Under special atmospheric conditions, we can sometimes see much farther than the curvature of the earth would normally allow us. Atmospheric refraction usually makes distant objects appear elevated. This is why we can sometimes see, for instance, a boat that would otherwise be hidden by the curving bulge of water between it and the observer. My question is: Why does atmospheric refraction only affect the boat in this case? Why does the boat appear to be elevated but not the bulge of water behind which it is located?