Constancy of c - second postulate

[harrylin]

[..] The alternative is that Maxwells equations as written are not a law of nature, and that the real laws of electrodynamics were Galilean invariant. [...]

Exactly, as I also mentioned - that is what Newton's theory of light had, and probably also Ritz's theory was Galilean invariant. The issue was how to match Maxwell's theory with the PoR.

Cheers,
Harald

PS: Maxwell thought that the speed of light was Galilean invariant in the same way as sound (to good approximation): that is also a law of nature, but it is expressed as the velocity relative to the medium.