Joseph Priestley, the discoverer of oxygen. Oil painting by Ernest Board, 1912.

Priestley (1733-1804), radical politician, chemist and Nonconformist minister, is portrayed playing backgammon in his house in Birmingham when he received the news that it was about to be attacked by an anti-radical mob. The attacks took place on 14-16 July 1791, and the library, furnishings and equipment represented in the present painting were all destroyed. Priestley himself fled to Hackney

On the back wall is an indistinct portrait of a man wearing a sash. Priestley, seated on the left, holds what looks like a jeweller's eyeglass. Behind him is a machine for experiments with gases (an airpump?). On the right a man enters the room with news of the rioters