O'Connor, J. J.; Robertson, E. F. (2003), "Roger Bacon"Arhivat în , la Wayback Machine., MacTutor. School of Mathematics and Statistics University of St Andrews, Scotland.
O'Connor, J. J.; Robertson, E. F. (2003), "Roger Bacon"Arhivat în , la Wayback Machine., MacTutor. School of Mathematics and Statistics University of St Andrews, Scotland.