His most influential book was "Sur l'homme et le développement de ses facultés, ou Essai de physique sociale", published in 1835 (In English translation, it is titled "Treatise on Man", but a literal translation would be "On Man and the Development of his Faculties, or Essays on Social Physics"). In it, he outlines the project of a social physics and describes his concept of the "average man" ("l'homme moyen") who is characterized by the mean values of measured variables that follow a normal distribution. He collected data about many such variables.