Thomas Robert Malthus (1798). “An Essay on the Principle of Population, as it Affects the Future Imporvement of Society, with Remarks on the Speculations of Mr. Godwin, M. Condorcet, and Other Writers”, p.346, The Lawbook Exchange, Ltd.
"Principles of political economy considered with a view to their practical application". Book by Thomas Malthus, Book II, Chapter I, "On The Progress of Wealth", Section X, p. 414, 1836.