Lambert Adolphe Jacques Quetelet (1796-1874), Belgian astronomer and sociologist. Quetelet was born at Ghent and studied at the school and university there. On achieving his doctorate in mathematics Quetelet persuaded the government to build the Brussels Observatory, which eventually opened in 1828. He applied the statistical tools he learned in astronomy to social sciences. In 1835 he demonstrated that the 'average man' was the central value (the mean) of measured variables (such as height or weight) that followed a normal distribution (a range of values that produce a bell-shaped curve on a graph). Quetelet also proposed a simple measure for classifying people's weight against the ideal weight for their height, which is known today as the body mass index (BMI), and made studies correlating various social and other factors with crime.