hey, I was just wondering if someone could give me an explanation about the following: 1. why, physically, does light travel at different speeds in different medium 2. why is the speed at which it travels through different media dependent of frequency, as is the case with dispersion. please don't explain snell's law. I know the equations. But the index of refraction is just a piece of algebraic information all bundled up in a package that you substitute in. I'm also aware of Hugens's Principle which explains how refraction works due to the changed velocity due to the medium in question. What I'm after is a more fundamental explanation, eg, relating to the inherent properties of glass vs water etc, Thanks a lot!