Michael Scot and the Four Rainbows

Tony Scott

doi:10.24117/2526-2270.2017.i2.18

Abstract

We apply a physical and historical analysis to a passage by the medieval scholar Michael Scot concerning multiple rainbows, a meteorological phenomenon whose existence has only been acknowledged in recent history. We survey various types of physical models to best decipher Scot’s description of four parallel rainbows as well as a linguistic analysis of Scot’s special etymology. The conclusions have implications on Scot’s whereabouts at the turn of the 13th century.

Highlights

The rainbow is an impressive and fascinating natural phenomenon that is observed when sunlight interacts with raindrops in the air and involves the splitting of white light into its constituent colors
The first, to the best of our knowledge, written record to that effect appears at the beginning of the thirteenth century and is due to Michael Scot, as quoted by Lynn Thorndike: It should be known that four bows, and maybe more, can be formed at once, at slight distance apart
Michael Scot’s record of multiple rainbows does not originate from the Muslim scholarship of his time, in which knowledge on rainbows was hardly more advanced than that of Aristotle, but rather from observations either in Scotland, where he lived at a young age, the or in the Sahara-Sahel and in particular the Aïr region, where the mountainous settings and weather conditions favor a more frequent realization of multiple rainbows

Summary

Introduction

The rainbow is an impressive and fascinating natural phenomenon that is observed when sunlight interacts with raindrops in the air and involves the splitting of white light into its constituent colors. The primary rainbow results from a single internal reflection of refracted light inside a raindrop. The angle of refraction depends on the frequency of radiation This effect is known as dispersion and causes sunlight to split into its constituent colors on entering the raindrop. When light travels from a medium with a higher refractive index, such as water or raindrop, to one with a lower refractive index, such as air, if the angle of incidence is large enough, Snell’s law requires that the sine of the angle of refraction be greater than one This is not possible, and the light in such cases is reflected by the boundary, a phenomenon known as total internal reflection.

Quaternary Rainbows

Discussion and Implications