See the "Gauss's Law Sketch Proof" paragraph [URL [Broken].[/URL] Griffiths uses mainly the same argument to prove Gauss's law, but I don't really see the connection between the fact that the flux is Q/epsilon for a sphere and the conclusion that it is worth this quantity too for any closed surface. Can someone point to a more mathematical proof? Or simply unveil what I'm missing in this argument. Thanks.