The whole page is taken up with the diagram, with notes above and below it:
but when it is considered that the Sun disk | [blank] miles in broad efulgence [‘miles distant’ inserted above] is opposed to a | column only 20 feet from the ground it cannot | be possible for the sun is below the Horizon | or more accuratly [?shining] <is upon the> [‘all these line are Horizontal line’ inserted above] | to shine and ceases to shine to us before he | appears upon those [?times].
Here there is a large gap with a tiny diagrammatic outline of St Paul’s Cathedral towards the left of the horizon line, and slight vertical and curving lines on the right-hand side, captioned:
supposing St Pauls for instance placed in | the same degree of distance opposed to the | Parrl [sic] ray, how can they in any way [?strike]
The whole passage follows on from the verso of this leaf (D07509), and continues on the opposite page, folio 89 verso (D07507). It is part of a sequence beginning on folio 91 verso (D07511), and running back to folio 82 verso (D07493). John Gage has discussed these provisional notes (not developed in the perspective lectures) as an example of Turner’s close observation of natural phenomena,1 in this case the question of sunlight travelling in parallel lines or otherwise, responding to a chapter of The Art of Painting by Gérard de Lairesse (1640–1711), in the English translation by John Frederick Frisch (London 1738 and later editions).2 See under D07511 for a discussion of Lairesse’s text. Maurice Davies has registered Turner’s notes as ‘on light and shadow’, as part of a longer sequence running back to folio 72 verso (D07473).3