This may be a study for the right hand of one of the poets honoured by Brown in his proposed triptych 'The Seeds and Fruits of English Poetry.' It is difficult to tell if this is a hand study for the figure of Robert Burns (1759-1796) or William Shakespeare (1564-1616) as both have similar right hand positions in the surviving studies for the triptych (1845, black chalk on paper, Cecil Higgins Art Gallery, Bedford; 1845-1853, oil on canvas, Ashmolean Museum, Oxford). It could also be a hand study for the man standing on the right of the Fool in Brown's painting 'Lear and Cordelia' (1848-49, oil on canvas, Tate) which he was also working on in 1848.
LM