Allow me to write once more about Fizeau experiment (on the light speed in moving medium : 1851) please.
Common explanation on this experiment may be wrong (Einstein's explanation also). A column made of glass is set horizontally. Two lights (emitted from two light sources) are passing through this glass (from left to right). One light source is at a stand-still (distance between the glass is fixed). Another light source is approaching toward the glass at an uniform speed. The frequency of two incident lights is just the same (thus arranged). Under this situation, the frequency of two lights that go out the glass is the same obviously (if not so, the number of waves that exist in the glass may increase or decrease endlessly). Therefore light speed of two lights in the glass is the same ("Drag" isn't partial).