Jules Regnault

Jules Augustin Frédéric Regnault (; 1 February 1834, Béthencourt – 9 December 1894, Paris) was a French stock broker's assistant who first suggested a modern theory of stock price changes in [https://archive.org/details/calculdeschances00regn ''Calcul des Chances et Philosophie de la Bourse''] (1863), using a random walk model. A key conclusion appears on Page 50: "''l'écart des cours est en raison directe de la racine carrée des temps''", in English: "the deviation of prices is directly proportional to the square root of time". He is also one of the first authors who tried to create a "stock exchange science" based on statistical and probabilistic analysis. His hypotheses were used by Louis Bachelier. Provided by Wikipedia