Although Gauss had discovered the method of least squares during the last decade of the eighteenth century and used it regularly after 1801 in astronomical calculations, it was Legendre who introduced it to the world in an appendix to an astronomical memoir. Legendre stated the principle of least squares for combining observations and derived the normal equations from which least squares estimates may be calculated. However, he provided no justification for the method, other than noting that it prevented extreme errors from prevailing by establishing a sort of equilibrium among all the errors, and he was content to refer the calculator to the methods of the day for solving linear systems.