  Though many experiments appear to have confirmed the light speed invariance
postulate of special relativity theory, this postulate is actually unverified.
This paper resolves this issue by first showing the manner in which an illusion
of light speed invariance occurs in two-way light speed measurement in the
framework of a semi-classical absolute space theory. It then demonstrates a
measurable variation of the one-way speed of light, which directly invalidates
the invariance postulate and confirms the existence of the preferred reference
frame of the absolute space theory.
