Charles Lyell (1863). “The Geological Evidences of the Antiquity of Man with Remarks on Theories of the Origin of Species by Variation by Charles Lyell”, p.421
Marcus Tullius Cicero (1855). “Cicero's Three books of offices, or moral duties: also his Cato Major, an essay on old age; Lælius, an essay on friendship; Paradoxes; Scipio's dream; and Letter to Quintus on the duties of a magistrate”, p.52
Florence Nightingale, Lynn McDonald (2004). “Florence Nightingale on Public Health Care: Collected Works of Florence Nightingale”, p.103, Wilfrid Laurier Univ. Press