Maurice Davies has registered the majority of Turner’s extensive inscriptions and diagrams running backwards from folio 91 verso (D07511) to folio 72 verso (D07473) as ‘on light and shadow’, acknowledging John Gage’s previous discussion of them; Gage only considers the pages towards the end of the sketchbook, from folio 91 verso to folio 82 verso (D07493),1 which are concerned with sunlight as parallel or divergent rays.
The present page and those running back to folio 72a are also 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.The actual text of this section of notes begins on folio 79 verso (D07487).
Passages on folio 78 verso (D07485) about ‘a boat passing | between the suns ray and a wall’ and folio 77 verso (D07483) appear to relate to the present drawing, which may have had its origin in direct observation, perhaps on the Thames west of London along the reaches so familiar to the artist. In discussing Turner’s various sketches of sailing boats, Anthony Bailey describes the configuration of the sails here as a forward, ‘lateen-rigged’ mainsail and a smaller ‘sprit-rig[ged]’ mizzen sail.2 There is a similar semi-diagramatic drawing (this time of a wall and trees), apparently from nature but put to a theoretical use, on folio 7 recto (D07366).