Bride's_Chair
Bride's Chair
Illustration of the Pythagorean theorem
In geometry, a Bride's Chair is an illustration of the Pythagorean theorem.[1] The figure appears in Proposition 47 of Book I of Euclid's Elements.[2] It is also known by several other names, such as the Franciscan's cowl, peacock's tail, windmill, Pythagorean pants, Figure of the Bride, theorem of the married women, and chase of the little married women.[1][3]
According to Swiss-American historian of mathematics Florian Cajori, the ultimate etymology of the term "Bride's Chair" lies in a Greek homonym: "Some Arabic writers [...] call the Pythagorean theorem 'figure of the bride'." The Greek word νυμφη has two relevant definitions: 'bride', and 'winged insect'. The figure of a right triangle with the three squares has reminded various writers of an insect, so the 'insect' sense of the Greek word came to be applied to right triangles with three squares, and to the Pythagorean theorem. Arabic speakers writing in Greek would often mistakenly assume the other sense of the word was intended, and would translate the phrase back into Arabic using the word for 'bride'.[4]
A nice illustration of the Bride's Chair showing a chair upon which, according to ancient tradition, a bride might have been carried to the marriage ceremony can be seen in Sidney J. Kolpas' The Pythagorean Theorem: Eight Classic Proofs (page 3).[5]