# Quetelet, Lambert Adolphe Jacques

# QUETELET, LAMBERT ADOLPHE JACQUES

**QUETELET, LAMBERT ADOLPHE JACQUES** (1796–1874), Belgian astronomer and statistician.

Adolphe Quetelet, prominent in his own time and since for work on social science and statistics, was trained in mathematics and began his scientific career in astronomy. In 1823 he persuaded the government of the Netherlands, which from 1815 to 1830 included Belgium, to construct in Brussels an observatory, of which he should be the first director. To this end he was authorized to travel to Paris and spend a season at the observatory there learning the ropes. The observatory in Brussels had a rocky start, for just as construction was nearing completion the 1830 revolution broke out in Belgium, and for a time the observatory was occupied by soldiers. But it endured, and Quetelet's whole career was framed by sciences of the observatory.

These sciences included not just astronomy, but geodesy (measurements concerning the shape and curvature of the earth), meteorology, and the study of tides, terrestrial magnetism, and other quantifiable phenomena such as blooming times of plants. As a leader of the Brussels Academy of Science, Quetelet aspired to organize its members into a single collaboration devoted to the study of periodic phenomena. This was work that required extensive, detailed observation, and for which scientific cooperation was essential. Although he could not control the careers of all his associates, he helped to create an international network devoted to quantitative natural history. His vast correspondence documents this important mid-nineteenth-century scientific movement, in which he took a central role.

Statistics, too, was for Quetelet a science of the observatory. From the 1820s until the end of the nineteenth century, "statistics" meant an empirical social science, the science of human collectives and of mass observation. Although it attained at least marginal status in the scientific academies, it was more often a bureaucratic study than an academic one. The statistical movement of the 1830s and 1840s was linked to new government bureaus that conducted censuses, registered births and deaths, and kept tabs on crime, trade, and schooling. Quetelet had an important role in the bureaucratic organization of statistics in his home country. Still more significant was his leadership of the International Statistical Congresses, which met more or less every second year for almost three decades beginning with the Brussels meeting of 1853. His great ambition, which proved very difficult in practice, was to harmonize statistical categories so that numbers could be compared across national boundaries. On this basis, he hoped, statistics would reveal the causes of crime, poverty, and disease, and show how to combat them.

Among the statisticians, Quetelet was unusual for his commitment to abstract science and to mathematics. He had in fact learned the methods for analyzing and managing error during his visit to the Paris Observatory, and he was very free in offering advice to his fellow statisticians about the indispensable role of probability theory for calculating the precision of rates and averages. In practice this was not easy in his time, because representative or random samples of the sort assumed by basic probability theory were hard to come by. In practice, Quetelet devoted himself above all to interpreting and popularizing the "laws" of statistics, the uniformity in the annual numbers of births, deaths, crimes, and the like. These regularities, especially of crime, had been shocking when Quetelet first noticed them in 1829 in a volume of French judicial statistics. For more than half a century, European moralists worried that human behavior, including moral behavior, appeared to be controlled by statistical law, leaving no room for personal freedom. Quetelet aimed to be conciliatory, emphasizing that lawlike behavior at the level of society still left room for a degree of freedom at the level of individuals.

This principle, that one could anticipate mass regularities even when individual causes were quite unknown, became a model for statistical reasoning in a range of sciences. In the 1860s the physicists James Clerk Maxwell and Ludwig Boltzmann invoked it as support for a statistical theory of gases, and Francis Galton drew on it for his statistical studies of heredity. Quetelet added one more crucial element to this mix, the idea that variability in nature and society was often governed by the astronomer's "error curve," known now as the bell curve or normal distribution. He was famous for his confidence in mean values, personified by his celebrated "average man," and for him, the bell curve gave evidence that departures from the mean were essentially error. But for his scientific descendants, the analysis of variation became fundamental to the emerging mathematical field of statistics.

*See also***Crime; Science and Technology; Sociology; Statistics.**

## bibliography

### Primary Sources

Quetelet, L. A. J. *On Man and the Development of his Faculties; or, Essay on Social Physics.* London, 1842. Translation of *Sur l'homme et le développement de ses facultés.* Paris, 1835.

——. Letters… *on the Theory of Probabilities, as Applied to the Moral and Political Sciences.* London, 1849. Translation of *Lettres sur la théorie des probabilités, appliquée aux sciences morales et politiques.* Brussels, 1846.

### Secondary Sources

Desrosières, Alain. *The Politics of Large Numbers: A History of Statistical Reasoning.* Translated by Camille Naish. Cambridge, Mass., 1998.

Lottin, Joseph. *Quetelet: Statisticien et sociologue.* Louvain, 1912.

Porter, Theodore M. *The Rise of Statistical Thinking, 1820–1900.* Princeton, N.J., 1986.

Stigler, Stephen M. *The History of Statistics: The Measurement of Uncertainty before 1900.* Cambridge, Mass., 1986.

Theodore M. Porter

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