Robert Stewart, 2nd Marquess of Londonderry, better known to his contemporaries and to history as Viscount Castlereagh, committed suicide on 12 August 1822, at the age of fifty-three, when Foreign Secretary and Leader of the House of Commons. He was one of the great statesmen of his age: as Chief Secretary in Ireland, he had ensured the passage of the Act of Union, and resigned when the prospect of emancipation held out to Catholics in order to ease its passage was blocked by George III; as Secretary of State for War, he had stood against Napoleon as surely as the generals and  Admirals, some of whom he had put in their places; as Foreign Secretary, he worked to form the alliances that finally brought  about Napoleon's defeat and contributed largely to the peace of Europe thereafter; he was not a good public speaker, but tact and courtesy made him a successful Leader of the House of Commons. It is likely that he would have become Prime Minister...