A Lagrangian for Water Waves by Sasha Balk JTB 320, 3:20pm Monday, April 7, 1997 Abstract In 1880 Stokes derived his system of cubic equations for the coefficients of the Fourier expansion of a steady water wave of finite amplitude. A century later Longuet-Higgins discovered a system of quadratic equations for the Stokes coefficients which is equivalent to the original Stokes system. What is the meaning of this quadratic system? Is this a shade of integrability? In this work we have found a Lagrangian for water waves (including overturning waves). It turns out that the Longuet-Higgins system directly follows from this Lagrangian. Besides applications of the Lagrangian to the stability of water waves and to numerical methods, we will point out the approach to the water surface singularities and to the investigation of nuclear fusion. Requests for preprints and reprints to: Alexander Balk, balk@ama.caltech.edu This source can be found at http://www.math.utah.edu/research/