Martin Dugard (2011). “To Be a Runner: How Racing Up Mountains, Running with the Bulls, or Just Taking On a 5-K Makes You a Better Person (and the World a Better Place)”, p.7, Rodale
James Boswell, Samuel Johnson (1799). “Life of Johnson: Including Boswell's Journal of a Tour to the Hebrides and Johnson's Diary of a Journey Into North Wales”, p.526