Thomas Clarkson, Ottobah Cugoano (2010). “Thomas Clarkson and Ottobah Cugoano: Essays on the Slavery and Commerce of the Human Species”, p.124, Broadview Press
Massachusetts. Board of Education, Horace Mann (1849). “The Massachusetts System of Common Schools: Being an Enlarged and Rev. Ed of the Tenth Annual Report of the First Secretary of the Massachusetts Board of Education”, p.113