The whole page is taken up with the following notes:
[...] a reflected light Ends as it must be | and perhaps more philosophically theoreticly | than would be practicable; it must be | the object rather to give instances even | of contradiction, when nature gives those | appearances that assert those contrary | [?conditions] most fully, suppose the | sun upon the [...] a boat passing | between the suns ray and a wall [...] | m[...] and [?perpendicular] surface – | the shadow of course according to the | former Lecture but the reflection <...> | prouduced by the reflected light of the | sun disk will be visible supposing that | that object would be reflected at that height has | a body of his own from being the prototype of | the Sun; and that it would throw the | shadow upon the same principle of the
The passage is part of a sequence of notes and diagrams which continues back through the sketchbook to folio 72 verso (D07473). The text continues from the opening passage, on folio 79 verso (D07487), and on to folio 77 verso (D07483), with diagrams in between on folio 79 recto opposite (D07486) and on the recto on the present leaf (D07484), which are both relevant to the text here. The semi-diagrammatic drawing of a boat 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.