1. Charles White,An Account of The Regular Gradations in Man, Simpkin, Marshall and Co., London, 1799.
2. Thomas Jefferson, Quoted in Gossett, Thomas F.Race: The History of An Idea in America, Schocken Books, New York, 1971, p. 42.
3. Samuel Morton,Crania America, Simpkin, Marshall and Co., London, 1839.
4. George Combe,Elements of Phrenology, Simpkin, Marshall and Co., London, 1824.
5. Hereditary genius: An inquiry into its laws and consequences.