Who discovered Napoleon's theorem?

Question

I read about Napoleon's Theorem in geometry. Was this the same Napoleon as the great warrior? Was he a mathematician too?

Answer 1

The name of the theorem (that centers of equilateral triangles erected externally on the sides of a triangle form another equilateral triangle) does refer to the famous French general and later emperor, which likely contributed to its popularity. However, its earliest attribution to him comes from an Italian textbook of elementary geometry by Faifofer published in 1911, almost a century after Napoleon's death. There is just a single phrase in parentheses without any named source:“theorem proposed for demonstration by Napoleon to Lagrange”. The earliest known occurence is as a challenge problem in Rutherford's Ladies Diary of 1825, four years after Napoleon's death. But the theorem was rediscovered multiple times by amateur geometers, so Rutherford may not have been the first either.

Coxeter and Greitzer claimed that "the possibility of [Napoleon] knowing enough geometry for this feat is as questionable as the possibility of his knowing enough English to compose the famous palindrome, ABLE WAS I ERE I SAW ELBA", but this is unwarranted. Napoleon was reported by biographers to have mathematical talent since boyhood, and closely interacted with prominent mathematicians and scientists of his day, including Fourier, Monge, Laplace and Lagrange. Monge and Fourier accompanied him on 1798 expedition to Egypt, along with 150 other scientists and engineers, with whom Napoleon held lengthy discussions on scientific matters. Laplace even briefly served as his Minister of Interior (for 6 weeks), but did not leave a good impression. Harris comments that “after the revolution, [Lagrange] fell into the favor of Napoleon Bonaparte, who enjoyed sharing geometrical puzzles with Lagrange and Laplace”, but without any specific reference to the Napoleon's theorem.

See Mathpages.