Like the other rapid sketches in this book, this relates to the arrival of Louis-Philippe, King of the French, at Portsmouth Harbour on 8 October 1844, as discussed in the Introductions to the sketchbook and the overall section.
With the page turned vertically, Turner has noted the mast of the semaphore station then above the Square Tower on the east side of the entrance to the harbour. Compare a drawing perhaps made in the summer of 1824 in the London Bridge and Portsmouth sketchbook (Tate D17913; Turner Bequest CCVI 1), among others on that page. See also folios 5 recto, 13 recto, 14 verso, 15 recto and 16 recto, 22 verso and possibly 27 verso of the present book (D35692, D35708, D35709, D35711, D35713, D35726, D35735).
The slight sketch made at right-angles presumably shows the waterfront in the vicinity, as do sketches on folio 3 recto opposite (D35689), of which this may be a continuation.