“Principles of Mechanics that are Susceptible of Application to Society”: An unpublished notebook of Adolphe Quetelet at the root of his social physics

Founder of the Brussels Observatory, Adolphe Quetelet (1796–1874) is especially well known for his theory of the average man. Like the average position of a star obtained through a large quantity of observed data, the average man was, according to Quetelet, subject to fixed causal laws. Published in 1835, his book On Man: Essay of Social Physics is one of the founding works of sociology and mathematical statistics. The sources of the analogy between astronomy and social physics have been debated by historians. To shed light on this question and the conditions of application of mathematics in the 19th century, we publish for the first time a manuscript that is kept in Quetelet's papers at the Royal Academy of Belgium, and give an English translation of it.