Henry David Thoreau, Jeffrey S. Cramer (2007). “I to Myself: An Annotated Selection from the Journal of Henry D. Thoreau”, p.298, Yale University Press
Joseph Lancaster (1803). “Improvements in Education, as it Respects the Industrious Classes of the Community: Containing, a Short Account of Its Present State, Hints Towards Its Improvement, and a Detail of Some Practical Experiments Conducive to that End”, p.50