The Sagnac Experiment was first conducted by French physicist Georges Sagnac in 1913. The experiment is essentially the same experiment as the Michelson-Morley Experiment, except that it is on a horizontal rotating turn-table. The results of the Sagnac Experiment show that when the table is rotated around on a horizontal axis during the experiment, the velocity of light indeed changes. This contradicts the Michelson-Morley Experiment that was designed to use the supposed movement of the earth to change position, and which showed no change in light velocity.
From a paper on the Sagnac Effect we read:
“ Since its discovery at the beginning of the XX century the Sagnac effect  has play an important role in the understanding and development of fundamental physics (for a review see ). The Sagnac effect is the dependence of the interference pattern of the rotating interferometer on the direction and speed of rotation. This phenomenon is universal and manifested for any kind of waves, including the matter waves and has found a variety of applications for the practical purposes and in the fundamental physics .
...In the context of the Sagnac effects the null result of the Michelson-Morley experiment is also not clear. Applying the same logic to Sun centered rotating frame in which Earth is fixed, one would expect different light speeds as seen from Earth. ”
A Critical Analysis
In Theory of Relativity: A Critical Analysis by Roberto A. Monti, the author states in the abstract:
“ Einstein's theory of relativity is shown to be a physical theory of limited experimental validity. Twelve different experiments seem to disprove its two postulates. ”
On the subject of the Sagnac Effect the author maintains:
“ The effect was tested in 1913 by Sagnac(46), and Sagnac’s experimental results disproved the second postulate of special relativity. ”
The geocentrist Malcom Bowden describes the Sagnac Experiment in the following video:
“ An animated explanation of how Sagnac's experiment proved the existence of the aether, thus demolishing Einstein's Theory of Relativity. Complaints by two experienced physicists that when they were at university, they were never informed about this important experiment. When other experiments - Airy's Failure, Michelson-Gale's experiment (also not taught at universities!) and of course the famous Michelson-Morley experiment- a completely different picture of the cosmos emerges - with the Earth at the centre of the universe. ”
The video author's personal views on geocentricity and creationism aside, Mr. Bowden provides an accurate description of the Sagnac Experiment and its results.