I've seen the diagrams they write up talking about refraction for ages .. where a light ray goes into a different medium of higher index of refraction at an angle, and then the light ray is bent. And that is used to illustrate Snel's law. I guess I haven't paid close enough attention! I'm reading this again, in Mark P Silverman's book "Waves and Grains", and paying attention, but I got some questions .. if I'm interpreting things right. Mark shows Snel's law is actually a series of laws: sin phi/sin theta = n1/n2 = v1/v2 = y1/y2 = p1/p2 phi = angle of incident to normal theta = angle of refraction to normal (1) = incident side (linear propogation) (2) = refracted side (linear propogation) n = index of refraction v = velocity of the light y = wavelength p = momentum I got 2 questions. Assume you have a pool of water, and shining light through the pool, the light entering the water at the top at an angle and going out the bottom of the pool. Q1) Since water bends the light towards the normal, it has a higher index of refraction, so the light slows down in the water. If you take the time a ray was in the water, and divide that by the depth of the water (not the distance the light moved through the water), wouldn't you come up with the speed of light in a vacumn? I mean, if you just consider the depth the light moved in the water, not its distance, it wouldn't have seemed to slow down any. Is that right? Q2) Now suppose the light goes straight down into the water. I was going to say a lot here .. but let me just ask: What would that do to Snel's ratio? Wouldn't it be sin(0)/sin(0) (maybe sin(90)/sin(90))? Wouldn't that also mean that the velocity of the light would not change while the light was in the water in this instance? I'm real confused here ..