With a view of Somer Hill near Tonbridge on folio 19 (D05375), this is evidence of Turner’s likely use of this sketchbook in 1810. That summer he probably visited Somer Hill on his way to Sussex to visit his patron John Fuller at Rosehill Park. This sketch of Tonbridge Castle is taken from across the moat, beneath the wooded mound with the ruins of the castle keep, connected by a rampart to the thirteenth-century gatehouse known as Gilbert de Clare. See Introduction to this sketchbook for the suggestion that Turner took the sketchbook with him to Kent and Sussex in 1810 to collect more material for his harvest pictures, Harvest Home and Cassiobury Park; Reaping (Tate N00562, N04663).1
Martin Butlin and Evelyn Joll, The Paintings of J.M.W. Turner, revised ed., New Haven and London 1984, p.128 nos. 209, 209a (pls.208, 209).