Einstein "borrowed" the constant-speed-of-light falsehood from the NONEXISTENT ether:
Albert Einstein: "...I introduced the principle of the constancy of the velocity of light, which I borrowed from H. A. Lorentz's theory of the stationary luminiferous ether..."
https://en.wikipedia.org/wiki/Lorentz_ether_theory
Below, Banesh Hoffmann and John Norton unwittingly say two things:
1. In 1887, prior to the ad hoc introduction of fudge factors ("without recourse to contracting lengths, local time, or Lorentz transformations"), the Michelson-Morley experiment unequivocally proved Newton's VARIABLE speed of light and disproved the constant (independent of the motion of the emitter) speed of light posited by the ether theory and later "borrowed" by Einstein.
2. Einsteinians ("later writers") are almost all liars.
Banesh Hoffmann, Relativity and Its Roots, p.92: "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."
https://www.amazon.com/Relativity-It.../dp/0486406768
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."
http://philsci-archive.pitt.edu/1743/2/Norton.pdf
Pentcho Valev