Catharine Cox’s book on "The Early Mental Traits of Three Hundred Geniuses" (1926), was similar to Galton's in its orientation. Using the method that her mentor, Stanford Psychology Professor Lewis Terman, had developed for differentiating children in terms of intelligence, Cox coded records of childhood and adolescent achievements of 301 historic eminent leaders and creators to estimate what their IQs would have been on the basis of intellectual level of such achievements relative to the age at which they were accomplished. For example, John Stuart Mill reportedly studied Greek at 3, read Plato at 7, and learned calculus at 11. As such, what he was doing at 5, the average person couldn't do until 9 years, 6 months of age, giving Mill an estimated IQ of 190.