This page is still under construction. I am very gratefull for comments. This effect was proven experimentally by Fizeau in 1851.
Light rays pass throught two tubes with water flowing in opposite directions.
The interference pattern observed behind the set up confirms the dependence of the velocity of light in a medium on the velocity of the medium as predicted by Fresnel in 1808. The changing light velocity does not contradict the laws of Special Relativity, because the statement that the velocity of light is constant is valid only for the vacuum velocity of light. In extreme cases the dragging of light by the medium can lead to extreme effects, e.g. when the velocity of the medium becomes higher as the velocity of the light in the medium effectively all light is moving in the same direction as the medium. This effect leads to the notion of an optical black hole, a vortex created in a transparent fluid with the velocity of the medium exceeding the velocity of light in the vicinity of the vortex core. In this situation light rays coming too close to the vortex are attracted and fall into it.