The phenomenological potentials were derived by a group in Bonn and a group in Paris which fit the scattering data very well, and Panderia Pandi at Illinois refined this still further. These are all phenomenological and we are only guided gently by fundamental theory. Gerald Brown has been very instrumental in that. The... back in 1947, 1948, 1949, we thought that the exchange of one pion between two nucleons would give the main force. Gerald Brown pointed out that a much stronger force comes from the simultaneous exchange of two pions, and one also has to take into account that you can also exchange a heavier meson, the rho meson, between two nucleons and only then can you fully explain the charge distribution in nuclear as well as the binding energy.