Arne Hansen, E. (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. Hentet fra https://tidsskrift.dk/historisktidsskrift/article/view/51462