Ripple tank refraction

I put the usual Perspex wedge into the water. It makes the water shallower. That makes the waves travel slower. All the waves have the same frequency because they are made by the same motor. I have highlighted the crests of the waves in red. These are the wavefronts, which was Huygens way of analysing wave motion. I have also added blue arrows to show Newton's rays which show the movement of the waves. Look at how the wavefronts bend when they reach the shallower water. That's because the end in the shallower water slows down and is left behind. The rays are at 90 degrees to wavefronts so the ray changes direction as well. Finally, the waves slow so they get closer together. The wavelength decreases.