From Alexander of aphrodisias to Young and Airy

A didactic discussion of the physics of rainbows is presented? with some em phasis on the history? especially the contributions of Thomas Young nearly 200 years ago. We begin with the simple geometrical optics of Descartes and Newton, including the reasons for Alexander's dark band between the main a nd secondary bows. We then show how dispersion produces the familiar colorf ul spectacle. Interference between waves emerging at the same angle, but tr aveling different optical paths within the water drops, accounts for the ex istence of distinct supernumerary rainbows under the right conditions (smal l drops, uniform in size). Young's and Airy's contributions are given their due. (C) 1999 Elsevier Science B.V. All rights reserved.