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The diagrams are labelled to the left of centre as ‘Du Cas | 1612’, and the squares and cube have various initial capital letters (‘A’, ‘B’, ‘C’, ‘D’, etc.) at their corners, with other letters (‘T’ and ‘X’) along a horizon line towards the top and at various vanishing points and intersections (‘L’, ‘M’, ‘N’, and ‘O’).
Maurice Davies has identified the notes and diagrams on folios 3 recto to 4 verso (D07359–D07361 and the present page) as taken from Salomon de Caus, La Perspective avec la raison des ombres et miroirs, London 1612 (see also folio 54 verso; D07450), in this case from unpaginated folio 42 verso. The same passages are translated from the French in Turner’s perspective lecture manuscripts, though apparently not in his hand.1
Davies 1994, pp.98, 287, 298 note 23; Davies notes the translations as in Turner, ‘Royal Academy Lectures’, circa 1807–38, Department of Western Manuscripts, British Library, London, ADD MS 46151 BB folios 62 recto, verso.