Who do objects that lie half in and half out of water appear distorted?

refraction -- light has a lower velocity in medium other than a vacuum, where light achieves the highest velocity (~3E8 m/s). In general, the denser the medium, the slower the speed. The actual relation is expressed as Snell's law, which relates the indices of refraction to the angles of entrance and exit relative to the normal. When light travels from one medium to a different medium, the path changes its direction right at the boundary (the angle of incidence is different from the angle of refraction), giving your eyes an illusion of the part of the object submerged in water being located a distance away from its actual location.