Lambert Adolphe Jacques Quetelet was one of the individuals most responsible in the ninteenth century for the quantification of in the physical and social sciences. He was born in Ghent on February 22, 1796, and was educated at the Lycee of Ghent. At age 19 he was appointed an instructor in mathematics at the Royal College in Ghent. In 1819 he was the first person to receive a doctorate from the University of Ghent for a dissertation on conic, and in the same year he moved to Brussels to take the chair of mathematics at the Athenaeum. Quetelet was elected to the Belgian Royal Academy in 1820. He married a Mlle. Curtet and they had two children.
In the early stages of his career, however, there was nothing to suggest that Quetelet's fame would spread throughout Europe. In 1824, he spent three months in Paris and learned two things: probability and how to run an observatory. As soon as he returned to Belgium, he began to campaign for the construction of a Royal Observatory. Successful in his efforts, Quetelet was appointed director of the Observatory in 1828. At the observatory, he could pursue celestial mechanics in the same manner as Pierre Simon Laplace, whose work he greatly admired.
In 1835, Quetelet published Sur l'homme et le developement de ses facultés ("On Man and the Development of his Faculties"). He explores two topics: the importance of gathering quantitative data in order to answer questions about human problems and the usefulness of the idea of "l'homme moyen" (the average man). Quetelet reveals a general understanding that the reliability of an average increases with the size of the population. What appears to have given the book some of its brilliance was Quetelet's vision of the average as something at which nature is aiming. Deviations from the average were seen as errors, although the notion of deviation as an object of study was familiar to Quetelet. This point also rendered Quetelet's perspective an easy subject for attack by the next generation of statisticians, who recognized the importance of variability in connection with the theory of evolution and other areas. The English statistician Francis Galton often criticized Quetelet's focus on the average rather than the deviations.
To some extent, Quetelet's portrayal of social phenomena as expressed in his book reflected the sources of his approach. On the one hand, he had a law of large numbers that had come down to him from more mathematically-minded statisticians, which indicated that when an experiment was repeated, the outcome is more reliable. On the other hand, he also had a Laplacean view of some deterministic mechanics underlying the phenomena. As a result, in every area Quetelet found the accumulation of data essential for the purpose of recognizing the normal distribution underneath. The law of large became the central principle of all science for Quetelet, and at the very least that encouraged him to promote data-gathering in every field.
In 1846, Quetelet published a volume of letters on the theory of probability. He was active in the reform of scientific teaching in Belgium and had become permanent secretary of the Brussels Academy in 1834. He was instrumental in the founding of the Statistical Society of London and was the first foreign member of the American Statistical Association. At a time when statistics began to play a role in settings outside the calculation of annuities and games of chance, Quetelet spoke for the statistical community. In addition to his scientific work, he wrote an opera and published poetry and popular essays.
Quetelet died on February 17, 1874, in Belgium. His funeral was distinguished by the presence of many scientists from abroad and his memory was honored by the erection of a monument in Brussels. For someone who seldom used mathematics, Quetelet had acquired quite a reputation as a mathematician. The "average man" as Quetelet envisioned may have been a figment of the imagination, but the recognition of the importance of data-gathering was a timely lesson for a scientific culture about to undergo a probabilistic revolution.
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