This diagram is based on an illustration from Samuel Cunn’s Euclid’s Elements of Geometry (London 1759, Plane Trigonometry). There are sketches of the diagram in Turner’s lecture notes.1
Turner, ‘Royal Academy Lectures’, circa 1807–38, Department of Western Manuscripts, British Library, London, ADD MS 46151 X folio 18.
Blank, save for an inscription by an unknown hand in pencil ‘20’ bottom left.
Supported by The Samuel H. Kress Foundation