  This paper presents the outcome of an experiment based on an improved version
of Fizeau's coupled-slotted-discs that tests the fundamental postulates of
Special Relativity for the one-way speed of light propagation. According to our
methodology, important phenomena - a limit on and the diurnal regularity of the
variation of the speed of light due to the movements of the Earth (assuming
that the speed of light follows a Galilean transformation) - can be tested by
the present experiment. However, these measurements do not indicate any
significant diurnal variation. Consequently, the limit of the present outcome
on the variation of the speed of light is insignificant. Assuming that the
speed of light is not invariant and performing a rigorous statistical analysis,
the limit established is approximately 1/50 of the previous Fizeau-type
experiment with 95% confidence level. These outcomes are consistent with the
assumptions of Einstein's Special Relativity.
