I think I heard somewhere that the speed of light changes when it passes through different medium, thus explaining the diffraction of water. Did I get that mixed up somehow? I also heard that the number we use for C is only referring to the speed of light in a vacuum, and that different mediums have different speeds of light. Or is it that the light slows down when transitioning between mediums? Or is all of the above irrelevant because the "refractive index" has nothing to do with the speed of light? I dunno. I do know that I probably got "refractive" and "diffractive" mixed up somewhere. It's been so many years since I've had physics, can anybody please enlighten me?

Thanx,
John W.