I am looking for Gauss's 1809 paper in which he introduced least squares regression, MLE and the gaussian distribution. I cannot find it online. Can someone tell me where I may find it?
According to author of several books on history of statistics, Stephen M. Stigler (1981), the method of least squares was first described by Carl Friedrich Gauss in 1809 in his Theoria Modus Corporum Coelestium [Theory of the Motion of Heavenly Bodies] book. In the same work Gauss proposed a form of normal distribution that is similar to what we use today. It seems to be the book you are referring to.