At the beginning of 1924, Bohr, Krams and Slater published a theory which had a great influence on the future, also called BKS theory, which was mainly based on the idea put forward by Slater, an American physicist who came to work in Copenhagen at that time. The central idea of this theory is that a virtual radiation field can be generated by introducing a group of virtual oscillators to each atom, and each virtual oscillator has a transition frequency (that is, the transition frequency of atoms). This links the discontinuous atomic process with the continuous radiation field, so that we can use the correspondence principle and adopt a method similar to the classical theory to deal with the dispersion problem of quantum theory. It is with this idea that Krams deduced his dispersion formula. If Krams's dispersion theory actually destroyed the basis of the concept of electron orbit, it can be said that Heisenberg prefers to abandon the electron orbit model and express Bohr's correspondence principle with the correct mathematical formula. Together with Krams, he studied dispersion with Born's method, and co-wrote a paper "On the Scattering of Radiation by Atoms".