Abstract: This chapter discusses limiting correspondence relations between the wave theory of light and the ray theory of light. The limit is singular and there is no reductive relation between the theories. The focus is on the particular problem of understanding certain universal features of rainbows. The fruitfulness of studying this singular limit is demonstrated. The main conclusion of this chapter is that the fundamental theory (the wave theory) turns out to be explanatorily deficient and a new (asymptotic) explanatory theory characterizes the asymptotic borderland between the two theories.

Keywords: catastrophe theory, caustics, diffraction, rainbow, ray theory, singular limits, wave theory,