An investigation into a half page from Newton's Principia in the wake of Chandra

There is a section in Chandrashekar's ''Newton's Principia for the Common Reader '', (Clarendon Press, Oxford, 1995) in which he claims to find a small error in the Principia. . However we believe that there is a mistake of interpretation underlying Chandra's claim and that the Principia is correct as it stands. This short paper describes Chandra's misinterpretation of a geometric construction of Newton and gives an outline of Newton's demonstration by following the standard English version of the Principia line by line and converting it into modern mathematical notation in the spirit of Chandra's book.