1. Whewell, W. (1853), Of the Plurality of Worlds: An Essay, London
2. Crowe, M.J. (1986) The Extraterrestrial Life Debate, 1750–1900: The Idea of a Plurality of Worlds from Kant to Lowell, Cambridge University Press (Cambridge, UK); and Guthke, K.S. (1990) The Last Frontier: Imagining Other Worlds from the Copernican Revolution to Modern Science Fiction, Cornell University Press (Ithaca, NY, USA)
3. Lovejoy, A.O. (1936) The Great Chain of Being: A Study of the History of an Idea, Harvard University Press (Cambridge, MA, USA); and Dick, S.J. (1982)
4. Hoyt, W.G. (1976) Lowell and Mars, University of Arizona Press (Tucson, AZ, USA); Strauss, D. (2001) Percival Lowell: the Culture and Science of a Boston Brahmin, Harvard University Press; Crowe, M.J. (1986); and Dick, S.J. (1996) The Biological Universe: The Twentieth Century Extraterrestrial Life Debate and the Limits of Science, Cambridge University Press
5. Strick, J.E. (2004) Creating a cosmic discipline: the crystallization and consolidation of exobiology 1957–1973. Journal of the History of Biology 37, pp. 131–180; and Dick, S.J. (1996), pp. 473–501