In 1921 Einstein informed the gullible world that the introduction of his 1905 (false) constant-speed-of-light postulate, which had allowed him to disfigure space and time, was "conditioned by observed facts":
http://fr.scribd.com/doc/225419961/Albert-Einstein-On-the-Theory-of-Relativity
Albert Einstein (1921): "Turning to the theory of relativity itself, I am anxious to draw attention to the fact that this theory is not speculative in origin; it owes its invention entirely to the desire to make physical theory fit observed fact as well as possible. We have here no revolutionary act but the natural continuation of a line that can be traced through centuries. The abandonment of certain notions connected with space, time, and motion hitherto treated as fundamentals must not be regarded as arbitrary, but only as conditioned by observed facts. The law of the constant velocity of light in empty space, which has been confirmed by the development of electro-dynamics and optics..."
Was the introduction of Einstein's 1905 constant-speed-of-light postulate "conditioned by observed facts"? Of course not:
http://www.amazon.com/Introduction-Special-Relativity-James-Smith/dp/048668895X
Introduction to Special Relativity, James H. Smith, p. 42: "We must emphasize that at the time Einstein proposed it [his second postulate], there was no direct experimental evidence whatever for the speed of light being independent of the speed of its source. He postulated it out of logical necessity."
http://philsci-archive.pitt.edu/1743/2/Norton.pdf
John Norton: "In addition to his work as editor of the Einstein papers in finding source material, Stachel assembled the many small clues that reveal Einstein's serious consideration of an emission theory of light; and he gave us the crucial insight that Einstein regarded the Michelson-Morley experiment as evidence for the principle of relativity, whereas later writers almost universally use it as support for the light postulate of special relativity. Even today, this point needs emphasis. The Michelson-Morley experiment is fully compatible with an emission theory of light that contradicts the light postulate."
Was the introduction of Einstein's 1905 false constant-speed-of-light postulate a "logical necessity"? Yes. Einstein took the postulate from the ether field theory and used it as a premise in order to deduce miraculous properties of space and time and become famous:
http://books.google.com/books?id=JokgnS1JtmMC
Relativity and Its Roots, 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."
In 1954 Einstein realized what he had done but it was too late:
http://www.perimeterinstitute.ca/pdf/files/975547d7-2d00-433a-b7e3-4a09145525ca.pdf
Albert Einstein (1954): "I consider it entirely possible that physics cannot be based upon the field concept, that is on continuous structures. Then nothing will remain of my whole castle in the air, including the theory of gravitation, but also nothing of the rest of contemporary physics."
Pentcho Valev