The Forgotten Night: The Number Devil Explores Spherical Geometry

This is a missing chapter from Hans Magnus Enzensberger’s mathematical adventure The Number Devil (Henry Holt and Company, New York, 1997). In the book, a math-hating boy named Robert is visited in his dreams by the clever Number Devil, who teaches him to love all things numerical. However, we all forget our dreams from time to time. Here is one adventure that Enzensberger overlooked, where the Number Devil introduces Robert to geometry not-of-Euclid, great circles, parallel transport, the pendulum of Foucault, and the genius of Euler.