Maurice Davies has listed the studies here, on folios 20 verso opposite and the verso (D07990, D07992) as ‘Perspective or reflective constructions’1 in relation to the preparations for Turner’s perspective lectures, delivered at the Royal Academy from January 1811 onwards (see the Introduction to the sketchbook). The three diagrams grow progressively more complex.
The stamped Turner number partly obscures a small disk drawn in pencil towards the bottom right, perhaps representing the sun or another light source. Alternatively it may be a letter ‘O’, relating to what is probably a capital ‘H’ at the centre right, indicating the horizon line.
Davies 1994, p.290.