Arne Hansen, Erik. 1973. “James Penick, Jr. : Progressive Politics and Conservation. The Ballinger-Pinchot Affair. Chicago and London, The University of Chicago Press, 1968. Xvi, 207 S. 79 Sh”. Historisk Tidsskrift 12 (januar). https://tidsskrift.dk/historisktidsskrift/article/view/51462.