  I show that Lamb-Retherford experiment can be fully described within the
framework of classical field theory without using concepts such as the discrete
states of the atom and jump-like electron transitions between them. The rate of
stimulated decay of the metastable state of a hydrogen atom in an external
periodic electric field is determined. The dependence of this rate on the
frequency and amplitude of the external electric field, as well as on the
parameters of the atom, has been obtained. It is shown that the maximum value
of the stimulated decay rate of the metastable state of a hydrogen atom is
achieved at an external electric field frequency equal to the frequency shift
corresponding to either the fine structure of the hydrogen atom or the Lamb
shift.
