This is the third of three diagrams made by Turner, as Professor of Perspective at the Royal Academy, for Lecture 2 to illustrate the geometry of the parabola (see also D17035 and D17036; Turner Bequest CXCV 65, 66). Diagram 23 is headed ‘Emmerson’ and presumably refers to William Emerson, author of The Elements of Optics in Four Books (1768). According to Maurice Davies, there is no evidence that Turner consulted Emerson directly.1 The diagram is based instead on one found in John Hamilton’s Stereography; or a Complete Body of Perspective in all its Branches (1738, fig.84, no.1). Davies states that all three diagrams have ‘little relevance to the discussion and Turner may have chosen to include them merely because [Thomas] Malton2 mentions works on conic sections by both authors at this point’. Sketches can be found Turner’s lecture notes and in his Perspective Sketchbook (Tate D07384–D07386; Turner Bequest CVIII folios17 verso–18 verso).3
Davies 1994, p.165.
Thomas Malton [Senior], A Compleat Treatise on Perspective ... (1775).
Turner, ‘Royal Academy Lectures’, circa 1807–38, Department of Western Manuscripts, British Library, London, ADD MS 46151 L folio 10. For discussion of ‘Emerson’s Conic Section’, see D folio 5 verso and E folio 11 verso and L folio 10.
Peter Bower states that the sheet is Super Royal size Whatman paper made by William Balston and Finch and Thomas Robert Hollingworth, at Turkey Mill, Maidstone, Kent. He writes that all ‘the sheets in this batch have some streaking across the sheet, probably from a fault in the sizing’.1
Notes in Tate catalogue files.
Blank, save for an inscription by an unknown hand in pencil ‘69’ top left.
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