"The assumption that the varies as the curvature is the basis of the 'Euler-Bernoulli' theory of flexure. This was developed in memoirs by James Bernoulli (1705) D. Bernoulli (1742), L. Euler (1744)."
January 1, 1970
https://en.wikiquote.org/wiki/Euler%E2%80%93Bernoulli_beam_theory