Fresnel Dragging Explained
Here is how Fresnel Dragging works on the microscopic level. This model is based on the Fizeau experiment. The light travels at c through the vacuum between water molecules, but is carried with a the water molecules at their speed v for a short time each time it encounters a water molecule. See the following paper for the theory, maths and explanation for how Fresnel Dragging works.
Note: There are two Red photon shown down each path - so you can track the progress of the photon through the water more easily.
This version of the demonstration illustrates the water molecules' charge oscillation whilst excited by the incident photons, prior to the re-emission of the light during its propagation through the water.
And for an experimental setup that is moving from left to right at 40% of the speed of light, the whole frame is length contracted and the light moves between water molecules from left to right through the frame at speed (c - v) and from right to left at speed (c+v).