Prepared in connection with his lectures as Professor of Perspective at the Royal Academy, Turner’s diagram is based on an illustration from Samuel Cunn’s Euclid’s Elements of Geometry (Book 12, Plate 2). The left figure illustrates Proposition 13: ‘Theorem. If a cylinder be divided by a plane parallel to the opposite planes; then, as one cylinder is to the other cylinder, so is the axis to the axis’.1 The right represents Proposition 14: ‘Theorem. Cones and cylinders, being upon equal bases, are to one another as their attitudes’.2 There are pencil sketches of the figures in Turner’s lecture notes.3
A pencil sketch illustrating Proposition 13 from Book 12 of Samuel Cunn’s Euclid’s Elements of Geometry (London 1759, Book 12, Plate 2); inscribed by an unknown hand in pencil ‘51’ bottom left.
Supported by The Samuel H. Kress Foundation