Editing Joseph-Louis Lagrange (section)

===Celestial mechanics===
A theory of the [[planetary motion]]s had formed the subject of some of the most remarkable of Lagrange's Berlin papers. In 1806 the subject was reopened by [[Siméon Poisson|Poisson]], who, in a paper read before the French Academy, showed that Lagrange's formulae led to certain limits for the stability of the orbits. Lagrange, who was present, now discussed the whole subject afresh, and in a letter communicated to the academy in 1808 explained how, by the variation of arbitrary constants, the periodical and secular inequalities of any system of mutually interacting bodies could be determined.