest - call it the ether as with Maxwell, or the universe as with Mach, or absolute space as with Newton, or what you will - or else all motion, including that with the speed of light, is relative, as with Ritz."
This is the rational dilemma but there is an irrational alternative - one can create a monstrous centaur with a body (the principle of relativity) taken from the Newton/Ritz emission theory of light and a head (the principle of constancy of the speed of light) taken from the ether theory:
http://books.google.com/books?id=JokgnS1JtmMC "Relativity and Its Roots" By Banesh Hoffmann, p.92: "There are various remarks to be made about this second principle. For instance, if it is so obvious, how could it turn out to be part of a revolution - especially when the first principle is also a natural one? Moreover, if light consists of particles, as Einstein had suggested in his paper submitted just thirteen weeks before this one, the second principle seems absurd: A stone thrown from a speeding train can do far more damage than one thrown from a train at rest; the speed of the particle is not independent of the motion of the object emitting it. And if we take light to consist of particles and assume that these particles obey Newton's laws, they will conform to Newtonian relativity and thus automatically account for the null result of the Michelson-Morley experiment without recourse to contracting lengths, local time, or Lorentz transformations. Yet, as we have seen, Einstein resisted the temptation to account for the null result in terms of particles of light and simple, familiar Newtonian ideas, and introduced as his second postulate something that was more or less obvious when thought of in terms of waves in an ether. If it was so obvious, though, why did he need to state it as a principle? Because, having taken from the idea of light waves in the ether the one aspect that he needed, he declared early in his paper, to quote his own words, that "the introduction of a 'luminiferous ether' will prove to be superfluous."