The combination of these two talks that by... by Kramers and that by Lamb, stimulated me greatly and I said to myself, well, let's try to calculate that Lamb shift. Let's try to calculate the difference between the self energy of a free electron and that of an electron bound in hydrogen in the inequal two states.

[Q] When you say that you said this to yourself, this was still at the conference?

This was still at the conference. I said to myself, I can do that. And indeed, once the conference was over, I traveled [unclear] by train to the General Electric research lab. And on the train I figured out how much that difference might be. I had to remember the interaction of electromagnetic quanta with electrons. And I wasn't sure about the factor of two. So if I remembered correctly, I seemed to get just about the right energy separation of 1000MHz. But I might be wrong by a factor of two. So the first thing I did when I came to the library at General Electric was to look up Heitler's book on Radiation Theory, and I found that, indeed, I had remembered the number correctly and that, indeed, I'd got a 1000MHz.

[Q] And this was describing the electron nonrelativistically.

Yes, I was helped very much by a previous paper by Weisskopf, who had shown that in the Dirac Pair Theory, the self energy of an electron... of a Dirac electron only diverges logarithmically when you get to high energy. So I said to myself, once I take the difference between bound electron and free electron, the logarithmic divergence will probably disappear and it will converge. So let's just calculate the effect of... of quanta up to the energy electron mass x C² - velocity of light square - and let's hope that a relativistic correction won't make any difference.