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 (London 1759, Book 11, Plate 1). It illustrates Propositions 1 and 3 from Book 11. The left figure represents Proposition 1: ‘Theorem. One part of a right line cannot be in a plane superficies, and another part above it’, while the right corresponds to Proposition 3: ‘Theorem. If two planes cut each other, their common section will be a right line’.1 There are pencil sketches of both Propositions in Turner’s lecture text.2
Blank, save for an inscription by an unknown hand in pencil ‘9’ bottom left.
Supported by The Samuel H. Kress Foundation