Galton then confirmed earlier investigations which proved the permanence of fingerprints from youth to old age, and devised a dictionary of prints whereby an individual leaving a mark may surely be identified. The method is now in use in the criminal departments of every civilised country. An account of Galton's work is contained in his 'Finger Prints' (1893); 'Blurred Finger Prints' (1893); and 'Finger Print Directory' (1895).
It is due to Galton more than to any other man that many attributes generally regarded as only susceptible of qualitative estimate have been reduced to measurement. For example, he showed how to obtain a numerical measure of the degree of resemblance between two persons, and he made a map to show the geographical distribution of beauty in Great Britain. He devised the method of composite photographs in which each member of a group of persons makes an equal impress on the resulting portrait. Another attempt to annul the resemblance and to register only the individuality was not very successful. To psychology Galton also made contributions which were important and very original. He showed that different minds work in different ways, and, for example, that visual images play a large part with some but not with others. He investigated visual memory as to illumination, definition, colouring, and the like, and the visions seen not very infrequently by the sane. Akin to this was an inquiry into the patterns or pictures associated in many minds with numbers. He also experimented on taste, on smell, on the muscular sense of weight, on the judgment of experts in guessing the weight of cattle, and on many cognate points. His investigations give him a high rank amongst experimental psychologists, and yet they were merely collateral to the main stream of his work.
On the publication in 1859 of the 'Origin of Species' by his cousin, Charles Robert Darwin (1809-1882) [q. v.], Galton at once became a convert to the views there enounced and began reflecting on the influence of heredity on the human race. He had been impressed by his own observation with the fact that distinction of any kind is apt to him in families. He therefore made a series of statistical inquiries whereby he proved the heritability of genius of all kinds. These investigations extended over forty years, and the results are set forth in his works: 'Hereditary Genius' (1869); 'English Men of Science' (1874); 'Human Faculty' (1883) 'Natural Inheritance' (1889); and 'Noteworthy Families' (1906).
Such investigations necessarily brought him to face the fundamental principles of statistics, and although his mathematical equipment was inadequate he obtained a remarkably clear insight into the subject. In the hands of Karl Pearson and of others his work led to the formulation of new statistical methods. The leading point is that he showed how the degree of relationship between any pair of attributes or any pair of individuals may be estimated by a numerical factor termed the correlation. He also gave a numerical estimate of the average contribution to each individual from his two parents and his remoter ancestry.
Collateral to these researches were experiments on Darwin's theory of pangenesis by transfusion of the blood of rabbits inter se; the results were however negative.
The study of heredity led Galton to the conviction that the human race might gain an indefinite improvement by breeding from the best and restricting the offspring of the worst. To this study he gave the name of 'eugenics,' and it is probably by this that he will be best known in the future. But he was under no illusion as to the rapidity with which favourable results may be attained, and he foresaw that it would need a prolonged education before an adequate knowledge of the power of heredity shall permeate the community. With the object of promoting this education he co-operated in the formation of 'eugenic societies,' and established in 1904 a eugenics laboratory to be worked in connection with the biometric laboratory mentioned above. He further founded in 1904 a research fellowship and in 1907 a scholarship in eugenic researches at University College. A quarterly journal entitled 'Biometrika' had already been initiated in 1901, and he was 'consulting editor.'
Galton received many honours, including medals from the English and French Geographical Societies in 1853 and 1854; a royal medal of the Royal Society in 1876; Huxley medal of the Anthropological Institute in 1901; Darwin medal of the Royal Society in 1902; Darwin-Wallace medal of the Linnaean Society in 1908; and the Copley medal of the Royal Society in 1910. He was made Officier de l'Instruction publique de France in 1891; hon. D.C.L. Oxford in 1894; hon. D.Sc. Cambridge in 1895; hon. fellow of Trinity College, Cambridge, in 1902; and was knighted by patent on 26 June 1909.
