‎"LAGRANGE, JOSEPH LOUIS.‎
‎Sur la Force des ressorts pliés. (+) Sur le Probleme de Kepler. (2 Memoirs).‎

‎(Berlin, Haude et Spener, 1771). 4to. No wrappers, as issued in ""Mémoires des l'Academie Royale des Sciences et Belles-Lettres"", tome XXV, pp. 167-203 a. pp. 204-233 a. 1 folded engraved plate. With titlepage to ""Classe de Mathematique.""‎

Reference : 45705

‎First appearance of these two importent memoirs, dealing with ""elastic stress"" and the Two-Body problem. In the first paper ""On the Force of bent springs"" Lagrange became the first to investigate mathematically ""elastic stress"" - the physical principles of elasticity - a problem suggested by the design of the spiral spring of a watch.""Although Lagrange's contributions to the strenght of materials are of more theoretical than practical interest, his method of generalized coordinates and generalized forces later found applications in the strenghts of materials and proved a great value in solving problems of practical importence.""(Timoshenko ""History of Strength of Materials""p. 40).The second paper offered deals with the Two-Body problem and here he comes up with the solution later called the lagrangian solution. In 1770 Lagrange read before the Academy his famous paper ""Nouvelle méthode pour résoudre les équations littérales par le moyen des séries."", the discovery of the Lagrange-Series. In the paper offered - read to the Academy on November 1, 1770 - Lagrange applies his Series to ""Kepler's Problem"".Together with 2 other papers, Jean Bernoulli ""Sur les Suites ou Sequences dans la Laotterie de Genes"", pp. 234-253 and D'Alembert ""Extrait d'une Lettre ...à M. de La Grange"", pp. 254-264.‎