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The drawing is part of a sequence of notes and diagrams which begins on folio 79 verso (D07487) and continues back through the sketchbook to folio 72 verso (D07473). The text continues from the verso (D07485) to folio 77 verso opposite (D07483), and the diagram relates to passages on both pages. It appears to be an unfinished version of the similar diagram on folio 79 recto (D07486); there is also a related diagram of a river bank on folio 76 recto (D07480). The semi-diagrammatic drawing on folio 81 verso (D07491) also appears to belong with these notes, concerned with sunlight or light in general in terms of reflections and the casting of light and shadow from polished objects or bodies of water. They relate to Turner’s fifth Royal Academy perspective lecture, on reflection and refraction.
Davies 1994, p.289.