* 'Great art has dreadful manners...' Simon Schama observes at the start of his epic exploration of the power, and whole point, of art. 'The hushed reverence of the gallery can fool you into believing masterpieces are polite things, visions that soothe, charm and beguile, but actually they are thugs. Merciless and wily, the greatest paintings grab you in a headlock, rough up your composure and then proceed in short order to re-arrange your sense of reality...'