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Turner notes above the diagram: ‘La Fenestre Albert Durer gives [‘gave’ inserted above] the demonstration of the present | Theorem ... ie will give here the moyen practical and after | the demonstration will be given’. The diagram is annotated at the centre, to the right and below respectively: ‘Plan | what the | cube would | appear’; ‘figure how | a [...] and | transferrd’; ‘Marking each | point as they cut the | Square -’.
Maurice Davies identifies this diagram as taken from Salomon de Caus, La Perspective avec la raison des ombres et miroirs, London 1612, tenth theorem, folio 6 recto. It presents a standard model of perspective from a single viewpoint, with the picture plane analogous to a static view through a window frame, with the plane ‘intersecting the cone of vision’.1 This model had been used in ancient and medieval times, and in the Renaissance by Leon Battista Alberti, preceding Dürer. In his perspective lectures, Turner persisted in using de Caus’s word ‘fenestre’ rather than simply translating it as ‘window’.2
Davies has further noted that Turner’s text and diagrams on folios 3 recto to 4 verso (D07359, the present page, D07361, D07362) are all taken from de Caus (see also folio 54 verso; D07450). The same passages are translated from the French in Turner’s perspective lecture manuscripts, though apparently not in his hand.3 There is another diagram derived from Dürer on folio 55 recto (D07451).
Davies 1992, pp.17, 37, 107 note 33; see also Davies 1994, pp.98, 287.
Davies 1994, p.43.
Ibid., pp.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.
This and the opposite page (folio 4 recto; D07361) are heavily stained in the centre with mottled ochre marks which appear within a roughly regular outline, suggesting that something may previously have been loosely placed at this point, perhaps as a bookmark. The staining includes distinct wavy lines, as if offset from a drawing or printed material.