Diagram, erroneous diagram for Brouncker's paper on the pendulum by Christopher Wren This appears to be an attempt at reproducing a diagram from William Brouncker’s paper (CLP/1/15) proving that the curve of isochronous descent is a cycloid (proved earlier by Huygens by other means), and that the centre of curvature of every point of the cycloid (evolute) is a cycloid. This diagram contained an error in including a line (with 'x' along it) from D that intersected with fm and DRS, which is not needed for the proof. Subject: Engineering / Geometry [1669]