Newton's \textit{Principia} and inverse-square orbits: The flaw reexamined (Q1183319)

About 100 years ago, F. Rosenberger has shown the invalidity of Newton's proof of the theorem that an inverse-square force implies a conic-section orbit (Principia, Book One, Prop. XI-XIII). This paper is a contribution to the discussion that has followed Rosenberger's statement. The author refutes a Principia-defending claim presented by Aiton in 1988 and discusses a valid line of argumentation in favor of the theorem under consideration. Such an argument can be constructed from ingredients offered by Newton, but does not accurately reflect the argument that is outlined in the Principia.