The Sagnac effect: correct and incorrect explanations

Different explanations of the Sagnac effect are discussed. It is shown that this effect is a consequence of the composition of velocities law of relat ivity theory and that it can also be explained adequately within the framew ork of general relativity. When certain rotation velocity restrictions are imposed, the Sagnac effect can be attributed to the difference in the time retardation (phase shift) of material particle wave functions in the scalar (vector) gravity potential of the inertial forces in a rotating reference frame for counter-propagating waves. It is also shown that all the non-rela tivistic interpretations of the Sagnac effect, which unfortunately are some times found in scientific papers, monographs and textbooks, are wrong in pr inciple, even though the results they yield are accurate up to relativistic corrections in some special cases.