I had spent one semester in Stuttgart with Ewald, which was a very happy time, but then Sommerfeld wrote Ewald a postcard, no more, in which he said 'Bethe is my student. I want him back.' So Ewald put me into a package and sent me back to Sommerfeld and I returned to Sommerfeld in the fall of '29. It should be mentioned that Sommerfeld had a sabbatic in the winter semester '28 to '29 in which he traveled all over the globe, among others to India, and had a very good time. When I returned to Sommerfeld and Sommerfeld suggested I should get my Habilitation and I had read the Born paper trying to... to get the inelastic scattering by hydrogen. I think I should mention that the actual calculation was done by Elsasser, which was another paper published. Well, the Born theory for first part approximation says you take the wave function of the system in the initial state and take its complex conjugate and then you take the wave function in the final state and you multiply them and you multiply by the interaction between the atom and the electron which comes in from the outside, e^2/r1,2, and you integrate that. Well, Elsasser had done that, by first integrating over the atomic electron wave function, and that's a very hard thing to do and it took him a long time to... to do it. But I noticed that the wave function of the incident particle electron or proton or whatever it may be is much simpler, it's just an exponential, e^ik.r, and if you multiply two of them, you get e^iq.r where q is the change of momentum in the scattering process and to integrate that with the interaction 1/r1,2. It's as easy as can be. Ewald had done it, and it is just taking the fourier transform of the wave function. And that's what people knew as the atomic form factor.