Discuss the results of Problem 4.38 in the light of Fermat's Principle; that is, how does the relative index 21 affect things? To see the lateral displacement, look at a broad source through a thick piece of glass ( ~~14 inch) or a stack (four will do) of microscope slides held at an angle. There will be an obvious shift between the region of the source seen directly and the region viewed through the glass.
