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Most of the page is taken up with a rough diagram of cubes in perspective. Maurice Davies has identified the source as notes on the history of perspective in Joshua Kirby’s Dr Brook Taylor’s Method of Perspective Made Easy Both in Theory and Practice: see the 1754 Ipswich edition, Book II, pp.81–4,1 and the 1768 London edition, Book II, pp.88–92.2 There are other notes from the same source on folios 11 verso, 12 recto, 14 recto and 14 verso (D07975, D07976, D07980, D07981).
This diagram shows a perspective method by Jacopo Barozzi da Vignola (1507–1573), taken from Kirby. In the 1768 edition it is shown in Book II, Pl.XIX, fig.1.3 There is a note on Vignola on folio 12 recto (D07976). As Andrea Fredericksen notes in her catalogue entry, diagram 33 (Tate D17047; Turner Bequest CXCV 77) for Turner’s third Royal Academy perspective lecture is a version of the same plate, derived from Vignola’s Le due regole della prospettiva pratica (1583).
For the dating of these and other notes made prior to Turner’s 1811 Royal Academy perspective lectures see the Introduction to the sketchbook.