Editing Joseph-Louis Lagrange (section)

===Astronomy===
Lastly, there are numerous papers on problems in [[astronomy]]. Of these the most important are the following:

*Attempting to solve the [[three-body problem|general three-body problem]], with the consequent discovery of the two constant-pattern solutions, collinear and equilateral, 1772. Those solutions were later seen to explain what are now known as the [[Lagrangian point]]s. <!-- Read Lagrange's "Essai" before fiddling with this entry. -->
*On the attraction of ellipsoids, 1773: this is founded on [[Colin Maclaurin|Maclaurin]]'s work.
*On the secular equation of the Moon, 1773; also noticeable for the earliest introduction of the idea of the potential. The potential of a body at any point is the sum of the mass of every element of the body when divided by its distance from the point. Lagrange showed that if the potential of a body at an external point were known, the attraction in any direction could be at once found. The theory of the potential was elaborated in a paper sent to Berlin in 1777.
*On the motion of the nodes of a planet's [[orbit]], 1774.
*On the stability of the planetary orbits, 1776.
*Two papers in which the method of determining the orbit of a [[comet]] from three observations is completely worked out, 1778 and 1783: this has not indeed proved practically available, but his system of calculating the perturbations by means of mechanical quadratures has formed the basis of most subsequent researches on the subject.
*His determination of the secular and periodic variations of the [[orbital elements|elements]] of the planets, 1781–1784: the upper limits assigned for these agree closely with those obtained later by [[Urbain Le Verrier|Le Verrier]], and Lagrange proceeded as far as the knowledge then possessed of the masses of the planets permitted.
*Three papers on the method of interpolation, 1783, 1792 and 1793: the part of finite differences dealing therewith is now in the same stage as that in which Lagrange left it.